1 Kernel Parameters 2 ~~~~~~~~~~~~~~~~~ 3 4The following is a consolidated list of the kernel parameters as 5implemented by the __setup(), core_param() and module_param() macros 6and sorted into English Dictionary order (defined as ignoring all 7punctuation and sorting digits before letters in a case insensitive 8manner), and with descriptions where known. 9 10The kernel parses parameters from the kernel command line up to "--"; 11if it doesn't recognize a parameter and it doesn't contain a '.', the 12parameter gets passed to init: parameters with '=' go into init's 13environment, others are passed as command line arguments to init. 14Everything after "--" is passed as an argument to init. 15 16Module parameters can be specified in two ways: via the kernel command 17line with a module name prefix, or via modprobe, e.g.: 18 19 (kernel command line) usbcore.blinkenlights=1 20 (modprobe command line) modprobe usbcore blinkenlights=1 21 22Parameters for modules which are built into the kernel need to be 23specified on the kernel command line. modprobe looks through the 24kernel command line (/proc/cmdline) and collects module parameters 25when it loads a module, so the kernel command line can be used for 26loadable modules too. 27 28Hyphens (dashes) and underscores are equivalent in parameter names, so 29 log_buf_len=1M print-fatal-signals=1 30can also be entered as 31 log-buf-len=1M print_fatal_signals=1 32 33Double-quotes can be used to protect spaces in values, e.g.: 34 param="spaces in here" 35 36This document may not be entirely up to date and comprehensive. The command 37"modinfo -p ${modulename}" shows a current list of all parameters of a loadable 38module. Loadable modules, after being loaded into the running kernel, also 39reveal their parameters in /sys/module/${modulename}/parameters/. Some of these 40parameters may be changed at runtime by the command 41"echo -n ${value} > /sys/module/${modulename}/parameters/${parm}". 42 43The parameters listed below are only valid if certain kernel build options were 44enabled and if respective hardware is present. The text in square brackets at 45the beginning of each description states the restrictions within which a 46parameter is applicable: 47 48 ACPI ACPI support is enabled. 49 AGP AGP (Accelerated Graphics Port) is enabled. 50 ALSA ALSA sound support is enabled. 51 APIC APIC support is enabled. 52 APM Advanced Power Management support is enabled. 53 ARM ARM architecture is enabled. 54 AVR32 AVR32 architecture is enabled. 55 AX25 Appropriate AX.25 support is enabled. 56 BLACKFIN Blackfin architecture is enabled. 57 CLK Common clock infrastructure is enabled. 58 CMA Contiguous Memory Area support is enabled. 59 DM Device mapper support is enabled. 60 DRM Direct Rendering Management support is enabled. 61 DYNAMIC_DEBUG Build in debug messages and enable them at runtime 62 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled 63 EFI EFI Partitioning (GPT) is enabled 64 EIDE EIDE/ATAPI support is enabled. 65 EVM Extended Verification Module 66 FB The frame buffer device is enabled. 67 FTRACE Function tracing enabled. 68 GCOV GCOV profiling is enabled. 69 HW Appropriate hardware is enabled. 70 IA-64 IA-64 architecture is enabled. 71 IMA Integrity measurement architecture is enabled. 72 IOSCHED More than one I/O scheduler is enabled. 73 IP_PNP IP DHCP, BOOTP, or RARP is enabled. 74 IPV6 IPv6 support is enabled. 75 ISAPNP ISA PnP code is enabled. 76 ISDN Appropriate ISDN support is enabled. 77 JOY Appropriate joystick support is enabled. 78 KGDB Kernel debugger support is enabled. 79 KVM Kernel Virtual Machine support is enabled. 80 LIBATA Libata driver is enabled 81 LP Printer support is enabled. 82 LOOP Loopback device support is enabled. 83 M68k M68k architecture is enabled. 84 These options have more detailed description inside of 85 Documentation/m68k/kernel-options.txt. 86 MDA MDA console support is enabled. 87 MIPS MIPS architecture is enabled. 88 MOUSE Appropriate mouse support is enabled. 89 MSI Message Signaled Interrupts (PCI). 90 MTD MTD (Memory Technology Device) support is enabled. 91 NET Appropriate network support is enabled. 92 NUMA NUMA support is enabled. 93 NFS Appropriate NFS support is enabled. 94 OSS OSS sound support is enabled. 95 PV_OPS A paravirtualized kernel is enabled. 96 PARIDE The ParIDE (parallel port IDE) subsystem is enabled. 97 PARISC The PA-RISC architecture is enabled. 98 PCI PCI bus support is enabled. 99 PCIE PCI Express support is enabled. 100 PCMCIA The PCMCIA subsystem is enabled. 101 PNP Plug & Play support is enabled. 102 PPC PowerPC architecture is enabled. 103 PPT Parallel port support is enabled. 104 PS2 Appropriate PS/2 support is enabled. 105 RAM RAM disk support is enabled. 106 S390 S390 architecture is enabled. 107 SCSI Appropriate SCSI support is enabled. 108 A lot of drivers have their options described inside 109 the Documentation/scsi/ sub-directory. 110 SECURITY Different security models are enabled. 111 SELINUX SELinux support is enabled. 112 APPARMOR AppArmor support is enabled. 113 SERIAL Serial support is enabled. 114 SH SuperH architecture is enabled. 115 SMP The kernel is an SMP kernel. 116 SPARC Sparc architecture is enabled. 117 SWSUSP Software suspend (hibernation) is enabled. 118 SUSPEND System suspend states are enabled. 119 TPM TPM drivers are enabled. 120 TS Appropriate touchscreen support is enabled. 121 UMS USB Mass Storage support is enabled. 122 USB USB support is enabled. 123 USBHID USB Human Interface Device support is enabled. 124 V4L Video For Linux support is enabled. 125 VMMIO Driver for memory mapped virtio devices is enabled. 126 VGA The VGA console has been enabled. 127 VT Virtual terminal support is enabled. 128 WDT Watchdog support is enabled. 129 XT IBM PC/XT MFM hard disk support is enabled. 130 X86-32 X86-32, aka i386 architecture is enabled. 131 X86-64 X86-64 architecture is enabled. 132 More X86-64 boot options can be found in 133 Documentation/x86/x86_64/boot-options.txt . 134 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64) 135 XEN Xen support is enabled 136 137In addition, the following text indicates that the option: 138 139 BUGS= Relates to possible processor bugs on the said processor. 140 KNL Is a kernel start-up parameter. 141 BOOT Is a boot loader parameter. 142 143Parameters denoted with BOOT are actually interpreted by the boot 144loader, and have no meaning to the kernel directly. 145Do not modify the syntax of boot loader parameters without extreme 146need or coordination with <Documentation/x86/boot.txt>. 147 148There are also arch-specific kernel-parameters not documented here. 149See for example <Documentation/x86/x86_64/boot-options.txt>. 150 151Note that ALL kernel parameters listed below are CASE SENSITIVE, and that 152a trailing = on the name of any parameter states that that parameter will 153be entered as an environment variable, whereas its absence indicates that 154it will appear as a kernel argument readable via /proc/cmdline by programs 155running once the system is up. 156 157The number of kernel parameters is not limited, but the length of the 158complete command line (parameters including spaces etc.) is limited to 159a fixed number of characters. This limit depends on the architecture 160and is between 256 and 4096 characters. It is defined in the file 161./include/asm/setup.h as COMMAND_LINE_SIZE. 162 163Finally, the [KMG] suffix is commonly described after a number of kernel 164parameter values. These 'K', 'M', and 'G' letters represent the _binary_ 165multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30 166bytes respectively. Such letter suffixes can also be entirely omitted. 167 168 169 acpi= [HW,ACPI,X86,ARM64] 170 Advanced Configuration and Power Interface 171 Format: { force | off | strict | noirq | rsdt | 172 copy_dsdt } 173 force -- enable ACPI if default was off 174 off -- disable ACPI if default was on 175 noirq -- do not use ACPI for IRQ routing 176 strict -- Be less tolerant of platforms that are not 177 strictly ACPI specification compliant. 178 rsdt -- prefer RSDT over (default) XSDT 179 copy_dsdt -- copy DSDT to memory 180 For ARM64, ONLY "acpi=off" or "acpi=force" are available 181 182 See also Documentation/power/runtime_pm.txt, pci=noacpi 183 184 acpi_apic_instance= [ACPI, IOAPIC] 185 Format: <int> 186 2: use 2nd APIC table, if available 187 1,0: use 1st APIC table 188 default: 0 189 190 acpi_backlight= [HW,ACPI] 191 acpi_backlight=vendor 192 acpi_backlight=video 193 If set to vendor, prefer vendor specific driver 194 (e.g. thinkpad_acpi, sony_acpi, etc.) instead 195 of the ACPI video.ko driver. 196 197 acpica_no_return_repair [HW, ACPI] 198 Disable AML predefined validation mechanism 199 This mechanism can repair the evaluation result to make 200 the return objects more ACPI specification compliant. 201 This option is useful for developers to identify the 202 root cause of an AML interpreter issue when the issue 203 has something to do with the repair mechanism. 204 205 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG] 206 acpi.debug_level= [HW,ACPI,ACPI_DEBUG] 207 Format: <int> 208 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI 209 debug output. Bits in debug_layer correspond to a 210 _COMPONENT in an ACPI source file, e.g., 211 #define _COMPONENT ACPI_PCI_COMPONENT 212 Bits in debug_level correspond to a level in 213 ACPI_DEBUG_PRINT statements, e.g., 214 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ... 215 The debug_level mask defaults to "info". See 216 Documentation/acpi/debug.txt for more information about 217 debug layers and levels. 218 219 Enable processor driver info messages: 220 acpi.debug_layer=0x20000000 221 Enable PCI/PCI interrupt routing info messages: 222 acpi.debug_layer=0x400000 223 Enable AML "Debug" output, i.e., stores to the Debug 224 object while interpreting AML: 225 acpi.debug_layer=0xffffffff acpi.debug_level=0x2 226 Enable all messages related to ACPI hardware: 227 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff 228 229 Some values produce so much output that the system is 230 unusable. The "log_buf_len" parameter may be useful 231 if you need to capture more output. 232 233 acpi_enforce_resources= [ACPI] 234 { strict | lax | no } 235 Check for resource conflicts between native drivers 236 and ACPI OperationRegions (SystemIO and SystemMemory 237 only). IO ports and memory declared in ACPI might be 238 used by the ACPI subsystem in arbitrary AML code and 239 can interfere with legacy drivers. 240 strict (default): access to resources claimed by ACPI 241 is denied; legacy drivers trying to access reserved 242 resources will fail to bind to device using them. 243 lax: access to resources claimed by ACPI is allowed; 244 legacy drivers trying to access reserved resources 245 will bind successfully but a warning message is logged. 246 no: ACPI OperationRegions are not marked as reserved, 247 no further checks are performed. 248 249 acpi_force_table_verification [HW,ACPI] 250 Enable table checksum verification during early stage. 251 By default, this is disabled due to x86 early mapping 252 size limitation. 253 254 acpi_irq_balance [HW,ACPI] 255 ACPI will balance active IRQs 256 default in APIC mode 257 258 acpi_irq_nobalance [HW,ACPI] 259 ACPI will not move active IRQs (default) 260 default in PIC mode 261 262 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA 263 Format: <irq>,<irq>... 264 265 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for 266 use by PCI 267 Format: <irq>,<irq>... 268 269 acpi_no_auto_serialize [HW,ACPI] 270 Disable auto-serialization of AML methods 271 AML control methods that contain the opcodes to create 272 named objects will be marked as "Serialized" by the 273 auto-serialization feature. 274 This feature is enabled by default. 275 This option allows to turn off the feature. 276 277 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump 278 kernels. 279 280 acpi_no_static_ssdt [HW,ACPI] 281 Disable installation of static SSDTs at early boot time 282 By default, SSDTs contained in the RSDT/XSDT will be 283 installed automatically and they will appear under 284 /sys/firmware/acpi/tables. 285 This option turns off this feature. 286 Note that specifying this option does not affect 287 dynamic table installation which will install SSDT 288 tables to /sys/firmware/acpi/tables/dynamic. 289 290 acpi_rsdp= [ACPI,EFI,KEXEC] 291 Pass the RSDP address to the kernel, mostly used 292 on machines running EFI runtime service to boot the 293 second kernel for kdump. 294 295 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS 296 Format: To spoof as Windows 98: ="Microsoft Windows" 297 298 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead 299 of 2 which is mandated by ACPI 6) as the supported ACPI 300 specification revision (when using this switch, it may 301 be necessary to carry out a cold reboot _twice_ in a 302 row to make it take effect on the platform firmware). 303 304 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings 305 acpi_osi="string1" # add string1 306 acpi_osi="!string2" # remove string2 307 acpi_osi=!* # remove all strings 308 acpi_osi=! # disable all built-in OS vendor 309 strings 310 acpi_osi= # disable all strings 311 312 'acpi_osi=!' can be used in combination with single or 313 multiple 'acpi_osi="string1"' to support specific OS 314 vendor string(s). Note that such command can only 315 affect the default state of the OS vendor strings, thus 316 it cannot affect the default state of the feature group 317 strings and the current state of the OS vendor strings, 318 specifying it multiple times through kernel command line 319 is meaningless. This command is useful when one do not 320 care about the state of the feature group strings which 321 should be controlled by the OSPM. 322 Examples: 323 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent 324 to 'acpi_osi="Windows 2000" acpi_osi=!', they all 325 can make '_OSI("Windows 2000")' TRUE. 326 327 'acpi_osi=' cannot be used in combination with other 328 'acpi_osi=' command lines, the _OSI method will not 329 exist in the ACPI namespace. NOTE that such command can 330 only affect the _OSI support state, thus specifying it 331 multiple times through kernel command line is also 332 meaningless. 333 Examples: 334 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)' 335 FALSE. 336 337 'acpi_osi=!*' can be used in combination with single or 338 multiple 'acpi_osi="string1"' to support specific 339 string(s). Note that such command can affect the 340 current state of both the OS vendor strings and the 341 feature group strings, thus specifying it multiple times 342 through kernel command line is meaningful. But it may 343 still not able to affect the final state of a string if 344 there are quirks related to this string. This command 345 is useful when one want to control the state of the 346 feature group strings to debug BIOS issues related to 347 the OSPM features. 348 Examples: 349 1. 'acpi_osi="Module Device" acpi_osi=!*' can make 350 '_OSI("Module Device")' FALSE. 351 2. 'acpi_osi=!* acpi_osi="Module Device"' can make 352 '_OSI("Module Device")' TRUE. 353 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is 354 equivalent to 355 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"' 356 and 357 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!', 358 they all will make '_OSI("Windows 2000")' TRUE. 359 360 acpi_pm_good [X86] 361 Override the pmtimer bug detection: force the kernel 362 to assume that this machine's pmtimer latches its value 363 and always returns good values. 364 365 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode 366 Format: { level | edge | high | low } 367 368 acpi_skip_timer_override [HW,ACPI] 369 Recognize and ignore IRQ0/pin2 Interrupt Override. 370 For broken nForce2 BIOS resulting in XT-PIC timer. 371 372 acpi_sleep= [HW,ACPI] Sleep options 373 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig, 374 old_ordering, nonvs, sci_force_enable } 375 See Documentation/power/video.txt for information on 376 s3_bios and s3_mode. 377 s3_beep is for debugging; it makes the PC's speaker beep 378 as soon as the kernel's real-mode entry point is called. 379 s4_nohwsig prevents ACPI hardware signature from being 380 used during resume from hibernation. 381 old_ordering causes the ACPI 1.0 ordering of the _PTS 382 control method, with respect to putting devices into 383 low power states, to be enforced (the ACPI 2.0 ordering 384 of _PTS is used by default). 385 nonvs prevents the kernel from saving/restoring the 386 ACPI NVS memory during suspend/hibernation and resume. 387 sci_force_enable causes the kernel to set SCI_EN directly 388 on resume from S1/S3 (which is against the ACPI spec, 389 but some broken systems don't work without it). 390 391 acpi_use_timer_override [HW,ACPI] 392 Use timer override. For some broken Nvidia NF5 boards 393 that require a timer override, but don't have HPET 394 395 add_efi_memmap [EFI; X86] Include EFI memory map in 396 kernel's map of available physical RAM. 397 398 agp= [AGP] 399 { off | try_unsupported } 400 off: disable AGP support 401 try_unsupported: try to drive unsupported chipsets 402 (may crash computer or cause data corruption) 403 404 ALSA [HW,ALSA] 405 See Documentation/sound/alsa/alsa-parameters.txt 406 407 alignment= [KNL,ARM] 408 Allow the default userspace alignment fault handler 409 behaviour to be specified. Bit 0 enables warnings, 410 bit 1 enables fixups, and bit 2 sends a segfault. 411 412 align_va_addr= [X86-64] 413 Align virtual addresses by clearing slice [14:12] when 414 allocating a VMA at process creation time. This option 415 gives you up to 3% performance improvement on AMD F15h 416 machines (where it is enabled by default) for a 417 CPU-intensive style benchmark, and it can vary highly in 418 a microbenchmark depending on workload and compiler. 419 420 32: only for 32-bit processes 421 64: only for 64-bit processes 422 on: enable for both 32- and 64-bit processes 423 off: disable for both 32- and 64-bit processes 424 425 alloc_snapshot [FTRACE] 426 Allocate the ftrace snapshot buffer on boot up when the 427 main buffer is allocated. This is handy if debugging 428 and you need to use tracing_snapshot() on boot up, and 429 do not want to use tracing_snapshot_alloc() as it needs 430 to be done where GFP_KERNEL allocations are allowed. 431 432 amd_iommu= [HW,X86-64] 433 Pass parameters to the AMD IOMMU driver in the system. 434 Possible values are: 435 fullflush - enable flushing of IO/TLB entries when 436 they are unmapped. Otherwise they are 437 flushed before they will be reused, which 438 is a lot of faster 439 off - do not initialize any AMD IOMMU found in 440 the system 441 force_isolation - Force device isolation for all 442 devices. The IOMMU driver is not 443 allowed anymore to lift isolation 444 requirements as needed. This option 445 does not override iommu=pt 446 447 amd_iommu_dump= [HW,X86-64] 448 Enable AMD IOMMU driver option to dump the ACPI table 449 for AMD IOMMU. With this option enabled, AMD IOMMU 450 driver will print ACPI tables for AMD IOMMU during 451 IOMMU initialization. 452 453 amijoy.map= [HW,JOY] Amiga joystick support 454 Map of devices attached to JOY0DAT and JOY1DAT 455 Format: <a>,<b> 456 See also Documentation/input/joystick.txt 457 458 analog.map= [HW,JOY] Analog joystick and gamepad support 459 Specifies type or capabilities of an analog joystick 460 connected to one of 16 gameports 461 Format: <type1>,<type2>,..<type16> 462 463 apc= [HW,SPARC] 464 Power management functions (SPARCstation-4/5 + deriv.) 465 Format: noidle 466 Disable APC CPU standby support. SPARCstation-Fox does 467 not play well with APC CPU idle - disable it if you have 468 APC and your system crashes randomly. 469 470 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller 471 Change the output verbosity whilst booting 472 Format: { quiet (default) | verbose | debug } 473 Change the amount of debugging information output 474 when initialising the APIC and IO-APIC components. 475 476 autoconf= [IPV6] 477 See Documentation/networking/ipv6.txt. 478 479 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller 480 Limit apic dumping. The parameter defines the maximal 481 number of local apics being dumped. Also it is possible 482 to set it to "all" by meaning -- no limit here. 483 Format: { 1 (default) | 2 | ... | all }. 484 The parameter valid if only apic=debug or 485 apic=verbose is specified. 486 Example: apic=debug show_lapic=all 487 488 apm= [APM] Advanced Power Management 489 See header of arch/x86/kernel/apm_32.c. 490 491 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards 492 Format: <io>,<irq>,<nodeID> 493 494 ataflop= [HW,M68k] 495 496 atarimouse= [HW,MOUSE] Atari Mouse 497 498 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess, 499 EzKey and similar keyboards 500 501 atkbd.reset= [HW] Reset keyboard during initialization 502 503 atkbd.set= [HW] Select keyboard code set 504 Format: <int> (2 = AT (default), 3 = PS/2) 505 506 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar 507 keyboards 508 509 atkbd.softraw= [HW] Choose between synthetic and real raw mode 510 Format: <bool> (0 = real, 1 = synthetic (default)) 511 512 atkbd.softrepeat= [HW] 513 Use software keyboard repeat 514 515 audit= [KNL] Enable the audit sub-system 516 Format: { "0" | "1" } (0 = disabled, 1 = enabled) 517 0 - kernel audit is disabled and can not be enabled 518 until the next reboot 519 unset - kernel audit is initialized but disabled and 520 will be fully enabled by the userspace auditd. 521 1 - kernel audit is initialized and partially enabled, 522 storing at most audit_backlog_limit messages in 523 RAM until it is fully enabled by the userspace 524 auditd. 525 Default: unset 526 527 audit_backlog_limit= [KNL] Set the audit queue size limit. 528 Format: <int> (must be >=0) 529 Default: 64 530 531 baycom_epp= [HW,AX25] 532 Format: <io>,<mode> 533 534 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem 535 Format: <io>,<mode> 536 See header of drivers/net/hamradio/baycom_par.c. 537 538 baycom_ser_fdx= [HW,AX25] 539 BayCom Serial Port AX.25 Modem (Full Duplex Mode) 540 Format: <io>,<irq>,<mode>[,<baud>] 541 See header of drivers/net/hamradio/baycom_ser_fdx.c. 542 543 baycom_ser_hdx= [HW,AX25] 544 BayCom Serial Port AX.25 Modem (Half Duplex Mode) 545 Format: <io>,<irq>,<mode> 546 See header of drivers/net/hamradio/baycom_ser_hdx.c. 547 548 blkdevparts= Manual partition parsing of block device(s) for 549 embedded devices based on command line input. 550 See Documentation/block/cmdline-partition.txt 551 552 boot_delay= Milliseconds to delay each printk during boot. 553 Values larger than 10 seconds (10000) are changed to 554 no delay (0). 555 Format: integer 556 557 bootmem_debug [KNL] Enable bootmem allocator debug messages. 558 559 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards) 560 bttv.radio= Most important insmod options are available as 561 kernel args too. 562 bttv.pll= See Documentation/video4linux/bttv/Insmod-options 563 bttv.tuner= 564 565 bulk_remove=off [PPC] This parameter disables the use of the pSeries 566 firmware feature for flushing multiple hpte entries 567 at a time. 568 569 c101= [NET] Moxa C101 synchronous serial card 570 571 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection. 572 Sometimes CPU hardware bugs make them report the cache 573 size incorrectly. The kernel will attempt work arounds 574 to fix known problems, but for some CPUs it is not 575 possible to determine what the correct size should be. 576 This option provides an override for these situations. 577 578 ca_keys= [KEYS] This parameter identifies a specific key(s) on 579 the system trusted keyring to be used for certificate 580 trust validation. 581 format: { id:<keyid> | builtin } 582 583 cca= [MIPS] Override the kernel pages' cache coherency 584 algorithm. Accepted values range from 0 to 7 585 inclusive. See arch/mips/include/asm/pgtable-bits.h 586 for platform specific values (SB1, Loongson3 and 587 others). 588 589 ccw_timeout_log [S390] 590 See Documentation/s390/CommonIO for details. 591 592 cgroup_disable= [KNL] Disable a particular controller 593 Format: {name of the controller(s) to disable} 594 The effects of cgroup_disable=foo are: 595 - foo isn't auto-mounted if you mount all cgroups in 596 a single hierarchy 597 - foo isn't visible as an individually mountable 598 subsystem 599 {Currently only "memory" controller deal with this and 600 cut the overhead, others just disable the usage. So 601 only cgroup_disable=memory is actually worthy} 602 603 checkreqprot [SELINUX] Set initial checkreqprot flag value. 604 Format: { "0" | "1" } 605 See security/selinux/Kconfig help text. 606 0 -- check protection applied by kernel (includes 607 any implied execute protection). 608 1 -- check protection requested by application. 609 Default value is set via a kernel config option. 610 Value can be changed at runtime via 611 /selinux/checkreqprot. 612 613 cio_ignore= [S390] 614 See Documentation/s390/CommonIO for details. 615 clk_ignore_unused 616 [CLK] 617 Prevents the clock framework from automatically gating 618 clocks that have not been explicitly enabled by a Linux 619 device driver but are enabled in hardware at reset or 620 by the bootloader/firmware. Note that this does not 621 force such clocks to be always-on nor does it reserve 622 those clocks in any way. This parameter is useful for 623 debug and development, but should not be needed on a 624 platform with proper driver support. For more 625 information, see Documentation/clk.txt. 626 627 clock= [BUGS=X86-32, HW] gettimeofday clocksource override. 628 [Deprecated] 629 Forces specified clocksource (if available) to be used 630 when calculating gettimeofday(). If specified 631 clocksource is not available, it defaults to PIT. 632 Format: { pit | tsc | cyclone | pmtmr } 633 634 clocksource= Override the default clocksource 635 Format: <string> 636 Override the default clocksource and use the clocksource 637 with the name specified. 638 Some clocksource names to choose from, depending on 639 the platform: 640 [all] jiffies (this is the base, fallback clocksource) 641 [ACPI] acpi_pm 642 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2, 643 pxa_timer,timer3,32k_counter,timer0_1 644 [AVR32] avr32 645 [X86-32] pit,hpet,tsc; 646 scx200_hrt on Geode; cyclone on IBM x440 647 [MIPS] MIPS 648 [PARISC] cr16 649 [S390] tod 650 [SH] SuperH 651 [SPARC64] tick 652 [X86-64] hpet,tsc 653 654 clearcpuid=BITNUM [X86] 655 Disable CPUID feature X for the kernel. See 656 arch/x86/include/asm/cpufeatures.h for the valid bit 657 numbers. Note the Linux specific bits are not necessarily 658 stable over kernel options, but the vendor specific 659 ones should be. 660 Also note that user programs calling CPUID directly 661 or using the feature without checking anything 662 will still see it. This just prevents it from 663 being used by the kernel or shown in /proc/cpuinfo. 664 Also note the kernel might malfunction if you disable 665 some critical bits. 666 667 cma=nn[MG]@[start[MG][-end[MG]]] 668 [ARM,X86,KNL] 669 Sets the size of kernel global memory area for 670 contiguous memory allocations and optionally the 671 placement constraint by the physical address range of 672 memory allocations. A value of 0 disables CMA 673 altogether. For more information, see 674 include/linux/dma-contiguous.h 675 676 cmo_free_hint= [PPC] Format: { yes | no } 677 Specify whether pages are marked as being inactive 678 when they are freed. This is used in CMO environments 679 to determine OS memory pressure for page stealing by 680 a hypervisor. 681 Default: yes 682 683 coherent_pool=nn[KMG] [ARM,KNL] 684 Sets the size of memory pool for coherent, atomic dma 685 allocations, by default set to 256K. 686 687 code_bytes [X86] How many bytes of object code to print 688 in an oops report. 689 Range: 0 - 8192 690 Default: 64 691 692 com20020= [HW,NET] ARCnet - COM20020 chipset 693 Format: 694 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]] 695 696 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers) 697 Format: <io>[,<irq>] 698 699 com90xx= [HW,NET] 700 ARCnet - COM90xx chipset (memory-mapped buffers) 701 Format: <io>[,<irq>[,<memstart>]] 702 703 condev= [HW,S390] console device 704 conmode= 705 706 console= [KNL] Output console device and options. 707 708 tty<n> Use the virtual console device <n>. 709 710 ttyS<n>[,options] 711 ttyUSB0[,options] 712 Use the specified serial port. The options are of 713 the form "bbbbpnf", where "bbbb" is the baud rate, 714 "p" is parity ("n", "o", or "e"), "n" is number of 715 bits, and "f" is flow control ("r" for RTS or 716 omit it). Default is "9600n8". 717 718 See Documentation/serial-console.txt for more 719 information. See 720 Documentation/networking/netconsole.txt for an 721 alternative. 722 723 uart[8250],io,<addr>[,options] 724 uart[8250],mmio,<addr>[,options] 725 uart[8250],mmio32,<addr>[,options] 726 uart[8250],0x<addr>[,options] 727 Start an early, polled-mode console on the 8250/16550 728 UART at the specified I/O port or MMIO address, 729 switching to the matching ttyS device later. 730 MMIO inter-register address stride is either 8-bit 731 (mmio) or 32-bit (mmio32). 732 If none of [io|mmio|mmio32], <addr> is assumed to be 733 equivalent to 'mmio'. 'options' are specified in the 734 same format described for ttyS above; if unspecified, 735 the h/w is not re-initialized. 736 737 hvc<n> Use the hypervisor console device <n>. This is for 738 both Xen and PowerPC hypervisors. 739 740 If the device connected to the port is not a TTY but a braille 741 device, prepend "brl," before the device type, for instance 742 console=brl,ttyS0 743 For now, only VisioBraille is supported. 744 745 consoleblank= [KNL] The console blank (screen saver) timeout in 746 seconds. Defaults to 10*60 = 10mins. A value of 0 747 disables the blank timer. 748 749 coredump_filter= 750 [KNL] Change the default value for 751 /proc/<pid>/coredump_filter. 752 See also Documentation/filesystems/proc.txt. 753 754 cpuidle.off=1 [CPU_IDLE] 755 disable the cpuidle sub-system 756 757 cpu_init_udelay=N 758 [X86] Delay for N microsec between assert and de-assert 759 of APIC INIT to start processors. This delay occurs 760 on every CPU online, such as boot, and resume from suspend. 761 Default: 10000 762 763 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver 764 Format: 765 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] 766 767 crashkernel=size[KMG][@offset[KMG]] 768 [KNL] Using kexec, Linux can switch to a 'crash kernel' 769 upon panic. This parameter reserves the physical 770 memory region [offset, offset + size] for that kernel 771 image. If '@offset' is omitted, then a suitable offset 772 is selected automatically. Check 773 Documentation/kdump/kdump.txt for further details. 774 775 crashkernel=range1:size1[,range2:size2,...][@offset] 776 [KNL] Same as above, but depends on the memory 777 in the running system. The syntax of range is 778 start-[end] where start and end are both 779 a memory unit (amount[KMG]). See also 780 Documentation/kdump/kdump.txt for an example. 781 782 crashkernel=size[KMG],high 783 [KNL, x86_64] range could be above 4G. Allow kernel 784 to allocate physical memory region from top, so could 785 be above 4G if system have more than 4G ram installed. 786 Otherwise memory region will be allocated below 4G, if 787 available. 788 It will be ignored if crashkernel=X is specified. 789 crashkernel=size[KMG],low 790 [KNL, x86_64] range under 4G. When crashkernel=X,high 791 is passed, kernel could allocate physical memory region 792 above 4G, that cause second kernel crash on system 793 that require some amount of low memory, e.g. swiotlb 794 requires at least 64M+32K low memory, also enough extra 795 low memory is needed to make sure DMA buffers for 32-bit 796 devices won't run out. Kernel would try to allocate at 797 at least 256M below 4G automatically. 798 This one let user to specify own low range under 4G 799 for second kernel instead. 800 0: to disable low allocation. 801 It will be ignored when crashkernel=X,high is not used 802 or memory reserved is below 4G. 803 804 cs89x0_dma= [HW,NET] 805 Format: <dma> 806 807 cs89x0_media= [HW,NET] 808 Format: { rj45 | aui | bnc } 809 810 dasd= [HW,NET] 811 See header of drivers/s390/block/dasd_devmap.c. 812 813 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port 814 (one device per port) 815 Format: <port#>,<type> 816 See also Documentation/input/joystick-parport.txt 817 818 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot 819 time. See Documentation/dynamic-debug-howto.txt for 820 details. Deprecated, see dyndbg. 821 822 debug [KNL] Enable kernel debugging (events log level). 823 824 debug_locks_verbose= 825 [KNL] verbose self-tests 826 Format=<0|1> 827 Print debugging info while doing the locking API 828 self-tests. 829 We default to 0 (no extra messages), setting it to 830 1 will print _a lot_ more information - normally 831 only useful to kernel developers. 832 833 debug_objects [KNL] Enable object debugging 834 835 no_debug_objects 836 [KNL] Disable object debugging 837 838 debug_guardpage_minorder= 839 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this 840 parameter allows control of the order of pages that will 841 be intentionally kept free (and hence protected) by the 842 buddy allocator. Bigger value increase the probability 843 of catching random memory corruption, but reduce the 844 amount of memory for normal system use. The maximum 845 possible value is MAX_ORDER/2. Setting this parameter 846 to 1 or 2 should be enough to identify most random 847 memory corruption problems caused by bugs in kernel or 848 driver code when a CPU writes to (or reads from) a 849 random memory location. Note that there exists a class 850 of memory corruptions problems caused by buggy H/W or 851 F/W or by drivers badly programing DMA (basically when 852 memory is written at bus level and the CPU MMU is 853 bypassed) which are not detectable by 854 CONFIG_DEBUG_PAGEALLOC, hence this option will not help 855 tracking down these problems. 856 857 debug_pagealloc= 858 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this 859 parameter enables the feature at boot time. In 860 default, it is disabled. We can avoid allocating huge 861 chunk of memory for debug pagealloc if we don't enable 862 it at boot time and the system will work mostly same 863 with the kernel built without CONFIG_DEBUG_PAGEALLOC. 864 on: enable the feature 865 866 debugpat [X86] Enable PAT debugging 867 868 decnet.addr= [HW,NET] 869 Format: <area>[,<node>] 870 See also Documentation/networking/decnet.txt. 871 872 default_hugepagesz= 873 [same as hugepagesz=] The size of the default 874 HugeTLB page size. This is the size represented by 875 the legacy /proc/ hugepages APIs, used for SHM, and 876 default size when mounting hugetlbfs filesystems. 877 Defaults to the default architecture's huge page size 878 if not specified. 879 880 dhash_entries= [KNL] 881 Set number of hash buckets for dentry cache. 882 883 disable= [IPV6] 884 See Documentation/networking/ipv6.txt. 885 886 disable_cpu_apicid= [X86,APIC,SMP] 887 Format: <int> 888 The number of initial APIC ID for the 889 corresponding CPU to be disabled at boot, 890 mostly used for the kdump 2nd kernel to 891 disable BSP to wake up multiple CPUs without 892 causing system reset or hang due to sending 893 INIT from AP to BSP. 894 895 disable_ddw [PPC/PSERIES] 896 Disable Dynamic DMA Window support. Use this if 897 to workaround buggy firmware. 898 899 disable_ipv6= [IPV6] 900 See Documentation/networking/ipv6.txt. 901 902 disable_mtrr_cleanup [X86] 903 The kernel tries to adjust MTRR layout from continuous 904 to discrete, to make X server driver able to add WB 905 entry later. This parameter disables that. 906 907 disable_mtrr_trim [X86, Intel and AMD only] 908 By default the kernel will trim any uncacheable 909 memory out of your available memory pool based on 910 MTRR settings. This parameter disables that behavior, 911 possibly causing your machine to run very slowly. 912 913 disable_timer_pin_1 [X86] 914 Disable PIN 1 of APIC timer 915 Can be useful to work around chipset bugs. 916 917 dis_ucode_ldr [X86] Disable the microcode loader. 918 919 dm= [DM] Allows early creation of a device-mapper device. 920 See Documentation/device-mapper/boot.txt. 921 922 dmasound= [HW,OSS] Sound subsystem buff 923 924 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, 925 this option disables the debugging code at boot. 926 927 dma_debug_entries=<number> 928 This option allows to tune the number of preallocated 929 entries for DMA-API debugging code. One entry is 930 required per DMA-API allocation. Use this if the 931 DMA-API debugging code disables itself because the 932 architectural default is too low. 933 934 dma_debug_driver=<driver_name> 935 With this option the DMA-API debugging driver 936 filter feature can be enabled at boot time. Just 937 pass the driver to filter for as the parameter. 938 The filter can be disabled or changed to another 939 driver later using sysfs. 940 941 drm_kms_helper.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>] 942 Broken monitors, graphic adapters, KVMs and EDIDless 943 panels may send no or incorrect EDID data sets. 944 This parameter allows to specify an EDID data sets 945 in the /lib/firmware directory that are used instead. 946 Generic built-in EDID data sets are used, if one of 947 edid/1024x768.bin, edid/1280x1024.bin, 948 edid/1680x1050.bin, or edid/1920x1080.bin is given 949 and no file with the same name exists. Details and 950 instructions how to build your own EDID data are 951 available in Documentation/EDID/HOWTO.txt. An EDID 952 data set will only be used for a particular connector, 953 if its name and a colon are prepended to the EDID 954 name. Each connector may use a unique EDID data 955 set by separating the files with a comma. An EDID 956 data set with no connector name will be used for 957 any connectors not explicitly specified. 958 959 dscc4.setup= [NET] 960 961 dyndbg[="val"] [KNL,DYNAMIC_DEBUG] 962 module.dyndbg[="val"] 963 Enable debug messages at boot time. See 964 Documentation/dynamic-debug-howto.txt for details. 965 966 nompx [X86] Disables Intel Memory Protection Extensions. 967 See Documentation/x86/intel_mpx.txt for more 968 information about the feature. 969 970 971 module.async_probe [KNL] 972 Enable asynchronous probe on this module. 973 974 early_ioremap_debug [KNL] 975 Enable debug messages in early_ioremap support. This 976 is useful for tracking down temporary early mappings 977 which are not unmapped. 978 979 earlycon= [KNL] Output early console device and options. 980 981 When used with no options, the early console is 982 determined by the stdout-path property in device 983 tree's chosen node. 984 985 cdns,<addr> 986 Start an early, polled-mode console on a cadence serial 987 port at the specified address. The cadence serial port 988 must already be setup and configured. Options are not 989 yet supported. 990 991 uart[8250],io,<addr>[,options] 992 uart[8250],mmio,<addr>[,options] 993 uart[8250],mmio32,<addr>[,options] 994 uart[8250],mmio32be,<addr>[,options] 995 uart[8250],0x<addr>[,options] 996 Start an early, polled-mode console on the 8250/16550 997 UART at the specified I/O port or MMIO address. 998 MMIO inter-register address stride is either 8-bit 999 (mmio) or 32-bit (mmio32 or mmio32be). 1000 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed 1001 to be equivalent to 'mmio'. 'options' are specified 1002 in the same format described for "console=ttyS<n>"; if 1003 unspecified, the h/w is not initialized. 1004 1005 pl011,<addr> 1006 Start an early, polled-mode console on a pl011 serial 1007 port at the specified address. The pl011 serial port 1008 must already be setup and configured. Options are not 1009 yet supported. 1010 1011 msm_serial,<addr> 1012 Start an early, polled-mode console on an msm serial 1013 port at the specified address. The serial port 1014 must already be setup and configured. Options are not 1015 yet supported. 1016 1017 msm_serial_dm,<addr> 1018 Start an early, polled-mode console on an msm serial 1019 dm port at the specified address. The serial port 1020 must already be setup and configured. Options are not 1021 yet supported. 1022 1023 smh Use ARM semihosting calls for early console. 1024 1025 s3c2410,<addr> 1026 s3c2412,<addr> 1027 s3c2440,<addr> 1028 s3c6400,<addr> 1029 s5pv210,<addr> 1030 exynos4210,<addr> 1031 Use early console provided by serial driver available 1032 on Samsung SoCs, requires selecting proper type and 1033 a correct base address of the selected UART port. The 1034 serial port must already be setup and configured. 1035 Options are not yet supported. 1036 1037 lpuart,<addr> 1038 lpuart32,<addr> 1039 Use early console provided by Freescale LP UART driver 1040 found on Freescale Vybrid and QorIQ LS1021A processors. 1041 A valid base address must be provided, and the serial 1042 port must already be setup and configured. 1043 1044 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k] 1045 earlyprintk=vga 1046 earlyprintk=efi 1047 earlyprintk=xen 1048 earlyprintk=serial[,ttySn[,baudrate]] 1049 earlyprintk=serial[,0x...[,baudrate]] 1050 earlyprintk=ttySn[,baudrate] 1051 earlyprintk=dbgp[debugController#] 1052 earlyprintk=pciserial,bus:device.function[,baudrate] 1053 1054 earlyprintk is useful when the kernel crashes before 1055 the normal console is initialized. It is not enabled by 1056 default because it has some cosmetic problems. 1057 1058 Append ",keep" to not disable it when the real console 1059 takes over. 1060 1061 Only one of vga, efi, serial, or usb debug port can 1062 be used at a time. 1063 1064 Currently only ttyS0 and ttyS1 may be specified by 1065 name. Other I/O ports may be explicitly specified 1066 on some architectures (x86 and arm at least) by 1067 replacing ttySn with an I/O port address, like this: 1068 earlyprintk=serial,0x1008,115200 1069 You can find the port for a given device in 1070 /proc/tty/driver/serial: 1071 2: uart:ST16650V2 port:00001008 irq:18 ... 1072 1073 Interaction with the standard serial driver is not 1074 very good. 1075 1076 The VGA and EFI output is eventually overwritten by 1077 the real console. 1078 1079 The xen output can only be used by Xen PV guests. 1080 1081 edac_report= [HW,EDAC] Control how to report EDAC event 1082 Format: {"on" | "off" | "force"} 1083 on: enable EDAC to report H/W event. May be overridden 1084 by other higher priority error reporting module. 1085 off: disable H/W event reporting through EDAC. 1086 force: enforce the use of EDAC to report H/W event. 1087 default: on. 1088 1089 ekgdboc= [X86,KGDB] Allow early kernel console debugging 1090 ekgdboc=kbd 1091 1092 This is designed to be used in conjunction with 1093 the boot argument: earlyprintk=vga 1094 1095 edd= [EDD] 1096 Format: {"off" | "on" | "skip[mbr]"} 1097 1098 efi= [EFI] 1099 Format: { "old_map", "nochunk", "noruntime", "debug" } 1100 old_map [X86-64]: switch to the old ioremap-based EFI 1101 runtime services mapping. 32-bit still uses this one by 1102 default. 1103 nochunk: disable reading files in "chunks" in the EFI 1104 boot stub, as chunking can cause problems with some 1105 firmware implementations. 1106 noruntime : disable EFI runtime services support 1107 debug: enable misc debug output 1108 1109 efi_no_storage_paranoia [EFI; X86] 1110 Using this parameter you can use more than 50% of 1111 your efi variable storage. Use this parameter only if 1112 you are really sure that your UEFI does sane gc and 1113 fulfills the spec otherwise your board may brick. 1114 1115 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86] 1116 Add arbitrary attribute to specific memory range by 1117 updating original EFI memory map. 1118 Region of memory which aa attribute is added to is 1119 from ss to ss+nn. 1120 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000 1121 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000) 1122 attribute is added to range 0x100000000-0x180000000 and 1123 0x10a0000000-0x1120000000. 1124 1125 Using this parameter you can do debugging of EFI memmap 1126 related feature. For example, you can do debugging of 1127 Address Range Mirroring feature even if your box 1128 doesn't support it. 1129 1130 eisa_irq_edge= [PARISC,HW] 1131 See header of drivers/parisc/eisa.c. 1132 1133 elanfreq= [X86-32] 1134 See comment before function elanfreq_setup() in 1135 arch/x86/kernel/cpu/cpufreq/elanfreq.c. 1136 1137 elevator= [IOSCHED] 1138 Format: {"cfq" | "deadline" | "noop"} 1139 See Documentation/block/cfq-iosched.txt and 1140 Documentation/block/deadline-iosched.txt for details. 1141 1142 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390] 1143 Specifies physical address of start of kernel core 1144 image elf header and optionally the size. Generally 1145 kexec loader will pass this option to capture kernel. 1146 See Documentation/kdump/kdump.txt for details. 1147 1148 enable_mtrr_cleanup [X86] 1149 The kernel tries to adjust MTRR layout from continuous 1150 to discrete, to make X server driver able to add WB 1151 entry later. This parameter enables that. 1152 1153 enable_timer_pin_1 [X86] 1154 Enable PIN 1 of APIC timer 1155 Can be useful to work around chipset bugs 1156 (in particular on some ATI chipsets). 1157 The kernel tries to set a reasonable default. 1158 1159 enforcing [SELINUX] Set initial enforcing status. 1160 Format: {"0" | "1"} 1161 See security/selinux/Kconfig help text. 1162 0 -- permissive (log only, no denials). 1163 1 -- enforcing (deny and log). 1164 Default value is 0. 1165 Value can be changed at runtime via /selinux/enforce. 1166 1167 erst_disable [ACPI] 1168 Disable Error Record Serialization Table (ERST) 1169 support. 1170 1171 ether= [HW,NET] Ethernet cards parameters 1172 This option is obsoleted by the "netdev=" option, which 1173 has equivalent usage. See its documentation for details. 1174 1175 evm= [EVM] 1176 Format: { "fix" } 1177 Permit 'security.evm' to be updated regardless of 1178 current integrity status. 1179 1180 failslab= 1181 fail_page_alloc= 1182 fail_make_request=[KNL] 1183 General fault injection mechanism. 1184 Format: <interval>,<probability>,<space>,<times> 1185 See also Documentation/fault-injection/. 1186 1187 floppy= [HW] 1188 See Documentation/blockdev/floppy.txt. 1189 1190 force_pal_cache_flush 1191 [IA-64] Avoid check_sal_cache_flush which may hang on 1192 buggy SAL_CACHE_FLUSH implementations. Using this 1193 parameter will force ia64_sal_cache_flush to call 1194 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH. 1195 1196 forcepae [X86-32] 1197 Forcefully enable Physical Address Extension (PAE). 1198 Many Pentium M systems disable PAE but may have a 1199 functionally usable PAE implementation. 1200 Warning: use of this parameter will taint the kernel 1201 and may cause unknown problems. 1202 1203 ftrace=[tracer] 1204 [FTRACE] will set and start the specified tracer 1205 as early as possible in order to facilitate early 1206 boot debugging. 1207 1208 ftrace_dump_on_oops[=orig_cpu] 1209 [FTRACE] will dump the trace buffers on oops. 1210 If no parameter is passed, ftrace will dump 1211 buffers of all CPUs, but if you pass orig_cpu, it will 1212 dump only the buffer of the CPU that triggered the 1213 oops. 1214 1215 ftrace_filter=[function-list] 1216 [FTRACE] Limit the functions traced by the function 1217 tracer at boot up. function-list is a comma separated 1218 list of functions. This list can be changed at run 1219 time by the set_ftrace_filter file in the debugfs 1220 tracing directory. 1221 1222 ftrace_notrace=[function-list] 1223 [FTRACE] Do not trace the functions specified in 1224 function-list. This list can be changed at run time 1225 by the set_ftrace_notrace file in the debugfs 1226 tracing directory. 1227 1228 ftrace_graph_filter=[function-list] 1229 [FTRACE] Limit the top level callers functions traced 1230 by the function graph tracer at boot up. 1231 function-list is a comma separated list of functions 1232 that can be changed at run time by the 1233 set_graph_function file in the debugfs tracing directory. 1234 1235 ftrace_graph_notrace=[function-list] 1236 [FTRACE] Do not trace from the functions specified in 1237 function-list. This list is a comma separated list of 1238 functions that can be changed at run time by the 1239 set_graph_notrace file in the debugfs tracing directory. 1240 1241 gamecon.map[2|3]= 1242 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 1243 support via parallel port (up to 5 devices per port) 1244 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 1245 See also Documentation/input/joystick-parport.txt 1246 1247 gamma= [HW,DRM] 1248 1249 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART 1250 Format: off | on 1251 default: on 1252 1253 gcov_persist= [GCOV] When non-zero (default), profiling data for 1254 kernel modules is saved and remains accessible via 1255 debugfs, even when the module is unloaded/reloaded. 1256 When zero, profiling data is discarded and associated 1257 debugfs files are removed at module unload time. 1258 1259 goldfish [X86] Enable the goldfish android emulator platform. 1260 Don't use this when you are not running on the 1261 android emulator 1262 1263 gpt [EFI] Forces disk with valid GPT signature but 1264 invalid Protective MBR to be treated as GPT. If the 1265 primary GPT is corrupted, it enables the backup/alternate 1266 GPT to be used instead. 1267 1268 grcan.enable0= [HW] Configuration of physical interface 0. Determines 1269 the "Enable 0" bit of the configuration register. 1270 Format: 0 | 1 1271 Default: 0 1272 grcan.enable1= [HW] Configuration of physical interface 1. Determines 1273 the "Enable 0" bit of the configuration register. 1274 Format: 0 | 1 1275 Default: 0 1276 grcan.select= [HW] Select which physical interface to use. 1277 Format: 0 | 1 1278 Default: 0 1279 grcan.txsize= [HW] Sets the size of the tx buffer. 1280 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. 1281 Default: 1024 1282 grcan.rxsize= [HW] Sets the size of the rx buffer. 1283 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. 1284 Default: 1024 1285 1286 hardlockup_all_cpu_backtrace= 1287 [KNL] Should the hard-lockup detector generate 1288 backtraces on all cpus. 1289 Format: <integer> 1290 1291 hashdist= [KNL,NUMA] Large hashes allocated during boot 1292 are distributed across NUMA nodes. Defaults on 1293 for 64-bit NUMA, off otherwise. 1294 Format: 0 | 1 (for off | on) 1295 1296 hcl= [IA-64] SGI's Hardware Graph compatibility layer 1297 1298 hd= [EIDE] (E)IDE hard drive subsystem geometry 1299 Format: <cyl>,<head>,<sect> 1300 1301 hest_disable [ACPI] 1302 Disable Hardware Error Source Table (HEST) support; 1303 corresponding firmware-first mode error processing 1304 logic will be disabled. 1305 1306 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact 1307 size of <nn>. This works even on boxes that have no 1308 highmem otherwise. This also works to reduce highmem 1309 size on bigger boxes. 1310 1311 highres= [KNL] Enable/disable high resolution timer mode. 1312 Valid parameters: "on", "off" 1313 Default: "on" 1314 1315 hisax= [HW,ISDN] 1316 See Documentation/isdn/README.HiSax. 1317 1318 hlt [BUGS=ARM,SH] 1319 1320 hpet= [X86-32,HPET] option to control HPET usage 1321 Format: { enable (default) | disable | force | 1322 verbose } 1323 disable: disable HPET and use PIT instead 1324 force: allow force enabled of undocumented chips (ICH4, 1325 VIA, nVidia) 1326 verbose: show contents of HPET registers during setup 1327 1328 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET 1329 registers. Default set by CONFIG_HPET_MMAP_DEFAULT. 1330 1331 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot. 1332 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages. 1333 On x86-64 and powerpc, this option can be specified 1334 multiple times interleaved with hugepages= to reserve 1335 huge pages of different sizes. Valid pages sizes on 1336 x86-64 are 2M (when the CPU supports "pse") and 1G 1337 (when the CPU supports the "pdpe1gb" cpuinfo flag). 1338 1339 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 1340 terminal devices. Valid values: 0..8 1341 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 1342 If specified, z/VM IUCV HVC accepts connections 1343 from listed z/VM user IDs only. 1344 1345 hwthread_map= [METAG] Comma-separated list of Linux cpu id to 1346 hardware thread id mappings. 1347 Format: <cpu>:<hwthread> 1348 1349 keep_bootcon [KNL] 1350 Do not unregister boot console at start. This is only 1351 useful for debugging when something happens in the window 1352 between unregistering the boot console and initializing 1353 the real console. 1354 1355 i2c_bus= [HW] Override the default board specific I2C bus speed 1356 or register an additional I2C bus that is not 1357 registered from board initialization code. 1358 Format: 1359 <bus_id>,<clkrate> 1360 1361 i8042.debug [HW] Toggle i8042 debug mode 1362 i8042.unmask_kbd_data 1363 [HW] Enable printing of interrupt data from the KBD port 1364 (disabled by default, and as a pre-condition 1365 requires that i8042.debug=1 be enabled) 1366 i8042.direct [HW] Put keyboard port into non-translated mode 1367 i8042.dumbkbd [HW] Pretend that controller can only read data from 1368 keyboard and cannot control its state 1369 (Don't attempt to blink the leds) 1370 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 1371 i8042.nokbd [HW] Don't check/create keyboard port 1372 i8042.noloop [HW] Disable the AUX Loopback command while probing 1373 for the AUX port 1374 i8042.nomux [HW] Don't check presence of an active multiplexing 1375 controller 1376 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 1377 controllers 1378 i8042.notimeout [HW] Ignore timeout condition signalled by controller 1379 i8042.reset [HW] Reset the controller during init, cleanup and 1380 suspend-to-ram transitions, only during s2r 1381 transitions, or never reset 1382 Format: { 1 | Y | y | 0 | N | n } 1383 1, Y, y: always reset controller 1384 0, N, n: don't ever reset controller 1385 Default: only on s2r transitions on x86; most other 1386 architectures force reset to be always executed 1387 i8042.unlock [HW] Unlock (ignore) the keylock 1388 i8042.kbdreset [HW] Reset device connected to KBD port 1389 1390 i810= [HW,DRM] 1391 1392 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data 1393 indicates that the driver is running on unsupported 1394 hardware. 1395 i8k.force [HW] Activate i8k driver even if SMM BIOS signature 1396 does not match list of supported models. 1397 i8k.power_status 1398 [HW] Report power status in /proc/i8k 1399 (disabled by default) 1400 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN 1401 capability is set. 1402 1403 i915.invert_brightness= 1404 [DRM] Invert the sense of the variable that is used to 1405 set the brightness of the panel backlight. Normally a 1406 brightness value of 0 indicates backlight switched off, 1407 and the maximum of the brightness value sets the backlight 1408 to maximum brightness. If this parameter is set to 0 1409 (default) and the machine requires it, or this parameter 1410 is set to 1, a brightness value of 0 sets the backlight 1411 to maximum brightness, and the maximum of the brightness 1412 value switches the backlight off. 1413 -1 -- never invert brightness 1414 0 -- machine default 1415 1 -- force brightness inversion 1416 1417 icn= [HW,ISDN] 1418 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]] 1419 1420 ide-core.nodma= [HW] (E)IDE subsystem 1421 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc 1422 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr 1423 .cdrom .chs .ignore_cable are additional options 1424 See Documentation/ide/ide.txt. 1425 1426 ide-generic.probe-mask= [HW] (E)IDE subsystem 1427 Format: <int> 1428 Probe mask for legacy ISA IDE ports. Depending on 1429 platform up to 6 ports are supported, enabled by 1430 setting corresponding bits in the mask to 1. The 1431 default value is 0x0, which has a special meaning. 1432 On systems that have PCI, it triggers scanning the 1433 PCI bus for the first and the second port, which 1434 are then probed. On systems without PCI the value 1435 of 0x0 enables probing the two first ports as if it 1436 was 0x3. 1437 1438 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem 1439 Claim all unknown PCI IDE storage controllers. 1440 1441 idle= [X86] 1442 Format: idle=poll, idle=halt, idle=nomwait 1443 Poll forces a polling idle loop that can slightly 1444 improve the performance of waking up a idle CPU, but 1445 will use a lot of power and make the system run hot. 1446 Not recommended. 1447 idle=halt: Halt is forced to be used for CPU idle. 1448 In such case C2/C3 won't be used again. 1449 idle=nomwait: Disable mwait for CPU C-states 1450 1451 ieee754= [MIPS] Select IEEE Std 754 conformance mode 1452 Format: { strict | legacy | 2008 | relaxed } 1453 Default: strict 1454 1455 Choose which programs will be accepted for execution 1456 based on the IEEE 754 NaN encoding(s) supported by 1457 the FPU and the NaN encoding requested with the value 1458 of an ELF file header flag individually set by each 1459 binary. Hardware implementations are permitted to 1460 support either or both of the legacy and the 2008 NaN 1461 encoding mode. 1462 1463 Available settings are as follows: 1464 strict accept binaries that request a NaN encoding 1465 supported by the FPU 1466 legacy only accept legacy-NaN binaries, if supported 1467 by the FPU 1468 2008 only accept 2008-NaN binaries, if supported 1469 by the FPU 1470 relaxed accept any binaries regardless of whether 1471 supported by the FPU 1472 1473 The FPU emulator is always able to support both NaN 1474 encodings, so if no FPU hardware is present or it has 1475 been disabled with 'nofpu', then the settings of 1476 'legacy' and '2008' strap the emulator accordingly, 1477 'relaxed' straps the emulator for both legacy-NaN and 1478 2008-NaN, whereas 'strict' enables legacy-NaN only on 1479 legacy processors and both NaN encodings on MIPS32 or 1480 MIPS64 CPUs. 1481 1482 The setting for ABS.fmt/NEG.fmt instruction execution 1483 mode generally follows that for the NaN encoding, 1484 except where unsupported by hardware. 1485 1486 ignore_loglevel [KNL] 1487 Ignore loglevel setting - this will print /all/ 1488 kernel messages to the console. Useful for debugging. 1489 We also add it as printk module parameter, so users 1490 could change it dynamically, usually by 1491 /sys/module/printk/parameters/ignore_loglevel. 1492 1493 ihash_entries= [KNL] 1494 Set number of hash buckets for inode cache. 1495 1496 ima_appraise= [IMA] appraise integrity measurements 1497 Format: { "off" | "enforce" | "fix" | "log" } 1498 default: "enforce" 1499 1500 ima_appraise_tcb [IMA] 1501 The builtin appraise policy appraises all files 1502 owned by uid=0. 1503 1504 ima_hash= [IMA] 1505 Format: { md5 | sha1 | rmd160 | sha256 | sha384 1506 | sha512 | ... } 1507 default: "sha1" 1508 1509 The list of supported hash algorithms is defined 1510 in crypto/hash_info.h. 1511 1512 ima_policy= [IMA] 1513 The builtin measurement policy to load during IMA 1514 setup. Specyfing "tcb" as the value, measures all 1515 programs exec'd, files mmap'd for exec, and all files 1516 opened with the read mode bit set by either the 1517 effective uid (euid=0) or uid=0. 1518 Format: "tcb" 1519 1520 ima_tcb [IMA] Deprecated. Use ima_policy= instead. 1521 Load a policy which meets the needs of the Trusted 1522 Computing Base. This means IMA will measure all 1523 programs exec'd, files mmap'd for exec, and all files 1524 opened for read by uid=0. 1525 1526 ima_template= [IMA] 1527 Select one of defined IMA measurements template formats. 1528 Formats: { "ima" | "ima-ng" | "ima-sig" } 1529 Default: "ima-ng" 1530 1531 ima_template_fmt= 1532 [IMA] Define a custom template format. 1533 Format: { "field1|...|fieldN" } 1534 1535 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage 1536 Format: <min_file_size> 1537 Set the minimal file size for using asynchronous hash. 1538 If left unspecified, ahash usage is disabled. 1539 1540 ahash performance varies for different data sizes on 1541 different crypto accelerators. This option can be used 1542 to achieve the best performance for a particular HW. 1543 1544 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size 1545 Format: <bufsize> 1546 Set hashing buffer size. Default: 4k. 1547 1548 ahash performance varies for different chunk sizes on 1549 different crypto accelerators. This option can be used 1550 to achieve best performance for particular HW. 1551 1552 init= [KNL] 1553 Format: <full_path> 1554 Run specified binary instead of /sbin/init as init 1555 process. 1556 1557 initcall_debug [KNL] Trace initcalls as they are executed. Useful 1558 for working out where the kernel is dying during 1559 startup. 1560 1561 initcall_blacklist= [KNL] Do not execute a comma-separated list of 1562 initcall functions. Useful for debugging built-in 1563 modules and initcalls. 1564 1565 initrd= [BOOT] Specify the location of the initial ramdisk 1566 1567 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 1568 Format: <irq> 1569 1570 int_pln_enable [x86] Enable power limit notification interrupt 1571 1572 integrity_audit=[IMA] 1573 Format: { "0" | "1" } 1574 0 -- basic integrity auditing messages. (Default) 1575 1 -- additional integrity auditing messages. 1576 1577 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 1578 on 1579 Enable intel iommu driver. 1580 off 1581 Disable intel iommu driver. 1582 igfx_off [Default Off] 1583 By default, gfx is mapped as normal device. If a gfx 1584 device has a dedicated DMAR unit, the DMAR unit is 1585 bypassed by not enabling DMAR with this option. In 1586 this case, gfx device will use physical address for 1587 DMA. 1588 forcedac [x86_64] 1589 With this option iommu will not optimize to look 1590 for io virtual address below 32-bit forcing dual 1591 address cycle on pci bus for cards supporting greater 1592 than 32-bit addressing. The default is to look 1593 for translation below 32-bit and if not available 1594 then look in the higher range. 1595 strict [Default Off] 1596 With this option on every unmap_single operation will 1597 result in a hardware IOTLB flush operation as opposed 1598 to batching them for performance. 1599 sp_off [Default Off] 1600 By default, super page will be supported if Intel IOMMU 1601 has the capability. With this option, super page will 1602 not be supported. 1603 ecs_off [Default Off] 1604 By default, extended context tables will be supported if 1605 the hardware advertises that it has support both for the 1606 extended tables themselves, and also PASID support. With 1607 this option set, extended tables will not be used even 1608 on hardware which claims to support them. 1609 1610 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 1611 0 disables intel_idle and fall back on acpi_idle. 1612 1 to 6 specify maximum depth of C-state. 1613 1614 intel_pstate= [X86] 1615 disable 1616 Do not enable intel_pstate as the default 1617 scaling driver for the supported processors 1618 force 1619 Enable intel_pstate on systems that prohibit it by default 1620 in favor of acpi-cpufreq. Forcing the intel_pstate driver 1621 instead of acpi-cpufreq may disable platform features, such 1622 as thermal controls and power capping, that rely on ACPI 1623 P-States information being indicated to OSPM and therefore 1624 should be used with caution. This option does not work with 1625 processors that aren't supported by the intel_pstate driver 1626 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 1627 no_hwp 1628 Do not enable hardware P state control (HWP) 1629 if available. 1630 hwp_only 1631 Only load intel_pstate on systems which support 1632 hardware P state control (HWP) if available. 1633 1634 intremap= [X86-64, Intel-IOMMU] 1635 on enable Interrupt Remapping (default) 1636 off disable Interrupt Remapping 1637 nosid disable Source ID checking 1638 no_x2apic_optout 1639 BIOS x2APIC opt-out request will be ignored 1640 nopost disable Interrupt Posting 1641 1642 iomem= Disable strict checking of access to MMIO memory 1643 strict regions from userspace. 1644 relaxed 1645 1646 iommu= [x86] 1647 off 1648 force 1649 noforce 1650 biomerge 1651 panic 1652 nopanic 1653 merge 1654 nomerge 1655 forcesac 1656 soft 1657 pt [x86, IA-64] 1658 nobypass [PPC/POWERNV] 1659 Disable IOMMU bypass, using IOMMU for PCI devices. 1660 1661 1662 io7= [HW] IO7 for Marvel based alpha systems 1663 See comment before marvel_specify_io7 in 1664 arch/alpha/kernel/core_marvel.c. 1665 1666 io_delay= [X86] I/O delay method 1667 0x80 1668 Standard port 0x80 based delay 1669 0xed 1670 Alternate port 0xed based delay (needed on some systems) 1671 udelay 1672 Simple two microseconds delay 1673 none 1674 No delay 1675 1676 ip= [IP_PNP] 1677 See Documentation/filesystems/nfs/nfsroot.txt. 1678 1679 irqfixup [HW] 1680 When an interrupt is not handled search all handlers 1681 for it. Intended to get systems with badly broken 1682 firmware running. 1683 1684 irqpoll [HW] 1685 When an interrupt is not handled search all handlers 1686 for it. Also check all handlers each timer 1687 interrupt. Intended to get systems with badly broken 1688 firmware running. 1689 1690 isapnp= [ISAPNP] 1691 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 1692 1693 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler. 1694 Format: 1695 <cpu number>,...,<cpu number> 1696 or 1697 <cpu number>-<cpu number> 1698 (must be a positive range in ascending order) 1699 or a mixture 1700 <cpu number>,...,<cpu number>-<cpu number> 1701 1702 This option can be used to specify one or more CPUs 1703 to isolate from the general SMP balancing and scheduling 1704 algorithms. You can move a process onto or off an 1705 "isolated" CPU via the CPU affinity syscalls or cpuset. 1706 <cpu number> begins at 0 and the maximum value is 1707 "number of CPUs in system - 1". 1708 1709 This option is the preferred way to isolate CPUs. The 1710 alternative -- manually setting the CPU mask of all 1711 tasks in the system -- can cause problems and 1712 suboptimal load balancer performance. 1713 1714 iucv= [HW,NET] 1715 1716 ivrs_ioapic [HW,X86_64] 1717 Provide an override to the IOAPIC-ID<->DEVICE-ID 1718 mapping provided in the IVRS ACPI table. For 1719 example, to map IOAPIC-ID decimal 10 to 1720 PCI device 00:14.0 write the parameter as: 1721 ivrs_ioapic[10]=00:14.0 1722 1723 ivrs_hpet [HW,X86_64] 1724 Provide an override to the HPET-ID<->DEVICE-ID 1725 mapping provided in the IVRS ACPI table. For 1726 example, to map HPET-ID decimal 0 to 1727 PCI device 00:14.0 write the parameter as: 1728 ivrs_hpet[0]=00:14.0 1729 1730 js= [HW,JOY] Analog joystick 1731 See Documentation/input/joystick.txt. 1732 1733 kaslr/nokaslr [X86] 1734 Enable/disable kernel and module base offset ASLR 1735 (Address Space Layout Randomization) if built into 1736 the kernel. When CONFIG_HIBERNATION is selected, 1737 kASLR is disabled by default. When kASLR is enabled, 1738 hibernation will be disabled. 1739 1740 keepinitrd [HW,ARM] 1741 1742 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter 1743 specifies the amount of memory usable by the kernel 1744 for non-movable allocations. The requested amount is 1745 spread evenly throughout all nodes in the system. The 1746 remaining memory in each node is used for Movable 1747 pages. In the event, a node is too small to have both 1748 kernelcore and Movable pages, kernelcore pages will 1749 take priority and other nodes will have a larger number 1750 of Movable pages. The Movable zone is used for the 1751 allocation of pages that may be reclaimed or moved 1752 by the page migration subsystem. This means that 1753 HugeTLB pages may not be allocated from this zone. 1754 Note that allocations like PTEs-from-HighMem still 1755 use the HighMem zone if it exists, and the Normal 1756 zone if it does not. 1757 1758 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port. 1759 Format: <Controller#>[,poll interval] 1760 The controller # is the number of the ehci usb debug 1761 port as it is probed via PCI. The poll interval is 1762 optional and is the number seconds in between 1763 each poll cycle to the debug port in case you need 1764 the functionality for interrupting the kernel with 1765 gdb or control-c on the dbgp connection. When 1766 not using this parameter you use sysrq-g to break into 1767 the kernel debugger. 1768 1769 kgdboc= [KGDB,HW] kgdb over consoles. 1770 Requires a tty driver that supports console polling, 1771 or a supported polling keyboard driver (non-usb). 1772 Serial only format: <serial_device>[,baud] 1773 keyboard only format: kbd 1774 keyboard and serial format: kbd,<serial_device>[,baud] 1775 Optional Kernel mode setting: 1776 kms, kbd format: kms,kbd 1777 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 1778 1779 kgdbwait [KGDB] Stop kernel execution and enter the 1780 kernel debugger at the earliest opportunity. 1781 1782 kmac= [MIPS] korina ethernet MAC address. 1783 Configure the RouterBoard 532 series on-chip 1784 Ethernet adapter MAC address. 1785 1786 kmemleak= [KNL] Boot-time kmemleak enable/disable 1787 Valid arguments: on, off 1788 Default: on 1789 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 1790 the default is off. 1791 1792 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode 1793 Valid arguments: 0, 1, 2 1794 kmemcheck=0 (disabled) 1795 kmemcheck=1 (enabled) 1796 kmemcheck=2 (one-shot mode) 1797 Default: 2 (one-shot mode) 1798 1799 kstack=N [X86] Print N words from the kernel stack 1800 in oops dumps. 1801 1802 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 1803 Default is 0 (don't ignore, but inject #GP) 1804 1805 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit 1806 KVM MMU at runtime. 1807 Default is 0 (off) 1808 1809 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM. 1810 Default is 1 (enabled) 1811 1812 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU) 1813 for all guests. 1814 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode. 1815 1816 kvm-intel.ept= [KVM,Intel] Disable extended page tables 1817 (virtualized MMU) support on capable Intel chips. 1818 Default is 1 (enabled) 1819 1820 kvm-intel.emulate_invalid_guest_state= 1821 [KVM,Intel] Enable emulation of invalid guest states 1822 Default is 0 (disabled) 1823 1824 kvm-intel.flexpriority= 1825 [KVM,Intel] Disable FlexPriority feature (TPR shadow). 1826 Default is 1 (enabled) 1827 1828 kvm-intel.nested= 1829 [KVM,Intel] Enable VMX nesting (nVMX). 1830 Default is 0 (disabled) 1831 1832 kvm-intel.unrestricted_guest= 1833 [KVM,Intel] Disable unrestricted guest feature 1834 (virtualized real and unpaged mode) on capable 1835 Intel chips. Default is 1 (enabled) 1836 1837 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification 1838 feature (tagged TLBs) on capable Intel chips. 1839 Default is 1 (enabled) 1840 1841 l2cr= [PPC] 1842 1843 l3cr= [PPC] 1844 1845 lapic [X86-32,APIC] Enable the local APIC even if BIOS 1846 disabled it. 1847 1848 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline 1849 value for LAPIC timer one-shot implementation. Default 1850 back to the programmable timer unit in the LAPIC. 1851 1852 lapic_timer_c2_ok [X86,APIC] trust the local apic timer 1853 in C2 power state. 1854 1855 libata.dma= [LIBATA] DMA control 1856 libata.dma=0 Disable all PATA and SATA DMA 1857 libata.dma=1 PATA and SATA Disk DMA only 1858 libata.dma=2 ATAPI (CDROM) DMA only 1859 libata.dma=4 Compact Flash DMA only 1860 Combinations also work, so libata.dma=3 enables DMA 1861 for disks and CDROMs, but not CFs. 1862 1863 libata.ignore_hpa= [LIBATA] Ignore HPA limit 1864 libata.ignore_hpa=0 keep BIOS limits (default) 1865 libata.ignore_hpa=1 ignore limits, using full disk 1866 1867 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 1868 when set. 1869 Format: <int> 1870 1871 libata.force= [LIBATA] Force configurations. The format is comma 1872 separated list of "[ID:]VAL" where ID is 1873 PORT[.DEVICE]. PORT and DEVICE are decimal numbers 1874 matching port, link or device. Basically, it matches 1875 the ATA ID string printed on console by libata. If 1876 the whole ID part is omitted, the last PORT and DEVICE 1877 values are used. If ID hasn't been specified yet, the 1878 configuration applies to all ports, links and devices. 1879 1880 If only DEVICE is omitted, the parameter applies to 1881 the port and all links and devices behind it. DEVICE 1882 number of 0 either selects the first device or the 1883 first fan-out link behind PMP device. It does not 1884 select the host link. DEVICE number of 15 selects the 1885 host link and device attached to it. 1886 1887 The VAL specifies the configuration to force. As long 1888 as there's no ambiguity shortcut notation is allowed. 1889 For example, both 1.5 and 1.5G would work for 1.5Gbps. 1890 The following configurations can be forced. 1891 1892 * Cable type: 40c, 80c, short40c, unk, ign or sata. 1893 Any ID with matching PORT is used. 1894 1895 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 1896 1897 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 1898 udma[/][16,25,33,44,66,100,133] notation is also 1899 allowed. 1900 1901 * [no]ncq: Turn on or off NCQ. 1902 1903 * [no]ncqtrim: Turn off queued DSM TRIM. 1904 1905 * nohrst, nosrst, norst: suppress hard, soft 1906 and both resets. 1907 1908 * rstonce: only attempt one reset during 1909 hot-unplug link recovery 1910 1911 * dump_id: dump IDENTIFY data. 1912 1913 * atapi_dmadir: Enable ATAPI DMADIR bridge support 1914 1915 * disable: Disable this device. 1916 1917 If there are multiple matching configurations changing 1918 the same attribute, the last one is used. 1919 1920 memblock=debug [KNL] Enable memblock debug messages. 1921 1922 load_ramdisk= [RAM] List of ramdisks to load from floppy 1923 See Documentation/blockdev/ramdisk.txt. 1924 1925 lockd.nlm_grace_period=P [NFS] Assign grace period. 1926 Format: <integer> 1927 1928 lockd.nlm_tcpport=N [NFS] Assign TCP port. 1929 Format: <integer> 1930 1931 lockd.nlm_timeout=T [NFS] Assign timeout value. 1932 Format: <integer> 1933 1934 lockd.nlm_udpport=M [NFS] Assign UDP port. 1935 Format: <integer> 1936 1937 locktorture.nreaders_stress= [KNL] 1938 Set the number of locking read-acquisition kthreads. 1939 Defaults to being automatically set based on the 1940 number of online CPUs. 1941 1942 locktorture.nwriters_stress= [KNL] 1943 Set the number of locking write-acquisition kthreads. 1944 1945 locktorture.onoff_holdoff= [KNL] 1946 Set time (s) after boot for CPU-hotplug testing. 1947 1948 locktorture.onoff_interval= [KNL] 1949 Set time (s) between CPU-hotplug operations, or 1950 zero to disable CPU-hotplug testing. 1951 1952 locktorture.shuffle_interval= [KNL] 1953 Set task-shuffle interval (jiffies). Shuffling 1954 tasks allows some CPUs to go into dyntick-idle 1955 mode during the locktorture test. 1956 1957 locktorture.shutdown_secs= [KNL] 1958 Set time (s) after boot system shutdown. This 1959 is useful for hands-off automated testing. 1960 1961 locktorture.stat_interval= [KNL] 1962 Time (s) between statistics printk()s. 1963 1964 locktorture.stutter= [KNL] 1965 Time (s) to stutter testing, for example, 1966 specifying five seconds causes the test to run for 1967 five seconds, wait for five seconds, and so on. 1968 This tests the locking primitive's ability to 1969 transition abruptly to and from idle. 1970 1971 locktorture.torture_runnable= [BOOT] 1972 Start locktorture running at boot time. 1973 1974 locktorture.torture_type= [KNL] 1975 Specify the locking implementation to test. 1976 1977 locktorture.verbose= [KNL] 1978 Enable additional printk() statements. 1979 1980 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 1981 Format: <irq> 1982 1983 loglevel= All Kernel Messages with a loglevel smaller than the 1984 console loglevel will be printed to the console. It can 1985 also be changed with klogd or other programs. The 1986 loglevels are defined as follows: 1987 1988 0 (KERN_EMERG) system is unusable 1989 1 (KERN_ALERT) action must be taken immediately 1990 2 (KERN_CRIT) critical conditions 1991 3 (KERN_ERR) error conditions 1992 4 (KERN_WARNING) warning conditions 1993 5 (KERN_NOTICE) normal but significant condition 1994 6 (KERN_INFO) informational 1995 7 (KERN_DEBUG) debug-level messages 1996 1997 log_buf_len=n[KMG] Sets the size of the printk ring buffer, 1998 in bytes. n must be a power of two and greater 1999 than the minimal size. The minimal size is defined 2000 by LOG_BUF_SHIFT kernel config parameter. There is 2001 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter 2002 that allows to increase the default size depending on 2003 the number of CPUs. See init/Kconfig for more details. 2004 2005 logo.nologo [FB] Disables display of the built-in Linux logo. 2006 This may be used to provide more screen space for 2007 kernel log messages and is useful when debugging 2008 kernel boot problems. 2009 2010 lp=0 [LP] Specify parallel ports to use, e.g, 2011 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 2012 lp=reset first parallel port). 'lp=0' disables the 2013 lp=auto printer driver. 'lp=reset' (which can be 2014 specified in addition to the ports) causes 2015 attached printers to be reset. Using 2016 lp=port1,port2,... specifies the parallel ports 2017 to associate lp devices with, starting with 2018 lp0. A port specification may be 'none' to skip 2019 that lp device, or a parport name such as 2020 'parport0'. Specifying 'lp=auto' instead of a 2021 port specification list means that device IDs 2022 from each port should be examined, to see if 2023 an IEEE 1284-compliant printer is attached; if 2024 so, the driver will manage that printer. 2025 See also header of drivers/char/lp.c. 2026 2027 lpj=n [KNL] 2028 Sets loops_per_jiffy to given constant, thus avoiding 2029 time-consuming boot-time autodetection (up to 250 ms per 2030 CPU). 0 enables autodetection (default). To determine 2031 the correct value for your kernel, boot with normal 2032 autodetection and see what value is printed. Note that 2033 on SMP systems the preset will be applied to all CPUs, 2034 which is likely to cause problems if your CPUs need 2035 significantly divergent settings. An incorrect value 2036 will cause delays in the kernel to be wrong, leading to 2037 unpredictable I/O errors and other breakage. Although 2038 unlikely, in the extreme case this might damage your 2039 hardware. 2040 2041 ltpc= [NET] 2042 Format: <io>,<irq>,<dma> 2043 2044 machvec= [IA-64] Force the use of a particular machine-vector 2045 (machvec) in a generic kernel. 2046 Example: machvec=hpzx1_swiotlb 2047 2048 machtype= [Loongson] Share the same kernel image file between different 2049 yeeloong laptop. 2050 Example: machtype=lemote-yeeloong-2f-7inch 2051 2052 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater 2053 than or equal to this physical address is ignored. 2054 2055 maxcpus= [SMP] Maximum number of processors that an SMP kernel 2056 should make use of. maxcpus=n : n >= 0 limits the 2057 kernel to using 'n' processors. n=0 is a special case, 2058 it is equivalent to "nosmp", which also disables 2059 the IO APIC. 2060 2061 max_loop= [LOOP] The number of loop block devices that get 2062 (loop.max_loop) unconditionally pre-created at init time. The default 2063 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 2064 of statically allocating a predefined number, loop 2065 devices can be requested on-demand with the 2066 /dev/loop-control interface. 2067 2068 mce [X86-32] Machine Check Exception 2069 2070 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt 2071 2072 md= [HW] RAID subsystems devices and level 2073 See Documentation/md.txt. 2074 2075 mdacon= [MDA] 2076 Format: <first>,<last> 2077 Specifies range of consoles to be captured by the MDA. 2078 2079 mds= [X86,INTEL] 2080 Control mitigation for the Micro-architectural Data 2081 Sampling (MDS) vulnerability. 2082 2083 Certain CPUs are vulnerable to an exploit against CPU 2084 internal buffers which can forward information to a 2085 disclosure gadget under certain conditions. 2086 2087 In vulnerable processors, the speculatively 2088 forwarded data can be used in a cache side channel 2089 attack, to access data to which the attacker does 2090 not have direct access. 2091 2092 This parameter controls the MDS mitigation. The 2093 options are: 2094 2095 full - Enable MDS mitigation on vulnerable CPUs 2096 off - Unconditionally disable MDS mitigation 2097 2098 On TAA-affected machines, mds=off can be prevented by 2099 an active TAA mitigation as both vulnerabilities are 2100 mitigated with the same mechanism so in order to disable 2101 this mitigation, you need to specify tsx_async_abort=off 2102 too. 2103 2104 Not specifying this option is equivalent to 2105 mds=full. 2106 2107 For details see: Documentation/hw-vuln/mds.rst 2108 2109 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory 2110 Amount of memory to be used when the kernel is not able 2111 to see the whole system memory or for test. 2112 [X86] Work as limiting max address. Use together 2113 with memmap= to avoid physical address space collisions. 2114 Without memmap= PCI devices could be placed at addresses 2115 belonging to unused RAM. 2116 2117 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 2118 memory. 2119 2120 memchunk=nn[KMG] 2121 [KNL,SH] Allow user to override the default size for 2122 per-device physically contiguous DMA buffers. 2123 2124 memmap=exactmap [KNL,X86] Enable setting of an exact 2125 E820 memory map, as specified by the user. 2126 Such memmap=exactmap lines can be constructed based on 2127 BIOS output or other requirements. See the memmap=nn@ss 2128 option description. 2129 2130 memmap=nn[KMG]@ss[KMG] 2131 [KNL] Force usage of a specific region of memory. 2132 Region of memory to be used is from ss to ss+nn. 2133 2134 memmap=nn[KMG]#ss[KMG] 2135 [KNL,ACPI] Mark specific memory as ACPI data. 2136 Region of memory to be marked is from ss to ss+nn. 2137 2138 memmap=nn[KMG]$ss[KMG] 2139 [KNL,ACPI] Mark specific memory as reserved. 2140 Region of memory to be reserved is from ss to ss+nn. 2141 Example: Exclude memory from 0x18690000-0x1869ffff 2142 memmap=64K$0x18690000 2143 or 2144 memmap=0x10000$0x18690000 2145 2146 memmap=nn[KMG]!ss[KMG] 2147 [KNL,X86] Mark specific memory as protected. 2148 Region of memory to be used, from ss to ss+nn. 2149 The memory region may be marked as e820 type 12 (0xc) 2150 and is NVDIMM or ADR memory. 2151 2152 memory_corruption_check=0/1 [X86] 2153 Some BIOSes seem to corrupt the first 64k of 2154 memory when doing things like suspend/resume. 2155 Setting this option will scan the memory 2156 looking for corruption. Enabling this will 2157 both detect corruption and prevent the kernel 2158 from using the memory being corrupted. 2159 However, its intended as a diagnostic tool; if 2160 repeatable BIOS-originated corruption always 2161 affects the same memory, you can use memmap= 2162 to prevent the kernel from using that memory. 2163 2164 memory_corruption_check_size=size [X86] 2165 By default it checks for corruption in the low 2166 64k, making this memory unavailable for normal 2167 use. Use this parameter to scan for 2168 corruption in more or less memory. 2169 2170 memory_corruption_check_period=seconds [X86] 2171 By default it checks for corruption every 60 2172 seconds. Use this parameter to check at some 2173 other rate. 0 disables periodic checking. 2174 2175 memtest= [KNL,X86,ARM] Enable memtest 2176 Format: <integer> 2177 default : 0 <disable> 2178 Specifies the number of memtest passes to be 2179 performed. Each pass selects another test 2180 pattern from a given set of patterns. Memtest 2181 fills the memory with this pattern, validates 2182 memory contents and reserves bad memory 2183 regions that are detected. 2184 2185 meye.*= [HW] Set MotionEye Camera parameters 2186 See Documentation/video4linux/meye.txt. 2187 2188 mfgpt_irq= [IA-32] Specify the IRQ to use for the 2189 Multi-Function General Purpose Timers on AMD Geode 2190 platforms. 2191 2192 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 2193 the BIOS has incorrectly applied a workaround. TinyBIOS 2194 version 0.98 is known to be affected, 0.99 fixes the 2195 problem by letting the user disable the workaround. 2196 2197 mga= [HW,DRM] 2198 2199 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this 2200 physical address is ignored. 2201 2202 mini2440= [ARM,HW,KNL] 2203 Format:[0..2][b][c][t] 2204 Default: "0tb" 2205 MINI2440 configuration specification: 2206 0 - The attached screen is the 3.5" TFT 2207 1 - The attached screen is the 7" TFT 2208 2 - The VGA Shield is attached (1024x768) 2209 Leaving out the screen size parameter will not load 2210 the TFT driver, and the framebuffer will be left 2211 unconfigured. 2212 b - Enable backlight. The TFT backlight pin will be 2213 linked to the kernel VESA blanking code and a GPIO 2214 LED. This parameter is not necessary when using the 2215 VGA shield. 2216 c - Enable the s3c camera interface. 2217 t - Reserved for enabling touchscreen support. The 2218 touchscreen support is not enabled in the mainstream 2219 kernel as of 2.6.30, a preliminary port can be found 2220 in the "bleeding edge" mini2440 support kernel at 2221 http://repo.or.cz/w/linux-2.6/mini2440.git 2222 2223 mitigations= 2224 [X86] Control optional mitigations for CPU 2225 vulnerabilities. This is a set of curated, 2226 arch-independent options, each of which is an 2227 aggregation of existing arch-specific options. 2228 2229 off 2230 Disable all optional CPU mitigations. This 2231 improves system performance, but it may also 2232 expose users to several CPU vulnerabilities. 2233 Equivalent to: nopti [X86] 2234 nospectre_v1 [X86] 2235 nospectre_v2 [X86] 2236 spectre_v2_user=off [X86] 2237 spec_store_bypass_disable=off [X86] 2238 mds=off [X86] 2239 tsx_async_abort=off [X86] 2240 no_entry_flush [PPC] 2241 no_uaccess_flush [PPC] 2242 2243 auto (default) 2244 Mitigate all CPU vulnerabilities, but leave SMT 2245 enabled, even if it's vulnerable. This is for 2246 users who don't want to be surprised by SMT 2247 getting disabled across kernel upgrades, or who 2248 have other ways of avoiding SMT-based attacks. 2249 Equivalent to: (default behavior) 2250 2251 mminit_loglevel= 2252 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this 2253 parameter allows control of the logging verbosity for 2254 the additional memory initialisation checks. A value 2255 of 0 disables mminit logging and a level of 4 will 2256 log everything. Information is printed at KERN_DEBUG 2257 so loglevel=8 may also need to be specified. 2258 2259 module.sig_enforce 2260 [KNL] When CONFIG_MODULE_SIG is set, this means that 2261 modules without (valid) signatures will fail to load. 2262 Note that if CONFIG_MODULE_SIG_FORCE is set, that 2263 is always true, so this option does nothing. 2264 2265 mousedev.tap_time= 2266 [MOUSE] Maximum time between finger touching and 2267 leaving touchpad surface for touch to be considered 2268 a tap and be reported as a left button click (for 2269 touchpads working in absolute mode only). 2270 Format: <msecs> 2271 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 2272 reporting absolute coordinates, such as tablets 2273 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 2274 reporting absolute coordinates, such as tablets 2275 2276 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter 2277 is similar to kernelcore except it specifies the 2278 amount of memory used for migratable allocations. 2279 If both kernelcore and movablecore is specified, 2280 then kernelcore will be at *least* the specified 2281 value but may be more. If movablecore on its own 2282 is specified, the administrator must be careful 2283 that the amount of memory usable for all allocations 2284 is not too small. 2285 2286 movable_node [KNL,X86] Boot-time switch to enable the effects 2287 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details. 2288 2289 MTD_Partition= [MTD] 2290 Format: <name>,<region-number>,<size>,<offset> 2291 2292 MTD_Region= [MTD] Format: 2293 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 2294 2295 mtdparts= [MTD] 2296 See drivers/mtd/cmdlinepart.c. 2297 2298 multitce=off [PPC] This parameter disables the use of the pSeries 2299 firmware feature for updating multiple TCE entries 2300 at a time. 2301 2302 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 2303 2304 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 2305 2306 boundary - index of last SLC block on Flex-OneNAND. 2307 The remaining blocks are configured as MLC blocks. 2308 lock - Configure if Flex-OneNAND boundary should be locked. 2309 Once locked, the boundary cannot be changed. 2310 1 indicates lock status, 0 indicates unlock status. 2311 2312 mtdset= [ARM] 2313 ARM/S3C2412 JIVE boot control 2314 2315 See arch/arm/mach-s3c2412/mach-jive.c 2316 2317 mtouchusb.raw_coordinates= 2318 [HW] Make the MicroTouch USB driver use raw coordinates 2319 ('y', default) or cooked coordinates ('n') 2320 2321 mtrr_chunk_size=nn[KMG] [X86] 2322 used for mtrr cleanup. It is largest continuous chunk 2323 that could hold holes aka. UC entries. 2324 2325 mtrr_gran_size=nn[KMG] [X86] 2326 Used for mtrr cleanup. It is granularity of mtrr block. 2327 Default is 1. 2328 Large value could prevent small alignment from 2329 using up MTRRs. 2330 2331 mtrr_spare_reg_nr=n [X86] 2332 Format: <integer> 2333 Range: 0,7 : spare reg number 2334 Default : 1 2335 Used for mtrr cleanup. It is spare mtrr entries number. 2336 Set to 2 or more if your graphical card needs more. 2337 2338 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 2339 2340 netdev= [NET] Network devices parameters 2341 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 2342 Note that mem_start is often overloaded to mean 2343 something different and driver-specific. 2344 This usage is only documented in each driver source 2345 file if at all. 2346 2347 nf_conntrack.acct= 2348 [NETFILTER] Enable connection tracking flow accounting 2349 0 to disable accounting 2350 1 to enable accounting 2351 Default value is 0. 2352 2353 nfsaddrs= [NFS] Deprecated. Use ip= instead. 2354 See Documentation/filesystems/nfs/nfsroot.txt. 2355 2356 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 2357 See Documentation/filesystems/nfs/nfsroot.txt. 2358 2359 nfsrootdebug [NFS] enable nfsroot debugging messages. 2360 See Documentation/filesystems/nfs/nfsroot.txt. 2361 2362 nfs.callback_tcpport= 2363 [NFS] set the TCP port on which the NFSv4 callback 2364 channel should listen. 2365 2366 nfs.cache_getent= 2367 [NFS] sets the pathname to the program which is used 2368 to update the NFS client cache entries. 2369 2370 nfs.cache_getent_timeout= 2371 [NFS] sets the timeout after which an attempt to 2372 update a cache entry is deemed to have failed. 2373 2374 nfs.idmap_cache_timeout= 2375 [NFS] set the maximum lifetime for idmapper cache 2376 entries. 2377 2378 nfs.enable_ino64= 2379 [NFS] enable 64-bit inode numbers. 2380 If zero, the NFS client will fake up a 32-bit inode 2381 number for the readdir() and stat() syscalls instead 2382 of returning the full 64-bit number. 2383 The default is to return 64-bit inode numbers. 2384 2385 nfs.max_session_slots= 2386 [NFSv4.1] Sets the maximum number of session slots 2387 the client will attempt to negotiate with the server. 2388 This limits the number of simultaneous RPC requests 2389 that the client can send to the NFSv4.1 server. 2390 Note that there is little point in setting this 2391 value higher than the max_tcp_slot_table_limit. 2392 2393 nfs.nfs4_disable_idmapping= 2394 [NFSv4] When set to the default of '1', this option 2395 ensures that both the RPC level authentication 2396 scheme and the NFS level operations agree to use 2397 numeric uids/gids if the mount is using the 2398 'sec=sys' security flavour. In effect it is 2399 disabling idmapping, which can make migration from 2400 legacy NFSv2/v3 systems to NFSv4 easier. 2401 Servers that do not support this mode of operation 2402 will be autodetected by the client, and it will fall 2403 back to using the idmapper. 2404 To turn off this behaviour, set the value to '0'. 2405 nfs.nfs4_unique_id= 2406 [NFS4] Specify an additional fixed unique ident- 2407 ification string that NFSv4 clients can insert into 2408 their nfs_client_id4 string. This is typically a 2409 UUID that is generated at system install time. 2410 2411 nfs.send_implementation_id = 2412 [NFSv4.1] Send client implementation identification 2413 information in exchange_id requests. 2414 If zero, no implementation identification information 2415 will be sent. 2416 The default is to send the implementation identification 2417 information. 2418 2419 nfs.recover_lost_locks = 2420 [NFSv4] Attempt to recover locks that were lost due 2421 to a lease timeout on the server. Please note that 2422 doing this risks data corruption, since there are 2423 no guarantees that the file will remain unchanged 2424 after the locks are lost. 2425 If you want to enable the kernel legacy behaviour of 2426 attempting to recover these locks, then set this 2427 parameter to '1'. 2428 The default parameter value of '0' causes the kernel 2429 not to attempt recovery of lost locks. 2430 2431 nfs4.layoutstats_timer = 2432 [NFSv4.2] Change the rate at which the kernel sends 2433 layoutstats to the pNFS metadata server. 2434 2435 Setting this to value to 0 causes the kernel to use 2436 whatever value is the default set by the layout 2437 driver. A non-zero value sets the minimum interval 2438 in seconds between layoutstats transmissions. 2439 2440 nfsd.nfs4_disable_idmapping= 2441 [NFSv4] When set to the default of '1', the NFSv4 2442 server will return only numeric uids and gids to 2443 clients using auth_sys, and will accept numeric uids 2444 and gids from such clients. This is intended to ease 2445 migration from NFSv2/v3. 2446 2447 objlayoutdriver.osd_login_prog= 2448 [NFS] [OBJLAYOUT] sets the pathname to the program which 2449 is used to automatically discover and login into new 2450 osd-targets. Please see: 2451 Documentation/filesystems/pnfs.txt for more explanations 2452 2453 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take 2454 when a NMI is triggered. 2455 Format: [state][,regs][,debounce][,die] 2456 2457 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 2458 Format: [panic,][nopanic,][num] 2459 Valid num: 0 or 1 2460 0 - turn hardlockup detector in nmi_watchdog off 2461 1 - turn hardlockup detector in nmi_watchdog on 2462 When panic is specified, panic when an NMI watchdog 2463 timeout occurs (or 'nopanic' to override the opposite 2464 default). To disable both hard and soft lockup detectors, 2465 please see 'nowatchdog'. 2466 This is useful when you use a panic=... timeout and 2467 need the box quickly up again. 2468 2469 netpoll.carrier_timeout= 2470 [NET] Specifies amount of time (in seconds) that 2471 netpoll should wait for a carrier. By default netpoll 2472 waits 4 seconds. 2473 2474 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 2475 emulation library even if a 387 maths coprocessor 2476 is present. 2477 2478 no_console_suspend 2479 [HW] Never suspend the console 2480 Disable suspending of consoles during suspend and 2481 hibernate operations. Once disabled, debugging 2482 messages can reach various consoles while the rest 2483 of the system is being put to sleep (ie, while 2484 debugging driver suspend/resume hooks). This may 2485 not work reliably with all consoles, but is known 2486 to work with serial and VGA consoles. 2487 To facilitate more flexible debugging, we also add 2488 console_suspend, a printk module parameter to control 2489 it. Users could use console_suspend (usually 2490 /sys/module/printk/parameters/console_suspend) to 2491 turn on/off it dynamically. 2492 2493 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien 2494 caches in the slab allocator. Saves per-node memory, 2495 but will impact performance. 2496 2497 noalign [KNL,ARM] 2498 2499 noaltinstr [S390] Disables alternative instructions patching 2500 (CPU alternatives feature). 2501 2502 noapic [SMP,APIC] Tells the kernel to not make use of any 2503 IOAPICs that may be present in the system. 2504 2505 noautogroup Disable scheduler automatic task group creation. 2506 2507 nobats [PPC] Do not use BATs for mapping kernel lowmem 2508 on "Classic" PPC cores. 2509 2510 nocache [ARM] 2511 2512 noclflush [BUGS=X86] Don't use the CLFLUSH instruction 2513 2514 nodelayacct [KNL] Disable per-task delay accounting 2515 2516 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects. 2517 2518 nodsp [SH] Disable hardware DSP at boot time. 2519 2520 noefi Disable EFI runtime services support. 2521 2522 no_entry_flush [PPC] Don't flush the L1-D cache when entering the kernel. 2523 2524 noexec [IA-64] 2525 2526 noexec [X86] 2527 On X86-32 available only on PAE configured kernels. 2528 noexec=on: enable non-executable mappings (default) 2529 noexec=off: disable non-executable mappings 2530 2531 noexec [MIPS] 2532 Force indicating stack and heap as non-executable or 2533 executable regardless of PT_GNU_STACK entry or CPU XI 2534 (execute inhibit) support. Valid valuess are: on, off. 2535 noexec=on: force indicating non-executable 2536 stack and heap 2537 noexec=off: force indicating executable 2538 stack and heap 2539 If this parameter is omitted, stack and heap will be 2540 indicated non-executable or executable as they are 2541 actually set up, which depends on PT_GNU_STACK entry 2542 and possibly other factors (for instance, CPU XI 2543 support). 2544 NOTE: Using noexec=on on a system without CPU XI 2545 support is not recommended since there is no actual 2546 HW support that provide non-executable stack/heap. 2547 Use only for debugging purposes and not in a 2548 production environment. 2549 2550 nosmap [X86] 2551 Disable SMAP (Supervisor Mode Access Prevention) 2552 even if it is supported by processor. 2553 2554 nosmep [X86] 2555 Disable SMEP (Supervisor Mode Execution Prevention) 2556 even if it is supported by processor. 2557 2558 noexec32 [X86-64] 2559 This affects only 32-bit executables. 2560 noexec32=on: enable non-executable mappings (default) 2561 read doesn't imply executable mappings 2562 noexec32=off: disable non-executable mappings 2563 read implies executable mappings 2564 2565 nofpu [MIPS,SH] Disable hardware FPU at boot time. 2566 2567 nofxsr [BUGS=X86-32] Disables x86 floating point extended 2568 register save and restore. The kernel will only save 2569 legacy floating-point registers on task switch. 2570 2571 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings. 2572 2573 nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1 2574 (bounds check bypass). With this option data leaks are 2575 possible in the system. 2576 2577 nospectre_v2 [X86,PPC_FSL_BOOK3E] Disable all mitigations for the Spectre variant 2 2578 (indirect branch prediction) vulnerability. System may 2579 allow data leaks with this option, which is equivalent 2580 to spectre_v2=off. 2581 2582 nospec_store_bypass_disable 2583 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability 2584 2585 no_uaccess_flush 2586 [PPC] Don't flush the L1-D cache after accessing user data. 2587 2588 noxsave [BUGS=X86] Disables x86 extended register state save 2589 and restore using xsave. The kernel will fallback to 2590 enabling legacy floating-point and sse state. 2591 2592 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 2593 register states. The kernel will fall back to use 2594 xsave to save the states. By using this parameter, 2595 performance of saving the states is degraded because 2596 xsave doesn't support modified optimization while 2597 xsaveopt supports it on xsaveopt enabled systems. 2598 2599 noxsaves [X86] Disables xsaves and xrstors used in saving and 2600 restoring x86 extended register state in compacted 2601 form of xsave area. The kernel will fall back to use 2602 xsaveopt and xrstor to save and restore the states 2603 in standard form of xsave area. By using this 2604 parameter, xsave area per process might occupy more 2605 memory on xsaves enabled systems. 2606 2607 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or 2608 wfi(ARM) instruction doesn't work correctly and not to 2609 use it. This is also useful when using JTAG debugger. 2610 2611 no_file_caps Tells the kernel not to honor file capabilities. The 2612 only way then for a file to be executed with privilege 2613 is to be setuid root or executed by root. 2614 2615 nohalt [IA-64] Tells the kernel not to use the power saving 2616 function PAL_HALT_LIGHT when idle. This increases 2617 power-consumption. On the positive side, it reduces 2618 interrupt wake-up latency, which may improve performance 2619 in certain environments such as networked servers or 2620 real-time systems. 2621 2622 nohibernate [HIBERNATION] Disable hibernation and resume. 2623 2624 nohz= [KNL] Boottime enable/disable dynamic ticks 2625 Valid arguments: on, off 2626 Default: on 2627 2628 nohz_full= [KNL,BOOT] 2629 In kernels built with CONFIG_NO_HZ_FULL=y, set 2630 the specified list of CPUs whose tick will be stopped 2631 whenever possible. The boot CPU will be forced outside 2632 the range to maintain the timekeeping. 2633 The CPUs in this range must also be included in the 2634 rcu_nocbs= set. 2635 2636 noiotrap [SH] Disables trapped I/O port accesses. 2637 2638 noirqdebug [X86-32] Disables the code which attempts to detect and 2639 disable unhandled interrupt sources. 2640 2641 no_timer_check [X86,APIC] Disables the code which tests for 2642 broken timer IRQ sources. 2643 2644 noisapnp [ISAPNP] Disables ISA PnP code. 2645 2646 noinitrd [RAM] Tells the kernel not to load any configured 2647 initial RAM disk. 2648 2649 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt 2650 remapping. 2651 [Deprecated - use intremap=off] 2652 2653 nointroute [IA-64] 2654 2655 noinvpcid [X86] Disable the INVPCID cpu feature. 2656 2657 nojitter [IA-64] Disables jitter checking for ITC timers. 2658 2659 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver 2660 2661 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page 2662 fault handling. 2663 2664 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting. 2665 steal time is computed, but won't influence scheduler 2666 behaviour 2667 2668 nolapic [X86-32,APIC] Do not enable or use the local APIC. 2669 2670 nolapic_timer [X86-32,APIC] Do not use the local APIC timer. 2671 2672 noltlbs [PPC] Do not use large page/tlb entries for kernel 2673 lowmem mapping on PPC40x. 2674 2675 nomca [IA-64] Disable machine check abort handling 2676 2677 nomce [X86-32] Disable Machine Check Exception 2678 2679 nomfgpt [X86-32] Disable Multi-Function General Purpose 2680 Timer usage (for AMD Geode machines). 2681 2682 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 2683 shutdown the other cpus. Instead use the REBOOT_VECTOR 2684 irq. 2685 2686 nomodule Disable module load 2687 2688 nopat [X86] Disable PAT (page attribute table extension of 2689 pagetables) support. 2690 2691 nopcid [X86-64] Disable the PCID cpu feature. 2692 2693 norandmaps Don't use address space randomization. Equivalent to 2694 echo 0 > /proc/sys/kernel/randomize_va_space 2695 2696 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 2697 with UP alternatives 2698 2699 nordrand [X86] Disable kernel use of the RDRAND and 2700 RDSEED instructions even if they are supported 2701 by the processor. RDRAND and RDSEED are still 2702 available to user space applications. 2703 2704 noresume [SWSUSP] Disables resume and restores original swap 2705 space. 2706 2707 no-scroll [VGA] Disables scrollback. 2708 This is required for the Braillex ib80-piezo Braille 2709 reader made by F.H. Papenmeier (Germany). 2710 2711 nosbagart [IA-64] 2712 2713 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support. 2714 2715 nosmp [SMP] Tells an SMP kernel to act as a UP kernel, 2716 and disable the IO APIC. legacy for "maxcpus=0". 2717 2718 nosoftlockup [KNL] Disable the soft-lockup detector. 2719 2720 nosync [HW,M68K] Disables sync negotiation for all devices. 2721 2722 notsc [BUGS=X86-32] Disable Time Stamp Counter 2723 2724 nousb [USB] Disable the USB subsystem 2725 2726 nowatchdog [KNL] Disable both lockup detectors, i.e. 2727 soft-lockup and NMI watchdog (hard-lockup). 2728 2729 nowb [ARM] 2730 2731 nox2apic [X86-64,APIC] Do not enable x2APIC mode. 2732 2733 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when 2734 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off. 2735 Some features depend on CPU0. Known dependencies are: 2736 1. Resume from suspend/hibernate depends on CPU0. 2737 Suspend/hibernate will fail if CPU0 is offline and you 2738 need to online CPU0 before suspend/hibernate. 2739 2. PIC interrupts also depend on CPU0. CPU0 can't be 2740 removed if a PIC interrupt is detected. 2741 It's said poweroff/reboot may depend on CPU0 on some 2742 machines although I haven't seen such issues so far 2743 after CPU0 is offline on a few tested machines. 2744 If the dependencies are under your control, you can 2745 turn on cpu0_hotplug. 2746 2747 nptcg= [IA-64] Override max number of concurrent global TLB 2748 purges which is reported from either PAL_VM_SUMMARY or 2749 SAL PALO. 2750 2751 nr_cpus= [SMP] Maximum number of processors that an SMP kernel 2752 could support. nr_cpus=n : n >= 1 limits the kernel to 2753 supporting 'n' processors. Later in runtime you can not 2754 use hotplug cpu feature to put more cpu back to online. 2755 just like you compile the kernel NR_CPUS=n 2756 2757 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 2758 2759 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing. 2760 Allowed values are enable and disable 2761 2762 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 2763 one of ['zone', 'node', 'default'] can be specified 2764 This can be set from sysctl after boot. 2765 See Documentation/sysctl/vm.txt for details. 2766 2767 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver. 2768 See Documentation/debugging-via-ohci1394.txt for more 2769 info. 2770 2771 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 2772 Rather than timing out after 20 ms if an EC 2773 command is not properly ACKed, override the length 2774 of the timeout. We have interrupts disabled while 2775 waiting for the ACK, so if this is set too high 2776 interrupts *may* be lost! 2777 2778 omap_mux= [OMAP] Override bootloader pin multiplexing. 2779 Format: <mux_mode0.mode_name=value>... 2780 For example, to override I2C bus2: 2781 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 2782 2783 oprofile.timer= [HW] 2784 Use timer interrupt instead of performance counters 2785 2786 oprofile.cpu_type= Force an oprofile cpu type 2787 This might be useful if you have an older oprofile 2788 userland or if you want common events. 2789 Format: { arch_perfmon } 2790 arch_perfmon: [X86] Force use of architectural 2791 perfmon on Intel CPUs instead of the 2792 CPU specific event set. 2793 timer: [X86] Force use of architectural NMI 2794 timer mode (see also oprofile.timer 2795 for generic hr timer mode) 2796 [s390] Force legacy basic mode sampling 2797 (report cpu_type "timer") 2798 2799 oops=panic Always panic on oopses. Default is to just kill the 2800 process, but there is a small probability of 2801 deadlocking the machine. 2802 This will also cause panics on machine check exceptions. 2803 Useful together with panic=30 to trigger a reboot. 2804 2805 OSS [HW,OSS] 2806 See Documentation/sound/oss/oss-parameters.txt 2807 2808 page_owner= [KNL] Boot-time page_owner enabling option. 2809 Storage of the information about who allocated 2810 each page is disabled in default. With this switch, 2811 we can turn it on. 2812 on: enable the feature 2813 2814 panic= [KNL] Kernel behaviour on panic: delay <timeout> 2815 timeout > 0: seconds before rebooting 2816 timeout = 0: wait forever 2817 timeout < 0: reboot immediately 2818 Format: <timeout> 2819 2820 panic_on_warn panic() instead of WARN(). Useful to cause kdump 2821 on a WARN(). 2822 2823 crash_kexec_post_notifiers 2824 Run kdump after running panic-notifiers and dumping 2825 kmsg. This only for the users who doubt kdump always 2826 succeeds in any situation. 2827 Note that this also increases risks of kdump failure, 2828 because some panic notifiers can make the crashed 2829 kernel more unstable. 2830 2831 parkbd.port= [HW] Parallel port number the keyboard adapter is 2832 connected to, default is 0. 2833 Format: <parport#> 2834 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 2835 0 for XT, 1 for AT (default is AT). 2836 Format: <mode> 2837 2838 parport= [HW,PPT] Specify parallel ports. 0 disables. 2839 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 2840 Use 'auto' to force the driver to use any 2841 IRQ/DMA settings detected (the default is to 2842 ignore detected IRQ/DMA settings because of 2843 possible conflicts). You can specify the base 2844 address, IRQ, and DMA settings; IRQ and DMA 2845 should be numbers, or 'auto' (for using detected 2846 settings on that particular port), or 'nofifo' 2847 (to avoid using a FIFO even if it is detected). 2848 Parallel ports are assigned in the order they 2849 are specified on the command line, starting 2850 with parport0. 2851 2852 parport_init_mode= [HW,PPT] 2853 Configure VIA parallel port to operate in 2854 a specific mode. This is necessary on Pegasos 2855 computer where firmware has no options for setting 2856 up parallel port mode and sets it to spp. 2857 Currently this function knows 686a and 8231 chips. 2858 Format: [spp|ps2|epp|ecp|ecpepp] 2859 2860 pause_on_oops= 2861 Halt all CPUs after the first oops has been printed for 2862 the specified number of seconds. This is to be used if 2863 your oopses keep scrolling off the screen. 2864 2865 pcbit= [HW,ISDN] 2866 2867 pcd. [PARIDE] 2868 See header of drivers/block/paride/pcd.c. 2869 See also Documentation/blockdev/paride.txt. 2870 2871 pci=option[,option...] [PCI] various PCI subsystem options: 2872 earlydump [X86] dump PCI config space before the kernel 2873 changes anything 2874 off [X86] don't probe for the PCI bus 2875 bios [X86-32] force use of PCI BIOS, don't access 2876 the hardware directly. Use this if your machine 2877 has a non-standard PCI host bridge. 2878 nobios [X86-32] disallow use of PCI BIOS, only direct 2879 hardware access methods are allowed. Use this 2880 if you experience crashes upon bootup and you 2881 suspect they are caused by the BIOS. 2882 conf1 [X86] Force use of PCI Configuration 2883 Mechanism 1. 2884 conf2 [X86] Force use of PCI Configuration 2885 Mechanism 2. 2886 noaer [PCIE] If the PCIEAER kernel config parameter is 2887 enabled, this kernel boot option can be used to 2888 disable the use of PCIE advanced error reporting. 2889 nodomains [PCI] Disable support for multiple PCI 2890 root domains (aka PCI segments, in ACPI-speak). 2891 nommconf [X86] Disable use of MMCONFIG for PCI 2892 Configuration 2893 check_enable_amd_mmconf [X86] check for and enable 2894 properly configured MMIO access to PCI 2895 config space on AMD family 10h CPU 2896 nomsi [MSI] If the PCI_MSI kernel config parameter is 2897 enabled, this kernel boot option can be used to 2898 disable the use of MSI interrupts system-wide. 2899 noioapicquirk [APIC] Disable all boot interrupt quirks. 2900 Safety option to keep boot IRQs enabled. This 2901 should never be necessary. 2902 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 2903 primary IO-APIC for bridges that cannot disable 2904 boot IRQs. This fixes a source of spurious IRQs 2905 when the system masks IRQs. 2906 noioapicreroute [APIC] Disable workaround that uses the 2907 boot IRQ equivalent of an IRQ that connects to 2908 a chipset where boot IRQs cannot be disabled. 2909 The opposite of ioapicreroute. 2910 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 2911 routing table. These calls are known to be buggy 2912 on several machines and they hang the machine 2913 when used, but on other computers it's the only 2914 way to get the interrupt routing table. Try 2915 this option if the kernel is unable to allocate 2916 IRQs or discover secondary PCI buses on your 2917 motherboard. 2918 rom [X86] Assign address space to expansion ROMs. 2919 Use with caution as certain devices share 2920 address decoders between ROMs and other 2921 resources. 2922 norom [X86] Do not assign address space to 2923 expansion ROMs that do not already have 2924 BIOS assigned address ranges. 2925 nobar [X86] Do not assign address space to the 2926 BARs that weren't assigned by the BIOS. 2927 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 2928 assigned automatically to PCI devices. You can 2929 make the kernel exclude IRQs of your ISA cards 2930 this way. 2931 pirqaddr=0xAAAAA [X86] Specify the physical address 2932 of the PIRQ table (normally generated 2933 by the BIOS) if it is outside the 2934 F0000h-100000h range. 2935 lastbus=N [X86] Scan all buses thru bus #N. Can be 2936 useful if the kernel is unable to find your 2937 secondary buses and you want to tell it 2938 explicitly which ones they are. 2939 assign-busses [X86] Always assign all PCI bus 2940 numbers ourselves, overriding 2941 whatever the firmware may have done. 2942 usepirqmask [X86] Honor the possible IRQ mask stored 2943 in the BIOS $PIR table. This is needed on 2944 some systems with broken BIOSes, notably 2945 some HP Pavilion N5400 and Omnibook XE3 2946 notebooks. This will have no effect if ACPI 2947 IRQ routing is enabled. 2948 noacpi [X86] Do not use ACPI for IRQ routing 2949 or for PCI scanning. 2950 use_crs [X86] Use PCI host bridge window information 2951 from ACPI. On BIOSes from 2008 or later, this 2952 is enabled by default. If you need to use this, 2953 please report a bug. 2954 nocrs [X86] Ignore PCI host bridge windows from ACPI. 2955 If you need to use this, please report a bug. 2956 routeirq Do IRQ routing for all PCI devices. 2957 This is normally done in pci_enable_device(), 2958 so this option is a temporary workaround 2959 for broken drivers that don't call it. 2960 skip_isa_align [X86] do not align io start addr, so can 2961 handle more pci cards 2962 firmware [ARM] Do not re-enumerate the bus but instead 2963 just use the configuration from the 2964 bootloader. This is currently used on 2965 IXP2000 systems where the bus has to be 2966 configured a certain way for adjunct CPUs. 2967 noearly [X86] Don't do any early type 1 scanning. 2968 This might help on some broken boards which 2969 machine check when some devices' config space 2970 is read. But various workarounds are disabled 2971 and some IOMMU drivers will not work. 2972 bfsort Sort PCI devices into breadth-first order. 2973 This sorting is done to get a device 2974 order compatible with older (<= 2.4) kernels. 2975 nobfsort Don't sort PCI devices into breadth-first order. 2976 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 2977 tuning and use the BIOS-configured MPS defaults. 2978 pcie_bus_safe Set every device's MPS to the largest value 2979 supported by all devices below the root complex. 2980 pcie_bus_perf Set device MPS to the largest allowable MPS 2981 based on its parent bus. Also set MRRS (Max 2982 Read Request Size) to the largest supported 2983 value (no larger than the MPS that the device 2984 or bus can support) for best performance. 2985 pcie_bus_peer2peer Set every device's MPS to 128B, which 2986 every device is guaranteed to support. This 2987 configuration allows peer-to-peer DMA between 2988 any pair of devices, possibly at the cost of 2989 reduced performance. This also guarantees 2990 that hot-added devices will work. 2991 cbiosize=nn[KMG] The fixed amount of bus space which is 2992 reserved for the CardBus bridge's IO window. 2993 The default value is 256 bytes. 2994 cbmemsize=nn[KMG] The fixed amount of bus space which is 2995 reserved for the CardBus bridge's memory 2996 window. The default value is 64 megabytes. 2997 resource_alignment= 2998 Format: 2999 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...] 3000 Specifies alignment and device to reassign 3001 aligned memory resources. 3002 If <order of align> is not specified, 3003 PAGE_SIZE is used as alignment. 3004 PCI-PCI bridge can be specified, if resource 3005 windows need to be expanded. 3006 ecrc= Enable/disable PCIe ECRC (transaction layer 3007 end-to-end CRC checking). 3008 bios: Use BIOS/firmware settings. This is the 3009 the default. 3010 off: Turn ECRC off 3011 on: Turn ECRC on. 3012 hpiosize=nn[KMG] The fixed amount of bus space which is 3013 reserved for hotplug bridge's IO window. 3014 Default size is 256 bytes. 3015 hpmemsize=nn[KMG] The fixed amount of bus space which is 3016 reserved for hotplug bridge's memory window. 3017 Default size is 2 megabytes. 3018 realloc= Enable/disable reallocating PCI bridge resources 3019 if allocations done by BIOS are too small to 3020 accommodate resources required by all child 3021 devices. 3022 off: Turn realloc off 3023 on: Turn realloc on 3024 realloc same as realloc=on 3025 noari do not use PCIe ARI. 3026 pcie_scan_all Scan all possible PCIe devices. Otherwise we 3027 only look for one device below a PCIe downstream 3028 port. 3029 3030 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power 3031 Management. 3032 off Disable ASPM. 3033 force Enable ASPM even on devices that claim not to support it. 3034 WARNING: Forcing ASPM on may cause system lockups. 3035 3036 pcie_hp= [PCIE] PCI Express Hotplug driver options: 3037 nomsi Do not use MSI for PCI Express Native Hotplug (this 3038 makes all PCIe ports use INTx for hotplug services). 3039 3040 pcie_ports= [PCIE] PCIe ports handling: 3041 auto Ask the BIOS whether or not to use native PCIe services 3042 associated with PCIe ports (PME, hot-plug, AER). Use 3043 them only if that is allowed by the BIOS. 3044 native Use native PCIe services associated with PCIe ports 3045 unconditionally. 3046 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe 3047 ports driver. 3048 3049 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 3050 nomsi Do not use MSI for native PCIe PME signaling (this makes 3051 all PCIe root ports use INTx for all services). 3052 3053 pcmv= [HW,PCMCIA] BadgePAD 4 3054 3055 pd_ignore_unused 3056 [PM] 3057 Keep all power-domains already enabled by bootloader on, 3058 even if no driver has claimed them. This is useful 3059 for debug and development, but should not be 3060 needed on a platform with proper driver support. 3061 3062 pd. [PARIDE] 3063 See Documentation/blockdev/paride.txt. 3064 3065 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 3066 boot time. 3067 Format: { 0 | 1 } 3068 See arch/parisc/kernel/pdc_chassis.c 3069 3070 percpu_alloc= Select which percpu first chunk allocator to use. 3071 Currently supported values are "embed" and "page". 3072 Archs may support subset or none of the selections. 3073 See comments in mm/percpu.c for details on each 3074 allocator. This parameter is primarily for debugging 3075 and performance comparison. 3076 3077 pf. [PARIDE] 3078 See Documentation/blockdev/paride.txt. 3079 3080 pg. [PARIDE] 3081 See Documentation/blockdev/paride.txt. 3082 3083 pirq= [SMP,APIC] Manual mp-table setup 3084 See Documentation/x86/i386/IO-APIC.txt. 3085 3086 plip= [PPT,NET] Parallel port network link 3087 Format: { parport<nr> | timid | 0 } 3088 See also Documentation/parport.txt. 3089 3090 pmtmr= [X86] Manual setup of pmtmr I/O Port. 3091 Override pmtimer IOPort with a hex value. 3092 e.g. pmtmr=0x508 3093 3094 pnp.debug=1 [PNP] 3095 Enable PNP debug messages (depends on the 3096 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 3097 via /sys/module/pnp/parameters/debug. We always show 3098 current resource usage; turning this on also shows 3099 possible settings and some assignment information. 3100 3101 pnpacpi= [ACPI] 3102 { off } 3103 3104 pnpbios= [ISAPNP] 3105 { on | off | curr | res | no-curr | no-res } 3106 3107 pnp_reserve_irq= 3108 [ISAPNP] Exclude IRQs for the autoconfiguration 3109 3110 pnp_reserve_dma= 3111 [ISAPNP] Exclude DMAs for the autoconfiguration 3112 3113 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 3114 Ranges are in pairs (I/O port base and size). 3115 3116 pnp_reserve_mem= 3117 [ISAPNP] Exclude memory regions for the 3118 autoconfiguration. 3119 Ranges are in pairs (memory base and size). 3120 3121 ports= [IP_VS_FTP] IPVS ftp helper module 3122 Default is 21. 3123 Up to 8 (IP_VS_APP_MAX_PORTS) ports 3124 may be specified. 3125 Format: <port>,<port>.... 3126 3127 print-fatal-signals= 3128 [KNL] debug: print fatal signals 3129 3130 If enabled, warn about various signal handling 3131 related application anomalies: too many signals, 3132 too many POSIX.1 timers, fatal signals causing a 3133 coredump - etc. 3134 3135 If you hit the warning due to signal overflow, 3136 you might want to try "ulimit -i unlimited". 3137 3138 default: off. 3139 3140 printk.always_kmsg_dump= 3141 Trigger kmsg_dump for cases other than kernel oops or 3142 panics 3143 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3144 default: disabled 3145 3146 printk.time= Show timing data prefixed to each printk message line 3147 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3148 3149 processor.max_cstate= [HW,ACPI] 3150 Limit processor to maximum C-state 3151 max_cstate=9 overrides any DMI blacklist limit. 3152 3153 processor.nocst [HW,ACPI] 3154 Ignore the _CST method to determine C-states, 3155 instead using the legacy FADT method 3156 3157 profile= [KNL] Enable kernel profiling via /proc/profile 3158 Format: [schedule,]<number> 3159 Param: "schedule" - profile schedule points. 3160 Param: <number> - step/bucket size as a power of 2 for 3161 statistical time based profiling. 3162 Param: "sleep" - profile D-state sleeping (millisecs). 3163 Requires CONFIG_SCHEDSTATS 3164 Param: "kvm" - profile VM exits. 3165 3166 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk 3167 before loading. 3168 See Documentation/blockdev/ramdisk.txt. 3169 3170 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 3171 probe for; one of (bare|imps|exps|lifebook|any). 3172 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 3173 per second. 3174 psmouse.resetafter= [HW,MOUSE] 3175 Try to reset the device after so many bad packets 3176 (0 = never). 3177 psmouse.resolution= 3178 [HW,MOUSE] Set desired mouse resolution, in dpi. 3179 psmouse.smartscroll= 3180 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 3181 0 = disabled, 1 = enabled (default). 3182 3183 pstore.backend= Specify the name of the pstore backend to use 3184 3185 pt. [PARIDE] 3186 See Documentation/blockdev/paride.txt. 3187 3188 pti= [X86_64] Control Page Table Isolation of user and 3189 kernel address spaces. Disabling this feature 3190 removes hardening, but improves performance of 3191 system calls and interrupts. 3192 3193 on - unconditionally enable 3194 off - unconditionally disable 3195 auto - kernel detects whether your CPU model is 3196 vulnerable to issues that PTI mitigates 3197 3198 Not specifying this option is equivalent to pti=auto. 3199 3200 nopti [X86_64] 3201 Equivalent to pti=off 3202 3203 pty.legacy_count= 3204 [KNL] Number of legacy pty's. Overwrites compiled-in 3205 default number. 3206 3207 quiet [KNL] Disable most log messages 3208 3209 r128= [HW,DRM] 3210 3211 raid= [HW,RAID] 3212 See Documentation/md.txt. 3213 3214 ramdisk_blocksize= [RAM] 3215 See Documentation/blockdev/ramdisk.txt. 3216 3217 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 3218 See Documentation/blockdev/ramdisk.txt. 3219 3220 rcu_nocbs= [KNL] 3221 In kernels built with CONFIG_RCU_NOCB_CPU=y, set 3222 the specified list of CPUs to be no-callback CPUs. 3223 Invocation of these CPUs' RCU callbacks will 3224 be offloaded to "rcuox/N" kthreads created for 3225 that purpose, where "x" is "b" for RCU-bh, "p" 3226 for RCU-preempt, and "s" for RCU-sched, and "N" 3227 is the CPU number. This reduces OS jitter on the 3228 offloaded CPUs, which can be useful for HPC and 3229 real-time workloads. It can also improve energy 3230 efficiency for asymmetric multiprocessors. 3231 3232 rcu_nocb_poll [KNL] 3233 Rather than requiring that offloaded CPUs 3234 (specified by rcu_nocbs= above) explicitly 3235 awaken the corresponding "rcuoN" kthreads, 3236 make these kthreads poll for callbacks. 3237 This improves the real-time response for the 3238 offloaded CPUs by relieving them of the need to 3239 wake up the corresponding kthread, but degrades 3240 energy efficiency by requiring that the kthreads 3241 periodically wake up to do the polling. 3242 3243 rcutree.blimit= [KNL] 3244 Set maximum number of finished RCU callbacks to 3245 process in one batch. 3246 3247 rcutree.dump_tree= [KNL] 3248 Dump the structure of the rcu_node combining tree 3249 out at early boot. This is used for diagnostic 3250 purposes, to verify correct tree setup. 3251 3252 rcutree.gp_cleanup_delay= [KNL] 3253 Set the number of jiffies to delay each step of 3254 RCU grace-period cleanup. This only has effect 3255 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set. 3256 3257 rcutree.gp_init_delay= [KNL] 3258 Set the number of jiffies to delay each step of 3259 RCU grace-period initialization. This only has 3260 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT 3261 is set. 3262 3263 rcutree.gp_preinit_delay= [KNL] 3264 Set the number of jiffies to delay each step of 3265 RCU grace-period pre-initialization, that is, 3266 the propagation of recent CPU-hotplug changes up 3267 the rcu_node combining tree. This only has effect 3268 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set. 3269 3270 rcutree.rcu_fanout_exact= [KNL] 3271 Disable autobalancing of the rcu_node combining 3272 tree. This is used by rcutorture, and might 3273 possibly be useful for architectures having high 3274 cache-to-cache transfer latencies. 3275 3276 rcutree.rcu_fanout_leaf= [KNL] 3277 Change the number of CPUs assigned to each 3278 leaf rcu_node structure. Useful for very 3279 large systems, which will choose the value 64, 3280 and for NUMA systems with large remote-access 3281 latencies, which will choose a value aligned 3282 with the appropriate hardware boundaries. 3283 3284 rcutree.jiffies_till_sched_qs= [KNL] 3285 Set required age in jiffies for a 3286 given grace period before RCU starts 3287 soliciting quiescent-state help from 3288 rcu_note_context_switch(). 3289 3290 rcutree.jiffies_till_first_fqs= [KNL] 3291 Set delay from grace-period initialization to 3292 first attempt to force quiescent states. 3293 Units are jiffies, minimum value is zero, 3294 and maximum value is HZ. 3295 3296 rcutree.jiffies_till_next_fqs= [KNL] 3297 Set delay between subsequent attempts to force 3298 quiescent states. Units are jiffies, minimum 3299 value is one, and maximum value is HZ. 3300 3301 rcutree.kthread_prio= [KNL,BOOT] 3302 Set the SCHED_FIFO priority of the RCU per-CPU 3303 kthreads (rcuc/N). This value is also used for 3304 the priority of the RCU boost threads (rcub/N) 3305 and for the RCU grace-period kthreads (rcu_bh, 3306 rcu_preempt, and rcu_sched). If RCU_BOOST is 3307 set, valid values are 1-99 and the default is 1 3308 (the least-favored priority). Otherwise, when 3309 RCU_BOOST is not set, valid values are 0-99 and 3310 the default is zero (non-realtime operation). 3311 3312 rcutree.rcu_nocb_leader_stride= [KNL] 3313 Set the number of NOCB kthread groups, which 3314 defaults to the square root of the number of 3315 CPUs. Larger numbers reduces the wakeup overhead 3316 on the per-CPU grace-period kthreads, but increases 3317 that same overhead on each group's leader. 3318 3319 rcutree.qhimark= [KNL] 3320 Set threshold of queued RCU callbacks beyond which 3321 batch limiting is disabled. 3322 3323 rcutree.qlowmark= [KNL] 3324 Set threshold of queued RCU callbacks below which 3325 batch limiting is re-enabled. 3326 3327 rcutree.rcu_idle_gp_delay= [KNL] 3328 Set wakeup interval for idle CPUs that have 3329 RCU callbacks (RCU_FAST_NO_HZ=y). 3330 3331 rcutree.rcu_idle_lazy_gp_delay= [KNL] 3332 Set wakeup interval for idle CPUs that have 3333 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y). 3334 Lazy RCU callbacks are those which RCU can 3335 prove do nothing more than free memory. 3336 3337 rcutorture.cbflood_inter_holdoff= [KNL] 3338 Set holdoff time (jiffies) between successive 3339 callback-flood tests. 3340 3341 rcutorture.cbflood_intra_holdoff= [KNL] 3342 Set holdoff time (jiffies) between successive 3343 bursts of callbacks within a given callback-flood 3344 test. 3345 3346 rcutorture.cbflood_n_burst= [KNL] 3347 Set the number of bursts making up a given 3348 callback-flood test. Set this to zero to 3349 disable callback-flood testing. 3350 3351 rcutorture.cbflood_n_per_burst= [KNL] 3352 Set the number of callbacks to be registered 3353 in a given burst of a callback-flood test. 3354 3355 rcutorture.fqs_duration= [KNL] 3356 Set duration of force_quiescent_state bursts 3357 in microseconds. 3358 3359 rcutorture.fqs_holdoff= [KNL] 3360 Set holdoff time within force_quiescent_state bursts 3361 in microseconds. 3362 3363 rcutorture.fqs_stutter= [KNL] 3364 Set wait time between force_quiescent_state bursts 3365 in seconds. 3366 3367 rcutorture.gp_cond= [KNL] 3368 Use conditional/asynchronous update-side 3369 primitives, if available. 3370 3371 rcutorture.gp_exp= [KNL] 3372 Use expedited update-side primitives, if available. 3373 3374 rcutorture.gp_normal= [KNL] 3375 Use normal (non-expedited) asynchronous 3376 update-side primitives, if available. 3377 3378 rcutorture.gp_sync= [KNL] 3379 Use normal (non-expedited) synchronous 3380 update-side primitives, if available. If all 3381 of rcutorture.gp_cond=, rcutorture.gp_exp=, 3382 rcutorture.gp_normal=, and rcutorture.gp_sync= 3383 are zero, rcutorture acts as if is interpreted 3384 they are all non-zero. 3385 3386 rcutorture.n_barrier_cbs= [KNL] 3387 Set callbacks/threads for rcu_barrier() testing. 3388 3389 rcutorture.nfakewriters= [KNL] 3390 Set number of concurrent RCU writers. These just 3391 stress RCU, they don't participate in the actual 3392 test, hence the "fake". 3393 3394 rcutorture.nreaders= [KNL] 3395 Set number of RCU readers. The value -1 selects 3396 N-1, where N is the number of CPUs. A value 3397 "n" less than -1 selects N-n-2, where N is again 3398 the number of CPUs. For example, -2 selects N 3399 (the number of CPUs), -3 selects N+1, and so on. 3400 3401 rcutorture.object_debug= [KNL] 3402 Enable debug-object double-call_rcu() testing. 3403 3404 rcutorture.onoff_holdoff= [KNL] 3405 Set time (s) after boot for CPU-hotplug testing. 3406 3407 rcutorture.onoff_interval= [KNL] 3408 Set time (s) between CPU-hotplug operations, or 3409 zero to disable CPU-hotplug testing. 3410 3411 rcutorture.shuffle_interval= [KNL] 3412 Set task-shuffle interval (s). Shuffling tasks 3413 allows some CPUs to go into dyntick-idle mode 3414 during the rcutorture test. 3415 3416 rcutorture.shutdown_secs= [KNL] 3417 Set time (s) after boot system shutdown. This 3418 is useful for hands-off automated testing. 3419 3420 rcutorture.stall_cpu= [KNL] 3421 Duration of CPU stall (s) to test RCU CPU stall 3422 warnings, zero to disable. 3423 3424 rcutorture.stall_cpu_holdoff= [KNL] 3425 Time to wait (s) after boot before inducing stall. 3426 3427 rcutorture.stat_interval= [KNL] 3428 Time (s) between statistics printk()s. 3429 3430 rcutorture.stutter= [KNL] 3431 Time (s) to stutter testing, for example, specifying 3432 five seconds causes the test to run for five seconds, 3433 wait for five seconds, and so on. This tests RCU's 3434 ability to transition abruptly to and from idle. 3435 3436 rcutorture.test_boost= [KNL] 3437 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 3438 "Maybe" means test if the RCU implementation 3439 under test support RCU priority boosting. 3440 3441 rcutorture.test_boost_duration= [KNL] 3442 Duration (s) of each individual boost test. 3443 3444 rcutorture.test_boost_interval= [KNL] 3445 Interval (s) between each boost test. 3446 3447 rcutorture.test_no_idle_hz= [KNL] 3448 Test RCU's dyntick-idle handling. See also the 3449 rcutorture.shuffle_interval parameter. 3450 3451 rcutorture.torture_runnable= [BOOT] 3452 Start rcutorture running at boot time. 3453 3454 rcutorture.torture_type= [KNL] 3455 Specify the RCU implementation to test. 3456 3457 rcutorture.verbose= [KNL] 3458 Enable additional printk() statements. 3459 3460 rcupdate.rcu_expedited= [KNL] 3461 Use expedited grace-period primitives, for 3462 example, synchronize_rcu_expedited() instead 3463 of synchronize_rcu(). This reduces latency, 3464 but can increase CPU utilization, degrade 3465 real-time latency, and degrade energy efficiency. 3466 3467 rcupdate.rcu_cpu_stall_suppress= [KNL] 3468 Suppress RCU CPU stall warning messages. 3469 3470 rcupdate.rcu_cpu_stall_timeout= [KNL] 3471 Set timeout for RCU CPU stall warning messages. 3472 3473 rcupdate.rcu_task_stall_timeout= [KNL] 3474 Set timeout in jiffies for RCU task stall warning 3475 messages. Disable with a value less than or equal 3476 to zero. 3477 3478 rcupdate.rcu_self_test= [KNL] 3479 Run the RCU early boot self tests 3480 3481 rcupdate.rcu_self_test_bh= [KNL] 3482 Run the RCU bh early boot self tests 3483 3484 rcupdate.rcu_self_test_sched= [KNL] 3485 Run the RCU sched early boot self tests 3486 3487 rdinit= [KNL] 3488 Format: <full_path> 3489 Run specified binary instead of /init from the ramdisk, 3490 used for early userspace startup. See initrd. 3491 3492 rdrand= [X86] 3493 force - Override the decision by the kernel to hide the 3494 advertisement of RDRAND support (this affects 3495 certain AMD processors because of buggy BIOS 3496 support, specifically around the suspend/resume 3497 path). 3498 3499 reboot= [KNL] 3500 Format (x86 or x86_64): 3501 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \ 3502 [[,]s[mp]#### \ 3503 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 3504 [[,]f[orce] 3505 Where reboot_mode is one of warm (soft) or cold (hard) or gpio, 3506 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 3507 reboot_force is either force or not specified, 3508 reboot_cpu is s[mp]#### with #### being the processor 3509 to be used for rebooting. 3510 3511 relax_domain_level= 3512 [KNL, SMP] Set scheduler's default relax_domain_level. 3513 See Documentation/cgroups/cpusets.txt. 3514 3515 relative_sleep_states= 3516 [SUSPEND] Use sleep state labeling where the deepest 3517 state available other than hibernation is always "mem". 3518 Format: { "0" | "1" } 3519 0 -- Traditional sleep state labels. 3520 1 -- Relative sleep state labels. 3521 3522 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area 3523 3524 reservetop= [X86-32] 3525 Format: nn[KMG] 3526 Reserves a hole at the top of the kernel virtual 3527 address space. 3528 3529 reservelow= [X86] 3530 Format: nn[K] 3531 Set the amount of memory to reserve for BIOS at 3532 the bottom of the address space. 3533 3534 reset_devices [KNL] Force drivers to reset the underlying device 3535 during initialization. 3536 3537 resume= [SWSUSP] 3538 Specify the partition device for software suspend 3539 Format: 3540 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 3541 3542 resume_offset= [SWSUSP] 3543 Specify the offset from the beginning of the partition 3544 given by "resume=" at which the swap header is located, 3545 in <PAGE_SIZE> units (needed only for swap files). 3546 See Documentation/power/swsusp-and-swap-files.txt 3547 3548 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 3549 read the resume files 3550 3551 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 3552 Useful for devices that are detected asynchronously 3553 (e.g. USB and MMC devices). 3554 3555 hibernate= [HIBERNATION] 3556 noresume Don't check if there's a hibernation image 3557 present during boot. 3558 nocompress Don't compress/decompress hibernation images. 3559 no Disable hibernation and resume. 3560 3561 retain_initrd [RAM] Keep initrd memory after extraction 3562 3563 rfkill.default_state= 3564 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 3565 etc. communication is blocked by default. 3566 1 Unblocked. 3567 3568 rfkill.master_switch_mode= 3569 0 The "airplane mode" button does nothing. 3570 1 The "airplane mode" button toggles between everything 3571 blocked and the previous configuration. 3572 2 The "airplane mode" button toggles between everything 3573 blocked and everything unblocked. 3574 3575 rhash_entries= [KNL,NET] 3576 Set number of hash buckets for route cache 3577 3578 ro [KNL] Mount root device read-only on boot 3579 3580 rodata= [KNL] 3581 on Mark read-only kernel memory as read-only (default). 3582 off Leave read-only kernel memory writable for debugging. 3583 3584 root= [KNL] Root filesystem 3585 See name_to_dev_t comment in init/do_mounts.c. 3586 3587 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 3588 mount the root filesystem 3589 3590 rootflags= [KNL] Set root filesystem mount option string 3591 3592 rootfstype= [KNL] Set root filesystem type 3593 3594 rootwait [KNL] Wait (indefinitely) for root device to show up. 3595 Useful for devices that are detected asynchronously 3596 (e.g. USB and MMC devices). 3597 3598 rproc_mem=nn[KMG][@address] 3599 [KNL,ARM,CMA] Remoteproc physical memory block. 3600 Memory area to be used by remote processor image, 3601 managed by CMA. 3602 3603 rw [KNL] Mount root device read-write on boot 3604 3605 S [KNL] Run init in single mode 3606 3607 s390_iommu= [HW,S390] 3608 Set s390 IOTLB flushing mode 3609 strict 3610 With strict flushing every unmap operation will result in 3611 an IOTLB flush. Default is lazy flushing before reuse, 3612 which is faster. 3613 3614 sa1100ir [NET] 3615 See drivers/net/irda/sa1100_ir.c. 3616 3617 sbni= [NET] Granch SBNI12 leased line adapter 3618 3619 sched_debug [KNL] Enables verbose scheduler debug messages. 3620 3621 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate 3622 xtime_lock contention on larger systems, and/or RCU lock 3623 contention on all systems with CONFIG_MAXSMP set. 3624 Format: { "0" | "1" } 3625 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 3626 1 -- enable. 3627 Note: increases power consumption, thus should only be 3628 enabled if running jitter sensitive (HPC/RT) workloads. 3629 3630 security= [SECURITY] Choose a security module to enable at boot. 3631 If this boot parameter is not specified, only the first 3632 security module asking for security registration will be 3633 loaded. An invalid security module name will be treated 3634 as if no module has been chosen. 3635 3636 selinux= [SELINUX] Disable or enable SELinux at boot time. 3637 Format: { "0" | "1" } 3638 See security/selinux/Kconfig help text. 3639 0 -- disable. 3640 1 -- enable. 3641 Default value is set via kernel config option. 3642 If enabled at boot time, /selinux/disable can be used 3643 later to disable prior to initial policy load. 3644 3645 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 3646 Format: { "0" | "1" } 3647 See security/apparmor/Kconfig help text 3648 0 -- disable. 3649 1 -- enable. 3650 Default value is set via kernel config option. 3651 3652 serialnumber [BUGS=X86-32] 3653 3654 shapers= [NET] 3655 Maximal number of shapers. 3656 3657 show_msr= [x86] show boot-time MSR settings 3658 Format: { <integer> } 3659 Show boot-time (BIOS-initialized) MSR settings. 3660 The parameter means the number of CPUs to show, 3661 for example 1 means boot CPU only. 3662 3663 simeth= [IA-64] 3664 simscsi= 3665 3666 slram= [HW,MTD] 3667 3668 slab_nomerge [MM] 3669 Disable merging of slabs with similar size. May be 3670 necessary if there is some reason to distinguish 3671 allocs to different slabs. Debug options disable 3672 merging on their own. 3673 For more information see Documentation/vm/slub.txt. 3674 3675 slab_max_order= [MM, SLAB] 3676 Determines the maximum allowed order for slabs. 3677 A high setting may cause OOMs due to memory 3678 fragmentation. Defaults to 1 for systems with 3679 more than 32MB of RAM, 0 otherwise. 3680 3681 slub_debug[=options[,slabs]] [MM, SLUB] 3682 Enabling slub_debug allows one to determine the 3683 culprit if slab objects become corrupted. Enabling 3684 slub_debug can create guard zones around objects and 3685 may poison objects when not in use. Also tracks the 3686 last alloc / free. For more information see 3687 Documentation/vm/slub.txt. 3688 3689 slub_max_order= [MM, SLUB] 3690 Determines the maximum allowed order for slabs. 3691 A high setting may cause OOMs due to memory 3692 fragmentation. For more information see 3693 Documentation/vm/slub.txt. 3694 3695 slub_min_objects= [MM, SLUB] 3696 The minimum number of objects per slab. SLUB will 3697 increase the slab order up to slub_max_order to 3698 generate a sufficiently large slab able to contain 3699 the number of objects indicated. The higher the number 3700 of objects the smaller the overhead of tracking slabs 3701 and the less frequently locks need to be acquired. 3702 For more information see Documentation/vm/slub.txt. 3703 3704 slub_min_order= [MM, SLUB] 3705 Determines the minimum page order for slabs. Must be 3706 lower than slub_max_order. 3707 For more information see Documentation/vm/slub.txt. 3708 3709 slub_nomerge [MM, SLUB] 3710 Same with slab_nomerge. This is supported for legacy. 3711 See slab_nomerge for more information. 3712 3713 smart2= [HW] 3714 Format: <io1>[,<io2>[,...,<io8>]] 3715 3716 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 3717 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 3718 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 3719 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 3720 smsc-ircc2.ircc_irq= [HW] IRQ line 3721 smsc-ircc2.ircc_dma= [HW] DMA channel 3722 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 3723 0: Toshiba Satellite 1800 (GP data pin select) 3724 1: Fast pin select (default) 3725 2: ATC IRMode 3726 3727 softlockup_panic= 3728 [KNL] Should the soft-lockup detector generate panics. 3729 Format: <integer> 3730 3731 softlockup_all_cpu_backtrace= 3732 [KNL] Should the soft-lockup detector generate 3733 backtraces on all cpus. 3734 Format: <integer> 3735 3736 sonypi.*= [HW] Sony Programmable I/O Control Device driver 3737 See Documentation/laptops/sonypi.txt 3738 3739 spectre_v2= [X86] Control mitigation of Spectre variant 2 3740 (indirect branch speculation) vulnerability. 3741 The default operation protects the kernel from 3742 user space attacks. 3743 3744 on - unconditionally enable, implies 3745 spectre_v2_user=on 3746 off - unconditionally disable, implies 3747 spectre_v2_user=off 3748 auto - kernel detects whether your CPU model is 3749 vulnerable 3750 3751 Selecting 'on' will, and 'auto' may, choose a 3752 mitigation method at run time according to the 3753 CPU, the available microcode, the setting of the 3754 CONFIG_RETPOLINE configuration option, and the 3755 compiler with which the kernel was built. 3756 3757 Selecting 'on' will also enable the mitigation 3758 against user space to user space task attacks. 3759 3760 Selecting 'off' will disable both the kernel and 3761 the user space protections. 3762 3763 Specific mitigations can also be selected manually: 3764 3765 retpoline - replace indirect branches 3766 retpoline,generic - google's original retpoline 3767 retpoline,amd - AMD-specific minimal thunk 3768 3769 Not specifying this option is equivalent to 3770 spectre_v2=auto. 3771 3772 spectre_v2_user= 3773 [X86] Control mitigation of Spectre variant 2 3774 (indirect branch speculation) vulnerability between 3775 user space tasks 3776 3777 on - Unconditionally enable mitigations. Is 3778 enforced by spectre_v2=on 3779 3780 off - Unconditionally disable mitigations. Is 3781 enforced by spectre_v2=off 3782 3783 prctl - Indirect branch speculation is enabled, 3784 but mitigation can be enabled via prctl 3785 per thread. The mitigation control state 3786 is inherited on fork. 3787 3788 prctl,ibpb 3789 - Like "prctl" above, but only STIBP is 3790 controlled per thread. IBPB is issued 3791 always when switching between different user 3792 space processes. 3793 3794 seccomp 3795 - Same as "prctl" above, but all seccomp 3796 threads will enable the mitigation unless 3797 they explicitly opt out. 3798 3799 seccomp,ibpb 3800 - Like "seccomp" above, but only STIBP is 3801 controlled per thread. IBPB is issued 3802 always when switching between different 3803 user space processes. 3804 3805 auto - Kernel selects the mitigation depending on 3806 the available CPU features and vulnerability. 3807 3808 Default mitigation: 3809 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl" 3810 3811 Not specifying this option is equivalent to 3812 spectre_v2_user=auto. 3813 3814 spec_store_bypass_disable= 3815 [HW] Control Speculative Store Bypass (SSB) Disable mitigation 3816 (Speculative Store Bypass vulnerability) 3817 3818 Certain CPUs are vulnerable to an exploit against a 3819 a common industry wide performance optimization known 3820 as "Speculative Store Bypass" in which recent stores 3821 to the same memory location may not be observed by 3822 later loads during speculative execution. The idea 3823 is that such stores are unlikely and that they can 3824 be detected prior to instruction retirement at the 3825 end of a particular speculation execution window. 3826 3827 In vulnerable processors, the speculatively forwarded 3828 store can be used in a cache side channel attack, for 3829 example to read memory to which the attacker does not 3830 directly have access (e.g. inside sandboxed code). 3831 3832 This parameter controls whether the Speculative Store 3833 Bypass optimization is used. 3834 3835 on - Unconditionally disable Speculative Store Bypass 3836 off - Unconditionally enable Speculative Store Bypass 3837 auto - Kernel detects whether the CPU model contains an 3838 implementation of Speculative Store Bypass and 3839 picks the most appropriate mitigation. If the 3840 CPU is not vulnerable, "off" is selected. If the 3841 CPU is vulnerable the default mitigation is 3842 architecture and Kconfig dependent. See below. 3843 prctl - Control Speculative Store Bypass per thread 3844 via prctl. Speculative Store Bypass is enabled 3845 for a process by default. The state of the control 3846 is inherited on fork. 3847 seccomp - Same as "prctl" above, but all seccomp threads 3848 will disable SSB unless they explicitly opt out. 3849 3850 Not specifying this option is equivalent to 3851 spec_store_bypass_disable=auto. 3852 3853 Default mitigations: 3854 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl" 3855 3856 spia_io_base= [HW,MTD] 3857 spia_fio_base= 3858 spia_pedr= 3859 spia_peddr= 3860 3861 srbds= [X86,INTEL] 3862 Control the Special Register Buffer Data Sampling 3863 (SRBDS) mitigation. 3864 3865 Certain CPUs are vulnerable to an MDS-like 3866 exploit which can leak bits from the random 3867 number generator. 3868 3869 By default, this issue is mitigated by 3870 microcode. However, the microcode fix can cause 3871 the RDRAND and RDSEED instructions to become 3872 much slower. Among other effects, this will 3873 result in reduced throughput from /dev/urandom. 3874 3875 The microcode mitigation can be disabled with 3876 the following option: 3877 3878 off: Disable mitigation and remove 3879 performance impact to RDRAND and RDSEED 3880 3881 stack_guard_gap= [MM] 3882 override the default stack gap protection. The value 3883 is in page units and it defines how many pages prior 3884 to (for stacks growing down) resp. after (for stacks 3885 growing up) the main stack are reserved for no other 3886 mapping. Default value is 256 pages. 3887 3888 stacktrace [FTRACE] 3889 Enabled the stack tracer on boot up. 3890 3891 stacktrace_filter=[function-list] 3892 [FTRACE] Limit the functions that the stack tracer 3893 will trace at boot up. function-list is a comma separated 3894 list of functions. This list can be changed at run 3895 time by the stack_trace_filter file in the debugfs 3896 tracing directory. Note, this enables stack tracing 3897 and the stacktrace above is not needed. 3898 3899 sti= [PARISC,HW] 3900 Format: <num> 3901 Set the STI (builtin display/keyboard on the HP-PARISC 3902 machines) console (graphic card) which should be used 3903 as the initial boot-console. 3904 See also comment in drivers/video/console/sticore.c. 3905 3906 sti_font= [HW] 3907 See comment in drivers/video/console/sticore.c. 3908 3909 stifb= [HW] 3910 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 3911 3912 sunrpc.min_resvport= 3913 sunrpc.max_resvport= 3914 [NFS,SUNRPC] 3915 SunRPC servers often require that client requests 3916 originate from a privileged port (i.e. a port in the 3917 range 0 < portnr < 1024). 3918 An administrator who wishes to reserve some of these 3919 ports for other uses may adjust the range that the 3920 kernel's sunrpc client considers to be privileged 3921 using these two parameters to set the minimum and 3922 maximum port values. 3923 3924 sunrpc.pool_mode= 3925 [NFS] 3926 Control how the NFS server code allocates CPUs to 3927 service thread pools. Depending on how many NICs 3928 you have and where their interrupts are bound, this 3929 option will affect which CPUs will do NFS serving. 3930 Note: this parameter cannot be changed while the 3931 NFS server is running. 3932 3933 auto the server chooses an appropriate mode 3934 automatically using heuristics 3935 global a single global pool contains all CPUs 3936 percpu one pool for each CPU 3937 pernode one pool for each NUMA node (equivalent 3938 to global on non-NUMA machines) 3939 3940 sunrpc.tcp_slot_table_entries= 3941 sunrpc.udp_slot_table_entries= 3942 [NFS,SUNRPC] 3943 Sets the upper limit on the number of simultaneous 3944 RPC calls that can be sent from the client to a 3945 server. Increasing these values may allow you to 3946 improve throughput, but will also increase the 3947 amount of memory reserved for use by the client. 3948 3949 suspend.pm_test_delay= 3950 [SUSPEND] 3951 Sets the number of seconds to remain in a suspend test 3952 mode before resuming the system (see 3953 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 3954 is set. Default value is 5. 3955 3956 swapaccount=[0|1] 3957 [KNL] Enable accounting of swap in memory resource 3958 controller if no parameter or 1 is given or disable 3959 it if 0 is given (See Documentation/cgroups/memory.txt) 3960 3961 swiotlb= [ARM,IA-64,PPC,MIPS,X86] 3962 Format: { <int> | force } 3963 <int> -- Number of I/O TLB slabs 3964 force -- force using of bounce buffers even if they 3965 wouldn't be automatically used by the kernel 3966 3967 switches= [HW,M68k] 3968 3969 sysfs.deprecated=0|1 [KNL] 3970 Enable/disable old style sysfs layout for old udev 3971 on older distributions. When this option is enabled 3972 very new udev will not work anymore. When this option 3973 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled) 3974 in older udev will not work anymore. 3975 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in 3976 the kernel configuration. 3977 3978 sysrq_always_enabled 3979 [KNL] 3980 Ignore sysrq setting - this boot parameter will 3981 neutralize any effect of /proc/sys/kernel/sysrq. 3982 Useful for debugging. 3983 3984 tcpmhash_entries= [KNL,NET] 3985 Set the number of tcp_metrics_hash slots. 3986 Default value is 8192 or 16384 depending on total 3987 ram pages. This is used to specify the TCP metrics 3988 cache size. See Documentation/networking/ip-sysctl.txt 3989 "tcp_no_metrics_save" section for more details. 3990 3991 tdfx= [HW,DRM] 3992 3993 test_suspend= [SUSPEND][,N] 3994 Specify "mem" (for Suspend-to-RAM) or "standby" (for 3995 standby suspend) or "freeze" (for suspend type freeze) 3996 as the system sleep state during system startup with 3997 the optional capability to repeat N number of times. 3998 The system is woken from this state using a 3999 wakeup-capable RTC alarm. 4000 4001 thash_entries= [KNL,NET] 4002 Set number of hash buckets for TCP connection 4003 4004 thermal.act= [HW,ACPI] 4005 -1: disable all active trip points in all thermal zones 4006 <degrees C>: override all lowest active trip points 4007 4008 thermal.crt= [HW,ACPI] 4009 -1: disable all critical trip points in all thermal zones 4010 <degrees C>: override all critical trip points 4011 4012 thermal.nocrt= [HW,ACPI] 4013 Set to disable actions on ACPI thermal zone 4014 critical and hot trip points. 4015 4016 thermal.off= [HW,ACPI] 4017 1: disable ACPI thermal control 4018 4019 thermal.psv= [HW,ACPI] 4020 -1: disable all passive trip points 4021 <degrees C>: override all passive trip points to this 4022 value 4023 4024 thermal.tzp= [HW,ACPI] 4025 Specify global default ACPI thermal zone polling rate 4026 <deci-seconds>: poll all this frequency 4027 0: no polling (default) 4028 4029 threadirqs [KNL] 4030 Force threading of all interrupt handlers except those 4031 marked explicitly IRQF_NO_THREAD. 4032 4033 tmem [KNL,XEN] 4034 Enable the Transcendent memory driver if built-in. 4035 4036 tmem.cleancache=0|1 [KNL, XEN] 4037 Default is on (1). Disable the usage of the cleancache 4038 API to send anonymous pages to the hypervisor. 4039 4040 tmem.frontswap=0|1 [KNL, XEN] 4041 Default is on (1). Disable the usage of the frontswap 4042 API to send swap pages to the hypervisor. If disabled 4043 the selfballooning and selfshrinking are force disabled. 4044 4045 tmem.selfballooning=0|1 [KNL, XEN] 4046 Default is on (1). Disable the driving of swap pages 4047 to the hypervisor. 4048 4049 tmem.selfshrinking=0|1 [KNL, XEN] 4050 Default is on (1). Partial swapoff that immediately 4051 transfers pages from Xen hypervisor back to the 4052 kernel based on different criteria. 4053 4054 topology= [S390] 4055 Format: {off | on} 4056 Specify if the kernel should make use of the cpu 4057 topology information if the hardware supports this. 4058 The scheduler will make use of this information and 4059 e.g. base its process migration decisions on it. 4060 Default is on. 4061 4062 topology_updates= [KNL, PPC, NUMA] 4063 Format: {off} 4064 Specify if the kernel should ignore (off) 4065 topology updates sent by the hypervisor to this 4066 LPAR. 4067 4068 tp720= [HW,PS2] 4069 4070 tpm_suspend_pcr=[HW,TPM] 4071 Format: integer pcr id 4072 Specify that at suspend time, the tpm driver 4073 should extend the specified pcr with zeros, 4074 as a workaround for some chips which fail to 4075 flush the last written pcr on TPM_SaveState. 4076 This will guarantee that all the other pcrs 4077 are saved. 4078 4079 trace_buf_size=nn[KMG] 4080 [FTRACE] will set tracing buffer size on each cpu. 4081 4082 trace_event=[event-list] 4083 [FTRACE] Set and start specified trace events in order 4084 to facilitate early boot debugging. 4085 See also Documentation/trace/events.txt 4086 4087 trace_options=[option-list] 4088 [FTRACE] Enable or disable tracer options at boot. 4089 The option-list is a comma delimited list of options 4090 that can be enabled or disabled just as if you were 4091 to echo the option name into 4092 4093 /sys/kernel/debug/tracing/trace_options 4094 4095 For example, to enable stacktrace option (to dump the 4096 stack trace of each event), add to the command line: 4097 4098 trace_options=stacktrace 4099 4100 See also Documentation/trace/ftrace.txt "trace options" 4101 section. 4102 4103 tp_printk[FTRACE] 4104 Have the tracepoints sent to printk as well as the 4105 tracing ring buffer. This is useful for early boot up 4106 where the system hangs or reboots and does not give the 4107 option for reading the tracing buffer or performing a 4108 ftrace_dump_on_oops. 4109 4110 To turn off having tracepoints sent to printk, 4111 echo 0 > /proc/sys/kernel/tracepoint_printk 4112 Note, echoing 1 into this file without the 4113 tracepoint_printk kernel cmdline option has no effect. 4114 4115 ** CAUTION ** 4116 4117 Having tracepoints sent to printk() and activating high 4118 frequency tracepoints such as irq or sched, can cause 4119 the system to live lock. 4120 4121 traceoff_on_warning 4122 [FTRACE] enable this option to disable tracing when a 4123 warning is hit. This turns off "tracing_on". Tracing can 4124 be enabled again by echoing '1' into the "tracing_on" 4125 file located in /sys/kernel/debug/tracing/ 4126 4127 This option is useful, as it disables the trace before 4128 the WARNING dump is called, which prevents the trace to 4129 be filled with content caused by the warning output. 4130 4131 This option can also be set at run time via the sysctl 4132 option: kernel/traceoff_on_warning 4133 4134 transparent_hugepage= 4135 [KNL] 4136 Format: [always|madvise|never] 4137 Can be used to control the default behavior of the system 4138 with respect to transparent hugepages. 4139 See Documentation/vm/transhuge.txt for more details. 4140 4141 tsc= Disable clocksource stability checks for TSC. 4142 Format: <string> 4143 [x86] reliable: mark tsc clocksource as reliable, this 4144 disables clocksource verification at runtime, as well 4145 as the stability checks done at bootup. Used to enable 4146 high-resolution timer mode on older hardware, and in 4147 virtualized environment. 4148 [x86] noirqtime: Do not use TSC to do irq accounting. 4149 Used to run time disable IRQ_TIME_ACCOUNTING on any 4150 platforms where RDTSC is slow and this accounting 4151 can add overhead. 4152 4153 tsx= [X86] Control Transactional Synchronization 4154 Extensions (TSX) feature in Intel processors that 4155 support TSX control. 4156 4157 This parameter controls the TSX feature. The options are: 4158 4159 on - Enable TSX on the system. Although there are 4160 mitigations for all known security vulnerabilities, 4161 TSX has been known to be an accelerator for 4162 several previous speculation-related CVEs, and 4163 so there may be unknown security risks associated 4164 with leaving it enabled. 4165 4166 off - Disable TSX on the system. (Note that this 4167 option takes effect only on newer CPUs which are 4168 not vulnerable to MDS, i.e., have 4169 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get 4170 the new IA32_TSX_CTRL MSR through a microcode 4171 update. This new MSR allows for the reliable 4172 deactivation of the TSX functionality.) 4173 4174 auto - Disable TSX if X86_BUG_TAA is present, 4175 otherwise enable TSX on the system. 4176 4177 Not specifying this option is equivalent to tsx=off. 4178 4179 See Documentation/hw-vuln/tsx_async_abort.rst 4180 for more details. 4181 4182 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async 4183 Abort (TAA) vulnerability. 4184 4185 Similar to Micro-architectural Data Sampling (MDS) 4186 certain CPUs that support Transactional 4187 Synchronization Extensions (TSX) are vulnerable to an 4188 exploit against CPU internal buffers which can forward 4189 information to a disclosure gadget under certain 4190 conditions. 4191 4192 In vulnerable processors, the speculatively forwarded 4193 data can be used in a cache side channel attack, to 4194 access data to which the attacker does not have direct 4195 access. 4196 4197 This parameter controls the TAA mitigation. The 4198 options are: 4199 4200 full - Enable TAA mitigation on vulnerable CPUs 4201 if TSX is enabled. 4202 4203 off - Unconditionally disable TAA mitigation 4204 4205 On MDS-affected machines, tsx_async_abort=off can be 4206 prevented by an active MDS mitigation as both vulnerabilities 4207 are mitigated with the same mechanism so in order to disable 4208 this mitigation, you need to specify mds=off too. 4209 4210 Not specifying this option is equivalent to 4211 tsx_async_abort=full. On CPUs which are MDS affected 4212 and deploy MDS mitigation, TAA mitigation is not 4213 required and doesn't provide any additional 4214 mitigation. 4215 4216 For details see: 4217 Documentation/hw-vuln/tsx_async_abort.rst 4218 4219 turbografx.map[2|3]= [HW,JOY] 4220 TurboGraFX parallel port interface 4221 Format: 4222 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 4223 See also Documentation/input/joystick-parport.txt 4224 4225 udbg-immortal [PPC] When debugging early kernel crashes that 4226 happen after console_init() and before a proper 4227 console driver takes over, this boot options might 4228 help "seeing" what's going on. 4229 4230 uhash_entries= [KNL,NET] 4231 Set number of hash buckets for UDP/UDP-Lite connections 4232 4233 uhci-hcd.ignore_oc= 4234 [USB] Ignore overcurrent events (default N). 4235 Some badly-designed motherboards generate lots of 4236 bogus events, for ports that aren't wired to 4237 anything. Set this parameter to avoid log spamming. 4238 Note that genuine overcurrent events won't be 4239 reported either. 4240 4241 unknown_nmi_panic 4242 [X86] Cause panic on unknown NMI. 4243 4244 usbcore.authorized_default= 4245 [USB] Default USB device authorization: 4246 (default -1 = authorized except for wireless USB, 4247 0 = not authorized, 1 = authorized) 4248 4249 usbcore.autosuspend= 4250 [USB] The autosuspend time delay (in seconds) used 4251 for newly-detected USB devices (default 2). This 4252 is the time required before an idle device will be 4253 autosuspended. Devices for which the delay is set 4254 to a negative value won't be autosuspended at all. 4255 4256 usbcore.usbfs_snoop= 4257 [USB] Set to log all usbfs traffic (default 0 = off). 4258 4259 usbcore.blinkenlights= 4260 [USB] Set to cycle leds on hubs (default 0 = off). 4261 4262 usbcore.old_scheme_first= 4263 [USB] Start with the old device initialization 4264 scheme (default 0 = off). 4265 4266 usbcore.usbfs_memory_mb= 4267 [USB] Memory limit (in MB) for buffers allocated by 4268 usbfs (default = 16, 0 = max = 2047). 4269 4270 usbcore.use_both_schemes= 4271 [USB] Try the other device initialization scheme 4272 if the first one fails (default 1 = enabled). 4273 4274 usbcore.initial_descriptor_timeout= 4275 [USB] Specifies timeout for the initial 64-byte 4276 USB_REQ_GET_DESCRIPTOR request in milliseconds 4277 (default 5000 = 5.0 seconds). 4278 4279 usbhid.mousepoll= 4280 [USBHID] The interval which mice are to be polled at. 4281 4282 usb-storage.delay_use= 4283 [UMS] The delay in seconds before a new device is 4284 scanned for Logical Units (default 1). 4285 4286 usb-storage.quirks= 4287 [UMS] A list of quirks entries to supplement or 4288 override the built-in unusual_devs list. List 4289 entries are separated by commas. Each entry has 4290 the form VID:PID:Flags where VID and PID are Vendor 4291 and Product ID values (4-digit hex numbers) and 4292 Flags is a set of characters, each corresponding 4293 to a common usb-storage quirk flag as follows: 4294 a = SANE_SENSE (collect more than 18 bytes 4295 of sense data); 4296 b = BAD_SENSE (don't collect more than 18 4297 bytes of sense data); 4298 c = FIX_CAPACITY (decrease the reported 4299 device capacity by one sector); 4300 d = NO_READ_DISC_INFO (don't use 4301 READ_DISC_INFO command); 4302 e = NO_READ_CAPACITY_16 (don't use 4303 READ_CAPACITY_16 command); 4304 f = NO_REPORT_OPCODES (don't use report opcodes 4305 command, uas only); 4306 g = MAX_SECTORS_240 (don't transfer more than 4307 240 sectors at a time, uas only); 4308 h = CAPACITY_HEURISTICS (decrease the 4309 reported device capacity by one 4310 sector if the number is odd); 4311 i = IGNORE_DEVICE (don't bind to this 4312 device); 4313 j = NO_REPORT_LUNS (don't use report luns 4314 command, uas only); 4315 l = NOT_LOCKABLE (don't try to lock and 4316 unlock ejectable media); 4317 m = MAX_SECTORS_64 (don't transfer more 4318 than 64 sectors = 32 KB at a time); 4319 n = INITIAL_READ10 (force a retry of the 4320 initial READ(10) command); 4321 o = CAPACITY_OK (accept the capacity 4322 reported by the device); 4323 p = WRITE_CACHE (the device cache is ON 4324 by default); 4325 r = IGNORE_RESIDUE (the device reports 4326 bogus residue values); 4327 s = SINGLE_LUN (the device has only one 4328 Logical Unit); 4329 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 4330 commands, uas only); 4331 u = IGNORE_UAS (don't bind to the uas driver); 4332 w = NO_WP_DETECT (don't test whether the 4333 medium is write-protected). 4334 Example: quirks=0419:aaf5:rl,0421:0433:rc 4335 4336 user_debug= [KNL,ARM] 4337 Format: <int> 4338 See arch/arm/Kconfig.debug help text. 4339 1 - undefined instruction events 4340 2 - system calls 4341 4 - invalid data aborts 4342 8 - SIGSEGV faults 4343 16 - SIGBUS faults 4344 Example: user_debug=31 4345 4346 userpte= 4347 [X86] Flags controlling user PTE allocations. 4348 4349 nohigh = do not allocate PTE pages in 4350 HIGHMEM regardless of setting 4351 of CONFIG_HIGHPTE. 4352 4353 vdso= [X86,SH] 4354 On X86_32, this is an alias for vdso32=. Otherwise: 4355 4356 vdso=1: enable VDSO (the default) 4357 vdso=0: disable VDSO mapping 4358 4359 vdso32= [X86] Control the 32-bit vDSO 4360 vdso32=1: enable 32-bit VDSO 4361 vdso32=0 or vdso32=2: disable 32-bit VDSO 4362 4363 See the help text for CONFIG_COMPAT_VDSO for more 4364 details. If CONFIG_COMPAT_VDSO is set, the default is 4365 vdso32=0; otherwise, the default is vdso32=1. 4366 4367 For compatibility with older kernels, vdso32=2 is an 4368 alias for vdso32=0. 4369 4370 Try vdso32=0 if you encounter an error that says: 4371 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 4372 4373 vector= [IA-64,SMP] 4374 vector=percpu: enable percpu vector domain 4375 4376 video= [FB] Frame buffer configuration 4377 See Documentation/fb/modedb.txt. 4378 4379 video.brightness_switch_enabled= [0,1] 4380 If set to 1, on receiving an ACPI notify event 4381 generated by hotkey, video driver will adjust brightness 4382 level and then send out the event to user space through 4383 the allocated input device; If set to 0, video driver 4384 will only send out the event without touching backlight 4385 brightness level. 4386 default: 1 4387 4388 virtio_mmio.device= 4389 [VMMIO] Memory mapped virtio (platform) device. 4390 4391 <size>@<baseaddr>:<irq>[:<id>] 4392 where: 4393 <size> := size (can use standard suffixes 4394 like K, M and G) 4395 <baseaddr> := physical base address 4396 <irq> := interrupt number (as passed to 4397 request_irq()) 4398 <id> := (optional) platform device id 4399 example: 4400 virtio_mmio.device=1K@0x100b0000:48:7 4401 4402 Can be used multiple times for multiple devices. 4403 4404 vga= [BOOT,X86-32] Select a particular video mode 4405 See Documentation/x86/boot.txt and 4406 Documentation/svga.txt. 4407 Use vga=ask for menu. 4408 This is actually a boot loader parameter; the value is 4409 passed to the kernel using a special protocol. 4410 4411 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact 4412 size of <nn>. This can be used to increase the 4413 minimum size (128MB on x86). It can also be used to 4414 decrease the size and leave more room for directly 4415 mapped kernel RAM. 4416 4417 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 4418 Format: <command> 4419 4420 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 4421 Format: <command> 4422 4423 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 4424 Format: <command> 4425 4426 vsyscall= [X86-64] 4427 Controls the behavior of vsyscalls (i.e. calls to 4428 fixed addresses of 0xffffffffff600x00 from legacy 4429 code). Most statically-linked binaries and older 4430 versions of glibc use these calls. Because these 4431 functions are at fixed addresses, they make nice 4432 targets for exploits that can control RIP. 4433 4434 emulate [default] Vsyscalls turn into traps and are 4435 emulated reasonably safely. 4436 4437 native Vsyscalls are native syscall instructions. 4438 This is a little bit faster than trapping 4439 and makes a few dynamic recompilers work 4440 better than they would in emulation mode. 4441 It also makes exploits much easier to write. 4442 4443 none Vsyscalls don't work at all. This makes 4444 them quite hard to use for exploits but 4445 might break your system. 4446 4447 vt.color= [VT] Default text color. 4448 Format: 0xYX, X = foreground, Y = background. 4449 Default: 0x07 = light gray on black. 4450 4451 vt.cur_default= [VT] Default cursor shape. 4452 Format: 0xCCBBAA, where AA, BB, and CC are the same as 4453 the parameters of the <Esc>[?A;B;Cc escape sequence; 4454 see VGA-softcursor.txt. Default: 2 = underline. 4455 4456 vt.default_blu= [VT] 4457 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 4458 Change the default blue palette of the console. 4459 This is a 16-member array composed of values 4460 ranging from 0-255. 4461 4462 vt.default_grn= [VT] 4463 Format: <green0>,<green1>,<green2>,...,<green15> 4464 Change the default green palette of the console. 4465 This is a 16-member array composed of values 4466 ranging from 0-255. 4467 4468 vt.default_red= [VT] 4469 Format: <red0>,<red1>,<red2>,...,<red15> 4470 Change the default red palette of the console. 4471 This is a 16-member array composed of values 4472 ranging from 0-255. 4473 4474 vt.default_utf8= 4475 [VT] 4476 Format=<0|1> 4477 Set system-wide default UTF-8 mode for all tty's. 4478 Default is 1, i.e. UTF-8 mode is enabled for all 4479 newly opened terminals. 4480 4481 vt.global_cursor_default= 4482 [VT] 4483 Format=<-1|0|1> 4484 Set system-wide default for whether a cursor 4485 is shown on new VTs. Default is -1, 4486 i.e. cursors will be created by default unless 4487 overridden by individual drivers. 0 will hide 4488 cursors, 1 will display them. 4489 4490 vt.italic= [VT] Default color for italic text; 0-15. 4491 Default: 2 = green. 4492 4493 vt.underline= [VT] Default color for underlined text; 0-15. 4494 Default: 3 = cyan. 4495 4496 watchdog timers [HW,WDT] For information on watchdog timers, 4497 see Documentation/watchdog/watchdog-parameters.txt 4498 or other driver-specific files in the 4499 Documentation/watchdog/ directory. 4500 4501 workqueue.disable_numa 4502 By default, all work items queued to unbound 4503 workqueues are affine to the NUMA nodes they're 4504 issued on, which results in better behavior in 4505 general. If NUMA affinity needs to be disabled for 4506 whatever reason, this option can be used. Note 4507 that this also can be controlled per-workqueue for 4508 workqueues visible under /sys/bus/workqueue/. 4509 4510 workqueue.power_efficient 4511 Per-cpu workqueues are generally preferred because 4512 they show better performance thanks to cache 4513 locality; unfortunately, per-cpu workqueues tend to 4514 be more power hungry than unbound workqueues. 4515 4516 Enabling this makes the per-cpu workqueues which 4517 were observed to contribute significantly to power 4518 consumption unbound, leading to measurably lower 4519 power usage at the cost of small performance 4520 overhead. 4521 4522 The default value of this parameter is determined by 4523 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 4524 4525 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of 4526 default x2apic cluster mode on platforms 4527 supporting x2apic. 4528 4529 x86_intel_mid_timer= [X86-32,APBT] 4530 Choose timer option for x86 Intel MID platform. 4531 Two valid options are apbt timer only and lapic timer 4532 plus one apbt timer for broadcast timer. 4533 x86_intel_mid_timer=apbt_only | lapic_and_apbt 4534 4535 xen_512gb_limit [KNL,X86-64,XEN] 4536 Restricts the kernel running paravirtualized under Xen 4537 to use only up to 512 GB of RAM. The reason to do so is 4538 crash analysis tools and Xen tools for doing domain 4539 save/restore/migration must be enabled to handle larger 4540 domains. 4541 4542 xen_emul_unplug= [HW,X86,XEN] 4543 Unplug Xen emulated devices 4544 Format: [unplug0,][unplug1] 4545 ide-disks -- unplug primary master IDE devices 4546 aux-ide-disks -- unplug non-primary-master IDE devices 4547 nics -- unplug network devices 4548 all -- unplug all emulated devices (NICs and IDE disks) 4549 unnecessary -- unplugging emulated devices is 4550 unnecessary even if the host did not respond to 4551 the unplug protocol 4552 never -- do not unplug even if version check succeeds 4553 4554 xen_nopvspin [X86,XEN] 4555 Disables the ticketlock slowpath using Xen PV 4556 optimizations. 4557 4558 xen_nopv [X86] 4559 Disables the PV optimizations forcing the HVM guest to 4560 run as generic HVM guest with no PV drivers. 4561 4562 xen.event_eoi_delay= [XEN] 4563 How long to delay EOI handling in case of event 4564 storms (jiffies). Default is 10. 4565 4566 xen.event_loop_timeout= [XEN] 4567 After which time (jiffies) the event handling loop 4568 should start to delay EOI handling. Default is 2. 4569 4570 xirc2ps_cs= [NET,PCMCIA] 4571 Format: 4572 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 4573 4574______________________________________________________________________ 4575 4576TODO: 4577 4578 Add more DRM drivers. 4579