1 acpi= [HW,ACPI,X86,ARM64] 2 Advanced Configuration and Power Interface 3 Format: { force | on | off | strict | noirq | rsdt | 4 copy_dsdt } 5 force -- enable ACPI if default was off 6 on -- enable ACPI but allow fallback to DT [arm64] 7 off -- disable ACPI if default was on 8 noirq -- do not use ACPI for IRQ routing 9 strict -- Be less tolerant of platforms that are not 10 strictly ACPI specification compliant. 11 rsdt -- prefer RSDT over (default) XSDT 12 copy_dsdt -- copy DSDT to memory 13 For ARM64, ONLY "acpi=off", "acpi=on" or "acpi=force" 14 are available 15 16 See also Documentation/power/runtime_pm.rst, pci=noacpi 17 18 acpi_apic_instance= [ACPI, IOAPIC] 19 Format: <int> 20 2: use 2nd APIC table, if available 21 1,0: use 1st APIC table 22 default: 0 23 24 acpi_backlight= [HW,ACPI] 25 { vendor | video | native | none } 26 If set to vendor, prefer vendor-specific driver 27 (e.g. thinkpad_acpi, sony_acpi, etc.) instead 28 of the ACPI video.ko driver. 29 If set to video, use the ACPI video.ko driver. 30 If set to native, use the device's native backlight mode. 31 If set to none, disable the ACPI backlight interface. 32 33 acpi_force_32bit_fadt_addr 34 force FADT to use 32 bit addresses rather than the 35 64 bit X_* addresses. Some firmware have broken 64 36 bit addresses for force ACPI ignore these and use 37 the older legacy 32 bit addresses. 38 39 acpica_no_return_repair [HW, ACPI] 40 Disable AML predefined validation mechanism 41 This mechanism can repair the evaluation result to make 42 the return objects more ACPI specification compliant. 43 This option is useful for developers to identify the 44 root cause of an AML interpreter issue when the issue 45 has something to do with the repair mechanism. 46 47 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG] 48 acpi.debug_level= [HW,ACPI,ACPI_DEBUG] 49 Format: <int> 50 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI 51 debug output. Bits in debug_layer correspond to a 52 _COMPONENT in an ACPI source file, e.g., 53 #define _COMPONENT ACPI_PCI_COMPONENT 54 Bits in debug_level correspond to a level in 55 ACPI_DEBUG_PRINT statements, e.g., 56 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ... 57 The debug_level mask defaults to "info". See 58 Documentation/firmware-guide/acpi/debug.rst for more information about 59 debug layers and levels. 60 61 Enable processor driver info messages: 62 acpi.debug_layer=0x20000000 63 Enable PCI/PCI interrupt routing info messages: 64 acpi.debug_layer=0x400000 65 Enable AML "Debug" output, i.e., stores to the Debug 66 object while interpreting AML: 67 acpi.debug_layer=0xffffffff acpi.debug_level=0x2 68 Enable all messages related to ACPI hardware: 69 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff 70 71 Some values produce so much output that the system is 72 unusable. The "log_buf_len" parameter may be useful 73 if you need to capture more output. 74 75 acpi_enforce_resources= [ACPI] 76 { strict | lax | no } 77 Check for resource conflicts between native drivers 78 and ACPI OperationRegions (SystemIO and SystemMemory 79 only). IO ports and memory declared in ACPI might be 80 used by the ACPI subsystem in arbitrary AML code and 81 can interfere with legacy drivers. 82 strict (default): access to resources claimed by ACPI 83 is denied; legacy drivers trying to access reserved 84 resources will fail to bind to device using them. 85 lax: access to resources claimed by ACPI is allowed; 86 legacy drivers trying to access reserved resources 87 will bind successfully but a warning message is logged. 88 no: ACPI OperationRegions are not marked as reserved, 89 no further checks are performed. 90 91 acpi_force_table_verification [HW,ACPI] 92 Enable table checksum verification during early stage. 93 By default, this is disabled due to x86 early mapping 94 size limitation. 95 96 acpi_irq_balance [HW,ACPI] 97 ACPI will balance active IRQs 98 default in APIC mode 99 100 acpi_irq_nobalance [HW,ACPI] 101 ACPI will not move active IRQs (default) 102 default in PIC mode 103 104 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA 105 Format: <irq>,<irq>... 106 107 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for 108 use by PCI 109 Format: <irq>,<irq>... 110 111 acpi_mask_gpe= [HW,ACPI] 112 Due to the existence of _Lxx/_Exx, some GPEs triggered 113 by unsupported hardware/firmware features can result in 114 GPE floodings that cannot be automatically disabled by 115 the GPE dispatcher. 116 This facility can be used to prevent such uncontrolled 117 GPE floodings. 118 Format: <byte> 119 120 acpi_no_auto_serialize [HW,ACPI] 121 Disable auto-serialization of AML methods 122 AML control methods that contain the opcodes to create 123 named objects will be marked as "Serialized" by the 124 auto-serialization feature. 125 This feature is enabled by default. 126 This option allows to turn off the feature. 127 128 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump 129 kernels. 130 131 acpi_no_static_ssdt [HW,ACPI] 132 Disable installation of static SSDTs at early boot time 133 By default, SSDTs contained in the RSDT/XSDT will be 134 installed automatically and they will appear under 135 /sys/firmware/acpi/tables. 136 This option turns off this feature. 137 Note that specifying this option does not affect 138 dynamic table installation which will install SSDT 139 tables to /sys/firmware/acpi/tables/dynamic. 140 141 acpi_no_watchdog [HW,ACPI,WDT] 142 Ignore the ACPI-based watchdog interface (WDAT) and let 143 a native driver control the watchdog device instead. 144 145 acpi_rsdp= [ACPI,EFI,KEXEC] 146 Pass the RSDP address to the kernel, mostly used 147 on machines running EFI runtime service to boot the 148 second kernel for kdump. 149 150 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS 151 Format: To spoof as Windows 98: ="Microsoft Windows" 152 153 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead 154 of 2 which is mandated by ACPI 6) as the supported ACPI 155 specification revision (when using this switch, it may 156 be necessary to carry out a cold reboot _twice_ in a 157 row to make it take effect on the platform firmware). 158 159 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings 160 acpi_osi="string1" # add string1 161 acpi_osi="!string2" # remove string2 162 acpi_osi=!* # remove all strings 163 acpi_osi=! # disable all built-in OS vendor 164 strings 165 acpi_osi=!! # enable all built-in OS vendor 166 strings 167 acpi_osi= # disable all strings 168 169 'acpi_osi=!' can be used in combination with single or 170 multiple 'acpi_osi="string1"' to support specific OS 171 vendor string(s). Note that such command can only 172 affect the default state of the OS vendor strings, thus 173 it cannot affect the default state of the feature group 174 strings and the current state of the OS vendor strings, 175 specifying it multiple times through kernel command line 176 is meaningless. This command is useful when one do not 177 care about the state of the feature group strings which 178 should be controlled by the OSPM. 179 Examples: 180 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent 181 to 'acpi_osi="Windows 2000" acpi_osi=!', they all 182 can make '_OSI("Windows 2000")' TRUE. 183 184 'acpi_osi=' cannot be used in combination with other 185 'acpi_osi=' command lines, the _OSI method will not 186 exist in the ACPI namespace. NOTE that such command can 187 only affect the _OSI support state, thus specifying it 188 multiple times through kernel command line is also 189 meaningless. 190 Examples: 191 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)' 192 FALSE. 193 194 'acpi_osi=!*' can be used in combination with single or 195 multiple 'acpi_osi="string1"' to support specific 196 string(s). Note that such command can affect the 197 current state of both the OS vendor strings and the 198 feature group strings, thus specifying it multiple times 199 through kernel command line is meaningful. But it may 200 still not able to affect the final state of a string if 201 there are quirks related to this string. This command 202 is useful when one want to control the state of the 203 feature group strings to debug BIOS issues related to 204 the OSPM features. 205 Examples: 206 1. 'acpi_osi="Module Device" acpi_osi=!*' can make 207 '_OSI("Module Device")' FALSE. 208 2. 'acpi_osi=!* acpi_osi="Module Device"' can make 209 '_OSI("Module Device")' TRUE. 210 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is 211 equivalent to 212 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"' 213 and 214 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!', 215 they all will make '_OSI("Windows 2000")' TRUE. 216 217 acpi_pm_good [X86] 218 Override the pmtimer bug detection: force the kernel 219 to assume that this machine's pmtimer latches its value 220 and always returns good values. 221 222 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode 223 Format: { level | edge | high | low } 224 225 acpi_skip_timer_override [HW,ACPI] 226 Recognize and ignore IRQ0/pin2 Interrupt Override. 227 For broken nForce2 BIOS resulting in XT-PIC timer. 228 229 acpi_sleep= [HW,ACPI] Sleep options 230 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig, 231 old_ordering, nonvs, sci_force_enable, nobl } 232 See Documentation/power/video.rst for information on 233 s3_bios and s3_mode. 234 s3_beep is for debugging; it makes the PC's speaker beep 235 as soon as the kernel's real-mode entry point is called. 236 s4_nohwsig prevents ACPI hardware signature from being 237 used during resume from hibernation. 238 old_ordering causes the ACPI 1.0 ordering of the _PTS 239 control method, with respect to putting devices into 240 low power states, to be enforced (the ACPI 2.0 ordering 241 of _PTS is used by default). 242 nonvs prevents the kernel from saving/restoring the 243 ACPI NVS memory during suspend/hibernation and resume. 244 sci_force_enable causes the kernel to set SCI_EN directly 245 on resume from S1/S3 (which is against the ACPI spec, 246 but some broken systems don't work without it). 247 nobl causes the internal blacklist of systems known to 248 behave incorrectly in some ways with respect to system 249 suspend and resume to be ignored (use wisely). 250 251 acpi_use_timer_override [HW,ACPI] 252 Use timer override. For some broken Nvidia NF5 boards 253 that require a timer override, but don't have HPET 254 255 add_efi_memmap [EFI; X86] Include EFI memory map in 256 kernel's map of available physical RAM. 257 258 agp= [AGP] 259 { off | try_unsupported } 260 off: disable AGP support 261 try_unsupported: try to drive unsupported chipsets 262 (may crash computer or cause data corruption) 263 264 ALSA [HW,ALSA] 265 See Documentation/sound/alsa-configuration.rst 266 267 alignment= [KNL,ARM] 268 Allow the default userspace alignment fault handler 269 behaviour to be specified. Bit 0 enables warnings, 270 bit 1 enables fixups, and bit 2 sends a segfault. 271 272 align_va_addr= [X86-64] 273 Align virtual addresses by clearing slice [14:12] when 274 allocating a VMA at process creation time. This option 275 gives you up to 3% performance improvement on AMD F15h 276 machines (where it is enabled by default) for a 277 CPU-intensive style benchmark, and it can vary highly in 278 a microbenchmark depending on workload and compiler. 279 280 32: only for 32-bit processes 281 64: only for 64-bit processes 282 on: enable for both 32- and 64-bit processes 283 off: disable for both 32- and 64-bit processes 284 285 alloc_snapshot [FTRACE] 286 Allocate the ftrace snapshot buffer on boot up when the 287 main buffer is allocated. This is handy if debugging 288 and you need to use tracing_snapshot() on boot up, and 289 do not want to use tracing_snapshot_alloc() as it needs 290 to be done where GFP_KERNEL allocations are allowed. 291 292 amd_iommu= [HW,X86-64] 293 Pass parameters to the AMD IOMMU driver in the system. 294 Possible values are: 295 fullflush - enable flushing of IO/TLB entries when 296 they are unmapped. Otherwise they are 297 flushed before they will be reused, which 298 is a lot of faster 299 off - do not initialize any AMD IOMMU found in 300 the system 301 force_isolation - Force device isolation for all 302 devices. The IOMMU driver is not 303 allowed anymore to lift isolation 304 requirements as needed. This option 305 does not override iommu=pt 306 307 amd_iommu_dump= [HW,X86-64] 308 Enable AMD IOMMU driver option to dump the ACPI table 309 for AMD IOMMU. With this option enabled, AMD IOMMU 310 driver will print ACPI tables for AMD IOMMU during 311 IOMMU initialization. 312 313 amd_iommu_intr= [HW,X86-64] 314 Specifies one of the following AMD IOMMU interrupt 315 remapping modes: 316 legacy - Use legacy interrupt remapping mode. 317 vapic - Use virtual APIC mode, which allows IOMMU 318 to inject interrupts directly into guest. 319 This mode requires kvm-amd.avic=1. 320 (Default when IOMMU HW support is present.) 321 322 amijoy.map= [HW,JOY] Amiga joystick support 323 Map of devices attached to JOY0DAT and JOY1DAT 324 Format: <a>,<b> 325 See also Documentation/input/joydev/joystick.rst 326 327 analog.map= [HW,JOY] Analog joystick and gamepad support 328 Specifies type or capabilities of an analog joystick 329 connected to one of 16 gameports 330 Format: <type1>,<type2>,..<type16> 331 332 apc= [HW,SPARC] 333 Power management functions (SPARCstation-4/5 + deriv.) 334 Format: noidle 335 Disable APC CPU standby support. SPARCstation-Fox does 336 not play well with APC CPU idle - disable it if you have 337 APC and your system crashes randomly. 338 339 apic= [APIC,X86] Advanced Programmable Interrupt Controller 340 Change the output verbosity while booting 341 Format: { quiet (default) | verbose | debug } 342 Change the amount of debugging information output 343 when initialising the APIC and IO-APIC components. 344 For X86-32, this can also be used to specify an APIC 345 driver name. 346 Format: apic=driver_name 347 Examples: apic=bigsmp 348 349 apic_extnmi= [APIC,X86] External NMI delivery setting 350 Format: { bsp (default) | all | none } 351 bsp: External NMI is delivered only to CPU 0 352 all: External NMIs are broadcast to all CPUs as a 353 backup of CPU 0 354 none: External NMI is masked for all CPUs. This is 355 useful so that a dump capture kernel won't be 356 shot down by NMI 357 358 autoconf= [IPV6] 359 See Documentation/networking/ipv6.rst. 360 361 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller 362 Limit apic dumping. The parameter defines the maximal 363 number of local apics being dumped. Also it is possible 364 to set it to "all" by meaning -- no limit here. 365 Format: { 1 (default) | 2 | ... | all }. 366 The parameter valid if only apic=debug or 367 apic=verbose is specified. 368 Example: apic=debug show_lapic=all 369 370 apm= [APM] Advanced Power Management 371 See header of arch/x86/kernel/apm_32.c. 372 373 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards 374 Format: <io>,<irq>,<nodeID> 375 376 ataflop= [HW,M68k] 377 378 atarimouse= [HW,MOUSE] Atari Mouse 379 380 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess, 381 EzKey and similar keyboards 382 383 atkbd.reset= [HW] Reset keyboard during initialization 384 385 atkbd.set= [HW] Select keyboard code set 386 Format: <int> (2 = AT (default), 3 = PS/2) 387 388 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar 389 keyboards 390 391 atkbd.softraw= [HW] Choose between synthetic and real raw mode 392 Format: <bool> (0 = real, 1 = synthetic (default)) 393 394 atkbd.softrepeat= [HW] 395 Use software keyboard repeat 396 397 audit= [KNL] Enable the audit sub-system 398 Format: { "0" | "1" | "off" | "on" } 399 0 | off - kernel audit is disabled and can not be 400 enabled until the next reboot 401 unset - kernel audit is initialized but disabled and 402 will be fully enabled by the userspace auditd. 403 1 | on - kernel audit is initialized and partially 404 enabled, storing at most audit_backlog_limit 405 messages in RAM until it is fully enabled by the 406 userspace auditd. 407 Default: unset 408 409 audit_backlog_limit= [KNL] Set the audit queue size limit. 410 Format: <int> (must be >=0) 411 Default: 64 412 413 bau= [X86_UV] Enable the BAU on SGI UV. The default 414 behavior is to disable the BAU (i.e. bau=0). 415 Format: { "0" | "1" } 416 0 - Disable the BAU. 417 1 - Enable the BAU. 418 unset - Disable the BAU. 419 420 baycom_epp= [HW,AX25] 421 Format: <io>,<mode> 422 423 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem 424 Format: <io>,<mode> 425 See header of drivers/net/hamradio/baycom_par.c. 426 427 baycom_ser_fdx= [HW,AX25] 428 BayCom Serial Port AX.25 Modem (Full Duplex Mode) 429 Format: <io>,<irq>,<mode>[,<baud>] 430 See header of drivers/net/hamradio/baycom_ser_fdx.c. 431 432 baycom_ser_hdx= [HW,AX25] 433 BayCom Serial Port AX.25 Modem (Half Duplex Mode) 434 Format: <io>,<irq>,<mode> 435 See header of drivers/net/hamradio/baycom_ser_hdx.c. 436 437 blkdevparts= Manual partition parsing of block device(s) for 438 embedded devices based on command line input. 439 See Documentation/block/cmdline-partition.rst 440 441 boot_delay= Milliseconds to delay each printk during boot. 442 Values larger than 10 seconds (10000) are changed to 443 no delay (0). 444 Format: integer 445 446 bootconfig [KNL] 447 Extended command line options can be added to an initrd 448 and this will cause the kernel to look for it. 449 450 See Documentation/admin-guide/bootconfig.rst 451 452 bert_disable [ACPI] 453 Disable BERT OS support on buggy BIOSes. 454 455 bgrt_disable [ACPI][X86] 456 Disable BGRT to avoid flickering OEM logo. 457 458 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards) 459 bttv.radio= Most important insmod options are available as 460 kernel args too. 461 bttv.pll= See Documentation/admin-guide/media/bttv.rst 462 bttv.tuner= 463 464 bulk_remove=off [PPC] This parameter disables the use of the pSeries 465 firmware feature for flushing multiple hpte entries 466 at a time. 467 468 c101= [NET] Moxa C101 synchronous serial card 469 470 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection. 471 Sometimes CPU hardware bugs make them report the cache 472 size incorrectly. The kernel will attempt work arounds 473 to fix known problems, but for some CPUs it is not 474 possible to determine what the correct size should be. 475 This option provides an override for these situations. 476 477 carrier_timeout= 478 [NET] Specifies amount of time (in seconds) that 479 the kernel should wait for a network carrier. By default 480 it waits 120 seconds. 481 482 ca_keys= [KEYS] This parameter identifies a specific key(s) on 483 the system trusted keyring to be used for certificate 484 trust validation. 485 format: { id:<keyid> | builtin } 486 487 cca= [MIPS] Override the kernel pages' cache coherency 488 algorithm. Accepted values range from 0 to 7 489 inclusive. See arch/mips/include/asm/pgtable-bits.h 490 for platform specific values (SB1, Loongson3 and 491 others). 492 493 ccw_timeout_log [S390] 494 See Documentation/s390/common_io.rst for details. 495 496 cgroup_disable= [KNL] Disable a particular controller 497 Format: {name of the controller(s) to disable} 498 The effects of cgroup_disable=foo are: 499 - foo isn't auto-mounted if you mount all cgroups in 500 a single hierarchy 501 - foo isn't visible as an individually mountable 502 subsystem 503 {Currently only "memory" controller deal with this and 504 cut the overhead, others just disable the usage. So 505 only cgroup_disable=memory is actually worthy} 506 507 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1 508 Format: { { controller | "all" | "named" } 509 [,{ controller | "all" | "named" }...] } 510 Like cgroup_disable, but only applies to cgroup v1; 511 the blacklisted controllers remain available in cgroup2. 512 "all" blacklists all controllers and "named" disables 513 named mounts. Specifying both "all" and "named" disables 514 all v1 hierarchies. 515 516 cgroup.memory= [KNL] Pass options to the cgroup memory controller. 517 Format: <string> 518 nosocket -- Disable socket memory accounting. 519 nokmem -- Disable kernel memory accounting. 520 kmem -- Enable kernel memory accounting. 521 522 checkreqprot [SELINUX] Set initial checkreqprot flag value. 523 Format: { "0" | "1" } 524 See security/selinux/Kconfig help text. 525 0 -- check protection applied by kernel (includes 526 any implied execute protection). 527 1 -- check protection requested by application. 528 Default value is set via a kernel config option. 529 Value can be changed at runtime via 530 /sys/fs/selinux/checkreqprot. 531 Setting checkreqprot to 1 is deprecated. 532 533 cio_ignore= [S390] 534 See Documentation/s390/common_io.rst for details. 535 clk_ignore_unused 536 [CLK] 537 Prevents the clock framework from automatically gating 538 clocks that have not been explicitly enabled by a Linux 539 device driver but are enabled in hardware at reset or 540 by the bootloader/firmware. Note that this does not 541 force such clocks to be always-on nor does it reserve 542 those clocks in any way. This parameter is useful for 543 debug and development, but should not be needed on a 544 platform with proper driver support. For more 545 information, see Documentation/driver-api/clk.rst. 546 547 clock= [BUGS=X86-32, HW] gettimeofday clocksource override. 548 [Deprecated] 549 Forces specified clocksource (if available) to be used 550 when calculating gettimeofday(). If specified 551 clocksource is not available, it defaults to PIT. 552 Format: { pit | tsc | cyclone | pmtmr } 553 554 clocksource= Override the default clocksource 555 Format: <string> 556 Override the default clocksource and use the clocksource 557 with the name specified. 558 Some clocksource names to choose from, depending on 559 the platform: 560 [all] jiffies (this is the base, fallback clocksource) 561 [ACPI] acpi_pm 562 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2, 563 pxa_timer,timer3,32k_counter,timer0_1 564 [X86-32] pit,hpet,tsc; 565 scx200_hrt on Geode; cyclone on IBM x440 566 [MIPS] MIPS 567 [PARISC] cr16 568 [S390] tod 569 [SH] SuperH 570 [SPARC64] tick 571 [X86-64] hpet,tsc 572 573 clocksource.arm_arch_timer.evtstrm= 574 [ARM,ARM64] 575 Format: <bool> 576 Enable/disable the eventstream feature of the ARM 577 architected timer so that code using WFE-based polling 578 loops can be debugged more effectively on production 579 systems. 580 581 clocksource.max_cswd_read_retries= [KNL] 582 Number of clocksource_watchdog() retries due to 583 external delays before the clock will be marked 584 unstable. Defaults to three retries, that is, 585 four attempts to read the clock under test. 586 587 clearcpuid=BITNUM[,BITNUM...] [X86] 588 Disable CPUID feature X for the kernel. See 589 arch/x86/include/asm/cpufeatures.h for the valid bit 590 numbers. Note the Linux specific bits are not necessarily 591 stable over kernel options, but the vendor specific 592 ones should be. 593 Also note that user programs calling CPUID directly 594 or using the feature without checking anything 595 will still see it. This just prevents it from 596 being used by the kernel or shown in /proc/cpuinfo. 597 Also note the kernel might malfunction if you disable 598 some critical bits. 599 600 cma=nn[MG]@[start[MG][-end[MG]]] 601 [KNL,CMA] 602 Sets the size of kernel global memory area for 603 contiguous memory allocations and optionally the 604 placement constraint by the physical address range of 605 memory allocations. A value of 0 disables CMA 606 altogether. For more information, see 607 kernel/dma/contiguous.c 608 609 cma_pernuma=nn[MG] 610 [ARM64,KNL] 611 Sets the size of kernel per-numa memory area for 612 contiguous memory allocations. A value of 0 disables 613 per-numa CMA altogether. And If this option is not 614 specificed, the default value is 0. 615 With per-numa CMA enabled, DMA users on node nid will 616 first try to allocate buffer from the pernuma area 617 which is located in node nid, if the allocation fails, 618 they will fallback to the global default memory area. 619 620 cmo_free_hint= [PPC] Format: { yes | no } 621 Specify whether pages are marked as being inactive 622 when they are freed. This is used in CMO environments 623 to determine OS memory pressure for page stealing by 624 a hypervisor. 625 Default: yes 626 627 coherent_pool=nn[KMG] [ARM,KNL] 628 Sets the size of memory pool for coherent, atomic dma 629 allocations, by default set to 256K. 630 631 com20020= [HW,NET] ARCnet - COM20020 chipset 632 Format: 633 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]] 634 635 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers) 636 Format: <io>[,<irq>] 637 638 com90xx= [HW,NET] 639 ARCnet - COM90xx chipset (memory-mapped buffers) 640 Format: <io>[,<irq>[,<memstart>]] 641 642 condev= [HW,S390] console device 643 conmode= 644 645 console= [KNL] Output console device and options. 646 647 tty<n> Use the virtual console device <n>. 648 649 ttyS<n>[,options] 650 ttyUSB0[,options] 651 Use the specified serial port. The options are of 652 the form "bbbbpnf", where "bbbb" is the baud rate, 653 "p" is parity ("n", "o", or "e"), "n" is number of 654 bits, and "f" is flow control ("r" for RTS or 655 omit it). Default is "9600n8". 656 657 See Documentation/admin-guide/serial-console.rst for more 658 information. See 659 Documentation/networking/netconsole.rst for an 660 alternative. 661 662 uart[8250],io,<addr>[,options] 663 uart[8250],mmio,<addr>[,options] 664 uart[8250],mmio16,<addr>[,options] 665 uart[8250],mmio32,<addr>[,options] 666 uart[8250],0x<addr>[,options] 667 Start an early, polled-mode console on the 8250/16550 668 UART at the specified I/O port or MMIO address, 669 switching to the matching ttyS device later. 670 MMIO inter-register address stride is either 8-bit 671 (mmio), 16-bit (mmio16), or 32-bit (mmio32). 672 If none of [io|mmio|mmio16|mmio32], <addr> is assumed 673 to be equivalent to 'mmio'. 'options' are specified in 674 the same format described for ttyS above; if unspecified, 675 the h/w is not re-initialized. 676 677 hvc<n> Use the hypervisor console device <n>. This is for 678 both Xen and PowerPC hypervisors. 679 680 If the device connected to the port is not a TTY but a braille 681 device, prepend "brl," before the device type, for instance 682 console=brl,ttyS0 683 For now, only VisioBraille is supported. 684 685 console_msg_format= 686 [KNL] Change console messages format 687 default 688 By default we print messages on consoles in 689 "[time stamp] text\n" format (time stamp may not be 690 printed, depending on CONFIG_PRINTK_TIME or 691 `printk_time' param). 692 syslog 693 Switch to syslog format: "<%u>[time stamp] text\n" 694 IOW, each message will have a facility and loglevel 695 prefix. The format is similar to one used by syslog() 696 syscall, or to executing "dmesg -S --raw" or to reading 697 from /proc/kmsg. 698 699 consoleblank= [KNL] The console blank (screen saver) timeout in 700 seconds. A value of 0 disables the blank timer. 701 Defaults to 0. 702 703 coredump_filter= 704 [KNL] Change the default value for 705 /proc/<pid>/coredump_filter. 706 See also Documentation/filesystems/proc.rst. 707 708 coresight_cpu_debug.enable 709 [ARM,ARM64] 710 Format: <bool> 711 Enable/disable the CPU sampling based debugging. 712 0: default value, disable debugging 713 1: enable debugging at boot time 714 715 cpuidle.off=1 [CPU_IDLE] 716 disable the cpuidle sub-system 717 718 cpuidle.governor= 719 [CPU_IDLE] Name of the cpuidle governor to use. 720 721 cpufreq.off=1 [CPU_FREQ] 722 disable the cpufreq sub-system 723 724 cpufreq.default_governor= 725 [CPU_FREQ] Name of the default cpufreq governor or 726 policy to use. This governor must be registered in the 727 kernel before the cpufreq driver probes. 728 729 cpu_init_udelay=N 730 [X86] Delay for N microsec between assert and de-assert 731 of APIC INIT to start processors. This delay occurs 732 on every CPU online, such as boot, and resume from suspend. 733 Default: 10000 734 735 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver 736 Format: 737 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] 738 739 crashkernel=size[KMG][@offset[KMG]] 740 [KNL] Using kexec, Linux can switch to a 'crash kernel' 741 upon panic. This parameter reserves the physical 742 memory region [offset, offset + size] for that kernel 743 image. If '@offset' is omitted, then a suitable offset 744 is selected automatically. 745 [KNL, X86-64] Select a region under 4G first, and 746 fall back to reserve region above 4G when '@offset' 747 hasn't been specified. 748 See Documentation/admin-guide/kdump/kdump.rst for further details. 749 750 crashkernel=range1:size1[,range2:size2,...][@offset] 751 [KNL] Same as above, but depends on the memory 752 in the running system. The syntax of range is 753 start-[end] where start and end are both 754 a memory unit (amount[KMG]). See also 755 Documentation/admin-guide/kdump/kdump.rst for an example. 756 757 crashkernel=size[KMG],high 758 [KNL, X86-64] range could be above 4G. Allow kernel 759 to allocate physical memory region from top, so could 760 be above 4G if system have more than 4G ram installed. 761 Otherwise memory region will be allocated below 4G, if 762 available. 763 It will be ignored if crashkernel=X is specified. 764 crashkernel=size[KMG],low 765 [KNL, X86-64] range under 4G. When crashkernel=X,high 766 is passed, kernel could allocate physical memory region 767 above 4G, that cause second kernel crash on system 768 that require some amount of low memory, e.g. swiotlb 769 requires at least 64M+32K low memory, also enough extra 770 low memory is needed to make sure DMA buffers for 32-bit 771 devices won't run out. Kernel would try to allocate at 772 at least 256M below 4G automatically. 773 This one let user to specify own low range under 4G 774 for second kernel instead. 775 0: to disable low allocation. 776 It will be ignored when crashkernel=X,high is not used 777 or memory reserved is below 4G. 778 779 cryptomgr.notests 780 [KNL] Disable crypto self-tests 781 782 cs89x0_dma= [HW,NET] 783 Format: <dma> 784 785 cs89x0_media= [HW,NET] 786 Format: { rj45 | aui | bnc } 787 788 dasd= [HW,NET] 789 See header of drivers/s390/block/dasd_devmap.c. 790 791 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port 792 (one device per port) 793 Format: <port#>,<type> 794 See also Documentation/input/devices/joystick-parport.rst 795 796 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot 797 time. See 798 Documentation/admin-guide/dynamic-debug-howto.rst for 799 details. Deprecated, see dyndbg. 800 801 debug [KNL] Enable kernel debugging (events log level). 802 803 debug_boot_weak_hash 804 [KNL] Enable printing [hashed] pointers early in the 805 boot sequence. If enabled, we use a weak hash instead 806 of siphash to hash pointers. Use this option if you are 807 seeing instances of '(___ptrval___)') and need to see a 808 value (hashed pointer) instead. Cryptographically 809 insecure, please do not use on production kernels. 810 811 debug_locks_verbose= 812 [KNL] verbose self-tests 813 Format=<0|1> 814 Print debugging info while doing the locking API 815 self-tests. 816 We default to 0 (no extra messages), setting it to 817 1 will print _a lot_ more information - normally 818 only useful to kernel developers. 819 820 debug_objects [KNL] Enable object debugging 821 822 no_debug_objects 823 [KNL] Disable object debugging 824 825 debug_guardpage_minorder= 826 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this 827 parameter allows control of the order of pages that will 828 be intentionally kept free (and hence protected) by the 829 buddy allocator. Bigger value increase the probability 830 of catching random memory corruption, but reduce the 831 amount of memory for normal system use. The maximum 832 possible value is MAX_ORDER/2. Setting this parameter 833 to 1 or 2 should be enough to identify most random 834 memory corruption problems caused by bugs in kernel or 835 driver code when a CPU writes to (or reads from) a 836 random memory location. Note that there exists a class 837 of memory corruptions problems caused by buggy H/W or 838 F/W or by drivers badly programing DMA (basically when 839 memory is written at bus level and the CPU MMU is 840 bypassed) which are not detectable by 841 CONFIG_DEBUG_PAGEALLOC, hence this option will not help 842 tracking down these problems. 843 844 debug_pagealloc= 845 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this parameter 846 enables the feature at boot time. By default, it is 847 disabled and the system will work mostly the same as a 848 kernel built without CONFIG_DEBUG_PAGEALLOC. 849 Note: to get most of debug_pagealloc error reports, it's 850 useful to also enable the page_owner functionality. 851 on: enable the feature 852 853 debugfs= [KNL] This parameter enables what is exposed to userspace 854 and debugfs internal clients. 855 Format: { on, no-mount, off } 856 on: All functions are enabled. 857 no-mount: 858 Filesystem is not registered but kernel clients can 859 access APIs and a crashkernel can be used to read 860 its content. There is nothing to mount. 861 off: Filesystem is not registered and clients 862 get a -EPERM as result when trying to register files 863 or directories within debugfs. 864 This is equivalent of the runtime functionality if 865 debugfs was not enabled in the kernel at all. 866 Default value is set in build-time with a kernel configuration. 867 868 debugpat [X86] Enable PAT debugging 869 870 decnet.addr= [HW,NET] 871 Format: <area>[,<node>] 872 See also Documentation/networking/decnet.rst. 873 874 default_hugepagesz= 875 [HW] The size of the default HugeTLB page. This is 876 the size represented by the legacy /proc/ hugepages 877 APIs. In addition, this is the default hugetlb size 878 used for shmget(), mmap() and mounting hugetlbfs 879 filesystems. If not specified, defaults to the 880 architecture's default huge page size. Huge page 881 sizes are architecture dependent. See also 882 Documentation/admin-guide/mm/hugetlbpage.rst. 883 Format: size[KMG] 884 885 deferred_probe_timeout= 886 [KNL] Debugging option to set a timeout in seconds for 887 deferred probe to give up waiting on dependencies to 888 probe. Only specific dependencies (subsystems or 889 drivers) that have opted in will be ignored. A timeout of 0 890 will timeout at the end of initcalls. This option will also 891 dump out devices still on the deferred probe list after 892 retrying. 893 894 dfltcc= [HW,S390] 895 Format: { on | off | def_only | inf_only | always } 896 on: s390 zlib hardware support for compression on 897 level 1 and decompression (default) 898 off: No s390 zlib hardware support 899 def_only: s390 zlib hardware support for deflate 900 only (compression on level 1) 901 inf_only: s390 zlib hardware support for inflate 902 only (decompression) 903 always: Same as 'on' but ignores the selected compression 904 level always using hardware support (used for debugging) 905 906 dhash_entries= [KNL] 907 Set number of hash buckets for dentry cache. 908 909 disable_1tb_segments [PPC] 910 Disables the use of 1TB hash page table segments. This 911 causes the kernel to fall back to 256MB segments which 912 can be useful when debugging issues that require an SLB 913 miss to occur. 914 915 stress_slb [PPC] 916 Limits the number of kernel SLB entries, and flushes 917 them frequently to increase the rate of SLB faults 918 on kernel addresses. 919 920 disable= [IPV6] 921 See Documentation/networking/ipv6.rst. 922 923 hardened_usercopy= 924 [KNL] Under CONFIG_HARDENED_USERCOPY, whether 925 hardening is enabled for this boot. Hardened 926 usercopy checking is used to protect the kernel 927 from reading or writing beyond known memory 928 allocation boundaries as a proactive defense 929 against bounds-checking flaws in the kernel's 930 copy_to_user()/copy_from_user() interface. 931 on Perform hardened usercopy checks (default). 932 off Disable hardened usercopy checks. 933 934 disable_radix [PPC] 935 Disable RADIX MMU mode on POWER9 936 937 radix_hcall_invalidate=on [PPC/PSERIES] 938 Disable RADIX GTSE feature and use hcall for TLB 939 invalidate. 940 941 disable_tlbie [PPC] 942 Disable TLBIE instruction. Currently does not work 943 with KVM, with HASH MMU, or with coherent accelerators. 944 945 disable_cpu_apicid= [X86,APIC,SMP] 946 Format: <int> 947 The number of initial APIC ID for the 948 corresponding CPU to be disabled at boot, 949 mostly used for the kdump 2nd kernel to 950 disable BSP to wake up multiple CPUs without 951 causing system reset or hang due to sending 952 INIT from AP to BSP. 953 954 perf_v4_pmi= [X86,INTEL] 955 Format: <bool> 956 Disable Intel PMU counter freezing feature. 957 The feature only exists starting from 958 Arch Perfmon v4 (Skylake and newer). 959 960 disable_ddw [PPC/PSERIES] 961 Disable Dynamic DMA Window support. Use this 962 to workaround buggy firmware. 963 964 disable_ipv6= [IPV6] 965 See Documentation/networking/ipv6.rst. 966 967 disable_mtrr_cleanup [X86] 968 The kernel tries to adjust MTRR layout from continuous 969 to discrete, to make X server driver able to add WB 970 entry later. This parameter disables that. 971 972 disable_mtrr_trim [X86, Intel and AMD only] 973 By default the kernel will trim any uncacheable 974 memory out of your available memory pool based on 975 MTRR settings. This parameter disables that behavior, 976 possibly causing your machine to run very slowly. 977 978 disable_timer_pin_1 [X86] 979 Disable PIN 1 of APIC timer 980 Can be useful to work around chipset bugs. 981 982 dis_ucode_ldr [X86] Disable the microcode loader. 983 984 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, 985 this option disables the debugging code at boot. 986 987 dma_debug_entries=<number> 988 This option allows to tune the number of preallocated 989 entries for DMA-API debugging code. One entry is 990 required per DMA-API allocation. Use this if the 991 DMA-API debugging code disables itself because the 992 architectural default is too low. 993 994 dma_debug_driver=<driver_name> 995 With this option the DMA-API debugging driver 996 filter feature can be enabled at boot time. Just 997 pass the driver to filter for as the parameter. 998 The filter can be disabled or changed to another 999 driver later using sysfs. 1000 1001 driver_async_probe= [KNL] 1002 List of driver names to be probed asynchronously. 1003 Format: <driver_name1>,<driver_name2>... 1004 1005 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>] 1006 Broken monitors, graphic adapters, KVMs and EDIDless 1007 panels may send no or incorrect EDID data sets. 1008 This parameter allows to specify an EDID data sets 1009 in the /lib/firmware directory that are used instead. 1010 Generic built-in EDID data sets are used, if one of 1011 edid/1024x768.bin, edid/1280x1024.bin, 1012 edid/1680x1050.bin, or edid/1920x1080.bin is given 1013 and no file with the same name exists. Details and 1014 instructions how to build your own EDID data are 1015 available in Documentation/admin-guide/edid.rst. An EDID 1016 data set will only be used for a particular connector, 1017 if its name and a colon are prepended to the EDID 1018 name. Each connector may use a unique EDID data 1019 set by separating the files with a comma. An EDID 1020 data set with no connector name will be used for 1021 any connectors not explicitly specified. 1022 1023 dscc4.setup= [NET] 1024 1025 dt_cpu_ftrs= [PPC] 1026 Format: {"off" | "known"} 1027 Control how the dt_cpu_ftrs device-tree binding is 1028 used for CPU feature discovery and setup (if it 1029 exists). 1030 off: Do not use it, fall back to legacy cpu table. 1031 known: Do not pass through unknown features to guests 1032 or userspace, only those that the kernel is aware of. 1033 1034 dump_apple_properties [X86] 1035 Dump name and content of EFI device properties on 1036 x86 Macs. Useful for driver authors to determine 1037 what data is available or for reverse-engineering. 1038 1039 dyndbg[="val"] [KNL,DYNAMIC_DEBUG] 1040 <module>.dyndbg[="val"] 1041 Enable debug messages at boot time. See 1042 Documentation/admin-guide/dynamic-debug-howto.rst 1043 for details. 1044 1045 nopku [X86] Disable Memory Protection Keys CPU feature found 1046 in some Intel CPUs. 1047 1048 <module>.async_probe [KNL] 1049 Enable asynchronous probe on this module. 1050 1051 early_ioremap_debug [KNL] 1052 Enable debug messages in early_ioremap support. This 1053 is useful for tracking down temporary early mappings 1054 which are not unmapped. 1055 1056 earlycon= [KNL] Output early console device and options. 1057 1058 When used with no options, the early console is 1059 determined by stdout-path property in device tree's 1060 chosen node or the ACPI SPCR table if supported by 1061 the platform. 1062 1063 cdns,<addr>[,options] 1064 Start an early, polled-mode console on a Cadence 1065 (xuartps) serial port at the specified address. Only 1066 supported option is baud rate. If baud rate is not 1067 specified, the serial port must already be setup and 1068 configured. 1069 1070 uart[8250],io,<addr>[,options] 1071 uart[8250],mmio,<addr>[,options] 1072 uart[8250],mmio32,<addr>[,options] 1073 uart[8250],mmio32be,<addr>[,options] 1074 uart[8250],0x<addr>[,options] 1075 Start an early, polled-mode console on the 8250/16550 1076 UART at the specified I/O port or MMIO address. 1077 MMIO inter-register address stride is either 8-bit 1078 (mmio) or 32-bit (mmio32 or mmio32be). 1079 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed 1080 to be equivalent to 'mmio'. 'options' are specified 1081 in the same format described for "console=ttyS<n>"; if 1082 unspecified, the h/w is not initialized. 1083 1084 pl011,<addr> 1085 pl011,mmio32,<addr> 1086 Start an early, polled-mode console on a pl011 serial 1087 port at the specified address. The pl011 serial port 1088 must already be setup and configured. Options are not 1089 yet supported. If 'mmio32' is specified, then only 1090 the driver will use only 32-bit accessors to read/write 1091 the device registers. 1092 1093 meson,<addr> 1094 Start an early, polled-mode console on a meson serial 1095 port at the specified address. The serial port must 1096 already be setup and configured. Options are not yet 1097 supported. 1098 1099 msm_serial,<addr> 1100 Start an early, polled-mode console on an msm serial 1101 port at the specified address. The serial port 1102 must already be setup and configured. Options are not 1103 yet supported. 1104 1105 msm_serial_dm,<addr> 1106 Start an early, polled-mode console on an msm serial 1107 dm port at the specified address. The serial port 1108 must already be setup and configured. Options are not 1109 yet supported. 1110 1111 owl,<addr> 1112 Start an early, polled-mode console on a serial port 1113 of an Actions Semi SoC, such as S500 or S900, at the 1114 specified address. The serial port must already be 1115 setup and configured. Options are not yet supported. 1116 1117 rda,<addr> 1118 Start an early, polled-mode console on a serial port 1119 of an RDA Micro SoC, such as RDA8810PL, at the 1120 specified address. The serial port must already be 1121 setup and configured. Options are not yet supported. 1122 1123 sbi 1124 Use RISC-V SBI (Supervisor Binary Interface) for early 1125 console. 1126 1127 smh Use ARM semihosting calls for early console. 1128 1129 s3c2410,<addr> 1130 s3c2412,<addr> 1131 s3c2440,<addr> 1132 s3c6400,<addr> 1133 s5pv210,<addr> 1134 exynos4210,<addr> 1135 Use early console provided by serial driver available 1136 on Samsung SoCs, requires selecting proper type and 1137 a correct base address of the selected UART port. The 1138 serial port must already be setup and configured. 1139 Options are not yet supported. 1140 1141 lantiq,<addr> 1142 Start an early, polled-mode console on a lantiq serial 1143 (lqasc) port at the specified address. The serial port 1144 must already be setup and configured. Options are not 1145 yet supported. 1146 1147 lpuart,<addr> 1148 lpuart32,<addr> 1149 Use early console provided by Freescale LP UART driver 1150 found on Freescale Vybrid and QorIQ LS1021A processors. 1151 A valid base address must be provided, and the serial 1152 port must already be setup and configured. 1153 1154 ec_imx21,<addr> 1155 ec_imx6q,<addr> 1156 Start an early, polled-mode, output-only console on the 1157 Freescale i.MX UART at the specified address. The UART 1158 must already be setup and configured. 1159 1160 ar3700_uart,<addr> 1161 Start an early, polled-mode console on the 1162 Armada 3700 serial port at the specified 1163 address. The serial port must already be setup 1164 and configured. Options are not yet supported. 1165 1166 qcom_geni,<addr> 1167 Start an early, polled-mode console on a Qualcomm 1168 Generic Interface (GENI) based serial port at the 1169 specified address. The serial port must already be 1170 setup and configured. Options are not yet supported. 1171 1172 efifb,[options] 1173 Start an early, unaccelerated console on the EFI 1174 memory mapped framebuffer (if available). On cache 1175 coherent non-x86 systems that use system memory for 1176 the framebuffer, pass the 'ram' option so that it is 1177 mapped with the correct attributes. 1178 1179 linflex,<addr> 1180 Use early console provided by Freescale LINFlexD UART 1181 serial driver for NXP S32V234 SoCs. A valid base 1182 address must be provided, and the serial port must 1183 already be setup and configured. 1184 1185 earlyprintk= [X86,SH,ARM,M68k,S390] 1186 earlyprintk=vga 1187 earlyprintk=sclp 1188 earlyprintk=xen 1189 earlyprintk=serial[,ttySn[,baudrate]] 1190 earlyprintk=serial[,0x...[,baudrate]] 1191 earlyprintk=ttySn[,baudrate] 1192 earlyprintk=dbgp[debugController#] 1193 earlyprintk=pciserial[,force],bus:device.function[,baudrate] 1194 earlyprintk=xdbc[xhciController#] 1195 1196 earlyprintk is useful when the kernel crashes before 1197 the normal console is initialized. It is not enabled by 1198 default because it has some cosmetic problems. 1199 1200 Append ",keep" to not disable it when the real console 1201 takes over. 1202 1203 Only one of vga, efi, serial, or usb debug port can 1204 be used at a time. 1205 1206 Currently only ttyS0 and ttyS1 may be specified by 1207 name. Other I/O ports may be explicitly specified 1208 on some architectures (x86 and arm at least) by 1209 replacing ttySn with an I/O port address, like this: 1210 earlyprintk=serial,0x1008,115200 1211 You can find the port for a given device in 1212 /proc/tty/driver/serial: 1213 2: uart:ST16650V2 port:00001008 irq:18 ... 1214 1215 Interaction with the standard serial driver is not 1216 very good. 1217 1218 The VGA and EFI output is eventually overwritten by 1219 the real console. 1220 1221 The xen output can only be used by Xen PV guests. 1222 1223 The sclp output can only be used on s390. 1224 1225 The optional "force" to "pciserial" enables use of a 1226 PCI device even when its classcode is not of the 1227 UART class. 1228 1229 edac_report= [HW,EDAC] Control how to report EDAC event 1230 Format: {"on" | "off" | "force"} 1231 on: enable EDAC to report H/W event. May be overridden 1232 by other higher priority error reporting module. 1233 off: disable H/W event reporting through EDAC. 1234 force: enforce the use of EDAC to report H/W event. 1235 default: on. 1236 1237 ekgdboc= [X86,KGDB] Allow early kernel console debugging 1238 ekgdboc=kbd 1239 1240 This is designed to be used in conjunction with 1241 the boot argument: earlyprintk=vga 1242 1243 This parameter works in place of the kgdboc parameter 1244 but can only be used if the backing tty is available 1245 very early in the boot process. For early debugging 1246 via a serial port see kgdboc_earlycon instead. 1247 1248 edd= [EDD] 1249 Format: {"off" | "on" | "skip[mbr]"} 1250 1251 efi= [EFI] 1252 Format: { "debug", "disable_early_pci_dma", 1253 "nochunk", "noruntime", "nosoftreserve", 1254 "novamap", "no_disable_early_pci_dma" } 1255 debug: enable misc debug output. 1256 disable_early_pci_dma: disable the busmaster bit on all 1257 PCI bridges while in the EFI boot stub. 1258 nochunk: disable reading files in "chunks" in the EFI 1259 boot stub, as chunking can cause problems with some 1260 firmware implementations. 1261 noruntime : disable EFI runtime services support 1262 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose) 1263 attribute may cause the kernel to reserve the 1264 memory range for a memory mapping driver to 1265 claim. Specify efi=nosoftreserve to disable this 1266 reservation and treat the memory by its base type 1267 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM"). 1268 novamap: do not call SetVirtualAddressMap(). 1269 no_disable_early_pci_dma: Leave the busmaster bit set 1270 on all PCI bridges while in the EFI boot stub 1271 1272 efi_no_storage_paranoia [EFI; X86] 1273 Using this parameter you can use more than 50% of 1274 your efi variable storage. Use this parameter only if 1275 you are really sure that your UEFI does sane gc and 1276 fulfills the spec otherwise your board may brick. 1277 1278 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86] 1279 Add arbitrary attribute to specific memory range by 1280 updating original EFI memory map. 1281 Region of memory which aa attribute is added to is 1282 from ss to ss+nn. 1283 1284 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000 1285 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000) 1286 attribute is added to range 0x100000000-0x180000000 and 1287 0x10a0000000-0x1120000000. 1288 1289 If efi_fake_mem=8G@9G:0x40000 is specified, the 1290 EFI_MEMORY_SP(0x40000) attribute is added to 1291 range 0x240000000-0x43fffffff. 1292 1293 Using this parameter you can do debugging of EFI memmap 1294 related features. For example, you can do debugging of 1295 Address Range Mirroring feature even if your box 1296 doesn't support it, or mark specific memory as 1297 "soft reserved". 1298 1299 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT 1300 that is to be dynamically loaded by Linux. If there are 1301 multiple variables with the same name but with different 1302 vendor GUIDs, all of them will be loaded. See 1303 Documentation/admin-guide/acpi/ssdt-overlays.rst for details. 1304 1305 1306 eisa_irq_edge= [PARISC,HW] 1307 See header of drivers/parisc/eisa.c. 1308 1309 elanfreq= [X86-32] 1310 See comment before function elanfreq_setup() in 1311 arch/x86/kernel/cpu/cpufreq/elanfreq.c. 1312 1313 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390] 1314 Specifies physical address of start of kernel core 1315 image elf header and optionally the size. Generally 1316 kexec loader will pass this option to capture kernel. 1317 See Documentation/admin-guide/kdump/kdump.rst for details. 1318 1319 enable_mtrr_cleanup [X86] 1320 The kernel tries to adjust MTRR layout from continuous 1321 to discrete, to make X server driver able to add WB 1322 entry later. This parameter enables that. 1323 1324 enable_timer_pin_1 [X86] 1325 Enable PIN 1 of APIC timer 1326 Can be useful to work around chipset bugs 1327 (in particular on some ATI chipsets). 1328 The kernel tries to set a reasonable default. 1329 1330 enforcing [SELINUX] Set initial enforcing status. 1331 Format: {"0" | "1"} 1332 See security/selinux/Kconfig help text. 1333 0 -- permissive (log only, no denials). 1334 1 -- enforcing (deny and log). 1335 Default value is 0. 1336 Value can be changed at runtime via 1337 /sys/fs/selinux/enforce. 1338 1339 erst_disable [ACPI] 1340 Disable Error Record Serialization Table (ERST) 1341 support. 1342 1343 ether= [HW,NET] Ethernet cards parameters 1344 This option is obsoleted by the "netdev=" option, which 1345 has equivalent usage. See its documentation for details. 1346 1347 evm= [EVM] 1348 Format: { "fix" } 1349 Permit 'security.evm' to be updated regardless of 1350 current integrity status. 1351 1352 failslab= 1353 fail_usercopy= 1354 fail_page_alloc= 1355 fail_make_request=[KNL] 1356 General fault injection mechanism. 1357 Format: <interval>,<probability>,<space>,<times> 1358 See also Documentation/fault-injection/. 1359 1360 fb_tunnels= [NET] 1361 Format: { initns | none } 1362 See Documentation/admin-guide/sysctl/net.rst for 1363 fb_tunnels_only_for_init_ns 1364 1365 floppy= [HW] 1366 See Documentation/admin-guide/blockdev/floppy.rst. 1367 1368 force_pal_cache_flush 1369 [IA-64] Avoid check_sal_cache_flush which may hang on 1370 buggy SAL_CACHE_FLUSH implementations. Using this 1371 parameter will force ia64_sal_cache_flush to call 1372 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH. 1373 1374 forcepae [X86-32] 1375 Forcefully enable Physical Address Extension (PAE). 1376 Many Pentium M systems disable PAE but may have a 1377 functionally usable PAE implementation. 1378 Warning: use of this parameter will taint the kernel 1379 and may cause unknown problems. 1380 1381 ftrace=[tracer] 1382 [FTRACE] will set and start the specified tracer 1383 as early as possible in order to facilitate early 1384 boot debugging. 1385 1386 ftrace_dump_on_oops[=orig_cpu] 1387 [FTRACE] will dump the trace buffers on oops. 1388 If no parameter is passed, ftrace will dump 1389 buffers of all CPUs, but if you pass orig_cpu, it will 1390 dump only the buffer of the CPU that triggered the 1391 oops. 1392 1393 ftrace_filter=[function-list] 1394 [FTRACE] Limit the functions traced by the function 1395 tracer at boot up. function-list is a comma separated 1396 list of functions. This list can be changed at run 1397 time by the set_ftrace_filter file in the debugfs 1398 tracing directory. 1399 1400 ftrace_notrace=[function-list] 1401 [FTRACE] Do not trace the functions specified in 1402 function-list. This list can be changed at run time 1403 by the set_ftrace_notrace file in the debugfs 1404 tracing directory. 1405 1406 ftrace_graph_filter=[function-list] 1407 [FTRACE] Limit the top level callers functions traced 1408 by the function graph tracer at boot up. 1409 function-list is a comma separated list of functions 1410 that can be changed at run time by the 1411 set_graph_function file in the debugfs tracing directory. 1412 1413 ftrace_graph_notrace=[function-list] 1414 [FTRACE] Do not trace from the functions specified in 1415 function-list. This list is a comma separated list of 1416 functions that can be changed at run time by the 1417 set_graph_notrace file in the debugfs tracing directory. 1418 1419 ftrace_graph_max_depth=<uint> 1420 [FTRACE] Used with the function graph tracer. This is 1421 the max depth it will trace into a function. This value 1422 can be changed at run time by the max_graph_depth file 1423 in the tracefs tracing directory. default: 0 (no limit) 1424 1425 fw_devlink= [KNL] Create device links between consumer and supplier 1426 devices by scanning the firmware to infer the 1427 consumer/supplier relationships. This feature is 1428 especially useful when drivers are loaded as modules as 1429 it ensures proper ordering of tasks like device probing 1430 (suppliers first, then consumers), supplier boot state 1431 clean up (only after all consumers have probed), 1432 suspend/resume & runtime PM (consumers first, then 1433 suppliers). 1434 Format: { off | permissive | on | rpm } 1435 off -- Don't create device links from firmware info. 1436 permissive -- Create device links from firmware info 1437 but use it only for ordering boot state clean 1438 up (sync_state() calls). 1439 on -- Create device links from firmware info and use it 1440 to enforce probe and suspend/resume ordering. 1441 rpm -- Like "on", but also use to order runtime PM. 1442 1443 gamecon.map[2|3]= 1444 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 1445 support via parallel port (up to 5 devices per port) 1446 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 1447 See also Documentation/input/devices/joystick-parport.rst 1448 1449 gamma= [HW,DRM] 1450 1451 gart_fix_e820= [X86-64] disable the fix e820 for K8 GART 1452 Format: off | on 1453 default: on 1454 1455 gcov_persist= [GCOV] When non-zero (default), profiling data for 1456 kernel modules is saved and remains accessible via 1457 debugfs, even when the module is unloaded/reloaded. 1458 When zero, profiling data is discarded and associated 1459 debugfs files are removed at module unload time. 1460 1461 goldfish [X86] Enable the goldfish android emulator platform. 1462 Don't use this when you are not running on the 1463 android emulator 1464 1465 gpt [EFI] Forces disk with valid GPT signature but 1466 invalid Protective MBR to be treated as GPT. If the 1467 primary GPT is corrupted, it enables the backup/alternate 1468 GPT to be used instead. 1469 1470 grcan.enable0= [HW] Configuration of physical interface 0. Determines 1471 the "Enable 0" bit of the configuration register. 1472 Format: 0 | 1 1473 Default: 0 1474 grcan.enable1= [HW] Configuration of physical interface 1. Determines 1475 the "Enable 0" bit of the configuration register. 1476 Format: 0 | 1 1477 Default: 0 1478 grcan.select= [HW] Select which physical interface to use. 1479 Format: 0 | 1 1480 Default: 0 1481 grcan.txsize= [HW] Sets the size of the tx buffer. 1482 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. 1483 Default: 1024 1484 grcan.rxsize= [HW] Sets the size of the rx buffer. 1485 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. 1486 Default: 1024 1487 1488 gpio-mockup.gpio_mockup_ranges 1489 [HW] Sets the ranges of gpiochip of for this device. 1490 Format: <start1>,<end1>,<start2>,<end2>... 1491 1492 hardlockup_all_cpu_backtrace= 1493 [KNL] Should the hard-lockup detector generate 1494 backtraces on all cpus. 1495 Format: 0 | 1 1496 1497 hashdist= [KNL,NUMA] Large hashes allocated during boot 1498 are distributed across NUMA nodes. Defaults on 1499 for 64-bit NUMA, off otherwise. 1500 Format: 0 | 1 (for off | on) 1501 1502 hcl= [IA-64] SGI's Hardware Graph compatibility layer 1503 1504 hd= [EIDE] (E)IDE hard drive subsystem geometry 1505 Format: <cyl>,<head>,<sect> 1506 1507 hest_disable [ACPI] 1508 Disable Hardware Error Source Table (HEST) support; 1509 corresponding firmware-first mode error processing 1510 logic will be disabled. 1511 1512 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact 1513 size of <nn>. This works even on boxes that have no 1514 highmem otherwise. This also works to reduce highmem 1515 size on bigger boxes. 1516 1517 highres= [KNL] Enable/disable high resolution timer mode. 1518 Valid parameters: "on", "off" 1519 Default: "on" 1520 1521 hlt [BUGS=ARM,SH] 1522 1523 hpet= [X86-32,HPET] option to control HPET usage 1524 Format: { enable (default) | disable | force | 1525 verbose } 1526 disable: disable HPET and use PIT instead 1527 force: allow force enabled of undocumented chips (ICH4, 1528 VIA, nVidia) 1529 verbose: show contents of HPET registers during setup 1530 1531 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET 1532 registers. Default set by CONFIG_HPET_MMAP_DEFAULT. 1533 1534 hugetlb_cma= [HW] The size of a cma area used for allocation 1535 of gigantic hugepages. 1536 Format: nn[KMGTPE] 1537 1538 Reserve a cma area of given size and allocate gigantic 1539 hugepages using the cma allocator. If enabled, the 1540 boot-time allocation of gigantic hugepages is skipped. 1541 1542 hugepages= [HW] Number of HugeTLB pages to allocate at boot. 1543 If this follows hugepagesz (below), it specifies 1544 the number of pages of hugepagesz to be allocated. 1545 If this is the first HugeTLB parameter on the command 1546 line, it specifies the number of pages to allocate for 1547 the default huge page size. See also 1548 Documentation/admin-guide/mm/hugetlbpage.rst. 1549 Format: <integer> 1550 1551 hugepagesz= 1552 [HW] The size of the HugeTLB pages. This is used in 1553 conjunction with hugepages (above) to allocate huge 1554 pages of a specific size at boot. The pair 1555 hugepagesz=X hugepages=Y can be specified once for 1556 each supported huge page size. Huge page sizes are 1557 architecture dependent. See also 1558 Documentation/admin-guide/mm/hugetlbpage.rst. 1559 Format: size[KMG] 1560 1561 hung_task_panic= 1562 [KNL] Should the hung task detector generate panics. 1563 Format: 0 | 1 1564 1565 A value of 1 instructs the kernel to panic when a 1566 hung task is detected. The default value is controlled 1567 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time 1568 option. The value selected by this boot parameter can 1569 be changed later by the kernel.hung_task_panic sysctl. 1570 1571 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 1572 terminal devices. Valid values: 0..8 1573 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 1574 If specified, z/VM IUCV HVC accepts connections 1575 from listed z/VM user IDs only. 1576 1577 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations 1578 which allow the hypervisor to 'idle' the 1579 guest on lock contention. 1580 1581 keep_bootcon [KNL] 1582 Do not unregister boot console at start. This is only 1583 useful for debugging when something happens in the window 1584 between unregistering the boot console and initializing 1585 the real console. 1586 1587 i2c_bus= [HW] Override the default board specific I2C bus speed 1588 or register an additional I2C bus that is not 1589 registered from board initialization code. 1590 Format: 1591 <bus_id>,<clkrate> 1592 1593 i8042.debug [HW] Toggle i8042 debug mode 1594 i8042.unmask_kbd_data 1595 [HW] Enable printing of interrupt data from the KBD port 1596 (disabled by default, and as a pre-condition 1597 requires that i8042.debug=1 be enabled) 1598 i8042.direct [HW] Put keyboard port into non-translated mode 1599 i8042.dumbkbd [HW] Pretend that controller can only read data from 1600 keyboard and cannot control its state 1601 (Don't attempt to blink the leds) 1602 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 1603 i8042.nokbd [HW] Don't check/create keyboard port 1604 i8042.noloop [HW] Disable the AUX Loopback command while probing 1605 for the AUX port 1606 i8042.nomux [HW] Don't check presence of an active multiplexing 1607 controller 1608 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 1609 controllers 1610 i8042.notimeout [HW] Ignore timeout condition signalled by controller 1611 i8042.reset [HW] Reset the controller during init, cleanup and 1612 suspend-to-ram transitions, only during s2r 1613 transitions, or never reset 1614 Format: { 1 | Y | y | 0 | N | n } 1615 1, Y, y: always reset controller 1616 0, N, n: don't ever reset controller 1617 Default: only on s2r transitions on x86; most other 1618 architectures force reset to be always executed 1619 i8042.unlock [HW] Unlock (ignore) the keylock 1620 i8042.kbdreset [HW] Reset device connected to KBD port 1621 i8042.probe_defer 1622 [HW] Allow deferred probing upon i8042 probe errors 1623 1624 i810= [HW,DRM] 1625 1626 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data 1627 indicates that the driver is running on unsupported 1628 hardware. 1629 i8k.force [HW] Activate i8k driver even if SMM BIOS signature 1630 does not match list of supported models. 1631 i8k.power_status 1632 [HW] Report power status in /proc/i8k 1633 (disabled by default) 1634 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN 1635 capability is set. 1636 1637 i915.invert_brightness= 1638 [DRM] Invert the sense of the variable that is used to 1639 set the brightness of the panel backlight. Normally a 1640 brightness value of 0 indicates backlight switched off, 1641 and the maximum of the brightness value sets the backlight 1642 to maximum brightness. If this parameter is set to 0 1643 (default) and the machine requires it, or this parameter 1644 is set to 1, a brightness value of 0 sets the backlight 1645 to maximum brightness, and the maximum of the brightness 1646 value switches the backlight off. 1647 -1 -- never invert brightness 1648 0 -- machine default 1649 1 -- force brightness inversion 1650 1651 icn= [HW,ISDN] 1652 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]] 1653 1654 ide-core.nodma= [HW] (E)IDE subsystem 1655 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc 1656 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr 1657 .cdrom .chs .ignore_cable are additional options 1658 See Documentation/ide/ide.rst. 1659 1660 ide-generic.probe-mask= [HW] (E)IDE subsystem 1661 Format: <int> 1662 Probe mask for legacy ISA IDE ports. Depending on 1663 platform up to 6 ports are supported, enabled by 1664 setting corresponding bits in the mask to 1. The 1665 default value is 0x0, which has a special meaning. 1666 On systems that have PCI, it triggers scanning the 1667 PCI bus for the first and the second port, which 1668 are then probed. On systems without PCI the value 1669 of 0x0 enables probing the two first ports as if it 1670 was 0x3. 1671 1672 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem 1673 Claim all unknown PCI IDE storage controllers. 1674 1675 idle= [X86] 1676 Format: idle=poll, idle=halt, idle=nomwait 1677 Poll forces a polling idle loop that can slightly 1678 improve the performance of waking up a idle CPU, but 1679 will use a lot of power and make the system run hot. 1680 Not recommended. 1681 idle=halt: Halt is forced to be used for CPU idle. 1682 In such case C2/C3 won't be used again. 1683 idle=nomwait: Disable mwait for CPU C-states 1684 1685 ieee754= [MIPS] Select IEEE Std 754 conformance mode 1686 Format: { strict | legacy | 2008 | relaxed } 1687 Default: strict 1688 1689 Choose which programs will be accepted for execution 1690 based on the IEEE 754 NaN encoding(s) supported by 1691 the FPU and the NaN encoding requested with the value 1692 of an ELF file header flag individually set by each 1693 binary. Hardware implementations are permitted to 1694 support either or both of the legacy and the 2008 NaN 1695 encoding mode. 1696 1697 Available settings are as follows: 1698 strict accept binaries that request a NaN encoding 1699 supported by the FPU 1700 legacy only accept legacy-NaN binaries, if supported 1701 by the FPU 1702 2008 only accept 2008-NaN binaries, if supported 1703 by the FPU 1704 relaxed accept any binaries regardless of whether 1705 supported by the FPU 1706 1707 The FPU emulator is always able to support both NaN 1708 encodings, so if no FPU hardware is present or it has 1709 been disabled with 'nofpu', then the settings of 1710 'legacy' and '2008' strap the emulator accordingly, 1711 'relaxed' straps the emulator for both legacy-NaN and 1712 2008-NaN, whereas 'strict' enables legacy-NaN only on 1713 legacy processors and both NaN encodings on MIPS32 or 1714 MIPS64 CPUs. 1715 1716 The setting for ABS.fmt/NEG.fmt instruction execution 1717 mode generally follows that for the NaN encoding, 1718 except where unsupported by hardware. 1719 1720 ignore_loglevel [KNL] 1721 Ignore loglevel setting - this will print /all/ 1722 kernel messages to the console. Useful for debugging. 1723 We also add it as printk module parameter, so users 1724 could change it dynamically, usually by 1725 /sys/module/printk/parameters/ignore_loglevel. 1726 1727 ignore_rlimit_data 1728 Ignore RLIMIT_DATA setting for data mappings, 1729 print warning at first misuse. Can be changed via 1730 /sys/module/kernel/parameters/ignore_rlimit_data. 1731 1732 ihash_entries= [KNL] 1733 Set number of hash buckets for inode cache. 1734 1735 ima_appraise= [IMA] appraise integrity measurements 1736 Format: { "off" | "enforce" | "fix" | "log" } 1737 default: "enforce" 1738 1739 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead. 1740 The builtin appraise policy appraises all files 1741 owned by uid=0. 1742 1743 ima_canonical_fmt [IMA] 1744 Use the canonical format for the binary runtime 1745 measurements, instead of host native format. 1746 1747 ima_hash= [IMA] 1748 Format: { md5 | sha1 | rmd160 | sha256 | sha384 1749 | sha512 | ... } 1750 default: "sha1" 1751 1752 The list of supported hash algorithms is defined 1753 in crypto/hash_info.h. 1754 1755 ima_policy= [IMA] 1756 The builtin policies to load during IMA setup. 1757 Format: "tcb | appraise_tcb | secure_boot | 1758 fail_securely" 1759 1760 The "tcb" policy measures all programs exec'd, files 1761 mmap'd for exec, and all files opened with the read 1762 mode bit set by either the effective uid (euid=0) or 1763 uid=0. 1764 1765 The "appraise_tcb" policy appraises the integrity of 1766 all files owned by root. 1767 1768 The "secure_boot" policy appraises the integrity 1769 of files (eg. kexec kernel image, kernel modules, 1770 firmware, policy, etc) based on file signatures. 1771 1772 The "fail_securely" policy forces file signature 1773 verification failure also on privileged mounted 1774 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE 1775 flag. 1776 1777 ima_tcb [IMA] Deprecated. Use ima_policy= instead. 1778 Load a policy which meets the needs of the Trusted 1779 Computing Base. This means IMA will measure all 1780 programs exec'd, files mmap'd for exec, and all files 1781 opened for read by uid=0. 1782 1783 ima_template= [IMA] 1784 Select one of defined IMA measurements template formats. 1785 Formats: { "ima" | "ima-ng" | "ima-sig" } 1786 Default: "ima-ng" 1787 1788 ima_template_fmt= 1789 [IMA] Define a custom template format. 1790 Format: { "field1|...|fieldN" } 1791 1792 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage 1793 Format: <min_file_size> 1794 Set the minimal file size for using asynchronous hash. 1795 If left unspecified, ahash usage is disabled. 1796 1797 ahash performance varies for different data sizes on 1798 different crypto accelerators. This option can be used 1799 to achieve the best performance for a particular HW. 1800 1801 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size 1802 Format: <bufsize> 1803 Set hashing buffer size. Default: 4k. 1804 1805 ahash performance varies for different chunk sizes on 1806 different crypto accelerators. This option can be used 1807 to achieve best performance for particular HW. 1808 1809 init= [KNL] 1810 Format: <full_path> 1811 Run specified binary instead of /sbin/init as init 1812 process. 1813 1814 initcall_debug [KNL] Trace initcalls as they are executed. Useful 1815 for working out where the kernel is dying during 1816 startup. 1817 1818 initcall_blacklist= [KNL] Do not execute a comma-separated list of 1819 initcall functions. Useful for debugging built-in 1820 modules and initcalls. 1821 1822 initrd= [BOOT] Specify the location of the initial ramdisk 1823 1824 initrdmem= [KNL] Specify a physical address and size from which to 1825 load the initrd. If an initrd is compiled in or 1826 specified in the bootparams, it takes priority over this 1827 setting. 1828 Format: ss[KMG],nn[KMG] 1829 Default is 0, 0 1830 1831 init_on_alloc= [MM] Fill newly allocated pages and heap objects with 1832 zeroes. 1833 Format: 0 | 1 1834 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON. 1835 1836 init_on_free= [MM] Fill freed pages and heap objects with zeroes. 1837 Format: 0 | 1 1838 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON. 1839 1840 init_pkru= [X86] Specify the default memory protection keys rights 1841 register contents for all processes. 0x55555554 by 1842 default (disallow access to all but pkey 0). Can 1843 override in debugfs after boot. 1844 1845 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 1846 Format: <irq> 1847 1848 int_pln_enable [X86] Enable power limit notification interrupt 1849 1850 integrity_audit=[IMA] 1851 Format: { "0" | "1" } 1852 0 -- basic integrity auditing messages. (Default) 1853 1 -- additional integrity auditing messages. 1854 1855 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 1856 on 1857 Enable intel iommu driver. 1858 off 1859 Disable intel iommu driver. 1860 igfx_off [Default Off] 1861 By default, gfx is mapped as normal device. If a gfx 1862 device has a dedicated DMAR unit, the DMAR unit is 1863 bypassed by not enabling DMAR with this option. In 1864 this case, gfx device will use physical address for 1865 DMA. 1866 forcedac [X86-64] 1867 With this option iommu will not optimize to look 1868 for io virtual address below 32-bit forcing dual 1869 address cycle on pci bus for cards supporting greater 1870 than 32-bit addressing. The default is to look 1871 for translation below 32-bit and if not available 1872 then look in the higher range. 1873 strict [Default Off] 1874 With this option on every unmap_single operation will 1875 result in a hardware IOTLB flush operation as opposed 1876 to batching them for performance. 1877 sp_off [Default Off] 1878 By default, super page will be supported if Intel IOMMU 1879 has the capability. With this option, super page will 1880 not be supported. 1881 sm_on [Default Off] 1882 By default, scalable mode will be disabled even if the 1883 hardware advertises that it has support for the scalable 1884 mode translation. With this option set, scalable mode 1885 will be used on hardware which claims to support it. 1886 tboot_noforce [Default Off] 1887 Do not force the Intel IOMMU enabled under tboot. 1888 By default, tboot will force Intel IOMMU on, which 1889 could harm performance of some high-throughput 1890 devices like 40GBit network cards, even if identity 1891 mapping is enabled. 1892 Note that using this option lowers the security 1893 provided by tboot because it makes the system 1894 vulnerable to DMA attacks. 1895 nobounce [Default off] 1896 Disable bounce buffer for untrusted devices such as 1897 the Thunderbolt devices. This will treat the untrusted 1898 devices as the trusted ones, hence might expose security 1899 risks of DMA attacks. 1900 1901 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 1902 0 disables intel_idle and fall back on acpi_idle. 1903 1 to 9 specify maximum depth of C-state. 1904 1905 intel_pstate= [X86] 1906 disable 1907 Do not enable intel_pstate as the default 1908 scaling driver for the supported processors 1909 passive 1910 Use intel_pstate as a scaling driver, but configure it 1911 to work with generic cpufreq governors (instead of 1912 enabling its internal governor). This mode cannot be 1913 used along with the hardware-managed P-states (HWP) 1914 feature. 1915 force 1916 Enable intel_pstate on systems that prohibit it by default 1917 in favor of acpi-cpufreq. Forcing the intel_pstate driver 1918 instead of acpi-cpufreq may disable platform features, such 1919 as thermal controls and power capping, that rely on ACPI 1920 P-States information being indicated to OSPM and therefore 1921 should be used with caution. This option does not work with 1922 processors that aren't supported by the intel_pstate driver 1923 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 1924 no_hwp 1925 Do not enable hardware P state control (HWP) 1926 if available. 1927 hwp_only 1928 Only load intel_pstate on systems which support 1929 hardware P state control (HWP) if available. 1930 support_acpi_ppc 1931 Enforce ACPI _PPC performance limits. If the Fixed ACPI 1932 Description Table, specifies preferred power management 1933 profile as "Enterprise Server" or "Performance Server", 1934 then this feature is turned on by default. 1935 per_cpu_perf_limits 1936 Allow per-logical-CPU P-State performance control limits using 1937 cpufreq sysfs interface 1938 1939 intremap= [X86-64, Intel-IOMMU] 1940 on enable Interrupt Remapping (default) 1941 off disable Interrupt Remapping 1942 nosid disable Source ID checking 1943 no_x2apic_optout 1944 BIOS x2APIC opt-out request will be ignored 1945 nopost disable Interrupt Posting 1946 1947 iomem= Disable strict checking of access to MMIO memory 1948 strict regions from userspace. 1949 relaxed 1950 1951 iommu= [X86] 1952 off 1953 force 1954 noforce 1955 biomerge 1956 panic 1957 nopanic 1958 merge 1959 nomerge 1960 soft 1961 pt [X86] 1962 nopt [X86] 1963 nobypass [PPC/POWERNV] 1964 Disable IOMMU bypass, using IOMMU for PCI devices. 1965 1966 iommu.strict= [ARM64] Configure TLB invalidation behaviour 1967 Format: { "0" | "1" } 1968 0 - Lazy mode. 1969 Request that DMA unmap operations use deferred 1970 invalidation of hardware TLBs, for increased 1971 throughput at the cost of reduced device isolation. 1972 Will fall back to strict mode if not supported by 1973 the relevant IOMMU driver. 1974 1 - Strict mode (default). 1975 DMA unmap operations invalidate IOMMU hardware TLBs 1976 synchronously. 1977 1978 iommu.passthrough= 1979 [ARM64, X86] Configure DMA to bypass the IOMMU by default. 1980 Format: { "0" | "1" } 1981 0 - Use IOMMU translation for DMA. 1982 1 - Bypass the IOMMU for DMA. 1983 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH. 1984 1985 io7= [HW] IO7 for Marvel-based Alpha systems 1986 See comment before marvel_specify_io7 in 1987 arch/alpha/kernel/core_marvel.c. 1988 1989 io_delay= [X86] I/O delay method 1990 0x80 1991 Standard port 0x80 based delay 1992 0xed 1993 Alternate port 0xed based delay (needed on some systems) 1994 udelay 1995 Simple two microseconds delay 1996 none 1997 No delay 1998 1999 ip= [IP_PNP] 2000 See Documentation/admin-guide/nfs/nfsroot.rst. 2001 2002 ipcmni_extend [KNL] Extend the maximum number of unique System V 2003 IPC identifiers from 32,768 to 16,777,216. 2004 2005 irqaffinity= [SMP] Set the default irq affinity mask 2006 The argument is a cpu list, as described above. 2007 2008 irqchip.gicv2_force_probe= 2009 [ARM, ARM64] 2010 Format: <bool> 2011 Force the kernel to look for the second 4kB page 2012 of a GICv2 controller even if the memory range 2013 exposed by the device tree is too small. 2014 2015 irqchip.gicv3_nolpi= 2016 [ARM, ARM64] 2017 Force the kernel to ignore the availability of 2018 LPIs (and by consequence ITSs). Intended for system 2019 that use the kernel as a bootloader, and thus want 2020 to let secondary kernels in charge of setting up 2021 LPIs. 2022 2023 irqchip.gicv3_pseudo_nmi= [ARM64] 2024 Enables support for pseudo-NMIs in the kernel. This 2025 requires the kernel to be built with 2026 CONFIG_ARM64_PSEUDO_NMI. 2027 2028 irqfixup [HW] 2029 When an interrupt is not handled search all handlers 2030 for it. Intended to get systems with badly broken 2031 firmware running. 2032 2033 irqpoll [HW] 2034 When an interrupt is not handled search all handlers 2035 for it. Also check all handlers each timer 2036 interrupt. Intended to get systems with badly broken 2037 firmware running. 2038 2039 isapnp= [ISAPNP] 2040 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 2041 2042 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance. 2043 [Deprecated - use cpusets instead] 2044 Format: [flag-list,]<cpu-list> 2045 2046 Specify one or more CPUs to isolate from disturbances 2047 specified in the flag list (default: domain): 2048 2049 nohz 2050 Disable the tick when a single task runs. 2051 2052 A residual 1Hz tick is offloaded to workqueues, which you 2053 need to affine to housekeeping through the global 2054 workqueue's affinity configured via the 2055 /sys/devices/virtual/workqueue/cpumask sysfs file, or 2056 by using the 'domain' flag described below. 2057 2058 NOTE: by default the global workqueue runs on all CPUs, 2059 so to protect individual CPUs the 'cpumask' file has to 2060 be configured manually after bootup. 2061 2062 domain 2063 Isolate from the general SMP balancing and scheduling 2064 algorithms. Note that performing domain isolation this way 2065 is irreversible: it's not possible to bring back a CPU to 2066 the domains once isolated through isolcpus. It's strongly 2067 advised to use cpusets instead to disable scheduler load 2068 balancing through the "cpuset.sched_load_balance" file. 2069 It offers a much more flexible interface where CPUs can 2070 move in and out of an isolated set anytime. 2071 2072 You can move a process onto or off an "isolated" CPU via 2073 the CPU affinity syscalls or cpuset. 2074 <cpu number> begins at 0 and the maximum value is 2075 "number of CPUs in system - 1". 2076 2077 managed_irq 2078 2079 Isolate from being targeted by managed interrupts 2080 which have an interrupt mask containing isolated 2081 CPUs. The affinity of managed interrupts is 2082 handled by the kernel and cannot be changed via 2083 the /proc/irq/* interfaces. 2084 2085 This isolation is best effort and only effective 2086 if the automatically assigned interrupt mask of a 2087 device queue contains isolated and housekeeping 2088 CPUs. If housekeeping CPUs are online then such 2089 interrupts are directed to the housekeeping CPU 2090 so that IO submitted on the housekeeping CPU 2091 cannot disturb the isolated CPU. 2092 2093 If a queue's affinity mask contains only isolated 2094 CPUs then this parameter has no effect on the 2095 interrupt routing decision, though interrupts are 2096 only delivered when tasks running on those 2097 isolated CPUs submit IO. IO submitted on 2098 housekeeping CPUs has no influence on those 2099 queues. 2100 2101 The format of <cpu-list> is described above. 2102 2103 iucv= [HW,NET] 2104 2105 ivrs_ioapic [HW,X86-64] 2106 Provide an override to the IOAPIC-ID<->DEVICE-ID 2107 mapping provided in the IVRS ACPI table. 2108 By default, PCI segment is 0, and can be omitted. 2109 2110 For example, to map IOAPIC-ID decimal 10 to 2111 PCI segment 0x1 and PCI device 00:14.0, 2112 write the parameter as: 2113 ivrs_ioapic=10@0001:00:14.0 2114 2115 Deprecated formats: 2116 * To map IOAPIC-ID decimal 10 to PCI device 00:14.0 2117 write the parameter as: 2118 ivrs_ioapic[10]=00:14.0 2119 * To map IOAPIC-ID decimal 10 to PCI segment 0x1 and 2120 PCI device 00:14.0 write the parameter as: 2121 ivrs_ioapic[10]=0001:00:14.0 2122 2123 ivrs_hpet [HW,X86-64] 2124 Provide an override to the HPET-ID<->DEVICE-ID 2125 mapping provided in the IVRS ACPI table. 2126 By default, PCI segment is 0, and can be omitted. 2127 2128 For example, to map HPET-ID decimal 10 to 2129 PCI segment 0x1 and PCI device 00:14.0, 2130 write the parameter as: 2131 ivrs_hpet=10@0001:00:14.0 2132 2133 Deprecated formats: 2134 * To map HPET-ID decimal 0 to PCI device 00:14.0 2135 write the parameter as: 2136 ivrs_hpet[0]=00:14.0 2137 * To map HPET-ID decimal 10 to PCI segment 0x1 and 2138 PCI device 00:14.0 write the parameter as: 2139 ivrs_ioapic[10]=0001:00:14.0 2140 2141 ivrs_acpihid [HW,X86-64] 2142 Provide an override to the ACPI-HID:UID<->DEVICE-ID 2143 mapping provided in the IVRS ACPI table. 2144 By default, PCI segment is 0, and can be omitted. 2145 2146 For example, to map UART-HID:UID AMD0020:0 to 2147 PCI segment 0x1 and PCI device ID 00:14.5, 2148 write the parameter as: 2149 ivrs_acpihid=AMD0020:0@0001:00:14.5 2150 2151 Deprecated formats: 2152 * To map UART-HID:UID AMD0020:0 to PCI segment is 0, 2153 PCI device ID 00:14.5, write the parameter as: 2154 ivrs_acpihid[00:14.5]=AMD0020:0 2155 * To map UART-HID:UID AMD0020:0 to PCI segment 0x1 and 2156 PCI device ID 00:14.5, write the parameter as: 2157 ivrs_acpihid[0001:00:14.5]=AMD0020:0 2158 2159 js= [HW,JOY] Analog joystick 2160 See Documentation/input/joydev/joystick.rst. 2161 2162 nokaslr [KNL] 2163 When CONFIG_RANDOMIZE_BASE is set, this disables 2164 kernel and module base offset ASLR (Address Space 2165 Layout Randomization). 2166 2167 kasan_multi_shot 2168 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print 2169 report on every invalid memory access. Without this 2170 parameter KASAN will print report only for the first 2171 invalid access. 2172 2173 keepinitrd [HW,ARM] 2174 2175 kernelcore= [KNL,X86,IA-64,PPC] 2176 Format: nn[KMGTPE] | nn% | "mirror" 2177 This parameter specifies the amount of memory usable by 2178 the kernel for non-movable allocations. The requested 2179 amount is spread evenly throughout all nodes in the 2180 system as ZONE_NORMAL. The remaining memory is used for 2181 movable memory in its own zone, ZONE_MOVABLE. In the 2182 event, a node is too small to have both ZONE_NORMAL and 2183 ZONE_MOVABLE, kernelcore memory will take priority and 2184 other nodes will have a larger ZONE_MOVABLE. 2185 2186 ZONE_MOVABLE is used for the allocation of pages that 2187 may be reclaimed or moved by the page migration 2188 subsystem. Note that allocations like PTEs-from-HighMem 2189 still use the HighMem zone if it exists, and the Normal 2190 zone if it does not. 2191 2192 It is possible to specify the exact amount of memory in 2193 the form of "nn[KMGTPE]", a percentage of total system 2194 memory in the form of "nn%", or "mirror". If "mirror" 2195 option is specified, mirrored (reliable) memory is used 2196 for non-movable allocations and remaining memory is used 2197 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror" 2198 are exclusive, so you cannot specify multiple forms. 2199 2200 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port. 2201 Format: <Controller#>[,poll interval] 2202 The controller # is the number of the ehci usb debug 2203 port as it is probed via PCI. The poll interval is 2204 optional and is the number seconds in between 2205 each poll cycle to the debug port in case you need 2206 the functionality for interrupting the kernel with 2207 gdb or control-c on the dbgp connection. When 2208 not using this parameter you use sysrq-g to break into 2209 the kernel debugger. 2210 2211 kgdboc= [KGDB,HW] kgdb over consoles. 2212 Requires a tty driver that supports console polling, 2213 or a supported polling keyboard driver (non-usb). 2214 Serial only format: <serial_device>[,baud] 2215 keyboard only format: kbd 2216 keyboard and serial format: kbd,<serial_device>[,baud] 2217 Optional Kernel mode setting: 2218 kms, kbd format: kms,kbd 2219 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 2220 2221 kgdboc_earlycon= [KGDB,HW] 2222 If the boot console provides the ability to read 2223 characters and can work in polling mode, you can use 2224 this parameter to tell kgdb to use it as a backend 2225 until the normal console is registered. Intended to 2226 be used together with the kgdboc parameter which 2227 specifies the normal console to transition to. 2228 2229 The name of the early console should be specified 2230 as the value of this parameter. Note that the name of 2231 the early console might be different than the tty 2232 name passed to kgdboc. It's OK to leave the value 2233 blank and the first boot console that implements 2234 read() will be picked. 2235 2236 kgdbwait [KGDB] Stop kernel execution and enter the 2237 kernel debugger at the earliest opportunity. 2238 2239 kmac= [MIPS] Korina ethernet MAC address. 2240 Configure the RouterBoard 532 series on-chip 2241 Ethernet adapter MAC address. 2242 2243 kmemleak= [KNL] Boot-time kmemleak enable/disable 2244 Valid arguments: on, off 2245 Default: on 2246 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 2247 the default is off. 2248 2249 kprobe_event=[probe-list] 2250 [FTRACE] Add kprobe events and enable at boot time. 2251 The probe-list is a semicolon delimited list of probe 2252 definitions. Each definition is same as kprobe_events 2253 interface, but the parameters are comma delimited. 2254 For example, to add a kprobe event on vfs_read with 2255 arg1 and arg2, add to the command line; 2256 2257 kprobe_event=p,vfs_read,$arg1,$arg2 2258 2259 See also Documentation/trace/kprobetrace.rst "Kernel 2260 Boot Parameter" section. 2261 2262 kpti= [ARM64] Control page table isolation of user 2263 and kernel address spaces. 2264 Default: enabled on cores which need mitigation. 2265 0: force disabled 2266 1: force enabled 2267 2268 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 2269 Default is 0 (don't ignore, but inject #GP) 2270 2271 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface. 2272 Default is false (don't support). 2273 2274 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit 2275 KVM MMU at runtime. 2276 Default is 0 (off) 2277 2278 kvm.nx_huge_pages= 2279 [KVM] Controls the software workaround for the 2280 X86_BUG_ITLB_MULTIHIT bug. 2281 force : Always deploy workaround. 2282 off : Never deploy workaround. 2283 auto : Deploy workaround based on the presence of 2284 X86_BUG_ITLB_MULTIHIT. 2285 2286 Default is 'auto'. 2287 2288 If the software workaround is enabled for the host, 2289 guests do need not to enable it for nested guests. 2290 2291 kvm.nx_huge_pages_recovery_ratio= 2292 [KVM] Controls how many 4KiB pages are periodically zapped 2293 back to huge pages. 0 disables the recovery, otherwise if 2294 the value is N KVM will zap 1/Nth of the 4KiB pages every 2295 minute. The default is 60. 2296 2297 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM. 2298 Default is 1 (enabled) 2299 2300 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU) 2301 for all guests. 2302 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode. 2303 2304 kvm-arm.vgic_v3_group0_trap= 2305 [KVM,ARM] Trap guest accesses to GICv3 group-0 2306 system registers 2307 2308 kvm-arm.vgic_v3_group1_trap= 2309 [KVM,ARM] Trap guest accesses to GICv3 group-1 2310 system registers 2311 2312 kvm-arm.vgic_v3_common_trap= 2313 [KVM,ARM] Trap guest accesses to GICv3 common 2314 system registers 2315 2316 kvm-arm.vgic_v4_enable= 2317 [KVM,ARM] Allow use of GICv4 for direct injection of 2318 LPIs. 2319 2320 kvm_cma_resv_ratio=n [PPC] 2321 Reserves given percentage from system memory area for 2322 contiguous memory allocation for KVM hash pagetable 2323 allocation. 2324 By default it reserves 5% of total system memory. 2325 Format: <integer> 2326 Default: 5 2327 2328 kvm-intel.ept= [KVM,Intel] Disable extended page tables 2329 (virtualized MMU) support on capable Intel chips. 2330 Default is 1 (enabled) 2331 2332 kvm-intel.emulate_invalid_guest_state= 2333 [KVM,Intel] Disable emulation of invalid guest state. 2334 Ignored if kvm-intel.enable_unrestricted_guest=1, as 2335 guest state is never invalid for unrestricted guests. 2336 This param doesn't apply to nested guests (L2), as KVM 2337 never emulates invalid L2 guest state. 2338 Default is 1 (enabled) 2339 2340 kvm-intel.flexpriority= 2341 [KVM,Intel] Disable FlexPriority feature (TPR shadow). 2342 Default is 1 (enabled) 2343 2344 kvm-intel.nested= 2345 [KVM,Intel] Enable VMX nesting (nVMX). 2346 Default is 0 (disabled) 2347 2348 kvm-intel.unrestricted_guest= 2349 [KVM,Intel] Disable unrestricted guest feature 2350 (virtualized real and unpaged mode) on capable 2351 Intel chips. Default is 1 (enabled) 2352 2353 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault 2354 CVE-2018-3620. 2355 2356 Valid arguments: never, cond, always 2357 2358 always: L1D cache flush on every VMENTER. 2359 cond: Flush L1D on VMENTER only when the code between 2360 VMEXIT and VMENTER can leak host memory. 2361 never: Disables the mitigation 2362 2363 Default is cond (do L1 cache flush in specific instances) 2364 2365 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification 2366 feature (tagged TLBs) on capable Intel chips. 2367 Default is 1 (enabled) 2368 2369 l1tf= [X86] Control mitigation of the L1TF vulnerability on 2370 affected CPUs 2371 2372 The kernel PTE inversion protection is unconditionally 2373 enabled and cannot be disabled. 2374 2375 full 2376 Provides all available mitigations for the 2377 L1TF vulnerability. Disables SMT and 2378 enables all mitigations in the 2379 hypervisors, i.e. unconditional L1D flush. 2380 2381 SMT control and L1D flush control via the 2382 sysfs interface is still possible after 2383 boot. Hypervisors will issue a warning 2384 when the first VM is started in a 2385 potentially insecure configuration, 2386 i.e. SMT enabled or L1D flush disabled. 2387 2388 full,force 2389 Same as 'full', but disables SMT and L1D 2390 flush runtime control. Implies the 2391 'nosmt=force' command line option. 2392 (i.e. sysfs control of SMT is disabled.) 2393 2394 flush 2395 Leaves SMT enabled and enables the default 2396 hypervisor mitigation, i.e. conditional 2397 L1D flush. 2398 2399 SMT control and L1D flush control via the 2400 sysfs interface is still possible after 2401 boot. Hypervisors will issue a warning 2402 when the first VM is started in a 2403 potentially insecure configuration, 2404 i.e. SMT enabled or L1D flush disabled. 2405 2406 flush,nosmt 2407 2408 Disables SMT and enables the default 2409 hypervisor mitigation. 2410 2411 SMT control and L1D flush control via the 2412 sysfs interface is still possible after 2413 boot. Hypervisors will issue a warning 2414 when the first VM is started in a 2415 potentially insecure configuration, 2416 i.e. SMT enabled or L1D flush disabled. 2417 2418 flush,nowarn 2419 Same as 'flush', but hypervisors will not 2420 warn when a VM is started in a potentially 2421 insecure configuration. 2422 2423 off 2424 Disables hypervisor mitigations and doesn't 2425 emit any warnings. 2426 It also drops the swap size and available 2427 RAM limit restriction on both hypervisor and 2428 bare metal. 2429 2430 Default is 'flush'. 2431 2432 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst 2433 2434 l2cr= [PPC] 2435 2436 l3cr= [PPC] 2437 2438 lapic [X86-32,APIC] Enable the local APIC even if BIOS 2439 disabled it. 2440 2441 lapic= [X86,APIC] Do not use TSC deadline 2442 value for LAPIC timer one-shot implementation. Default 2443 back to the programmable timer unit in the LAPIC. 2444 Format: notscdeadline 2445 2446 lapic_timer_c2_ok [X86,APIC] trust the local apic timer 2447 in C2 power state. 2448 2449 libata.dma= [LIBATA] DMA control 2450 libata.dma=0 Disable all PATA and SATA DMA 2451 libata.dma=1 PATA and SATA Disk DMA only 2452 libata.dma=2 ATAPI (CDROM) DMA only 2453 libata.dma=4 Compact Flash DMA only 2454 Combinations also work, so libata.dma=3 enables DMA 2455 for disks and CDROMs, but not CFs. 2456 2457 libata.ignore_hpa= [LIBATA] Ignore HPA limit 2458 libata.ignore_hpa=0 keep BIOS limits (default) 2459 libata.ignore_hpa=1 ignore limits, using full disk 2460 2461 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 2462 when set. 2463 Format: <int> 2464 2465 libata.force= [LIBATA] Force configurations. The format is comma 2466 separated list of "[ID:]VAL" where ID is 2467 PORT[.DEVICE]. PORT and DEVICE are decimal numbers 2468 matching port, link or device. Basically, it matches 2469 the ATA ID string printed on console by libata. If 2470 the whole ID part is omitted, the last PORT and DEVICE 2471 values are used. If ID hasn't been specified yet, the 2472 configuration applies to all ports, links and devices. 2473 2474 If only DEVICE is omitted, the parameter applies to 2475 the port and all links and devices behind it. DEVICE 2476 number of 0 either selects the first device or the 2477 first fan-out link behind PMP device. It does not 2478 select the host link. DEVICE number of 15 selects the 2479 host link and device attached to it. 2480 2481 The VAL specifies the configuration to force. As long 2482 as there's no ambiguity shortcut notation is allowed. 2483 For example, both 1.5 and 1.5G would work for 1.5Gbps. 2484 The following configurations can be forced. 2485 2486 * Cable type: 40c, 80c, short40c, unk, ign or sata. 2487 Any ID with matching PORT is used. 2488 2489 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 2490 2491 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 2492 udma[/][16,25,33,44,66,100,133] notation is also 2493 allowed. 2494 2495 * [no]ncq: Turn on or off NCQ. 2496 2497 * [no]ncqtrim: Turn off queued DSM TRIM. 2498 2499 * nohrst, nosrst, norst: suppress hard, soft 2500 and both resets. 2501 2502 * rstonce: only attempt one reset during 2503 hot-unplug link recovery 2504 2505 * dump_id: dump IDENTIFY data. 2506 2507 * atapi_dmadir: Enable ATAPI DMADIR bridge support 2508 2509 * disable: Disable this device. 2510 2511 If there are multiple matching configurations changing 2512 the same attribute, the last one is used. 2513 2514 memblock=debug [KNL] Enable memblock debug messages. 2515 2516 load_ramdisk= [RAM] [Deprecated] 2517 2518 lockd.nlm_grace_period=P [NFS] Assign grace period. 2519 Format: <integer> 2520 2521 lockd.nlm_tcpport=N [NFS] Assign TCP port. 2522 Format: <integer> 2523 2524 lockd.nlm_timeout=T [NFS] Assign timeout value. 2525 Format: <integer> 2526 2527 lockd.nlm_udpport=M [NFS] Assign UDP port. 2528 Format: <integer> 2529 2530 lockdown= [SECURITY] 2531 { integrity | confidentiality } 2532 Enable the kernel lockdown feature. If set to 2533 integrity, kernel features that allow userland to 2534 modify the running kernel are disabled. If set to 2535 confidentiality, kernel features that allow userland 2536 to extract confidential information from the kernel 2537 are also disabled. 2538 2539 locktorture.nreaders_stress= [KNL] 2540 Set the number of locking read-acquisition kthreads. 2541 Defaults to being automatically set based on the 2542 number of online CPUs. 2543 2544 locktorture.nwriters_stress= [KNL] 2545 Set the number of locking write-acquisition kthreads. 2546 2547 locktorture.onoff_holdoff= [KNL] 2548 Set time (s) after boot for CPU-hotplug testing. 2549 2550 locktorture.onoff_interval= [KNL] 2551 Set time (s) between CPU-hotplug operations, or 2552 zero to disable CPU-hotplug testing. 2553 2554 locktorture.shuffle_interval= [KNL] 2555 Set task-shuffle interval (jiffies). Shuffling 2556 tasks allows some CPUs to go into dyntick-idle 2557 mode during the locktorture test. 2558 2559 locktorture.shutdown_secs= [KNL] 2560 Set time (s) after boot system shutdown. This 2561 is useful for hands-off automated testing. 2562 2563 locktorture.stat_interval= [KNL] 2564 Time (s) between statistics printk()s. 2565 2566 locktorture.stutter= [KNL] 2567 Time (s) to stutter testing, for example, 2568 specifying five seconds causes the test to run for 2569 five seconds, wait for five seconds, and so on. 2570 This tests the locking primitive's ability to 2571 transition abruptly to and from idle. 2572 2573 locktorture.torture_type= [KNL] 2574 Specify the locking implementation to test. 2575 2576 locktorture.verbose= [KNL] 2577 Enable additional printk() statements. 2578 2579 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 2580 Format: <irq> 2581 2582 loglevel= All Kernel Messages with a loglevel smaller than the 2583 console loglevel will be printed to the console. It can 2584 also be changed with klogd or other programs. The 2585 loglevels are defined as follows: 2586 2587 0 (KERN_EMERG) system is unusable 2588 1 (KERN_ALERT) action must be taken immediately 2589 2 (KERN_CRIT) critical conditions 2590 3 (KERN_ERR) error conditions 2591 4 (KERN_WARNING) warning conditions 2592 5 (KERN_NOTICE) normal but significant condition 2593 6 (KERN_INFO) informational 2594 7 (KERN_DEBUG) debug-level messages 2595 2596 log_buf_len=n[KMG] Sets the size of the printk ring buffer, 2597 in bytes. n must be a power of two and greater 2598 than the minimal size. The minimal size is defined 2599 by LOG_BUF_SHIFT kernel config parameter. There is 2600 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter 2601 that allows to increase the default size depending on 2602 the number of CPUs. See init/Kconfig for more details. 2603 2604 logo.nologo [FB] Disables display of the built-in Linux logo. 2605 This may be used to provide more screen space for 2606 kernel log messages and is useful when debugging 2607 kernel boot problems. 2608 2609 lp=0 [LP] Specify parallel ports to use, e.g, 2610 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 2611 lp=reset first parallel port). 'lp=0' disables the 2612 lp=auto printer driver. 'lp=reset' (which can be 2613 specified in addition to the ports) causes 2614 attached printers to be reset. Using 2615 lp=port1,port2,... specifies the parallel ports 2616 to associate lp devices with, starting with 2617 lp0. A port specification may be 'none' to skip 2618 that lp device, or a parport name such as 2619 'parport0'. Specifying 'lp=auto' instead of a 2620 port specification list means that device IDs 2621 from each port should be examined, to see if 2622 an IEEE 1284-compliant printer is attached; if 2623 so, the driver will manage that printer. 2624 See also header of drivers/char/lp.c. 2625 2626 lpj=n [KNL] 2627 Sets loops_per_jiffy to given constant, thus avoiding 2628 time-consuming boot-time autodetection (up to 250 ms per 2629 CPU). 0 enables autodetection (default). To determine 2630 the correct value for your kernel, boot with normal 2631 autodetection and see what value is printed. Note that 2632 on SMP systems the preset will be applied to all CPUs, 2633 which is likely to cause problems if your CPUs need 2634 significantly divergent settings. An incorrect value 2635 will cause delays in the kernel to be wrong, leading to 2636 unpredictable I/O errors and other breakage. Although 2637 unlikely, in the extreme case this might damage your 2638 hardware. 2639 2640 ltpc= [NET] 2641 Format: <io>,<irq>,<dma> 2642 2643 lsm.debug [SECURITY] Enable LSM initialization debugging output. 2644 2645 lsm=lsm1,...,lsmN 2646 [SECURITY] Choose order of LSM initialization. This 2647 overrides CONFIG_LSM, and the "security=" parameter. 2648 2649 machvec= [IA-64] Force the use of a particular machine-vector 2650 (machvec) in a generic kernel. 2651 Example: machvec=hpzx1 2652 2653 machtype= [Loongson] Share the same kernel image file between 2654 different yeeloong laptops. 2655 Example: machtype=lemote-yeeloong-2f-7inch 2656 2657 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater 2658 than or equal to this physical address is ignored. 2659 2660 maxcpus= [SMP] Maximum number of processors that an SMP kernel 2661 will bring up during bootup. maxcpus=n : n >= 0 limits 2662 the kernel to bring up 'n' processors. Surely after 2663 bootup you can bring up the other plugged cpu by executing 2664 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 2665 only takes effect during system bootup. 2666 While n=0 is a special case, it is equivalent to "nosmp", 2667 which also disables the IO APIC. 2668 2669 max_loop= [LOOP] The number of loop block devices that get 2670 (loop.max_loop) unconditionally pre-created at init time. The default 2671 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 2672 of statically allocating a predefined number, loop 2673 devices can be requested on-demand with the 2674 /dev/loop-control interface. 2675 2676 mce [X86-32] Machine Check Exception 2677 2678 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.rst 2679 2680 md= [HW] RAID subsystems devices and level 2681 See Documentation/admin-guide/md.rst. 2682 2683 mdacon= [MDA] 2684 Format: <first>,<last> 2685 Specifies range of consoles to be captured by the MDA. 2686 2687 mds= [X86,INTEL] 2688 Control mitigation for the Micro-architectural Data 2689 Sampling (MDS) vulnerability. 2690 2691 Certain CPUs are vulnerable to an exploit against CPU 2692 internal buffers which can forward information to a 2693 disclosure gadget under certain conditions. 2694 2695 In vulnerable processors, the speculatively 2696 forwarded data can be used in a cache side channel 2697 attack, to access data to which the attacker does 2698 not have direct access. 2699 2700 This parameter controls the MDS mitigation. The 2701 options are: 2702 2703 full - Enable MDS mitigation on vulnerable CPUs 2704 full,nosmt - Enable MDS mitigation and disable 2705 SMT on vulnerable CPUs 2706 off - Unconditionally disable MDS mitigation 2707 2708 On TAA-affected machines, mds=off can be prevented by 2709 an active TAA mitigation as both vulnerabilities are 2710 mitigated with the same mechanism so in order to disable 2711 this mitigation, you need to specify tsx_async_abort=off 2712 too. 2713 2714 Not specifying this option is equivalent to 2715 mds=full. 2716 2717 For details see: Documentation/admin-guide/hw-vuln/mds.rst 2718 2719 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory 2720 Amount of memory to be used in cases as follows: 2721 2722 1 for test; 2723 2 when the kernel is not able to see the whole system memory; 2724 3 memory that lies after 'mem=' boundary is excluded from 2725 the hypervisor, then assigned to KVM guests. 2726 2727 [X86] Work as limiting max address. Use together 2728 with memmap= to avoid physical address space collisions. 2729 Without memmap= PCI devices could be placed at addresses 2730 belonging to unused RAM. 2731 2732 Note that this only takes effects during boot time since 2733 in above case 3, memory may need be hot added after boot 2734 if system memory of hypervisor is not sufficient. 2735 2736 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 2737 memory. 2738 2739 memchunk=nn[KMG] 2740 [KNL,SH] Allow user to override the default size for 2741 per-device physically contiguous DMA buffers. 2742 2743 memhp_default_state=online/offline 2744 [KNL] Set the initial state for the memory hotplug 2745 onlining policy. If not specified, the default value is 2746 set according to the 2747 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config 2748 option. 2749 See Documentation/admin-guide/mm/memory-hotplug.rst. 2750 2751 memmap=exactmap [KNL,X86] Enable setting of an exact 2752 E820 memory map, as specified by the user. 2753 Such memmap=exactmap lines can be constructed based on 2754 BIOS output or other requirements. See the memmap=nn@ss 2755 option description. 2756 2757 memmap=nn[KMG]@ss[KMG] 2758 [KNL] Force usage of a specific region of memory. 2759 Region of memory to be used is from ss to ss+nn. 2760 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], 2761 which limits max address to nn[KMG]. 2762 Multiple different regions can be specified, 2763 comma delimited. 2764 Example: 2765 memmap=100M@2G,100M#3G,1G!1024G 2766 2767 memmap=nn[KMG]#ss[KMG] 2768 [KNL,ACPI] Mark specific memory as ACPI data. 2769 Region of memory to be marked is from ss to ss+nn. 2770 2771 memmap=nn[KMG]$ss[KMG] 2772 [KNL,ACPI] Mark specific memory as reserved. 2773 Region of memory to be reserved is from ss to ss+nn. 2774 Example: Exclude memory from 0x18690000-0x1869ffff 2775 memmap=64K$0x18690000 2776 or 2777 memmap=0x10000$0x18690000 2778 Some bootloaders may need an escape character before '$', 2779 like Grub2, otherwise '$' and the following number 2780 will be eaten. 2781 2782 memmap=nn[KMG]!ss[KMG] 2783 [KNL,X86] Mark specific memory as protected. 2784 Region of memory to be used, from ss to ss+nn. 2785 The memory region may be marked as e820 type 12 (0xc) 2786 and is NVDIMM or ADR memory. 2787 2788 memmap=<size>%<offset>-<oldtype>+<newtype> 2789 [KNL,ACPI] Convert memory within the specified region 2790 from <oldtype> to <newtype>. If "-<oldtype>" is left 2791 out, the whole region will be marked as <newtype>, 2792 even if previously unavailable. If "+<newtype>" is left 2793 out, matching memory will be removed. Types are 2794 specified as e820 types, e.g., 1 = RAM, 2 = reserved, 2795 3 = ACPI, 12 = PRAM. 2796 2797 memory_corruption_check=0/1 [X86] 2798 Some BIOSes seem to corrupt the first 64k of 2799 memory when doing things like suspend/resume. 2800 Setting this option will scan the memory 2801 looking for corruption. Enabling this will 2802 both detect corruption and prevent the kernel 2803 from using the memory being corrupted. 2804 However, its intended as a diagnostic tool; if 2805 repeatable BIOS-originated corruption always 2806 affects the same memory, you can use memmap= 2807 to prevent the kernel from using that memory. 2808 2809 memory_corruption_check_size=size [X86] 2810 By default it checks for corruption in the low 2811 64k, making this memory unavailable for normal 2812 use. Use this parameter to scan for 2813 corruption in more or less memory. 2814 2815 memory_corruption_check_period=seconds [X86] 2816 By default it checks for corruption every 60 2817 seconds. Use this parameter to check at some 2818 other rate. 0 disables periodic checking. 2819 2820 memtest= [KNL,X86,ARM,PPC] Enable memtest 2821 Format: <integer> 2822 default : 0 <disable> 2823 Specifies the number of memtest passes to be 2824 performed. Each pass selects another test 2825 pattern from a given set of patterns. Memtest 2826 fills the memory with this pattern, validates 2827 memory contents and reserves bad memory 2828 regions that are detected. 2829 2830 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control 2831 Valid arguments: on, off 2832 Default (depends on kernel configuration option): 2833 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y) 2834 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n) 2835 mem_encrypt=on: Activate SME 2836 mem_encrypt=off: Do not activate SME 2837 2838 Refer to Documentation/virt/kvm/amd-memory-encryption.rst 2839 for details on when memory encryption can be activated. 2840 2841 mem_sleep_default= [SUSPEND] Default system suspend mode: 2842 s2idle - Suspend-To-Idle 2843 shallow - Power-On Suspend or equivalent (if supported) 2844 deep - Suspend-To-RAM or equivalent (if supported) 2845 See Documentation/admin-guide/pm/sleep-states.rst. 2846 2847 meye.*= [HW] Set MotionEye Camera parameters 2848 See Documentation/admin-guide/media/meye.rst. 2849 2850 mfgpt_irq= [IA-32] Specify the IRQ to use for the 2851 Multi-Function General Purpose Timers on AMD Geode 2852 platforms. 2853 2854 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 2855 the BIOS has incorrectly applied a workaround. TinyBIOS 2856 version 0.98 is known to be affected, 0.99 fixes the 2857 problem by letting the user disable the workaround. 2858 2859 mga= [HW,DRM] 2860 2861 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this 2862 physical address is ignored. 2863 2864 mini2440= [ARM,HW,KNL] 2865 Format:[0..2][b][c][t] 2866 Default: "0tb" 2867 MINI2440 configuration specification: 2868 0 - The attached screen is the 3.5" TFT 2869 1 - The attached screen is the 7" TFT 2870 2 - The VGA Shield is attached (1024x768) 2871 Leaving out the screen size parameter will not load 2872 the TFT driver, and the framebuffer will be left 2873 unconfigured. 2874 b - Enable backlight. The TFT backlight pin will be 2875 linked to the kernel VESA blanking code and a GPIO 2876 LED. This parameter is not necessary when using the 2877 VGA shield. 2878 c - Enable the s3c camera interface. 2879 t - Reserved for enabling touchscreen support. The 2880 touchscreen support is not enabled in the mainstream 2881 kernel as of 2.6.30, a preliminary port can be found 2882 in the "bleeding edge" mini2440 support kernel at 2883 https://repo.or.cz/w/linux-2.6/mini2440.git 2884 2885 mitigations= 2886 [X86,PPC,S390,ARM64] Control optional mitigations for 2887 CPU vulnerabilities. This is a set of curated, 2888 arch-independent options, each of which is an 2889 aggregation of existing arch-specific options. 2890 2891 off 2892 Disable all optional CPU mitigations. This 2893 improves system performance, but it may also 2894 expose users to several CPU vulnerabilities. 2895 Equivalent to: nopti [X86,PPC] 2896 kpti=0 [ARM64] 2897 nospectre_v1 [X86,PPC] 2898 nobp=0 [S390] 2899 nospectre_v2 [X86,PPC,S390,ARM64] 2900 spectre_v2_user=off [X86] 2901 spec_store_bypass_disable=off [X86,PPC] 2902 ssbd=force-off [ARM64] 2903 l1tf=off [X86] 2904 mds=off [X86] 2905 tsx_async_abort=off [X86] 2906 kvm.nx_huge_pages=off [X86] 2907 no_entry_flush [PPC] 2908 no_uaccess_flush [PPC] 2909 mmio_stale_data=off [X86] 2910 retbleed=off [X86] 2911 2912 Exceptions: 2913 This does not have any effect on 2914 kvm.nx_huge_pages when 2915 kvm.nx_huge_pages=force. 2916 2917 auto (default) 2918 Mitigate all CPU vulnerabilities, but leave SMT 2919 enabled, even if it's vulnerable. This is for 2920 users who don't want to be surprised by SMT 2921 getting disabled across kernel upgrades, or who 2922 have other ways of avoiding SMT-based attacks. 2923 Equivalent to: (default behavior) 2924 2925 auto,nosmt 2926 Mitigate all CPU vulnerabilities, disabling SMT 2927 if needed. This is for users who always want to 2928 be fully mitigated, even if it means losing SMT. 2929 Equivalent to: l1tf=flush,nosmt [X86] 2930 mds=full,nosmt [X86] 2931 tsx_async_abort=full,nosmt [X86] 2932 mmio_stale_data=full,nosmt [X86] 2933 retbleed=auto,nosmt [X86] 2934 2935 mminit_loglevel= 2936 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this 2937 parameter allows control of the logging verbosity for 2938 the additional memory initialisation checks. A value 2939 of 0 disables mminit logging and a level of 4 will 2940 log everything. Information is printed at KERN_DEBUG 2941 so loglevel=8 may also need to be specified. 2942 2943 mmio_stale_data= 2944 [X86,INTEL] Control mitigation for the Processor 2945 MMIO Stale Data vulnerabilities. 2946 2947 Processor MMIO Stale Data is a class of 2948 vulnerabilities that may expose data after an MMIO 2949 operation. Exposed data could originate or end in 2950 the same CPU buffers as affected by MDS and TAA. 2951 Therefore, similar to MDS and TAA, the mitigation 2952 is to clear the affected CPU buffers. 2953 2954 This parameter controls the mitigation. The 2955 options are: 2956 2957 full - Enable mitigation on vulnerable CPUs 2958 2959 full,nosmt - Enable mitigation and disable SMT on 2960 vulnerable CPUs. 2961 2962 off - Unconditionally disable mitigation 2963 2964 On MDS or TAA affected machines, 2965 mmio_stale_data=off can be prevented by an active 2966 MDS or TAA mitigation as these vulnerabilities are 2967 mitigated with the same mechanism so in order to 2968 disable this mitigation, you need to specify 2969 mds=off and tsx_async_abort=off too. 2970 2971 Not specifying this option is equivalent to 2972 mmio_stale_data=full. 2973 2974 For details see: 2975 Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst 2976 2977 module.sig_enforce 2978 [KNL] When CONFIG_MODULE_SIG is set, this means that 2979 modules without (valid) signatures will fail to load. 2980 Note that if CONFIG_MODULE_SIG_FORCE is set, that 2981 is always true, so this option does nothing. 2982 2983 module_blacklist= [KNL] Do not load a comma-separated list of 2984 modules. Useful for debugging problem modules. 2985 2986 mousedev.tap_time= 2987 [MOUSE] Maximum time between finger touching and 2988 leaving touchpad surface for touch to be considered 2989 a tap and be reported as a left button click (for 2990 touchpads working in absolute mode only). 2991 Format: <msecs> 2992 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 2993 reporting absolute coordinates, such as tablets 2994 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 2995 reporting absolute coordinates, such as tablets 2996 2997 movablecore= [KNL,X86,IA-64,PPC] 2998 Format: nn[KMGTPE] | nn% 2999 This parameter is the complement to kernelcore=, it 3000 specifies the amount of memory used for migratable 3001 allocations. If both kernelcore and movablecore is 3002 specified, then kernelcore will be at *least* the 3003 specified value but may be more. If movablecore on its 3004 own is specified, the administrator must be careful 3005 that the amount of memory usable for all allocations 3006 is not too small. 3007 3008 movable_node [KNL] Boot-time switch to make hotplugable memory 3009 NUMA nodes to be movable. This means that the memory 3010 of such nodes will be usable only for movable 3011 allocations which rules out almost all kernel 3012 allocations. Use with caution! 3013 3014 MTD_Partition= [MTD] 3015 Format: <name>,<region-number>,<size>,<offset> 3016 3017 MTD_Region= [MTD] Format: 3018 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 3019 3020 mtdparts= [MTD] 3021 See drivers/mtd/parsers/cmdlinepart.c 3022 3023 multitce=off [PPC] This parameter disables the use of the pSeries 3024 firmware feature for updating multiple TCE entries 3025 at a time. 3026 3027 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 3028 3029 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 3030 3031 boundary - index of last SLC block on Flex-OneNAND. 3032 The remaining blocks are configured as MLC blocks. 3033 lock - Configure if Flex-OneNAND boundary should be locked. 3034 Once locked, the boundary cannot be changed. 3035 1 indicates lock status, 0 indicates unlock status. 3036 3037 mtdset= [ARM] 3038 ARM/S3C2412 JIVE boot control 3039 3040 See arch/arm/mach-s3c2412/mach-jive.c 3041 3042 mtouchusb.raw_coordinates= 3043 [HW] Make the MicroTouch USB driver use raw coordinates 3044 ('y', default) or cooked coordinates ('n') 3045 3046 mtrr_chunk_size=nn[KMG] [X86] 3047 used for mtrr cleanup. It is largest continuous chunk 3048 that could hold holes aka. UC entries. 3049 3050 mtrr_gran_size=nn[KMG] [X86] 3051 Used for mtrr cleanup. It is granularity of mtrr block. 3052 Default is 1. 3053 Large value could prevent small alignment from 3054 using up MTRRs. 3055 3056 mtrr_spare_reg_nr=n [X86] 3057 Format: <integer> 3058 Range: 0,7 : spare reg number 3059 Default : 1 3060 Used for mtrr cleanup. It is spare mtrr entries number. 3061 Set to 2 or more if your graphical card needs more. 3062 3063 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 3064 3065 netdev= [NET] Network devices parameters 3066 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 3067 Note that mem_start is often overloaded to mean 3068 something different and driver-specific. 3069 This usage is only documented in each driver source 3070 file if at all. 3071 3072 nf_conntrack.acct= 3073 [NETFILTER] Enable connection tracking flow accounting 3074 0 to disable accounting 3075 1 to enable accounting 3076 Default value is 0. 3077 3078 nfsaddrs= [NFS] Deprecated. Use ip= instead. 3079 See Documentation/admin-guide/nfs/nfsroot.rst. 3080 3081 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 3082 See Documentation/admin-guide/nfs/nfsroot.rst. 3083 3084 nfsrootdebug [NFS] enable nfsroot debugging messages. 3085 See Documentation/admin-guide/nfs/nfsroot.rst. 3086 3087 nfs.callback_nr_threads= 3088 [NFSv4] set the total number of threads that the 3089 NFS client will assign to service NFSv4 callback 3090 requests. 3091 3092 nfs.callback_tcpport= 3093 [NFS] set the TCP port on which the NFSv4 callback 3094 channel should listen. 3095 3096 nfs.cache_getent= 3097 [NFS] sets the pathname to the program which is used 3098 to update the NFS client cache entries. 3099 3100 nfs.cache_getent_timeout= 3101 [NFS] sets the timeout after which an attempt to 3102 update a cache entry is deemed to have failed. 3103 3104 nfs.idmap_cache_timeout= 3105 [NFS] set the maximum lifetime for idmapper cache 3106 entries. 3107 3108 nfs.enable_ino64= 3109 [NFS] enable 64-bit inode numbers. 3110 If zero, the NFS client will fake up a 32-bit inode 3111 number for the readdir() and stat() syscalls instead 3112 of returning the full 64-bit number. 3113 The default is to return 64-bit inode numbers. 3114 3115 nfs.max_session_cb_slots= 3116 [NFSv4.1] Sets the maximum number of session 3117 slots the client will assign to the callback 3118 channel. This determines the maximum number of 3119 callbacks the client will process in parallel for 3120 a particular server. 3121 3122 nfs.max_session_slots= 3123 [NFSv4.1] Sets the maximum number of session slots 3124 the client will attempt to negotiate with the server. 3125 This limits the number of simultaneous RPC requests 3126 that the client can send to the NFSv4.1 server. 3127 Note that there is little point in setting this 3128 value higher than the max_tcp_slot_table_limit. 3129 3130 nfs.nfs4_disable_idmapping= 3131 [NFSv4] When set to the default of '1', this option 3132 ensures that both the RPC level authentication 3133 scheme and the NFS level operations agree to use 3134 numeric uids/gids if the mount is using the 3135 'sec=sys' security flavour. In effect it is 3136 disabling idmapping, which can make migration from 3137 legacy NFSv2/v3 systems to NFSv4 easier. 3138 Servers that do not support this mode of operation 3139 will be autodetected by the client, and it will fall 3140 back to using the idmapper. 3141 To turn off this behaviour, set the value to '0'. 3142 nfs.nfs4_unique_id= 3143 [NFS4] Specify an additional fixed unique ident- 3144 ification string that NFSv4 clients can insert into 3145 their nfs_client_id4 string. This is typically a 3146 UUID that is generated at system install time. 3147 3148 nfs.send_implementation_id = 3149 [NFSv4.1] Send client implementation identification 3150 information in exchange_id requests. 3151 If zero, no implementation identification information 3152 will be sent. 3153 The default is to send the implementation identification 3154 information. 3155 3156 nfs.recover_lost_locks = 3157 [NFSv4] Attempt to recover locks that were lost due 3158 to a lease timeout on the server. Please note that 3159 doing this risks data corruption, since there are 3160 no guarantees that the file will remain unchanged 3161 after the locks are lost. 3162 If you want to enable the kernel legacy behaviour of 3163 attempting to recover these locks, then set this 3164 parameter to '1'. 3165 The default parameter value of '0' causes the kernel 3166 not to attempt recovery of lost locks. 3167 3168 nfs4.layoutstats_timer = 3169 [NFSv4.2] Change the rate at which the kernel sends 3170 layoutstats to the pNFS metadata server. 3171 3172 Setting this to value to 0 causes the kernel to use 3173 whatever value is the default set by the layout 3174 driver. A non-zero value sets the minimum interval 3175 in seconds between layoutstats transmissions. 3176 3177 nfsd.nfs4_disable_idmapping= 3178 [NFSv4] When set to the default of '1', the NFSv4 3179 server will return only numeric uids and gids to 3180 clients using auth_sys, and will accept numeric uids 3181 and gids from such clients. This is intended to ease 3182 migration from NFSv2/v3. 3183 3184 nmi_backtrace.backtrace_idle [KNL] 3185 Dump stacks even of idle CPUs in response to an 3186 NMI stack-backtrace request. 3187 3188 nmi_debug= [KNL,SH] Specify one or more actions to take 3189 when a NMI is triggered. 3190 Format: [state][,regs][,debounce][,die] 3191 3192 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 3193 Format: [panic,][nopanic,][num] 3194 Valid num: 0 or 1 3195 0 - turn hardlockup detector in nmi_watchdog off 3196 1 - turn hardlockup detector in nmi_watchdog on 3197 When panic is specified, panic when an NMI watchdog 3198 timeout occurs (or 'nopanic' to not panic on an NMI 3199 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set) 3200 To disable both hard and soft lockup detectors, 3201 please see 'nowatchdog'. 3202 This is useful when you use a panic=... timeout and 3203 need the box quickly up again. 3204 3205 These settings can be accessed at runtime via 3206 the nmi_watchdog and hardlockup_panic sysctls. 3207 3208 netpoll.carrier_timeout= 3209 [NET] Specifies amount of time (in seconds) that 3210 netpoll should wait for a carrier. By default netpoll 3211 waits 4 seconds. 3212 3213 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 3214 emulation library even if a 387 maths coprocessor 3215 is present. 3216 3217 no5lvl [X86-64] Disable 5-level paging mode. Forces 3218 kernel to use 4-level paging instead. 3219 3220 nofsgsbase [X86] Disables FSGSBASE instructions. 3221 3222 no_console_suspend 3223 [HW] Never suspend the console 3224 Disable suspending of consoles during suspend and 3225 hibernate operations. Once disabled, debugging 3226 messages can reach various consoles while the rest 3227 of the system is being put to sleep (ie, while 3228 debugging driver suspend/resume hooks). This may 3229 not work reliably with all consoles, but is known 3230 to work with serial and VGA consoles. 3231 To facilitate more flexible debugging, we also add 3232 console_suspend, a printk module parameter to control 3233 it. Users could use console_suspend (usually 3234 /sys/module/printk/parameters/console_suspend) to 3235 turn on/off it dynamically. 3236 3237 novmcoredd [KNL,KDUMP] 3238 Disable device dump. Device dump allows drivers to 3239 append dump data to vmcore so you can collect driver 3240 specified debug info. Drivers can append the data 3241 without any limit and this data is stored in memory, 3242 so this may cause significant memory stress. Disabling 3243 device dump can help save memory but the driver debug 3244 data will be no longer available. This parameter 3245 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP 3246 is set. 3247 3248 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien 3249 caches in the slab allocator. Saves per-node memory, 3250 but will impact performance. 3251 3252 noalign [KNL,ARM] 3253 3254 noaltinstr [S390] Disables alternative instructions patching 3255 (CPU alternatives feature). 3256 3257 noapic [SMP,APIC] Tells the kernel to not make use of any 3258 IOAPICs that may be present in the system. 3259 3260 noautogroup Disable scheduler automatic task group creation. 3261 3262 nobats [PPC] Do not use BATs for mapping kernel lowmem 3263 on "Classic" PPC cores. 3264 3265 nocache [ARM] 3266 3267 noclflush [BUGS=X86] Don't use the CLFLUSH instruction 3268 3269 nodelayacct [KNL] Disable per-task delay accounting 3270 3271 nodsp [SH] Disable hardware DSP at boot time. 3272 3273 noefi Disable EFI runtime services support. 3274 3275 no_entry_flush [PPC] Don't flush the L1-D cache when entering the kernel. 3276 3277 noexec [IA-64] 3278 3279 noexec [X86] 3280 On X86-32 available only on PAE configured kernels. 3281 noexec=on: enable non-executable mappings (default) 3282 noexec=off: disable non-executable mappings 3283 3284 nosmap [X86,PPC] 3285 Disable SMAP (Supervisor Mode Access Prevention) 3286 even if it is supported by processor. 3287 3288 nosmep [X86,PPC] 3289 Disable SMEP (Supervisor Mode Execution Prevention) 3290 even if it is supported by processor. 3291 3292 noexec32 [X86-64] 3293 This affects only 32-bit executables. 3294 noexec32=on: enable non-executable mappings (default) 3295 read doesn't imply executable mappings 3296 noexec32=off: disable non-executable mappings 3297 read implies executable mappings 3298 3299 nofpu [MIPS,SH] Disable hardware FPU at boot time. 3300 3301 nofxsr [BUGS=X86-32] Disables x86 floating point extended 3302 register save and restore. The kernel will only save 3303 legacy floating-point registers on task switch. 3304 3305 nohugeiomap [KNL,X86,PPC,ARM64] Disable kernel huge I/O mappings. 3306 3307 nosmt [KNL,S390] Disable symmetric multithreading (SMT). 3308 Equivalent to smt=1. 3309 3310 [KNL,X86] Disable symmetric multithreading (SMT). 3311 nosmt=force: Force disable SMT, cannot be undone 3312 via the sysfs control file. 3313 3314 nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1 3315 (bounds check bypass). With this option data leaks are 3316 possible in the system. 3317 3318 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for 3319 the Spectre variant 2 (indirect branch prediction) 3320 vulnerability. System may allow data leaks with this 3321 option. 3322 3323 nospec_store_bypass_disable 3324 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability 3325 3326 no_uaccess_flush 3327 [PPC] Don't flush the L1-D cache after accessing user data. 3328 3329 noxsave [BUGS=X86] Disables x86 extended register state save 3330 and restore using xsave. The kernel will fallback to 3331 enabling legacy floating-point and sse state. 3332 3333 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 3334 register states. The kernel will fall back to use 3335 xsave to save the states. By using this parameter, 3336 performance of saving the states is degraded because 3337 xsave doesn't support modified optimization while 3338 xsaveopt supports it on xsaveopt enabled systems. 3339 3340 noxsaves [X86] Disables xsaves and xrstors used in saving and 3341 restoring x86 extended register state in compacted 3342 form of xsave area. The kernel will fall back to use 3343 xsaveopt and xrstor to save and restore the states 3344 in standard form of xsave area. By using this 3345 parameter, xsave area per process might occupy more 3346 memory on xsaves enabled systems. 3347 3348 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or 3349 wfi(ARM) instruction doesn't work correctly and not to 3350 use it. This is also useful when using JTAG debugger. 3351 3352 no_file_caps Tells the kernel not to honor file capabilities. The 3353 only way then for a file to be executed with privilege 3354 is to be setuid root or executed by root. 3355 3356 nohalt [IA-64] Tells the kernel not to use the power saving 3357 function PAL_HALT_LIGHT when idle. This increases 3358 power-consumption. On the positive side, it reduces 3359 interrupt wake-up latency, which may improve performance 3360 in certain environments such as networked servers or 3361 real-time systems. 3362 3363 nohibernate [HIBERNATION] Disable hibernation and resume. 3364 3365 nohz= [KNL] Boottime enable/disable dynamic ticks 3366 Valid arguments: on, off 3367 Default: on 3368 3369 nohz_full= [KNL,BOOT,SMP,ISOL] 3370 The argument is a cpu list, as described above. 3371 In kernels built with CONFIG_NO_HZ_FULL=y, set 3372 the specified list of CPUs whose tick will be stopped 3373 whenever possible. The boot CPU will be forced outside 3374 the range to maintain the timekeeping. Any CPUs 3375 in this list will have their RCU callbacks offloaded, 3376 just as if they had also been called out in the 3377 rcu_nocbs= boot parameter. 3378 3379 noiotrap [SH] Disables trapped I/O port accesses. 3380 3381 noirqdebug [X86-32] Disables the code which attempts to detect and 3382 disable unhandled interrupt sources. 3383 3384 no_timer_check [X86,APIC] Disables the code which tests for 3385 broken timer IRQ sources. 3386 3387 noisapnp [ISAPNP] Disables ISA PnP code. 3388 3389 noinitrd [RAM] Tells the kernel not to load any configured 3390 initial RAM disk. 3391 3392 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt 3393 remapping. 3394 [Deprecated - use intremap=off] 3395 3396 nointroute [IA-64] 3397 3398 noinvpcid [X86] Disable the INVPCID cpu feature. 3399 3400 nojitter [IA-64] Disables jitter checking for ITC timers. 3401 3402 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver 3403 3404 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page 3405 fault handling. 3406 3407 no-vmw-sched-clock 3408 [X86,PV_OPS] Disable paravirtualized VMware scheduler 3409 clock and use the default one. 3410 3411 no-steal-acc [X86,PV_OPS,ARM64] Disable paravirtualized steal time 3412 accounting. steal time is computed, but won't 3413 influence scheduler behaviour 3414 3415 nolapic [X86-32,APIC] Do not enable or use the local APIC. 3416 3417 nolapic_timer [X86-32,APIC] Do not use the local APIC timer. 3418 3419 noltlbs [PPC] Do not use large page/tlb entries for kernel 3420 lowmem mapping on PPC40x and PPC8xx 3421 3422 nomca [IA-64] Disable machine check abort handling 3423 3424 nomce [X86-32] Disable Machine Check Exception 3425 3426 nomfgpt [X86-32] Disable Multi-Function General Purpose 3427 Timer usage (for AMD Geode machines). 3428 3429 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 3430 shutdown the other cpus. Instead use the REBOOT_VECTOR 3431 irq. 3432 3433 nomodule Disable module load 3434 3435 nopat [X86] Disable PAT (page attribute table extension of 3436 pagetables) support. 3437 3438 nopcid [X86-64] Disable the PCID cpu feature. 3439 3440 norandmaps Don't use address space randomization. Equivalent to 3441 echo 0 > /proc/sys/kernel/randomize_va_space 3442 3443 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 3444 with UP alternatives 3445 3446 nordrand [X86] Disable kernel use of the RDRAND and 3447 RDSEED instructions even if they are supported 3448 by the processor. RDRAND and RDSEED are still 3449 available to user space applications. 3450 3451 noresume [SWSUSP] Disables resume and restores original swap 3452 space. 3453 3454 no-scroll [VGA] Disables scrollback. 3455 This is required for the Braillex ib80-piezo Braille 3456 reader made by F.H. Papenmeier (Germany). 3457 3458 nosbagart [IA-64] 3459 3460 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support. 3461 3462 nosmp [SMP] Tells an SMP kernel to act as a UP kernel, 3463 and disable the IO APIC. legacy for "maxcpus=0". 3464 3465 nosoftlockup [KNL] Disable the soft-lockup detector. 3466 3467 nosync [HW,M68K] Disables sync negotiation for all devices. 3468 3469 nowatchdog [KNL] Disable both lockup detectors, i.e. 3470 soft-lockup and NMI watchdog (hard-lockup). 3471 3472 nowb [ARM] 3473 3474 nox2apic [X86-64,APIC] Do not enable x2APIC mode. 3475 3476 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when 3477 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off. 3478 Some features depend on CPU0. Known dependencies are: 3479 1. Resume from suspend/hibernate depends on CPU0. 3480 Suspend/hibernate will fail if CPU0 is offline and you 3481 need to online CPU0 before suspend/hibernate. 3482 2. PIC interrupts also depend on CPU0. CPU0 can't be 3483 removed if a PIC interrupt is detected. 3484 It's said poweroff/reboot may depend on CPU0 on some 3485 machines although I haven't seen such issues so far 3486 after CPU0 is offline on a few tested machines. 3487 If the dependencies are under your control, you can 3488 turn on cpu0_hotplug. 3489 3490 nps_mtm_hs_ctr= [KNL,ARC] 3491 This parameter sets the maximum duration, in 3492 cycles, each HW thread of the CTOP can run 3493 without interruptions, before HW switches it. 3494 The actual maximum duration is 16 times this 3495 parameter's value. 3496 Format: integer between 1 and 255 3497 Default: 255 3498 3499 nptcg= [IA-64] Override max number of concurrent global TLB 3500 purges which is reported from either PAL_VM_SUMMARY or 3501 SAL PALO. 3502 3503 nr_cpus= [SMP] Maximum number of processors that an SMP kernel 3504 could support. nr_cpus=n : n >= 1 limits the kernel to 3505 support 'n' processors. It could be larger than the 3506 number of already plugged CPU during bootup, later in 3507 runtime you can physically add extra cpu until it reaches 3508 n. So during boot up some boot time memory for per-cpu 3509 variables need be pre-allocated for later physical cpu 3510 hot plugging. 3511 3512 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 3513 3514 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing. 3515 Allowed values are enable and disable 3516 3517 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 3518 'node', 'default' can be specified 3519 This can be set from sysctl after boot. 3520 See Documentation/admin-guide/sysctl/vm.rst for details. 3521 3522 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver. 3523 See Documentation/core-api/debugging-via-ohci1394.rst for more 3524 info. 3525 3526 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 3527 Rather than timing out after 20 ms if an EC 3528 command is not properly ACKed, override the length 3529 of the timeout. We have interrupts disabled while 3530 waiting for the ACK, so if this is set too high 3531 interrupts *may* be lost! 3532 3533 omap_mux= [OMAP] Override bootloader pin multiplexing. 3534 Format: <mux_mode0.mode_name=value>... 3535 For example, to override I2C bus2: 3536 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 3537 3538 oprofile.timer= [HW] 3539 Use timer interrupt instead of performance counters 3540 3541 oprofile.cpu_type= Force an oprofile cpu type 3542 This might be useful if you have an older oprofile 3543 userland or if you want common events. 3544 Format: { arch_perfmon } 3545 arch_perfmon: [X86] Force use of architectural 3546 perfmon on Intel CPUs instead of the 3547 CPU specific event set. 3548 timer: [X86] Force use of architectural NMI 3549 timer mode (see also oprofile.timer 3550 for generic hr timer mode) 3551 3552 oops=panic Always panic on oopses. Default is to just kill the 3553 process, but there is a small probability of 3554 deadlocking the machine. 3555 This will also cause panics on machine check exceptions. 3556 Useful together with panic=30 to trigger a reboot. 3557 3558 page_alloc.shuffle= 3559 [KNL] Boolean flag to control whether the page allocator 3560 should randomize its free lists. The randomization may 3561 be automatically enabled if the kernel detects it is 3562 running on a platform with a direct-mapped memory-side 3563 cache, and this parameter can be used to 3564 override/disable that behavior. The state of the flag 3565 can be read from sysfs at: 3566 /sys/module/page_alloc/parameters/shuffle. 3567 3568 page_owner= [KNL] Boot-time page_owner enabling option. 3569 Storage of the information about who allocated 3570 each page is disabled in default. With this switch, 3571 we can turn it on. 3572 on: enable the feature 3573 3574 page_poison= [KNL] Boot-time parameter changing the state of 3575 poisoning on the buddy allocator, available with 3576 CONFIG_PAGE_POISONING=y. 3577 off: turn off poisoning (default) 3578 on: turn on poisoning 3579 3580 panic= [KNL] Kernel behaviour on panic: delay <timeout> 3581 timeout > 0: seconds before rebooting 3582 timeout = 0: wait forever 3583 timeout < 0: reboot immediately 3584 Format: <timeout> 3585 3586 panic_print= Bitmask for printing system info when panic happens. 3587 User can chose combination of the following bits: 3588 bit 0: print all tasks info 3589 bit 1: print system memory info 3590 bit 2: print timer info 3591 bit 3: print locks info if CONFIG_LOCKDEP is on 3592 bit 4: print ftrace buffer 3593 bit 5: print all printk messages in buffer 3594 3595 panic_on_taint= Bitmask for conditionally calling panic() in add_taint() 3596 Format: <hex>[,nousertaint] 3597 Hexadecimal bitmask representing the set of TAINT flags 3598 that will cause the kernel to panic when add_taint() is 3599 called with any of the flags in this set. 3600 The optional switch "nousertaint" can be utilized to 3601 prevent userspace forced crashes by writing to sysctl 3602 /proc/sys/kernel/tainted any flagset matching with the 3603 bitmask set on panic_on_taint. 3604 See Documentation/admin-guide/tainted-kernels.rst for 3605 extra details on the taint flags that users can pick 3606 to compose the bitmask to assign to panic_on_taint. 3607 3608 panic_on_warn panic() instead of WARN(). Useful to cause kdump 3609 on a WARN(). 3610 3611 crash_kexec_post_notifiers 3612 Run kdump after running panic-notifiers and dumping 3613 kmsg. This only for the users who doubt kdump always 3614 succeeds in any situation. 3615 Note that this also increases risks of kdump failure, 3616 because some panic notifiers can make the crashed 3617 kernel more unstable. 3618 3619 parkbd.port= [HW] Parallel port number the keyboard adapter is 3620 connected to, default is 0. 3621 Format: <parport#> 3622 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 3623 0 for XT, 1 for AT (default is AT). 3624 Format: <mode> 3625 3626 parport= [HW,PPT] Specify parallel ports. 0 disables. 3627 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 3628 Use 'auto' to force the driver to use any 3629 IRQ/DMA settings detected (the default is to 3630 ignore detected IRQ/DMA settings because of 3631 possible conflicts). You can specify the base 3632 address, IRQ, and DMA settings; IRQ and DMA 3633 should be numbers, or 'auto' (for using detected 3634 settings on that particular port), or 'nofifo' 3635 (to avoid using a FIFO even if it is detected). 3636 Parallel ports are assigned in the order they 3637 are specified on the command line, starting 3638 with parport0. 3639 3640 parport_init_mode= [HW,PPT] 3641 Configure VIA parallel port to operate in 3642 a specific mode. This is necessary on Pegasos 3643 computer where firmware has no options for setting 3644 up parallel port mode and sets it to spp. 3645 Currently this function knows 686a and 8231 chips. 3646 Format: [spp|ps2|epp|ecp|ecpepp] 3647 3648 pause_on_oops= 3649 Halt all CPUs after the first oops has been printed for 3650 the specified number of seconds. This is to be used if 3651 your oopses keep scrolling off the screen. 3652 3653 pcbit= [HW,ISDN] 3654 3655 pcd. [PARIDE] 3656 See header of drivers/block/paride/pcd.c. 3657 See also Documentation/admin-guide/blockdev/paride.rst. 3658 3659 pci=option[,option...] [PCI] various PCI subsystem options. 3660 3661 Some options herein operate on a specific device 3662 or a set of devices (<pci_dev>). These are 3663 specified in one of the following formats: 3664 3665 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* 3666 pci:<vendor>:<device>[:<subvendor>:<subdevice>] 3667 3668 Note: the first format specifies a PCI 3669 bus/device/function address which may change 3670 if new hardware is inserted, if motherboard 3671 firmware changes, or due to changes caused 3672 by other kernel parameters. If the 3673 domain is left unspecified, it is 3674 taken to be zero. Optionally, a path 3675 to a device through multiple device/function 3676 addresses can be specified after the base 3677 address (this is more robust against 3678 renumbering issues). The second format 3679 selects devices using IDs from the 3680 configuration space which may match multiple 3681 devices in the system. 3682 3683 earlydump dump PCI config space before the kernel 3684 changes anything 3685 off [X86] don't probe for the PCI bus 3686 bios [X86-32] force use of PCI BIOS, don't access 3687 the hardware directly. Use this if your machine 3688 has a non-standard PCI host bridge. 3689 nobios [X86-32] disallow use of PCI BIOS, only direct 3690 hardware access methods are allowed. Use this 3691 if you experience crashes upon bootup and you 3692 suspect they are caused by the BIOS. 3693 conf1 [X86] Force use of PCI Configuration Access 3694 Mechanism 1 (config address in IO port 0xCF8, 3695 data in IO port 0xCFC, both 32-bit). 3696 conf2 [X86] Force use of PCI Configuration Access 3697 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 3698 the function, IO port 0xCFA, also 8-bit, sets 3699 bus number. The config space is then accessed 3700 through ports 0xC000-0xCFFF). 3701 See http://wiki.osdev.org/PCI for more info 3702 on the configuration access mechanisms. 3703 noaer [PCIE] If the PCIEAER kernel config parameter is 3704 enabled, this kernel boot option can be used to 3705 disable the use of PCIE advanced error reporting. 3706 nodomains [PCI] Disable support for multiple PCI 3707 root domains (aka PCI segments, in ACPI-speak). 3708 nommconf [X86] Disable use of MMCONFIG for PCI 3709 Configuration 3710 check_enable_amd_mmconf [X86] check for and enable 3711 properly configured MMIO access to PCI 3712 config space on AMD family 10h CPU 3713 nomsi [MSI] If the PCI_MSI kernel config parameter is 3714 enabled, this kernel boot option can be used to 3715 disable the use of MSI interrupts system-wide. 3716 noioapicquirk [APIC] Disable all boot interrupt quirks. 3717 Safety option to keep boot IRQs enabled. This 3718 should never be necessary. 3719 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 3720 primary IO-APIC for bridges that cannot disable 3721 boot IRQs. This fixes a source of spurious IRQs 3722 when the system masks IRQs. 3723 noioapicreroute [APIC] Disable workaround that uses the 3724 boot IRQ equivalent of an IRQ that connects to 3725 a chipset where boot IRQs cannot be disabled. 3726 The opposite of ioapicreroute. 3727 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 3728 routing table. These calls are known to be buggy 3729 on several machines and they hang the machine 3730 when used, but on other computers it's the only 3731 way to get the interrupt routing table. Try 3732 this option if the kernel is unable to allocate 3733 IRQs or discover secondary PCI buses on your 3734 motherboard. 3735 rom [X86] Assign address space to expansion ROMs. 3736 Use with caution as certain devices share 3737 address decoders between ROMs and other 3738 resources. 3739 norom [X86] Do not assign address space to 3740 expansion ROMs that do not already have 3741 BIOS assigned address ranges. 3742 nobar [X86] Do not assign address space to the 3743 BARs that weren't assigned by the BIOS. 3744 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 3745 assigned automatically to PCI devices. You can 3746 make the kernel exclude IRQs of your ISA cards 3747 this way. 3748 pirqaddr=0xAAAAA [X86] Specify the physical address 3749 of the PIRQ table (normally generated 3750 by the BIOS) if it is outside the 3751 F0000h-100000h range. 3752 lastbus=N [X86] Scan all buses thru bus #N. Can be 3753 useful if the kernel is unable to find your 3754 secondary buses and you want to tell it 3755 explicitly which ones they are. 3756 assign-busses [X86] Always assign all PCI bus 3757 numbers ourselves, overriding 3758 whatever the firmware may have done. 3759 usepirqmask [X86] Honor the possible IRQ mask stored 3760 in the BIOS $PIR table. This is needed on 3761 some systems with broken BIOSes, notably 3762 some HP Pavilion N5400 and Omnibook XE3 3763 notebooks. This will have no effect if ACPI 3764 IRQ routing is enabled. 3765 noacpi [X86] Do not use ACPI for IRQ routing 3766 or for PCI scanning. 3767 use_crs [X86] Use PCI host bridge window information 3768 from ACPI. On BIOSes from 2008 or later, this 3769 is enabled by default. If you need to use this, 3770 please report a bug. 3771 nocrs [X86] Ignore PCI host bridge windows from ACPI. 3772 If you need to use this, please report a bug. 3773 routeirq Do IRQ routing for all PCI devices. 3774 This is normally done in pci_enable_device(), 3775 so this option is a temporary workaround 3776 for broken drivers that don't call it. 3777 skip_isa_align [X86] do not align io start addr, so can 3778 handle more pci cards 3779 noearly [X86] Don't do any early type 1 scanning. 3780 This might help on some broken boards which 3781 machine check when some devices' config space 3782 is read. But various workarounds are disabled 3783 and some IOMMU drivers will not work. 3784 bfsort Sort PCI devices into breadth-first order. 3785 This sorting is done to get a device 3786 order compatible with older (<= 2.4) kernels. 3787 nobfsort Don't sort PCI devices into breadth-first order. 3788 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 3789 tuning and use the BIOS-configured MPS defaults. 3790 pcie_bus_safe Set every device's MPS to the largest value 3791 supported by all devices below the root complex. 3792 pcie_bus_perf Set device MPS to the largest allowable MPS 3793 based on its parent bus. Also set MRRS (Max 3794 Read Request Size) to the largest supported 3795 value (no larger than the MPS that the device 3796 or bus can support) for best performance. 3797 pcie_bus_peer2peer Set every device's MPS to 128B, which 3798 every device is guaranteed to support. This 3799 configuration allows peer-to-peer DMA between 3800 any pair of devices, possibly at the cost of 3801 reduced performance. This also guarantees 3802 that hot-added devices will work. 3803 cbiosize=nn[KMG] The fixed amount of bus space which is 3804 reserved for the CardBus bridge's IO window. 3805 The default value is 256 bytes. 3806 cbmemsize=nn[KMG] The fixed amount of bus space which is 3807 reserved for the CardBus bridge's memory 3808 window. The default value is 64 megabytes. 3809 resource_alignment= 3810 Format: 3811 [<order of align>@]<pci_dev>[; ...] 3812 Specifies alignment and device to reassign 3813 aligned memory resources. How to 3814 specify the device is described above. 3815 If <order of align> is not specified, 3816 PAGE_SIZE is used as alignment. 3817 A PCI-PCI bridge can be specified if resource 3818 windows need to be expanded. 3819 To specify the alignment for several 3820 instances of a device, the PCI vendor, 3821 device, subvendor, and subdevice may be 3822 specified, e.g., 12@pci:8086:9c22:103c:198f 3823 for 4096-byte alignment. 3824 ecrc= Enable/disable PCIe ECRC (transaction layer 3825 end-to-end CRC checking). 3826 bios: Use BIOS/firmware settings. This is the 3827 the default. 3828 off: Turn ECRC off 3829 on: Turn ECRC on. 3830 hpiosize=nn[KMG] The fixed amount of bus space which is 3831 reserved for hotplug bridge's IO window. 3832 Default size is 256 bytes. 3833 hpmmiosize=nn[KMG] The fixed amount of bus space which is 3834 reserved for hotplug bridge's MMIO window. 3835 Default size is 2 megabytes. 3836 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is 3837 reserved for hotplug bridge's MMIO_PREF window. 3838 Default size is 2 megabytes. 3839 hpmemsize=nn[KMG] The fixed amount of bus space which is 3840 reserved for hotplug bridge's MMIO and 3841 MMIO_PREF window. 3842 Default size is 2 megabytes. 3843 hpbussize=nn The minimum amount of additional bus numbers 3844 reserved for buses below a hotplug bridge. 3845 Default is 1. 3846 realloc= Enable/disable reallocating PCI bridge resources 3847 if allocations done by BIOS are too small to 3848 accommodate resources required by all child 3849 devices. 3850 off: Turn realloc off 3851 on: Turn realloc on 3852 realloc same as realloc=on 3853 noari do not use PCIe ARI. 3854 noats [PCIE, Intel-IOMMU, AMD-IOMMU] 3855 do not use PCIe ATS (and IOMMU device IOTLB). 3856 pcie_scan_all Scan all possible PCIe devices. Otherwise we 3857 only look for one device below a PCIe downstream 3858 port. 3859 big_root_window Try to add a big 64bit memory window to the PCIe 3860 root complex on AMD CPUs. Some GFX hardware 3861 can resize a BAR to allow access to all VRAM. 3862 Adding the window is slightly risky (it may 3863 conflict with unreported devices), so this 3864 taints the kernel. 3865 disable_acs_redir=<pci_dev>[; ...] 3866 Specify one or more PCI devices (in the format 3867 specified above) separated by semicolons. 3868 Each device specified will have the PCI ACS 3869 redirect capabilities forced off which will 3870 allow P2P traffic between devices through 3871 bridges without forcing it upstream. Note: 3872 this removes isolation between devices and 3873 may put more devices in an IOMMU group. 3874 force_floating [S390] Force usage of floating interrupts. 3875 nomio [S390] Do not use MIO instructions. 3876 norid [S390] ignore the RID field and force use of 3877 one PCI domain per PCI function 3878 3879 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power 3880 Management. 3881 off Disable ASPM. 3882 force Enable ASPM even on devices that claim not to support it. 3883 WARNING: Forcing ASPM on may cause system lockups. 3884 3885 pcie_ports= [PCIE] PCIe port services handling: 3886 native Use native PCIe services (PME, AER, DPC, PCIe hotplug) 3887 even if the platform doesn't give the OS permission to 3888 use them. This may cause conflicts if the platform 3889 also tries to use these services. 3890 dpc-native Use native PCIe service for DPC only. May 3891 cause conflicts if firmware uses AER or DPC. 3892 compat Disable native PCIe services (PME, AER, DPC, PCIe 3893 hotplug). 3894 3895 pcie_port_pm= [PCIE] PCIe port power management handling: 3896 off Disable power management of all PCIe ports 3897 force Forcibly enable power management of all PCIe ports 3898 3899 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 3900 nomsi Do not use MSI for native PCIe PME signaling (this makes 3901 all PCIe root ports use INTx for all services). 3902 3903 pcmv= [HW,PCMCIA] BadgePAD 4 3904 3905 pd_ignore_unused 3906 [PM] 3907 Keep all power-domains already enabled by bootloader on, 3908 even if no driver has claimed them. This is useful 3909 for debug and development, but should not be 3910 needed on a platform with proper driver support. 3911 3912 pd. [PARIDE] 3913 See Documentation/admin-guide/blockdev/paride.rst. 3914 3915 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 3916 boot time. 3917 Format: { 0 | 1 } 3918 See arch/parisc/kernel/pdc_chassis.c 3919 3920 percpu_alloc= Select which percpu first chunk allocator to use. 3921 Currently supported values are "embed" and "page". 3922 Archs may support subset or none of the selections. 3923 See comments in mm/percpu.c for details on each 3924 allocator. This parameter is primarily for debugging 3925 and performance comparison. 3926 3927 pf. [PARIDE] 3928 See Documentation/admin-guide/blockdev/paride.rst. 3929 3930 pg. [PARIDE] 3931 See Documentation/admin-guide/blockdev/paride.rst. 3932 3933 pirq= [SMP,APIC] Manual mp-table setup 3934 See Documentation/x86/i386/IO-APIC.rst. 3935 3936 plip= [PPT,NET] Parallel port network link 3937 Format: { parport<nr> | timid | 0 } 3938 See also Documentation/admin-guide/parport.rst. 3939 3940 pmtmr= [X86] Manual setup of pmtmr I/O Port. 3941 Override pmtimer IOPort with a hex value. 3942 e.g. pmtmr=0x508 3943 3944 pm_debug_messages [SUSPEND,KNL] 3945 Enable suspend/resume debug messages during boot up. 3946 3947 pnp.debug=1 [PNP] 3948 Enable PNP debug messages (depends on the 3949 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 3950 via /sys/module/pnp/parameters/debug. We always show 3951 current resource usage; turning this on also shows 3952 possible settings and some assignment information. 3953 3954 pnpacpi= [ACPI] 3955 { off } 3956 3957 pnpbios= [ISAPNP] 3958 { on | off | curr | res | no-curr | no-res } 3959 3960 pnp_reserve_irq= 3961 [ISAPNP] Exclude IRQs for the autoconfiguration 3962 3963 pnp_reserve_dma= 3964 [ISAPNP] Exclude DMAs for the autoconfiguration 3965 3966 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 3967 Ranges are in pairs (I/O port base and size). 3968 3969 pnp_reserve_mem= 3970 [ISAPNP] Exclude memory regions for the 3971 autoconfiguration. 3972 Ranges are in pairs (memory base and size). 3973 3974 ports= [IP_VS_FTP] IPVS ftp helper module 3975 Default is 21. 3976 Up to 8 (IP_VS_APP_MAX_PORTS) ports 3977 may be specified. 3978 Format: <port>,<port>.... 3979 3980 powersave=off [PPC] This option disables power saving features. 3981 It specifically disables cpuidle and sets the 3982 platform machine description specific power_save 3983 function to NULL. On Idle the CPU just reduces 3984 execution priority. 3985 3986 ppc_strict_facility_enable 3987 [PPC] This option catches any kernel floating point, 3988 Altivec, VSX and SPE outside of regions specifically 3989 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 3990 There is some performance impact when enabling this. 3991 3992 ppc_tm= [PPC] 3993 Format: {"off"} 3994 Disable Hardware Transactional Memory 3995 3996 print-fatal-signals= 3997 [KNL] debug: print fatal signals 3998 3999 If enabled, warn about various signal handling 4000 related application anomalies: too many signals, 4001 too many POSIX.1 timers, fatal signals causing a 4002 coredump - etc. 4003 4004 If you hit the warning due to signal overflow, 4005 you might want to try "ulimit -i unlimited". 4006 4007 default: off. 4008 4009 printk.always_kmsg_dump= 4010 Trigger kmsg_dump for cases other than kernel oops or 4011 panics 4012 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 4013 default: disabled 4014 4015 printk.devkmsg={on,off,ratelimit} 4016 Control writing to /dev/kmsg. 4017 on - unlimited logging to /dev/kmsg from userspace 4018 off - logging to /dev/kmsg disabled 4019 ratelimit - ratelimit the logging 4020 Default: ratelimit 4021 4022 printk.time= Show timing data prefixed to each printk message line 4023 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 4024 4025 processor.max_cstate= [HW,ACPI] 4026 Limit processor to maximum C-state 4027 max_cstate=9 overrides any DMI blacklist limit. 4028 4029 processor.nocst [HW,ACPI] 4030 Ignore the _CST method to determine C-states, 4031 instead using the legacy FADT method 4032 4033 profile= [KNL] Enable kernel profiling via /proc/profile 4034 Format: [<profiletype>,]<number> 4035 Param: <profiletype>: "schedule", "sleep", or "kvm" 4036 [defaults to kernel profiling] 4037 Param: "schedule" - profile schedule points. 4038 Param: "sleep" - profile D-state sleeping (millisecs). 4039 Requires CONFIG_SCHEDSTATS 4040 Param: "kvm" - profile VM exits. 4041 Param: <number> - step/bucket size as a power of 2 for 4042 statistical time based profiling. 4043 4044 prompt_ramdisk= [RAM] [Deprecated] 4045 4046 prot_virt= [S390] enable hosting protected virtual machines 4047 isolated from the hypervisor (if hardware supports 4048 that). 4049 Format: <bool> 4050 4051 psi= [KNL] Enable or disable pressure stall information 4052 tracking. 4053 Format: <bool> 4054 4055 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 4056 probe for; one of (bare|imps|exps|lifebook|any). 4057 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 4058 per second. 4059 psmouse.resetafter= [HW,MOUSE] 4060 Try to reset the device after so many bad packets 4061 (0 = never). 4062 psmouse.resolution= 4063 [HW,MOUSE] Set desired mouse resolution, in dpi. 4064 psmouse.smartscroll= 4065 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 4066 0 = disabled, 1 = enabled (default). 4067 4068 pstore.backend= Specify the name of the pstore backend to use 4069 4070 pt. [PARIDE] 4071 See Documentation/admin-guide/blockdev/paride.rst. 4072 4073 pti= [X86-64] Control Page Table Isolation of user and 4074 kernel address spaces. Disabling this feature 4075 removes hardening, but improves performance of 4076 system calls and interrupts. 4077 4078 on - unconditionally enable 4079 off - unconditionally disable 4080 auto - kernel detects whether your CPU model is 4081 vulnerable to issues that PTI mitigates 4082 4083 Not specifying this option is equivalent to pti=auto. 4084 4085 nopti [X86-64] 4086 Equivalent to pti=off 4087 4088 pty.legacy_count= 4089 [KNL] Number of legacy pty's. Overwrites compiled-in 4090 default number. 4091 4092 quiet [KNL] Disable most log messages 4093 4094 r128= [HW,DRM] 4095 4096 raid= [HW,RAID] 4097 See Documentation/admin-guide/md.rst. 4098 4099 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 4100 See Documentation/admin-guide/blockdev/ramdisk.rst. 4101 4102 ramdisk_start= [RAM] RAM disk image start address 4103 4104 random.trust_cpu={on,off} 4105 [KNL] Enable or disable trusting the use of the 4106 CPU's random number generator (if available) to 4107 fully seed the kernel's CRNG. Default is controlled 4108 by CONFIG_RANDOM_TRUST_CPU. 4109 4110 random.trust_bootloader={on,off} 4111 [KNL] Enable or disable trusting the use of a 4112 seed passed by the bootloader (if available) to 4113 fully seed the kernel's CRNG. Default is controlled 4114 by CONFIG_RANDOM_TRUST_BOOTLOADER. 4115 4116 ras=option[,option,...] [KNL] RAS-specific options 4117 4118 cec_disable [X86] 4119 Disable the Correctable Errors Collector, 4120 see CONFIG_RAS_CEC help text. 4121 4122 rcu_nocbs= [KNL] 4123 The argument is a cpu list, as described above, 4124 except that the string "all" can be used to 4125 specify every CPU on the system. 4126 4127 In kernels built with CONFIG_RCU_NOCB_CPU=y, set 4128 the specified list of CPUs to be no-callback CPUs. 4129 Invocation of these CPUs' RCU callbacks will be 4130 offloaded to "rcuox/N" kthreads created for that 4131 purpose, where "x" is "p" for RCU-preempt, and 4132 "s" for RCU-sched, and "N" is the CPU number. 4133 This reduces OS jitter on the offloaded CPUs, 4134 which can be useful for HPC and real-time 4135 workloads. It can also improve energy efficiency 4136 for asymmetric multiprocessors. 4137 4138 rcu_nocb_poll [KNL] 4139 Rather than requiring that offloaded CPUs 4140 (specified by rcu_nocbs= above) explicitly 4141 awaken the corresponding "rcuoN" kthreads, 4142 make these kthreads poll for callbacks. 4143 This improves the real-time response for the 4144 offloaded CPUs by relieving them of the need to 4145 wake up the corresponding kthread, but degrades 4146 energy efficiency by requiring that the kthreads 4147 periodically wake up to do the polling. 4148 4149 rcutree.blimit= [KNL] 4150 Set maximum number of finished RCU callbacks to 4151 process in one batch. 4152 4153 rcutree.dump_tree= [KNL] 4154 Dump the structure of the rcu_node combining tree 4155 out at early boot. This is used for diagnostic 4156 purposes, to verify correct tree setup. 4157 4158 rcutree.gp_cleanup_delay= [KNL] 4159 Set the number of jiffies to delay each step of 4160 RCU grace-period cleanup. 4161 4162 rcutree.gp_init_delay= [KNL] 4163 Set the number of jiffies to delay each step of 4164 RCU grace-period initialization. 4165 4166 rcutree.gp_preinit_delay= [KNL] 4167 Set the number of jiffies to delay each step of 4168 RCU grace-period pre-initialization, that is, 4169 the propagation of recent CPU-hotplug changes up 4170 the rcu_node combining tree. 4171 4172 rcutree.use_softirq= [KNL] 4173 If set to zero, move all RCU_SOFTIRQ processing to 4174 per-CPU rcuc kthreads. Defaults to a non-zero 4175 value, meaning that RCU_SOFTIRQ is used by default. 4176 Specify rcutree.use_softirq=0 to use rcuc kthreads. 4177 4178 rcutree.rcu_fanout_exact= [KNL] 4179 Disable autobalancing of the rcu_node combining 4180 tree. This is used by rcutorture, and might 4181 possibly be useful for architectures having high 4182 cache-to-cache transfer latencies. 4183 4184 rcutree.rcu_fanout_leaf= [KNL] 4185 Change the number of CPUs assigned to each 4186 leaf rcu_node structure. Useful for very 4187 large systems, which will choose the value 64, 4188 and for NUMA systems with large remote-access 4189 latencies, which will choose a value aligned 4190 with the appropriate hardware boundaries. 4191 4192 rcutree.rcu_min_cached_objs= [KNL] 4193 Minimum number of objects which are cached and 4194 maintained per one CPU. Object size is equal 4195 to PAGE_SIZE. The cache allows to reduce the 4196 pressure to page allocator, also it makes the 4197 whole algorithm to behave better in low memory 4198 condition. 4199 4200 rcutree.jiffies_till_first_fqs= [KNL] 4201 Set delay from grace-period initialization to 4202 first attempt to force quiescent states. 4203 Units are jiffies, minimum value is zero, 4204 and maximum value is HZ. 4205 4206 rcutree.jiffies_till_next_fqs= [KNL] 4207 Set delay between subsequent attempts to force 4208 quiescent states. Units are jiffies, minimum 4209 value is one, and maximum value is HZ. 4210 4211 rcutree.jiffies_till_sched_qs= [KNL] 4212 Set required age in jiffies for a 4213 given grace period before RCU starts 4214 soliciting quiescent-state help from 4215 rcu_note_context_switch() and cond_resched(). 4216 If not specified, the kernel will calculate 4217 a value based on the most recent settings 4218 of rcutree.jiffies_till_first_fqs 4219 and rcutree.jiffies_till_next_fqs. 4220 This calculated value may be viewed in 4221 rcutree.jiffies_to_sched_qs. Any attempt to set 4222 rcutree.jiffies_to_sched_qs will be cheerfully 4223 overwritten. 4224 4225 rcutree.kthread_prio= [KNL,BOOT] 4226 Set the SCHED_FIFO priority of the RCU per-CPU 4227 kthreads (rcuc/N). This value is also used for 4228 the priority of the RCU boost threads (rcub/N) 4229 and for the RCU grace-period kthreads (rcu_bh, 4230 rcu_preempt, and rcu_sched). If RCU_BOOST is 4231 set, valid values are 1-99 and the default is 1 4232 (the least-favored priority). Otherwise, when 4233 RCU_BOOST is not set, valid values are 0-99 and 4234 the default is zero (non-realtime operation). 4235 4236 rcutree.rcu_nocb_gp_stride= [KNL] 4237 Set the number of NOCB callback kthreads in 4238 each group, which defaults to the square root 4239 of the number of CPUs. Larger numbers reduce 4240 the wakeup overhead on the global grace-period 4241 kthread, but increases that same overhead on 4242 each group's NOCB grace-period kthread. 4243 4244 rcutree.qhimark= [KNL] 4245 Set threshold of queued RCU callbacks beyond which 4246 batch limiting is disabled. 4247 4248 rcutree.qlowmark= [KNL] 4249 Set threshold of queued RCU callbacks below which 4250 batch limiting is re-enabled. 4251 4252 rcutree.qovld= [KNL] 4253 Set threshold of queued RCU callbacks beyond which 4254 RCU's force-quiescent-state scan will aggressively 4255 enlist help from cond_resched() and sched IPIs to 4256 help CPUs more quickly reach quiescent states. 4257 Set to less than zero to make this be set based 4258 on rcutree.qhimark at boot time and to zero to 4259 disable more aggressive help enlistment. 4260 4261 rcutree.rcu_idle_gp_delay= [KNL] 4262 Set wakeup interval for idle CPUs that have 4263 RCU callbacks (RCU_FAST_NO_HZ=y). 4264 4265 rcutree.rcu_idle_lazy_gp_delay= [KNL] 4266 Set wakeup interval for idle CPUs that have 4267 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y). 4268 Lazy RCU callbacks are those which RCU can 4269 prove do nothing more than free memory. 4270 4271 rcutree.rcu_kick_kthreads= [KNL] 4272 Cause the grace-period kthread to get an extra 4273 wake_up() if it sleeps three times longer than 4274 it should at force-quiescent-state time. 4275 This wake_up() will be accompanied by a 4276 WARN_ONCE() splat and an ftrace_dump(). 4277 4278 rcutree.rcu_unlock_delay= [KNL] 4279 In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels, 4280 this specifies an rcu_read_unlock()-time delay 4281 in microseconds. This defaults to zero. 4282 Larger delays increase the probability of 4283 catching RCU pointer leaks, that is, buggy use 4284 of RCU-protected pointers after the relevant 4285 rcu_read_unlock() has completed. 4286 4287 rcutree.sysrq_rcu= [KNL] 4288 Commandeer a sysrq key to dump out Tree RCU's 4289 rcu_node tree with an eye towards determining 4290 why a new grace period has not yet started. 4291 4292 rcuscale.gp_async= [KNL] 4293 Measure performance of asynchronous 4294 grace-period primitives such as call_rcu(). 4295 4296 rcuscale.gp_async_max= [KNL] 4297 Specify the maximum number of outstanding 4298 callbacks per writer thread. When a writer 4299 thread exceeds this limit, it invokes the 4300 corresponding flavor of rcu_barrier() to allow 4301 previously posted callbacks to drain. 4302 4303 rcuscale.gp_exp= [KNL] 4304 Measure performance of expedited synchronous 4305 grace-period primitives. 4306 4307 rcuscale.holdoff= [KNL] 4308 Set test-start holdoff period. The purpose of 4309 this parameter is to delay the start of the 4310 test until boot completes in order to avoid 4311 interference. 4312 4313 rcuscale.kfree_rcu_test= [KNL] 4314 Set to measure performance of kfree_rcu() flooding. 4315 4316 rcuscale.kfree_nthreads= [KNL] 4317 The number of threads running loops of kfree_rcu(). 4318 4319 rcuscale.kfree_alloc_num= [KNL] 4320 Number of allocations and frees done in an iteration. 4321 4322 rcuscale.kfree_loops= [KNL] 4323 Number of loops doing rcuscale.kfree_alloc_num number 4324 of allocations and frees. 4325 4326 rcuscale.nreaders= [KNL] 4327 Set number of RCU readers. The value -1 selects 4328 N, where N is the number of CPUs. A value 4329 "n" less than -1 selects N-n+1, where N is again 4330 the number of CPUs. For example, -2 selects N 4331 (the number of CPUs), -3 selects N+1, and so on. 4332 A value of "n" less than or equal to -N selects 4333 a single reader. 4334 4335 rcuscale.nwriters= [KNL] 4336 Set number of RCU writers. The values operate 4337 the same as for rcuscale.nreaders. 4338 N, where N is the number of CPUs 4339 4340 rcuscale.perf_type= [KNL] 4341 Specify the RCU implementation to test. 4342 4343 rcuscale.shutdown= [KNL] 4344 Shut the system down after performance tests 4345 complete. This is useful for hands-off automated 4346 testing. 4347 4348 rcuscale.verbose= [KNL] 4349 Enable additional printk() statements. 4350 4351 rcuscale.writer_holdoff= [KNL] 4352 Write-side holdoff between grace periods, 4353 in microseconds. The default of zero says 4354 no holdoff. 4355 4356 rcutorture.fqs_duration= [KNL] 4357 Set duration of force_quiescent_state bursts 4358 in microseconds. 4359 4360 rcutorture.fqs_holdoff= [KNL] 4361 Set holdoff time within force_quiescent_state bursts 4362 in microseconds. 4363 4364 rcutorture.fqs_stutter= [KNL] 4365 Set wait time between force_quiescent_state bursts 4366 in seconds. 4367 4368 rcutorture.fwd_progress= [KNL] 4369 Enable RCU grace-period forward-progress testing 4370 for the types of RCU supporting this notion. 4371 4372 rcutorture.fwd_progress_div= [KNL] 4373 Specify the fraction of a CPU-stall-warning 4374 period to do tight-loop forward-progress testing. 4375 4376 rcutorture.fwd_progress_holdoff= [KNL] 4377 Number of seconds to wait between successive 4378 forward-progress tests. 4379 4380 rcutorture.fwd_progress_need_resched= [KNL] 4381 Enclose cond_resched() calls within checks for 4382 need_resched() during tight-loop forward-progress 4383 testing. 4384 4385 rcutorture.gp_cond= [KNL] 4386 Use conditional/asynchronous update-side 4387 primitives, if available. 4388 4389 rcutorture.gp_exp= [KNL] 4390 Use expedited update-side primitives, if available. 4391 4392 rcutorture.gp_normal= [KNL] 4393 Use normal (non-expedited) asynchronous 4394 update-side primitives, if available. 4395 4396 rcutorture.gp_sync= [KNL] 4397 Use normal (non-expedited) synchronous 4398 update-side primitives, if available. If all 4399 of rcutorture.gp_cond=, rcutorture.gp_exp=, 4400 rcutorture.gp_normal=, and rcutorture.gp_sync= 4401 are zero, rcutorture acts as if is interpreted 4402 they are all non-zero. 4403 4404 rcutorture.irqreader= [KNL] 4405 Run RCU readers from irq handlers, or, more 4406 accurately, from a timer handler. Not all RCU 4407 flavors take kindly to this sort of thing. 4408 4409 rcutorture.leakpointer= [KNL] 4410 Leak an RCU-protected pointer out of the reader. 4411 This can of course result in splats, and is 4412 intended to test the ability of things like 4413 CONFIG_RCU_STRICT_GRACE_PERIOD=y to detect 4414 such leaks. 4415 4416 rcutorture.n_barrier_cbs= [KNL] 4417 Set callbacks/threads for rcu_barrier() testing. 4418 4419 rcutorture.nfakewriters= [KNL] 4420 Set number of concurrent RCU writers. These just 4421 stress RCU, they don't participate in the actual 4422 test, hence the "fake". 4423 4424 rcutorture.nreaders= [KNL] 4425 Set number of RCU readers. The value -1 selects 4426 N-1, where N is the number of CPUs. A value 4427 "n" less than -1 selects N-n-2, where N is again 4428 the number of CPUs. For example, -2 selects N 4429 (the number of CPUs), -3 selects N+1, and so on. 4430 4431 rcutorture.object_debug= [KNL] 4432 Enable debug-object double-call_rcu() testing. 4433 4434 rcutorture.onoff_holdoff= [KNL] 4435 Set time (s) after boot for CPU-hotplug testing. 4436 4437 rcutorture.onoff_interval= [KNL] 4438 Set time (jiffies) between CPU-hotplug operations, 4439 or zero to disable CPU-hotplug testing. 4440 4441 rcutorture.read_exit= [KNL] 4442 Set the number of read-then-exit kthreads used 4443 to test the interaction of RCU updaters and 4444 task-exit processing. 4445 4446 rcutorture.read_exit_burst= [KNL] 4447 The number of times in a given read-then-exit 4448 episode that a set of read-then-exit kthreads 4449 is spawned. 4450 4451 rcutorture.read_exit_delay= [KNL] 4452 The delay, in seconds, between successive 4453 read-then-exit testing episodes. 4454 4455 rcutorture.shuffle_interval= [KNL] 4456 Set task-shuffle interval (s). Shuffling tasks 4457 allows some CPUs to go into dyntick-idle mode 4458 during the rcutorture test. 4459 4460 rcutorture.shutdown_secs= [KNL] 4461 Set time (s) after boot system shutdown. This 4462 is useful for hands-off automated testing. 4463 4464 rcutorture.stall_cpu= [KNL] 4465 Duration of CPU stall (s) to test RCU CPU stall 4466 warnings, zero to disable. 4467 4468 rcutorture.stall_cpu_block= [KNL] 4469 Sleep while stalling if set. This will result 4470 in warnings from preemptible RCU in addition 4471 to any other stall-related activity. 4472 4473 rcutorture.stall_cpu_holdoff= [KNL] 4474 Time to wait (s) after boot before inducing stall. 4475 4476 rcutorture.stall_cpu_irqsoff= [KNL] 4477 Disable interrupts while stalling if set. 4478 4479 rcutorture.stall_gp_kthread= [KNL] 4480 Duration (s) of forced sleep within RCU 4481 grace-period kthread to test RCU CPU stall 4482 warnings, zero to disable. If both stall_cpu 4483 and stall_gp_kthread are specified, the 4484 kthread is starved first, then the CPU. 4485 4486 rcutorture.stat_interval= [KNL] 4487 Time (s) between statistics printk()s. 4488 4489 rcutorture.stutter= [KNL] 4490 Time (s) to stutter testing, for example, specifying 4491 five seconds causes the test to run for five seconds, 4492 wait for five seconds, and so on. This tests RCU's 4493 ability to transition abruptly to and from idle. 4494 4495 rcutorture.test_boost= [KNL] 4496 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 4497 "Maybe" means test if the RCU implementation 4498 under test support RCU priority boosting. 4499 4500 rcutorture.test_boost_duration= [KNL] 4501 Duration (s) of each individual boost test. 4502 4503 rcutorture.test_boost_interval= [KNL] 4504 Interval (s) between each boost test. 4505 4506 rcutorture.test_no_idle_hz= [KNL] 4507 Test RCU's dyntick-idle handling. See also the 4508 rcutorture.shuffle_interval parameter. 4509 4510 rcutorture.torture_type= [KNL] 4511 Specify the RCU implementation to test. 4512 4513 rcutorture.verbose= [KNL] 4514 Enable additional printk() statements. 4515 4516 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL] 4517 Dump ftrace buffer after reporting RCU CPU 4518 stall warning. 4519 4520 rcupdate.rcu_cpu_stall_suppress= [KNL] 4521 Suppress RCU CPU stall warning messages. 4522 4523 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL] 4524 Suppress RCU CPU stall warning messages and 4525 rcutorture writer stall warnings that occur 4526 during early boot, that is, during the time 4527 before the init task is spawned. 4528 4529 rcupdate.rcu_cpu_stall_timeout= [KNL] 4530 Set timeout for RCU CPU stall warning messages. 4531 4532 rcupdate.rcu_expedited= [KNL] 4533 Use expedited grace-period primitives, for 4534 example, synchronize_rcu_expedited() instead 4535 of synchronize_rcu(). This reduces latency, 4536 but can increase CPU utilization, degrade 4537 real-time latency, and degrade energy efficiency. 4538 No effect on CONFIG_TINY_RCU kernels. 4539 4540 rcupdate.rcu_normal= [KNL] 4541 Use only normal grace-period primitives, 4542 for example, synchronize_rcu() instead of 4543 synchronize_rcu_expedited(). This improves 4544 real-time latency, CPU utilization, and 4545 energy efficiency, but can expose users to 4546 increased grace-period latency. This parameter 4547 overrides rcupdate.rcu_expedited. No effect on 4548 CONFIG_TINY_RCU kernels. 4549 4550 rcupdate.rcu_normal_after_boot= [KNL] 4551 Once boot has completed (that is, after 4552 rcu_end_inkernel_boot() has been invoked), use 4553 only normal grace-period primitives. No effect 4554 on CONFIG_TINY_RCU kernels. 4555 4556 rcupdate.rcu_task_ipi_delay= [KNL] 4557 Set time in jiffies during which RCU tasks will 4558 avoid sending IPIs, starting with the beginning 4559 of a given grace period. Setting a large 4560 number avoids disturbing real-time workloads, 4561 but lengthens grace periods. 4562 4563 rcupdate.rcu_task_stall_timeout= [KNL] 4564 Set timeout in jiffies for RCU task stall warning 4565 messages. Disable with a value less than or equal 4566 to zero. 4567 4568 rcupdate.rcu_self_test= [KNL] 4569 Run the RCU early boot self tests 4570 4571 rdinit= [KNL] 4572 Format: <full_path> 4573 Run specified binary instead of /init from the ramdisk, 4574 used for early userspace startup. See initrd. 4575 4576 rdrand= [X86] 4577 force - Override the decision by the kernel to hide the 4578 advertisement of RDRAND support (this affects 4579 certain AMD processors because of buggy BIOS 4580 support, specifically around the suspend/resume 4581 path). 4582 4583 rdt= [HW,X86,RDT] 4584 Turn on/off individual RDT features. List is: 4585 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, 4586 mba. 4587 E.g. to turn on cmt and turn off mba use: 4588 rdt=cmt,!mba 4589 4590 reboot= [KNL] 4591 Format (x86 or x86_64): 4592 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \ 4593 [[,]s[mp]#### \ 4594 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 4595 [[,]f[orce] 4596 Where reboot_mode is one of warm (soft) or cold (hard) or gpio 4597 (prefix with 'panic_' to set mode for panic 4598 reboot only), 4599 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 4600 reboot_force is either force or not specified, 4601 reboot_cpu is s[mp]#### with #### being the processor 4602 to be used for rebooting. 4603 4604 refscale.holdoff= [KNL] 4605 Set test-start holdoff period. The purpose of 4606 this parameter is to delay the start of the 4607 test until boot completes in order to avoid 4608 interference. 4609 4610 refscale.loops= [KNL] 4611 Set the number of loops over the synchronization 4612 primitive under test. Increasing this number 4613 reduces noise due to loop start/end overhead, 4614 but the default has already reduced the per-pass 4615 noise to a handful of picoseconds on ca. 2020 4616 x86 laptops. 4617 4618 refscale.nreaders= [KNL] 4619 Set number of readers. The default value of -1 4620 selects N, where N is roughly 75% of the number 4621 of CPUs. A value of zero is an interesting choice. 4622 4623 refscale.nruns= [KNL] 4624 Set number of runs, each of which is dumped onto 4625 the console log. 4626 4627 refscale.readdelay= [KNL] 4628 Set the read-side critical-section duration, 4629 measured in microseconds. 4630 4631 refscale.scale_type= [KNL] 4632 Specify the read-protection implementation to test. 4633 4634 refscale.shutdown= [KNL] 4635 Shut down the system at the end of the performance 4636 test. This defaults to 1 (shut it down) when 4637 refscale is built into the kernel and to 0 (leave 4638 it running) when refscale is built as a module. 4639 4640 refscale.verbose= [KNL] 4641 Enable additional printk() statements. 4642 4643 relax_domain_level= 4644 [KNL, SMP] Set scheduler's default relax_domain_level. 4645 See Documentation/admin-guide/cgroup-v1/cpusets.rst. 4646 4647 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory 4648 Format: <base1>,<size1>[,<base2>,<size2>,...] 4649 Reserve I/O ports or memory so the kernel won't use 4650 them. If <base> is less than 0x10000, the region 4651 is assumed to be I/O ports; otherwise it is memory. 4652 4653 reservetop= [X86-32] 4654 Format: nn[KMG] 4655 Reserves a hole at the top of the kernel virtual 4656 address space. 4657 4658 reservelow= [X86] 4659 Format: nn[K] 4660 Set the amount of memory to reserve for BIOS at 4661 the bottom of the address space. 4662 4663 reset_devices [KNL] Force drivers to reset the underlying device 4664 during initialization. 4665 4666 resume= [SWSUSP] 4667 Specify the partition device for software suspend 4668 Format: 4669 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 4670 4671 resume_offset= [SWSUSP] 4672 Specify the offset from the beginning of the partition 4673 given by "resume=" at which the swap header is located, 4674 in <PAGE_SIZE> units (needed only for swap files). 4675 See Documentation/power/swsusp-and-swap-files.rst 4676 4677 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 4678 read the resume files 4679 4680 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 4681 Useful for devices that are detected asynchronously 4682 (e.g. USB and MMC devices). 4683 4684 hibernate= [HIBERNATION] 4685 noresume Don't check if there's a hibernation image 4686 present during boot. 4687 nocompress Don't compress/decompress hibernation images. 4688 no Disable hibernation and resume. 4689 protect_image Turn on image protection during restoration 4690 (that will set all pages holding image data 4691 during restoration read-only). 4692 4693 retain_initrd [RAM] Keep initrd memory after extraction 4694 4695 retbleed= [X86] Control mitigation of RETBleed (Arbitrary 4696 Speculative Code Execution with Return Instructions) 4697 vulnerability. 4698 4699 AMD-based UNRET and IBPB mitigations alone do not stop 4700 sibling threads from influencing the predictions of other 4701 sibling threads. For that reason, STIBP is used on pro- 4702 cessors that support it, and mitigate SMT on processors 4703 that don't. 4704 4705 off - no mitigation 4706 auto - automatically select a migitation 4707 auto,nosmt - automatically select a mitigation, 4708 disabling SMT if necessary for 4709 the full mitigation (only on Zen1 4710 and older without STIBP). 4711 ibpb - On AMD, mitigate short speculation 4712 windows on basic block boundaries too. 4713 Safe, highest perf impact. It also 4714 enables STIBP if present. Not suitable 4715 on Intel. 4716 ibpb,nosmt - Like "ibpb" above but will disable SMT 4717 when STIBP is not available. This is 4718 the alternative for systems which do not 4719 have STIBP. 4720 unret - Force enable untrained return thunks, 4721 only effective on AMD f15h-f17h based 4722 systems. 4723 unret,nosmt - Like unret, but will disable SMT when STIBP 4724 is not available. This is the alternative for 4725 systems which do not have STIBP. 4726 4727 Selecting 'auto' will choose a mitigation method at run 4728 time according to the CPU. 4729 4730 Not specifying this option is equivalent to retbleed=auto. 4731 4732 rfkill.default_state= 4733 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 4734 etc. communication is blocked by default. 4735 1 Unblocked. 4736 4737 rfkill.master_switch_mode= 4738 0 The "airplane mode" button does nothing. 4739 1 The "airplane mode" button toggles between everything 4740 blocked and the previous configuration. 4741 2 The "airplane mode" button toggles between everything 4742 blocked and everything unblocked. 4743 4744 rhash_entries= [KNL,NET] 4745 Set number of hash buckets for route cache 4746 4747 ring3mwait=disable 4748 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 4749 CPUs. 4750 4751 ro [KNL] Mount root device read-only on boot 4752 4753 rodata= [KNL] 4754 on Mark read-only kernel memory as read-only (default). 4755 off Leave read-only kernel memory writable for debugging. 4756 4757 rockchip.usb_uart 4758 Enable the uart passthrough on the designated usb port 4759 on Rockchip SoCs. When active, the signals of the 4760 debug-uart get routed to the D+ and D- pins of the usb 4761 port and the regular usb controller gets disabled. 4762 4763 root= [KNL] Root filesystem 4764 See name_to_dev_t comment in init/do_mounts.c. 4765 4766 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 4767 mount the root filesystem 4768 4769 rootflags= [KNL] Set root filesystem mount option string 4770 4771 rootfstype= [KNL] Set root filesystem type 4772 4773 rootwait [KNL] Wait (indefinitely) for root device to show up. 4774 Useful for devices that are detected asynchronously 4775 (e.g. USB and MMC devices). 4776 4777 rproc_mem=nn[KMG][@address] 4778 [KNL,ARM,CMA] Remoteproc physical memory block. 4779 Memory area to be used by remote processor image, 4780 managed by CMA. 4781 4782 rw [KNL] Mount root device read-write on boot 4783 4784 S [KNL] Run init in single mode 4785 4786 s390_iommu= [HW,S390] 4787 Set s390 IOTLB flushing mode 4788 strict 4789 With strict flushing every unmap operation will result in 4790 an IOTLB flush. Default is lazy flushing before reuse, 4791 which is faster. 4792 4793 sa1100ir [NET] 4794 See drivers/net/irda/sa1100_ir.c. 4795 4796 sbni= [NET] Granch SBNI12 leased line adapter 4797 4798 sched_debug [KNL] Enables verbose scheduler debug messages. 4799 4800 schedstats= [KNL,X86] Enable or disable scheduled statistics. 4801 Allowed values are enable and disable. This feature 4802 incurs a small amount of overhead in the scheduler 4803 but is useful for debugging and performance tuning. 4804 4805 sched_thermal_decay_shift= 4806 [KNL, SMP] Set a decay shift for scheduler thermal 4807 pressure signal. Thermal pressure signal follows the 4808 default decay period of other scheduler pelt 4809 signals(usually 32 ms but configurable). Setting 4810 sched_thermal_decay_shift will left shift the decay 4811 period for the thermal pressure signal by the shift 4812 value. 4813 i.e. with the default pelt decay period of 32 ms 4814 sched_thermal_decay_shift thermal pressure decay pr 4815 1 64 ms 4816 2 128 ms 4817 and so on. 4818 Format: integer between 0 and 10 4819 Default is 0. 4820 4821 scftorture.holdoff= [KNL] 4822 Number of seconds to hold off before starting 4823 test. Defaults to zero for module insertion and 4824 to 10 seconds for built-in smp_call_function() 4825 tests. 4826 4827 scftorture.longwait= [KNL] 4828 Request ridiculously long waits randomly selected 4829 up to the chosen limit in seconds. Zero (the 4830 default) disables this feature. Please note 4831 that requesting even small non-zero numbers of 4832 seconds can result in RCU CPU stall warnings, 4833 softlockup complaints, and so on. 4834 4835 scftorture.nthreads= [KNL] 4836 Number of kthreads to spawn to invoke the 4837 smp_call_function() family of functions. 4838 The default of -1 specifies a number of kthreads 4839 equal to the number of CPUs. 4840 4841 scftorture.onoff_holdoff= [KNL] 4842 Number seconds to wait after the start of the 4843 test before initiating CPU-hotplug operations. 4844 4845 scftorture.onoff_interval= [KNL] 4846 Number seconds to wait between successive 4847 CPU-hotplug operations. Specifying zero (which 4848 is the default) disables CPU-hotplug operations. 4849 4850 scftorture.shutdown_secs= [KNL] 4851 The number of seconds following the start of the 4852 test after which to shut down the system. The 4853 default of zero avoids shutting down the system. 4854 Non-zero values are useful for automated tests. 4855 4856 scftorture.stat_interval= [KNL] 4857 The number of seconds between outputting the 4858 current test statistics to the console. A value 4859 of zero disables statistics output. 4860 4861 scftorture.stutter_cpus= [KNL] 4862 The number of jiffies to wait between each change 4863 to the set of CPUs under test. 4864 4865 scftorture.use_cpus_read_lock= [KNL] 4866 Use use_cpus_read_lock() instead of the default 4867 preempt_disable() to disable CPU hotplug 4868 while invoking one of the smp_call_function*() 4869 functions. 4870 4871 scftorture.verbose= [KNL] 4872 Enable additional printk() statements. 4873 4874 scftorture.weight_single= [KNL] 4875 The probability weighting to use for the 4876 smp_call_function_single() function with a zero 4877 "wait" parameter. A value of -1 selects the 4878 default if all other weights are -1. However, 4879 if at least one weight has some other value, a 4880 value of -1 will instead select a weight of zero. 4881 4882 scftorture.weight_single_wait= [KNL] 4883 The probability weighting to use for the 4884 smp_call_function_single() function with a 4885 non-zero "wait" parameter. See weight_single. 4886 4887 scftorture.weight_many= [KNL] 4888 The probability weighting to use for the 4889 smp_call_function_many() function with a zero 4890 "wait" parameter. See weight_single. 4891 Note well that setting a high probability for 4892 this weighting can place serious IPI load 4893 on the system. 4894 4895 scftorture.weight_many_wait= [KNL] 4896 The probability weighting to use for the 4897 smp_call_function_many() function with a 4898 non-zero "wait" parameter. See weight_single 4899 and weight_many. 4900 4901 scftorture.weight_all= [KNL] 4902 The probability weighting to use for the 4903 smp_call_function_all() function with a zero 4904 "wait" parameter. See weight_single and 4905 weight_many. 4906 4907 scftorture.weight_all_wait= [KNL] 4908 The probability weighting to use for the 4909 smp_call_function_all() function with a 4910 non-zero "wait" parameter. See weight_single 4911 and weight_many. 4912 4913 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate 4914 xtime_lock contention on larger systems, and/or RCU lock 4915 contention on all systems with CONFIG_MAXSMP set. 4916 Format: { "0" | "1" } 4917 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 4918 1 -- enable. 4919 Note: increases power consumption, thus should only be 4920 enabled if running jitter sensitive (HPC/RT) workloads. 4921 4922 security= [SECURITY] Choose a legacy "major" security module to 4923 enable at boot. This has been deprecated by the 4924 "lsm=" parameter. 4925 4926 selinux= [SELINUX] Disable or enable SELinux at boot time. 4927 Format: { "0" | "1" } 4928 See security/selinux/Kconfig help text. 4929 0 -- disable. 4930 1 -- enable. 4931 Default value is 1. 4932 4933 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 4934 Format: { "0" | "1" } 4935 See security/apparmor/Kconfig help text 4936 0 -- disable. 4937 1 -- enable. 4938 Default value is set via kernel config option. 4939 4940 serialnumber [BUGS=X86-32] 4941 4942 shapers= [NET] 4943 Maximal number of shapers. 4944 4945 simeth= [IA-64] 4946 simscsi= 4947 4948 slram= [HW,MTD] 4949 4950 slab_nomerge [MM] 4951 Disable merging of slabs with similar size. May be 4952 necessary if there is some reason to distinguish 4953 allocs to different slabs, especially in hardened 4954 environments where the risk of heap overflows and 4955 layout control by attackers can usually be 4956 frustrated by disabling merging. This will reduce 4957 most of the exposure of a heap attack to a single 4958 cache (risks via metadata attacks are mostly 4959 unchanged). Debug options disable merging on their 4960 own. 4961 For more information see Documentation/vm/slub.rst. 4962 4963 slab_max_order= [MM, SLAB] 4964 Determines the maximum allowed order for slabs. 4965 A high setting may cause OOMs due to memory 4966 fragmentation. Defaults to 1 for systems with 4967 more than 32MB of RAM, 0 otherwise. 4968 4969 slub_debug[=options[,slabs][;[options[,slabs]]...] [MM, SLUB] 4970 Enabling slub_debug allows one to determine the 4971 culprit if slab objects become corrupted. Enabling 4972 slub_debug can create guard zones around objects and 4973 may poison objects when not in use. Also tracks the 4974 last alloc / free. For more information see 4975 Documentation/vm/slub.rst. 4976 4977 slub_memcg_sysfs= [MM, SLUB] 4978 Determines whether to enable sysfs directories for 4979 memory cgroup sub-caches. 1 to enable, 0 to disable. 4980 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON. 4981 Enabling this can lead to a very high number of debug 4982 directories and files being created under 4983 /sys/kernel/slub. 4984 4985 slub_max_order= [MM, SLUB] 4986 Determines the maximum allowed order for slabs. 4987 A high setting may cause OOMs due to memory 4988 fragmentation. For more information see 4989 Documentation/vm/slub.rst. 4990 4991 slub_min_objects= [MM, SLUB] 4992 The minimum number of objects per slab. SLUB will 4993 increase the slab order up to slub_max_order to 4994 generate a sufficiently large slab able to contain 4995 the number of objects indicated. The higher the number 4996 of objects the smaller the overhead of tracking slabs 4997 and the less frequently locks need to be acquired. 4998 For more information see Documentation/vm/slub.rst. 4999 5000 slub_min_order= [MM, SLUB] 5001 Determines the minimum page order for slabs. Must be 5002 lower than slub_max_order. 5003 For more information see Documentation/vm/slub.rst. 5004 5005 slub_nomerge [MM, SLUB] 5006 Same with slab_nomerge. This is supported for legacy. 5007 See slab_nomerge for more information. 5008 5009 smart2= [HW] 5010 Format: <io1>[,<io2>[,...,<io8>]] 5011 5012 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 5013 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 5014 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 5015 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 5016 smsc-ircc2.ircc_irq= [HW] IRQ line 5017 smsc-ircc2.ircc_dma= [HW] DMA channel 5018 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 5019 0: Toshiba Satellite 1800 (GP data pin select) 5020 1: Fast pin select (default) 5021 2: ATC IRMode 5022 5023 smt [KNL,S390] Set the maximum number of threads (logical 5024 CPUs) to use per physical CPU on systems capable of 5025 symmetric multithreading (SMT). Will be capped to the 5026 actual hardware limit. 5027 Format: <integer> 5028 Default: -1 (no limit) 5029 5030 softlockup_panic= 5031 [KNL] Should the soft-lockup detector generate panics. 5032 Format: 0 | 1 5033 5034 A value of 1 instructs the soft-lockup detector 5035 to panic the machine when a soft-lockup occurs. It is 5036 also controlled by the kernel.softlockup_panic sysctl 5037 and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the 5038 respective build-time switch to that functionality. 5039 5040 softlockup_all_cpu_backtrace= 5041 [KNL] Should the soft-lockup detector generate 5042 backtraces on all cpus. 5043 Format: 0 | 1 5044 5045 sonypi.*= [HW] Sony Programmable I/O Control Device driver 5046 See Documentation/admin-guide/laptops/sonypi.rst 5047 5048 spectre_v2= [X86] Control mitigation of Spectre variant 2 5049 (indirect branch speculation) vulnerability. 5050 The default operation protects the kernel from 5051 user space attacks. 5052 5053 on - unconditionally enable, implies 5054 spectre_v2_user=on 5055 off - unconditionally disable, implies 5056 spectre_v2_user=off 5057 auto - kernel detects whether your CPU model is 5058 vulnerable 5059 5060 Selecting 'on' will, and 'auto' may, choose a 5061 mitigation method at run time according to the 5062 CPU, the available microcode, the setting of the 5063 CONFIG_RETPOLINE configuration option, and the 5064 compiler with which the kernel was built. 5065 5066 Selecting 'on' will also enable the mitigation 5067 against user space to user space task attacks. 5068 5069 Selecting 'off' will disable both the kernel and 5070 the user space protections. 5071 5072 Specific mitigations can also be selected manually: 5073 5074 retpoline - replace indirect branches 5075 retpoline,generic - Retpolines 5076 retpoline,lfence - LFENCE; indirect branch 5077 retpoline,amd - alias for retpoline,lfence 5078 eibrs - enhanced IBRS 5079 eibrs,retpoline - enhanced IBRS + Retpolines 5080 eibrs,lfence - enhanced IBRS + LFENCE 5081 ibrs - use IBRS to protect kernel 5082 5083 Not specifying this option is equivalent to 5084 spectre_v2=auto. 5085 5086 spectre_v2_user= 5087 [X86] Control mitigation of Spectre variant 2 5088 (indirect branch speculation) vulnerability between 5089 user space tasks 5090 5091 on - Unconditionally enable mitigations. Is 5092 enforced by spectre_v2=on 5093 5094 off - Unconditionally disable mitigations. Is 5095 enforced by spectre_v2=off 5096 5097 prctl - Indirect branch speculation is enabled, 5098 but mitigation can be enabled via prctl 5099 per thread. The mitigation control state 5100 is inherited on fork. 5101 5102 prctl,ibpb 5103 - Like "prctl" above, but only STIBP is 5104 controlled per thread. IBPB is issued 5105 always when switching between different user 5106 space processes. 5107 5108 seccomp 5109 - Same as "prctl" above, but all seccomp 5110 threads will enable the mitigation unless 5111 they explicitly opt out. 5112 5113 seccomp,ibpb 5114 - Like "seccomp" above, but only STIBP is 5115 controlled per thread. IBPB is issued 5116 always when switching between different 5117 user space processes. 5118 5119 auto - Kernel selects the mitigation depending on 5120 the available CPU features and vulnerability. 5121 5122 Default mitigation: 5123 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl" 5124 5125 Not specifying this option is equivalent to 5126 spectre_v2_user=auto. 5127 5128 spec_store_bypass_disable= 5129 [HW] Control Speculative Store Bypass (SSB) Disable mitigation 5130 (Speculative Store Bypass vulnerability) 5131 5132 Certain CPUs are vulnerable to an exploit against a 5133 a common industry wide performance optimization known 5134 as "Speculative Store Bypass" in which recent stores 5135 to the same memory location may not be observed by 5136 later loads during speculative execution. The idea 5137 is that such stores are unlikely and that they can 5138 be detected prior to instruction retirement at the 5139 end of a particular speculation execution window. 5140 5141 In vulnerable processors, the speculatively forwarded 5142 store can be used in a cache side channel attack, for 5143 example to read memory to which the attacker does not 5144 directly have access (e.g. inside sandboxed code). 5145 5146 This parameter controls whether the Speculative Store 5147 Bypass optimization is used. 5148 5149 On x86 the options are: 5150 5151 on - Unconditionally disable Speculative Store Bypass 5152 off - Unconditionally enable Speculative Store Bypass 5153 auto - Kernel detects whether the CPU model contains an 5154 implementation of Speculative Store Bypass and 5155 picks the most appropriate mitigation. If the 5156 CPU is not vulnerable, "off" is selected. If the 5157 CPU is vulnerable the default mitigation is 5158 architecture and Kconfig dependent. See below. 5159 prctl - Control Speculative Store Bypass per thread 5160 via prctl. Speculative Store Bypass is enabled 5161 for a process by default. The state of the control 5162 is inherited on fork. 5163 seccomp - Same as "prctl" above, but all seccomp threads 5164 will disable SSB unless they explicitly opt out. 5165 5166 Default mitigations: 5167 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl" 5168 5169 On powerpc the options are: 5170 5171 on,auto - On Power8 and Power9 insert a store-forwarding 5172 barrier on kernel entry and exit. On Power7 5173 perform a software flush on kernel entry and 5174 exit. 5175 off - No action. 5176 5177 Not specifying this option is equivalent to 5178 spec_store_bypass_disable=auto. 5179 5180 spia_io_base= [HW,MTD] 5181 spia_fio_base= 5182 spia_pedr= 5183 spia_peddr= 5184 5185 split_lock_detect= 5186 [X86] Enable split lock detection 5187 5188 When enabled (and if hardware support is present), atomic 5189 instructions that access data across cache line 5190 boundaries will result in an alignment check exception. 5191 5192 off - not enabled 5193 5194 warn - the kernel will emit rate limited warnings 5195 about applications triggering the #AC 5196 exception. This mode is the default on CPUs 5197 that supports split lock detection. 5198 5199 fatal - the kernel will send SIGBUS to applications 5200 that trigger the #AC exception. 5201 5202 If an #AC exception is hit in the kernel or in 5203 firmware (i.e. not while executing in user mode) 5204 the kernel will oops in either "warn" or "fatal" 5205 mode. 5206 5207 srbds= [X86,INTEL] 5208 Control the Special Register Buffer Data Sampling 5209 (SRBDS) mitigation. 5210 5211 Certain CPUs are vulnerable to an MDS-like 5212 exploit which can leak bits from the random 5213 number generator. 5214 5215 By default, this issue is mitigated by 5216 microcode. However, the microcode fix can cause 5217 the RDRAND and RDSEED instructions to become 5218 much slower. Among other effects, this will 5219 result in reduced throughput from /dev/urandom. 5220 5221 The microcode mitigation can be disabled with 5222 the following option: 5223 5224 off: Disable mitigation and remove 5225 performance impact to RDRAND and RDSEED 5226 5227 srcutree.counter_wrap_check [KNL] 5228 Specifies how frequently to check for 5229 grace-period sequence counter wrap for the 5230 srcu_data structure's ->srcu_gp_seq_needed field. 5231 The greater the number of bits set in this kernel 5232 parameter, the less frequently counter wrap will 5233 be checked for. Note that the bottom two bits 5234 are ignored. 5235 5236 srcutree.exp_holdoff [KNL] 5237 Specifies how many nanoseconds must elapse 5238 since the end of the last SRCU grace period for 5239 a given srcu_struct until the next normal SRCU 5240 grace period will be considered for automatic 5241 expediting. Set to zero to disable automatic 5242 expediting. 5243 5244 ssbd= [ARM64,HW] 5245 Speculative Store Bypass Disable control 5246 5247 On CPUs that are vulnerable to the Speculative 5248 Store Bypass vulnerability and offer a 5249 firmware based mitigation, this parameter 5250 indicates how the mitigation should be used: 5251 5252 force-on: Unconditionally enable mitigation for 5253 for both kernel and userspace 5254 force-off: Unconditionally disable mitigation for 5255 for both kernel and userspace 5256 kernel: Always enable mitigation in the 5257 kernel, and offer a prctl interface 5258 to allow userspace to register its 5259 interest in being mitigated too. 5260 5261 stack_guard_gap= [MM] 5262 override the default stack gap protection. The value 5263 is in page units and it defines how many pages prior 5264 to (for stacks growing down) resp. after (for stacks 5265 growing up) the main stack are reserved for no other 5266 mapping. Default value is 256 pages. 5267 5268 stacktrace [FTRACE] 5269 Enabled the stack tracer on boot up. 5270 5271 stacktrace_filter=[function-list] 5272 [FTRACE] Limit the functions that the stack tracer 5273 will trace at boot up. function-list is a comma separated 5274 list of functions. This list can be changed at run 5275 time by the stack_trace_filter file in the debugfs 5276 tracing directory. Note, this enables stack tracing 5277 and the stacktrace above is not needed. 5278 5279 sti= [PARISC,HW] 5280 Format: <num> 5281 Set the STI (builtin display/keyboard on the HP-PARISC 5282 machines) console (graphic card) which should be used 5283 as the initial boot-console. 5284 See also comment in drivers/video/console/sticore.c. 5285 5286 sti_font= [HW] 5287 See comment in drivers/video/console/sticore.c. 5288 5289 stifb= [HW] 5290 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 5291 5292 sunrpc.min_resvport= 5293 sunrpc.max_resvport= 5294 [NFS,SUNRPC] 5295 SunRPC servers often require that client requests 5296 originate from a privileged port (i.e. a port in the 5297 range 0 < portnr < 1024). 5298 An administrator who wishes to reserve some of these 5299 ports for other uses may adjust the range that the 5300 kernel's sunrpc client considers to be privileged 5301 using these two parameters to set the minimum and 5302 maximum port values. 5303 5304 sunrpc.svc_rpc_per_connection_limit= 5305 [NFS,SUNRPC] 5306 Limit the number of requests that the server will 5307 process in parallel from a single connection. 5308 The default value is 0 (no limit). 5309 5310 sunrpc.pool_mode= 5311 [NFS] 5312 Control how the NFS server code allocates CPUs to 5313 service thread pools. Depending on how many NICs 5314 you have and where their interrupts are bound, this 5315 option will affect which CPUs will do NFS serving. 5316 Note: this parameter cannot be changed while the 5317 NFS server is running. 5318 5319 auto the server chooses an appropriate mode 5320 automatically using heuristics 5321 global a single global pool contains all CPUs 5322 percpu one pool for each CPU 5323 pernode one pool for each NUMA node (equivalent 5324 to global on non-NUMA machines) 5325 5326 sunrpc.tcp_slot_table_entries= 5327 sunrpc.udp_slot_table_entries= 5328 [NFS,SUNRPC] 5329 Sets the upper limit on the number of simultaneous 5330 RPC calls that can be sent from the client to a 5331 server. Increasing these values may allow you to 5332 improve throughput, but will also increase the 5333 amount of memory reserved for use by the client. 5334 5335 suspend.pm_test_delay= 5336 [SUSPEND] 5337 Sets the number of seconds to remain in a suspend test 5338 mode before resuming the system (see 5339 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 5340 is set. Default value is 5. 5341 5342 svm= [PPC] 5343 Format: { on | off | y | n | 1 | 0 } 5344 This parameter controls use of the Protected 5345 Execution Facility on pSeries. 5346 5347 swapaccount=[0|1] 5348 [KNL] Enable accounting of swap in memory resource 5349 controller if no parameter or 1 is given or disable 5350 it if 0 is given (See Documentation/admin-guide/cgroup-v1/memory.rst) 5351 5352 swiotlb= [ARM,IA-64,PPC,MIPS,X86] 5353 Format: { <int> | force | noforce } 5354 <int> -- Number of I/O TLB slabs 5355 force -- force using of bounce buffers even if they 5356 wouldn't be automatically used by the kernel 5357 noforce -- Never use bounce buffers (for debugging) 5358 5359 switches= [HW,M68k] 5360 5361 sysctl.*= [KNL] 5362 Set a sysctl parameter, right before loading the init 5363 process, as if the value was written to the respective 5364 /proc/sys/... file. Both '.' and '/' are recognized as 5365 separators. Unrecognized parameters and invalid values 5366 are reported in the kernel log. Sysctls registered 5367 later by a loaded module cannot be set this way. 5368 Example: sysctl.vm.swappiness=40 5369 5370 sysfs.deprecated=0|1 [KNL] 5371 Enable/disable old style sysfs layout for old udev 5372 on older distributions. When this option is enabled 5373 very new udev will not work anymore. When this option 5374 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled) 5375 in older udev will not work anymore. 5376 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in 5377 the kernel configuration. 5378 5379 sysrq_always_enabled 5380 [KNL] 5381 Ignore sysrq setting - this boot parameter will 5382 neutralize any effect of /proc/sys/kernel/sysrq. 5383 Useful for debugging. 5384 5385 tcpmhash_entries= [KNL,NET] 5386 Set the number of tcp_metrics_hash slots. 5387 Default value is 8192 or 16384 depending on total 5388 ram pages. This is used to specify the TCP metrics 5389 cache size. See Documentation/networking/ip-sysctl.rst 5390 "tcp_no_metrics_save" section for more details. 5391 5392 tdfx= [HW,DRM] 5393 5394 test_suspend= [SUSPEND][,N] 5395 Specify "mem" (for Suspend-to-RAM) or "standby" (for 5396 standby suspend) or "freeze" (for suspend type freeze) 5397 as the system sleep state during system startup with 5398 the optional capability to repeat N number of times. 5399 The system is woken from this state using a 5400 wakeup-capable RTC alarm. 5401 5402 thash_entries= [KNL,NET] 5403 Set number of hash buckets for TCP connection 5404 5405 thermal.act= [HW,ACPI] 5406 -1: disable all active trip points in all thermal zones 5407 <degrees C>: override all lowest active trip points 5408 5409 thermal.crt= [HW,ACPI] 5410 -1: disable all critical trip points in all thermal zones 5411 <degrees C>: override all critical trip points 5412 5413 thermal.nocrt= [HW,ACPI] 5414 Set to disable actions on ACPI thermal zone 5415 critical and hot trip points. 5416 5417 thermal.off= [HW,ACPI] 5418 1: disable ACPI thermal control 5419 5420 thermal.psv= [HW,ACPI] 5421 -1: disable all passive trip points 5422 <degrees C>: override all passive trip points to this 5423 value 5424 5425 thermal.tzp= [HW,ACPI] 5426 Specify global default ACPI thermal zone polling rate 5427 <deci-seconds>: poll all this frequency 5428 0: no polling (default) 5429 5430 threadirqs [KNL] 5431 Force threading of all interrupt handlers except those 5432 marked explicitly IRQF_NO_THREAD. 5433 5434 topology= [S390] 5435 Format: {off | on} 5436 Specify if the kernel should make use of the cpu 5437 topology information if the hardware supports this. 5438 The scheduler will make use of this information and 5439 e.g. base its process migration decisions on it. 5440 Default is on. 5441 5442 topology_updates= [KNL, PPC, NUMA] 5443 Format: {off} 5444 Specify if the kernel should ignore (off) 5445 topology updates sent by the hypervisor to this 5446 LPAR. 5447 5448 torture.disable_onoff_at_boot= [KNL] 5449 Prevent the CPU-hotplug component of torturing 5450 until after init has spawned. 5451 5452 torture.ftrace_dump_at_shutdown= [KNL] 5453 Dump the ftrace buffer at torture-test shutdown, 5454 even if there were no errors. This can be a 5455 very costly operation when many torture tests 5456 are running concurrently, especially on systems 5457 with rotating-rust storage. 5458 5459 tp720= [HW,PS2] 5460 5461 tpm_suspend_pcr=[HW,TPM] 5462 Format: integer pcr id 5463 Specify that at suspend time, the tpm driver 5464 should extend the specified pcr with zeros, 5465 as a workaround for some chips which fail to 5466 flush the last written pcr on TPM_SaveState. 5467 This will guarantee that all the other pcrs 5468 are saved. 5469 5470 trace_buf_size=nn[KMG] 5471 [FTRACE] will set tracing buffer size on each cpu. 5472 5473 trace_event=[event-list] 5474 [FTRACE] Set and start specified trace events in order 5475 to facilitate early boot debugging. The event-list is a 5476 comma separated list of trace events to enable. See 5477 also Documentation/trace/events.rst 5478 5479 trace_options=[option-list] 5480 [FTRACE] Enable or disable tracer options at boot. 5481 The option-list is a comma delimited list of options 5482 that can be enabled or disabled just as if you were 5483 to echo the option name into 5484 5485 /sys/kernel/debug/tracing/trace_options 5486 5487 For example, to enable stacktrace option (to dump the 5488 stack trace of each event), add to the command line: 5489 5490 trace_options=stacktrace 5491 5492 See also Documentation/trace/ftrace.rst "trace options" 5493 section. 5494 5495 tp_printk[FTRACE] 5496 Have the tracepoints sent to printk as well as the 5497 tracing ring buffer. This is useful for early boot up 5498 where the system hangs or reboots and does not give the 5499 option for reading the tracing buffer or performing a 5500 ftrace_dump_on_oops. 5501 5502 To turn off having tracepoints sent to printk, 5503 echo 0 > /proc/sys/kernel/tracepoint_printk 5504 Note, echoing 1 into this file without the 5505 tracepoint_printk kernel cmdline option has no effect. 5506 5507 ** CAUTION ** 5508 5509 Having tracepoints sent to printk() and activating high 5510 frequency tracepoints such as irq or sched, can cause 5511 the system to live lock. 5512 5513 traceoff_on_warning 5514 [FTRACE] enable this option to disable tracing when a 5515 warning is hit. This turns off "tracing_on". Tracing can 5516 be enabled again by echoing '1' into the "tracing_on" 5517 file located in /sys/kernel/debug/tracing/ 5518 5519 This option is useful, as it disables the trace before 5520 the WARNING dump is called, which prevents the trace to 5521 be filled with content caused by the warning output. 5522 5523 This option can also be set at run time via the sysctl 5524 option: kernel/traceoff_on_warning 5525 5526 transparent_hugepage= 5527 [KNL] 5528 Format: [always|madvise|never] 5529 Can be used to control the default behavior of the system 5530 with respect to transparent hugepages. 5531 See Documentation/admin-guide/mm/transhuge.rst 5532 for more details. 5533 5534 tsc= Disable clocksource stability checks for TSC. 5535 Format: <string> 5536 [x86] reliable: mark tsc clocksource as reliable, this 5537 disables clocksource verification at runtime, as well 5538 as the stability checks done at bootup. Used to enable 5539 high-resolution timer mode on older hardware, and in 5540 virtualized environment. 5541 [x86] noirqtime: Do not use TSC to do irq accounting. 5542 Used to run time disable IRQ_TIME_ACCOUNTING on any 5543 platforms where RDTSC is slow and this accounting 5544 can add overhead. 5545 [x86] unstable: mark the TSC clocksource as unstable, this 5546 marks the TSC unconditionally unstable at bootup and 5547 avoids any further wobbles once the TSC watchdog notices. 5548 [x86] nowatchdog: disable clocksource watchdog. Used 5549 in situations with strict latency requirements (where 5550 interruptions from clocksource watchdog are not 5551 acceptable). 5552 5553 tsc_early_khz= [X86] Skip early TSC calibration and use the given 5554 value instead. Useful when the early TSC frequency discovery 5555 procedure is not reliable, such as on overclocked systems 5556 with CPUID.16h support and partial CPUID.15h support. 5557 Format: <unsigned int> 5558 5559 tsx= [X86] Control Transactional Synchronization 5560 Extensions (TSX) feature in Intel processors that 5561 support TSX control. 5562 5563 This parameter controls the TSX feature. The options are: 5564 5565 on - Enable TSX on the system. Although there are 5566 mitigations for all known security vulnerabilities, 5567 TSX has been known to be an accelerator for 5568 several previous speculation-related CVEs, and 5569 so there may be unknown security risks associated 5570 with leaving it enabled. 5571 5572 off - Disable TSX on the system. (Note that this 5573 option takes effect only on newer CPUs which are 5574 not vulnerable to MDS, i.e., have 5575 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get 5576 the new IA32_TSX_CTRL MSR through a microcode 5577 update. This new MSR allows for the reliable 5578 deactivation of the TSX functionality.) 5579 5580 auto - Disable TSX if X86_BUG_TAA is present, 5581 otherwise enable TSX on the system. 5582 5583 Not specifying this option is equivalent to tsx=off. 5584 5585 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 5586 for more details. 5587 5588 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async 5589 Abort (TAA) vulnerability. 5590 5591 Similar to Micro-architectural Data Sampling (MDS) 5592 certain CPUs that support Transactional 5593 Synchronization Extensions (TSX) are vulnerable to an 5594 exploit against CPU internal buffers which can forward 5595 information to a disclosure gadget under certain 5596 conditions. 5597 5598 In vulnerable processors, the speculatively forwarded 5599 data can be used in a cache side channel attack, to 5600 access data to which the attacker does not have direct 5601 access. 5602 5603 This parameter controls the TAA mitigation. The 5604 options are: 5605 5606 full - Enable TAA mitigation on vulnerable CPUs 5607 if TSX is enabled. 5608 5609 full,nosmt - Enable TAA mitigation and disable SMT on 5610 vulnerable CPUs. If TSX is disabled, SMT 5611 is not disabled because CPU is not 5612 vulnerable to cross-thread TAA attacks. 5613 off - Unconditionally disable TAA mitigation 5614 5615 On MDS-affected machines, tsx_async_abort=off can be 5616 prevented by an active MDS mitigation as both vulnerabilities 5617 are mitigated with the same mechanism so in order to disable 5618 this mitigation, you need to specify mds=off too. 5619 5620 Not specifying this option is equivalent to 5621 tsx_async_abort=full. On CPUs which are MDS affected 5622 and deploy MDS mitigation, TAA mitigation is not 5623 required and doesn't provide any additional 5624 mitigation. 5625 5626 For details see: 5627 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 5628 5629 turbografx.map[2|3]= [HW,JOY] 5630 TurboGraFX parallel port interface 5631 Format: 5632 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 5633 See also Documentation/input/devices/joystick-parport.rst 5634 5635 udbg-immortal [PPC] When debugging early kernel crashes that 5636 happen after console_init() and before a proper 5637 console driver takes over, this boot options might 5638 help "seeing" what's going on. 5639 5640 uhash_entries= [KNL,NET] 5641 Set number of hash buckets for UDP/UDP-Lite connections 5642 5643 uhci-hcd.ignore_oc= 5644 [USB] Ignore overcurrent events (default N). 5645 Some badly-designed motherboards generate lots of 5646 bogus events, for ports that aren't wired to 5647 anything. Set this parameter to avoid log spamming. 5648 Note that genuine overcurrent events won't be 5649 reported either. 5650 5651 unknown_nmi_panic 5652 [X86] Cause panic on unknown NMI. 5653 5654 usbcore.authorized_default= 5655 [USB] Default USB device authorization: 5656 (default -1 = authorized except for wireless USB, 5657 0 = not authorized, 1 = authorized, 2 = authorized 5658 if device connected to internal port) 5659 5660 usbcore.autosuspend= 5661 [USB] The autosuspend time delay (in seconds) used 5662 for newly-detected USB devices (default 2). This 5663 is the time required before an idle device will be 5664 autosuspended. Devices for which the delay is set 5665 to a negative value won't be autosuspended at all. 5666 5667 usbcore.usbfs_snoop= 5668 [USB] Set to log all usbfs traffic (default 0 = off). 5669 5670 usbcore.usbfs_snoop_max= 5671 [USB] Maximum number of bytes to snoop in each URB 5672 (default = 65536). 5673 5674 usbcore.blinkenlights= 5675 [USB] Set to cycle leds on hubs (default 0 = off). 5676 5677 usbcore.old_scheme_first= 5678 [USB] Start with the old device initialization 5679 scheme (default 0 = off). 5680 5681 usbcore.usbfs_memory_mb= 5682 [USB] Memory limit (in MB) for buffers allocated by 5683 usbfs (default = 16, 0 = max = 2047). 5684 5685 usbcore.use_both_schemes= 5686 [USB] Try the other device initialization scheme 5687 if the first one fails (default 1 = enabled). 5688 5689 usbcore.initial_descriptor_timeout= 5690 [USB] Specifies timeout for the initial 64-byte 5691 USB_REQ_GET_DESCRIPTOR request in milliseconds 5692 (default 5000 = 5.0 seconds). 5693 5694 usbcore.nousb [USB] Disable the USB subsystem 5695 5696 usbcore.quirks= 5697 [USB] A list of quirk entries to augment the built-in 5698 usb core quirk list. List entries are separated by 5699 commas. Each entry has the form 5700 VendorID:ProductID:Flags. The IDs are 4-digit hex 5701 numbers and Flags is a set of letters. Each letter 5702 will change the built-in quirk; setting it if it is 5703 clear and clearing it if it is set. The letters have 5704 the following meanings: 5705 a = USB_QUIRK_STRING_FETCH_255 (string 5706 descriptors must not be fetched using 5707 a 255-byte read); 5708 b = USB_QUIRK_RESET_RESUME (device can't resume 5709 correctly so reset it instead); 5710 c = USB_QUIRK_NO_SET_INTF (device can't handle 5711 Set-Interface requests); 5712 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't 5713 handle its Configuration or Interface 5714 strings); 5715 e = USB_QUIRK_RESET (device can't be reset 5716 (e.g morph devices), don't use reset); 5717 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has 5718 more interface descriptions than the 5719 bNumInterfaces count, and can't handle 5720 talking to these interfaces); 5721 g = USB_QUIRK_DELAY_INIT (device needs a pause 5722 during initialization, after we read 5723 the device descriptor); 5724 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For 5725 high speed and super speed interrupt 5726 endpoints, the USB 2.0 and USB 3.0 spec 5727 require the interval in microframes (1 5728 microframe = 125 microseconds) to be 5729 calculated as interval = 2 ^ 5730 (bInterval-1). 5731 Devices with this quirk report their 5732 bInterval as the result of this 5733 calculation instead of the exponent 5734 variable used in the calculation); 5735 i = USB_QUIRK_DEVICE_QUALIFIER (device can't 5736 handle device_qualifier descriptor 5737 requests); 5738 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device 5739 generates spurious wakeup, ignore 5740 remote wakeup capability); 5741 k = USB_QUIRK_NO_LPM (device can't handle Link 5742 Power Management); 5743 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL 5744 (Device reports its bInterval as linear 5745 frames instead of the USB 2.0 5746 calculation); 5747 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs 5748 to be disconnected before suspend to 5749 prevent spurious wakeup); 5750 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a 5751 pause after every control message); 5752 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra 5753 delay after resetting its port); 5754 Example: quirks=0781:5580:bk,0a5c:5834:gij 5755 5756 usbhid.mousepoll= 5757 [USBHID] The interval which mice are to be polled at. 5758 5759 usbhid.jspoll= 5760 [USBHID] The interval which joysticks are to be polled at. 5761 5762 usbhid.kbpoll= 5763 [USBHID] The interval which keyboards are to be polled at. 5764 5765 usb-storage.delay_use= 5766 [UMS] The delay in seconds before a new device is 5767 scanned for Logical Units (default 1). 5768 5769 usb-storage.quirks= 5770 [UMS] A list of quirks entries to supplement or 5771 override the built-in unusual_devs list. List 5772 entries are separated by commas. Each entry has 5773 the form VID:PID:Flags where VID and PID are Vendor 5774 and Product ID values (4-digit hex numbers) and 5775 Flags is a set of characters, each corresponding 5776 to a common usb-storage quirk flag as follows: 5777 a = SANE_SENSE (collect more than 18 bytes 5778 of sense data, not on uas); 5779 b = BAD_SENSE (don't collect more than 18 5780 bytes of sense data, not on uas); 5781 c = FIX_CAPACITY (decrease the reported 5782 device capacity by one sector); 5783 d = NO_READ_DISC_INFO (don't use 5784 READ_DISC_INFO command, not on uas); 5785 e = NO_READ_CAPACITY_16 (don't use 5786 READ_CAPACITY_16 command); 5787 f = NO_REPORT_OPCODES (don't use report opcodes 5788 command, uas only); 5789 g = MAX_SECTORS_240 (don't transfer more than 5790 240 sectors at a time, uas only); 5791 h = CAPACITY_HEURISTICS (decrease the 5792 reported device capacity by one 5793 sector if the number is odd); 5794 i = IGNORE_DEVICE (don't bind to this 5795 device); 5796 j = NO_REPORT_LUNS (don't use report luns 5797 command, uas only); 5798 k = NO_SAME (do not use WRITE_SAME, uas only) 5799 l = NOT_LOCKABLE (don't try to lock and 5800 unlock ejectable media, not on uas); 5801 m = MAX_SECTORS_64 (don't transfer more 5802 than 64 sectors = 32 KB at a time, 5803 not on uas); 5804 n = INITIAL_READ10 (force a retry of the 5805 initial READ(10) command, not on uas); 5806 o = CAPACITY_OK (accept the capacity 5807 reported by the device, not on uas); 5808 p = WRITE_CACHE (the device cache is ON 5809 by default, not on uas); 5810 r = IGNORE_RESIDUE (the device reports 5811 bogus residue values, not on uas); 5812 s = SINGLE_LUN (the device has only one 5813 Logical Unit); 5814 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 5815 commands, uas only); 5816 u = IGNORE_UAS (don't bind to the uas driver); 5817 w = NO_WP_DETECT (don't test whether the 5818 medium is write-protected). 5819 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 5820 even if the device claims no cache, 5821 not on uas) 5822 Example: quirks=0419:aaf5:rl,0421:0433:rc 5823 5824 user_debug= [KNL,ARM] 5825 Format: <int> 5826 See arch/arm/Kconfig.debug help text. 5827 1 - undefined instruction events 5828 2 - system calls 5829 4 - invalid data aborts 5830 8 - SIGSEGV faults 5831 16 - SIGBUS faults 5832 Example: user_debug=31 5833 5834 userpte= 5835 [X86] Flags controlling user PTE allocations. 5836 5837 nohigh = do not allocate PTE pages in 5838 HIGHMEM regardless of setting 5839 of CONFIG_HIGHPTE. 5840 5841 vdso= [X86,SH] 5842 On X86_32, this is an alias for vdso32=. Otherwise: 5843 5844 vdso=1: enable VDSO (the default) 5845 vdso=0: disable VDSO mapping 5846 5847 vdso32= [X86] Control the 32-bit vDSO 5848 vdso32=1: enable 32-bit VDSO 5849 vdso32=0 or vdso32=2: disable 32-bit VDSO 5850 5851 See the help text for CONFIG_COMPAT_VDSO for more 5852 details. If CONFIG_COMPAT_VDSO is set, the default is 5853 vdso32=0; otherwise, the default is vdso32=1. 5854 5855 For compatibility with older kernels, vdso32=2 is an 5856 alias for vdso32=0. 5857 5858 Try vdso32=0 if you encounter an error that says: 5859 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 5860 5861 vector= [IA-64,SMP] 5862 vector=percpu: enable percpu vector domain 5863 5864 video= [FB] Frame buffer configuration 5865 See Documentation/fb/modedb.rst. 5866 5867 video.brightness_switch_enabled= [0,1] 5868 If set to 1, on receiving an ACPI notify event 5869 generated by hotkey, video driver will adjust brightness 5870 level and then send out the event to user space through 5871 the allocated input device; If set to 0, video driver 5872 will only send out the event without touching backlight 5873 brightness level. 5874 default: 1 5875 5876 virtio_mmio.device= 5877 [VMMIO] Memory mapped virtio (platform) device. 5878 5879 <size>@<baseaddr>:<irq>[:<id>] 5880 where: 5881 <size> := size (can use standard suffixes 5882 like K, M and G) 5883 <baseaddr> := physical base address 5884 <irq> := interrupt number (as passed to 5885 request_irq()) 5886 <id> := (optional) platform device id 5887 example: 5888 virtio_mmio.device=1K@0x100b0000:48:7 5889 5890 Can be used multiple times for multiple devices. 5891 5892 vga= [BOOT,X86-32] Select a particular video mode 5893 See Documentation/x86/boot.rst and 5894 Documentation/admin-guide/svga.rst. 5895 Use vga=ask for menu. 5896 This is actually a boot loader parameter; the value is 5897 passed to the kernel using a special protocol. 5898 5899 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. 5900 May slow down system boot speed, especially when 5901 enabled on systems with a large amount of memory. 5902 All options are enabled by default, and this 5903 interface is meant to allow for selectively 5904 enabling or disabling specific virtual memory 5905 debugging features. 5906 5907 Available options are: 5908 P Enable page structure init time poisoning 5909 - Disable all of the above options 5910 5911 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact 5912 size of <nn>. This can be used to increase the 5913 minimum size (128MB on x86). It can also be used to 5914 decrease the size and leave more room for directly 5915 mapped kernel RAM. 5916 5917 vmcp_cma=nn[MG] [KNL,S390] 5918 Sets the memory size reserved for contiguous memory 5919 allocations for the vmcp device driver. 5920 5921 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 5922 Format: <command> 5923 5924 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 5925 Format: <command> 5926 5927 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 5928 Format: <command> 5929 5930 vsyscall= [X86-64] 5931 Controls the behavior of vsyscalls (i.e. calls to 5932 fixed addresses of 0xffffffffff600x00 from legacy 5933 code). Most statically-linked binaries and older 5934 versions of glibc use these calls. Because these 5935 functions are at fixed addresses, they make nice 5936 targets for exploits that can control RIP. 5937 5938 emulate [default] Vsyscalls turn into traps and are 5939 emulated reasonably safely. The vsyscall 5940 page is readable. 5941 5942 xonly Vsyscalls turn into traps and are 5943 emulated reasonably safely. The vsyscall 5944 page is not readable. 5945 5946 none Vsyscalls don't work at all. This makes 5947 them quite hard to use for exploits but 5948 might break your system. 5949 5950 vt.color= [VT] Default text color. 5951 Format: 0xYX, X = foreground, Y = background. 5952 Default: 0x07 = light gray on black. 5953 5954 vt.cur_default= [VT] Default cursor shape. 5955 Format: 0xCCBBAA, where AA, BB, and CC are the same as 5956 the parameters of the <Esc>[?A;B;Cc escape sequence; 5957 see VGA-softcursor.txt. Default: 2 = underline. 5958 5959 vt.default_blu= [VT] 5960 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 5961 Change the default blue palette of the console. 5962 This is a 16-member array composed of values 5963 ranging from 0-255. 5964 5965 vt.default_grn= [VT] 5966 Format: <green0>,<green1>,<green2>,...,<green15> 5967 Change the default green palette of the console. 5968 This is a 16-member array composed of values 5969 ranging from 0-255. 5970 5971 vt.default_red= [VT] 5972 Format: <red0>,<red1>,<red2>,...,<red15> 5973 Change the default red palette of the console. 5974 This is a 16-member array composed of values 5975 ranging from 0-255. 5976 5977 vt.default_utf8= 5978 [VT] 5979 Format=<0|1> 5980 Set system-wide default UTF-8 mode for all tty's. 5981 Default is 1, i.e. UTF-8 mode is enabled for all 5982 newly opened terminals. 5983 5984 vt.global_cursor_default= 5985 [VT] 5986 Format=<-1|0|1> 5987 Set system-wide default for whether a cursor 5988 is shown on new VTs. Default is -1, 5989 i.e. cursors will be created by default unless 5990 overridden by individual drivers. 0 will hide 5991 cursors, 1 will display them. 5992 5993 vt.italic= [VT] Default color for italic text; 0-15. 5994 Default: 2 = green. 5995 5996 vt.underline= [VT] Default color for underlined text; 0-15. 5997 Default: 3 = cyan. 5998 5999 watchdog timers [HW,WDT] For information on watchdog timers, 6000 see Documentation/watchdog/watchdog-parameters.rst 6001 or other driver-specific files in the 6002 Documentation/watchdog/ directory. 6003 6004 watchdog_thresh= 6005 [KNL] 6006 Set the hard lockup detector stall duration 6007 threshold in seconds. The soft lockup detector 6008 threshold is set to twice the value. A value of 0 6009 disables both lockup detectors. Default is 10 6010 seconds. 6011 6012 workqueue.watchdog_thresh= 6013 If CONFIG_WQ_WATCHDOG is configured, workqueue can 6014 warn stall conditions and dump internal state to 6015 help debugging. 0 disables workqueue stall 6016 detection; otherwise, it's the stall threshold 6017 duration in seconds. The default value is 30 and 6018 it can be updated at runtime by writing to the 6019 corresponding sysfs file. 6020 6021 workqueue.disable_numa 6022 By default, all work items queued to unbound 6023 workqueues are affine to the NUMA nodes they're 6024 issued on, which results in better behavior in 6025 general. If NUMA affinity needs to be disabled for 6026 whatever reason, this option can be used. Note 6027 that this also can be controlled per-workqueue for 6028 workqueues visible under /sys/bus/workqueue/. 6029 6030 workqueue.power_efficient 6031 Per-cpu workqueues are generally preferred because 6032 they show better performance thanks to cache 6033 locality; unfortunately, per-cpu workqueues tend to 6034 be more power hungry than unbound workqueues. 6035 6036 Enabling this makes the per-cpu workqueues which 6037 were observed to contribute significantly to power 6038 consumption unbound, leading to measurably lower 6039 power usage at the cost of small performance 6040 overhead. 6041 6042 The default value of this parameter is determined by 6043 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 6044 6045 workqueue.debug_force_rr_cpu 6046 Workqueue used to implicitly guarantee that work 6047 items queued without explicit CPU specified are put 6048 on the local CPU. This guarantee is no longer true 6049 and while local CPU is still preferred work items 6050 may be put on foreign CPUs. This debug option 6051 forces round-robin CPU selection to flush out 6052 usages which depend on the now broken guarantee. 6053 When enabled, memory and cache locality will be 6054 impacted. 6055 6056 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of 6057 default x2apic cluster mode on platforms 6058 supporting x2apic. 6059 6060 x86_intel_mid_timer= [X86-32,APBT] 6061 Choose timer option for x86 Intel MID platform. 6062 Two valid options are apbt timer only and lapic timer 6063 plus one apbt timer for broadcast timer. 6064 x86_intel_mid_timer=apbt_only | lapic_and_apbt 6065 6066 xen_512gb_limit [KNL,X86-64,XEN] 6067 Restricts the kernel running paravirtualized under Xen 6068 to use only up to 512 GB of RAM. The reason to do so is 6069 crash analysis tools and Xen tools for doing domain 6070 save/restore/migration must be enabled to handle larger 6071 domains. 6072 6073 xen_emul_unplug= [HW,X86,XEN] 6074 Unplug Xen emulated devices 6075 Format: [unplug0,][unplug1] 6076 ide-disks -- unplug primary master IDE devices 6077 aux-ide-disks -- unplug non-primary-master IDE devices 6078 nics -- unplug network devices 6079 all -- unplug all emulated devices (NICs and IDE disks) 6080 unnecessary -- unplugging emulated devices is 6081 unnecessary even if the host did not respond to 6082 the unplug protocol 6083 never -- do not unplug even if version check succeeds 6084 6085 xen_legacy_crash [X86,XEN] 6086 Crash from Xen panic notifier, without executing late 6087 panic() code such as dumping handler. 6088 6089 xen_nopvspin [X86,XEN] 6090 Disables the qspinlock slowpath using Xen PV optimizations. 6091 This parameter is obsoleted by "nopvspin" parameter, which 6092 has equivalent effect for XEN platform. 6093 6094 xen_nopv [X86] 6095 Disables the PV optimizations forcing the HVM guest to 6096 run as generic HVM guest with no PV drivers. 6097 This option is obsoleted by the "nopv" option, which 6098 has equivalent effect for XEN platform. 6099 6100 xen_no_vector_callback 6101 [KNL,X86,XEN] Disable the vector callback for Xen 6102 event channel interrupts. 6103 6104 xen_scrub_pages= [XEN] 6105 Boolean option to control scrubbing pages before giving them back 6106 to Xen, for use by other domains. Can be also changed at runtime 6107 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. 6108 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. 6109 6110 xen_timer_slop= [X86-64,XEN] 6111 Set the timer slop (in nanoseconds) for the virtual Xen 6112 timers (default is 100000). This adjusts the minimum 6113 delta of virtualized Xen timers, where lower values 6114 improve timer resolution at the expense of processing 6115 more timer interrupts. 6116 6117 xen.balloon_boot_timeout= [XEN] 6118 The time (in seconds) to wait before giving up to boot 6119 in case initial ballooning fails to free enough memory. 6120 Applies only when running as HVM or PVH guest and 6121 started with less memory configured than allowed at 6122 max. Default is 180. 6123 6124 xen.event_eoi_delay= [XEN] 6125 How long to delay EOI handling in case of event 6126 storms (jiffies). Default is 10. 6127 6128 xen.event_loop_timeout= [XEN] 6129 After which time (jiffies) the event handling loop 6130 should start to delay EOI handling. Default is 2. 6131 6132 xen.fifo_events= [XEN] 6133 Boolean parameter to disable using fifo event handling 6134 even if available. Normally fifo event handling is 6135 preferred over the 2-level event handling, as it is 6136 fairer and the number of possible event channels is 6137 much higher. Default is on (use fifo events). 6138 6139 nopv= [X86,XEN,KVM,HYPER_V,VMWARE] 6140 Disables the PV optimizations forcing the guest to run 6141 as generic guest with no PV drivers. Currently support 6142 XEN HVM, KVM, HYPER_V and VMWARE guest. 6143 6144 nopvspin [X86,XEN,KVM] 6145 Disables the qspinlock slow path using PV optimizations 6146 which allow the hypervisor to 'idle' the guest on lock 6147 contention. 6148 6149 xirc2ps_cs= [NET,PCMCIA] 6150 Format: 6151 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 6152 6153 xive= [PPC] 6154 By default on POWER9 and above, the kernel will 6155 natively use the XIVE interrupt controller. This option 6156 allows the fallback firmware mode to be used: 6157 6158 off Fallback to firmware control of XIVE interrupt 6159 controller on both pseries and powernv 6160 platforms. Only useful on POWER9 and above. 6161 6162 xhci-hcd.quirks [USB,KNL] 6163 A hex value specifying bitmask with supplemental xhci 6164 host controller quirks. Meaning of each bit can be 6165 consulted in header drivers/usb/host/xhci.h. 6166 6167 xmon [PPC] 6168 Format: { early | on | rw | ro | off } 6169 Controls if xmon debugger is enabled. Default is off. 6170 Passing only "xmon" is equivalent to "xmon=early". 6171 early Call xmon as early as possible on boot; xmon 6172 debugger is called from setup_arch(). 6173 on xmon debugger hooks will be installed so xmon 6174 is only called on a kernel crash. Default mode, 6175 i.e. either "ro" or "rw" mode, is controlled 6176 with CONFIG_XMON_DEFAULT_RO_MODE. 6177 rw xmon debugger hooks will be installed so xmon 6178 is called only on a kernel crash, mode is write, 6179 meaning SPR registers, memory and, other data 6180 can be written using xmon commands. 6181 ro same as "rw" option above but SPR registers, 6182 memory, and other data can't be written using 6183 xmon commands. 6184 off xmon is disabled. 6185