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