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 acpi_backlight=vendor 26 acpi_backlight=video 27 If set to vendor, prefer vendor specific driver 28 (e.g. thinkpad_acpi, sony_acpi, etc.) instead 29 of the ACPI video.ko driver. 30 31 acpi_force_32bit_fadt_addr 32 force FADT to use 32 bit addresses rather than the 33 64 bit X_* addresses. Some firmware have broken 64 34 bit addresses for force ACPI ignore these and use 35 the older legacy 32 bit addresses. 36 37 acpica_no_return_repair [HW, ACPI] 38 Disable AML predefined validation mechanism 39 This mechanism can repair the evaluation result to make 40 the return objects more ACPI specification compliant. 41 This option is useful for developers to identify the 42 root cause of an AML interpreter issue when the issue 43 has something to do with the repair mechanism. 44 45 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG] 46 acpi.debug_level= [HW,ACPI,ACPI_DEBUG] 47 Format: <int> 48 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI 49 debug output. Bits in debug_layer correspond to a 50 _COMPONENT in an ACPI source file, e.g., 51 #define _COMPONENT ACPI_PCI_COMPONENT 52 Bits in debug_level correspond to a level in 53 ACPI_DEBUG_PRINT statements, e.g., 54 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ... 55 The debug_level mask defaults to "info". See 56 Documentation/firmware-guide/acpi/debug.rst for more information about 57 debug layers and levels. 58 59 Enable processor driver info messages: 60 acpi.debug_layer=0x20000000 61 Enable PCI/PCI interrupt routing info messages: 62 acpi.debug_layer=0x400000 63 Enable AML "Debug" output, i.e., stores to the Debug 64 object while interpreting AML: 65 acpi.debug_layer=0xffffffff acpi.debug_level=0x2 66 Enable all messages related to ACPI hardware: 67 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff 68 69 Some values produce so much output that the system is 70 unusable. The "log_buf_len" parameter may be useful 71 if you need to capture more output. 72 73 acpi_enforce_resources= [ACPI] 74 { strict | lax | no } 75 Check for resource conflicts between native drivers 76 and ACPI OperationRegions (SystemIO and SystemMemory 77 only). IO ports and memory declared in ACPI might be 78 used by the ACPI subsystem in arbitrary AML code and 79 can interfere with legacy drivers. 80 strict (default): access to resources claimed by ACPI 81 is denied; legacy drivers trying to access reserved 82 resources will fail to bind to device using them. 83 lax: access to resources claimed by ACPI is allowed; 84 legacy drivers trying to access reserved resources 85 will bind successfully but a warning message is logged. 86 no: ACPI OperationRegions are not marked as reserved, 87 no further checks are performed. 88 89 acpi_force_table_verification [HW,ACPI] 90 Enable table checksum verification during early stage. 91 By default, this is disabled due to x86 early mapping 92 size limitation. 93 94 acpi_irq_balance [HW,ACPI] 95 ACPI will balance active IRQs 96 default in APIC mode 97 98 acpi_irq_nobalance [HW,ACPI] 99 ACPI will not move active IRQs (default) 100 default in PIC mode 101 102 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA 103 Format: <irq>,<irq>... 104 105 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for 106 use by PCI 107 Format: <irq>,<irq>... 108 109 acpi_mask_gpe= [HW,ACPI] 110 Due to the existence of _Lxx/_Exx, some GPEs triggered 111 by unsupported hardware/firmware features can result in 112 GPE floodings that cannot be automatically disabled by 113 the GPE dispatcher. 114 This facility can be used to prevent such uncontrolled 115 GPE floodings. 116 Format: <byte> 117 118 acpi_no_auto_serialize [HW,ACPI] 119 Disable auto-serialization of AML methods 120 AML control methods that contain the opcodes to create 121 named objects will be marked as "Serialized" by the 122 auto-serialization feature. 123 This feature is enabled by default. 124 This option allows to turn off the feature. 125 126 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump 127 kernels. 128 129 acpi_no_static_ssdt [HW,ACPI] 130 Disable installation of static SSDTs at early boot time 131 By default, SSDTs contained in the RSDT/XSDT will be 132 installed automatically and they will appear under 133 /sys/firmware/acpi/tables. 134 This option turns off this feature. 135 Note that specifying this option does not affect 136 dynamic table installation which will install SSDT 137 tables to /sys/firmware/acpi/tables/dynamic. 138 139 acpi_no_watchdog [HW,ACPI,WDT] 140 Ignore the ACPI-based watchdog interface (WDAT) and let 141 a native driver control the watchdog device instead. 142 143 acpi_rsdp= [ACPI,EFI,KEXEC] 144 Pass the RSDP address to the kernel, mostly used 145 on machines running EFI runtime service to boot the 146 second kernel for kdump. 147 148 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS 149 Format: To spoof as Windows 98: ="Microsoft Windows" 150 151 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead 152 of 2 which is mandated by ACPI 6) as the supported ACPI 153 specification revision (when using this switch, it may 154 be necessary to carry out a cold reboot _twice_ in a 155 row to make it take effect on the platform firmware). 156 157 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings 158 acpi_osi="string1" # add string1 159 acpi_osi="!string2" # remove string2 160 acpi_osi=!* # remove all strings 161 acpi_osi=! # disable all built-in OS vendor 162 strings 163 acpi_osi=!! # enable all built-in OS vendor 164 strings 165 acpi_osi= # disable all strings 166 167 'acpi_osi=!' can be used in combination with single or 168 multiple 'acpi_osi="string1"' to support specific OS 169 vendor string(s). Note that such command can only 170 affect the default state of the OS vendor strings, thus 171 it cannot affect the default state of the feature group 172 strings and the current state of the OS vendor strings, 173 specifying it multiple times through kernel command line 174 is meaningless. This command is useful when one do not 175 care about the state of the feature group strings which 176 should be controlled by the OSPM. 177 Examples: 178 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent 179 to 'acpi_osi="Windows 2000" acpi_osi=!', they all 180 can make '_OSI("Windows 2000")' TRUE. 181 182 'acpi_osi=' cannot be used in combination with other 183 'acpi_osi=' command lines, the _OSI method will not 184 exist in the ACPI namespace. NOTE that such command can 185 only affect the _OSI support state, thus specifying it 186 multiple times through kernel command line is also 187 meaningless. 188 Examples: 189 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)' 190 FALSE. 191 192 'acpi_osi=!*' can be used in combination with single or 193 multiple 'acpi_osi="string1"' to support specific 194 string(s). Note that such command can affect the 195 current state of both the OS vendor strings and the 196 feature group strings, thus specifying it multiple times 197 through kernel command line is meaningful. But it may 198 still not able to affect the final state of a string if 199 there are quirks related to this string. This command 200 is useful when one want to control the state of the 201 feature group strings to debug BIOS issues related to 202 the OSPM features. 203 Examples: 204 1. 'acpi_osi="Module Device" acpi_osi=!*' can make 205 '_OSI("Module Device")' FALSE. 206 2. 'acpi_osi=!* acpi_osi="Module Device"' can make 207 '_OSI("Module Device")' TRUE. 208 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is 209 equivalent to 210 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"' 211 and 212 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!', 213 they all will make '_OSI("Windows 2000")' TRUE. 214 215 acpi_pm_good [X86] 216 Override the pmtimer bug detection: force the kernel 217 to assume that this machine's pmtimer latches its value 218 and always returns good values. 219 220 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode 221 Format: { level | edge | high | low } 222 223 acpi_skip_timer_override [HW,ACPI] 224 Recognize and ignore IRQ0/pin2 Interrupt Override. 225 For broken nForce2 BIOS resulting in XT-PIC timer. 226 227 acpi_sleep= [HW,ACPI] Sleep options 228 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig, 229 old_ordering, nonvs, sci_force_enable, nobl } 230 See Documentation/power/video.rst for information on 231 s3_bios and s3_mode. 232 s3_beep is for debugging; it makes the PC's speaker beep 233 as soon as the kernel's real-mode entry point is called. 234 s4_nohwsig prevents ACPI hardware signature from being 235 used during resume from hibernation. 236 old_ordering causes the ACPI 1.0 ordering of the _PTS 237 control method, with respect to putting devices into 238 low power states, to be enforced (the ACPI 2.0 ordering 239 of _PTS is used by default). 240 nonvs prevents the kernel from saving/restoring the 241 ACPI NVS memory during suspend/hibernation and resume. 242 sci_force_enable causes the kernel to set SCI_EN directly 243 on resume from S1/S3 (which is against the ACPI spec, 244 but some broken systems don't work without it). 245 nobl causes the internal blacklist of systems known to 246 behave incorrectly in some ways with respect to system 247 suspend and resume to be ignored (use wisely). 248 249 acpi_use_timer_override [HW,ACPI] 250 Use timer override. For some broken Nvidia NF5 boards 251 that require a timer override, but don't have HPET 252 253 add_efi_memmap [EFI; X86] Include EFI memory map in 254 kernel's map of available physical RAM. 255 256 agp= [AGP] 257 { off | try_unsupported } 258 off: disable AGP support 259 try_unsupported: try to drive unsupported chipsets 260 (may crash computer or cause data corruption) 261 262 ALSA [HW,ALSA] 263 See Documentation/sound/alsa-configuration.rst 264 265 alignment= [KNL,ARM] 266 Allow the default userspace alignment fault handler 267 behaviour to be specified. Bit 0 enables warnings, 268 bit 1 enables fixups, and bit 2 sends a segfault. 269 270 align_va_addr= [X86-64] 271 Align virtual addresses by clearing slice [14:12] when 272 allocating a VMA at process creation time. This option 273 gives you up to 3% performance improvement on AMD F15h 274 machines (where it is enabled by default) for a 275 CPU-intensive style benchmark, and it can vary highly in 276 a microbenchmark depending on workload and compiler. 277 278 32: only for 32-bit processes 279 64: only for 64-bit processes 280 on: enable for both 32- and 64-bit processes 281 off: disable for both 32- and 64-bit processes 282 283 alloc_snapshot [FTRACE] 284 Allocate the ftrace snapshot buffer on boot up when the 285 main buffer is allocated. This is handy if debugging 286 and you need to use tracing_snapshot() on boot up, and 287 do not want to use tracing_snapshot_alloc() as it needs 288 to be done where GFP_KERNEL allocations are allowed. 289 290 amd_iommu= [HW,X86-64] 291 Pass parameters to the AMD IOMMU driver in the system. 292 Possible values are: 293 fullflush - enable flushing of IO/TLB entries when 294 they are unmapped. Otherwise they are 295 flushed before they will be reused, which 296 is a lot of faster 297 off - do not initialize any AMD IOMMU found in 298 the system 299 force_isolation - Force device isolation for all 300 devices. The IOMMU driver is not 301 allowed anymore to lift isolation 302 requirements as needed. This option 303 does not override iommu=pt 304 305 amd_iommu_dump= [HW,X86-64] 306 Enable AMD IOMMU driver option to dump the ACPI table 307 for AMD IOMMU. With this option enabled, AMD IOMMU 308 driver will print ACPI tables for AMD IOMMU during 309 IOMMU initialization. 310 311 amd_iommu_intr= [HW,X86-64] 312 Specifies one of the following AMD IOMMU interrupt 313 remapping modes: 314 legacy - Use legacy interrupt remapping mode. 315 vapic - Use virtual APIC mode, which allows IOMMU 316 to inject interrupts directly into guest. 317 This mode requires kvm-amd.avic=1. 318 (Default when IOMMU HW support is present.) 319 320 amijoy.map= [HW,JOY] Amiga joystick support 321 Map of devices attached to JOY0DAT and JOY1DAT 322 Format: <a>,<b> 323 See also Documentation/input/joydev/joystick.rst 324 325 analog.map= [HW,JOY] Analog joystick and gamepad support 326 Specifies type or capabilities of an analog joystick 327 connected to one of 16 gameports 328 Format: <type1>,<type2>,..<type16> 329 330 apc= [HW,SPARC] 331 Power management functions (SPARCstation-4/5 + deriv.) 332 Format: noidle 333 Disable APC CPU standby support. SPARCstation-Fox does 334 not play well with APC CPU idle - disable it if you have 335 APC and your system crashes randomly. 336 337 apic= [APIC,X86] Advanced Programmable Interrupt Controller 338 Change the output verbosity while booting 339 Format: { quiet (default) | verbose | debug } 340 Change the amount of debugging information output 341 when initialising the APIC and IO-APIC components. 342 For X86-32, this can also be used to specify an APIC 343 driver name. 344 Format: apic=driver_name 345 Examples: apic=bigsmp 346 347 apic_extnmi= [APIC,X86] External NMI delivery setting 348 Format: { bsp (default) | all | none } 349 bsp: External NMI is delivered only to CPU 0 350 all: External NMIs are broadcast to all CPUs as a 351 backup of CPU 0 352 none: External NMI is masked for all CPUs. This is 353 useful so that a dump capture kernel won't be 354 shot down by NMI 355 356 autoconf= [IPV6] 357 See Documentation/networking/ipv6.txt. 358 359 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller 360 Limit apic dumping. The parameter defines the maximal 361 number of local apics being dumped. Also it is possible 362 to set it to "all" by meaning -- no limit here. 363 Format: { 1 (default) | 2 | ... | all }. 364 The parameter valid if only apic=debug or 365 apic=verbose is specified. 366 Example: apic=debug show_lapic=all 367 368 apm= [APM] Advanced Power Management 369 See header of arch/x86/kernel/apm_32.c. 370 371 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards 372 Format: <io>,<irq>,<nodeID> 373 374 ataflop= [HW,M68k] 375 376 atarimouse= [HW,MOUSE] Atari Mouse 377 378 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess, 379 EzKey and similar keyboards 380 381 atkbd.reset= [HW] Reset keyboard during initialization 382 383 atkbd.set= [HW] Select keyboard code set 384 Format: <int> (2 = AT (default), 3 = PS/2) 385 386 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar 387 keyboards 388 389 atkbd.softraw= [HW] Choose between synthetic and real raw mode 390 Format: <bool> (0 = real, 1 = synthetic (default)) 391 392 atkbd.softrepeat= [HW] 393 Use software keyboard repeat 394 395 audit= [KNL] Enable the audit sub-system 396 Format: { "0" | "1" | "off" | "on" } 397 0 | off - kernel audit is disabled and can not be 398 enabled until the next reboot 399 unset - kernel audit is initialized but disabled and 400 will be fully enabled by the userspace auditd. 401 1 | on - kernel audit is initialized and partially 402 enabled, storing at most audit_backlog_limit 403 messages in RAM until it is fully enabled by the 404 userspace auditd. 405 Default: unset 406 407 audit_backlog_limit= [KNL] Set the audit queue size limit. 408 Format: <int> (must be >=0) 409 Default: 64 410 411 bau= [X86_UV] Enable the BAU on SGI UV. The default 412 behavior is to disable the BAU (i.e. bau=0). 413 Format: { "0" | "1" } 414 0 - Disable the BAU. 415 1 - Enable the BAU. 416 unset - Disable the BAU. 417 418 baycom_epp= [HW,AX25] 419 Format: <io>,<mode> 420 421 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem 422 Format: <io>,<mode> 423 See header of drivers/net/hamradio/baycom_par.c. 424 425 baycom_ser_fdx= [HW,AX25] 426 BayCom Serial Port AX.25 Modem (Full Duplex Mode) 427 Format: <io>,<irq>,<mode>[,<baud>] 428 See header of drivers/net/hamradio/baycom_ser_fdx.c. 429 430 baycom_ser_hdx= [HW,AX25] 431 BayCom Serial Port AX.25 Modem (Half Duplex Mode) 432 Format: <io>,<irq>,<mode> 433 See header of drivers/net/hamradio/baycom_ser_hdx.c. 434 435 blkdevparts= Manual partition parsing of block device(s) for 436 embedded devices based on command line input. 437 See Documentation/block/cmdline-partition.rst 438 439 boot_delay= Milliseconds to delay each printk during boot. 440 Values larger than 10 seconds (10000) are changed to 441 no delay (0). 442 Format: integer 443 444 bootmem_debug [KNL] Enable bootmem allocator debug messages. 445 446 bert_disable [ACPI] 447 Disable BERT OS support on buggy BIOSes. 448 449 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards) 450 bttv.radio= Most important insmod options are available as 451 kernel args too. 452 bttv.pll= See Documentation/media/v4l-drivers/bttv.rst 453 bttv.tuner= 454 455 bulk_remove=off [PPC] This parameter disables the use of the pSeries 456 firmware feature for flushing multiple hpte entries 457 at a time. 458 459 c101= [NET] Moxa C101 synchronous serial card 460 461 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection. 462 Sometimes CPU hardware bugs make them report the cache 463 size incorrectly. The kernel will attempt work arounds 464 to fix known problems, but for some CPUs it is not 465 possible to determine what the correct size should be. 466 This option provides an override for these situations. 467 468 carrier_timeout= 469 [NET] Specifies amount of time (in seconds) that 470 the kernel should wait for a network carrier. By default 471 it waits 120 seconds. 472 473 ca_keys= [KEYS] This parameter identifies a specific key(s) on 474 the system trusted keyring to be used for certificate 475 trust validation. 476 format: { id:<keyid> | builtin } 477 478 cca= [MIPS] Override the kernel pages' cache coherency 479 algorithm. Accepted values range from 0 to 7 480 inclusive. See arch/mips/include/asm/pgtable-bits.h 481 for platform specific values (SB1, Loongson3 and 482 others). 483 484 ccw_timeout_log [S390] 485 See Documentation/s390/common_io.rst for details. 486 487 cgroup_disable= [KNL] Disable a particular controller 488 Format: {name of the controller(s) to disable} 489 The effects of cgroup_disable=foo are: 490 - foo isn't auto-mounted if you mount all cgroups in 491 a single hierarchy 492 - foo isn't visible as an individually mountable 493 subsystem 494 {Currently only "memory" controller deal with this and 495 cut the overhead, others just disable the usage. So 496 only cgroup_disable=memory is actually worthy} 497 498 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1 499 Format: { { controller | "all" | "named" } 500 [,{ controller | "all" | "named" }...] } 501 Like cgroup_disable, but only applies to cgroup v1; 502 the blacklisted controllers remain available in cgroup2. 503 "all" blacklists all controllers and "named" disables 504 named mounts. Specifying both "all" and "named" disables 505 all v1 hierarchies. 506 507 cgroup.memory= [KNL] Pass options to the cgroup memory controller. 508 Format: <string> 509 nosocket -- Disable socket memory accounting. 510 nokmem -- Disable kernel memory accounting. 511 512 checkreqprot [SELINUX] Set initial checkreqprot flag value. 513 Format: { "0" | "1" } 514 See security/selinux/Kconfig help text. 515 0 -- check protection applied by kernel (includes 516 any implied execute protection). 517 1 -- check protection requested by application. 518 Default value is set via a kernel config option. 519 Value can be changed at runtime via 520 /selinux/checkreqprot. 521 522 cio_ignore= [S390] 523 See Documentation/s390/common_io.rst for details. 524 clk_ignore_unused 525 [CLK] 526 Prevents the clock framework from automatically gating 527 clocks that have not been explicitly enabled by a Linux 528 device driver but are enabled in hardware at reset or 529 by the bootloader/firmware. Note that this does not 530 force such clocks to be always-on nor does it reserve 531 those clocks in any way. This parameter is useful for 532 debug and development, but should not be needed on a 533 platform with proper driver support. For more 534 information, see Documentation/driver-api/clk.rst. 535 536 clock= [BUGS=X86-32, HW] gettimeofday clocksource override. 537 [Deprecated] 538 Forces specified clocksource (if available) to be used 539 when calculating gettimeofday(). If specified 540 clocksource is not available, it defaults to PIT. 541 Format: { pit | tsc | cyclone | pmtmr } 542 543 clocksource= Override the default clocksource 544 Format: <string> 545 Override the default clocksource and use the clocksource 546 with the name specified. 547 Some clocksource names to choose from, depending on 548 the platform: 549 [all] jiffies (this is the base, fallback clocksource) 550 [ACPI] acpi_pm 551 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2, 552 pxa_timer,timer3,32k_counter,timer0_1 553 [X86-32] pit,hpet,tsc; 554 scx200_hrt on Geode; cyclone on IBM x440 555 [MIPS] MIPS 556 [PARISC] cr16 557 [S390] tod 558 [SH] SuperH 559 [SPARC64] tick 560 [X86-64] hpet,tsc 561 562 clocksource.arm_arch_timer.evtstrm= 563 [ARM,ARM64] 564 Format: <bool> 565 Enable/disable the eventstream feature of the ARM 566 architected timer so that code using WFE-based polling 567 loops can be debugged more effectively on production 568 systems. 569 570 clocksource.max_cswd_read_retries= [KNL] 571 Number of clocksource_watchdog() retries due to 572 external delays before the clock will be marked 573 unstable. Defaults to three retries, that is, 574 four attempts to read the clock under test. 575 576 clearcpuid=BITNUM[,BITNUM...] [X86] 577 Disable CPUID feature X for the kernel. See 578 arch/x86/include/asm/cpufeatures.h for the valid bit 579 numbers. Note the Linux specific bits are not necessarily 580 stable over kernel options, but the vendor specific 581 ones should be. 582 Also note that user programs calling CPUID directly 583 or using the feature without checking anything 584 will still see it. This just prevents it from 585 being used by the kernel or shown in /proc/cpuinfo. 586 Also note the kernel might malfunction if you disable 587 some critical bits. 588 589 cma=nn[MG]@[start[MG][-end[MG]]] 590 [ARM,X86,KNL] 591 Sets the size of kernel global memory area for 592 contiguous memory allocations and optionally the 593 placement constraint by the physical address range of 594 memory allocations. A value of 0 disables CMA 595 altogether. For more information, see 596 include/linux/dma-contiguous.h 597 598 cmo_free_hint= [PPC] Format: { yes | no } 599 Specify whether pages are marked as being inactive 600 when they are freed. This is used in CMO environments 601 to determine OS memory pressure for page stealing by 602 a hypervisor. 603 Default: yes 604 605 coherent_pool=nn[KMG] [ARM,KNL] 606 Sets the size of memory pool for coherent, atomic dma 607 allocations, by default set to 256K. 608 609 com20020= [HW,NET] ARCnet - COM20020 chipset 610 Format: 611 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]] 612 613 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers) 614 Format: <io>[,<irq>] 615 616 com90xx= [HW,NET] 617 ARCnet - COM90xx chipset (memory-mapped buffers) 618 Format: <io>[,<irq>[,<memstart>]] 619 620 condev= [HW,S390] console device 621 conmode= 622 623 console= [KNL] Output console device and options. 624 625 tty<n> Use the virtual console device <n>. 626 627 ttyS<n>[,options] 628 ttyUSB0[,options] 629 Use the specified serial port. The options are of 630 the form "bbbbpnf", where "bbbb" is the baud rate, 631 "p" is parity ("n", "o", or "e"), "n" is number of 632 bits, and "f" is flow control ("r" for RTS or 633 omit it). Default is "9600n8". 634 635 See Documentation/admin-guide/serial-console.rst for more 636 information. See 637 Documentation/networking/netconsole.txt for an 638 alternative. 639 640 uart[8250],io,<addr>[,options] 641 uart[8250],mmio,<addr>[,options] 642 uart[8250],mmio16,<addr>[,options] 643 uart[8250],mmio32,<addr>[,options] 644 uart[8250],0x<addr>[,options] 645 Start an early, polled-mode console on the 8250/16550 646 UART at the specified I/O port or MMIO address, 647 switching to the matching ttyS device later. 648 MMIO inter-register address stride is either 8-bit 649 (mmio), 16-bit (mmio16), or 32-bit (mmio32). 650 If none of [io|mmio|mmio16|mmio32], <addr> is assumed 651 to be equivalent to 'mmio'. 'options' are specified in 652 the same format described for ttyS above; if unspecified, 653 the h/w is not re-initialized. 654 655 hvc<n> Use the hypervisor console device <n>. This is for 656 both Xen and PowerPC hypervisors. 657 658 If the device connected to the port is not a TTY but a braille 659 device, prepend "brl," before the device type, for instance 660 console=brl,ttyS0 661 For now, only VisioBraille is supported. 662 663 console_msg_format= 664 [KNL] Change console messages format 665 default 666 By default we print messages on consoles in 667 "[time stamp] text\n" format (time stamp may not be 668 printed, depending on CONFIG_PRINTK_TIME or 669 `printk_time' param). 670 syslog 671 Switch to syslog format: "<%u>[time stamp] text\n" 672 IOW, each message will have a facility and loglevel 673 prefix. The format is similar to one used by syslog() 674 syscall, or to executing "dmesg -S --raw" or to reading 675 from /proc/kmsg. 676 677 consoleblank= [KNL] The console blank (screen saver) timeout in 678 seconds. A value of 0 disables the blank timer. 679 Defaults to 0. 680 681 coredump_filter= 682 [KNL] Change the default value for 683 /proc/<pid>/coredump_filter. 684 See also Documentation/filesystems/proc.txt. 685 686 coresight_cpu_debug.enable 687 [ARM,ARM64] 688 Format: <bool> 689 Enable/disable the CPU sampling based debugging. 690 0: default value, disable debugging 691 1: enable debugging at boot time 692 693 cpuidle.off=1 [CPU_IDLE] 694 disable the cpuidle sub-system 695 696 cpuidle.governor= 697 [CPU_IDLE] Name of the cpuidle governor to use. 698 699 cpufreq.off=1 [CPU_FREQ] 700 disable the cpufreq sub-system 701 702 cpu_init_udelay=N 703 [X86] Delay for N microsec between assert and de-assert 704 of APIC INIT to start processors. This delay occurs 705 on every CPU online, such as boot, and resume from suspend. 706 Default: 10000 707 708 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver 709 Format: 710 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] 711 712 crashkernel=size[KMG][@offset[KMG]] 713 [KNL] Using kexec, Linux can switch to a 'crash kernel' 714 upon panic. This parameter reserves the physical 715 memory region [offset, offset + size] for that kernel 716 image. If '@offset' is omitted, then a suitable offset 717 is selected automatically. 718 [KNL, x86_64] select a region under 4G first, and 719 fall back to reserve region above 4G when '@offset' 720 hasn't been specified. 721 See Documentation/admin-guide/kdump/kdump.rst for further details. 722 723 crashkernel=range1:size1[,range2:size2,...][@offset] 724 [KNL] Same as above, but depends on the memory 725 in the running system. The syntax of range is 726 start-[end] where start and end are both 727 a memory unit (amount[KMG]). See also 728 Documentation/admin-guide/kdump/kdump.rst for an example. 729 730 crashkernel=size[KMG],high 731 [KNL, x86_64] range could be above 4G. Allow kernel 732 to allocate physical memory region from top, so could 733 be above 4G if system have more than 4G ram installed. 734 Otherwise memory region will be allocated below 4G, if 735 available. 736 It will be ignored if crashkernel=X is specified. 737 crashkernel=size[KMG],low 738 [KNL, x86_64] range under 4G. When crashkernel=X,high 739 is passed, kernel could allocate physical memory region 740 above 4G, that cause second kernel crash on system 741 that require some amount of low memory, e.g. swiotlb 742 requires at least 64M+32K low memory, also enough extra 743 low memory is needed to make sure DMA buffers for 32-bit 744 devices won't run out. Kernel would try to allocate at 745 at least 256M below 4G automatically. 746 This one let user to specify own low range under 4G 747 for second kernel instead. 748 0: to disable low allocation. 749 It will be ignored when crashkernel=X,high is not used 750 or memory reserved is below 4G. 751 752 cryptomgr.notests 753 [KNL] Disable crypto self-tests 754 755 cs89x0_dma= [HW,NET] 756 Format: <dma> 757 758 cs89x0_media= [HW,NET] 759 Format: { rj45 | aui | bnc } 760 761 dasd= [HW,NET] 762 See header of drivers/s390/block/dasd_devmap.c. 763 764 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port 765 (one device per port) 766 Format: <port#>,<type> 767 See also Documentation/input/devices/joystick-parport.rst 768 769 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot 770 time. See 771 Documentation/admin-guide/dynamic-debug-howto.rst for 772 details. Deprecated, see dyndbg. 773 774 debug [KNL] Enable kernel debugging (events log level). 775 776 debug_boot_weak_hash 777 [KNL] Enable printing [hashed] pointers early in the 778 boot sequence. If enabled, we use a weak hash instead 779 of siphash to hash pointers. Use this option if you are 780 seeing instances of '(___ptrval___)') and need to see a 781 value (hashed pointer) instead. Cryptographically 782 insecure, please do not use on production kernels. 783 784 debug_locks_verbose= 785 [KNL] verbose self-tests 786 Format=<0|1> 787 Print debugging info while doing the locking API 788 self-tests. 789 We default to 0 (no extra messages), setting it to 790 1 will print _a lot_ more information - normally 791 only useful to kernel developers. 792 793 debug_objects [KNL] Enable object debugging 794 795 no_debug_objects 796 [KNL] Disable object debugging 797 798 debug_guardpage_minorder= 799 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this 800 parameter allows control of the order of pages that will 801 be intentionally kept free (and hence protected) by the 802 buddy allocator. Bigger value increase the probability 803 of catching random memory corruption, but reduce the 804 amount of memory for normal system use. The maximum 805 possible value is MAX_ORDER/2. Setting this parameter 806 to 1 or 2 should be enough to identify most random 807 memory corruption problems caused by bugs in kernel or 808 driver code when a CPU writes to (or reads from) a 809 random memory location. Note that there exists a class 810 of memory corruptions problems caused by buggy H/W or 811 F/W or by drivers badly programing DMA (basically when 812 memory is written at bus level and the CPU MMU is 813 bypassed) which are not detectable by 814 CONFIG_DEBUG_PAGEALLOC, hence this option will not help 815 tracking down these problems. 816 817 debug_pagealloc= 818 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this parameter 819 enables the feature at boot time. By default, it is 820 disabled and the system will work mostly the same as a 821 kernel built without CONFIG_DEBUG_PAGEALLOC. 822 Note: to get most of debug_pagealloc error reports, it's 823 useful to also enable the page_owner functionality. 824 on: enable the feature 825 826 debugpat [X86] Enable PAT debugging 827 828 default_hugepagesz= 829 [same as hugepagesz=] The size of the default 830 HugeTLB page size. This is the size represented by 831 the legacy /proc/ hugepages APIs, used for SHM, and 832 default size when mounting hugetlbfs filesystems. 833 Defaults to the default architecture's huge page size 834 if not specified. 835 836 deferred_probe_timeout= 837 [KNL] Debugging option to set a timeout in seconds for 838 deferred probe to give up waiting on dependencies to 839 probe. Only specific dependencies (subsystems or 840 drivers) that have opted in will be ignored. A timeout of 0 841 will timeout at the end of initcalls. This option will also 842 dump out devices still on the deferred probe list after 843 retrying. 844 845 dhash_entries= [KNL] 846 Set number of hash buckets for dentry cache. 847 848 disable_1tb_segments [PPC] 849 Disables the use of 1TB hash page table segments. This 850 causes the kernel to fall back to 256MB segments which 851 can be useful when debugging issues that require an SLB 852 miss to occur. 853 854 disable= [IPV6] 855 See Documentation/networking/ipv6.txt. 856 857 hardened_usercopy= 858 [KNL] Under CONFIG_HARDENED_USERCOPY, whether 859 hardening is enabled for this boot. Hardened 860 usercopy checking is used to protect the kernel 861 from reading or writing beyond known memory 862 allocation boundaries as a proactive defense 863 against bounds-checking flaws in the kernel's 864 copy_to_user()/copy_from_user() interface. 865 on Perform hardened usercopy checks (default). 866 off Disable hardened usercopy checks. 867 868 disable_radix [PPC] 869 Disable RADIX MMU mode on POWER9 870 871 disable_tlbie [PPC] 872 Disable TLBIE instruction. Currently does not work 873 with KVM, with HASH MMU, or with coherent accelerators. 874 875 disable_cpu_apicid= [X86,APIC,SMP] 876 Format: <int> 877 The number of initial APIC ID for the 878 corresponding CPU to be disabled at boot, 879 mostly used for the kdump 2nd kernel to 880 disable BSP to wake up multiple CPUs without 881 causing system reset or hang due to sending 882 INIT from AP to BSP. 883 884 perf_v4_pmi= [X86,INTEL] 885 Format: <bool> 886 Disable Intel PMU counter freezing feature. 887 The feature only exists starting from 888 Arch Perfmon v4 (Skylake and newer). 889 890 disable_ddw [PPC/PSERIES] 891 Disable Dynamic DMA Window support. Use this if 892 to workaround buggy firmware. 893 894 disable_ipv6= [IPV6] 895 See Documentation/networking/ipv6.txt. 896 897 disable_mtrr_cleanup [X86] 898 The kernel tries to adjust MTRR layout from continuous 899 to discrete, to make X server driver able to add WB 900 entry later. This parameter disables that. 901 902 disable_mtrr_trim [X86, Intel and AMD only] 903 By default the kernel will trim any uncacheable 904 memory out of your available memory pool based on 905 MTRR settings. This parameter disables that behavior, 906 possibly causing your machine to run very slowly. 907 908 disable_timer_pin_1 [X86] 909 Disable PIN 1 of APIC timer 910 Can be useful to work around chipset bugs. 911 912 dis_ucode_ldr [X86] Disable the microcode loader. 913 914 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, 915 this option disables the debugging code at boot. 916 917 dma_debug_entries=<number> 918 This option allows to tune the number of preallocated 919 entries for DMA-API debugging code. One entry is 920 required per DMA-API allocation. Use this if the 921 DMA-API debugging code disables itself because the 922 architectural default is too low. 923 924 dma_debug_driver=<driver_name> 925 With this option the DMA-API debugging driver 926 filter feature can be enabled at boot time. Just 927 pass the driver to filter for as the parameter. 928 The filter can be disabled or changed to another 929 driver later using sysfs. 930 931 driver_async_probe= [KNL] 932 List of driver names to be probed asynchronously. 933 Format: <driver_name1>,<driver_name2>... 934 935 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>] 936 Broken monitors, graphic adapters, KVMs and EDIDless 937 panels may send no or incorrect EDID data sets. 938 This parameter allows to specify an EDID data sets 939 in the /lib/firmware directory that are used instead. 940 Generic built-in EDID data sets are used, if one of 941 edid/1024x768.bin, edid/1280x1024.bin, 942 edid/1680x1050.bin, or edid/1920x1080.bin is given 943 and no file with the same name exists. Details and 944 instructions how to build your own EDID data are 945 available in Documentation/driver-api/edid.rst. An EDID 946 data set will only be used for a particular connector, 947 if its name and a colon are prepended to the EDID 948 name. Each connector may use a unique EDID data 949 set by separating the files with a comma. An EDID 950 data set with no connector name will be used for 951 any connectors not explicitly specified. 952 953 dscc4.setup= [NET] 954 955 dt_cpu_ftrs= [PPC] 956 Format: {"off" | "known"} 957 Control how the dt_cpu_ftrs device-tree binding is 958 used for CPU feature discovery and setup (if it 959 exists). 960 off: Do not use it, fall back to legacy cpu table. 961 known: Do not pass through unknown features to guests 962 or userspace, only those that the kernel is aware of. 963 964 dump_apple_properties [X86] 965 Dump name and content of EFI device properties on 966 x86 Macs. Useful for driver authors to determine 967 what data is available or for reverse-engineering. 968 969 dyndbg[="val"] [KNL,DYNAMIC_DEBUG] 970 module.dyndbg[="val"] 971 Enable debug messages at boot time. See 972 Documentation/admin-guide/dynamic-debug-howto.rst 973 for details. 974 975 nompx [X86] Disables Intel Memory Protection Extensions. 976 See Documentation/x86/intel_mpx.rst for more 977 information about the feature. 978 979 nopku [X86] Disable Memory Protection Keys CPU feature found 980 in some Intel CPUs. 981 982 module.async_probe [KNL] 983 Enable asynchronous probe on this module. 984 985 early_ioremap_debug [KNL] 986 Enable debug messages in early_ioremap support. This 987 is useful for tracking down temporary early mappings 988 which are not unmapped. 989 990 earlycon= [KNL] Output early console device and options. 991 992 [ARM64] The early console is determined by the 993 stdout-path property in device tree's chosen node, 994 or determined by the ACPI SPCR table. 995 996 [X86] When used with no options the early console is 997 determined by the ACPI SPCR table. 998 999 cdns,<addr>[,options] 1000 Start an early, polled-mode console on a Cadence 1001 (xuartps) serial port at the specified address. Only 1002 supported option is baud rate. If baud rate is not 1003 specified, the serial port must already be setup and 1004 configured. 1005 1006 uart[8250],io,<addr>[,options] 1007 uart[8250],mmio,<addr>[,options] 1008 uart[8250],mmio32,<addr>[,options] 1009 uart[8250],mmio32be,<addr>[,options] 1010 uart[8250],0x<addr>[,options] 1011 Start an early, polled-mode console on the 8250/16550 1012 UART at the specified I/O port or MMIO address. 1013 MMIO inter-register address stride is either 8-bit 1014 (mmio) or 32-bit (mmio32 or mmio32be). 1015 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed 1016 to be equivalent to 'mmio'. 'options' are specified 1017 in the same format described for "console=ttyS<n>"; if 1018 unspecified, the h/w is not initialized. 1019 1020 pl011,<addr> 1021 pl011,mmio32,<addr> 1022 Start an early, polled-mode console on a pl011 serial 1023 port at the specified address. The pl011 serial port 1024 must already be setup and configured. Options are not 1025 yet supported. If 'mmio32' is specified, then only 1026 the driver will use only 32-bit accessors to read/write 1027 the device registers. 1028 1029 meson,<addr> 1030 Start an early, polled-mode console on a meson serial 1031 port at the specified address. The serial port must 1032 already be setup and configured. Options are not yet 1033 supported. 1034 1035 msm_serial,<addr> 1036 Start an early, polled-mode console on an msm serial 1037 port at the specified address. The serial port 1038 must already be setup and configured. Options are not 1039 yet supported. 1040 1041 msm_serial_dm,<addr> 1042 Start an early, polled-mode console on an msm serial 1043 dm port at the specified address. The serial port 1044 must already be setup and configured. Options are not 1045 yet supported. 1046 1047 owl,<addr> 1048 Start an early, polled-mode console on a serial port 1049 of an Actions Semi SoC, such as S500 or S900, at the 1050 specified address. The serial port must already be 1051 setup and configured. Options are not yet supported. 1052 1053 rda,<addr> 1054 Start an early, polled-mode console on a serial port 1055 of an RDA Micro SoC, such as RDA8810PL, at the 1056 specified address. The serial port must already be 1057 setup and configured. Options are not yet supported. 1058 1059 sbi 1060 Use RISC-V SBI (Supervisor Binary Interface) for early 1061 console. 1062 1063 smh Use ARM semihosting calls for early console. 1064 1065 s3c2410,<addr> 1066 s3c2412,<addr> 1067 s3c2440,<addr> 1068 s3c6400,<addr> 1069 s5pv210,<addr> 1070 exynos4210,<addr> 1071 Use early console provided by serial driver available 1072 on Samsung SoCs, requires selecting proper type and 1073 a correct base address of the selected UART port. The 1074 serial port must already be setup and configured. 1075 Options are not yet supported. 1076 1077 lantiq,<addr> 1078 Start an early, polled-mode console on a lantiq serial 1079 (lqasc) port at the specified address. The serial port 1080 must already be setup and configured. Options are not 1081 yet supported. 1082 1083 lpuart,<addr> 1084 lpuart32,<addr> 1085 Use early console provided by Freescale LP UART driver 1086 found on Freescale Vybrid and QorIQ LS1021A processors. 1087 A valid base address must be provided, and the serial 1088 port must already be setup and configured. 1089 1090 ar3700_uart,<addr> 1091 Start an early, polled-mode console on the 1092 Armada 3700 serial port at the specified 1093 address. The serial port must already be setup 1094 and configured. Options are not yet supported. 1095 1096 qcom_geni,<addr> 1097 Start an early, polled-mode console on a Qualcomm 1098 Generic Interface (GENI) based serial port at the 1099 specified address. The serial port must already be 1100 setup and configured. Options are not yet supported. 1101 1102 efifb,[options] 1103 Start an early, unaccelerated console on the EFI 1104 memory mapped framebuffer (if available). On cache 1105 coherent non-x86 systems that use system memory for 1106 the framebuffer, pass the 'ram' option so that it is 1107 mapped with the correct attributes. 1108 1109 linflex,<addr> 1110 Use early console provided by Freescale LinFlex UART 1111 serial driver for NXP S32V234 SoCs. A valid base 1112 address must be provided, and the serial port must 1113 already be setup and configured. 1114 1115 earlyprintk= [X86,SH,ARM,M68k,S390] 1116 earlyprintk=vga 1117 earlyprintk=sclp 1118 earlyprintk=xen 1119 earlyprintk=serial[,ttySn[,baudrate]] 1120 earlyprintk=serial[,0x...[,baudrate]] 1121 earlyprintk=ttySn[,baudrate] 1122 earlyprintk=dbgp[debugController#] 1123 earlyprintk=pciserial[,force],bus:device.function[,baudrate] 1124 earlyprintk=xdbc[xhciController#] 1125 1126 earlyprintk is useful when the kernel crashes before 1127 the normal console is initialized. It is not enabled by 1128 default because it has some cosmetic problems. 1129 1130 Append ",keep" to not disable it when the real console 1131 takes over. 1132 1133 Only one of vga, efi, serial, or usb debug port can 1134 be used at a time. 1135 1136 Currently only ttyS0 and ttyS1 may be specified by 1137 name. Other I/O ports may be explicitly specified 1138 on some architectures (x86 and arm at least) by 1139 replacing ttySn with an I/O port address, like this: 1140 earlyprintk=serial,0x1008,115200 1141 You can find the port for a given device in 1142 /proc/tty/driver/serial: 1143 2: uart:ST16650V2 port:00001008 irq:18 ... 1144 1145 Interaction with the standard serial driver is not 1146 very good. 1147 1148 The VGA and EFI output is eventually overwritten by 1149 the real console. 1150 1151 The xen output can only be used by Xen PV guests. 1152 1153 The sclp output can only be used on s390. 1154 1155 The optional "force" to "pciserial" enables use of a 1156 PCI device even when its classcode is not of the 1157 UART class. 1158 1159 edac_report= [HW,EDAC] Control how to report EDAC event 1160 Format: {"on" | "off" | "force"} 1161 on: enable EDAC to report H/W event. May be overridden 1162 by other higher priority error reporting module. 1163 off: disable H/W event reporting through EDAC. 1164 force: enforce the use of EDAC to report H/W event. 1165 default: on. 1166 1167 ekgdboc= [X86,KGDB] Allow early kernel console debugging 1168 ekgdboc=kbd 1169 1170 This is designed to be used in conjunction with 1171 the boot argument: earlyprintk=vga 1172 1173 edd= [EDD] 1174 Format: {"off" | "on" | "skip[mbr]"} 1175 1176 efi= [EFI] 1177 Format: { "old_map", "nochunk", "noruntime", "debug" } 1178 old_map [X86-64]: switch to the old ioremap-based EFI 1179 runtime services mapping. 32-bit still uses this one by 1180 default. 1181 nochunk: disable reading files in "chunks" in the EFI 1182 boot stub, as chunking can cause problems with some 1183 firmware implementations. 1184 noruntime : disable EFI runtime services support 1185 debug: enable misc debug output 1186 1187 efi_no_storage_paranoia [EFI; X86] 1188 Using this parameter you can use more than 50% of 1189 your efi variable storage. Use this parameter only if 1190 you are really sure that your UEFI does sane gc and 1191 fulfills the spec otherwise your board may brick. 1192 1193 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86] 1194 Add arbitrary attribute to specific memory range by 1195 updating original EFI memory map. 1196 Region of memory which aa attribute is added to is 1197 from ss to ss+nn. 1198 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000 1199 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000) 1200 attribute is added to range 0x100000000-0x180000000 and 1201 0x10a0000000-0x1120000000. 1202 1203 Using this parameter you can do debugging of EFI memmap 1204 related feature. For example, you can do debugging of 1205 Address Range Mirroring feature even if your box 1206 doesn't support it. 1207 1208 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT 1209 that is to be dynamically loaded by Linux. If there are 1210 multiple variables with the same name but with different 1211 vendor GUIDs, all of them will be loaded. See 1212 Documentation/admin-guide/acpi/ssdt-overlays.rst for details. 1213 1214 1215 eisa_irq_edge= [PARISC,HW] 1216 See header of drivers/parisc/eisa.c. 1217 1218 elanfreq= [X86-32] 1219 See comment before function elanfreq_setup() in 1220 arch/x86/kernel/cpu/cpufreq/elanfreq.c. 1221 1222 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390] 1223 Specifies physical address of start of kernel core 1224 image elf header and optionally the size. Generally 1225 kexec loader will pass this option to capture kernel. 1226 See Documentation/admin-guide/kdump/kdump.rst for details. 1227 1228 enable_mtrr_cleanup [X86] 1229 The kernel tries to adjust MTRR layout from continuous 1230 to discrete, to make X server driver able to add WB 1231 entry later. This parameter enables that. 1232 1233 enable_timer_pin_1 [X86] 1234 Enable PIN 1 of APIC timer 1235 Can be useful to work around chipset bugs 1236 (in particular on some ATI chipsets). 1237 The kernel tries to set a reasonable default. 1238 1239 enforcing [SELINUX] Set initial enforcing status. 1240 Format: {"0" | "1"} 1241 See security/selinux/Kconfig help text. 1242 0 -- permissive (log only, no denials). 1243 1 -- enforcing (deny and log). 1244 Default value is 0. 1245 Value can be changed at runtime via /selinux/enforce. 1246 1247 erst_disable [ACPI] 1248 Disable Error Record Serialization Table (ERST) 1249 support. 1250 1251 ether= [HW,NET] Ethernet cards parameters 1252 This option is obsoleted by the "netdev=" option, which 1253 has equivalent usage. See its documentation for details. 1254 1255 evm= [EVM] 1256 Format: { "fix" } 1257 Permit 'security.evm' to be updated regardless of 1258 current integrity status. 1259 1260 failslab= 1261 fail_page_alloc= 1262 fail_make_request=[KNL] 1263 General fault injection mechanism. 1264 Format: <interval>,<probability>,<space>,<times> 1265 See also Documentation/fault-injection/. 1266 1267 floppy= [HW] 1268 See Documentation/admin-guide/blockdev/floppy.rst. 1269 1270 force_pal_cache_flush 1271 [IA-64] Avoid check_sal_cache_flush which may hang on 1272 buggy SAL_CACHE_FLUSH implementations. Using this 1273 parameter will force ia64_sal_cache_flush to call 1274 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH. 1275 1276 forcepae [X86-32] 1277 Forcefully enable Physical Address Extension (PAE). 1278 Many Pentium M systems disable PAE but may have a 1279 functionally usable PAE implementation. 1280 Warning: use of this parameter will taint the kernel 1281 and may cause unknown problems. 1282 1283 ftrace=[tracer] 1284 [FTRACE] will set and start the specified tracer 1285 as early as possible in order to facilitate early 1286 boot debugging. 1287 1288 ftrace_dump_on_oops[=orig_cpu] 1289 [FTRACE] will dump the trace buffers on oops. 1290 If no parameter is passed, ftrace will dump 1291 buffers of all CPUs, but if you pass orig_cpu, it will 1292 dump only the buffer of the CPU that triggered the 1293 oops. 1294 1295 ftrace_filter=[function-list] 1296 [FTRACE] Limit the functions traced by the function 1297 tracer at boot up. function-list is a comma separated 1298 list of functions. This list can be changed at run 1299 time by the set_ftrace_filter file in the debugfs 1300 tracing directory. 1301 1302 ftrace_notrace=[function-list] 1303 [FTRACE] Do not trace the functions specified in 1304 function-list. This list can be changed at run time 1305 by the set_ftrace_notrace file in the debugfs 1306 tracing directory. 1307 1308 ftrace_graph_filter=[function-list] 1309 [FTRACE] Limit the top level callers functions traced 1310 by the function graph tracer at boot up. 1311 function-list is a comma separated list of functions 1312 that can be changed at run time by the 1313 set_graph_function file in the debugfs tracing directory. 1314 1315 ftrace_graph_notrace=[function-list] 1316 [FTRACE] Do not trace from the functions specified in 1317 function-list. This list is a comma separated list of 1318 functions that can be changed at run time by the 1319 set_graph_notrace file in the debugfs tracing directory. 1320 1321 ftrace_graph_max_depth=<uint> 1322 [FTRACE] Used with the function graph tracer. This is 1323 the max depth it will trace into a function. This value 1324 can be changed at run time by the max_graph_depth file 1325 in the tracefs tracing directory. default: 0 (no limit) 1326 1327 gamecon.map[2|3]= 1328 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 1329 support via parallel port (up to 5 devices per port) 1330 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 1331 See also Documentation/input/devices/joystick-parport.rst 1332 1333 gamma= [HW,DRM] 1334 1335 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART 1336 Format: off | on 1337 default: on 1338 1339 gather_data_sampling= 1340 [X86,INTEL] Control the Gather Data Sampling (GDS) 1341 mitigation. 1342 1343 Gather Data Sampling is a hardware vulnerability which 1344 allows unprivileged speculative access to data which was 1345 previously stored in vector registers. 1346 1347 This issue is mitigated by default in updated microcode. 1348 The mitigation may have a performance impact but can be 1349 disabled. On systems without the microcode mitigation 1350 disabling AVX serves as a mitigation. 1351 1352 force: Disable AVX to mitigate systems without 1353 microcode mitigation. No effect if the microcode 1354 mitigation is present. Known to cause crashes in 1355 userspace with buggy AVX enumeration. 1356 1357 off: Disable GDS mitigation. 1358 1359 gcov_persist= [GCOV] When non-zero (default), profiling data for 1360 kernel modules is saved and remains accessible via 1361 debugfs, even when the module is unloaded/reloaded. 1362 When zero, profiling data is discarded and associated 1363 debugfs files are removed at module unload time. 1364 1365 goldfish [X86] Enable the goldfish android emulator platform. 1366 Don't use this when you are not running on the 1367 android emulator 1368 1369 gpt [EFI] Forces disk with valid GPT signature but 1370 invalid Protective MBR to be treated as GPT. If the 1371 primary GPT is corrupted, it enables the backup/alternate 1372 GPT to be used instead. 1373 1374 grcan.enable0= [HW] Configuration of physical interface 0. Determines 1375 the "Enable 0" bit of the configuration register. 1376 Format: 0 | 1 1377 Default: 0 1378 grcan.enable1= [HW] Configuration of physical interface 1. Determines 1379 the "Enable 0" bit of the configuration register. 1380 Format: 0 | 1 1381 Default: 0 1382 grcan.select= [HW] Select which physical interface to use. 1383 Format: 0 | 1 1384 Default: 0 1385 grcan.txsize= [HW] Sets the size of the tx buffer. 1386 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. 1387 Default: 1024 1388 grcan.rxsize= [HW] Sets the size of the rx buffer. 1389 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. 1390 Default: 1024 1391 1392 gpio-mockup.gpio_mockup_ranges 1393 [HW] Sets the ranges of gpiochip of for this device. 1394 Format: <start1>,<end1>,<start2>,<end2>... 1395 1396 hardlockup_all_cpu_backtrace= 1397 [KNL] Should the hard-lockup detector generate 1398 backtraces on all cpus. 1399 Format: <integer> 1400 1401 hashdist= [KNL,NUMA] Large hashes allocated during boot 1402 are distributed across NUMA nodes. Defaults on 1403 for 64-bit NUMA, off otherwise. 1404 Format: 0 | 1 (for off | on) 1405 1406 hcl= [IA-64] SGI's Hardware Graph compatibility layer 1407 1408 hd= [EIDE] (E)IDE hard drive subsystem geometry 1409 Format: <cyl>,<head>,<sect> 1410 1411 hest_disable [ACPI] 1412 Disable Hardware Error Source Table (HEST) support; 1413 corresponding firmware-first mode error processing 1414 logic will be disabled. 1415 1416 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact 1417 size of <nn>. This works even on boxes that have no 1418 highmem otherwise. This also works to reduce highmem 1419 size on bigger boxes. 1420 1421 highres= [KNL] Enable/disable high resolution timer mode. 1422 Valid parameters: "on", "off" 1423 Default: "on" 1424 1425 hlt [BUGS=ARM,SH] 1426 1427 hpet= [X86-32,HPET] option to control HPET usage 1428 Format: { enable (default) | disable | force | 1429 verbose } 1430 disable: disable HPET and use PIT instead 1431 force: allow force enabled of undocumented chips (ICH4, 1432 VIA, nVidia) 1433 verbose: show contents of HPET registers during setup 1434 1435 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET 1436 registers. Default set by CONFIG_HPET_MMAP_DEFAULT. 1437 1438 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot. 1439 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages. 1440 On x86-64 and powerpc, this option can be specified 1441 multiple times interleaved with hugepages= to reserve 1442 huge pages of different sizes. Valid pages sizes on 1443 x86-64 are 2M (when the CPU supports "pse") and 1G 1444 (when the CPU supports the "pdpe1gb" cpuinfo flag). 1445 1446 hung_task_panic= 1447 [KNL] Should the hung task detector generate panics. 1448 Format: <integer> 1449 1450 A nonzero value instructs the kernel to panic when a 1451 hung task is detected. The default value is controlled 1452 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time 1453 option. The value selected by this boot parameter can 1454 be changed later by the kernel.hung_task_panic sysctl. 1455 1456 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 1457 terminal devices. Valid values: 0..8 1458 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 1459 If specified, z/VM IUCV HVC accepts connections 1460 from listed z/VM user IDs only. 1461 1462 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations 1463 which allow the hypervisor to 'idle' the 1464 guest on lock contention. 1465 1466 keep_bootcon [KNL] 1467 Do not unregister boot console at start. This is only 1468 useful for debugging when something happens in the window 1469 between unregistering the boot console and initializing 1470 the real console. 1471 1472 i2c_bus= [HW] Override the default board specific I2C bus speed 1473 or register an additional I2C bus that is not 1474 registered from board initialization code. 1475 Format: 1476 <bus_id>,<clkrate> 1477 1478 i8042.debug [HW] Toggle i8042 debug mode 1479 i8042.unmask_kbd_data 1480 [HW] Enable printing of interrupt data from the KBD port 1481 (disabled by default, and as a pre-condition 1482 requires that i8042.debug=1 be enabled) 1483 i8042.direct [HW] Put keyboard port into non-translated mode 1484 i8042.dumbkbd [HW] Pretend that controller can only read data from 1485 keyboard and cannot control its state 1486 (Don't attempt to blink the leds) 1487 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 1488 i8042.nokbd [HW] Don't check/create keyboard port 1489 i8042.noloop [HW] Disable the AUX Loopback command while probing 1490 for the AUX port 1491 i8042.nomux [HW] Don't check presence of an active multiplexing 1492 controller 1493 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 1494 controllers 1495 i8042.notimeout [HW] Ignore timeout condition signalled by controller 1496 i8042.reset [HW] Reset the controller during init, cleanup and 1497 suspend-to-ram transitions, only during s2r 1498 transitions, or never reset 1499 Format: { 1 | Y | y | 0 | N | n } 1500 1, Y, y: always reset controller 1501 0, N, n: don't ever reset controller 1502 Default: only on s2r transitions on x86; most other 1503 architectures force reset to be always executed 1504 i8042.unlock [HW] Unlock (ignore) the keylock 1505 i8042.kbdreset [HW] Reset device connected to KBD port 1506 i8042.probe_defer 1507 [HW] Allow deferred probing upon i8042 probe errors 1508 1509 i810= [HW,DRM] 1510 1511 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data 1512 indicates that the driver is running on unsupported 1513 hardware. 1514 i8k.force [HW] Activate i8k driver even if SMM BIOS signature 1515 does not match list of supported models. 1516 i8k.power_status 1517 [HW] Report power status in /proc/i8k 1518 (disabled by default) 1519 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN 1520 capability is set. 1521 1522 i915.invert_brightness= 1523 [DRM] Invert the sense of the variable that is used to 1524 set the brightness of the panel backlight. Normally a 1525 brightness value of 0 indicates backlight switched off, 1526 and the maximum of the brightness value sets the backlight 1527 to maximum brightness. If this parameter is set to 0 1528 (default) and the machine requires it, or this parameter 1529 is set to 1, a brightness value of 0 sets the backlight 1530 to maximum brightness, and the maximum of the brightness 1531 value switches the backlight off. 1532 -1 -- never invert brightness 1533 0 -- machine default 1534 1 -- force brightness inversion 1535 1536 icn= [HW,ISDN] 1537 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]] 1538 1539 ide-core.nodma= [HW] (E)IDE subsystem 1540 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc 1541 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr 1542 .cdrom .chs .ignore_cable are additional options 1543 See Documentation/ide/ide.rst. 1544 1545 ide-generic.probe-mask= [HW] (E)IDE subsystem 1546 Format: <int> 1547 Probe mask for legacy ISA IDE ports. Depending on 1548 platform up to 6 ports are supported, enabled by 1549 setting corresponding bits in the mask to 1. The 1550 default value is 0x0, which has a special meaning. 1551 On systems that have PCI, it triggers scanning the 1552 PCI bus for the first and the second port, which 1553 are then probed. On systems without PCI the value 1554 of 0x0 enables probing the two first ports as if it 1555 was 0x3. 1556 1557 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem 1558 Claim all unknown PCI IDE storage controllers. 1559 1560 idle= [X86] 1561 Format: idle=poll, idle=halt, idle=nomwait 1562 Poll forces a polling idle loop that can slightly 1563 improve the performance of waking up a idle CPU, but 1564 will use a lot of power and make the system run hot. 1565 Not recommended. 1566 idle=halt: Halt is forced to be used for CPU idle. 1567 In such case C2/C3 won't be used again. 1568 idle=nomwait: Disable mwait for CPU C-states 1569 1570 ieee754= [MIPS] Select IEEE Std 754 conformance mode 1571 Format: { strict | legacy | 2008 | relaxed } 1572 Default: strict 1573 1574 Choose which programs will be accepted for execution 1575 based on the IEEE 754 NaN encoding(s) supported by 1576 the FPU and the NaN encoding requested with the value 1577 of an ELF file header flag individually set by each 1578 binary. Hardware implementations are permitted to 1579 support either or both of the legacy and the 2008 NaN 1580 encoding mode. 1581 1582 Available settings are as follows: 1583 strict accept binaries that request a NaN encoding 1584 supported by the FPU 1585 legacy only accept legacy-NaN binaries, if supported 1586 by the FPU 1587 2008 only accept 2008-NaN binaries, if supported 1588 by the FPU 1589 relaxed accept any binaries regardless of whether 1590 supported by the FPU 1591 1592 The FPU emulator is always able to support both NaN 1593 encodings, so if no FPU hardware is present or it has 1594 been disabled with 'nofpu', then the settings of 1595 'legacy' and '2008' strap the emulator accordingly, 1596 'relaxed' straps the emulator for both legacy-NaN and 1597 2008-NaN, whereas 'strict' enables legacy-NaN only on 1598 legacy processors and both NaN encodings on MIPS32 or 1599 MIPS64 CPUs. 1600 1601 The setting for ABS.fmt/NEG.fmt instruction execution 1602 mode generally follows that for the NaN encoding, 1603 except where unsupported by hardware. 1604 1605 ignore_loglevel [KNL] 1606 Ignore loglevel setting - this will print /all/ 1607 kernel messages to the console. Useful for debugging. 1608 We also add it as printk module parameter, so users 1609 could change it dynamically, usually by 1610 /sys/module/printk/parameters/ignore_loglevel. 1611 1612 ignore_rlimit_data 1613 Ignore RLIMIT_DATA setting for data mappings, 1614 print warning at first misuse. Can be changed via 1615 /sys/module/kernel/parameters/ignore_rlimit_data. 1616 1617 ihash_entries= [KNL] 1618 Set number of hash buckets for inode cache. 1619 1620 ima_appraise= [IMA] appraise integrity measurements 1621 Format: { "off" | "enforce" | "fix" | "log" } 1622 default: "enforce" 1623 1624 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead. 1625 The builtin appraise policy appraises all files 1626 owned by uid=0. 1627 1628 ima_canonical_fmt [IMA] 1629 Use the canonical format for the binary runtime 1630 measurements, instead of host native format. 1631 1632 ima_hash= [IMA] 1633 Format: { md5 | sha1 | rmd160 | sha256 | sha384 1634 | sha512 | ... } 1635 default: "sha1" 1636 1637 The list of supported hash algorithms is defined 1638 in crypto/hash_info.h. 1639 1640 ima_policy= [IMA] 1641 The builtin policies to load during IMA setup. 1642 Format: "tcb | appraise_tcb | secure_boot | 1643 fail_securely" 1644 1645 The "tcb" policy measures all programs exec'd, files 1646 mmap'd for exec, and all files opened with the read 1647 mode bit set by either the effective uid (euid=0) or 1648 uid=0. 1649 1650 The "appraise_tcb" policy appraises the integrity of 1651 all files owned by root. 1652 1653 The "secure_boot" policy appraises the integrity 1654 of files (eg. kexec kernel image, kernel modules, 1655 firmware, policy, etc) based on file signatures. 1656 1657 The "fail_securely" policy forces file signature 1658 verification failure also on privileged mounted 1659 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE 1660 flag. 1661 1662 ima_tcb [IMA] Deprecated. Use ima_policy= instead. 1663 Load a policy which meets the needs of the Trusted 1664 Computing Base. This means IMA will measure all 1665 programs exec'd, files mmap'd for exec, and all files 1666 opened for read by uid=0. 1667 1668 ima_template= [IMA] 1669 Select one of defined IMA measurements template formats. 1670 Formats: { "ima" | "ima-ng" | "ima-sig" } 1671 Default: "ima-ng" 1672 1673 ima_template_fmt= 1674 [IMA] Define a custom template format. 1675 Format: { "field1|...|fieldN" } 1676 1677 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage 1678 Format: <min_file_size> 1679 Set the minimal file size for using asynchronous hash. 1680 If left unspecified, ahash usage is disabled. 1681 1682 ahash performance varies for different data sizes on 1683 different crypto accelerators. This option can be used 1684 to achieve the best performance for a particular HW. 1685 1686 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size 1687 Format: <bufsize> 1688 Set hashing buffer size. Default: 4k. 1689 1690 ahash performance varies for different chunk sizes on 1691 different crypto accelerators. This option can be used 1692 to achieve best performance for particular HW. 1693 1694 init= [KNL] 1695 Format: <full_path> 1696 Run specified binary instead of /sbin/init as init 1697 process. 1698 1699 initcall_debug [KNL] Trace initcalls as they are executed. Useful 1700 for working out where the kernel is dying during 1701 startup. 1702 1703 initcall_blacklist= [KNL] Do not execute a comma-separated list of 1704 initcall functions. Useful for debugging built-in 1705 modules and initcalls. 1706 1707 initrd= [BOOT] Specify the location of the initial ramdisk 1708 1709 init_on_alloc= [MM] Fill newly allocated pages and heap objects with 1710 zeroes. 1711 Format: 0 | 1 1712 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON. 1713 1714 init_on_free= [MM] Fill freed pages and heap objects with zeroes. 1715 Format: 0 | 1 1716 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON. 1717 1718 init_pkru= [x86] Specify the default memory protection keys rights 1719 register contents for all processes. 0x55555554 by 1720 default (disallow access to all but pkey 0). Can 1721 override in debugfs after boot. 1722 1723 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 1724 Format: <irq> 1725 1726 int_pln_enable [x86] Enable power limit notification interrupt 1727 1728 integrity_audit=[IMA] 1729 Format: { "0" | "1" } 1730 0 -- basic integrity auditing messages. (Default) 1731 1 -- additional integrity auditing messages. 1732 1733 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 1734 on 1735 Enable intel iommu driver. 1736 off 1737 Disable intel iommu driver. 1738 igfx_off [Default Off] 1739 By default, gfx is mapped as normal device. If a gfx 1740 device has a dedicated DMAR unit, the DMAR unit is 1741 bypassed by not enabling DMAR with this option. In 1742 this case, gfx device will use physical address for 1743 DMA. 1744 forcedac [x86_64] 1745 With this option iommu will not optimize to look 1746 for io virtual address below 32-bit forcing dual 1747 address cycle on pci bus for cards supporting greater 1748 than 32-bit addressing. The default is to look 1749 for translation below 32-bit and if not available 1750 then look in the higher range. 1751 strict [Default Off] 1752 With this option on every unmap_single operation will 1753 result in a hardware IOTLB flush operation as opposed 1754 to batching them for performance. 1755 sp_off [Default Off] 1756 By default, super page will be supported if Intel IOMMU 1757 has the capability. With this option, super page will 1758 not be supported. 1759 sm_on [Default Off] 1760 By default, scalable mode will be disabled even if the 1761 hardware advertises that it has support for the scalable 1762 mode translation. With this option set, scalable mode 1763 will be used on hardware which claims to support it. 1764 tboot_noforce [Default Off] 1765 Do not force the Intel IOMMU enabled under tboot. 1766 By default, tboot will force Intel IOMMU on, which 1767 could harm performance of some high-throughput 1768 devices like 40GBit network cards, even if identity 1769 mapping is enabled. 1770 Note that using this option lowers the security 1771 provided by tboot because it makes the system 1772 vulnerable to DMA attacks. 1773 nobounce [Default off] 1774 Disable bounce buffer for unstrusted devices such as 1775 the Thunderbolt devices. This will treat the untrusted 1776 devices as the trusted ones, hence might expose security 1777 risks of DMA attacks. 1778 1779 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 1780 0 disables intel_idle and fall back on acpi_idle. 1781 1 to 9 specify maximum depth of C-state. 1782 1783 intel_pstate= [X86] 1784 disable 1785 Do not enable intel_pstate as the default 1786 scaling driver for the supported processors 1787 passive 1788 Use intel_pstate as a scaling driver, but configure it 1789 to work with generic cpufreq governors (instead of 1790 enabling its internal governor). This mode cannot be 1791 used along with the hardware-managed P-states (HWP) 1792 feature. 1793 force 1794 Enable intel_pstate on systems that prohibit it by default 1795 in favor of acpi-cpufreq. Forcing the intel_pstate driver 1796 instead of acpi-cpufreq may disable platform features, such 1797 as thermal controls and power capping, that rely on ACPI 1798 P-States information being indicated to OSPM and therefore 1799 should be used with caution. This option does not work with 1800 processors that aren't supported by the intel_pstate driver 1801 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 1802 no_hwp 1803 Do not enable hardware P state control (HWP) 1804 if available. 1805 hwp_only 1806 Only load intel_pstate on systems which support 1807 hardware P state control (HWP) if available. 1808 support_acpi_ppc 1809 Enforce ACPI _PPC performance limits. If the Fixed ACPI 1810 Description Table, specifies preferred power management 1811 profile as "Enterprise Server" or "Performance Server", 1812 then this feature is turned on by default. 1813 per_cpu_perf_limits 1814 Allow per-logical-CPU P-State performance control limits using 1815 cpufreq sysfs interface 1816 1817 intremap= [X86-64, Intel-IOMMU] 1818 on enable Interrupt Remapping (default) 1819 off disable Interrupt Remapping 1820 nosid disable Source ID checking 1821 no_x2apic_optout 1822 BIOS x2APIC opt-out request will be ignored 1823 nopost disable Interrupt Posting 1824 1825 iomem= Disable strict checking of access to MMIO memory 1826 strict regions from userspace. 1827 relaxed 1828 1829 iommu= [x86] 1830 off 1831 force 1832 noforce 1833 biomerge 1834 panic 1835 nopanic 1836 merge 1837 nomerge 1838 soft 1839 pt [x86] 1840 nopt [x86] 1841 nobypass [PPC/POWERNV] 1842 Disable IOMMU bypass, using IOMMU for PCI devices. 1843 1844 iommu.strict= [ARM64] Configure TLB invalidation behaviour 1845 Format: { "0" | "1" } 1846 0 - Lazy mode. 1847 Request that DMA unmap operations use deferred 1848 invalidation of hardware TLBs, for increased 1849 throughput at the cost of reduced device isolation. 1850 Will fall back to strict mode if not supported by 1851 the relevant IOMMU driver. 1852 1 - Strict mode (default). 1853 DMA unmap operations invalidate IOMMU hardware TLBs 1854 synchronously. 1855 1856 iommu.passthrough= 1857 [ARM64, X86] Configure DMA to bypass the IOMMU by default. 1858 Format: { "0" | "1" } 1859 0 - Use IOMMU translation for DMA. 1860 1 - Bypass the IOMMU for DMA. 1861 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH. 1862 1863 io7= [HW] IO7 for Marvel based alpha systems 1864 See comment before marvel_specify_io7 in 1865 arch/alpha/kernel/core_marvel.c. 1866 1867 io_delay= [X86] I/O delay method 1868 0x80 1869 Standard port 0x80 based delay 1870 0xed 1871 Alternate port 0xed based delay (needed on some systems) 1872 udelay 1873 Simple two microseconds delay 1874 none 1875 No delay 1876 1877 ip= [IP_PNP] 1878 See Documentation/filesystems/nfs/nfsroot.txt. 1879 1880 ipcmni_extend [KNL] Extend the maximum number of unique System V 1881 IPC identifiers from 32,768 to 16,777,216. 1882 1883 irqaffinity= [SMP] Set the default irq affinity mask 1884 The argument is a cpu list, as described above. 1885 1886 irqchip.gicv2_force_probe= 1887 [ARM, ARM64] 1888 Format: <bool> 1889 Force the kernel to look for the second 4kB page 1890 of a GICv2 controller even if the memory range 1891 exposed by the device tree is too small. 1892 1893 irqchip.gicv3_nolpi= 1894 [ARM, ARM64] 1895 Force the kernel to ignore the availability of 1896 LPIs (and by consequence ITSs). Intended for system 1897 that use the kernel as a bootloader, and thus want 1898 to let secondary kernels in charge of setting up 1899 LPIs. 1900 1901 irqchip.gicv3_pseudo_nmi= [ARM64] 1902 Enables support for pseudo-NMIs in the kernel. This 1903 requires the kernel to be built with 1904 CONFIG_ARM64_PSEUDO_NMI. 1905 1906 irqfixup [HW] 1907 When an interrupt is not handled search all handlers 1908 for it. Intended to get systems with badly broken 1909 firmware running. 1910 1911 irqpoll [HW] 1912 When an interrupt is not handled search all handlers 1913 for it. Also check all handlers each timer 1914 interrupt. Intended to get systems with badly broken 1915 firmware running. 1916 1917 isapnp= [ISAPNP] 1918 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 1919 1920 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance. 1921 [Deprecated - use cpusets instead] 1922 Format: [flag-list,]<cpu-list> 1923 1924 Specify one or more CPUs to isolate from disturbances 1925 specified in the flag list (default: domain): 1926 1927 nohz 1928 Disable the tick when a single task runs. 1929 1930 A residual 1Hz tick is offloaded to workqueues, which you 1931 need to affine to housekeeping through the global 1932 workqueue's affinity configured via the 1933 /sys/devices/virtual/workqueue/cpumask sysfs file, or 1934 by using the 'domain' flag described below. 1935 1936 NOTE: by default the global workqueue runs on all CPUs, 1937 so to protect individual CPUs the 'cpumask' file has to 1938 be configured manually after bootup. 1939 1940 domain 1941 Isolate from the general SMP balancing and scheduling 1942 algorithms. Note that performing domain isolation this way 1943 is irreversible: it's not possible to bring back a CPU to 1944 the domains once isolated through isolcpus. It's strongly 1945 advised to use cpusets instead to disable scheduler load 1946 balancing through the "cpuset.sched_load_balance" file. 1947 It offers a much more flexible interface where CPUs can 1948 move in and out of an isolated set anytime. 1949 1950 You can move a process onto or off an "isolated" CPU via 1951 the CPU affinity syscalls or cpuset. 1952 <cpu number> begins at 0 and the maximum value is 1953 "number of CPUs in system - 1". 1954 1955 The format of <cpu-list> is described above. 1956 1957 1958 1959 iucv= [HW,NET] 1960 1961 ivrs_ioapic [HW,X86_64] 1962 Provide an override to the IOAPIC-ID<->DEVICE-ID 1963 mapping provided in the IVRS ACPI table. 1964 By default, PCI segment is 0, and can be omitted. 1965 1966 For example, to map IOAPIC-ID decimal 10 to 1967 PCI segment 0x1 and PCI device 00:14.0, 1968 write the parameter as: 1969 ivrs_ioapic=10@0001:00:14.0 1970 1971 Deprecated formats: 1972 * To map IOAPIC-ID decimal 10 to PCI device 00:14.0 1973 write the parameter as: 1974 ivrs_ioapic[10]=00:14.0 1975 * To map IOAPIC-ID decimal 10 to PCI segment 0x1 and 1976 PCI device 00:14.0 write the parameter as: 1977 ivrs_ioapic[10]=0001:00:14.0 1978 1979 ivrs_hpet [HW,X86_64] 1980 Provide an override to the HPET-ID<->DEVICE-ID 1981 mapping provided in the IVRS ACPI table. 1982 By default, PCI segment is 0, and can be omitted. 1983 1984 For example, to map HPET-ID decimal 10 to 1985 PCI segment 0x1 and PCI device 00:14.0, 1986 write the parameter as: 1987 ivrs_hpet=10@0001:00:14.0 1988 1989 Deprecated formats: 1990 * To map HPET-ID decimal 0 to PCI device 00:14.0 1991 write the parameter as: 1992 ivrs_hpet[0]=00:14.0 1993 * To map HPET-ID decimal 10 to PCI segment 0x1 and 1994 PCI device 00:14.0 write the parameter as: 1995 ivrs_ioapic[10]=0001:00:14.0 1996 1997 ivrs_acpihid [HW,X86_64] 1998 Provide an override to the ACPI-HID:UID<->DEVICE-ID 1999 mapping provided in the IVRS ACPI table. 2000 By default, PCI segment is 0, and can be omitted. 2001 2002 For example, to map UART-HID:UID AMD0020:0 to 2003 PCI segment 0x1 and PCI device ID 00:14.5, 2004 write the parameter as: 2005 ivrs_acpihid=AMD0020:0@0001:00:14.5 2006 2007 Deprecated formats: 2008 * To map UART-HID:UID AMD0020:0 to PCI segment is 0, 2009 PCI device ID 00:14.5, write the parameter as: 2010 ivrs_acpihid[00:14.5]=AMD0020:0 2011 * To map UART-HID:UID AMD0020:0 to PCI segment 0x1 and 2012 PCI device ID 00:14.5, write the parameter as: 2013 ivrs_acpihid[0001:00:14.5]=AMD0020:0 2014 2015 js= [HW,JOY] Analog joystick 2016 See Documentation/input/joydev/joystick.rst. 2017 2018 nokaslr [KNL] 2019 When CONFIG_RANDOMIZE_BASE is set, this disables 2020 kernel and module base offset ASLR (Address Space 2021 Layout Randomization). 2022 2023 kasan_multi_shot 2024 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print 2025 report on every invalid memory access. Without this 2026 parameter KASAN will print report only for the first 2027 invalid access. 2028 2029 keepinitrd [HW,ARM] 2030 2031 kernelcore= [KNL,X86,IA-64,PPC] 2032 Format: nn[KMGTPE] | nn% | "mirror" 2033 This parameter specifies the amount of memory usable by 2034 the kernel for non-movable allocations. The requested 2035 amount is spread evenly throughout all nodes in the 2036 system as ZONE_NORMAL. The remaining memory is used for 2037 movable memory in its own zone, ZONE_MOVABLE. In the 2038 event, a node is too small to have both ZONE_NORMAL and 2039 ZONE_MOVABLE, kernelcore memory will take priority and 2040 other nodes will have a larger ZONE_MOVABLE. 2041 2042 ZONE_MOVABLE is used for the allocation of pages that 2043 may be reclaimed or moved by the page migration 2044 subsystem. Note that allocations like PTEs-from-HighMem 2045 still use the HighMem zone if it exists, and the Normal 2046 zone if it does not. 2047 2048 It is possible to specify the exact amount of memory in 2049 the form of "nn[KMGTPE]", a percentage of total system 2050 memory in the form of "nn%", or "mirror". If "mirror" 2051 option is specified, mirrored (reliable) memory is used 2052 for non-movable allocations and remaining memory is used 2053 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror" 2054 are exclusive, so you cannot specify multiple forms. 2055 2056 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port. 2057 Format: <Controller#>[,poll interval] 2058 The controller # is the number of the ehci usb debug 2059 port as it is probed via PCI. The poll interval is 2060 optional and is the number seconds in between 2061 each poll cycle to the debug port in case you need 2062 the functionality for interrupting the kernel with 2063 gdb or control-c on the dbgp connection. When 2064 not using this parameter you use sysrq-g to break into 2065 the kernel debugger. 2066 2067 kgdboc= [KGDB,HW] kgdb over consoles. 2068 Requires a tty driver that supports console polling, 2069 or a supported polling keyboard driver (non-usb). 2070 Serial only format: <serial_device>[,baud] 2071 keyboard only format: kbd 2072 keyboard and serial format: kbd,<serial_device>[,baud] 2073 Optional Kernel mode setting: 2074 kms, kbd format: kms,kbd 2075 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 2076 2077 kgdbwait [KGDB] Stop kernel execution and enter the 2078 kernel debugger at the earliest opportunity. 2079 2080 kmac= [MIPS] korina ethernet MAC address. 2081 Configure the RouterBoard 532 series on-chip 2082 Ethernet adapter MAC address. 2083 2084 kmemleak= [KNL] Boot-time kmemleak enable/disable 2085 Valid arguments: on, off 2086 Default: on 2087 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 2088 the default is off. 2089 2090 kprobe_event=[probe-list] 2091 [FTRACE] Add kprobe events and enable at boot time. 2092 The probe-list is a semicolon delimited list of probe 2093 definitions. Each definition is same as kprobe_events 2094 interface, but the parameters are comma delimited. 2095 For example, to add a kprobe event on vfs_read with 2096 arg1 and arg2, add to the command line; 2097 2098 kprobe_event=p,vfs_read,$arg1,$arg2 2099 2100 See also Documentation/trace/kprobetrace.rst "Kernel 2101 Boot Parameter" section. 2102 2103 kpti= [ARM64] Control page table isolation of user 2104 and kernel address spaces. 2105 Default: enabled on cores which need mitigation. 2106 0: force disabled 2107 1: force enabled 2108 2109 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 2110 Default is 0 (don't ignore, but inject #GP) 2111 2112 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface. 2113 Default is false (don't support). 2114 2115 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit 2116 KVM MMU at runtime. 2117 Default is 0 (off) 2118 2119 kvm.nx_huge_pages= 2120 [KVM] Controls the software workaround for the 2121 X86_BUG_ITLB_MULTIHIT bug. 2122 force : Always deploy workaround. 2123 off : Never deploy workaround. 2124 auto : Deploy workaround based on the presence of 2125 X86_BUG_ITLB_MULTIHIT. 2126 2127 Default is 'auto'. 2128 2129 If the software workaround is enabled for the host, 2130 guests do need not to enable it for nested guests. 2131 2132 kvm.nx_huge_pages_recovery_ratio= 2133 [KVM] Controls how many 4KiB pages are periodically zapped 2134 back to huge pages. 0 disables the recovery, otherwise if 2135 the value is N KVM will zap 1/Nth of the 4KiB pages every 2136 minute. The default is 60. 2137 2138 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM. 2139 Default is 1 (enabled) 2140 2141 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU) 2142 for all guests. 2143 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode. 2144 2145 kvm-arm.vgic_v3_group0_trap= 2146 [KVM,ARM] Trap guest accesses to GICv3 group-0 2147 system registers 2148 2149 kvm-arm.vgic_v3_group1_trap= 2150 [KVM,ARM] Trap guest accesses to GICv3 group-1 2151 system registers 2152 2153 kvm-arm.vgic_v3_common_trap= 2154 [KVM,ARM] Trap guest accesses to GICv3 common 2155 system registers 2156 2157 kvm-arm.vgic_v4_enable= 2158 [KVM,ARM] Allow use of GICv4 for direct injection of 2159 LPIs. 2160 2161 kvm-intel.ept= [KVM,Intel] Disable extended page tables 2162 (virtualized MMU) support on capable Intel chips. 2163 Default is 1 (enabled) 2164 2165 kvm-intel.emulate_invalid_guest_state= 2166 [KVM,Intel] Disable emulation of invalid guest state. 2167 Ignored if kvm-intel.enable_unrestricted_guest=1, as 2168 guest state is never invalid for unrestricted guests. 2169 This param doesn't apply to nested guests (L2), as KVM 2170 never emulates invalid L2 guest state. 2171 Default is 1 (enabled) 2172 2173 kvm-intel.flexpriority= 2174 [KVM,Intel] Disable FlexPriority feature (TPR shadow). 2175 Default is 1 (enabled) 2176 2177 kvm-intel.nested= 2178 [KVM,Intel] Enable VMX nesting (nVMX). 2179 Default is 0 (disabled) 2180 2181 kvm-intel.unrestricted_guest= 2182 [KVM,Intel] Disable unrestricted guest feature 2183 (virtualized real and unpaged mode) on capable 2184 Intel chips. Default is 1 (enabled) 2185 2186 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault 2187 CVE-2018-3620. 2188 2189 Valid arguments: never, cond, always 2190 2191 always: L1D cache flush on every VMENTER. 2192 cond: Flush L1D on VMENTER only when the code between 2193 VMEXIT and VMENTER can leak host memory. 2194 never: Disables the mitigation 2195 2196 Default is cond (do L1 cache flush in specific instances) 2197 2198 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification 2199 feature (tagged TLBs) on capable Intel chips. 2200 Default is 1 (enabled) 2201 2202 l1tf= [X86] Control mitigation of the L1TF vulnerability on 2203 affected CPUs 2204 2205 The kernel PTE inversion protection is unconditionally 2206 enabled and cannot be disabled. 2207 2208 full 2209 Provides all available mitigations for the 2210 L1TF vulnerability. Disables SMT and 2211 enables all mitigations in the 2212 hypervisors, i.e. unconditional L1D flush. 2213 2214 SMT control and L1D flush control via the 2215 sysfs interface is still possible after 2216 boot. Hypervisors will issue a warning 2217 when the first VM is started in a 2218 potentially insecure configuration, 2219 i.e. SMT enabled or L1D flush disabled. 2220 2221 full,force 2222 Same as 'full', but disables SMT and L1D 2223 flush runtime control. Implies the 2224 'nosmt=force' command line option. 2225 (i.e. sysfs control of SMT is disabled.) 2226 2227 flush 2228 Leaves SMT enabled and enables the default 2229 hypervisor mitigation, i.e. conditional 2230 L1D flush. 2231 2232 SMT control and L1D flush control via the 2233 sysfs interface is still possible after 2234 boot. Hypervisors will issue a warning 2235 when the first VM is started in a 2236 potentially insecure configuration, 2237 i.e. SMT enabled or L1D flush disabled. 2238 2239 flush,nosmt 2240 2241 Disables SMT and enables the default 2242 hypervisor mitigation. 2243 2244 SMT control and L1D flush control via the 2245 sysfs interface is still possible after 2246 boot. Hypervisors will issue a warning 2247 when the first VM is started in a 2248 potentially insecure configuration, 2249 i.e. SMT enabled or L1D flush disabled. 2250 2251 flush,nowarn 2252 Same as 'flush', but hypervisors will not 2253 warn when a VM is started in a potentially 2254 insecure configuration. 2255 2256 off 2257 Disables hypervisor mitigations and doesn't 2258 emit any warnings. 2259 It also drops the swap size and available 2260 RAM limit restriction on both hypervisor and 2261 bare metal. 2262 2263 Default is 'flush'. 2264 2265 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst 2266 2267 l2cr= [PPC] 2268 2269 l3cr= [PPC] 2270 2271 lapic [X86-32,APIC] Enable the local APIC even if BIOS 2272 disabled it. 2273 2274 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline 2275 value for LAPIC timer one-shot implementation. Default 2276 back to the programmable timer unit in the LAPIC. 2277 2278 lapic_timer_c2_ok [X86,APIC] trust the local apic timer 2279 in C2 power state. 2280 2281 libata.dma= [LIBATA] DMA control 2282 libata.dma=0 Disable all PATA and SATA DMA 2283 libata.dma=1 PATA and SATA Disk DMA only 2284 libata.dma=2 ATAPI (CDROM) DMA only 2285 libata.dma=4 Compact Flash DMA only 2286 Combinations also work, so libata.dma=3 enables DMA 2287 for disks and CDROMs, but not CFs. 2288 2289 libata.ignore_hpa= [LIBATA] Ignore HPA limit 2290 libata.ignore_hpa=0 keep BIOS limits (default) 2291 libata.ignore_hpa=1 ignore limits, using full disk 2292 2293 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 2294 when set. 2295 Format: <int> 2296 2297 libata.force= [LIBATA] Force configurations. The format is comma 2298 separated list of "[ID:]VAL" where ID is 2299 PORT[.DEVICE]. PORT and DEVICE are decimal numbers 2300 matching port, link or device. Basically, it matches 2301 the ATA ID string printed on console by libata. If 2302 the whole ID part is omitted, the last PORT and DEVICE 2303 values are used. If ID hasn't been specified yet, the 2304 configuration applies to all ports, links and devices. 2305 2306 If only DEVICE is omitted, the parameter applies to 2307 the port and all links and devices behind it. DEVICE 2308 number of 0 either selects the first device or the 2309 first fan-out link behind PMP device. It does not 2310 select the host link. DEVICE number of 15 selects the 2311 host link and device attached to it. 2312 2313 The VAL specifies the configuration to force. As long 2314 as there's no ambiguity shortcut notation is allowed. 2315 For example, both 1.5 and 1.5G would work for 1.5Gbps. 2316 The following configurations can be forced. 2317 2318 * Cable type: 40c, 80c, short40c, unk, ign or sata. 2319 Any ID with matching PORT is used. 2320 2321 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 2322 2323 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 2324 udma[/][16,25,33,44,66,100,133] notation is also 2325 allowed. 2326 2327 * [no]ncq: Turn on or off NCQ. 2328 2329 * [no]ncqtrim: Turn off queued DSM TRIM. 2330 2331 * nohrst, nosrst, norst: suppress hard, soft 2332 and both resets. 2333 2334 * rstonce: only attempt one reset during 2335 hot-unplug link recovery 2336 2337 * dump_id: dump IDENTIFY data. 2338 2339 * atapi_dmadir: Enable ATAPI DMADIR bridge support 2340 2341 * disable: Disable this device. 2342 2343 If there are multiple matching configurations changing 2344 the same attribute, the last one is used. 2345 2346 memblock=debug [KNL] Enable memblock debug messages. 2347 2348 load_ramdisk= [RAM] List of ramdisks to load from floppy 2349 See Documentation/admin-guide/blockdev/ramdisk.rst. 2350 2351 lockd.nlm_grace_period=P [NFS] Assign grace period. 2352 Format: <integer> 2353 2354 lockd.nlm_tcpport=N [NFS] Assign TCP port. 2355 Format: <integer> 2356 2357 lockd.nlm_timeout=T [NFS] Assign timeout value. 2358 Format: <integer> 2359 2360 lockd.nlm_udpport=M [NFS] Assign UDP port. 2361 Format: <integer> 2362 2363 lockdown= [SECURITY] 2364 { integrity | confidentiality } 2365 Enable the kernel lockdown feature. If set to 2366 integrity, kernel features that allow userland to 2367 modify the running kernel are disabled. If set to 2368 confidentiality, kernel features that allow userland 2369 to extract confidential information from the kernel 2370 are also disabled. 2371 2372 locktorture.nreaders_stress= [KNL] 2373 Set the number of locking read-acquisition kthreads. 2374 Defaults to being automatically set based on the 2375 number of online CPUs. 2376 2377 locktorture.nwriters_stress= [KNL] 2378 Set the number of locking write-acquisition kthreads. 2379 2380 locktorture.onoff_holdoff= [KNL] 2381 Set time (s) after boot for CPU-hotplug testing. 2382 2383 locktorture.onoff_interval= [KNL] 2384 Set time (s) between CPU-hotplug operations, or 2385 zero to disable CPU-hotplug testing. 2386 2387 locktorture.shuffle_interval= [KNL] 2388 Set task-shuffle interval (jiffies). Shuffling 2389 tasks allows some CPUs to go into dyntick-idle 2390 mode during the locktorture test. 2391 2392 locktorture.shutdown_secs= [KNL] 2393 Set time (s) after boot system shutdown. This 2394 is useful for hands-off automated testing. 2395 2396 locktorture.stat_interval= [KNL] 2397 Time (s) between statistics printk()s. 2398 2399 locktorture.stutter= [KNL] 2400 Time (s) to stutter testing, for example, 2401 specifying five seconds causes the test to run for 2402 five seconds, wait for five seconds, and so on. 2403 This tests the locking primitive's ability to 2404 transition abruptly to and from idle. 2405 2406 locktorture.torture_type= [KNL] 2407 Specify the locking implementation to test. 2408 2409 locktorture.verbose= [KNL] 2410 Enable additional printk() statements. 2411 2412 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 2413 Format: <irq> 2414 2415 loglevel= All Kernel Messages with a loglevel smaller than the 2416 console loglevel will be printed to the console. It can 2417 also be changed with klogd or other programs. The 2418 loglevels are defined as follows: 2419 2420 0 (KERN_EMERG) system is unusable 2421 1 (KERN_ALERT) action must be taken immediately 2422 2 (KERN_CRIT) critical conditions 2423 3 (KERN_ERR) error conditions 2424 4 (KERN_WARNING) warning conditions 2425 5 (KERN_NOTICE) normal but significant condition 2426 6 (KERN_INFO) informational 2427 7 (KERN_DEBUG) debug-level messages 2428 2429 log_buf_len=n[KMG] Sets the size of the printk ring buffer, 2430 in bytes. n must be a power of two and greater 2431 than the minimal size. The minimal size is defined 2432 by LOG_BUF_SHIFT kernel config parameter. There is 2433 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter 2434 that allows to increase the default size depending on 2435 the number of CPUs. See init/Kconfig for more details. 2436 2437 logo.nologo [FB] Disables display of the built-in Linux logo. 2438 This may be used to provide more screen space for 2439 kernel log messages and is useful when debugging 2440 kernel boot problems. 2441 2442 lp=0 [LP] Specify parallel ports to use, e.g, 2443 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 2444 lp=reset first parallel port). 'lp=0' disables the 2445 lp=auto printer driver. 'lp=reset' (which can be 2446 specified in addition to the ports) causes 2447 attached printers to be reset. Using 2448 lp=port1,port2,... specifies the parallel ports 2449 to associate lp devices with, starting with 2450 lp0. A port specification may be 'none' to skip 2451 that lp device, or a parport name such as 2452 'parport0'. Specifying 'lp=auto' instead of a 2453 port specification list means that device IDs 2454 from each port should be examined, to see if 2455 an IEEE 1284-compliant printer is attached; if 2456 so, the driver will manage that printer. 2457 See also header of drivers/char/lp.c. 2458 2459 lpj=n [KNL] 2460 Sets loops_per_jiffy to given constant, thus avoiding 2461 time-consuming boot-time autodetection (up to 250 ms per 2462 CPU). 0 enables autodetection (default). To determine 2463 the correct value for your kernel, boot with normal 2464 autodetection and see what value is printed. Note that 2465 on SMP systems the preset will be applied to all CPUs, 2466 which is likely to cause problems if your CPUs need 2467 significantly divergent settings. An incorrect value 2468 will cause delays in the kernel to be wrong, leading to 2469 unpredictable I/O errors and other breakage. Although 2470 unlikely, in the extreme case this might damage your 2471 hardware. 2472 2473 ltpc= [NET] 2474 Format: <io>,<irq>,<dma> 2475 2476 lsm.debug [SECURITY] Enable LSM initialization debugging output. 2477 2478 lsm=lsm1,...,lsmN 2479 [SECURITY] Choose order of LSM initialization. This 2480 overrides CONFIG_LSM, and the "security=" parameter. 2481 2482 machvec= [IA-64] Force the use of a particular machine-vector 2483 (machvec) in a generic kernel. 2484 Example: machvec=hpzx1 2485 2486 machtype= [Loongson] Share the same kernel image file between different 2487 yeeloong laptop. 2488 Example: machtype=lemote-yeeloong-2f-7inch 2489 2490 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater 2491 than or equal to this physical address is ignored. 2492 2493 maxcpus= [SMP] Maximum number of processors that an SMP kernel 2494 will bring up during bootup. maxcpus=n : n >= 0 limits 2495 the kernel to bring up 'n' processors. Surely after 2496 bootup you can bring up the other plugged cpu by executing 2497 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 2498 only takes effect during system bootup. 2499 While n=0 is a special case, it is equivalent to "nosmp", 2500 which also disables the IO APIC. 2501 2502 max_loop= [LOOP] The number of loop block devices that get 2503 (loop.max_loop) unconditionally pre-created at init time. The default 2504 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 2505 of statically allocating a predefined number, loop 2506 devices can be requested on-demand with the 2507 /dev/loop-control interface. 2508 2509 mce [X86-32] Machine Check Exception 2510 2511 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.rst 2512 2513 md= [HW] RAID subsystems devices and level 2514 See Documentation/admin-guide/md.rst. 2515 2516 mdacon= [MDA] 2517 Format: <first>,<last> 2518 Specifies range of consoles to be captured by the MDA. 2519 2520 mds= [X86,INTEL] 2521 Control mitigation for the Micro-architectural Data 2522 Sampling (MDS) vulnerability. 2523 2524 Certain CPUs are vulnerable to an exploit against CPU 2525 internal buffers which can forward information to a 2526 disclosure gadget under certain conditions. 2527 2528 In vulnerable processors, the speculatively 2529 forwarded data can be used in a cache side channel 2530 attack, to access data to which the attacker does 2531 not have direct access. 2532 2533 This parameter controls the MDS mitigation. The 2534 options are: 2535 2536 full - Enable MDS mitigation on vulnerable CPUs 2537 full,nosmt - Enable MDS mitigation and disable 2538 SMT on vulnerable CPUs 2539 off - Unconditionally disable MDS mitigation 2540 2541 On TAA-affected machines, mds=off can be prevented by 2542 an active TAA mitigation as both vulnerabilities are 2543 mitigated with the same mechanism so in order to disable 2544 this mitigation, you need to specify tsx_async_abort=off 2545 too. 2546 2547 Not specifying this option is equivalent to 2548 mds=full. 2549 2550 For details see: Documentation/admin-guide/hw-vuln/mds.rst 2551 2552 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory 2553 Amount of memory to be used when the kernel is not able 2554 to see the whole system memory or for test. 2555 [X86] Work as limiting max address. Use together 2556 with memmap= to avoid physical address space collisions. 2557 Without memmap= PCI devices could be placed at addresses 2558 belonging to unused RAM. 2559 2560 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 2561 memory. 2562 2563 memchunk=nn[KMG] 2564 [KNL,SH] Allow user to override the default size for 2565 per-device physically contiguous DMA buffers. 2566 2567 memhp_default_state=online/offline 2568 [KNL] Set the initial state for the memory hotplug 2569 onlining policy. If not specified, the default value is 2570 set according to the 2571 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config 2572 option. 2573 See Documentation/admin-guide/mm/memory-hotplug.rst. 2574 2575 memmap=exactmap [KNL,X86] Enable setting of an exact 2576 E820 memory map, as specified by the user. 2577 Such memmap=exactmap lines can be constructed based on 2578 BIOS output or other requirements. See the memmap=nn@ss 2579 option description. 2580 2581 memmap=nn[KMG]@ss[KMG] 2582 [KNL] Force usage of a specific region of memory. 2583 Region of memory to be used is from ss to ss+nn. 2584 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], 2585 which limits max address to nn[KMG]. 2586 Multiple different regions can be specified, 2587 comma delimited. 2588 Example: 2589 memmap=100M@2G,100M#3G,1G!1024G 2590 2591 memmap=nn[KMG]#ss[KMG] 2592 [KNL,ACPI] Mark specific memory as ACPI data. 2593 Region of memory to be marked is from ss to ss+nn. 2594 2595 memmap=nn[KMG]$ss[KMG] 2596 [KNL,ACPI] Mark specific memory as reserved. 2597 Region of memory to be reserved is from ss to ss+nn. 2598 Example: Exclude memory from 0x18690000-0x1869ffff 2599 memmap=64K$0x18690000 2600 or 2601 memmap=0x10000$0x18690000 2602 Some bootloaders may need an escape character before '$', 2603 like Grub2, otherwise '$' and the following number 2604 will be eaten. 2605 2606 memmap=nn[KMG]!ss[KMG] 2607 [KNL,X86] Mark specific memory as protected. 2608 Region of memory to be used, from ss to ss+nn. 2609 The memory region may be marked as e820 type 12 (0xc) 2610 and is NVDIMM or ADR memory. 2611 2612 memmap=<size>%<offset>-<oldtype>+<newtype> 2613 [KNL,ACPI] Convert memory within the specified region 2614 from <oldtype> to <newtype>. If "-<oldtype>" is left 2615 out, the whole region will be marked as <newtype>, 2616 even if previously unavailable. If "+<newtype>" is left 2617 out, matching memory will be removed. Types are 2618 specified as e820 types, e.g., 1 = RAM, 2 = reserved, 2619 3 = ACPI, 12 = PRAM. 2620 2621 memory_corruption_check=0/1 [X86] 2622 Some BIOSes seem to corrupt the first 64k of 2623 memory when doing things like suspend/resume. 2624 Setting this option will scan the memory 2625 looking for corruption. Enabling this will 2626 both detect corruption and prevent the kernel 2627 from using the memory being corrupted. 2628 However, its intended as a diagnostic tool; if 2629 repeatable BIOS-originated corruption always 2630 affects the same memory, you can use memmap= 2631 to prevent the kernel from using that memory. 2632 2633 memory_corruption_check_size=size [X86] 2634 By default it checks for corruption in the low 2635 64k, making this memory unavailable for normal 2636 use. Use this parameter to scan for 2637 corruption in more or less memory. 2638 2639 memory_corruption_check_period=seconds [X86] 2640 By default it checks for corruption every 60 2641 seconds. Use this parameter to check at some 2642 other rate. 0 disables periodic checking. 2643 2644 memtest= [KNL,X86,ARM,PPC] Enable memtest 2645 Format: <integer> 2646 default : 0 <disable> 2647 Specifies the number of memtest passes to be 2648 performed. Each pass selects another test 2649 pattern from a given set of patterns. Memtest 2650 fills the memory with this pattern, validates 2651 memory contents and reserves bad memory 2652 regions that are detected. 2653 2654 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control 2655 Valid arguments: on, off 2656 Default (depends on kernel configuration option): 2657 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y) 2658 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n) 2659 mem_encrypt=on: Activate SME 2660 mem_encrypt=off: Do not activate SME 2661 2662 Refer to Documentation/virt/kvm/amd-memory-encryption.rst 2663 for details on when memory encryption can be activated. 2664 2665 mem_sleep_default= [SUSPEND] Default system suspend mode: 2666 s2idle - Suspend-To-Idle 2667 shallow - Power-On Suspend or equivalent (if supported) 2668 deep - Suspend-To-RAM or equivalent (if supported) 2669 See Documentation/admin-guide/pm/sleep-states.rst. 2670 2671 meye.*= [HW] Set MotionEye Camera parameters 2672 See Documentation/media/v4l-drivers/meye.rst. 2673 2674 mfgpt_irq= [IA-32] Specify the IRQ to use for the 2675 Multi-Function General Purpose Timers on AMD Geode 2676 platforms. 2677 2678 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 2679 the BIOS has incorrectly applied a workaround. TinyBIOS 2680 version 0.98 is known to be affected, 0.99 fixes the 2681 problem by letting the user disable the workaround. 2682 2683 mga= [HW,DRM] 2684 2685 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this 2686 physical address is ignored. 2687 2688 mini2440= [ARM,HW,KNL] 2689 Format:[0..2][b][c][t] 2690 Default: "0tb" 2691 MINI2440 configuration specification: 2692 0 - The attached screen is the 3.5" TFT 2693 1 - The attached screen is the 7" TFT 2694 2 - The VGA Shield is attached (1024x768) 2695 Leaving out the screen size parameter will not load 2696 the TFT driver, and the framebuffer will be left 2697 unconfigured. 2698 b - Enable backlight. The TFT backlight pin will be 2699 linked to the kernel VESA blanking code and a GPIO 2700 LED. This parameter is not necessary when using the 2701 VGA shield. 2702 c - Enable the s3c camera interface. 2703 t - Reserved for enabling touchscreen support. The 2704 touchscreen support is not enabled in the mainstream 2705 kernel as of 2.6.30, a preliminary port can be found 2706 in the "bleeding edge" mini2440 support kernel at 2707 http://repo.or.cz/w/linux-2.6/mini2440.git 2708 2709 mitigations= 2710 [X86,PPC,S390,ARM64] Control optional mitigations for 2711 CPU vulnerabilities. This is a set of curated, 2712 arch-independent options, each of which is an 2713 aggregation of existing arch-specific options. 2714 2715 off 2716 Disable all optional CPU mitigations. This 2717 improves system performance, but it may also 2718 expose users to several CPU vulnerabilities. 2719 Equivalent to: gather_data_sampling=off [X86] 2720 kpti=0 [ARM64] 2721 kvm.nx_huge_pages=off [X86] 2722 l1tf=off [X86] 2723 mds=off [X86] 2724 mmio_stale_data=off [X86] 2725 no_entry_flush [PPC] 2726 no_uaccess_flush [PPC] 2727 nobp=0 [S390] 2728 nopti [X86,PPC] 2729 nospectre_v1 [X86,PPC] 2730 nospectre_v2 [X86,PPC,S390,ARM64] 2731 spec_store_bypass_disable=off [X86,PPC] 2732 spectre_v2_user=off [X86] 2733 ssbd=force-off [ARM64] 2734 tsx_async_abort=off [X86] 2735 2736 Exceptions: 2737 This does not have any effect on 2738 kvm.nx_huge_pages when 2739 kvm.nx_huge_pages=force. 2740 2741 auto (default) 2742 Mitigate all CPU vulnerabilities, but leave SMT 2743 enabled, even if it's vulnerable. This is for 2744 users who don't want to be surprised by SMT 2745 getting disabled across kernel upgrades, or who 2746 have other ways of avoiding SMT-based attacks. 2747 Equivalent to: (default behavior) 2748 2749 auto,nosmt 2750 Mitigate all CPU vulnerabilities, disabling SMT 2751 if needed. This is for users who always want to 2752 be fully mitigated, even if it means losing SMT. 2753 Equivalent to: l1tf=flush,nosmt [X86] 2754 mds=full,nosmt [X86] 2755 tsx_async_abort=full,nosmt [X86] 2756 mmio_stale_data=full,nosmt [X86] 2757 2758 mminit_loglevel= 2759 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this 2760 parameter allows control of the logging verbosity for 2761 the additional memory initialisation checks. A value 2762 of 0 disables mminit logging and a level of 4 will 2763 log everything. Information is printed at KERN_DEBUG 2764 so loglevel=8 may also need to be specified. 2765 2766 mmio_stale_data= 2767 [X86,INTEL] Control mitigation for the Processor 2768 MMIO Stale Data vulnerabilities. 2769 2770 Processor MMIO Stale Data is a class of 2771 vulnerabilities that may expose data after an MMIO 2772 operation. Exposed data could originate or end in 2773 the same CPU buffers as affected by MDS and TAA. 2774 Therefore, similar to MDS and TAA, the mitigation 2775 is to clear the affected CPU buffers. 2776 2777 This parameter controls the mitigation. The 2778 options are: 2779 2780 full - Enable mitigation on vulnerable CPUs 2781 2782 full,nosmt - Enable mitigation and disable SMT on 2783 vulnerable CPUs. 2784 2785 off - Unconditionally disable mitigation 2786 2787 On MDS or TAA affected machines, 2788 mmio_stale_data=off can be prevented by an active 2789 MDS or TAA mitigation as these vulnerabilities are 2790 mitigated with the same mechanism so in order to 2791 disable this mitigation, you need to specify 2792 mds=off and tsx_async_abort=off too. 2793 2794 Not specifying this option is equivalent to 2795 mmio_stale_data=full. 2796 2797 For details see: 2798 Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst 2799 2800 module.sig_enforce 2801 [KNL] When CONFIG_MODULE_SIG is set, this means that 2802 modules without (valid) signatures will fail to load. 2803 Note that if CONFIG_MODULE_SIG_FORCE is set, that 2804 is always true, so this option does nothing. 2805 2806 module_blacklist= [KNL] Do not load a comma-separated list of 2807 modules. Useful for debugging problem modules. 2808 2809 mousedev.tap_time= 2810 [MOUSE] Maximum time between finger touching and 2811 leaving touchpad surface for touch to be considered 2812 a tap and be reported as a left button click (for 2813 touchpads working in absolute mode only). 2814 Format: <msecs> 2815 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 2816 reporting absolute coordinates, such as tablets 2817 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 2818 reporting absolute coordinates, such as tablets 2819 2820 movablecore= [KNL,X86,IA-64,PPC] 2821 Format: nn[KMGTPE] | nn% 2822 This parameter is the complement to kernelcore=, it 2823 specifies the amount of memory used for migratable 2824 allocations. If both kernelcore and movablecore is 2825 specified, then kernelcore will be at *least* the 2826 specified value but may be more. If movablecore on its 2827 own is specified, the administrator must be careful 2828 that the amount of memory usable for all allocations 2829 is not too small. 2830 2831 movable_node [KNL] Boot-time switch to make hotplugable memory 2832 NUMA nodes to be movable. This means that the memory 2833 of such nodes will be usable only for movable 2834 allocations which rules out almost all kernel 2835 allocations. Use with caution! 2836 2837 MTD_Partition= [MTD] 2838 Format: <name>,<region-number>,<size>,<offset> 2839 2840 MTD_Region= [MTD] Format: 2841 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 2842 2843 mtdparts= [MTD] 2844 See drivers/mtd/parsers/cmdlinepart.c 2845 2846 multitce=off [PPC] This parameter disables the use of the pSeries 2847 firmware feature for updating multiple TCE entries 2848 at a time. 2849 2850 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 2851 2852 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 2853 2854 boundary - index of last SLC block on Flex-OneNAND. 2855 The remaining blocks are configured as MLC blocks. 2856 lock - Configure if Flex-OneNAND boundary should be locked. 2857 Once locked, the boundary cannot be changed. 2858 1 indicates lock status, 0 indicates unlock status. 2859 2860 mtdset= [ARM] 2861 ARM/S3C2412 JIVE boot control 2862 2863 See arch/arm/mach-s3c2412/mach-jive.c 2864 2865 mtouchusb.raw_coordinates= 2866 [HW] Make the MicroTouch USB driver use raw coordinates 2867 ('y', default) or cooked coordinates ('n') 2868 2869 mtrr_chunk_size=nn[KMG] [X86] 2870 used for mtrr cleanup. It is largest continuous chunk 2871 that could hold holes aka. UC entries. 2872 2873 mtrr_gran_size=nn[KMG] [X86] 2874 Used for mtrr cleanup. It is granularity of mtrr block. 2875 Default is 1. 2876 Large value could prevent small alignment from 2877 using up MTRRs. 2878 2879 mtrr_spare_reg_nr=n [X86] 2880 Format: <integer> 2881 Range: 0,7 : spare reg number 2882 Default : 1 2883 Used for mtrr cleanup. It is spare mtrr entries number. 2884 Set to 2 or more if your graphical card needs more. 2885 2886 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 2887 2888 netdev= [NET] Network devices parameters 2889 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 2890 Note that mem_start is often overloaded to mean 2891 something different and driver-specific. 2892 This usage is only documented in each driver source 2893 file if at all. 2894 2895 nf_conntrack.acct= 2896 [NETFILTER] Enable connection tracking flow accounting 2897 0 to disable accounting 2898 1 to enable accounting 2899 Default value is 0. 2900 2901 nfsaddrs= [NFS] Deprecated. Use ip= instead. 2902 See Documentation/filesystems/nfs/nfsroot.txt. 2903 2904 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 2905 See Documentation/filesystems/nfs/nfsroot.txt. 2906 2907 nfsrootdebug [NFS] enable nfsroot debugging messages. 2908 See Documentation/filesystems/nfs/nfsroot.txt. 2909 2910 nfs.callback_nr_threads= 2911 [NFSv4] set the total number of threads that the 2912 NFS client will assign to service NFSv4 callback 2913 requests. 2914 2915 nfs.callback_tcpport= 2916 [NFS] set the TCP port on which the NFSv4 callback 2917 channel should listen. 2918 2919 nfs.cache_getent= 2920 [NFS] sets the pathname to the program which is used 2921 to update the NFS client cache entries. 2922 2923 nfs.cache_getent_timeout= 2924 [NFS] sets the timeout after which an attempt to 2925 update a cache entry is deemed to have failed. 2926 2927 nfs.idmap_cache_timeout= 2928 [NFS] set the maximum lifetime for idmapper cache 2929 entries. 2930 2931 nfs.enable_ino64= 2932 [NFS] enable 64-bit inode numbers. 2933 If zero, the NFS client will fake up a 32-bit inode 2934 number for the readdir() and stat() syscalls instead 2935 of returning the full 64-bit number. 2936 The default is to return 64-bit inode numbers. 2937 2938 nfs.max_session_cb_slots= 2939 [NFSv4.1] Sets the maximum number of session 2940 slots the client will assign to the callback 2941 channel. This determines the maximum number of 2942 callbacks the client will process in parallel for 2943 a particular server. 2944 2945 nfs.max_session_slots= 2946 [NFSv4.1] Sets the maximum number of session slots 2947 the client will attempt to negotiate with the server. 2948 This limits the number of simultaneous RPC requests 2949 that the client can send to the NFSv4.1 server. 2950 Note that there is little point in setting this 2951 value higher than the max_tcp_slot_table_limit. 2952 2953 nfs.nfs4_disable_idmapping= 2954 [NFSv4] When set to the default of '1', this option 2955 ensures that both the RPC level authentication 2956 scheme and the NFS level operations agree to use 2957 numeric uids/gids if the mount is using the 2958 'sec=sys' security flavour. In effect it is 2959 disabling idmapping, which can make migration from 2960 legacy NFSv2/v3 systems to NFSv4 easier. 2961 Servers that do not support this mode of operation 2962 will be autodetected by the client, and it will fall 2963 back to using the idmapper. 2964 To turn off this behaviour, set the value to '0'. 2965 nfs.nfs4_unique_id= 2966 [NFS4] Specify an additional fixed unique ident- 2967 ification string that NFSv4 clients can insert into 2968 their nfs_client_id4 string. This is typically a 2969 UUID that is generated at system install time. 2970 2971 nfs.send_implementation_id = 2972 [NFSv4.1] Send client implementation identification 2973 information in exchange_id requests. 2974 If zero, no implementation identification information 2975 will be sent. 2976 The default is to send the implementation identification 2977 information. 2978 2979 nfs.recover_lost_locks = 2980 [NFSv4] Attempt to recover locks that were lost due 2981 to a lease timeout on the server. Please note that 2982 doing this risks data corruption, since there are 2983 no guarantees that the file will remain unchanged 2984 after the locks are lost. 2985 If you want to enable the kernel legacy behaviour of 2986 attempting to recover these locks, then set this 2987 parameter to '1'. 2988 The default parameter value of '0' causes the kernel 2989 not to attempt recovery of lost locks. 2990 2991 nfs4.layoutstats_timer = 2992 [NFSv4.2] Change the rate at which the kernel sends 2993 layoutstats to the pNFS metadata server. 2994 2995 Setting this to value to 0 causes the kernel to use 2996 whatever value is the default set by the layout 2997 driver. A non-zero value sets the minimum interval 2998 in seconds between layoutstats transmissions. 2999 3000 nfsd.nfs4_disable_idmapping= 3001 [NFSv4] When set to the default of '1', the NFSv4 3002 server will return only numeric uids and gids to 3003 clients using auth_sys, and will accept numeric uids 3004 and gids from such clients. This is intended to ease 3005 migration from NFSv2/v3. 3006 3007 nmi_debug= [KNL,SH] Specify one or more actions to take 3008 when a NMI is triggered. 3009 Format: [state][,regs][,debounce][,die] 3010 3011 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 3012 Format: [panic,][nopanic,][num] 3013 Valid num: 0 or 1 3014 0 - turn hardlockup detector in nmi_watchdog off 3015 1 - turn hardlockup detector in nmi_watchdog on 3016 When panic is specified, panic when an NMI watchdog 3017 timeout occurs (or 'nopanic' to not panic on an NMI 3018 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set) 3019 To disable both hard and soft lockup detectors, 3020 please see 'nowatchdog'. 3021 This is useful when you use a panic=... timeout and 3022 need the box quickly up again. 3023 3024 These settings can be accessed at runtime via 3025 the nmi_watchdog and hardlockup_panic sysctls. 3026 3027 netpoll.carrier_timeout= 3028 [NET] Specifies amount of time (in seconds) that 3029 netpoll should wait for a carrier. By default netpoll 3030 waits 4 seconds. 3031 3032 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 3033 emulation library even if a 387 maths coprocessor 3034 is present. 3035 3036 no5lvl [X86-64] Disable 5-level paging mode. Forces 3037 kernel to use 4-level paging instead. 3038 3039 no_console_suspend 3040 [HW] Never suspend the console 3041 Disable suspending of consoles during suspend and 3042 hibernate operations. Once disabled, debugging 3043 messages can reach various consoles while the rest 3044 of the system is being put to sleep (ie, while 3045 debugging driver suspend/resume hooks). This may 3046 not work reliably with all consoles, but is known 3047 to work with serial and VGA consoles. 3048 To facilitate more flexible debugging, we also add 3049 console_suspend, a printk module parameter to control 3050 it. Users could use console_suspend (usually 3051 /sys/module/printk/parameters/console_suspend) to 3052 turn on/off it dynamically. 3053 3054 novmcoredd [KNL,KDUMP] 3055 Disable device dump. Device dump allows drivers to 3056 append dump data to vmcore so you can collect driver 3057 specified debug info. Drivers can append the data 3058 without any limit and this data is stored in memory, 3059 so this may cause significant memory stress. Disabling 3060 device dump can help save memory but the driver debug 3061 data will be no longer available. This parameter 3062 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP 3063 is set. 3064 3065 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien 3066 caches in the slab allocator. Saves per-node memory, 3067 but will impact performance. 3068 3069 noalign [KNL,ARM] 3070 3071 noaltinstr [S390] Disables alternative instructions patching 3072 (CPU alternatives feature). 3073 3074 noapic [SMP,APIC] Tells the kernel to not make use of any 3075 IOAPICs that may be present in the system. 3076 3077 noautogroup Disable scheduler automatic task group creation. 3078 3079 nobats [PPC] Do not use BATs for mapping kernel lowmem 3080 on "Classic" PPC cores. 3081 3082 nocache [ARM] 3083 3084 noclflush [BUGS=X86] Don't use the CLFLUSH instruction 3085 3086 nodelayacct [KNL] Disable per-task delay accounting 3087 3088 nodsp [SH] Disable hardware DSP at boot time. 3089 3090 noefi Disable EFI runtime services support. 3091 3092 no_entry_flush [PPC] Don't flush the L1-D cache when entering the kernel. 3093 3094 noexec [IA-64] 3095 3096 noexec [X86] 3097 On X86-32 available only on PAE configured kernels. 3098 noexec=on: enable non-executable mappings (default) 3099 noexec=off: disable non-executable mappings 3100 3101 nosmap [X86,PPC] 3102 Disable SMAP (Supervisor Mode Access Prevention) 3103 even if it is supported by processor. 3104 3105 nosmep [X86,PPC] 3106 Disable SMEP (Supervisor Mode Execution Prevention) 3107 even if it is supported by processor. 3108 3109 noexec32 [X86-64] 3110 This affects only 32-bit executables. 3111 noexec32=on: enable non-executable mappings (default) 3112 read doesn't imply executable mappings 3113 noexec32=off: disable non-executable mappings 3114 read implies executable mappings 3115 3116 nofpu [MIPS,SH] Disable hardware FPU at boot time. 3117 3118 nofxsr [BUGS=X86-32] Disables x86 floating point extended 3119 register save and restore. The kernel will only save 3120 legacy floating-point registers on task switch. 3121 3122 nohugeiomap [KNL,x86,PPC] Disable kernel huge I/O mappings. 3123 3124 nosmt [KNL,S390] Disable symmetric multithreading (SMT). 3125 Equivalent to smt=1. 3126 3127 [KNL,x86] Disable symmetric multithreading (SMT). 3128 nosmt=force: Force disable SMT, cannot be undone 3129 via the sysfs control file. 3130 3131 nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1 3132 (bounds check bypass). With this option data leaks are 3133 possible in the system. 3134 3135 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for 3136 the Spectre variant 2 (indirect branch prediction) 3137 vulnerability. System may allow data leaks with this 3138 option. 3139 3140 nospec_store_bypass_disable 3141 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability 3142 3143 no_uaccess_flush 3144 [PPC] Don't flush the L1-D cache after accessing user data. 3145 3146 noxsave [BUGS=X86] Disables x86 extended register state save 3147 and restore using xsave. The kernel will fallback to 3148 enabling legacy floating-point and sse state. 3149 3150 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 3151 register states. The kernel will fall back to use 3152 xsave to save the states. By using this parameter, 3153 performance of saving the states is degraded because 3154 xsave doesn't support modified optimization while 3155 xsaveopt supports it on xsaveopt enabled systems. 3156 3157 noxsaves [X86] Disables xsaves and xrstors used in saving and 3158 restoring x86 extended register state in compacted 3159 form of xsave area. The kernel will fall back to use 3160 xsaveopt and xrstor to save and restore the states 3161 in standard form of xsave area. By using this 3162 parameter, xsave area per process might occupy more 3163 memory on xsaves enabled systems. 3164 3165 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or 3166 wfi(ARM) instruction doesn't work correctly and not to 3167 use it. This is also useful when using JTAG debugger. 3168 3169 no_file_caps Tells the kernel not to honor file capabilities. The 3170 only way then for a file to be executed with privilege 3171 is to be setuid root or executed by root. 3172 3173 nohalt [IA-64] Tells the kernel not to use the power saving 3174 function PAL_HALT_LIGHT when idle. This increases 3175 power-consumption. On the positive side, it reduces 3176 interrupt wake-up latency, which may improve performance 3177 in certain environments such as networked servers or 3178 real-time systems. 3179 3180 nohibernate [HIBERNATION] Disable hibernation and resume. 3181 3182 nohz= [KNL] Boottime enable/disable dynamic ticks 3183 Valid arguments: on, off 3184 Default: on 3185 3186 nohz_full= [KNL,BOOT,SMP,ISOL] 3187 The argument is a cpu list, as described above. 3188 In kernels built with CONFIG_NO_HZ_FULL=y, set 3189 the specified list of CPUs whose tick will be stopped 3190 whenever possible. The boot CPU will be forced outside 3191 the range to maintain the timekeeping. Any CPUs 3192 in this list will have their RCU callbacks offloaded, 3193 just as if they had also been called out in the 3194 rcu_nocbs= boot parameter. 3195 3196 noiotrap [SH] Disables trapped I/O port accesses. 3197 3198 noirqdebug [X86-32] Disables the code which attempts to detect and 3199 disable unhandled interrupt sources. 3200 3201 no_timer_check [X86,APIC] Disables the code which tests for 3202 broken timer IRQ sources. 3203 3204 noisapnp [ISAPNP] Disables ISA PnP code. 3205 3206 noinitrd [RAM] Tells the kernel not to load any configured 3207 initial RAM disk. 3208 3209 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt 3210 remapping. 3211 [Deprecated - use intremap=off] 3212 3213 nointroute [IA-64] 3214 3215 noinvpcid [X86] Disable the INVPCID cpu feature. 3216 3217 nojitter [IA-64] Disables jitter checking for ITC timers. 3218 3219 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver 3220 3221 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page 3222 fault handling. 3223 3224 no-vmw-sched-clock 3225 [X86,PV_OPS] Disable paravirtualized VMware scheduler 3226 clock and use the default one. 3227 3228 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting. 3229 steal time is computed, but won't influence scheduler 3230 behaviour 3231 3232 nolapic [X86-32,APIC] Do not enable or use the local APIC. 3233 3234 nolapic_timer [X86-32,APIC] Do not use the local APIC timer. 3235 3236 noltlbs [PPC] Do not use large page/tlb entries for kernel 3237 lowmem mapping on PPC40x and PPC8xx 3238 3239 nomca [IA-64] Disable machine check abort handling 3240 3241 nomce [X86-32] Disable Machine Check Exception 3242 3243 nomfgpt [X86-32] Disable Multi-Function General Purpose 3244 Timer usage (for AMD Geode machines). 3245 3246 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 3247 shutdown the other cpus. Instead use the REBOOT_VECTOR 3248 irq. 3249 3250 nomodule Disable module load 3251 3252 nopat [X86] Disable PAT (page attribute table extension of 3253 pagetables) support. 3254 3255 nopcid [X86-64] Disable the PCID cpu feature. 3256 3257 norandmaps Don't use address space randomization. Equivalent to 3258 echo 0 > /proc/sys/kernel/randomize_va_space 3259 3260 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 3261 with UP alternatives 3262 3263 nordrand [X86] Disable kernel use of the RDRAND and 3264 RDSEED instructions even if they are supported 3265 by the processor. RDRAND and RDSEED are still 3266 available to user space applications. 3267 3268 noresume [SWSUSP] Disables resume and restores original swap 3269 space. 3270 3271 no-scroll [VGA] Disables scrollback. 3272 This is required for the Braillex ib80-piezo Braille 3273 reader made by F.H. Papenmeier (Germany). 3274 3275 nosbagart [IA-64] 3276 3277 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support. 3278 3279 nosmp [SMP] Tells an SMP kernel to act as a UP kernel, 3280 and disable the IO APIC. legacy for "maxcpus=0". 3281 3282 nosoftlockup [KNL] Disable the soft-lockup detector. 3283 3284 nosync [HW,M68K] Disables sync negotiation for all devices. 3285 3286 nowatchdog [KNL] Disable both lockup detectors, i.e. 3287 soft-lockup and NMI watchdog (hard-lockup). 3288 3289 nowb [ARM] 3290 3291 nox2apic [X86-64,APIC] Do not enable x2APIC mode. 3292 3293 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when 3294 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off. 3295 Some features depend on CPU0. Known dependencies are: 3296 1. Resume from suspend/hibernate depends on CPU0. 3297 Suspend/hibernate will fail if CPU0 is offline and you 3298 need to online CPU0 before suspend/hibernate. 3299 2. PIC interrupts also depend on CPU0. CPU0 can't be 3300 removed if a PIC interrupt is detected. 3301 It's said poweroff/reboot may depend on CPU0 on some 3302 machines although I haven't seen such issues so far 3303 after CPU0 is offline on a few tested machines. 3304 If the dependencies are under your control, you can 3305 turn on cpu0_hotplug. 3306 3307 nps_mtm_hs_ctr= [KNL,ARC] 3308 This parameter sets the maximum duration, in 3309 cycles, each HW thread of the CTOP can run 3310 without interruptions, before HW switches it. 3311 The actual maximum duration is 16 times this 3312 parameter's value. 3313 Format: integer between 1 and 255 3314 Default: 255 3315 3316 nptcg= [IA-64] Override max number of concurrent global TLB 3317 purges which is reported from either PAL_VM_SUMMARY or 3318 SAL PALO. 3319 3320 nr_cpus= [SMP] Maximum number of processors that an SMP kernel 3321 could support. nr_cpus=n : n >= 1 limits the kernel to 3322 support 'n' processors. It could be larger than the 3323 number of already plugged CPU during bootup, later in 3324 runtime you can physically add extra cpu until it reaches 3325 n. So during boot up some boot time memory for per-cpu 3326 variables need be pre-allocated for later physical cpu 3327 hot plugging. 3328 3329 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 3330 3331 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing. 3332 Allowed values are enable and disable 3333 3334 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 3335 'node', 'default' can be specified 3336 This can be set from sysctl after boot. 3337 See Documentation/admin-guide/sysctl/vm.rst for details. 3338 3339 of_devlink [OF, KNL] Create device links between consumer and 3340 supplier devices by scanning the devictree to infer the 3341 consumer/supplier relationships. A consumer device 3342 will not be probed until all the supplier devices have 3343 probed successfully. 3344 3345 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver. 3346 See Documentation/debugging-via-ohci1394.txt for more 3347 info. 3348 3349 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 3350 Rather than timing out after 20 ms if an EC 3351 command is not properly ACKed, override the length 3352 of the timeout. We have interrupts disabled while 3353 waiting for the ACK, so if this is set too high 3354 interrupts *may* be lost! 3355 3356 omap_mux= [OMAP] Override bootloader pin multiplexing. 3357 Format: <mux_mode0.mode_name=value>... 3358 For example, to override I2C bus2: 3359 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 3360 3361 oprofile.timer= [HW] 3362 Use timer interrupt instead of performance counters 3363 3364 oprofile.cpu_type= Force an oprofile cpu type 3365 This might be useful if you have an older oprofile 3366 userland or if you want common events. 3367 Format: { arch_perfmon } 3368 arch_perfmon: [X86] Force use of architectural 3369 perfmon on Intel CPUs instead of the 3370 CPU specific event set. 3371 timer: [X86] Force use of architectural NMI 3372 timer mode (see also oprofile.timer 3373 for generic hr timer mode) 3374 3375 oops=panic Always panic on oopses. Default is to just kill the 3376 process, but there is a small probability of 3377 deadlocking the machine. 3378 This will also cause panics on machine check exceptions. 3379 Useful together with panic=30 to trigger a reboot. 3380 3381 page_alloc.shuffle= 3382 [KNL] Boolean flag to control whether the page allocator 3383 should randomize its free lists. The randomization may 3384 be automatically enabled if the kernel detects it is 3385 running on a platform with a direct-mapped memory-side 3386 cache, and this parameter can be used to 3387 override/disable that behavior. The state of the flag 3388 can be read from sysfs at: 3389 /sys/module/page_alloc/parameters/shuffle. 3390 3391 page_owner= [KNL] Boot-time page_owner enabling option. 3392 Storage of the information about who allocated 3393 each page is disabled in default. With this switch, 3394 we can turn it on. 3395 on: enable the feature 3396 3397 page_poison= [KNL] Boot-time parameter changing the state of 3398 poisoning on the buddy allocator, available with 3399 CONFIG_PAGE_POISONING=y. 3400 off: turn off poisoning (default) 3401 on: turn on poisoning 3402 3403 panic= [KNL] Kernel behaviour on panic: delay <timeout> 3404 timeout > 0: seconds before rebooting 3405 timeout = 0: wait forever 3406 timeout < 0: reboot immediately 3407 Format: <timeout> 3408 3409 panic_print= Bitmask for printing system info when panic happens. 3410 User can chose combination of the following bits: 3411 bit 0: print all tasks info 3412 bit 1: print system memory info 3413 bit 2: print timer info 3414 bit 3: print locks info if CONFIG_LOCKDEP is on 3415 bit 4: print ftrace buffer 3416 bit 5: print all printk messages in buffer 3417 3418 panic_on_warn panic() instead of WARN(). Useful to cause kdump 3419 on a WARN(). 3420 3421 crash_kexec_post_notifiers 3422 Run kdump after running panic-notifiers and dumping 3423 kmsg. This only for the users who doubt kdump always 3424 succeeds in any situation. 3425 Note that this also increases risks of kdump failure, 3426 because some panic notifiers can make the crashed 3427 kernel more unstable. 3428 3429 parkbd.port= [HW] Parallel port number the keyboard adapter is 3430 connected to, default is 0. 3431 Format: <parport#> 3432 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 3433 0 for XT, 1 for AT (default is AT). 3434 Format: <mode> 3435 3436 parport= [HW,PPT] Specify parallel ports. 0 disables. 3437 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 3438 Use 'auto' to force the driver to use any 3439 IRQ/DMA settings detected (the default is to 3440 ignore detected IRQ/DMA settings because of 3441 possible conflicts). You can specify the base 3442 address, IRQ, and DMA settings; IRQ and DMA 3443 should be numbers, or 'auto' (for using detected 3444 settings on that particular port), or 'nofifo' 3445 (to avoid using a FIFO even if it is detected). 3446 Parallel ports are assigned in the order they 3447 are specified on the command line, starting 3448 with parport0. 3449 3450 parport_init_mode= [HW,PPT] 3451 Configure VIA parallel port to operate in 3452 a specific mode. This is necessary on Pegasos 3453 computer where firmware has no options for setting 3454 up parallel port mode and sets it to spp. 3455 Currently this function knows 686a and 8231 chips. 3456 Format: [spp|ps2|epp|ecp|ecpepp] 3457 3458 pause_on_oops= 3459 Halt all CPUs after the first oops has been printed for 3460 the specified number of seconds. This is to be used if 3461 your oopses keep scrolling off the screen. 3462 3463 pcbit= [HW,ISDN] 3464 3465 pcd. [PARIDE] 3466 See header of drivers/block/paride/pcd.c. 3467 See also Documentation/admin-guide/blockdev/paride.rst. 3468 3469 pci=option[,option...] [PCI] various PCI subsystem options. 3470 3471 Some options herein operate on a specific device 3472 or a set of devices (<pci_dev>). These are 3473 specified in one of the following formats: 3474 3475 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* 3476 pci:<vendor>:<device>[:<subvendor>:<subdevice>] 3477 3478 Note: the first format specifies a PCI 3479 bus/device/function address which may change 3480 if new hardware is inserted, if motherboard 3481 firmware changes, or due to changes caused 3482 by other kernel parameters. If the 3483 domain is left unspecified, it is 3484 taken to be zero. Optionally, a path 3485 to a device through multiple device/function 3486 addresses can be specified after the base 3487 address (this is more robust against 3488 renumbering issues). The second format 3489 selects devices using IDs from the 3490 configuration space which may match multiple 3491 devices in the system. 3492 3493 earlydump dump PCI config space before the kernel 3494 changes anything 3495 off [X86] don't probe for the PCI bus 3496 bios [X86-32] force use of PCI BIOS, don't access 3497 the hardware directly. Use this if your machine 3498 has a non-standard PCI host bridge. 3499 nobios [X86-32] disallow use of PCI BIOS, only direct 3500 hardware access methods are allowed. Use this 3501 if you experience crashes upon bootup and you 3502 suspect they are caused by the BIOS. 3503 conf1 [X86] Force use of PCI Configuration Access 3504 Mechanism 1 (config address in IO port 0xCF8, 3505 data in IO port 0xCFC, both 32-bit). 3506 conf2 [X86] Force use of PCI Configuration Access 3507 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 3508 the function, IO port 0xCFA, also 8-bit, sets 3509 bus number. The config space is then accessed 3510 through ports 0xC000-0xCFFF). 3511 See http://wiki.osdev.org/PCI for more info 3512 on the configuration access mechanisms. 3513 noaer [PCIE] If the PCIEAER kernel config parameter is 3514 enabled, this kernel boot option can be used to 3515 disable the use of PCIE advanced error reporting. 3516 nodomains [PCI] Disable support for multiple PCI 3517 root domains (aka PCI segments, in ACPI-speak). 3518 nommconf [X86] Disable use of MMCONFIG for PCI 3519 Configuration 3520 check_enable_amd_mmconf [X86] check for and enable 3521 properly configured MMIO access to PCI 3522 config space on AMD family 10h CPU 3523 nomsi [MSI] If the PCI_MSI kernel config parameter is 3524 enabled, this kernel boot option can be used to 3525 disable the use of MSI interrupts system-wide. 3526 noioapicquirk [APIC] Disable all boot interrupt quirks. 3527 Safety option to keep boot IRQs enabled. This 3528 should never be necessary. 3529 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 3530 primary IO-APIC for bridges that cannot disable 3531 boot IRQs. This fixes a source of spurious IRQs 3532 when the system masks IRQs. 3533 noioapicreroute [APIC] Disable workaround that uses the 3534 boot IRQ equivalent of an IRQ that connects to 3535 a chipset where boot IRQs cannot be disabled. 3536 The opposite of ioapicreroute. 3537 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 3538 routing table. These calls are known to be buggy 3539 on several machines and they hang the machine 3540 when used, but on other computers it's the only 3541 way to get the interrupt routing table. Try 3542 this option if the kernel is unable to allocate 3543 IRQs or discover secondary PCI buses on your 3544 motherboard. 3545 rom [X86] Assign address space to expansion ROMs. 3546 Use with caution as certain devices share 3547 address decoders between ROMs and other 3548 resources. 3549 norom [X86] Do not assign address space to 3550 expansion ROMs that do not already have 3551 BIOS assigned address ranges. 3552 nobar [X86] Do not assign address space to the 3553 BARs that weren't assigned by the BIOS. 3554 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 3555 assigned automatically to PCI devices. You can 3556 make the kernel exclude IRQs of your ISA cards 3557 this way. 3558 pirqaddr=0xAAAAA [X86] Specify the physical address 3559 of the PIRQ table (normally generated 3560 by the BIOS) if it is outside the 3561 F0000h-100000h range. 3562 lastbus=N [X86] Scan all buses thru bus #N. Can be 3563 useful if the kernel is unable to find your 3564 secondary buses and you want to tell it 3565 explicitly which ones they are. 3566 assign-busses [X86] Always assign all PCI bus 3567 numbers ourselves, overriding 3568 whatever the firmware may have done. 3569 usepirqmask [X86] Honor the possible IRQ mask stored 3570 in the BIOS $PIR table. This is needed on 3571 some systems with broken BIOSes, notably 3572 some HP Pavilion N5400 and Omnibook XE3 3573 notebooks. This will have no effect if ACPI 3574 IRQ routing is enabled. 3575 noacpi [X86] Do not use ACPI for IRQ routing 3576 or for PCI scanning. 3577 use_crs [X86] Use PCI host bridge window information 3578 from ACPI. On BIOSes from 2008 or later, this 3579 is enabled by default. If you need to use this, 3580 please report a bug. 3581 nocrs [X86] Ignore PCI host bridge windows from ACPI. 3582 If you need to use this, please report a bug. 3583 routeirq Do IRQ routing for all PCI devices. 3584 This is normally done in pci_enable_device(), 3585 so this option is a temporary workaround 3586 for broken drivers that don't call it. 3587 skip_isa_align [X86] do not align io start addr, so can 3588 handle more pci cards 3589 noearly [X86] Don't do any early type 1 scanning. 3590 This might help on some broken boards which 3591 machine check when some devices' config space 3592 is read. But various workarounds are disabled 3593 and some IOMMU drivers will not work. 3594 bfsort Sort PCI devices into breadth-first order. 3595 This sorting is done to get a device 3596 order compatible with older (<= 2.4) kernels. 3597 nobfsort Don't sort PCI devices into breadth-first order. 3598 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 3599 tuning and use the BIOS-configured MPS defaults. 3600 pcie_bus_safe Set every device's MPS to the largest value 3601 supported by all devices below the root complex. 3602 pcie_bus_perf Set device MPS to the largest allowable MPS 3603 based on its parent bus. Also set MRRS (Max 3604 Read Request Size) to the largest supported 3605 value (no larger than the MPS that the device 3606 or bus can support) for best performance. 3607 pcie_bus_peer2peer Set every device's MPS to 128B, which 3608 every device is guaranteed to support. This 3609 configuration allows peer-to-peer DMA between 3610 any pair of devices, possibly at the cost of 3611 reduced performance. This also guarantees 3612 that hot-added devices will work. 3613 cbiosize=nn[KMG] The fixed amount of bus space which is 3614 reserved for the CardBus bridge's IO window. 3615 The default value is 256 bytes. 3616 cbmemsize=nn[KMG] The fixed amount of bus space which is 3617 reserved for the CardBus bridge's memory 3618 window. The default value is 64 megabytes. 3619 resource_alignment= 3620 Format: 3621 [<order of align>@]<pci_dev>[; ...] 3622 Specifies alignment and device to reassign 3623 aligned memory resources. How to 3624 specify the device is described above. 3625 If <order of align> is not specified, 3626 PAGE_SIZE is used as alignment. 3627 A PCI-PCI bridge can be specified if resource 3628 windows need to be expanded. 3629 To specify the alignment for several 3630 instances of a device, the PCI vendor, 3631 device, subvendor, and subdevice may be 3632 specified, e.g., 12@pci:8086:9c22:103c:198f 3633 for 4096-byte alignment. 3634 ecrc= Enable/disable PCIe ECRC (transaction layer 3635 end-to-end CRC checking). 3636 bios: Use BIOS/firmware settings. This is the 3637 the default. 3638 off: Turn ECRC off 3639 on: Turn ECRC on. 3640 hpiosize=nn[KMG] The fixed amount of bus space which is 3641 reserved for hotplug bridge's IO window. 3642 Default size is 256 bytes. 3643 hpmemsize=nn[KMG] The fixed amount of bus space which is 3644 reserved for hotplug bridge's memory window. 3645 Default size is 2 megabytes. 3646 hpbussize=nn The minimum amount of additional bus numbers 3647 reserved for buses below a hotplug bridge. 3648 Default is 1. 3649 realloc= Enable/disable reallocating PCI bridge resources 3650 if allocations done by BIOS are too small to 3651 accommodate resources required by all child 3652 devices. 3653 off: Turn realloc off 3654 on: Turn realloc on 3655 realloc same as realloc=on 3656 noari do not use PCIe ARI. 3657 noats [PCIE, Intel-IOMMU, AMD-IOMMU] 3658 do not use PCIe ATS (and IOMMU device IOTLB). 3659 pcie_scan_all Scan all possible PCIe devices. Otherwise we 3660 only look for one device below a PCIe downstream 3661 port. 3662 big_root_window Try to add a big 64bit memory window to the PCIe 3663 root complex on AMD CPUs. Some GFX hardware 3664 can resize a BAR to allow access to all VRAM. 3665 Adding the window is slightly risky (it may 3666 conflict with unreported devices), so this 3667 taints the kernel. 3668 disable_acs_redir=<pci_dev>[; ...] 3669 Specify one or more PCI devices (in the format 3670 specified above) separated by semicolons. 3671 Each device specified will have the PCI ACS 3672 redirect capabilities forced off which will 3673 allow P2P traffic between devices through 3674 bridges without forcing it upstream. Note: 3675 this removes isolation between devices and 3676 may put more devices in an IOMMU group. 3677 force_floating [S390] Force usage of floating interrupts. 3678 nomio [S390] Do not use MIO instructions. 3679 3680 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power 3681 Management. 3682 off Disable ASPM. 3683 force Enable ASPM even on devices that claim not to support it. 3684 WARNING: Forcing ASPM on may cause system lockups. 3685 3686 pcie_ports= [PCIE] PCIe port services handling: 3687 native Use native PCIe services (PME, AER, DPC, PCIe hotplug) 3688 even if the platform doesn't give the OS permission to 3689 use them. This may cause conflicts if the platform 3690 also tries to use these services. 3691 compat Disable native PCIe services (PME, AER, DPC, PCIe 3692 hotplug). 3693 3694 pcie_port_pm= [PCIE] PCIe port power management handling: 3695 off Disable power management of all PCIe ports 3696 force Forcibly enable power management of all PCIe ports 3697 3698 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 3699 nomsi Do not use MSI for native PCIe PME signaling (this makes 3700 all PCIe root ports use INTx for all services). 3701 3702 pcmv= [HW,PCMCIA] BadgePAD 4 3703 3704 pd_ignore_unused 3705 [PM] 3706 Keep all power-domains already enabled by bootloader on, 3707 even if no driver has claimed them. This is useful 3708 for debug and development, but should not be 3709 needed on a platform with proper driver support. 3710 3711 pd. [PARIDE] 3712 See Documentation/admin-guide/blockdev/paride.rst. 3713 3714 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 3715 boot time. 3716 Format: { 0 | 1 } 3717 See arch/parisc/kernel/pdc_chassis.c 3718 3719 percpu_alloc= Select which percpu first chunk allocator to use. 3720 Currently supported values are "embed" and "page". 3721 Archs may support subset or none of the selections. 3722 See comments in mm/percpu.c for details on each 3723 allocator. This parameter is primarily for debugging 3724 and performance comparison. 3725 3726 pf. [PARIDE] 3727 See Documentation/admin-guide/blockdev/paride.rst. 3728 3729 pg. [PARIDE] 3730 See Documentation/admin-guide/blockdev/paride.rst. 3731 3732 pirq= [SMP,APIC] Manual mp-table setup 3733 See Documentation/x86/i386/IO-APIC.rst. 3734 3735 plip= [PPT,NET] Parallel port network link 3736 Format: { parport<nr> | timid | 0 } 3737 See also Documentation/admin-guide/parport.rst. 3738 3739 pmtmr= [X86] Manual setup of pmtmr I/O Port. 3740 Override pmtimer IOPort with a hex value. 3741 e.g. pmtmr=0x508 3742 3743 pnp.debug=1 [PNP] 3744 Enable PNP debug messages (depends on the 3745 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 3746 via /sys/module/pnp/parameters/debug. We always show 3747 current resource usage; turning this on also shows 3748 possible settings and some assignment information. 3749 3750 pnpacpi= [ACPI] 3751 { off } 3752 3753 pnpbios= [ISAPNP] 3754 { on | off | curr | res | no-curr | no-res } 3755 3756 pnp_reserve_irq= 3757 [ISAPNP] Exclude IRQs for the autoconfiguration 3758 3759 pnp_reserve_dma= 3760 [ISAPNP] Exclude DMAs for the autoconfiguration 3761 3762 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 3763 Ranges are in pairs (I/O port base and size). 3764 3765 pnp_reserve_mem= 3766 [ISAPNP] Exclude memory regions for the 3767 autoconfiguration. 3768 Ranges are in pairs (memory base and size). 3769 3770 ports= [IP_VS_FTP] IPVS ftp helper module 3771 Default is 21. 3772 Up to 8 (IP_VS_APP_MAX_PORTS) ports 3773 may be specified. 3774 Format: <port>,<port>.... 3775 3776 powersave=off [PPC] This option disables power saving features. 3777 It specifically disables cpuidle and sets the 3778 platform machine description specific power_save 3779 function to NULL. On Idle the CPU just reduces 3780 execution priority. 3781 3782 ppc_strict_facility_enable 3783 [PPC] This option catches any kernel floating point, 3784 Altivec, VSX and SPE outside of regions specifically 3785 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 3786 There is some performance impact when enabling this. 3787 3788 ppc_tm= [PPC] 3789 Format: {"off"} 3790 Disable Hardware Transactional Memory 3791 3792 print-fatal-signals= 3793 [KNL] debug: print fatal signals 3794 3795 If enabled, warn about various signal handling 3796 related application anomalies: too many signals, 3797 too many POSIX.1 timers, fatal signals causing a 3798 coredump - etc. 3799 3800 If you hit the warning due to signal overflow, 3801 you might want to try "ulimit -i unlimited". 3802 3803 default: off. 3804 3805 printk.always_kmsg_dump= 3806 Trigger kmsg_dump for cases other than kernel oops or 3807 panics 3808 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3809 default: disabled 3810 3811 printk.devkmsg={on,off,ratelimit} 3812 Control writing to /dev/kmsg. 3813 on - unlimited logging to /dev/kmsg from userspace 3814 off - logging to /dev/kmsg disabled 3815 ratelimit - ratelimit the logging 3816 Default: ratelimit 3817 3818 printk.time= Show timing data prefixed to each printk message line 3819 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3820 3821 processor.max_cstate= [HW,ACPI] 3822 Limit processor to maximum C-state 3823 max_cstate=9 overrides any DMI blacklist limit. 3824 3825 processor.nocst [HW,ACPI] 3826 Ignore the _CST method to determine C-states, 3827 instead using the legacy FADT method 3828 3829 profile= [KNL] Enable kernel profiling via /proc/profile 3830 Format: [<profiletype>,]<number> 3831 Param: <profiletype>: "schedule", "sleep", or "kvm" 3832 [defaults to kernel profiling] 3833 Param: "schedule" - profile schedule points. 3834 Param: "sleep" - profile D-state sleeping (millisecs). 3835 Requires CONFIG_SCHEDSTATS 3836 Param: "kvm" - profile VM exits. 3837 Param: <number> - step/bucket size as a power of 2 for 3838 statistical time based profiling. 3839 3840 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk 3841 before loading. 3842 See Documentation/admin-guide/blockdev/ramdisk.rst. 3843 3844 psi= [KNL] Enable or disable pressure stall information 3845 tracking. 3846 Format: <bool> 3847 3848 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 3849 probe for; one of (bare|imps|exps|lifebook|any). 3850 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 3851 per second. 3852 psmouse.resetafter= [HW,MOUSE] 3853 Try to reset the device after so many bad packets 3854 (0 = never). 3855 psmouse.resolution= 3856 [HW,MOUSE] Set desired mouse resolution, in dpi. 3857 psmouse.smartscroll= 3858 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 3859 0 = disabled, 1 = enabled (default). 3860 3861 pstore.backend= Specify the name of the pstore backend to use 3862 3863 pt. [PARIDE] 3864 See Documentation/admin-guide/blockdev/paride.rst. 3865 3866 pti= [X86_64] Control Page Table Isolation of user and 3867 kernel address spaces. Disabling this feature 3868 removes hardening, but improves performance of 3869 system calls and interrupts. 3870 3871 on - unconditionally enable 3872 off - unconditionally disable 3873 auto - kernel detects whether your CPU model is 3874 vulnerable to issues that PTI mitigates 3875 3876 Not specifying this option is equivalent to pti=auto. 3877 3878 nopti [X86_64] 3879 Equivalent to pti=off 3880 3881 pty.legacy_count= 3882 [KNL] Number of legacy pty's. Overwrites compiled-in 3883 default number. 3884 3885 quiet [KNL] Disable most log messages 3886 3887 r128= [HW,DRM] 3888 3889 raid= [HW,RAID] 3890 See Documentation/admin-guide/md.rst. 3891 3892 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 3893 See Documentation/admin-guide/blockdev/ramdisk.rst. 3894 3895 random.trust_cpu={on,off} 3896 [KNL] Enable or disable trusting the use of the 3897 CPU's random number generator (if available) to 3898 fully seed the kernel's CRNG. Default is controlled 3899 by CONFIG_RANDOM_TRUST_CPU. 3900 3901 random.trust_bootloader={on,off} 3902 [KNL] Enable or disable trusting the use of a 3903 seed passed by the bootloader (if available) to 3904 fully seed the kernel's CRNG. Default is controlled 3905 by CONFIG_RANDOM_TRUST_BOOTLOADER. 3906 3907 ras=option[,option,...] [KNL] RAS-specific options 3908 3909 cec_disable [X86] 3910 Disable the Correctable Errors Collector, 3911 see CONFIG_RAS_CEC help text. 3912 3913 rcu_nocbs= [KNL] 3914 The argument is a cpu list, as described above, 3915 except that the string "all" can be used to 3916 specify every CPU on the system. 3917 3918 In kernels built with CONFIG_RCU_NOCB_CPU=y, set 3919 the specified list of CPUs to be no-callback CPUs. 3920 Invocation of these CPUs' RCU callbacks will be 3921 offloaded to "rcuox/N" kthreads created for that 3922 purpose, where "x" is "p" for RCU-preempt, and 3923 "s" for RCU-sched, and "N" is the CPU number. 3924 This reduces OS jitter on the offloaded CPUs, 3925 which can be useful for HPC and real-time 3926 workloads. It can also improve energy efficiency 3927 for asymmetric multiprocessors. 3928 3929 rcu_nocb_poll [KNL] 3930 Rather than requiring that offloaded CPUs 3931 (specified by rcu_nocbs= above) explicitly 3932 awaken the corresponding "rcuoN" kthreads, 3933 make these kthreads poll for callbacks. 3934 This improves the real-time response for the 3935 offloaded CPUs by relieving them of the need to 3936 wake up the corresponding kthread, but degrades 3937 energy efficiency by requiring that the kthreads 3938 periodically wake up to do the polling. 3939 3940 rcutree.blimit= [KNL] 3941 Set maximum number of finished RCU callbacks to 3942 process in one batch. 3943 3944 rcutree.dump_tree= [KNL] 3945 Dump the structure of the rcu_node combining tree 3946 out at early boot. This is used for diagnostic 3947 purposes, to verify correct tree setup. 3948 3949 rcutree.gp_cleanup_delay= [KNL] 3950 Set the number of jiffies to delay each step of 3951 RCU grace-period cleanup. 3952 3953 rcutree.gp_init_delay= [KNL] 3954 Set the number of jiffies to delay each step of 3955 RCU grace-period initialization. 3956 3957 rcutree.gp_preinit_delay= [KNL] 3958 Set the number of jiffies to delay each step of 3959 RCU grace-period pre-initialization, that is, 3960 the propagation of recent CPU-hotplug changes up 3961 the rcu_node combining tree. 3962 3963 rcutree.use_softirq= [KNL] 3964 If set to zero, move all RCU_SOFTIRQ processing to 3965 per-CPU rcuc kthreads. Defaults to a non-zero 3966 value, meaning that RCU_SOFTIRQ is used by default. 3967 Specify rcutree.use_softirq=0 to use rcuc kthreads. 3968 3969 rcutree.rcu_fanout_exact= [KNL] 3970 Disable autobalancing of the rcu_node combining 3971 tree. This is used by rcutorture, and might 3972 possibly be useful for architectures having high 3973 cache-to-cache transfer latencies. 3974 3975 rcutree.rcu_fanout_leaf= [KNL] 3976 Change the number of CPUs assigned to each 3977 leaf rcu_node structure. Useful for very 3978 large systems, which will choose the value 64, 3979 and for NUMA systems with large remote-access 3980 latencies, which will choose a value aligned 3981 with the appropriate hardware boundaries. 3982 3983 rcutree.jiffies_till_first_fqs= [KNL] 3984 Set delay from grace-period initialization to 3985 first attempt to force quiescent states. 3986 Units are jiffies, minimum value is zero, 3987 and maximum value is HZ. 3988 3989 rcutree.jiffies_till_next_fqs= [KNL] 3990 Set delay between subsequent attempts to force 3991 quiescent states. Units are jiffies, minimum 3992 value is one, and maximum value is HZ. 3993 3994 rcutree.jiffies_till_sched_qs= [KNL] 3995 Set required age in jiffies for a 3996 given grace period before RCU starts 3997 soliciting quiescent-state help from 3998 rcu_note_context_switch() and cond_resched(). 3999 If not specified, the kernel will calculate 4000 a value based on the most recent settings 4001 of rcutree.jiffies_till_first_fqs 4002 and rcutree.jiffies_till_next_fqs. 4003 This calculated value may be viewed in 4004 rcutree.jiffies_to_sched_qs. Any attempt to set 4005 rcutree.jiffies_to_sched_qs will be cheerfully 4006 overwritten. 4007 4008 rcutree.kthread_prio= [KNL,BOOT] 4009 Set the SCHED_FIFO priority of the RCU per-CPU 4010 kthreads (rcuc/N). This value is also used for 4011 the priority of the RCU boost threads (rcub/N) 4012 and for the RCU grace-period kthreads (rcu_bh, 4013 rcu_preempt, and rcu_sched). If RCU_BOOST is 4014 set, valid values are 1-99 and the default is 1 4015 (the least-favored priority). Otherwise, when 4016 RCU_BOOST is not set, valid values are 0-99 and 4017 the default is zero (non-realtime operation). 4018 4019 rcutree.rcu_nocb_gp_stride= [KNL] 4020 Set the number of NOCB callback kthreads in 4021 each group, which defaults to the square root 4022 of the number of CPUs. Larger numbers reduce 4023 the wakeup overhead on the global grace-period 4024 kthread, but increases that same overhead on 4025 each group's NOCB grace-period kthread. 4026 4027 rcutree.qhimark= [KNL] 4028 Set threshold of queued RCU callbacks beyond which 4029 batch limiting is disabled. 4030 4031 rcutree.qlowmark= [KNL] 4032 Set threshold of queued RCU callbacks below which 4033 batch limiting is re-enabled. 4034 4035 rcutree.rcu_idle_gp_delay= [KNL] 4036 Set wakeup interval for idle CPUs that have 4037 RCU callbacks (RCU_FAST_NO_HZ=y). 4038 4039 rcutree.rcu_idle_lazy_gp_delay= [KNL] 4040 Set wakeup interval for idle CPUs that have 4041 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y). 4042 Lazy RCU callbacks are those which RCU can 4043 prove do nothing more than free memory. 4044 4045 rcutree.rcu_kick_kthreads= [KNL] 4046 Cause the grace-period kthread to get an extra 4047 wake_up() if it sleeps three times longer than 4048 it should at force-quiescent-state time. 4049 This wake_up() will be accompanied by a 4050 WARN_ONCE() splat and an ftrace_dump(). 4051 4052 rcutree.sysrq_rcu= [KNL] 4053 Commandeer a sysrq key to dump out Tree RCU's 4054 rcu_node tree with an eye towards determining 4055 why a new grace period has not yet started. 4056 4057 rcuperf.gp_async= [KNL] 4058 Measure performance of asynchronous 4059 grace-period primitives such as call_rcu(). 4060 4061 rcuperf.gp_async_max= [KNL] 4062 Specify the maximum number of outstanding 4063 callbacks per writer thread. When a writer 4064 thread exceeds this limit, it invokes the 4065 corresponding flavor of rcu_barrier() to allow 4066 previously posted callbacks to drain. 4067 4068 rcuperf.gp_exp= [KNL] 4069 Measure performance of expedited synchronous 4070 grace-period primitives. 4071 4072 rcuperf.holdoff= [KNL] 4073 Set test-start holdoff period. The purpose of 4074 this parameter is to delay the start of the 4075 test until boot completes in order to avoid 4076 interference. 4077 4078 rcuperf.nreaders= [KNL] 4079 Set number of RCU readers. The value -1 selects 4080 N, where N is the number of CPUs. A value 4081 "n" less than -1 selects N-n+1, where N is again 4082 the number of CPUs. For example, -2 selects N 4083 (the number of CPUs), -3 selects N+1, and so on. 4084 A value of "n" less than or equal to -N selects 4085 a single reader. 4086 4087 rcuperf.nwriters= [KNL] 4088 Set number of RCU writers. The values operate 4089 the same as for rcuperf.nreaders. 4090 N, where N is the number of CPUs 4091 4092 rcuperf.perf_type= [KNL] 4093 Specify the RCU implementation to test. 4094 4095 rcuperf.shutdown= [KNL] 4096 Shut the system down after performance tests 4097 complete. This is useful for hands-off automated 4098 testing. 4099 4100 rcuperf.verbose= [KNL] 4101 Enable additional printk() statements. 4102 4103 rcuperf.writer_holdoff= [KNL] 4104 Write-side holdoff between grace periods, 4105 in microseconds. The default of zero says 4106 no holdoff. 4107 4108 rcutorture.fqs_duration= [KNL] 4109 Set duration of force_quiescent_state bursts 4110 in microseconds. 4111 4112 rcutorture.fqs_holdoff= [KNL] 4113 Set holdoff time within force_quiescent_state bursts 4114 in microseconds. 4115 4116 rcutorture.fqs_stutter= [KNL] 4117 Set wait time between force_quiescent_state bursts 4118 in seconds. 4119 4120 rcutorture.fwd_progress= [KNL] 4121 Enable RCU grace-period forward-progress testing 4122 for the types of RCU supporting this notion. 4123 4124 rcutorture.fwd_progress_div= [KNL] 4125 Specify the fraction of a CPU-stall-warning 4126 period to do tight-loop forward-progress testing. 4127 4128 rcutorture.fwd_progress_holdoff= [KNL] 4129 Number of seconds to wait between successive 4130 forward-progress tests. 4131 4132 rcutorture.fwd_progress_need_resched= [KNL] 4133 Enclose cond_resched() calls within checks for 4134 need_resched() during tight-loop forward-progress 4135 testing. 4136 4137 rcutorture.gp_cond= [KNL] 4138 Use conditional/asynchronous update-side 4139 primitives, if available. 4140 4141 rcutorture.gp_exp= [KNL] 4142 Use expedited update-side primitives, if available. 4143 4144 rcutorture.gp_normal= [KNL] 4145 Use normal (non-expedited) asynchronous 4146 update-side primitives, if available. 4147 4148 rcutorture.gp_sync= [KNL] 4149 Use normal (non-expedited) synchronous 4150 update-side primitives, if available. If all 4151 of rcutorture.gp_cond=, rcutorture.gp_exp=, 4152 rcutorture.gp_normal=, and rcutorture.gp_sync= 4153 are zero, rcutorture acts as if is interpreted 4154 they are all non-zero. 4155 4156 rcutorture.n_barrier_cbs= [KNL] 4157 Set callbacks/threads for rcu_barrier() testing. 4158 4159 rcutorture.nfakewriters= [KNL] 4160 Set number of concurrent RCU writers. These just 4161 stress RCU, they don't participate in the actual 4162 test, hence the "fake". 4163 4164 rcutorture.nreaders= [KNL] 4165 Set number of RCU readers. The value -1 selects 4166 N-1, where N is the number of CPUs. A value 4167 "n" less than -1 selects N-n-2, where N is again 4168 the number of CPUs. For example, -2 selects N 4169 (the number of CPUs), -3 selects N+1, and so on. 4170 4171 rcutorture.object_debug= [KNL] 4172 Enable debug-object double-call_rcu() testing. 4173 4174 rcutorture.onoff_holdoff= [KNL] 4175 Set time (s) after boot for CPU-hotplug testing. 4176 4177 rcutorture.onoff_interval= [KNL] 4178 Set time (jiffies) between CPU-hotplug operations, 4179 or zero to disable CPU-hotplug testing. 4180 4181 rcutorture.shuffle_interval= [KNL] 4182 Set task-shuffle interval (s). Shuffling tasks 4183 allows some CPUs to go into dyntick-idle mode 4184 during the rcutorture test. 4185 4186 rcutorture.shutdown_secs= [KNL] 4187 Set time (s) after boot system shutdown. This 4188 is useful for hands-off automated testing. 4189 4190 rcutorture.stall_cpu= [KNL] 4191 Duration of CPU stall (s) to test RCU CPU stall 4192 warnings, zero to disable. 4193 4194 rcutorture.stall_cpu_holdoff= [KNL] 4195 Time to wait (s) after boot before inducing stall. 4196 4197 rcutorture.stall_cpu_irqsoff= [KNL] 4198 Disable interrupts while stalling if set. 4199 4200 rcutorture.stat_interval= [KNL] 4201 Time (s) between statistics printk()s. 4202 4203 rcutorture.stutter= [KNL] 4204 Time (s) to stutter testing, for example, specifying 4205 five seconds causes the test to run for five seconds, 4206 wait for five seconds, and so on. This tests RCU's 4207 ability to transition abruptly to and from idle. 4208 4209 rcutorture.test_boost= [KNL] 4210 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 4211 "Maybe" means test if the RCU implementation 4212 under test support RCU priority boosting. 4213 4214 rcutorture.test_boost_duration= [KNL] 4215 Duration (s) of each individual boost test. 4216 4217 rcutorture.test_boost_interval= [KNL] 4218 Interval (s) between each boost test. 4219 4220 rcutorture.test_no_idle_hz= [KNL] 4221 Test RCU's dyntick-idle handling. See also the 4222 rcutorture.shuffle_interval parameter. 4223 4224 rcutorture.torture_type= [KNL] 4225 Specify the RCU implementation to test. 4226 4227 rcutorture.verbose= [KNL] 4228 Enable additional printk() statements. 4229 4230 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL] 4231 Dump ftrace buffer after reporting RCU CPU 4232 stall warning. 4233 4234 rcupdate.rcu_cpu_stall_suppress= [KNL] 4235 Suppress RCU CPU stall warning messages. 4236 4237 rcupdate.rcu_cpu_stall_timeout= [KNL] 4238 Set timeout for RCU CPU stall warning messages. 4239 4240 rcupdate.rcu_expedited= [KNL] 4241 Use expedited grace-period primitives, for 4242 example, synchronize_rcu_expedited() instead 4243 of synchronize_rcu(). This reduces latency, 4244 but can increase CPU utilization, degrade 4245 real-time latency, and degrade energy efficiency. 4246 No effect on CONFIG_TINY_RCU kernels. 4247 4248 rcupdate.rcu_normal= [KNL] 4249 Use only normal grace-period primitives, 4250 for example, synchronize_rcu() instead of 4251 synchronize_rcu_expedited(). This improves 4252 real-time latency, CPU utilization, and 4253 energy efficiency, but can expose users to 4254 increased grace-period latency. This parameter 4255 overrides rcupdate.rcu_expedited. No effect on 4256 CONFIG_TINY_RCU kernels. 4257 4258 rcupdate.rcu_normal_after_boot= [KNL] 4259 Once boot has completed (that is, after 4260 rcu_end_inkernel_boot() has been invoked), use 4261 only normal grace-period primitives. No effect 4262 on CONFIG_TINY_RCU kernels. 4263 4264 rcupdate.rcu_task_stall_timeout= [KNL] 4265 Set timeout in jiffies for RCU task stall warning 4266 messages. Disable with a value less than or equal 4267 to zero. 4268 4269 rcupdate.rcu_self_test= [KNL] 4270 Run the RCU early boot self tests 4271 4272 rdinit= [KNL] 4273 Format: <full_path> 4274 Run specified binary instead of /init from the ramdisk, 4275 used for early userspace startup. See initrd. 4276 4277 rdrand= [X86] 4278 force - Override the decision by the kernel to hide the 4279 advertisement of RDRAND support (this affects 4280 certain AMD processors because of buggy BIOS 4281 support, specifically around the suspend/resume 4282 path). 4283 4284 rdt= [HW,X86,RDT] 4285 Turn on/off individual RDT features. List is: 4286 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, 4287 mba. 4288 E.g. to turn on cmt and turn off mba use: 4289 rdt=cmt,!mba 4290 4291 reboot= [KNL] 4292 Format (x86 or x86_64): 4293 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \ 4294 [[,]s[mp]#### \ 4295 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 4296 [[,]f[orce] 4297 Where reboot_mode is one of warm (soft) or cold (hard) or gpio 4298 (prefix with 'panic_' to set mode for panic 4299 reboot only), 4300 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 4301 reboot_force is either force or not specified, 4302 reboot_cpu is s[mp]#### with #### being the processor 4303 to be used for rebooting. 4304 4305 relax_domain_level= 4306 [KNL, SMP] Set scheduler's default relax_domain_level. 4307 See Documentation/admin-guide/cgroup-v1/cpusets.rst. 4308 4309 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory 4310 Format: <base1>,<size1>[,<base2>,<size2>,...] 4311 Reserve I/O ports or memory so the kernel won't use 4312 them. If <base> is less than 0x10000, the region 4313 is assumed to be I/O ports; otherwise it is memory. 4314 4315 reservetop= [X86-32] 4316 Format: nn[KMG] 4317 Reserves a hole at the top of the kernel virtual 4318 address space. 4319 4320 reservelow= [X86] 4321 Format: nn[K] 4322 Set the amount of memory to reserve for BIOS at 4323 the bottom of the address space. 4324 4325 reset_devices [KNL] Force drivers to reset the underlying device 4326 during initialization. 4327 4328 resume= [SWSUSP] 4329 Specify the partition device for software suspend 4330 Format: 4331 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 4332 4333 resume_offset= [SWSUSP] 4334 Specify the offset from the beginning of the partition 4335 given by "resume=" at which the swap header is located, 4336 in <PAGE_SIZE> units (needed only for swap files). 4337 See Documentation/power/swsusp-and-swap-files.rst 4338 4339 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 4340 read the resume files 4341 4342 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 4343 Useful for devices that are detected asynchronously 4344 (e.g. USB and MMC devices). 4345 4346 hibernate= [HIBERNATION] 4347 noresume Don't check if there's a hibernation image 4348 present during boot. 4349 nocompress Don't compress/decompress hibernation images. 4350 no Disable hibernation and resume. 4351 protect_image Turn on image protection during restoration 4352 (that will set all pages holding image data 4353 during restoration read-only). 4354 4355 retain_initrd [RAM] Keep initrd memory after extraction 4356 4357 retbleed= [X86] Control mitigation of RETBleed (Arbitrary 4358 Speculative Code Execution with Return Instructions) 4359 vulnerability. 4360 4361 off - unconditionally disable 4362 auto - automatically select a migitation 4363 4364 Selecting 'auto' will choose a mitigation method at run 4365 time according to the CPU. 4366 4367 Not specifying this option is equivalent to retbleed=auto. 4368 4369 rfkill.default_state= 4370 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 4371 etc. communication is blocked by default. 4372 1 Unblocked. 4373 4374 rfkill.master_switch_mode= 4375 0 The "airplane mode" button does nothing. 4376 1 The "airplane mode" button toggles between everything 4377 blocked and the previous configuration. 4378 2 The "airplane mode" button toggles between everything 4379 blocked and everything unblocked. 4380 4381 rhash_entries= [KNL,NET] 4382 Set number of hash buckets for route cache 4383 4384 ring3mwait=disable 4385 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 4386 CPUs. 4387 4388 ro [KNL] Mount root device read-only on boot 4389 4390 rodata= [KNL] 4391 on Mark read-only kernel memory as read-only (default). 4392 off Leave read-only kernel memory writable for debugging. 4393 4394 rockchip.usb_uart 4395 Enable the uart passthrough on the designated usb port 4396 on Rockchip SoCs. When active, the signals of the 4397 debug-uart get routed to the D+ and D- pins of the usb 4398 port and the regular usb controller gets disabled. 4399 4400 root= [KNL] Root filesystem 4401 See name_to_dev_t comment in init/do_mounts.c. 4402 4403 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 4404 mount the root filesystem 4405 4406 rootflags= [KNL] Set root filesystem mount option string 4407 4408 rootfstype= [KNL] Set root filesystem type 4409 4410 rootwait [KNL] Wait (indefinitely) for root device to show up. 4411 Useful for devices that are detected asynchronously 4412 (e.g. USB and MMC devices). 4413 4414 rproc_mem=nn[KMG][@address] 4415 [KNL,ARM,CMA] Remoteproc physical memory block. 4416 Memory area to be used by remote processor image, 4417 managed by CMA. 4418 4419 rw [KNL] Mount root device read-write on boot 4420 4421 S [KNL] Run init in single mode 4422 4423 s390_iommu= [HW,S390] 4424 Set s390 IOTLB flushing mode 4425 strict 4426 With strict flushing every unmap operation will result in 4427 an IOTLB flush. Default is lazy flushing before reuse, 4428 which is faster. 4429 4430 sa1100ir [NET] 4431 See drivers/net/irda/sa1100_ir.c. 4432 4433 sbni= [NET] Granch SBNI12 leased line adapter 4434 4435 sched_debug [KNL] Enables verbose scheduler debug messages. 4436 4437 schedstats= [KNL,X86] Enable or disable scheduled statistics. 4438 Allowed values are enable and disable. This feature 4439 incurs a small amount of overhead in the scheduler 4440 but is useful for debugging and performance tuning. 4441 4442 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate 4443 xtime_lock contention on larger systems, and/or RCU lock 4444 contention on all systems with CONFIG_MAXSMP set. 4445 Format: { "0" | "1" } 4446 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 4447 1 -- enable. 4448 Note: increases power consumption, thus should only be 4449 enabled if running jitter sensitive (HPC/RT) workloads. 4450 4451 security= [SECURITY] Choose a legacy "major" security module to 4452 enable at boot. This has been deprecated by the 4453 "lsm=" parameter. 4454 4455 selinux= [SELINUX] Disable or enable SELinux at boot time. 4456 Format: { "0" | "1" } 4457 See security/selinux/Kconfig help text. 4458 0 -- disable. 4459 1 -- enable. 4460 Default value is set via kernel config option. 4461 If enabled at boot time, /selinux/disable can be used 4462 later to disable prior to initial policy load. 4463 4464 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 4465 Format: { "0" | "1" } 4466 See security/apparmor/Kconfig help text 4467 0 -- disable. 4468 1 -- enable. 4469 Default value is set via kernel config option. 4470 4471 serialnumber [BUGS=X86-32] 4472 4473 shapers= [NET] 4474 Maximal number of shapers. 4475 4476 simeth= [IA-64] 4477 simscsi= 4478 4479 slram= [HW,MTD] 4480 4481 slab_nomerge [MM] 4482 Disable merging of slabs with similar size. May be 4483 necessary if there is some reason to distinguish 4484 allocs to different slabs, especially in hardened 4485 environments where the risk of heap overflows and 4486 layout control by attackers can usually be 4487 frustrated by disabling merging. This will reduce 4488 most of the exposure of a heap attack to a single 4489 cache (risks via metadata attacks are mostly 4490 unchanged). Debug options disable merging on their 4491 own. 4492 For more information see Documentation/vm/slub.rst. 4493 4494 slab_max_order= [MM, SLAB] 4495 Determines the maximum allowed order for slabs. 4496 A high setting may cause OOMs due to memory 4497 fragmentation. Defaults to 1 for systems with 4498 more than 32MB of RAM, 0 otherwise. 4499 4500 slub_debug[=options[,slabs]] [MM, SLUB] 4501 Enabling slub_debug allows one to determine the 4502 culprit if slab objects become corrupted. Enabling 4503 slub_debug can create guard zones around objects and 4504 may poison objects when not in use. Also tracks the 4505 last alloc / free. For more information see 4506 Documentation/vm/slub.rst. 4507 4508 slub_memcg_sysfs= [MM, SLUB] 4509 Determines whether to enable sysfs directories for 4510 memory cgroup sub-caches. 1 to enable, 0 to disable. 4511 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON. 4512 Enabling this can lead to a very high number of debug 4513 directories and files being created under 4514 /sys/kernel/slub. 4515 4516 slub_max_order= [MM, SLUB] 4517 Determines the maximum allowed order for slabs. 4518 A high setting may cause OOMs due to memory 4519 fragmentation. For more information see 4520 Documentation/vm/slub.rst. 4521 4522 slub_min_objects= [MM, SLUB] 4523 The minimum number of objects per slab. SLUB will 4524 increase the slab order up to slub_max_order to 4525 generate a sufficiently large slab able to contain 4526 the number of objects indicated. The higher the number 4527 of objects the smaller the overhead of tracking slabs 4528 and the less frequently locks need to be acquired. 4529 For more information see Documentation/vm/slub.rst. 4530 4531 slub_min_order= [MM, SLUB] 4532 Determines the minimum page order for slabs. Must be 4533 lower than slub_max_order. 4534 For more information see Documentation/vm/slub.rst. 4535 4536 slub_nomerge [MM, SLUB] 4537 Same with slab_nomerge. This is supported for legacy. 4538 See slab_nomerge for more information. 4539 4540 smart2= [HW] 4541 Format: <io1>[,<io2>[,...,<io8>]] 4542 4543 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 4544 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 4545 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 4546 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 4547 smsc-ircc2.ircc_irq= [HW] IRQ line 4548 smsc-ircc2.ircc_dma= [HW] DMA channel 4549 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 4550 0: Toshiba Satellite 1800 (GP data pin select) 4551 1: Fast pin select (default) 4552 2: ATC IRMode 4553 4554 smt [KNL,S390] Set the maximum number of threads (logical 4555 CPUs) to use per physical CPU on systems capable of 4556 symmetric multithreading (SMT). Will be capped to the 4557 actual hardware limit. 4558 Format: <integer> 4559 Default: -1 (no limit) 4560 4561 softlockup_panic= 4562 [KNL] Should the soft-lockup detector generate panics. 4563 Format: <integer> 4564 4565 A nonzero value instructs the soft-lockup detector 4566 to panic the machine when a soft-lockup occurs. This 4567 is also controlled by CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC 4568 which is the respective build-time switch to that 4569 functionality. 4570 4571 softlockup_all_cpu_backtrace= 4572 [KNL] Should the soft-lockup detector generate 4573 backtraces on all cpus. 4574 Format: <integer> 4575 4576 sonypi.*= [HW] Sony Programmable I/O Control Device driver 4577 See Documentation/admin-guide/laptops/sonypi.rst 4578 4579 spectre_v2= [X86] Control mitigation of Spectre variant 2 4580 (indirect branch speculation) vulnerability. 4581 The default operation protects the kernel from 4582 user space attacks. 4583 4584 on - unconditionally enable, implies 4585 spectre_v2_user=on 4586 off - unconditionally disable, implies 4587 spectre_v2_user=off 4588 auto - kernel detects whether your CPU model is 4589 vulnerable 4590 4591 Selecting 'on' will, and 'auto' may, choose a 4592 mitigation method at run time according to the 4593 CPU, the available microcode, the setting of the 4594 CONFIG_RETPOLINE configuration option, and the 4595 compiler with which the kernel was built. 4596 4597 Selecting 'on' will also enable the mitigation 4598 against user space to user space task attacks. 4599 4600 Selecting 'off' will disable both the kernel and 4601 the user space protections. 4602 4603 Specific mitigations can also be selected manually: 4604 4605 retpoline - replace indirect branches 4606 retpoline,generic - Retpolines 4607 retpoline,lfence - LFENCE; indirect branch 4608 retpoline,amd - alias for retpoline,lfence 4609 eibrs - Enhanced/Auto IBRS 4610 eibrs,retpoline - Enhanced/Auto IBRS + Retpolines 4611 eibrs,lfence - Enhanced/Auto IBRS + LFENCE 4612 ibrs - use IBRS to protect kernel 4613 4614 Not specifying this option is equivalent to 4615 spectre_v2=auto. 4616 4617 spectre_v2_user= 4618 [X86] Control mitigation of Spectre variant 2 4619 (indirect branch speculation) vulnerability between 4620 user space tasks 4621 4622 on - Unconditionally enable mitigations. Is 4623 enforced by spectre_v2=on 4624 4625 off - Unconditionally disable mitigations. Is 4626 enforced by spectre_v2=off 4627 4628 prctl - Indirect branch speculation is enabled, 4629 but mitigation can be enabled via prctl 4630 per thread. The mitigation control state 4631 is inherited on fork. 4632 4633 prctl,ibpb 4634 - Like "prctl" above, but only STIBP is 4635 controlled per thread. IBPB is issued 4636 always when switching between different user 4637 space processes. 4638 4639 seccomp 4640 - Same as "prctl" above, but all seccomp 4641 threads will enable the mitigation unless 4642 they explicitly opt out. 4643 4644 seccomp,ibpb 4645 - Like "seccomp" above, but only STIBP is 4646 controlled per thread. IBPB is issued 4647 always when switching between different 4648 user space processes. 4649 4650 auto - Kernel selects the mitigation depending on 4651 the available CPU features and vulnerability. 4652 4653 Default mitigation: 4654 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl" 4655 4656 Not specifying this option is equivalent to 4657 spectre_v2_user=auto. 4658 4659 spec_store_bypass_disable= 4660 [HW] Control Speculative Store Bypass (SSB) Disable mitigation 4661 (Speculative Store Bypass vulnerability) 4662 4663 Certain CPUs are vulnerable to an exploit against a 4664 a common industry wide performance optimization known 4665 as "Speculative Store Bypass" in which recent stores 4666 to the same memory location may not be observed by 4667 later loads during speculative execution. The idea 4668 is that such stores are unlikely and that they can 4669 be detected prior to instruction retirement at the 4670 end of a particular speculation execution window. 4671 4672 In vulnerable processors, the speculatively forwarded 4673 store can be used in a cache side channel attack, for 4674 example to read memory to which the attacker does not 4675 directly have access (e.g. inside sandboxed code). 4676 4677 This parameter controls whether the Speculative Store 4678 Bypass optimization is used. 4679 4680 On x86 the options are: 4681 4682 on - Unconditionally disable Speculative Store Bypass 4683 off - Unconditionally enable Speculative Store Bypass 4684 auto - Kernel detects whether the CPU model contains an 4685 implementation of Speculative Store Bypass and 4686 picks the most appropriate mitigation. If the 4687 CPU is not vulnerable, "off" is selected. If the 4688 CPU is vulnerable the default mitigation is 4689 architecture and Kconfig dependent. See below. 4690 prctl - Control Speculative Store Bypass per thread 4691 via prctl. Speculative Store Bypass is enabled 4692 for a process by default. The state of the control 4693 is inherited on fork. 4694 seccomp - Same as "prctl" above, but all seccomp threads 4695 will disable SSB unless they explicitly opt out. 4696 4697 Default mitigations: 4698 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl" 4699 4700 On powerpc the options are: 4701 4702 on,auto - On Power8 and Power9 insert a store-forwarding 4703 barrier on kernel entry and exit. On Power7 4704 perform a software flush on kernel entry and 4705 exit. 4706 off - No action. 4707 4708 Not specifying this option is equivalent to 4709 spec_store_bypass_disable=auto. 4710 4711 spia_io_base= [HW,MTD] 4712 spia_fio_base= 4713 spia_pedr= 4714 spia_peddr= 4715 4716 srbds= [X86,INTEL] 4717 Control the Special Register Buffer Data Sampling 4718 (SRBDS) mitigation. 4719 4720 Certain CPUs are vulnerable to an MDS-like 4721 exploit which can leak bits from the random 4722 number generator. 4723 4724 By default, this issue is mitigated by 4725 microcode. However, the microcode fix can cause 4726 the RDRAND and RDSEED instructions to become 4727 much slower. Among other effects, this will 4728 result in reduced throughput from /dev/urandom. 4729 4730 The microcode mitigation can be disabled with 4731 the following option: 4732 4733 off: Disable mitigation and remove 4734 performance impact to RDRAND and RDSEED 4735 4736 srcutree.counter_wrap_check [KNL] 4737 Specifies how frequently to check for 4738 grace-period sequence counter wrap for the 4739 srcu_data structure's ->srcu_gp_seq_needed field. 4740 The greater the number of bits set in this kernel 4741 parameter, the less frequently counter wrap will 4742 be checked for. Note that the bottom two bits 4743 are ignored. 4744 4745 srcutree.exp_holdoff [KNL] 4746 Specifies how many nanoseconds must elapse 4747 since the end of the last SRCU grace period for 4748 a given srcu_struct until the next normal SRCU 4749 grace period will be considered for automatic 4750 expediting. Set to zero to disable automatic 4751 expediting. 4752 4753 ssbd= [ARM64,HW] 4754 Speculative Store Bypass Disable control 4755 4756 On CPUs that are vulnerable to the Speculative 4757 Store Bypass vulnerability and offer a 4758 firmware based mitigation, this parameter 4759 indicates how the mitigation should be used: 4760 4761 force-on: Unconditionally enable mitigation for 4762 for both kernel and userspace 4763 force-off: Unconditionally disable mitigation for 4764 for both kernel and userspace 4765 kernel: Always enable mitigation in the 4766 kernel, and offer a prctl interface 4767 to allow userspace to register its 4768 interest in being mitigated too. 4769 4770 stack_guard_gap= [MM] 4771 override the default stack gap protection. The value 4772 is in page units and it defines how many pages prior 4773 to (for stacks growing down) resp. after (for stacks 4774 growing up) the main stack are reserved for no other 4775 mapping. Default value is 256 pages. 4776 4777 stacktrace [FTRACE] 4778 Enabled the stack tracer on boot up. 4779 4780 stacktrace_filter=[function-list] 4781 [FTRACE] Limit the functions that the stack tracer 4782 will trace at boot up. function-list is a comma separated 4783 list of functions. This list can be changed at run 4784 time by the stack_trace_filter file in the debugfs 4785 tracing directory. Note, this enables stack tracing 4786 and the stacktrace above is not needed. 4787 4788 sti= [PARISC,HW] 4789 Format: <num> 4790 Set the STI (builtin display/keyboard on the HP-PARISC 4791 machines) console (graphic card) which should be used 4792 as the initial boot-console. 4793 See also comment in drivers/video/console/sticore.c. 4794 4795 sti_font= [HW] 4796 See comment in drivers/video/console/sticore.c. 4797 4798 stifb= [HW] 4799 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 4800 4801 sunrpc.min_resvport= 4802 sunrpc.max_resvport= 4803 [NFS,SUNRPC] 4804 SunRPC servers often require that client requests 4805 originate from a privileged port (i.e. a port in the 4806 range 0 < portnr < 1024). 4807 An administrator who wishes to reserve some of these 4808 ports for other uses may adjust the range that the 4809 kernel's sunrpc client considers to be privileged 4810 using these two parameters to set the minimum and 4811 maximum port values. 4812 4813 sunrpc.svc_rpc_per_connection_limit= 4814 [NFS,SUNRPC] 4815 Limit the number of requests that the server will 4816 process in parallel from a single connection. 4817 The default value is 0 (no limit). 4818 4819 sunrpc.pool_mode= 4820 [NFS] 4821 Control how the NFS server code allocates CPUs to 4822 service thread pools. Depending on how many NICs 4823 you have and where their interrupts are bound, this 4824 option will affect which CPUs will do NFS serving. 4825 Note: this parameter cannot be changed while the 4826 NFS server is running. 4827 4828 auto the server chooses an appropriate mode 4829 automatically using heuristics 4830 global a single global pool contains all CPUs 4831 percpu one pool for each CPU 4832 pernode one pool for each NUMA node (equivalent 4833 to global on non-NUMA machines) 4834 4835 sunrpc.tcp_slot_table_entries= 4836 sunrpc.udp_slot_table_entries= 4837 [NFS,SUNRPC] 4838 Sets the upper limit on the number of simultaneous 4839 RPC calls that can be sent from the client to a 4840 server. Increasing these values may allow you to 4841 improve throughput, but will also increase the 4842 amount of memory reserved for use by the client. 4843 4844 suspend.pm_test_delay= 4845 [SUSPEND] 4846 Sets the number of seconds to remain in a suspend test 4847 mode before resuming the system (see 4848 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 4849 is set. Default value is 5. 4850 4851 svm= [PPC] 4852 Format: { on | off | y | n | 1 | 0 } 4853 This parameter controls use of the Protected 4854 Execution Facility on pSeries. 4855 4856 swapaccount=[0|1] 4857 [KNL] Enable accounting of swap in memory resource 4858 controller if no parameter or 1 is given or disable 4859 it if 0 is given (See Documentation/admin-guide/cgroup-v1/memory.rst) 4860 4861 swiotlb= [ARM,IA-64,PPC,MIPS,X86] 4862 Format: { <int> | force | noforce } 4863 <int> -- Number of I/O TLB slabs 4864 force -- force using of bounce buffers even if they 4865 wouldn't be automatically used by the kernel 4866 noforce -- Never use bounce buffers (for debugging) 4867 4868 switches= [HW,M68k] 4869 4870 sysfs.deprecated=0|1 [KNL] 4871 Enable/disable old style sysfs layout for old udev 4872 on older distributions. When this option is enabled 4873 very new udev will not work anymore. When this option 4874 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled) 4875 in older udev will not work anymore. 4876 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in 4877 the kernel configuration. 4878 4879 sysrq_always_enabled 4880 [KNL] 4881 Ignore sysrq setting - this boot parameter will 4882 neutralize any effect of /proc/sys/kernel/sysrq. 4883 Useful for debugging. 4884 4885 tcpmhash_entries= [KNL,NET] 4886 Set the number of tcp_metrics_hash slots. 4887 Default value is 8192 or 16384 depending on total 4888 ram pages. This is used to specify the TCP metrics 4889 cache size. See Documentation/networking/ip-sysctl.txt 4890 "tcp_no_metrics_save" section for more details. 4891 4892 tdfx= [HW,DRM] 4893 4894 test_suspend= [SUSPEND][,N] 4895 Specify "mem" (for Suspend-to-RAM) or "standby" (for 4896 standby suspend) or "freeze" (for suspend type freeze) 4897 as the system sleep state during system startup with 4898 the optional capability to repeat N number of times. 4899 The system is woken from this state using a 4900 wakeup-capable RTC alarm. 4901 4902 thash_entries= [KNL,NET] 4903 Set number of hash buckets for TCP connection 4904 4905 thermal.act= [HW,ACPI] 4906 -1: disable all active trip points in all thermal zones 4907 <degrees C>: override all lowest active trip points 4908 4909 thermal.crt= [HW,ACPI] 4910 -1: disable all critical trip points in all thermal zones 4911 <degrees C>: override all critical trip points 4912 4913 thermal.nocrt= [HW,ACPI] 4914 Set to disable actions on ACPI thermal zone 4915 critical and hot trip points. 4916 4917 thermal.off= [HW,ACPI] 4918 1: disable ACPI thermal control 4919 4920 thermal.psv= [HW,ACPI] 4921 -1: disable all passive trip points 4922 <degrees C>: override all passive trip points to this 4923 value 4924 4925 thermal.tzp= [HW,ACPI] 4926 Specify global default ACPI thermal zone polling rate 4927 <deci-seconds>: poll all this frequency 4928 0: no polling (default) 4929 4930 threadirqs [KNL] 4931 Force threading of all interrupt handlers except those 4932 marked explicitly IRQF_NO_THREAD. 4933 4934 topology= [S390] 4935 Format: {off | on} 4936 Specify if the kernel should make use of the cpu 4937 topology information if the hardware supports this. 4938 The scheduler will make use of this information and 4939 e.g. base its process migration decisions on it. 4940 Default is on. 4941 4942 topology_updates= [KNL, PPC, NUMA] 4943 Format: {off} 4944 Specify if the kernel should ignore (off) 4945 topology updates sent by the hypervisor to this 4946 LPAR. 4947 4948 tp720= [HW,PS2] 4949 4950 tpm_suspend_pcr=[HW,TPM] 4951 Format: integer pcr id 4952 Specify that at suspend time, the tpm driver 4953 should extend the specified pcr with zeros, 4954 as a workaround for some chips which fail to 4955 flush the last written pcr on TPM_SaveState. 4956 This will guarantee that all the other pcrs 4957 are saved. 4958 4959 trace_buf_size=nn[KMG] 4960 [FTRACE] will set tracing buffer size on each cpu. 4961 4962 trace_event=[event-list] 4963 [FTRACE] Set and start specified trace events in order 4964 to facilitate early boot debugging. The event-list is a 4965 comma separated list of trace events to enable. See 4966 also Documentation/trace/events.rst 4967 4968 trace_options=[option-list] 4969 [FTRACE] Enable or disable tracer options at boot. 4970 The option-list is a comma delimited list of options 4971 that can be enabled or disabled just as if you were 4972 to echo the option name into 4973 4974 /sys/kernel/debug/tracing/trace_options 4975 4976 For example, to enable stacktrace option (to dump the 4977 stack trace of each event), add to the command line: 4978 4979 trace_options=stacktrace 4980 4981 See also Documentation/trace/ftrace.rst "trace options" 4982 section. 4983 4984 tp_printk[FTRACE] 4985 Have the tracepoints sent to printk as well as the 4986 tracing ring buffer. This is useful for early boot up 4987 where the system hangs or reboots and does not give the 4988 option for reading the tracing buffer or performing a 4989 ftrace_dump_on_oops. 4990 4991 To turn off having tracepoints sent to printk, 4992 echo 0 > /proc/sys/kernel/tracepoint_printk 4993 Note, echoing 1 into this file without the 4994 tracepoint_printk kernel cmdline option has no effect. 4995 4996 ** CAUTION ** 4997 4998 Having tracepoints sent to printk() and activating high 4999 frequency tracepoints such as irq or sched, can cause 5000 the system to live lock. 5001 5002 traceoff_on_warning 5003 [FTRACE] enable this option to disable tracing when a 5004 warning is hit. This turns off "tracing_on". Tracing can 5005 be enabled again by echoing '1' into the "tracing_on" 5006 file located in /sys/kernel/debug/tracing/ 5007 5008 This option is useful, as it disables the trace before 5009 the WARNING dump is called, which prevents the trace to 5010 be filled with content caused by the warning output. 5011 5012 This option can also be set at run time via the sysctl 5013 option: kernel/traceoff_on_warning 5014 5015 transparent_hugepage= 5016 [KNL] 5017 Format: [always|madvise|never] 5018 Can be used to control the default behavior of the system 5019 with respect to transparent hugepages. 5020 See Documentation/admin-guide/mm/transhuge.rst 5021 for more details. 5022 5023 tsc= Disable clocksource stability checks for TSC. 5024 Format: <string> 5025 [x86] reliable: mark tsc clocksource as reliable, this 5026 disables clocksource verification at runtime, as well 5027 as the stability checks done at bootup. Used to enable 5028 high-resolution timer mode on older hardware, and in 5029 virtualized environment. 5030 [x86] noirqtime: Do not use TSC to do irq accounting. 5031 Used to run time disable IRQ_TIME_ACCOUNTING on any 5032 platforms where RDTSC is slow and this accounting 5033 can add overhead. 5034 [x86] unstable: mark the TSC clocksource as unstable, this 5035 marks the TSC unconditionally unstable at bootup and 5036 avoids any further wobbles once the TSC watchdog notices. 5037 [x86] nowatchdog: disable clocksource watchdog. Used 5038 in situations with strict latency requirements (where 5039 interruptions from clocksource watchdog are not 5040 acceptable). 5041 5042 tsx= [X86] Control Transactional Synchronization 5043 Extensions (TSX) feature in Intel processors that 5044 support TSX control. 5045 5046 This parameter controls the TSX feature. The options are: 5047 5048 on - Enable TSX on the system. Although there are 5049 mitigations for all known security vulnerabilities, 5050 TSX has been known to be an accelerator for 5051 several previous speculation-related CVEs, and 5052 so there may be unknown security risks associated 5053 with leaving it enabled. 5054 5055 off - Disable TSX on the system. (Note that this 5056 option takes effect only on newer CPUs which are 5057 not vulnerable to MDS, i.e., have 5058 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get 5059 the new IA32_TSX_CTRL MSR through a microcode 5060 update. This new MSR allows for the reliable 5061 deactivation of the TSX functionality.) 5062 5063 auto - Disable TSX if X86_BUG_TAA is present, 5064 otherwise enable TSX on the system. 5065 5066 Not specifying this option is equivalent to tsx=off. 5067 5068 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 5069 for more details. 5070 5071 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async 5072 Abort (TAA) vulnerability. 5073 5074 Similar to Micro-architectural Data Sampling (MDS) 5075 certain CPUs that support Transactional 5076 Synchronization Extensions (TSX) are vulnerable to an 5077 exploit against CPU internal buffers which can forward 5078 information to a disclosure gadget under certain 5079 conditions. 5080 5081 In vulnerable processors, the speculatively forwarded 5082 data can be used in a cache side channel attack, to 5083 access data to which the attacker does not have direct 5084 access. 5085 5086 This parameter controls the TAA mitigation. The 5087 options are: 5088 5089 full - Enable TAA mitigation on vulnerable CPUs 5090 if TSX is enabled. 5091 5092 full,nosmt - Enable TAA mitigation and disable SMT on 5093 vulnerable CPUs. If TSX is disabled, SMT 5094 is not disabled because CPU is not 5095 vulnerable to cross-thread TAA attacks. 5096 off - Unconditionally disable TAA mitigation 5097 5098 On MDS-affected machines, tsx_async_abort=off can be 5099 prevented by an active MDS mitigation as both vulnerabilities 5100 are mitigated with the same mechanism so in order to disable 5101 this mitigation, you need to specify mds=off too. 5102 5103 Not specifying this option is equivalent to 5104 tsx_async_abort=full. On CPUs which are MDS affected 5105 and deploy MDS mitigation, TAA mitigation is not 5106 required and doesn't provide any additional 5107 mitigation. 5108 5109 For details see: 5110 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 5111 5112 turbografx.map[2|3]= [HW,JOY] 5113 TurboGraFX parallel port interface 5114 Format: 5115 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 5116 See also Documentation/input/devices/joystick-parport.rst 5117 5118 udbg-immortal [PPC] When debugging early kernel crashes that 5119 happen after console_init() and before a proper 5120 console driver takes over, this boot options might 5121 help "seeing" what's going on. 5122 5123 uhash_entries= [KNL,NET] 5124 Set number of hash buckets for UDP/UDP-Lite connections 5125 5126 uhci-hcd.ignore_oc= 5127 [USB] Ignore overcurrent events (default N). 5128 Some badly-designed motherboards generate lots of 5129 bogus events, for ports that aren't wired to 5130 anything. Set this parameter to avoid log spamming. 5131 Note that genuine overcurrent events won't be 5132 reported either. 5133 5134 unknown_nmi_panic 5135 [X86] Cause panic on unknown NMI. 5136 5137 usbcore.authorized_default= 5138 [USB] Default USB device authorization: 5139 (default -1 = authorized except for wireless USB, 5140 0 = not authorized, 1 = authorized, 2 = authorized 5141 if device connected to internal port) 5142 5143 usbcore.autosuspend= 5144 [USB] The autosuspend time delay (in seconds) used 5145 for newly-detected USB devices (default 2). This 5146 is the time required before an idle device will be 5147 autosuspended. Devices for which the delay is set 5148 to a negative value won't be autosuspended at all. 5149 5150 usbcore.usbfs_snoop= 5151 [USB] Set to log all usbfs traffic (default 0 = off). 5152 5153 usbcore.usbfs_snoop_max= 5154 [USB] Maximum number of bytes to snoop in each URB 5155 (default = 65536). 5156 5157 usbcore.blinkenlights= 5158 [USB] Set to cycle leds on hubs (default 0 = off). 5159 5160 usbcore.old_scheme_first= 5161 [USB] Start with the old device initialization 5162 scheme (default 0 = off). 5163 5164 usbcore.usbfs_memory_mb= 5165 [USB] Memory limit (in MB) for buffers allocated by 5166 usbfs (default = 16, 0 = max = 2047). 5167 5168 usbcore.use_both_schemes= 5169 [USB] Try the other device initialization scheme 5170 if the first one fails (default 1 = enabled). 5171 5172 usbcore.initial_descriptor_timeout= 5173 [USB] Specifies timeout for the initial 64-byte 5174 USB_REQ_GET_DESCRIPTOR request in milliseconds 5175 (default 5000 = 5.0 seconds). 5176 5177 usbcore.nousb [USB] Disable the USB subsystem 5178 5179 usbcore.quirks= 5180 [USB] A list of quirk entries to augment the built-in 5181 usb core quirk list. List entries are separated by 5182 commas. Each entry has the form 5183 VendorID:ProductID:Flags. The IDs are 4-digit hex 5184 numbers and Flags is a set of letters. Each letter 5185 will change the built-in quirk; setting it if it is 5186 clear and clearing it if it is set. The letters have 5187 the following meanings: 5188 a = USB_QUIRK_STRING_FETCH_255 (string 5189 descriptors must not be fetched using 5190 a 255-byte read); 5191 b = USB_QUIRK_RESET_RESUME (device can't resume 5192 correctly so reset it instead); 5193 c = USB_QUIRK_NO_SET_INTF (device can't handle 5194 Set-Interface requests); 5195 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't 5196 handle its Configuration or Interface 5197 strings); 5198 e = USB_QUIRK_RESET (device can't be reset 5199 (e.g morph devices), don't use reset); 5200 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has 5201 more interface descriptions than the 5202 bNumInterfaces count, and can't handle 5203 talking to these interfaces); 5204 g = USB_QUIRK_DELAY_INIT (device needs a pause 5205 during initialization, after we read 5206 the device descriptor); 5207 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For 5208 high speed and super speed interrupt 5209 endpoints, the USB 2.0 and USB 3.0 spec 5210 require the interval in microframes (1 5211 microframe = 125 microseconds) to be 5212 calculated as interval = 2 ^ 5213 (bInterval-1). 5214 Devices with this quirk report their 5215 bInterval as the result of this 5216 calculation instead of the exponent 5217 variable used in the calculation); 5218 i = USB_QUIRK_DEVICE_QUALIFIER (device can't 5219 handle device_qualifier descriptor 5220 requests); 5221 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device 5222 generates spurious wakeup, ignore 5223 remote wakeup capability); 5224 k = USB_QUIRK_NO_LPM (device can't handle Link 5225 Power Management); 5226 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL 5227 (Device reports its bInterval as linear 5228 frames instead of the USB 2.0 5229 calculation); 5230 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs 5231 to be disconnected before suspend to 5232 prevent spurious wakeup); 5233 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a 5234 pause after every control message); 5235 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra 5236 delay after resetting its port); 5237 Example: quirks=0781:5580:bk,0a5c:5834:gij 5238 5239 usbhid.mousepoll= 5240 [USBHID] The interval which mice are to be polled at. 5241 5242 usbhid.jspoll= 5243 [USBHID] The interval which joysticks are to be polled at. 5244 5245 usbhid.kbpoll= 5246 [USBHID] The interval which keyboards are to be polled at. 5247 5248 usb-storage.delay_use= 5249 [UMS] The delay in seconds before a new device is 5250 scanned for Logical Units (default 1). 5251 5252 usb-storage.quirks= 5253 [UMS] A list of quirks entries to supplement or 5254 override the built-in unusual_devs list. List 5255 entries are separated by commas. Each entry has 5256 the form VID:PID:Flags where VID and PID are Vendor 5257 and Product ID values (4-digit hex numbers) and 5258 Flags is a set of characters, each corresponding 5259 to a common usb-storage quirk flag as follows: 5260 a = SANE_SENSE (collect more than 18 bytes 5261 of sense data, not on uas); 5262 b = BAD_SENSE (don't collect more than 18 5263 bytes of sense data, not on uas); 5264 c = FIX_CAPACITY (decrease the reported 5265 device capacity by one sector); 5266 d = NO_READ_DISC_INFO (don't use 5267 READ_DISC_INFO command, not on uas); 5268 e = NO_READ_CAPACITY_16 (don't use 5269 READ_CAPACITY_16 command); 5270 f = NO_REPORT_OPCODES (don't use report opcodes 5271 command, uas only); 5272 g = MAX_SECTORS_240 (don't transfer more than 5273 240 sectors at a time, uas only); 5274 h = CAPACITY_HEURISTICS (decrease the 5275 reported device capacity by one 5276 sector if the number is odd); 5277 i = IGNORE_DEVICE (don't bind to this 5278 device); 5279 j = NO_REPORT_LUNS (don't use report luns 5280 command, uas only); 5281 k = NO_SAME (do not use WRITE_SAME, uas only) 5282 l = NOT_LOCKABLE (don't try to lock and 5283 unlock ejectable media, not on uas); 5284 m = MAX_SECTORS_64 (don't transfer more 5285 than 64 sectors = 32 KB at a time, 5286 not on uas); 5287 n = INITIAL_READ10 (force a retry of the 5288 initial READ(10) command, not on uas); 5289 o = CAPACITY_OK (accept the capacity 5290 reported by the device, not on uas); 5291 p = WRITE_CACHE (the device cache is ON 5292 by default, not on uas); 5293 r = IGNORE_RESIDUE (the device reports 5294 bogus residue values, not on uas); 5295 s = SINGLE_LUN (the device has only one 5296 Logical Unit); 5297 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 5298 commands, uas only); 5299 u = IGNORE_UAS (don't bind to the uas driver); 5300 w = NO_WP_DETECT (don't test whether the 5301 medium is write-protected). 5302 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 5303 even if the device claims no cache, 5304 not on uas) 5305 Example: quirks=0419:aaf5:rl,0421:0433:rc 5306 5307 user_debug= [KNL,ARM] 5308 Format: <int> 5309 See arch/arm/Kconfig.debug help text. 5310 1 - undefined instruction events 5311 2 - system calls 5312 4 - invalid data aborts 5313 8 - SIGSEGV faults 5314 16 - SIGBUS faults 5315 Example: user_debug=31 5316 5317 userpte= 5318 [X86] Flags controlling user PTE allocations. 5319 5320 nohigh = do not allocate PTE pages in 5321 HIGHMEM regardless of setting 5322 of CONFIG_HIGHPTE. 5323 5324 vdso= [X86,SH] 5325 On X86_32, this is an alias for vdso32=. Otherwise: 5326 5327 vdso=1: enable VDSO (the default) 5328 vdso=0: disable VDSO mapping 5329 5330 vdso32= [X86] Control the 32-bit vDSO 5331 vdso32=1: enable 32-bit VDSO 5332 vdso32=0 or vdso32=2: disable 32-bit VDSO 5333 5334 See the help text for CONFIG_COMPAT_VDSO for more 5335 details. If CONFIG_COMPAT_VDSO is set, the default is 5336 vdso32=0; otherwise, the default is vdso32=1. 5337 5338 For compatibility with older kernels, vdso32=2 is an 5339 alias for vdso32=0. 5340 5341 Try vdso32=0 if you encounter an error that says: 5342 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 5343 5344 vector= [IA-64,SMP] 5345 vector=percpu: enable percpu vector domain 5346 5347 video= [FB] Frame buffer configuration 5348 See Documentation/fb/modedb.rst. 5349 5350 video.brightness_switch_enabled= [0,1] 5351 If set to 1, on receiving an ACPI notify event 5352 generated by hotkey, video driver will adjust brightness 5353 level and then send out the event to user space through 5354 the allocated input device; If set to 0, video driver 5355 will only send out the event without touching backlight 5356 brightness level. 5357 default: 1 5358 5359 virtio_mmio.device= 5360 [VMMIO] Memory mapped virtio (platform) device. 5361 5362 <size>@<baseaddr>:<irq>[:<id>] 5363 where: 5364 <size> := size (can use standard suffixes 5365 like K, M and G) 5366 <baseaddr> := physical base address 5367 <irq> := interrupt number (as passed to 5368 request_irq()) 5369 <id> := (optional) platform device id 5370 example: 5371 virtio_mmio.device=1K@0x100b0000:48:7 5372 5373 Can be used multiple times for multiple devices. 5374 5375 vga= [BOOT,X86-32] Select a particular video mode 5376 See Documentation/x86/boot.rst and 5377 Documentation/admin-guide/svga.rst. 5378 Use vga=ask for menu. 5379 This is actually a boot loader parameter; the value is 5380 passed to the kernel using a special protocol. 5381 5382 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. 5383 May slow down system boot speed, especially when 5384 enabled on systems with a large amount of memory. 5385 All options are enabled by default, and this 5386 interface is meant to allow for selectively 5387 enabling or disabling specific virtual memory 5388 debugging features. 5389 5390 Available options are: 5391 P Enable page structure init time poisoning 5392 - Disable all of the above options 5393 5394 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact 5395 size of <nn>. This can be used to increase the 5396 minimum size (128MB on x86). It can also be used to 5397 decrease the size and leave more room for directly 5398 mapped kernel RAM. 5399 5400 vmcp_cma=nn[MG] [KNL,S390] 5401 Sets the memory size reserved for contiguous memory 5402 allocations for the vmcp device driver. 5403 5404 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 5405 Format: <command> 5406 5407 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 5408 Format: <command> 5409 5410 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 5411 Format: <command> 5412 5413 vsyscall= [X86-64] 5414 Controls the behavior of vsyscalls (i.e. calls to 5415 fixed addresses of 0xffffffffff600x00 from legacy 5416 code). Most statically-linked binaries and older 5417 versions of glibc use these calls. Because these 5418 functions are at fixed addresses, they make nice 5419 targets for exploits that can control RIP. 5420 5421 emulate [default] Vsyscalls turn into traps and are 5422 emulated reasonably safely. The vsyscall 5423 page is readable. 5424 5425 xonly Vsyscalls turn into traps and are 5426 emulated reasonably safely. The vsyscall 5427 page is not readable. 5428 5429 none Vsyscalls don't work at all. This makes 5430 them quite hard to use for exploits but 5431 might break your system. 5432 5433 vt.color= [VT] Default text color. 5434 Format: 0xYX, X = foreground, Y = background. 5435 Default: 0x07 = light gray on black. 5436 5437 vt.cur_default= [VT] Default cursor shape. 5438 Format: 0xCCBBAA, where AA, BB, and CC are the same as 5439 the parameters of the <Esc>[?A;B;Cc escape sequence; 5440 see VGA-softcursor.txt. Default: 2 = underline. 5441 5442 vt.default_blu= [VT] 5443 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 5444 Change the default blue palette of the console. 5445 This is a 16-member array composed of values 5446 ranging from 0-255. 5447 5448 vt.default_grn= [VT] 5449 Format: <green0>,<green1>,<green2>,...,<green15> 5450 Change the default green palette of the console. 5451 This is a 16-member array composed of values 5452 ranging from 0-255. 5453 5454 vt.default_red= [VT] 5455 Format: <red0>,<red1>,<red2>,...,<red15> 5456 Change the default red palette of the console. 5457 This is a 16-member array composed of values 5458 ranging from 0-255. 5459 5460 vt.default_utf8= 5461 [VT] 5462 Format=<0|1> 5463 Set system-wide default UTF-8 mode for all tty's. 5464 Default is 1, i.e. UTF-8 mode is enabled for all 5465 newly opened terminals. 5466 5467 vt.global_cursor_default= 5468 [VT] 5469 Format=<-1|0|1> 5470 Set system-wide default for whether a cursor 5471 is shown on new VTs. Default is -1, 5472 i.e. cursors will be created by default unless 5473 overridden by individual drivers. 0 will hide 5474 cursors, 1 will display them. 5475 5476 vt.italic= [VT] Default color for italic text; 0-15. 5477 Default: 2 = green. 5478 5479 vt.underline= [VT] Default color for underlined text; 0-15. 5480 Default: 3 = cyan. 5481 5482 watchdog timers [HW,WDT] For information on watchdog timers, 5483 see Documentation/watchdog/watchdog-parameters.rst 5484 or other driver-specific files in the 5485 Documentation/watchdog/ directory. 5486 5487 watchdog_thresh= 5488 [KNL] 5489 Set the hard lockup detector stall duration 5490 threshold in seconds. The soft lockup detector 5491 threshold is set to twice the value. A value of 0 5492 disables both lockup detectors. Default is 10 5493 seconds. 5494 5495 workqueue.watchdog_thresh= 5496 If CONFIG_WQ_WATCHDOG is configured, workqueue can 5497 warn stall conditions and dump internal state to 5498 help debugging. 0 disables workqueue stall 5499 detection; otherwise, it's the stall threshold 5500 duration in seconds. The default value is 30 and 5501 it can be updated at runtime by writing to the 5502 corresponding sysfs file. 5503 5504 workqueue.disable_numa 5505 By default, all work items queued to unbound 5506 workqueues are affine to the NUMA nodes they're 5507 issued on, which results in better behavior in 5508 general. If NUMA affinity needs to be disabled for 5509 whatever reason, this option can be used. Note 5510 that this also can be controlled per-workqueue for 5511 workqueues visible under /sys/bus/workqueue/. 5512 5513 workqueue.power_efficient 5514 Per-cpu workqueues are generally preferred because 5515 they show better performance thanks to cache 5516 locality; unfortunately, per-cpu workqueues tend to 5517 be more power hungry than unbound workqueues. 5518 5519 Enabling this makes the per-cpu workqueues which 5520 were observed to contribute significantly to power 5521 consumption unbound, leading to measurably lower 5522 power usage at the cost of small performance 5523 overhead. 5524 5525 The default value of this parameter is determined by 5526 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 5527 5528 workqueue.debug_force_rr_cpu 5529 Workqueue used to implicitly guarantee that work 5530 items queued without explicit CPU specified are put 5531 on the local CPU. This guarantee is no longer true 5532 and while local CPU is still preferred work items 5533 may be put on foreign CPUs. This debug option 5534 forces round-robin CPU selection to flush out 5535 usages which depend on the now broken guarantee. 5536 When enabled, memory and cache locality will be 5537 impacted. 5538 5539 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of 5540 default x2apic cluster mode on platforms 5541 supporting x2apic. 5542 5543 x86_intel_mid_timer= [X86-32,APBT] 5544 Choose timer option for x86 Intel MID platform. 5545 Two valid options are apbt timer only and lapic timer 5546 plus one apbt timer for broadcast timer. 5547 x86_intel_mid_timer=apbt_only | lapic_and_apbt 5548 5549 xen_512gb_limit [KNL,X86-64,XEN] 5550 Restricts the kernel running paravirtualized under Xen 5551 to use only up to 512 GB of RAM. The reason to do so is 5552 crash analysis tools and Xen tools for doing domain 5553 save/restore/migration must be enabled to handle larger 5554 domains. 5555 5556 xen_emul_unplug= [HW,X86,XEN] 5557 Unplug Xen emulated devices 5558 Format: [unplug0,][unplug1] 5559 ide-disks -- unplug primary master IDE devices 5560 aux-ide-disks -- unplug non-primary-master IDE devices 5561 nics -- unplug network devices 5562 all -- unplug all emulated devices (NICs and IDE disks) 5563 unnecessary -- unplugging emulated devices is 5564 unnecessary even if the host did not respond to 5565 the unplug protocol 5566 never -- do not unplug even if version check succeeds 5567 5568 xen_legacy_crash [X86,XEN] 5569 Crash from Xen panic notifier, without executing late 5570 panic() code such as dumping handler. 5571 5572 xen_nopvspin [X86,XEN] 5573 Disables the ticketlock slowpath using Xen PV 5574 optimizations. 5575 5576 xen_nopv [X86] 5577 Disables the PV optimizations forcing the HVM guest to 5578 run as generic HVM guest with no PV drivers. 5579 This option is obsoleted by the "nopv" option, which 5580 has equivalent effect for XEN platform. 5581 5582 xen_no_vector_callback 5583 [KNL,X86,XEN] Disable the vector callback for Xen 5584 event channel interrupts. 5585 5586 xen_scrub_pages= [XEN] 5587 Boolean option to control scrubbing pages before giving them back 5588 to Xen, for use by other domains. Can be also changed at runtime 5589 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. 5590 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. 5591 5592 xen_timer_slop= [X86-64,XEN] 5593 Set the timer slop (in nanoseconds) for the virtual Xen 5594 timers (default is 100000). This adjusts the minimum 5595 delta of virtualized Xen timers, where lower values 5596 improve timer resolution at the expense of processing 5597 more timer interrupts. 5598 5599 nopv= [X86,XEN,KVM,HYPER_V,VMWARE] 5600 Disables the PV optimizations forcing the guest to run 5601 as generic guest with no PV drivers. Currently support 5602 XEN HVM, KVM, HYPER_V and VMWARE guest. 5603 5604 xen.balloon_boot_timeout= [XEN] 5605 The time (in seconds) to wait before giving up to boot 5606 in case initial ballooning fails to free enough memory. 5607 Applies only when running as HVM or PVH guest and 5608 started with less memory configured than allowed at 5609 max. Default is 180. 5610 5611 xen.event_eoi_delay= [XEN] 5612 How long to delay EOI handling in case of event 5613 storms (jiffies). Default is 10. 5614 5615 xen.event_loop_timeout= [XEN] 5616 After which time (jiffies) the event handling loop 5617 should start to delay EOI handling. Default is 2. 5618 5619 xirc2ps_cs= [NET,PCMCIA] 5620 Format: 5621 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 5622 5623 xive= [PPC] 5624 By default on POWER9 and above, the kernel will 5625 natively use the XIVE interrupt controller. This option 5626 allows the fallback firmware mode to be used: 5627 5628 off Fallback to firmware control of XIVE interrupt 5629 controller on both pseries and powernv 5630 platforms. Only useful on POWER9 and above. 5631 5632 xhci-hcd.quirks [USB,KNL] 5633 A hex value specifying bitmask with supplemental xhci 5634 host controller quirks. Meaning of each bit can be 5635 consulted in header drivers/usb/host/xhci.h. 5636 5637 xmon [PPC] 5638 Format: { early | on | rw | ro | off } 5639 Controls if xmon debugger is enabled. Default is off. 5640 Passing only "xmon" is equivalent to "xmon=early". 5641 early Call xmon as early as possible on boot; xmon 5642 debugger is called from setup_arch(). 5643 on xmon debugger hooks will be installed so xmon 5644 is only called on a kernel crash. Default mode, 5645 i.e. either "ro" or "rw" mode, is controlled 5646 with CONFIG_XMON_DEFAULT_RO_MODE. 5647 rw xmon debugger hooks will be installed so xmon 5648 is called only on a kernel crash, mode is write, 5649 meaning SPR registers, memory and, other data 5650 can be written using xmon commands. 5651 ro same as "rw" option above but SPR registers, 5652 memory, and other data can't be written using 5653 xmon commands. 5654 off xmon is disabled. 5655