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