Based on kernel version 3.19. Page generated on 2015-02-13 21:21 EST.
1 Kernel Parameters 2 ~~~~~~~~~~~~~~~~~ 3 4 The following is a consolidated list of the kernel parameters as 5 implemented by the __setup(), core_param() and module_param() macros 6 and sorted into English Dictionary order (defined as ignoring all 7 punctuation and sorting digits before letters in a case insensitive 8 manner), and with descriptions where known. 9 10 The kernel parses parameters from the kernel command line up to "--"; 11 if it doesn't recognize a parameter and it doesn't contain a '.', the 12 parameter gets passed to init: parameters with '=' go into init's 13 environment, others are passed as command line arguments to init. 14 Everything after "--" is passed as an argument to init. 15 16 Module parameters can be specified in two ways: via the kernel command 17 line 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 22 Parameters for modules which are built into the kernel need to be 23 specified on the kernel command line. modprobe looks through the 24 kernel command line (/proc/cmdline) and collects module parameters 25 when it loads a module, so the kernel command line can be used for 26 loadable modules too. 27 28 Hyphens (dashes) and underscores are equivalent in parameter names, so 29 log_buf_len=1M print-fatal-signals=1 30 can also be entered as 31 log-buf-len=1M print_fatal_signals=1 32 33 Double-quotes can be used to protect spaces in values, e.g.: 34 param="spaces in here" 35 36 This document may not be entirely up to date and comprehensive. The command 37 "modinfo -p ${modulename}" shows a current list of all parameters of a loadable 38 module. Loadable modules, after being loaded into the running kernel, also 39 reveal their parameters in /sys/module/${modulename}/parameters/. Some of these 40 parameters may be changed at runtime by the command 41 "echo -n ${value} > /sys/module/${modulename}/parameters/${parm}". 42 43 The parameters listed below are only valid if certain kernel build options were 44 enabled and if respective hardware is present. The text in square brackets at 45 the beginning of each description states the restrictions within which a 46 parameter is applicable: 47 48 ACPI ACPI support is enabled. 49 AGP AGP (Accelerated Graphics Port) is enabled. 50 ALSA ALSA sound support is enabled. 51 APIC APIC support is enabled. 52 APM Advanced Power Management support is enabled. 53 ARM ARM architecture is enabled. 54 AVR32 AVR32 architecture is enabled. 55 AX25 Appropriate AX.25 support is enabled. 56 BLACKFIN Blackfin architecture is enabled. 57 CLK Common clock infrastructure is enabled. 58 CMA Contiguous Memory Area support is enabled. 59 DRM Direct Rendering Management support is enabled. 60 DYNAMIC_DEBUG Build in debug messages and enable them at runtime 61 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled 62 EFI EFI Partitioning (GPT) is enabled 63 EIDE EIDE/ATAPI support is enabled. 64 EVM Extended Verification Module 65 FB The frame buffer device is enabled. 66 FTRACE Function tracing enabled. 67 GCOV GCOV profiling is enabled. 68 HW Appropriate hardware is enabled. 69 IA-64 IA-64 architecture is enabled. 70 IMA Integrity measurement architecture is enabled. 71 IOSCHED More than one I/O scheduler is enabled. 72 IP_PNP IP DHCP, BOOTP, or RARP is enabled. 73 IPV6 IPv6 support is enabled. 74 ISAPNP ISA PnP code is enabled. 75 ISDN Appropriate ISDN support is enabled. 76 JOY Appropriate joystick support is enabled. 77 KGDB Kernel debugger support is enabled. 78 KVM Kernel Virtual Machine support is enabled. 79 LIBATA Libata driver is enabled 80 LP Printer support is enabled. 81 LOOP Loopback device support is enabled. 82 M68k M68k architecture is enabled. 83 These options have more detailed description inside of 84 Documentation/m68k/kernel-options.txt. 85 MDA MDA console support is enabled. 86 MIPS MIPS architecture is enabled. 87 MOUSE Appropriate mouse support is enabled. 88 MSI Message Signaled Interrupts (PCI). 89 MTD MTD (Memory Technology Device) support is enabled. 90 NET Appropriate network support is enabled. 91 NUMA NUMA support is enabled. 92 NFS Appropriate NFS support is enabled. 93 OSS OSS sound support is enabled. 94 PV_OPS A paravirtualized kernel is enabled. 95 PARIDE The ParIDE (parallel port IDE) subsystem is enabled. 96 PARISC The PA-RISC architecture is enabled. 97 PCI PCI bus support is enabled. 98 PCIE PCI Express support is enabled. 99 PCMCIA The PCMCIA subsystem is enabled. 100 PNP Plug & Play support is enabled. 101 PPC PowerPC architecture is enabled. 102 PPT Parallel port support is enabled. 103 PS2 Appropriate PS/2 support is enabled. 104 RAM RAM disk support is enabled. 105 S390 S390 architecture is enabled. 106 SCSI Appropriate SCSI support is enabled. 107 A lot of drivers have their options described inside 108 the Documentation/scsi/ sub-directory. 109 SECURITY Different security models are enabled. 110 SELINUX SELinux support is enabled. 111 APPARMOR AppArmor support is enabled. 112 SERIAL Serial support is enabled. 113 SH SuperH architecture is enabled. 114 SMP The kernel is an SMP kernel. 115 SPARC Sparc architecture is enabled. 116 SWSUSP Software suspend (hibernation) is enabled. 117 SUSPEND System suspend states are enabled. 118 TPM TPM drivers are enabled. 119 TS Appropriate touchscreen support is enabled. 120 UMS USB Mass Storage support is enabled. 121 USB USB support is enabled. 122 USBHID USB Human Interface Device support is enabled. 123 V4L Video For Linux support is enabled. 124 VMMIO Driver for memory mapped virtio devices is enabled. 125 VGA The VGA console has been enabled. 126 VT Virtual terminal support is enabled. 127 WDT Watchdog support is enabled. 128 XT IBM PC/XT MFM hard disk support is enabled. 129 X86-32 X86-32, aka i386 architecture is enabled. 130 X86-64 X86-64 architecture is enabled. 131 More X86-64 boot options can be found in 132 Documentation/x86/x86_64/boot-options.txt . 133 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64) 134 XEN Xen support is enabled 135 136 In addition, the following text indicates that the option: 137 138 BUGS= Relates to possible processor bugs on the said processor. 139 KNL Is a kernel start-up parameter. 140 BOOT Is a boot loader parameter. 141 142 Parameters denoted with BOOT are actually interpreted by the boot 143 loader, and have no meaning to the kernel directly. 144 Do not modify the syntax of boot loader parameters without extreme 145 need or coordination with <Documentation/x86/boot.txt>. 146 147 There are also arch-specific kernel-parameters not documented here. 148 See for example <Documentation/x86/x86_64/boot-options.txt>. 149 150 Note that ALL kernel parameters listed below are CASE SENSITIVE, and that 151 a trailing = on the name of any parameter states that that parameter will 152 be entered as an environment variable, whereas its absence indicates that 153 it will appear as a kernel argument readable via /proc/cmdline by programs 154 running once the system is up. 155 156 The number of kernel parameters is not limited, but the length of the 157 complete command line (parameters including spaces etc.) is limited to 158 a fixed number of characters. This limit depends on the architecture 159 and is between 256 and 4096 characters. It is defined in the file 160 ./include/asm/setup.h as COMMAND_LINE_SIZE. 161 162 Finally, the [KMG] suffix is commonly described after a number of kernel 163 parameter values. These 'K', 'M', and 'G' letters represent the _binary_ 164 multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30 165 bytes respectively. Such letter suffixes can also be entirely omitted. 166 167 168 acpi= [HW,ACPI,X86] 169 Advanced Configuration and Power Interface 170 Format: { force | off | strict | noirq | rsdt } 171 force -- enable ACPI if default was off 172 off -- disable ACPI if default was on 173 noirq -- do not use ACPI for IRQ routing 174 strict -- Be less tolerant of platforms that are not 175 strictly ACPI specification compliant. 176 rsdt -- prefer RSDT over (default) XSDT 177 copy_dsdt -- copy DSDT to memory 178 179 See also Documentation/power/runtime_pm.txt, pci=noacpi 180 181 acpi_rsdp= [ACPI,EFI,KEXEC] 182 Pass the RSDP address to the kernel, mostly used 183 on machines running EFI runtime service to boot the 184 second kernel for kdump. 185 186 acpi_apic_instance= [ACPI, IOAPIC] 187 Format: <int> 188 2: use 2nd APIC table, if available 189 1,0: use 1st APIC table 190 default: 0 191 192 acpi_backlight= [HW,ACPI] 193 acpi_backlight=vendor 194 acpi_backlight=video 195 If set to vendor, prefer vendor specific driver 196 (e.g. thinkpad_acpi, sony_acpi, etc.) instead 197 of the ACPI video.ko driver. 198 199 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG] 200 acpi.debug_level= [HW,ACPI,ACPI_DEBUG] 201 Format: <int> 202 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI 203 debug output. Bits in debug_layer correspond to a 204 _COMPONENT in an ACPI source file, e.g., 205 #define _COMPONENT ACPI_PCI_COMPONENT 206 Bits in debug_level correspond to a level in 207 ACPI_DEBUG_PRINT statements, e.g., 208 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ... 209 The debug_level mask defaults to "info". See 210 Documentation/acpi/debug.txt for more information about 211 debug layers and levels. 212 213 Enable processor driver info messages: 214 acpi.debug_layer=0x20000000 215 Enable PCI/PCI interrupt routing info messages: 216 acpi.debug_layer=0x400000 217 Enable AML "Debug" output, i.e., stores to the Debug 218 object while interpreting AML: 219 acpi.debug_layer=0xffffffff acpi.debug_level=0x2 220 Enable all messages related to ACPI hardware: 221 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff 222 223 Some values produce so much output that the system is 224 unusable. The "log_buf_len" parameter may be useful 225 if you need to capture more output. 226 227 acpi_force_table_verification [HW,ACPI] 228 Enable table checksum verification during early stage. 229 By default, this is disabled due to x86 early mapping 230 size limitation. 231 232 acpi_irq_balance [HW,ACPI] 233 ACPI will balance active IRQs 234 default in APIC mode 235 236 acpi_irq_nobalance [HW,ACPI] 237 ACPI will not move active IRQs (default) 238 default in PIC mode 239 240 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA 241 Format: <irq>,<irq>... 242 243 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for 244 use by PCI 245 Format: <irq>,<irq>... 246 247 acpi_no_auto_serialize [HW,ACPI] 248 Disable auto-serialization of AML methods 249 AML control methods that contain the opcodes to create 250 named objects will be marked as "Serialized" by the 251 auto-serialization feature. 252 This feature is enabled by default. 253 This option allows to turn off the feature. 254 255 acpi_no_static_ssdt [HW,ACPI] 256 Disable installation of static SSDTs at early boot time 257 By default, SSDTs contained in the RSDT/XSDT will be 258 installed automatically and they will appear under 259 /sys/firmware/acpi/tables. 260 This option turns off this feature. 261 Note that specifying this option does not affect 262 dynamic table installation which will install SSDT 263 tables to /sys/firmware/acpi/tables/dynamic. 264 265 acpica_no_return_repair [HW, ACPI] 266 Disable AML predefined validation mechanism 267 This mechanism can repair the evaluation result to make 268 the return objects more ACPI specification compliant. 269 This option is useful for developers to identify the 270 root cause of an AML interpreter issue when the issue 271 has something to do with the repair mechanism. 272 273 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS 274 Format: To spoof as Windows 98: ="Microsoft Windows" 275 276 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings 277 acpi_osi="string1" # add string1 278 acpi_osi="!string2" # remove string2 279 acpi_osi=!* # remove all strings 280 acpi_osi=! # disable all built-in OS vendor 281 strings 282 acpi_osi= # disable all strings 283 284 'acpi_osi=!' can be used in combination with single or 285 multiple 'acpi_osi="string1"' to support specific OS 286 vendor string(s). Note that such command can only 287 affect the default state of the OS vendor strings, thus 288 it cannot affect the default state of the feature group 289 strings and the current state of the OS vendor strings, 290 specifying it multiple times through kernel command line 291 is meaningless. This command is useful when one do not 292 care about the state of the feature group strings which 293 should be controlled by the OSPM. 294 Examples: 295 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent 296 to 'acpi_osi="Windows 2000" acpi_osi=!', they all 297 can make '_OSI("Windows 2000")' TRUE. 298 299 'acpi_osi=' cannot be used in combination with other 300 'acpi_osi=' command lines, the _OSI method will not 301 exist in the ACPI namespace. NOTE that such command can 302 only affect the _OSI support state, thus specifying it 303 multiple times through kernel command line is also 304 meaningless. 305 Examples: 306 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)' 307 FALSE. 308 309 'acpi_osi=!*' can be used in combination with single or 310 multiple 'acpi_osi="string1"' to support specific 311 string(s). Note that such command can affect the 312 current state of both the OS vendor strings and the 313 feature group strings, thus specifying it multiple times 314 through kernel command line is meaningful. But it may 315 still not able to affect the final state of a string if 316 there are quirks related to this string. This command 317 is useful when one want to control the state of the 318 feature group strings to debug BIOS issues related to 319 the OSPM features. 320 Examples: 321 1. 'acpi_osi="Module Device" acpi_osi=!*' can make 322 '_OSI("Module Device")' FALSE. 323 2. 'acpi_osi=!* acpi_osi="Module Device"' can make 324 '_OSI("Module Device")' TRUE. 325 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is 326 equivalent to 327 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"' 328 and 329 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!', 330 they all will make '_OSI("Windows 2000")' TRUE. 331 332 acpi_pm_good [X86] 333 Override the pmtimer bug detection: force the kernel 334 to assume that this machine's pmtimer latches its value 335 and always returns good values. 336 337 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode 338 Format: { level | edge | high | low } 339 340 acpi_skip_timer_override [HW,ACPI] 341 Recognize and ignore IRQ0/pin2 Interrupt Override. 342 For broken nForce2 BIOS resulting in XT-PIC timer. 343 344 acpi_sleep= [HW,ACPI] Sleep options 345 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig, 346 old_ordering, nonvs, sci_force_enable } 347 See Documentation/power/video.txt for information on 348 s3_bios and s3_mode. 349 s3_beep is for debugging; it makes the PC's speaker beep 350 as soon as the kernel's real-mode entry point is called. 351 s4_nohwsig prevents ACPI hardware signature from being 352 used during resume from hibernation. 353 old_ordering causes the ACPI 1.0 ordering of the _PTS 354 control method, with respect to putting devices into 355 low power states, to be enforced (the ACPI 2.0 ordering 356 of _PTS is used by default). 357 nonvs prevents the kernel from saving/restoring the 358 ACPI NVS memory during suspend/hibernation and resume. 359 sci_force_enable causes the kernel to set SCI_EN directly 360 on resume from S1/S3 (which is against the ACPI spec, 361 but some broken systems don't work without it). 362 363 acpi_use_timer_override [HW,ACPI] 364 Use timer override. For some broken Nvidia NF5 boards 365 that require a timer override, but don't have HPET 366 367 acpi_enforce_resources= [ACPI] 368 { strict | lax | no } 369 Check for resource conflicts between native drivers 370 and ACPI OperationRegions (SystemIO and SystemMemory 371 only). IO ports and memory declared in ACPI might be 372 used by the ACPI subsystem in arbitrary AML code and 373 can interfere with legacy drivers. 374 strict (default): access to resources claimed by ACPI 375 is denied; legacy drivers trying to access reserved 376 resources will fail to bind to device using them. 377 lax: access to resources claimed by ACPI is allowed; 378 legacy drivers trying to access reserved resources 379 will bind successfully but a warning message is logged. 380 no: ACPI OperationRegions are not marked as reserved, 381 no further checks are performed. 382 383 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump 384 kernels. 385 386 add_efi_memmap [EFI; X86] Include EFI memory map in 387 kernel's map of available physical RAM. 388 389 agp= [AGP] 390 { off | try_unsupported } 391 off: disable AGP support 392 try_unsupported: try to drive unsupported chipsets 393 (may crash computer or cause data corruption) 394 395 ALSA [HW,ALSA] 396 See Documentation/sound/alsa/alsa-parameters.txt 397 398 alignment= [KNL,ARM] 399 Allow the default userspace alignment fault handler 400 behaviour to be specified. Bit 0 enables warnings, 401 bit 1 enables fixups, and bit 2 sends a segfault. 402 403 align_va_addr= [X86-64] 404 Align virtual addresses by clearing slice [14:12] when 405 allocating a VMA at process creation time. This option 406 gives you up to 3% performance improvement on AMD F15h 407 machines (where it is enabled by default) for a 408 CPU-intensive style benchmark, and it can vary highly in 409 a microbenchmark depending on workload and compiler. 410 411 32: only for 32-bit processes 412 64: only for 64-bit processes 413 on: enable for both 32- and 64-bit processes 414 off: disable for both 32- and 64-bit processes 415 416 alloc_snapshot [FTRACE] 417 Allocate the ftrace snapshot buffer on boot up when the 418 main buffer is allocated. This is handy if debugging 419 and you need to use tracing_snapshot() on boot up, and 420 do not want to use tracing_snapshot_alloc() as it needs 421 to be done where GFP_KERNEL allocations are allowed. 422 423 amd_iommu= [HW,X86-64] 424 Pass parameters to the AMD IOMMU driver in the system. 425 Possible values are: 426 fullflush - enable flushing of IO/TLB entries when 427 they are unmapped. Otherwise they are 428 flushed before they will be reused, which 429 is a lot of faster 430 off - do not initialize any AMD IOMMU found in 431 the system 432 force_isolation - Force device isolation for all 433 devices. The IOMMU driver is not 434 allowed anymore to lift isolation 435 requirements as needed. This option 436 does not override iommu=pt 437 438 amd_iommu_dump= [HW,X86-64] 439 Enable AMD IOMMU driver option to dump the ACPI table 440 for AMD IOMMU. With this option enabled, AMD IOMMU 441 driver will print ACPI tables for AMD IOMMU during 442 IOMMU initialization. 443 444 amijoy.map= [HW,JOY] Amiga joystick support 445 Map of devices attached to JOY0DAT and JOY1DAT 446 Format: <a>,<b> 447 See also Documentation/input/joystick.txt 448 449 analog.map= [HW,JOY] Analog joystick and gamepad support 450 Specifies type or capabilities of an analog joystick 451 connected to one of 16 gameports 452 Format: <type1>,<type2>,..<type16> 453 454 apc= [HW,SPARC] 455 Power management functions (SPARCstation-4/5 + deriv.) 456 Format: noidle 457 Disable APC CPU standby support. SPARCstation-Fox does 458 not play well with APC CPU idle - disable it if you have 459 APC and your system crashes randomly. 460 461 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller 462 Change the output verbosity whilst booting 463 Format: { quiet (default) | verbose | debug } 464 Change the amount of debugging information output 465 when initialising the APIC and IO-APIC components. 466 467 autoconf= [IPV6] 468 See Documentation/networking/ipv6.txt. 469 470 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller 471 Limit apic dumping. The parameter defines the maximal 472 number of local apics being dumped. Also it is possible 473 to set it to "all" by meaning -- no limit here. 474 Format: { 1 (default) | 2 | ... | all }. 475 The parameter valid if only apic=debug or 476 apic=verbose is specified. 477 Example: apic=debug show_lapic=all 478 479 apm= [APM] Advanced Power Management 480 See header of arch/x86/kernel/apm_32.c. 481 482 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards 483 Format: <io>,<irq>,<nodeID> 484 485 ataflop= [HW,M68k] 486 487 atarimouse= [HW,MOUSE] Atari Mouse 488 489 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess, 490 EzKey and similar keyboards 491 492 atkbd.reset= [HW] Reset keyboard during initialization 493 494 atkbd.set= [HW] Select keyboard code set 495 Format: <int> (2 = AT (default), 3 = PS/2) 496 497 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar 498 keyboards 499 500 atkbd.softraw= [HW] Choose between synthetic and real raw mode 501 Format: <bool> (0 = real, 1 = synthetic (default)) 502 503 atkbd.softrepeat= [HW] 504 Use software keyboard repeat 505 506 audit= [KNL] Enable the audit sub-system 507 Format: { "0" | "1" } (0 = disabled, 1 = enabled) 508 0 - kernel audit is disabled and can not be enabled 509 until the next reboot 510 unset - kernel audit is initialized but disabled and 511 will be fully enabled by the userspace auditd. 512 1 - kernel audit is initialized and partially enabled, 513 storing at most audit_backlog_limit messages in 514 RAM until it is fully enabled by the userspace 515 auditd. 516 Default: unset 517 518 audit_backlog_limit= [KNL] Set the audit queue size limit. 519 Format: <int> (must be >=0) 520 Default: 64 521 522 baycom_epp= [HW,AX25] 523 Format: <io>,<mode> 524 525 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem 526 Format: <io>,<mode> 527 See header of drivers/net/hamradio/baycom_par.c. 528 529 baycom_ser_fdx= [HW,AX25] 530 BayCom Serial Port AX.25 Modem (Full Duplex Mode) 531 Format: <io>,<irq>,<mode>[,<baud>] 532 See header of drivers/net/hamradio/baycom_ser_fdx.c. 533 534 baycom_ser_hdx= [HW,AX25] 535 BayCom Serial Port AX.25 Modem (Half Duplex Mode) 536 Format: <io>,<irq>,<mode> 537 See header of drivers/net/hamradio/baycom_ser_hdx.c. 538 539 blkdevparts= Manual partition parsing of block device(s) for 540 embedded devices based on command line input. 541 See Documentation/block/cmdline-partition.txt 542 543 boot_delay= Milliseconds to delay each printk during boot. 544 Values larger than 10 seconds (10000) are changed to 545 no delay (0). 546 Format: integer 547 548 bootmem_debug [KNL] Enable bootmem allocator debug messages. 549 550 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards) 551 bttv.radio= Most important insmod options are available as 552 kernel args too. 553 bttv.pll= See Documentation/video4linux/bttv/Insmod-options 554 bttv.tuner= 555 556 bulk_remove=off [PPC] This parameter disables the use of the pSeries 557 firmware feature for flushing multiple hpte entries 558 at a time. 559 560 c101= [NET] Moxa C101 synchronous serial card 561 562 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection. 563 Sometimes CPU hardware bugs make them report the cache 564 size incorrectly. The kernel will attempt work arounds 565 to fix known problems, but for some CPUs it is not 566 possible to determine what the correct size should be. 567 This option provides an override for these situations. 568 569 ca_keys= [KEYS] This parameter identifies a specific key(s) on 570 the system trusted keyring to be used for certificate 571 trust validation. 572 format: { id:<keyid> | builtin } 573 574 cca= [MIPS] Override the kernel pages' cache coherency 575 algorithm. Accepted values range from 0 to 7 576 inclusive. See arch/mips/include/asm/pgtable-bits.h 577 for platform specific values (SB1, Loongson3 and 578 others). 579 580 ccw_timeout_log [S390] 581 See Documentation/s390/CommonIO for details. 582 583 cgroup_disable= [KNL] Disable a particular controller 584 Format: {name of the controller(s) to disable} 585 The effects of cgroup_disable=foo are: 586 - foo isn't auto-mounted if you mount all cgroups in 587 a single hierarchy 588 - foo isn't visible as an individually mountable 589 subsystem 590 {Currently only "memory" controller deal with this and 591 cut the overhead, others just disable the usage. So 592 only cgroup_disable=memory is actually worthy} 593 594 checkreqprot [SELINUX] Set initial checkreqprot flag value. 595 Format: { "0" | "1" } 596 See security/selinux/Kconfig help text. 597 0 -- check protection applied by kernel (includes 598 any implied execute protection). 599 1 -- check protection requested by application. 600 Default value is set via a kernel config option. 601 Value can be changed at runtime via 602 /selinux/checkreqprot. 603 604 cio_ignore= [S390] 605 See Documentation/s390/CommonIO for details. 606 clk_ignore_unused 607 [CLK] 608 Prevents the clock framework from automatically gating 609 clocks that have not been explicitly enabled by a Linux 610 device driver but are enabled in hardware at reset or 611 by the bootloader/firmware. Note that this does not 612 force such clocks to be always-on nor does it reserve 613 those clocks in any way. This parameter is useful for 614 debug and development, but should not be needed on a 615 platform with proper driver support. For more 616 information, see Documentation/clk.txt. 617 618 clock= [BUGS=X86-32, HW] gettimeofday clocksource override. 619 [Deprecated] 620 Forces specified clocksource (if available) to be used 621 when calculating gettimeofday(). If specified 622 clocksource is not available, it defaults to PIT. 623 Format: { pit | tsc | cyclone | pmtmr } 624 625 clocksource= Override the default clocksource 626 Format: <string> 627 Override the default clocksource and use the clocksource 628 with the name specified. 629 Some clocksource names to choose from, depending on 630 the platform: 631 [all] jiffies (this is the base, fallback clocksource) 632 [ACPI] acpi_pm 633 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2, 634 pxa_timer,timer3,32k_counter,timer0_1 635 [AVR32] avr32 636 [X86-32] pit,hpet,tsc; 637 scx200_hrt on Geode; cyclone on IBM x440 638 [MIPS] MIPS 639 [PARISC] cr16 640 [S390] tod 641 [SH] SuperH 642 [SPARC64] tick 643 [X86-64] hpet,tsc 644 645 clearcpuid=BITNUM [X86] 646 Disable CPUID feature X for the kernel. See 647 arch/x86/include/asm/cpufeature.h for the valid bit 648 numbers. Note the Linux specific bits are not necessarily 649 stable over kernel options, but the vendor specific 650 ones should be. 651 Also note that user programs calling CPUID directly 652 or using the feature without checking anything 653 will still see it. This just prevents it from 654 being used by the kernel or shown in /proc/cpuinfo. 655 Also note the kernel might malfunction if you disable 656 some critical bits. 657 658 cma=nn[MG]@[start[MG][-end[MG]]] 659 [ARM,X86,KNL] 660 Sets the size of kernel global memory area for 661 contiguous memory allocations and optionally the 662 placement constraint by the physical address range of 663 memory allocations. A value of 0 disables CMA 664 altogether. For more information, see 665 include/linux/dma-contiguous.h 666 667 cmo_free_hint= [PPC] Format: { yes | no } 668 Specify whether pages are marked as being inactive 669 when they are freed. This is used in CMO environments 670 to determine OS memory pressure for page stealing by 671 a hypervisor. 672 Default: yes 673 674 coherent_pool=nn[KMG] [ARM,KNL] 675 Sets the size of memory pool for coherent, atomic dma 676 allocations, by default set to 256K. 677 678 code_bytes [X86] How many bytes of object code to print 679 in an oops report. 680 Range: 0 - 8192 681 Default: 64 682 683 com20020= [HW,NET] ARCnet - COM20020 chipset 684 Format: 685 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]] 686 687 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers) 688 Format: <io>[,<irq>] 689 690 com90xx= [HW,NET] 691 ARCnet - COM90xx chipset (memory-mapped buffers) 692 Format: <io>[,<irq>[,<memstart>]] 693 694 condev= [HW,S390] console device 695 conmode= 696 697 console= [KNL] Output console device and options. 698 699 tty<n> Use the virtual console device <n>. 700 701 ttyS<n>[,options] 702 ttyUSB0[,options] 703 Use the specified serial port. The options are of 704 the form "bbbbpnf", where "bbbb" is the baud rate, 705 "p" is parity ("n", "o", or "e"), "n" is number of 706 bits, and "f" is flow control ("r" for RTS or 707 omit it). Default is "9600n8". 708 709 See Documentation/serial-console.txt for more 710 information. See 711 Documentation/networking/netconsole.txt for an 712 alternative. 713 714 uart[8250],io,<addr>[,options] 715 uart[8250],mmio,<addr>[,options] 716 Start an early, polled-mode console on the 8250/16550 717 UART at the specified I/O port or MMIO address, 718 switching to the matching ttyS device later. The 719 options are the same as for ttyS, above. 720 hvc<n> Use the hypervisor console device <n>. This is for 721 both Xen and PowerPC hypervisors. 722 723 If the device connected to the port is not a TTY but a braille 724 device, prepend "brl," before the device type, for instance 725 console=brl,ttyS0 726 For now, only VisioBraille is supported. 727 728 consoleblank= [KNL] The console blank (screen saver) timeout in 729 seconds. Defaults to 10*60 = 10mins. A value of 0 730 disables the blank timer. 731 732 coredump_filter= 733 [KNL] Change the default value for 734 /proc/<pid>/coredump_filter. 735 See also Documentation/filesystems/proc.txt. 736 737 cpuidle.off=1 [CPU_IDLE] 738 disable the cpuidle sub-system 739 740 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver 741 Format: 742 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] 743 744 crashkernel=size[KMG][@offset[KMG]] 745 [KNL] Using kexec, Linux can switch to a 'crash kernel' 746 upon panic. This parameter reserves the physical 747 memory region [offset, offset + size] for that kernel 748 image. If '@offset' is omitted, then a suitable offset 749 is selected automatically. Check 750 Documentation/kdump/kdump.txt for further details. 751 752 crashkernel=range1:size1[,range2:size2,...][@offset] 753 [KNL] Same as above, but depends on the memory 754 in the running system. The syntax of range is 755 start-[end] where start and end are both 756 a memory unit (amount[KMG]). See also 757 Documentation/kdump/kdump.txt for an example. 758 759 crashkernel=size[KMG],high 760 [KNL, x86_64] range could be above 4G. Allow kernel 761 to allocate physical memory region from top, so could 762 be above 4G if system have more than 4G ram installed. 763 Otherwise memory region will be allocated below 4G, if 764 available. 765 It will be ignored if crashkernel=X is specified. 766 crashkernel=size[KMG],low 767 [KNL, x86_64] range under 4G. When crashkernel=X,high 768 is passed, kernel could allocate physical memory region 769 above 4G, that cause second kernel crash on system 770 that require some amount of low memory, e.g. swiotlb 771 requires at least 64M+32K low memory. Kernel would 772 try to allocate 72M below 4G automatically. 773 This one let user to specify own low range under 4G 774 for second kernel instead. 775 0: to disable low allocation. 776 It will be ignored when crashkernel=X,high is not used 777 or memory reserved is below 4G. 778 779 cs89x0_dma= [HW,NET] 780 Format: <dma> 781 782 cs89x0_media= [HW,NET] 783 Format: { rj45 | aui | bnc } 784 785 dasd= [HW,NET] 786 See header of drivers/s390/block/dasd_devmap.c. 787 788 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port 789 (one device per port) 790 Format: <port#>,<type> 791 See also Documentation/input/joystick-parport.txt 792 793 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot 794 time. See Documentation/dynamic-debug-howto.txt for 795 details. Deprecated, see dyndbg. 796 797 debug [KNL] Enable kernel debugging (events log level). 798 799 debug_locks_verbose= 800 [KNL] verbose self-tests 801 Format=<0|1> 802 Print debugging info while doing the locking API 803 self-tests. 804 We default to 0 (no extra messages), setting it to 805 1 will print _a lot_ more information - normally 806 only useful to kernel developers. 807 808 debug_objects [KNL] Enable object debugging 809 810 no_debug_objects 811 [KNL] Disable object debugging 812 813 debug_guardpage_minorder= 814 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this 815 parameter allows control of the order of pages that will 816 be intentionally kept free (and hence protected) by the 817 buddy allocator. Bigger value increase the probability 818 of catching random memory corruption, but reduce the 819 amount of memory for normal system use. The maximum 820 possible value is MAX_ORDER/2. Setting this parameter 821 to 1 or 2 should be enough to identify most random 822 memory corruption problems caused by bugs in kernel or 823 driver code when a CPU writes to (or reads from) a 824 random memory location. Note that there exists a class 825 of memory corruptions problems caused by buggy H/W or 826 F/W or by drivers badly programing DMA (basically when 827 memory is written at bus level and the CPU MMU is 828 bypassed) which are not detectable by 829 CONFIG_DEBUG_PAGEALLOC, hence this option will not help 830 tracking down these problems. 831 832 debug_pagealloc= 833 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this 834 parameter enables the feature at boot time. In 835 default, it is disabled. We can avoid allocating huge 836 chunk of memory for debug pagealloc if we don't enable 837 it at boot time and the system will work mostly same 838 with the kernel built without CONFIG_DEBUG_PAGEALLOC. 839 on: enable the feature 840 841 debugpat [X86] Enable PAT debugging 842 843 decnet.addr= [HW,NET] 844 Format: <area>[,<node>] 845 See also Documentation/networking/decnet.txt. 846 847 default_hugepagesz= 848 [same as hugepagesz=] The size of the default 849 HugeTLB page size. This is the size represented by 850 the legacy /proc/ hugepages APIs, used for SHM, and 851 default size when mounting hugetlbfs filesystems. 852 Defaults to the default architecture's huge page size 853 if not specified. 854 855 dhash_entries= [KNL] 856 Set number of hash buckets for dentry cache. 857 858 disable= [IPV6] 859 See Documentation/networking/ipv6.txt. 860 861 disable_cpu_apicid= [X86,APIC,SMP] 862 Format: <int> 863 The number of initial APIC ID for the 864 corresponding CPU to be disabled at boot, 865 mostly used for the kdump 2nd kernel to 866 disable BSP to wake up multiple CPUs without 867 causing system reset or hang due to sending 868 INIT from AP to BSP. 869 870 disable_ddw [PPC/PSERIES] 871 Disable Dynamic DMA Window support. Use this if 872 to workaround buggy firmware. 873 874 disable_ipv6= [IPV6] 875 See Documentation/networking/ipv6.txt. 876 877 disable_mtrr_cleanup [X86] 878 The kernel tries to adjust MTRR layout from continuous 879 to discrete, to make X server driver able to add WB 880 entry later. This parameter disables that. 881 882 disable_mtrr_trim [X86, Intel and AMD only] 883 By default the kernel will trim any uncacheable 884 memory out of your available memory pool based on 885 MTRR settings. This parameter disables that behavior, 886 possibly causing your machine to run very slowly. 887 888 disable_timer_pin_1 [X86] 889 Disable PIN 1 of APIC timer 890 Can be useful to work around chipset bugs. 891 892 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, 893 this option disables the debugging code at boot. 894 895 dma_debug_entries=<number> 896 This option allows to tune the number of preallocated 897 entries for DMA-API debugging code. One entry is 898 required per DMA-API allocation. Use this if the 899 DMA-API debugging code disables itself because the 900 architectural default is too low. 901 902 dma_debug_driver=<driver_name> 903 With this option the DMA-API debugging driver 904 filter feature can be enabled at boot time. Just 905 pass the driver to filter for as the parameter. 906 The filter can be disabled or changed to another 907 driver later using sysfs. 908 909 drm_kms_helper.edid_firmware=[<connector>:]<file> 910 Broken monitors, graphic adapters and KVMs may 911 send no or incorrect EDID data sets. This parameter 912 allows to specify an EDID data set in the 913 /lib/firmware directory that is used instead. 914 Generic built-in EDID data sets are used, if one of 915 edid/1024x768.bin, edid/1280x1024.bin, 916 edid/1680x1050.bin, or edid/1920x1080.bin is given 917 and no file with the same name exists. Details and 918 instructions how to build your own EDID data are 919 available in Documentation/EDID/HOWTO.txt. An EDID 920 data set will only be used for a particular connector, 921 if its name and a colon are prepended to the EDID 922 name. 923 924 dscc4.setup= [NET] 925 926 dyndbg[="val"] [KNL,DYNAMIC_DEBUG] 927 module.dyndbg[="val"] 928 Enable debug messages at boot time. See 929 Documentation/dynamic-debug-howto.txt for details. 930 931 early_ioremap_debug [KNL] 932 Enable debug messages in early_ioremap support. This 933 is useful for tracking down temporary early mappings 934 which are not unmapped. 935 936 earlycon= [KNL] Output early console device and options. 937 938 cdns,<addr> 939 Start an early, polled-mode console on a cadence serial 940 port at the specified address. The cadence serial port 941 must already be setup and configured. Options are not 942 yet supported. 943 944 uart[8250],io,<addr>[,options] 945 uart[8250],mmio,<addr>[,options] 946 uart[8250],mmio32,<addr>[,options] 947 Start an early, polled-mode console on the 8250/16550 948 UART at the specified I/O port or MMIO address. 949 MMIO inter-register address stride is either 8-bit 950 (mmio) or 32-bit (mmio32). 951 The options are the same as for ttyS, above. 952 953 pl011,<addr> 954 Start an early, polled-mode console on a pl011 serial 955 port at the specified address. The pl011 serial port 956 must already be setup and configured. Options are not 957 yet supported. 958 959 msm_serial,<addr> 960 Start an early, polled-mode console on an msm serial 961 port at the specified address. The serial port 962 must already be setup and configured. Options are not 963 yet supported. 964 965 msm_serial_dm,<addr> 966 Start an early, polled-mode console on an msm serial 967 dm port at the specified address. The serial port 968 must already be setup and configured. Options are not 969 yet supported. 970 971 smh Use ARM semihosting calls for early console. 972 973 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k] 974 earlyprintk=vga 975 earlyprintk=efi 976 earlyprintk=xen 977 earlyprintk=serial[,ttySn[,baudrate]] 978 earlyprintk=serial[,0x...[,baudrate]] 979 earlyprintk=ttySn[,baudrate] 980 earlyprintk=dbgp[debugController#] 981 982 earlyprintk is useful when the kernel crashes before 983 the normal console is initialized. It is not enabled by 984 default because it has some cosmetic problems. 985 986 Append ",keep" to not disable it when the real console 987 takes over. 988 989 Only one of vga, efi, serial, or usb debug port can 990 be used at a time. 991 992 Currently only ttyS0 and ttyS1 may be specified by 993 name. Other I/O ports may be explicitly specified 994 on some architectures (x86 and arm at least) by 995 replacing ttySn with an I/O port address, like this: 996 earlyprintk=serial,0x1008,115200 997 You can find the port for a given device in 998 /proc/tty/driver/serial: 999 2: uart:ST16650V2 port:00001008 irq:18 ... 1000 1001 Interaction with the standard serial driver is not 1002 very good. 1003 1004 The VGA and EFI output is eventually overwritten by 1005 the real console. 1006 1007 The xen output can only be used by Xen PV guests. 1008 1009 edac_report= [HW,EDAC] Control how to report EDAC event 1010 Format: {"on" | "off" | "force"} 1011 on: enable EDAC to report H/W event. May be overridden 1012 by other higher priority error reporting module. 1013 off: disable H/W event reporting through EDAC. 1014 force: enforce the use of EDAC to report H/W event. 1015 default: on. 1016 1017 ekgdboc= [X86,KGDB] Allow early kernel console debugging 1018 ekgdboc=kbd 1019 1020 This is designed to be used in conjunction with 1021 the boot argument: earlyprintk=vga 1022 1023 edd= [EDD] 1024 Format: {"off" | "on" | "skip[mbr]"} 1025 1026 efi= [EFI] 1027 Format: { "old_map", "nochunk", "noruntime" } 1028 old_map [X86-64]: switch to the old ioremap-based EFI 1029 runtime services mapping. 32-bit still uses this one by 1030 default. 1031 nochunk: disable reading files in "chunks" in the EFI 1032 boot stub, as chunking can cause problems with some 1033 firmware implementations. 1034 noruntime : disable EFI runtime services support 1035 1036 efi_no_storage_paranoia [EFI; X86] 1037 Using this parameter you can use more than 50% of 1038 your efi variable storage. Use this parameter only if 1039 you are really sure that your UEFI does sane gc and 1040 fulfills the spec otherwise your board may brick. 1041 1042 eisa_irq_edge= [PARISC,HW] 1043 See header of drivers/parisc/eisa.c. 1044 1045 elanfreq= [X86-32] 1046 See comment before function elanfreq_setup() in 1047 arch/x86/kernel/cpu/cpufreq/elanfreq.c. 1048 1049 elevator= [IOSCHED] 1050 Format: {"cfq" | "deadline" | "noop"} 1051 See Documentation/block/cfq-iosched.txt and 1052 Documentation/block/deadline-iosched.txt for details. 1053 1054 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390] 1055 Specifies physical address of start of kernel core 1056 image elf header and optionally the size. Generally 1057 kexec loader will pass this option to capture kernel. 1058 See Documentation/kdump/kdump.txt for details. 1059 1060 enable_mtrr_cleanup [X86] 1061 The kernel tries to adjust MTRR layout from continuous 1062 to discrete, to make X server driver able to add WB 1063 entry later. This parameter enables that. 1064 1065 enable_timer_pin_1 [X86] 1066 Enable PIN 1 of APIC timer 1067 Can be useful to work around chipset bugs 1068 (in particular on some ATI chipsets). 1069 The kernel tries to set a reasonable default. 1070 1071 enforcing [SELINUX] Set initial enforcing status. 1072 Format: {"0" | "1"} 1073 See security/selinux/Kconfig help text. 1074 0 -- permissive (log only, no denials). 1075 1 -- enforcing (deny and log). 1076 Default value is 0. 1077 Value can be changed at runtime via /selinux/enforce. 1078 1079 erst_disable [ACPI] 1080 Disable Error Record Serialization Table (ERST) 1081 support. 1082 1083 ether= [HW,NET] Ethernet cards parameters 1084 This option is obsoleted by the "netdev=" option, which 1085 has equivalent usage. See its documentation for details. 1086 1087 evm= [EVM] 1088 Format: { "fix" } 1089 Permit 'security.evm' to be updated regardless of 1090 current integrity status. 1091 1092 failslab= 1093 fail_page_alloc= 1094 fail_make_request=[KNL] 1095 General fault injection mechanism. 1096 Format: <interval>,<probability>,<space>,<times> 1097 See also Documentation/fault-injection/. 1098 1099 floppy= [HW] 1100 See Documentation/blockdev/floppy.txt. 1101 1102 force_pal_cache_flush 1103 [IA-64] Avoid check_sal_cache_flush which may hang on 1104 buggy SAL_CACHE_FLUSH implementations. Using this 1105 parameter will force ia64_sal_cache_flush to call 1106 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH. 1107 1108 forcepae [X86-32] 1109 Forcefully enable Physical Address Extension (PAE). 1110 Many Pentium M systems disable PAE but may have a 1111 functionally usable PAE implementation. 1112 Warning: use of this parameter will taint the kernel 1113 and may cause unknown problems. 1114 1115 ftrace=[tracer] 1116 [FTRACE] will set and start the specified tracer 1117 as early as possible in order to facilitate early 1118 boot debugging. 1119 1120 ftrace_dump_on_oops[=orig_cpu] 1121 [FTRACE] will dump the trace buffers on oops. 1122 If no parameter is passed, ftrace will dump 1123 buffers of all CPUs, but if you pass orig_cpu, it will 1124 dump only the buffer of the CPU that triggered the 1125 oops. 1126 1127 ftrace_filter=[function-list] 1128 [FTRACE] Limit the functions traced by the function 1129 tracer at boot up. function-list is a comma separated 1130 list of functions. This list can be changed at run 1131 time by the set_ftrace_filter file in the debugfs 1132 tracing directory. 1133 1134 ftrace_notrace=[function-list] 1135 [FTRACE] Do not trace the functions specified in 1136 function-list. This list can be changed at run time 1137 by the set_ftrace_notrace file in the debugfs 1138 tracing directory. 1139 1140 ftrace_graph_filter=[function-list] 1141 [FTRACE] Limit the top level callers functions traced 1142 by the function graph tracer at boot up. 1143 function-list is a comma separated list of functions 1144 that can be changed at run time by the 1145 set_graph_function file in the debugfs tracing directory. 1146 1147 ftrace_graph_notrace=[function-list] 1148 [FTRACE] Do not trace from the functions specified in 1149 function-list. This list is a comma separated list of 1150 functions that can be changed at run time by the 1151 set_graph_notrace file in the debugfs tracing directory. 1152 1153 gamecon.map[2|3]= 1154 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 1155 support via parallel port (up to 5 devices per port) 1156 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 1157 See also Documentation/input/joystick-parport.txt 1158 1159 gamma= [HW,DRM] 1160 1161 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART 1162 Format: off | on 1163 default: on 1164 1165 gcov_persist= [GCOV] When non-zero (default), profiling data for 1166 kernel modules is saved and remains accessible via 1167 debugfs, even when the module is unloaded/reloaded. 1168 When zero, profiling data is discarded and associated 1169 debugfs files are removed at module unload time. 1170 1171 gpt [EFI] Forces disk with valid GPT signature but 1172 invalid Protective MBR to be treated as GPT. If the 1173 primary GPT is corrupted, it enables the backup/alternate 1174 GPT to be used instead. 1175 1176 grcan.enable0= [HW] Configuration of physical interface 0. Determines 1177 the "Enable 0" bit of the configuration register. 1178 Format: 0 | 1 1179 Default: 0 1180 grcan.enable1= [HW] Configuration of physical interface 1. Determines 1181 the "Enable 0" bit of the configuration register. 1182 Format: 0 | 1 1183 Default: 0 1184 grcan.select= [HW] Select which physical interface to use. 1185 Format: 0 | 1 1186 Default: 0 1187 grcan.txsize= [HW] Sets the size of the tx buffer. 1188 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. 1189 Default: 1024 1190 grcan.rxsize= [HW] Sets the size of the rx buffer. 1191 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. 1192 Default: 1024 1193 1194 hashdist= [KNL,NUMA] Large hashes allocated during boot 1195 are distributed across NUMA nodes. Defaults on 1196 for 64-bit NUMA, off otherwise. 1197 Format: 0 | 1 (for off | on) 1198 1199 hcl= [IA-64] SGI's Hardware Graph compatibility layer 1200 1201 hd= [EIDE] (E)IDE hard drive subsystem geometry 1202 Format: <cyl>,<head>,<sect> 1203 1204 hest_disable [ACPI] 1205 Disable Hardware Error Source Table (HEST) support; 1206 corresponding firmware-first mode error processing 1207 logic will be disabled. 1208 1209 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact 1210 size of <nn>. This works even on boxes that have no 1211 highmem otherwise. This also works to reduce highmem 1212 size on bigger boxes. 1213 1214 highres= [KNL] Enable/disable high resolution timer mode. 1215 Valid parameters: "on", "off" 1216 Default: "on" 1217 1218 hisax= [HW,ISDN] 1219 See Documentation/isdn/README.HiSax. 1220 1221 hlt [BUGS=ARM,SH] 1222 1223 hpet= [X86-32,HPET] option to control HPET usage 1224 Format: { enable (default) | disable | force | 1225 verbose } 1226 disable: disable HPET and use PIT instead 1227 force: allow force enabled of undocumented chips (ICH4, 1228 VIA, nVidia) 1229 verbose: show contents of HPET registers during setup 1230 1231 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET 1232 registers. Default set by CONFIG_HPET_MMAP_DEFAULT. 1233 1234 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot. 1235 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages. 1236 On x86-64 and powerpc, this option can be specified 1237 multiple times interleaved with hugepages= to reserve 1238 huge pages of different sizes. Valid pages sizes on 1239 x86-64 are 2M (when the CPU supports "pse") and 1G 1240 (when the CPU supports the "pdpe1gb" cpuinfo flag). 1241 1242 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 1243 terminal devices. Valid values: 0..8 1244 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 1245 If specified, z/VM IUCV HVC accepts connections 1246 from listed z/VM user IDs only. 1247 1248 hwthread_map= [METAG] Comma-separated list of Linux cpu id to 1249 hardware thread id mappings. 1250 Format: <cpu>:<hwthread> 1251 1252 keep_bootcon [KNL] 1253 Do not unregister boot console at start. This is only 1254 useful for debugging when something happens in the window 1255 between unregistering the boot console and initializing 1256 the real console. 1257 1258 i2c_bus= [HW] Override the default board specific I2C bus speed 1259 or register an additional I2C bus that is not 1260 registered from board initialization code. 1261 Format: 1262 <bus_id>,<clkrate> 1263 1264 i8042.debug [HW] Toggle i8042 debug mode 1265 i8042.direct [HW] Put keyboard port into non-translated mode 1266 i8042.dumbkbd [HW] Pretend that controller can only read data from 1267 keyboard and cannot control its state 1268 (Don't attempt to blink the leds) 1269 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 1270 i8042.nokbd [HW] Don't check/create keyboard port 1271 i8042.noloop [HW] Disable the AUX Loopback command while probing 1272 for the AUX port 1273 i8042.nomux [HW] Don't check presence of an active multiplexing 1274 controller 1275 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 1276 controllers 1277 i8042.notimeout [HW] Ignore timeout condition signalled by controller 1278 i8042.reset [HW] Reset the controller during init and cleanup 1279 i8042.unlock [HW] Unlock (ignore) the keylock 1280 i8042.kbdreset [HW] Reset device connected to KBD port 1281 1282 i810= [HW,DRM] 1283 1284 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data 1285 indicates that the driver is running on unsupported 1286 hardware. 1287 i8k.force [HW] Activate i8k driver even if SMM BIOS signature 1288 does not match list of supported models. 1289 i8k.power_status 1290 [HW] Report power status in /proc/i8k 1291 (disabled by default) 1292 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN 1293 capability is set. 1294 1295 i915.invert_brightness= 1296 [DRM] Invert the sense of the variable that is used to 1297 set the brightness of the panel backlight. Normally a 1298 brightness value of 0 indicates backlight switched off, 1299 and the maximum of the brightness value sets the backlight 1300 to maximum brightness. If this parameter is set to 0 1301 (default) and the machine requires it, or this parameter 1302 is set to 1, a brightness value of 0 sets the backlight 1303 to maximum brightness, and the maximum of the brightness 1304 value switches the backlight off. 1305 -1 -- never invert brightness 1306 0 -- machine default 1307 1 -- force brightness inversion 1308 1309 icn= [HW,ISDN] 1310 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]] 1311 1312 ide-core.nodma= [HW] (E)IDE subsystem 1313 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc 1314 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr 1315 .cdrom .chs .ignore_cable are additional options 1316 See Documentation/ide/ide.txt. 1317 1318 ide-generic.probe-mask= [HW] (E)IDE subsystem 1319 Format: <int> 1320 Probe mask for legacy ISA IDE ports. Depending on 1321 platform up to 6 ports are supported, enabled by 1322 setting corresponding bits in the mask to 1. The 1323 default value is 0x0, which has a special meaning. 1324 On systems that have PCI, it triggers scanning the 1325 PCI bus for the first and the second port, which 1326 are then probed. On systems without PCI the value 1327 of 0x0 enables probing the two first ports as if it 1328 was 0x3. 1329 1330 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem 1331 Claim all unknown PCI IDE storage controllers. 1332 1333 idle= [X86] 1334 Format: idle=poll, idle=halt, idle=nomwait 1335 Poll forces a polling idle loop that can slightly 1336 improve the performance of waking up a idle CPU, but 1337 will use a lot of power and make the system run hot. 1338 Not recommended. 1339 idle=halt: Halt is forced to be used for CPU idle. 1340 In such case C2/C3 won't be used again. 1341 idle=nomwait: Disable mwait for CPU C-states 1342 1343 ignore_loglevel [KNL] 1344 Ignore loglevel setting - this will print /all/ 1345 kernel messages to the console. Useful for debugging. 1346 We also add it as printk module parameter, so users 1347 could change it dynamically, usually by 1348 /sys/module/printk/parameters/ignore_loglevel. 1349 1350 ihash_entries= [KNL] 1351 Set number of hash buckets for inode cache. 1352 1353 ima_appraise= [IMA] appraise integrity measurements 1354 Format: { "off" | "enforce" | "fix" | "log" } 1355 default: "enforce" 1356 1357 ima_appraise_tcb [IMA] 1358 The builtin appraise policy appraises all files 1359 owned by uid=0. 1360 1361 ima_hash= [IMA] 1362 Format: { md5 | sha1 | rmd160 | sha256 | sha384 1363 | sha512 | ... } 1364 default: "sha1" 1365 1366 The list of supported hash algorithms is defined 1367 in crypto/hash_info.h. 1368 1369 ima_tcb [IMA] 1370 Load a policy which meets the needs of the Trusted 1371 Computing Base. This means IMA will measure all 1372 programs exec'd, files mmap'd for exec, and all files 1373 opened for read by uid=0. 1374 1375 ima_template= [IMA] 1376 Select one of defined IMA measurements template formats. 1377 Formats: { "ima" | "ima-ng" } 1378 Default: "ima-ng" 1379 1380 ima_template_fmt= 1381 [IMA] Define a custom template format. 1382 Format: { "field1|...|fieldN" } 1383 1384 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage 1385 Format: <min_file_size> 1386 Set the minimal file size for using asynchronous hash. 1387 If left unspecified, ahash usage is disabled. 1388 1389 ahash performance varies for different data sizes on 1390 different crypto accelerators. This option can be used 1391 to achieve the best performance for a particular HW. 1392 1393 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size 1394 Format: <bufsize> 1395 Set hashing buffer size. Default: 4k. 1396 1397 ahash performance varies for different chunk sizes on 1398 different crypto accelerators. This option can be used 1399 to achieve best performance for particular HW. 1400 1401 init= [KNL] 1402 Format: <full_path> 1403 Run specified binary instead of /sbin/init as init 1404 process. 1405 1406 initcall_debug [KNL] Trace initcalls as they are executed. Useful 1407 for working out where the kernel is dying during 1408 startup. 1409 1410 initcall_blacklist= [KNL] Do not execute a comma-separated list of 1411 initcall functions. Useful for debugging built-in 1412 modules and initcalls. 1413 1414 initrd= [BOOT] Specify the location of the initial ramdisk 1415 1416 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 1417 Format: <irq> 1418 1419 int_pln_enable [x86] Enable power limit notification interrupt 1420 1421 integrity_audit=[IMA] 1422 Format: { "0" | "1" } 1423 0 -- basic integrity auditing messages. (Default) 1424 1 -- additional integrity auditing messages. 1425 1426 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 1427 on 1428 Enable intel iommu driver. 1429 off 1430 Disable intel iommu driver. 1431 igfx_off [Default Off] 1432 By default, gfx is mapped as normal device. If a gfx 1433 device has a dedicated DMAR unit, the DMAR unit is 1434 bypassed by not enabling DMAR with this option. In 1435 this case, gfx device will use physical address for 1436 DMA. 1437 forcedac [x86_64] 1438 With this option iommu will not optimize to look 1439 for io virtual address below 32-bit forcing dual 1440 address cycle on pci bus for cards supporting greater 1441 than 32-bit addressing. The default is to look 1442 for translation below 32-bit and if not available 1443 then look in the higher range. 1444 strict [Default Off] 1445 With this option on every unmap_single operation will 1446 result in a hardware IOTLB flush operation as opposed 1447 to batching them for performance. 1448 sp_off [Default Off] 1449 By default, super page will be supported if Intel IOMMU 1450 has the capability. With this option, super page will 1451 not be supported. 1452 1453 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 1454 0 disables intel_idle and fall back on acpi_idle. 1455 1 to 6 specify maximum depth of C-state. 1456 1457 intel_pstate= [X86] 1458 disable 1459 Do not enable intel_pstate as the default 1460 scaling driver for the supported processors 1461 force 1462 Enable intel_pstate on systems that prohibit it by default 1463 in favor of acpi-cpufreq. Forcing the intel_pstate driver 1464 instead of acpi-cpufreq may disable platform features, such 1465 as thermal controls and power capping, that rely on ACPI 1466 P-States information being indicated to OSPM and therefore 1467 should be used with caution. This option does not work with 1468 processors that aren't supported by the intel_pstate driver 1469 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 1470 no_hwp 1471 Do not enable hardware P state control (HWP) 1472 if available. 1473 1474 intremap= [X86-64, Intel-IOMMU] 1475 on enable Interrupt Remapping (default) 1476 off disable Interrupt Remapping 1477 nosid disable Source ID checking 1478 no_x2apic_optout 1479 BIOS x2APIC opt-out request will be ignored 1480 1481 iomem= Disable strict checking of access to MMIO memory 1482 strict regions from userspace. 1483 relaxed 1484 1485 iommu= [x86] 1486 off 1487 force 1488 noforce 1489 biomerge 1490 panic 1491 nopanic 1492 merge 1493 nomerge 1494 forcesac 1495 soft 1496 pt [x86, IA-64] 1497 1498 1499 io7= [HW] IO7 for Marvel based alpha systems 1500 See comment before marvel_specify_io7 in 1501 arch/alpha/kernel/core_marvel.c. 1502 1503 io_delay= [X86] I/O delay method 1504 0x80 1505 Standard port 0x80 based delay 1506 0xed 1507 Alternate port 0xed based delay (needed on some systems) 1508 udelay 1509 Simple two microseconds delay 1510 none 1511 No delay 1512 1513 ip= [IP_PNP] 1514 See Documentation/filesystems/nfs/nfsroot.txt. 1515 1516 irqfixup [HW] 1517 When an interrupt is not handled search all handlers 1518 for it. Intended to get systems with badly broken 1519 firmware running. 1520 1521 irqpoll [HW] 1522 When an interrupt is not handled search all handlers 1523 for it. Also check all handlers each timer 1524 interrupt. Intended to get systems with badly broken 1525 firmware running. 1526 1527 isapnp= [ISAPNP] 1528 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 1529 1530 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler. 1531 Format: 1532 <cpu number>,...,<cpu number> 1533 or 1534 <cpu number>-<cpu number> 1535 (must be a positive range in ascending order) 1536 or a mixture 1537 <cpu number>,...,<cpu number>-<cpu number> 1538 1539 This option can be used to specify one or more CPUs 1540 to isolate from the general SMP balancing and scheduling 1541 algorithms. You can move a process onto or off an 1542 "isolated" CPU via the CPU affinity syscalls or cpuset. 1543 <cpu number> begins at 0 and the maximum value is 1544 "number of CPUs in system - 1". 1545 1546 This option is the preferred way to isolate CPUs. The 1547 alternative -- manually setting the CPU mask of all 1548 tasks in the system -- can cause problems and 1549 suboptimal load balancer performance. 1550 1551 iucv= [HW,NET] 1552 1553 ivrs_ioapic [HW,X86_64] 1554 Provide an override to the IOAPIC-ID<->DEVICE-ID 1555 mapping provided in the IVRS ACPI table. For 1556 example, to map IOAPIC-ID decimal 10 to 1557 PCI device 00:14.0 write the parameter as: 1558 ivrs_ioapic[10]=00:14.0 1559 1560 ivrs_hpet [HW,X86_64] 1561 Provide an override to the HPET-ID<->DEVICE-ID 1562 mapping provided in the IVRS ACPI table. For 1563 example, to map HPET-ID decimal 0 to 1564 PCI device 00:14.0 write the parameter as: 1565 ivrs_hpet[0]=00:14.0 1566 1567 js= [HW,JOY] Analog joystick 1568 See Documentation/input/joystick.txt. 1569 1570 kaslr/nokaslr [X86] 1571 Enable/disable kernel and module base offset ASLR 1572 (Address Space Layout Randomization) if built into 1573 the kernel. When CONFIG_HIBERNATION is selected, 1574 kASLR is disabled by default. When kASLR is enabled, 1575 hibernation will be disabled. 1576 1577 keepinitrd [HW,ARM] 1578 1579 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter 1580 specifies the amount of memory usable by the kernel 1581 for non-movable allocations. The requested amount is 1582 spread evenly throughout all nodes in the system. The 1583 remaining memory in each node is used for Movable 1584 pages. In the event, a node is too small to have both 1585 kernelcore and Movable pages, kernelcore pages will 1586 take priority and other nodes will have a larger number 1587 of Movable pages. The Movable zone is used for the 1588 allocation of pages that may be reclaimed or moved 1589 by the page migration subsystem. This means that 1590 HugeTLB pages may not be allocated from this zone. 1591 Note that allocations like PTEs-from-HighMem still 1592 use the HighMem zone if it exists, and the Normal 1593 zone if it does not. 1594 1595 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port. 1596 Format: <Controller#>[,poll interval] 1597 The controller # is the number of the ehci usb debug 1598 port as it is probed via PCI. The poll interval is 1599 optional and is the number seconds in between 1600 each poll cycle to the debug port in case you need 1601 the functionality for interrupting the kernel with 1602 gdb or control-c on the dbgp connection. When 1603 not using this parameter you use sysrq-g to break into 1604 the kernel debugger. 1605 1606 kgdboc= [KGDB,HW] kgdb over consoles. 1607 Requires a tty driver that supports console polling, 1608 or a supported polling keyboard driver (non-usb). 1609 Serial only format: <serial_device>[,baud] 1610 keyboard only format: kbd 1611 keyboard and serial format: kbd,<serial_device>[,baud] 1612 Optional Kernel mode setting: 1613 kms, kbd format: kms,kbd 1614 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 1615 1616 kgdbwait [KGDB] Stop kernel execution and enter the 1617 kernel debugger at the earliest opportunity. 1618 1619 kmac= [MIPS] korina ethernet MAC address. 1620 Configure the RouterBoard 532 series on-chip 1621 Ethernet adapter MAC address. 1622 1623 kmemleak= [KNL] Boot-time kmemleak enable/disable 1624 Valid arguments: on, off 1625 Default: on 1626 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 1627 the default is off. 1628 1629 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode 1630 Valid arguments: 0, 1, 2 1631 kmemcheck=0 (disabled) 1632 kmemcheck=1 (enabled) 1633 kmemcheck=2 (one-shot mode) 1634 Default: 2 (one-shot mode) 1635 1636 kstack=N [X86] Print N words from the kernel stack 1637 in oops dumps. 1638 1639 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 1640 Default is 0 (don't ignore, but inject #GP) 1641 1642 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit 1643 KVM MMU at runtime. 1644 Default is 0 (off) 1645 1646 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM. 1647 Default is 1 (enabled) 1648 1649 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU) 1650 for all guests. 1651 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode. 1652 1653 kvm-intel.ept= [KVM,Intel] Disable extended page tables 1654 (virtualized MMU) support on capable Intel chips. 1655 Default is 1 (enabled) 1656 1657 kvm-intel.emulate_invalid_guest_state= 1658 [KVM,Intel] Enable emulation of invalid guest states 1659 Default is 0 (disabled) 1660 1661 kvm-intel.flexpriority= 1662 [KVM,Intel] Disable FlexPriority feature (TPR shadow). 1663 Default is 1 (enabled) 1664 1665 kvm-intel.nested= 1666 [KVM,Intel] Enable VMX nesting (nVMX). 1667 Default is 0 (disabled) 1668 1669 kvm-intel.unrestricted_guest= 1670 [KVM,Intel] Disable unrestricted guest feature 1671 (virtualized real and unpaged mode) on capable 1672 Intel chips. Default is 1 (enabled) 1673 1674 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification 1675 feature (tagged TLBs) on capable Intel chips. 1676 Default is 1 (enabled) 1677 1678 l2cr= [PPC] 1679 1680 l3cr= [PPC] 1681 1682 lapic [X86-32,APIC] Enable the local APIC even if BIOS 1683 disabled it. 1684 1685 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline 1686 value for LAPIC timer one-shot implementation. Default 1687 back to the programmable timer unit in the LAPIC. 1688 1689 lapic_timer_c2_ok [X86,APIC] trust the local apic timer 1690 in C2 power state. 1691 1692 libata.dma= [LIBATA] DMA control 1693 libata.dma=0 Disable all PATA and SATA DMA 1694 libata.dma=1 PATA and SATA Disk DMA only 1695 libata.dma=2 ATAPI (CDROM) DMA only 1696 libata.dma=4 Compact Flash DMA only 1697 Combinations also work, so libata.dma=3 enables DMA 1698 for disks and CDROMs, but not CFs. 1699 1700 libata.ignore_hpa= [LIBATA] Ignore HPA limit 1701 libata.ignore_hpa=0 keep BIOS limits (default) 1702 libata.ignore_hpa=1 ignore limits, using full disk 1703 1704 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 1705 when set. 1706 Format: <int> 1707 1708 libata.force= [LIBATA] Force configurations. The format is comma 1709 separated list of "[ID:]VAL" where ID is 1710 PORT[.DEVICE]. PORT and DEVICE are decimal numbers 1711 matching port, link or device. Basically, it matches 1712 the ATA ID string printed on console by libata. If 1713 the whole ID part is omitted, the last PORT and DEVICE 1714 values are used. If ID hasn't been specified yet, the 1715 configuration applies to all ports, links and devices. 1716 1717 If only DEVICE is omitted, the parameter applies to 1718 the port and all links and devices behind it. DEVICE 1719 number of 0 either selects the first device or the 1720 first fan-out link behind PMP device. It does not 1721 select the host link. DEVICE number of 15 selects the 1722 host link and device attached to it. 1723 1724 The VAL specifies the configuration to force. As long 1725 as there's no ambiguity shortcut notation is allowed. 1726 For example, both 1.5 and 1.5G would work for 1.5Gbps. 1727 The following configurations can be forced. 1728 1729 * Cable type: 40c, 80c, short40c, unk, ign or sata. 1730 Any ID with matching PORT is used. 1731 1732 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 1733 1734 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 1735 udma[/][16,25,33,44,66,100,133] notation is also 1736 allowed. 1737 1738 * [no]ncq: Turn on or off NCQ. 1739 1740 * nohrst, nosrst, norst: suppress hard, soft 1741 and both resets. 1742 1743 * rstonce: only attempt one reset during 1744 hot-unplug link recovery 1745 1746 * dump_id: dump IDENTIFY data. 1747 1748 * atapi_dmadir: Enable ATAPI DMADIR bridge support 1749 1750 * disable: Disable this device. 1751 1752 If there are multiple matching configurations changing 1753 the same attribute, the last one is used. 1754 1755 memblock=debug [KNL] Enable memblock debug messages. 1756 1757 load_ramdisk= [RAM] List of ramdisks to load from floppy 1758 See Documentation/blockdev/ramdisk.txt. 1759 1760 lockd.nlm_grace_period=P [NFS] Assign grace period. 1761 Format: <integer> 1762 1763 lockd.nlm_tcpport=N [NFS] Assign TCP port. 1764 Format: <integer> 1765 1766 lockd.nlm_timeout=T [NFS] Assign timeout value. 1767 Format: <integer> 1768 1769 lockd.nlm_udpport=M [NFS] Assign UDP port. 1770 Format: <integer> 1771 1772 locktorture.nreaders_stress= [KNL] 1773 Set the number of locking read-acquisition kthreads. 1774 Defaults to being automatically set based on the 1775 number of online CPUs. 1776 1777 locktorture.nwriters_stress= [KNL] 1778 Set the number of locking write-acquisition kthreads. 1779 1780 locktorture.onoff_holdoff= [KNL] 1781 Set time (s) after boot for CPU-hotplug testing. 1782 1783 locktorture.onoff_interval= [KNL] 1784 Set time (s) between CPU-hotplug operations, or 1785 zero to disable CPU-hotplug testing. 1786 1787 locktorture.shuffle_interval= [KNL] 1788 Set task-shuffle interval (jiffies). Shuffling 1789 tasks allows some CPUs to go into dyntick-idle 1790 mode during the locktorture test. 1791 1792 locktorture.shutdown_secs= [KNL] 1793 Set time (s) after boot system shutdown. This 1794 is useful for hands-off automated testing. 1795 1796 locktorture.stat_interval= [KNL] 1797 Time (s) between statistics printk()s. 1798 1799 locktorture.stutter= [KNL] 1800 Time (s) to stutter testing, for example, 1801 specifying five seconds causes the test to run for 1802 five seconds, wait for five seconds, and so on. 1803 This tests the locking primitive's ability to 1804 transition abruptly to and from idle. 1805 1806 locktorture.torture_runnable= [BOOT] 1807 Start locktorture running at boot time. 1808 1809 locktorture.torture_type= [KNL] 1810 Specify the locking implementation to test. 1811 1812 locktorture.verbose= [KNL] 1813 Enable additional printk() statements. 1814 1815 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 1816 Format: <irq> 1817 1818 loglevel= All Kernel Messages with a loglevel smaller than the 1819 console loglevel will be printed to the console. It can 1820 also be changed with klogd or other programs. The 1821 loglevels are defined as follows: 1822 1823 0 (KERN_EMERG) system is unusable 1824 1 (KERN_ALERT) action must be taken immediately 1825 2 (KERN_CRIT) critical conditions 1826 3 (KERN_ERR) error conditions 1827 4 (KERN_WARNING) warning conditions 1828 5 (KERN_NOTICE) normal but significant condition 1829 6 (KERN_INFO) informational 1830 7 (KERN_DEBUG) debug-level messages 1831 1832 log_buf_len=n[KMG] Sets the size of the printk ring buffer, 1833 in bytes. n must be a power of two and greater 1834 than the minimal size. The minimal size is defined 1835 by LOG_BUF_SHIFT kernel config parameter. There is 1836 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter 1837 that allows to increase the default size depending on 1838 the number of CPUs. See init/Kconfig for more details. 1839 1840 logo.nologo [FB] Disables display of the built-in Linux logo. 1841 This may be used to provide more screen space for 1842 kernel log messages and is useful when debugging 1843 kernel boot problems. 1844 1845 lp=0 [LP] Specify parallel ports to use, e.g, 1846 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 1847 lp=reset first parallel port). 'lp=0' disables the 1848 lp=auto printer driver. 'lp=reset' (which can be 1849 specified in addition to the ports) causes 1850 attached printers to be reset. Using 1851 lp=port1,port2,... specifies the parallel ports 1852 to associate lp devices with, starting with 1853 lp0. A port specification may be 'none' to skip 1854 that lp device, or a parport name such as 1855 'parport0'. Specifying 'lp=auto' instead of a 1856 port specification list means that device IDs 1857 from each port should be examined, to see if 1858 an IEEE 1284-compliant printer is attached; if 1859 so, the driver will manage that printer. 1860 See also header of drivers/char/lp.c. 1861 1862 lpj=n [KNL] 1863 Sets loops_per_jiffy to given constant, thus avoiding 1864 time-consuming boot-time autodetection (up to 250 ms per 1865 CPU). 0 enables autodetection (default). To determine 1866 the correct value for your kernel, boot with normal 1867 autodetection and see what value is printed. Note that 1868 on SMP systems the preset will be applied to all CPUs, 1869 which is likely to cause problems if your CPUs need 1870 significantly divergent settings. An incorrect value 1871 will cause delays in the kernel to be wrong, leading to 1872 unpredictable I/O errors and other breakage. Although 1873 unlikely, in the extreme case this might damage your 1874 hardware. 1875 1876 ltpc= [NET] 1877 Format: <io>,<irq>,<dma> 1878 1879 machvec= [IA-64] Force the use of a particular machine-vector 1880 (machvec) in a generic kernel. 1881 Example: machvec=hpzx1_swiotlb 1882 1883 machtype= [Loongson] Share the same kernel image file between different 1884 yeeloong laptop. 1885 Example: machtype=lemote-yeeloong-2f-7inch 1886 1887 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater 1888 than or equal to this physical address is ignored. 1889 1890 maxcpus= [SMP] Maximum number of processors that an SMP kernel 1891 should make use of. maxcpus=n : n >= 0 limits the 1892 kernel to using 'n' processors. n=0 is a special case, 1893 it is equivalent to "nosmp", which also disables 1894 the IO APIC. 1895 1896 max_loop= [LOOP] The number of loop block devices that get 1897 (loop.max_loop) unconditionally pre-created at init time. The default 1898 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 1899 of statically allocating a predefined number, loop 1900 devices can be requested on-demand with the 1901 /dev/loop-control interface. 1902 1903 mce [X86-32] Machine Check Exception 1904 1905 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt 1906 1907 md= [HW] RAID subsystems devices and level 1908 See Documentation/md.txt. 1909 1910 mdacon= [MDA] 1911 Format: <first>,<last> 1912 Specifies range of consoles to be captured by the MDA. 1913 1914 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory 1915 Amount of memory to be used when the kernel is not able 1916 to see the whole system memory or for test. 1917 [X86] Work as limiting max address. Use together 1918 with memmap= to avoid physical address space collisions. 1919 Without memmap= PCI devices could be placed at addresses 1920 belonging to unused RAM. 1921 1922 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 1923 memory. 1924 1925 memchunk=nn[KMG] 1926 [KNL,SH] Allow user to override the default size for 1927 per-device physically contiguous DMA buffers. 1928 1929 memmap=exactmap [KNL,X86] Enable setting of an exact 1930 E820 memory map, as specified by the user. 1931 Such memmap=exactmap lines can be constructed based on 1932 BIOS output or other requirements. See the memmap=nn@ss 1933 option description. 1934 1935 memmap=nn[KMG]@ss[KMG] 1936 [KNL] Force usage of a specific region of memory. 1937 Region of memory to be used is from ss to ss+nn. 1938 1939 memmap=nn[KMG]#ss[KMG] 1940 [KNL,ACPI] Mark specific memory as ACPI data. 1941 Region of memory to be marked is from ss to ss+nn. 1942 1943 memmap=nn[KMG]$ss[KMG] 1944 [KNL,ACPI] Mark specific memory as reserved. 1945 Region of memory to be reserved is from ss to ss+nn. 1946 Example: Exclude memory from 0x18690000-0x1869ffff 1947 memmap=64K$0x18690000 1948 or 1949 memmap=0x10000$0x18690000 1950 1951 memory_corruption_check=0/1 [X86] 1952 Some BIOSes seem to corrupt the first 64k of 1953 memory when doing things like suspend/resume. 1954 Setting this option will scan the memory 1955 looking for corruption. Enabling this will 1956 both detect corruption and prevent the kernel 1957 from using the memory being corrupted. 1958 However, its intended as a diagnostic tool; if 1959 repeatable BIOS-originated corruption always 1960 affects the same memory, you can use memmap= 1961 to prevent the kernel from using that memory. 1962 1963 memory_corruption_check_size=size [X86] 1964 By default it checks for corruption in the low 1965 64k, making this memory unavailable for normal 1966 use. Use this parameter to scan for 1967 corruption in more or less memory. 1968 1969 memory_corruption_check_period=seconds [X86] 1970 By default it checks for corruption every 60 1971 seconds. Use this parameter to check at some 1972 other rate. 0 disables periodic checking. 1973 1974 memtest= [KNL,X86] Enable memtest 1975 Format: <integer> 1976 default : 0 <disable> 1977 Specifies the number of memtest passes to be 1978 performed. Each pass selects another test 1979 pattern from a given set of patterns. Memtest 1980 fills the memory with this pattern, validates 1981 memory contents and reserves bad memory 1982 regions that are detected. 1983 1984 meye.*= [HW] Set MotionEye Camera parameters 1985 See Documentation/video4linux/meye.txt. 1986 1987 mfgpt_irq= [IA-32] Specify the IRQ to use for the 1988 Multi-Function General Purpose Timers on AMD Geode 1989 platforms. 1990 1991 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 1992 the BIOS has incorrectly applied a workaround. TinyBIOS 1993 version 0.98 is known to be affected, 0.99 fixes the 1994 problem by letting the user disable the workaround. 1995 1996 mga= [HW,DRM] 1997 1998 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this 1999 physical address is ignored. 2000 2001 mini2440= [ARM,HW,KNL] 2002 Format:[0..2][b][c][t] 2003 Default: "0tb" 2004 MINI2440 configuration specification: 2005 0 - The attached screen is the 3.5" TFT 2006 1 - The attached screen is the 7" TFT 2007 2 - The VGA Shield is attached (1024x768) 2008 Leaving out the screen size parameter will not load 2009 the TFT driver, and the framebuffer will be left 2010 unconfigured. 2011 b - Enable backlight. The TFT backlight pin will be 2012 linked to the kernel VESA blanking code and a GPIO 2013 LED. This parameter is not necessary when using the 2014 VGA shield. 2015 c - Enable the s3c camera interface. 2016 t - Reserved for enabling touchscreen support. The 2017 touchscreen support is not enabled in the mainstream 2018 kernel as of 2.6.30, a preliminary port can be found 2019 in the "bleeding edge" mini2440 support kernel at 2020 http://repo.or.cz/w/linux-2.6/mini2440.git 2021 2022 mminit_loglevel= 2023 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this 2024 parameter allows control of the logging verbosity for 2025 the additional memory initialisation checks. A value 2026 of 0 disables mminit logging and a level of 4 will 2027 log everything. Information is printed at KERN_DEBUG 2028 so loglevel=8 may also need to be specified. 2029 2030 module.sig_enforce 2031 [KNL] When CONFIG_MODULE_SIG is set, this means that 2032 modules without (valid) signatures will fail to load. 2033 Note that if CONFIG_MODULE_SIG_FORCE is set, that 2034 is always true, so this option does nothing. 2035 2036 mousedev.tap_time= 2037 [MOUSE] Maximum time between finger touching and 2038 leaving touchpad surface for touch to be considered 2039 a tap and be reported as a left button click (for 2040 touchpads working in absolute mode only). 2041 Format: <msecs> 2042 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 2043 reporting absolute coordinates, such as tablets 2044 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 2045 reporting absolute coordinates, such as tablets 2046 2047 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter 2048 is similar to kernelcore except it specifies the 2049 amount of memory used for migratable allocations. 2050 If both kernelcore and movablecore is specified, 2051 then kernelcore will be at *least* the specified 2052 value but may be more. If movablecore on its own 2053 is specified, the administrator must be careful 2054 that the amount of memory usable for all allocations 2055 is not too small. 2056 2057 movable_node [KNL,X86] Boot-time switch to enable the effects 2058 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details. 2059 2060 MTD_Partition= [MTD] 2061 Format: <name>,<region-number>,<size>,<offset> 2062 2063 MTD_Region= [MTD] Format: 2064 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 2065 2066 mtdparts= [MTD] 2067 See drivers/mtd/cmdlinepart.c. 2068 2069 multitce=off [PPC] This parameter disables the use of the pSeries 2070 firmware feature for updating multiple TCE entries 2071 at a time. 2072 2073 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 2074 2075 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 2076 2077 boundary - index of last SLC block on Flex-OneNAND. 2078 The remaining blocks are configured as MLC blocks. 2079 lock - Configure if Flex-OneNAND boundary should be locked. 2080 Once locked, the boundary cannot be changed. 2081 1 indicates lock status, 0 indicates unlock status. 2082 2083 mtdset= [ARM] 2084 ARM/S3C2412 JIVE boot control 2085 2086 See arch/arm/mach-s3c2412/mach-jive.c 2087 2088 mtouchusb.raw_coordinates= 2089 [HW] Make the MicroTouch USB driver use raw coordinates 2090 ('y', default) or cooked coordinates ('n') 2091 2092 mtrr_chunk_size=nn[KMG] [X86] 2093 used for mtrr cleanup. It is largest continuous chunk 2094 that could hold holes aka. UC entries. 2095 2096 mtrr_gran_size=nn[KMG] [X86] 2097 Used for mtrr cleanup. It is granularity of mtrr block. 2098 Default is 1. 2099 Large value could prevent small alignment from 2100 using up MTRRs. 2101 2102 mtrr_spare_reg_nr=n [X86] 2103 Format: <integer> 2104 Range: 0,7 : spare reg number 2105 Default : 1 2106 Used for mtrr cleanup. It is spare mtrr entries number. 2107 Set to 2 or more if your graphical card needs more. 2108 2109 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 2110 2111 netdev= [NET] Network devices parameters 2112 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 2113 Note that mem_start is often overloaded to mean 2114 something different and driver-specific. 2115 This usage is only documented in each driver source 2116 file if at all. 2117 2118 nf_conntrack.acct= 2119 [NETFILTER] Enable connection tracking flow accounting 2120 0 to disable accounting 2121 1 to enable accounting 2122 Default value is 0. 2123 2124 nfsaddrs= [NFS] Deprecated. Use ip= instead. 2125 See Documentation/filesystems/nfs/nfsroot.txt. 2126 2127 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 2128 See Documentation/filesystems/nfs/nfsroot.txt. 2129 2130 nfsrootdebug [NFS] enable nfsroot debugging messages. 2131 See Documentation/filesystems/nfs/nfsroot.txt. 2132 2133 nfs.callback_tcpport= 2134 [NFS] set the TCP port on which the NFSv4 callback 2135 channel should listen. 2136 2137 nfs.cache_getent= 2138 [NFS] sets the pathname to the program which is used 2139 to update the NFS client cache entries. 2140 2141 nfs.cache_getent_timeout= 2142 [NFS] sets the timeout after which an attempt to 2143 update a cache entry is deemed to have failed. 2144 2145 nfs.idmap_cache_timeout= 2146 [NFS] set the maximum lifetime for idmapper cache 2147 entries. 2148 2149 nfs.enable_ino64= 2150 [NFS] enable 64-bit inode numbers. 2151 If zero, the NFS client will fake up a 32-bit inode 2152 number for the readdir() and stat() syscalls instead 2153 of returning the full 64-bit number. 2154 The default is to return 64-bit inode numbers. 2155 2156 nfs.max_session_slots= 2157 [NFSv4.1] Sets the maximum number of session slots 2158 the client will attempt to negotiate with the server. 2159 This limits the number of simultaneous RPC requests 2160 that the client can send to the NFSv4.1 server. 2161 Note that there is little point in setting this 2162 value higher than the max_tcp_slot_table_limit. 2163 2164 nfs.nfs4_disable_idmapping= 2165 [NFSv4] When set to the default of '1', this option 2166 ensures that both the RPC level authentication 2167 scheme and the NFS level operations agree to use 2168 numeric uids/gids if the mount is using the 2169 'sec=sys' security flavour. In effect it is 2170 disabling idmapping, which can make migration from 2171 legacy NFSv2/v3 systems to NFSv4 easier. 2172 Servers that do not support this mode of operation 2173 will be autodetected by the client, and it will fall 2174 back to using the idmapper. 2175 To turn off this behaviour, set the value to '0'. 2176 nfs.nfs4_unique_id= 2177 [NFS4] Specify an additional fixed unique ident- 2178 ification string that NFSv4 clients can insert into 2179 their nfs_client_id4 string. This is typically a 2180 UUID that is generated at system install time. 2181 2182 nfs.send_implementation_id = 2183 [NFSv4.1] Send client implementation identification 2184 information in exchange_id requests. 2185 If zero, no implementation identification information 2186 will be sent. 2187 The default is to send the implementation identification 2188 information. 2189 2190 nfs.recover_lost_locks = 2191 [NFSv4] Attempt to recover locks that were lost due 2192 to a lease timeout on the server. Please note that 2193 doing this risks data corruption, since there are 2194 no guarantees that the file will remain unchanged 2195 after the locks are lost. 2196 If you want to enable the kernel legacy behaviour of 2197 attempting to recover these locks, then set this 2198 parameter to '1'. 2199 The default parameter value of '0' causes the kernel 2200 not to attempt recovery of lost locks. 2201 2202 nfsd.nfs4_disable_idmapping= 2203 [NFSv4] When set to the default of '1', the NFSv4 2204 server will return only numeric uids and gids to 2205 clients using auth_sys, and will accept numeric uids 2206 and gids from such clients. This is intended to ease 2207 migration from NFSv2/v3. 2208 2209 objlayoutdriver.osd_login_prog= 2210 [NFS] [OBJLAYOUT] sets the pathname to the program which 2211 is used to automatically discover and login into new 2212 osd-targets. Please see: 2213 Documentation/filesystems/pnfs.txt for more explanations 2214 2215 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take 2216 when a NMI is triggered. 2217 Format: [state][,regs][,debounce][,die] 2218 2219 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 2220 Format: [panic,][nopanic,][num] 2221 Valid num: 0 2222 0 - turn nmi_watchdog off 2223 When panic is specified, panic when an NMI watchdog 2224 timeout occurs (or 'nopanic' to override the opposite 2225 default). 2226 This is useful when you use a panic=... timeout and 2227 need the box quickly up again. 2228 2229 netpoll.carrier_timeout= 2230 [NET] Specifies amount of time (in seconds) that 2231 netpoll should wait for a carrier. By default netpoll 2232 waits 4 seconds. 2233 2234 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 2235 emulation library even if a 387 maths coprocessor 2236 is present. 2237 2238 no_console_suspend 2239 [HW] Never suspend the console 2240 Disable suspending of consoles during suspend and 2241 hibernate operations. Once disabled, debugging 2242 messages can reach various consoles while the rest 2243 of the system is being put to sleep (ie, while 2244 debugging driver suspend/resume hooks). This may 2245 not work reliably with all consoles, but is known 2246 to work with serial and VGA consoles. 2247 To facilitate more flexible debugging, we also add 2248 console_suspend, a printk module parameter to control 2249 it. Users could use console_suspend (usually 2250 /sys/module/printk/parameters/console_suspend) to 2251 turn on/off it dynamically. 2252 2253 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien 2254 caches in the slab allocator. Saves per-node memory, 2255 but will impact performance. 2256 2257 noalign [KNL,ARM] 2258 2259 noapic [SMP,APIC] Tells the kernel to not make use of any 2260 IOAPICs that may be present in the system. 2261 2262 noautogroup Disable scheduler automatic task group creation. 2263 2264 nobats [PPC] Do not use BATs for mapping kernel lowmem 2265 on "Classic" PPC cores. 2266 2267 nocache [ARM] 2268 2269 noclflush [BUGS=X86] Don't use the CLFLUSH instruction 2270 2271 nodelayacct [KNL] Disable per-task delay accounting 2272 2273 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects. 2274 2275 nodsp [SH] Disable hardware DSP at boot time. 2276 2277 noefi Disable EFI runtime services support. 2278 2279 noexec [IA-64] 2280 2281 noexec [X86] 2282 On X86-32 available only on PAE configured kernels. 2283 noexec=on: enable non-executable mappings (default) 2284 noexec=off: disable non-executable mappings 2285 2286 nosmap [X86] 2287 Disable SMAP (Supervisor Mode Access Prevention) 2288 even if it is supported by processor. 2289 2290 nosmep [X86] 2291 Disable SMEP (Supervisor Mode Execution Prevention) 2292 even if it is supported by processor. 2293 2294 noexec32 [X86-64] 2295 This affects only 32-bit executables. 2296 noexec32=on: enable non-executable mappings (default) 2297 read doesn't imply executable mappings 2298 noexec32=off: disable non-executable mappings 2299 read implies executable mappings 2300 2301 nofpu [SH] Disable hardware FPU at boot time. 2302 2303 nofxsr [BUGS=X86-32] Disables x86 floating point extended 2304 register save and restore. The kernel will only save 2305 legacy floating-point registers on task switch. 2306 2307 noxsave [BUGS=X86] Disables x86 extended register state save 2308 and restore using xsave. The kernel will fallback to 2309 enabling legacy floating-point and sse state. 2310 2311 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 2312 register states. The kernel will fall back to use 2313 xsave to save the states. By using this parameter, 2314 performance of saving the states is degraded because 2315 xsave doesn't support modified optimization while 2316 xsaveopt supports it on xsaveopt enabled systems. 2317 2318 noxsaves [X86] Disables xsaves and xrstors used in saving and 2319 restoring x86 extended register state in compacted 2320 form of xsave area. The kernel will fall back to use 2321 xsaveopt and xrstor to save and restore the states 2322 in standard form of xsave area. By using this 2323 parameter, xsave area per process might occupy more 2324 memory on xsaves enabled systems. 2325 2326 eagerfpu= [X86] 2327 on enable eager fpu restore 2328 off disable eager fpu restore 2329 auto selects the default scheme, which automatically 2330 enables eagerfpu restore for xsaveopt. 2331 2332 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or 2333 wfi(ARM) instruction doesn't work correctly and not to 2334 use it. This is also useful when using JTAG debugger. 2335 2336 no_file_caps Tells the kernel not to honor file capabilities. The 2337 only way then for a file to be executed with privilege 2338 is to be setuid root or executed by root. 2339 2340 nohalt [IA-64] Tells the kernel not to use the power saving 2341 function PAL_HALT_LIGHT when idle. This increases 2342 power-consumption. On the positive side, it reduces 2343 interrupt wake-up latency, which may improve performance 2344 in certain environments such as networked servers or 2345 real-time systems. 2346 2347 nohibernate [HIBERNATION] Disable hibernation and resume. 2348 2349 nohz= [KNL] Boottime enable/disable dynamic ticks 2350 Valid arguments: on, off 2351 Default: on 2352 2353 nohz_full= [KNL,BOOT] 2354 In kernels built with CONFIG_NO_HZ_FULL=y, set 2355 the specified list of CPUs whose tick will be stopped 2356 whenever possible. The boot CPU will be forced outside 2357 the range to maintain the timekeeping. 2358 The CPUs in this range must also be included in the 2359 rcu_nocbs= set. 2360 2361 noiotrap [SH] Disables trapped I/O port accesses. 2362 2363 noirqdebug [X86-32] Disables the code which attempts to detect and 2364 disable unhandled interrupt sources. 2365 2366 no_timer_check [X86,APIC] Disables the code which tests for 2367 broken timer IRQ sources. 2368 2369 noisapnp [ISAPNP] Disables ISA PnP code. 2370 2371 noinitrd [RAM] Tells the kernel not to load any configured 2372 initial RAM disk. 2373 2374 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt 2375 remapping. 2376 [Deprecated - use intremap=off] 2377 2378 nointroute [IA-64] 2379 2380 nojitter [IA-64] Disables jitter checking for ITC timers. 2381 2382 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver 2383 2384 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page 2385 fault handling. 2386 2387 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting. 2388 steal time is computed, but won't influence scheduler 2389 behaviour 2390 2391 nolapic [X86-32,APIC] Do not enable or use the local APIC. 2392 2393 nolapic_timer [X86-32,APIC] Do not use the local APIC timer. 2394 2395 noltlbs [PPC] Do not use large page/tlb entries for kernel 2396 lowmem mapping on PPC40x. 2397 2398 nomca [IA-64] Disable machine check abort handling 2399 2400 nomce [X86-32] Machine Check Exception 2401 2402 nomfgpt [X86-32] Disable Multi-Function General Purpose 2403 Timer usage (for AMD Geode machines). 2404 2405 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 2406 shutdown the other cpus. Instead use the REBOOT_VECTOR 2407 irq. 2408 2409 nomodule Disable module load 2410 2411 nopat [X86] Disable PAT (page attribute table extension of 2412 pagetables) support. 2413 2414 norandmaps Don't use address space randomization. Equivalent to 2415 echo 0 > /proc/sys/kernel/randomize_va_space 2416 2417 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops 2418 2419 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 2420 with UP alternatives 2421 2422 nordrand [X86] Disable kernel use of the RDRAND and 2423 RDSEED instructions even if they are supported 2424 by the processor. RDRAND and RDSEED are still 2425 available to user space applications. 2426 2427 noresume [SWSUSP] Disables resume and restores original swap 2428 space. 2429 2430 no-scroll [VGA] Disables scrollback. 2431 This is required for the Braillex ib80-piezo Braille 2432 reader made by F.H. Papenmeier (Germany). 2433 2434 nosbagart [IA-64] 2435 2436 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support. 2437 2438 nosmp [SMP] Tells an SMP kernel to act as a UP kernel, 2439 and disable the IO APIC. legacy for "maxcpus=0". 2440 2441 nosoftlockup [KNL] Disable the soft-lockup detector. 2442 2443 nosync [HW,M68K] Disables sync negotiation for all devices. 2444 2445 notsc [BUGS=X86-32] Disable Time Stamp Counter 2446 2447 nousb [USB] Disable the USB subsystem 2448 2449 nowatchdog [KNL] Disable the lockup detector (NMI watchdog). 2450 2451 nowb [ARM] 2452 2453 nox2apic [X86-64,APIC] Do not enable x2APIC mode. 2454 2455 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when 2456 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off. 2457 Some features depend on CPU0. Known dependencies are: 2458 1. Resume from suspend/hibernate depends on CPU0. 2459 Suspend/hibernate will fail if CPU0 is offline and you 2460 need to online CPU0 before suspend/hibernate. 2461 2. PIC interrupts also depend on CPU0. CPU0 can't be 2462 removed if a PIC interrupt is detected. 2463 It's said poweroff/reboot may depend on CPU0 on some 2464 machines although I haven't seen such issues so far 2465 after CPU0 is offline on a few tested machines. 2466 If the dependencies are under your control, you can 2467 turn on cpu0_hotplug. 2468 2469 nptcg= [IA-64] Override max number of concurrent global TLB 2470 purges which is reported from either PAL_VM_SUMMARY or 2471 SAL PALO. 2472 2473 nr_cpus= [SMP] Maximum number of processors that an SMP kernel 2474 could support. nr_cpus=n : n >= 1 limits the kernel to 2475 supporting 'n' processors. Later in runtime you can not 2476 use hotplug cpu feature to put more cpu back to online. 2477 just like you compile the kernel NR_CPUS=n 2478 2479 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 2480 2481 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing. 2482 Allowed values are enable and disable 2483 2484 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 2485 one of ['zone', 'node', 'default'] can be specified 2486 This can be set from sysctl after boot. 2487 See Documentation/sysctl/vm.txt for details. 2488 2489 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver. 2490 See Documentation/debugging-via-ohci1394.txt for more 2491 info. 2492 2493 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 2494 Rather than timing out after 20 ms if an EC 2495 command is not properly ACKed, override the length 2496 of the timeout. We have interrupts disabled while 2497 waiting for the ACK, so if this is set too high 2498 interrupts *may* be lost! 2499 2500 omap_mux= [OMAP] Override bootloader pin multiplexing. 2501 Format: <mux_mode0.mode_name=value>... 2502 For example, to override I2C bus2: 2503 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 2504 2505 oprofile.timer= [HW] 2506 Use timer interrupt instead of performance counters 2507 2508 oprofile.cpu_type= Force an oprofile cpu type 2509 This might be useful if you have an older oprofile 2510 userland or if you want common events. 2511 Format: { arch_perfmon } 2512 arch_perfmon: [X86] Force use of architectural 2513 perfmon on Intel CPUs instead of the 2514 CPU specific event set. 2515 timer: [X86] Force use of architectural NMI 2516 timer mode (see also oprofile.timer 2517 for generic hr timer mode) 2518 [s390] Force legacy basic mode sampling 2519 (report cpu_type "timer") 2520 2521 oops=panic Always panic on oopses. Default is to just kill the 2522 process, but there is a small probability of 2523 deadlocking the machine. 2524 This will also cause panics on machine check exceptions. 2525 Useful together with panic=30 to trigger a reboot. 2526 2527 OSS [HW,OSS] 2528 See Documentation/sound/oss/oss-parameters.txt 2529 2530 page_owner= [KNL] Boot-time page_owner enabling option. 2531 Storage of the information about who allocated 2532 each page is disabled in default. With this switch, 2533 we can turn it on. 2534 on: enable the feature 2535 2536 panic= [KNL] Kernel behaviour on panic: delay <timeout> 2537 timeout > 0: seconds before rebooting 2538 timeout = 0: wait forever 2539 timeout < 0: reboot immediately 2540 Format: <timeout> 2541 2542 panic_on_warn panic() instead of WARN(). Useful to cause kdump 2543 on a WARN(). 2544 2545 crash_kexec_post_notifiers 2546 Run kdump after running panic-notifiers and dumping 2547 kmsg. This only for the users who doubt kdump always 2548 succeeds in any situation. 2549 Note that this also increases risks of kdump failure, 2550 because some panic notifiers can make the crashed 2551 kernel more unstable. 2552 2553 parkbd.port= [HW] Parallel port number the keyboard adapter is 2554 connected to, default is 0. 2555 Format: <parport#> 2556 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 2557 0 for XT, 1 for AT (default is AT). 2558 Format: <mode> 2559 2560 parport= [HW,PPT] Specify parallel ports. 0 disables. 2561 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 2562 Use 'auto' to force the driver to use any 2563 IRQ/DMA settings detected (the default is to 2564 ignore detected IRQ/DMA settings because of 2565 possible conflicts). You can specify the base 2566 address, IRQ, and DMA settings; IRQ and DMA 2567 should be numbers, or 'auto' (for using detected 2568 settings on that particular port), or 'nofifo' 2569 (to avoid using a FIFO even if it is detected). 2570 Parallel ports are assigned in the order they 2571 are specified on the command line, starting 2572 with parport0. 2573 2574 parport_init_mode= [HW,PPT] 2575 Configure VIA parallel port to operate in 2576 a specific mode. This is necessary on Pegasos 2577 computer where firmware has no options for setting 2578 up parallel port mode and sets it to spp. 2579 Currently this function knows 686a and 8231 chips. 2580 Format: [spp|ps2|epp|ecp|ecpepp] 2581 2582 pause_on_oops= 2583 Halt all CPUs after the first oops has been printed for 2584 the specified number of seconds. This is to be used if 2585 your oopses keep scrolling off the screen. 2586 2587 pcbit= [HW,ISDN] 2588 2589 pcd. [PARIDE] 2590 See header of drivers/block/paride/pcd.c. 2591 See also Documentation/blockdev/paride.txt. 2592 2593 pci=option[,option...] [PCI] various PCI subsystem options: 2594 earlydump [X86] dump PCI config space before the kernel 2595 changes anything 2596 off [X86] don't probe for the PCI bus 2597 bios [X86-32] force use of PCI BIOS, don't access 2598 the hardware directly. Use this if your machine 2599 has a non-standard PCI host bridge. 2600 nobios [X86-32] disallow use of PCI BIOS, only direct 2601 hardware access methods are allowed. Use this 2602 if you experience crashes upon bootup and you 2603 suspect they are caused by the BIOS. 2604 conf1 [X86] Force use of PCI Configuration 2605 Mechanism 1. 2606 conf2 [X86] Force use of PCI Configuration 2607 Mechanism 2. 2608 noaer [PCIE] If the PCIEAER kernel config parameter is 2609 enabled, this kernel boot option can be used to 2610 disable the use of PCIE advanced error reporting. 2611 nodomains [PCI] Disable support for multiple PCI 2612 root domains (aka PCI segments, in ACPI-speak). 2613 nommconf [X86] Disable use of MMCONFIG for PCI 2614 Configuration 2615 check_enable_amd_mmconf [X86] check for and enable 2616 properly configured MMIO access to PCI 2617 config space on AMD family 10h CPU 2618 nomsi [MSI] If the PCI_MSI kernel config parameter is 2619 enabled, this kernel boot option can be used to 2620 disable the use of MSI interrupts system-wide. 2621 noioapicquirk [APIC] Disable all boot interrupt quirks. 2622 Safety option to keep boot IRQs enabled. This 2623 should never be necessary. 2624 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 2625 primary IO-APIC for bridges that cannot disable 2626 boot IRQs. This fixes a source of spurious IRQs 2627 when the system masks IRQs. 2628 noioapicreroute [APIC] Disable workaround that uses the 2629 boot IRQ equivalent of an IRQ that connects to 2630 a chipset where boot IRQs cannot be disabled. 2631 The opposite of ioapicreroute. 2632 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 2633 routing table. These calls are known to be buggy 2634 on several machines and they hang the machine 2635 when used, but on other computers it's the only 2636 way to get the interrupt routing table. Try 2637 this option if the kernel is unable to allocate 2638 IRQs or discover secondary PCI buses on your 2639 motherboard. 2640 rom [X86] Assign address space to expansion ROMs. 2641 Use with caution as certain devices share 2642 address decoders between ROMs and other 2643 resources. 2644 norom [X86] Do not assign address space to 2645 expansion ROMs that do not already have 2646 BIOS assigned address ranges. 2647 nobar [X86] Do not assign address space to the 2648 BARs that weren't assigned by the BIOS. 2649 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 2650 assigned automatically to PCI devices. You can 2651 make the kernel exclude IRQs of your ISA cards 2652 this way. 2653 pirqaddr=0xAAAAA [X86] Specify the physical address 2654 of the PIRQ table (normally generated 2655 by the BIOS) if it is outside the 2656 F0000h-100000h range. 2657 lastbus=N [X86] Scan all buses thru bus #N. Can be 2658 useful if the kernel is unable to find your 2659 secondary buses and you want to tell it 2660 explicitly which ones they are. 2661 assign-busses [X86] Always assign all PCI bus 2662 numbers ourselves, overriding 2663 whatever the firmware may have done. 2664 usepirqmask [X86] Honor the possible IRQ mask stored 2665 in the BIOS $PIR table. This is needed on 2666 some systems with broken BIOSes, notably 2667 some HP Pavilion N5400 and Omnibook XE3 2668 notebooks. This will have no effect if ACPI 2669 IRQ routing is enabled. 2670 noacpi [X86] Do not use ACPI for IRQ routing 2671 or for PCI scanning. 2672 use_crs [X86] Use PCI host bridge window information 2673 from ACPI. On BIOSes from 2008 or later, this 2674 is enabled by default. If you need to use this, 2675 please report a bug. 2676 nocrs [X86] Ignore PCI host bridge windows from ACPI. 2677 If you need to use this, please report a bug. 2678 routeirq Do IRQ routing for all PCI devices. 2679 This is normally done in pci_enable_device(), 2680 so this option is a temporary workaround 2681 for broken drivers that don't call it. 2682 skip_isa_align [X86] do not align io start addr, so can 2683 handle more pci cards 2684 firmware [ARM] Do not re-enumerate the bus but instead 2685 just use the configuration from the 2686 bootloader. This is currently used on 2687 IXP2000 systems where the bus has to be 2688 configured a certain way for adjunct CPUs. 2689 noearly [X86] Don't do any early type 1 scanning. 2690 This might help on some broken boards which 2691 machine check when some devices' config space 2692 is read. But various workarounds are disabled 2693 and some IOMMU drivers will not work. 2694 bfsort Sort PCI devices into breadth-first order. 2695 This sorting is done to get a device 2696 order compatible with older (<= 2.4) kernels. 2697 nobfsort Don't sort PCI devices into breadth-first order. 2698 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 2699 tuning and use the BIOS-configured MPS defaults. 2700 pcie_bus_safe Set every device's MPS to the largest value 2701 supported by all devices below the root complex. 2702 pcie_bus_perf Set device MPS to the largest allowable MPS 2703 based on its parent bus. Also set MRRS (Max 2704 Read Request Size) to the largest supported 2705 value (no larger than the MPS that the device 2706 or bus can support) for best performance. 2707 pcie_bus_peer2peer Set every device's MPS to 128B, which 2708 every device is guaranteed to support. This 2709 configuration allows peer-to-peer DMA between 2710 any pair of devices, possibly at the cost of 2711 reduced performance. This also guarantees 2712 that hot-added devices will work. 2713 cbiosize=nn[KMG] The fixed amount of bus space which is 2714 reserved for the CardBus bridge's IO window. 2715 The default value is 256 bytes. 2716 cbmemsize=nn[KMG] The fixed amount of bus space which is 2717 reserved for the CardBus bridge's memory 2718 window. The default value is 64 megabytes. 2719 resource_alignment= 2720 Format: 2721 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...] 2722 Specifies alignment and device to reassign 2723 aligned memory resources. 2724 If <order of align> is not specified, 2725 PAGE_SIZE is used as alignment. 2726 PCI-PCI bridge can be specified, if resource 2727 windows need to be expanded. 2728 ecrc= Enable/disable PCIe ECRC (transaction layer 2729 end-to-end CRC checking). 2730 bios: Use BIOS/firmware settings. This is the 2731 the default. 2732 off: Turn ECRC off 2733 on: Turn ECRC on. 2734 hpiosize=nn[KMG] The fixed amount of bus space which is 2735 reserved for hotplug bridge's IO window. 2736 Default size is 256 bytes. 2737 hpmemsize=nn[KMG] The fixed amount of bus space which is 2738 reserved for hotplug bridge's memory window. 2739 Default size is 2 megabytes. 2740 realloc= Enable/disable reallocating PCI bridge resources 2741 if allocations done by BIOS are too small to 2742 accommodate resources required by all child 2743 devices. 2744 off: Turn realloc off 2745 on: Turn realloc on 2746 realloc same as realloc=on 2747 noari do not use PCIe ARI. 2748 pcie_scan_all Scan all possible PCIe devices. Otherwise we 2749 only look for one device below a PCIe downstream 2750 port. 2751 2752 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power 2753 Management. 2754 off Disable ASPM. 2755 force Enable ASPM even on devices that claim not to support it. 2756 WARNING: Forcing ASPM on may cause system lockups. 2757 2758 pcie_hp= [PCIE] PCI Express Hotplug driver options: 2759 nomsi Do not use MSI for PCI Express Native Hotplug (this 2760 makes all PCIe ports use INTx for hotplug services). 2761 2762 pcie_ports= [PCIE] PCIe ports handling: 2763 auto Ask the BIOS whether or not to use native PCIe services 2764 associated with PCIe ports (PME, hot-plug, AER). Use 2765 them only if that is allowed by the BIOS. 2766 native Use native PCIe services associated with PCIe ports 2767 unconditionally. 2768 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe 2769 ports driver. 2770 2771 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 2772 nomsi Do not use MSI for native PCIe PME signaling (this makes 2773 all PCIe root ports use INTx for all services). 2774 2775 pcmv= [HW,PCMCIA] BadgePAD 4 2776 2777 pd_ignore_unused 2778 [PM] 2779 Keep all power-domains already enabled by bootloader on, 2780 even if no driver has claimed them. This is useful 2781 for debug and development, but should not be 2782 needed on a platform with proper driver support. 2783 2784 pd. [PARIDE] 2785 See Documentation/blockdev/paride.txt. 2786 2787 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 2788 boot time. 2789 Format: { 0 | 1 } 2790 See arch/parisc/kernel/pdc_chassis.c 2791 2792 percpu_alloc= Select which percpu first chunk allocator to use. 2793 Currently supported values are "embed" and "page". 2794 Archs may support subset or none of the selections. 2795 See comments in mm/percpu.c for details on each 2796 allocator. This parameter is primarily for debugging 2797 and performance comparison. 2798 2799 pf. [PARIDE] 2800 See Documentation/blockdev/paride.txt. 2801 2802 pg. [PARIDE] 2803 See Documentation/blockdev/paride.txt. 2804 2805 pirq= [SMP,APIC] Manual mp-table setup 2806 See Documentation/x86/i386/IO-APIC.txt. 2807 2808 plip= [PPT,NET] Parallel port network link 2809 Format: { parport<nr> | timid | 0 } 2810 See also Documentation/parport.txt. 2811 2812 pmtmr= [X86] Manual setup of pmtmr I/O Port. 2813 Override pmtimer IOPort with a hex value. 2814 e.g. pmtmr=0x508 2815 2816 pnp.debug=1 [PNP] 2817 Enable PNP debug messages (depends on the 2818 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 2819 via /sys/module/pnp/parameters/debug. We always show 2820 current resource usage; turning this on also shows 2821 possible settings and some assignment information. 2822 2823 pnpacpi= [ACPI] 2824 { off } 2825 2826 pnpbios= [ISAPNP] 2827 { on | off | curr | res | no-curr | no-res } 2828 2829 pnp_reserve_irq= 2830 [ISAPNP] Exclude IRQs for the autoconfiguration 2831 2832 pnp_reserve_dma= 2833 [ISAPNP] Exclude DMAs for the autoconfiguration 2834 2835 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 2836 Ranges are in pairs (I/O port base and size). 2837 2838 pnp_reserve_mem= 2839 [ISAPNP] Exclude memory regions for the 2840 autoconfiguration. 2841 Ranges are in pairs (memory base and size). 2842 2843 ports= [IP_VS_FTP] IPVS ftp helper module 2844 Default is 21. 2845 Up to 8 (IP_VS_APP_MAX_PORTS) ports 2846 may be specified. 2847 Format: <port>,<port>.... 2848 2849 print-fatal-signals= 2850 [KNL] debug: print fatal signals 2851 2852 If enabled, warn about various signal handling 2853 related application anomalies: too many signals, 2854 too many POSIX.1 timers, fatal signals causing a 2855 coredump - etc. 2856 2857 If you hit the warning due to signal overflow, 2858 you might want to try "ulimit -i unlimited". 2859 2860 default: off. 2861 2862 printk.always_kmsg_dump= 2863 Trigger kmsg_dump for cases other than kernel oops or 2864 panics 2865 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 2866 default: disabled 2867 2868 printk.time= Show timing data prefixed to each printk message line 2869 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 2870 2871 processor.max_cstate= [HW,ACPI] 2872 Limit processor to maximum C-state 2873 max_cstate=9 overrides any DMI blacklist limit. 2874 2875 processor.nocst [HW,ACPI] 2876 Ignore the _CST method to determine C-states, 2877 instead using the legacy FADT method 2878 2879 profile= [KNL] Enable kernel profiling via /proc/profile 2880 Format: [schedule,]<number> 2881 Param: "schedule" - profile schedule points. 2882 Param: <number> - step/bucket size as a power of 2 for 2883 statistical time based profiling. 2884 Param: "sleep" - profile D-state sleeping (millisecs). 2885 Requires CONFIG_SCHEDSTATS 2886 Param: "kvm" - profile VM exits. 2887 2888 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk 2889 before loading. 2890 See Documentation/blockdev/ramdisk.txt. 2891 2892 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 2893 probe for; one of (bare|imps|exps|lifebook|any). 2894 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 2895 per second. 2896 psmouse.resetafter= [HW,MOUSE] 2897 Try to reset the device after so many bad packets 2898 (0 = never). 2899 psmouse.resolution= 2900 [HW,MOUSE] Set desired mouse resolution, in dpi. 2901 psmouse.smartscroll= 2902 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 2903 0 = disabled, 1 = enabled (default). 2904 2905 pstore.backend= Specify the name of the pstore backend to use 2906 2907 pt. [PARIDE] 2908 See Documentation/blockdev/paride.txt. 2909 2910 pty.legacy_count= 2911 [KNL] Number of legacy pty's. Overwrites compiled-in 2912 default number. 2913 2914 quiet [KNL] Disable most log messages 2915 2916 r128= [HW,DRM] 2917 2918 raid= [HW,RAID] 2919 See Documentation/md.txt. 2920 2921 ramdisk_blocksize= [RAM] 2922 See Documentation/blockdev/ramdisk.txt. 2923 2924 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 2925 See Documentation/blockdev/ramdisk.txt. 2926 2927 rcu_nocbs= [KNL] 2928 In kernels built with CONFIG_RCU_NOCB_CPU=y, set 2929 the specified list of CPUs to be no-callback CPUs. 2930 Invocation of these CPUs' RCU callbacks will 2931 be offloaded to "rcuox/N" kthreads created for 2932 that purpose, where "x" is "b" for RCU-bh, "p" 2933 for RCU-preempt, and "s" for RCU-sched, and "N" 2934 is the CPU number. This reduces OS jitter on the 2935 offloaded CPUs, which can be useful for HPC and 2936 real-time workloads. It can also improve energy 2937 efficiency for asymmetric multiprocessors. 2938 2939 rcu_nocb_poll [KNL] 2940 Rather than requiring that offloaded CPUs 2941 (specified by rcu_nocbs= above) explicitly 2942 awaken the corresponding "rcuoN" kthreads, 2943 make these kthreads poll for callbacks. 2944 This improves the real-time response for the 2945 offloaded CPUs by relieving them of the need to 2946 wake up the corresponding kthread, but degrades 2947 energy efficiency by requiring that the kthreads 2948 periodically wake up to do the polling. 2949 2950 rcutree.blimit= [KNL] 2951 Set maximum number of finished RCU callbacks to 2952 process in one batch. 2953 2954 rcutree.rcu_fanout_leaf= [KNL] 2955 Increase the number of CPUs assigned to each 2956 leaf rcu_node structure. Useful for very large 2957 systems. 2958 2959 rcutree.jiffies_till_sched_qs= [KNL] 2960 Set required age in jiffies for a 2961 given grace period before RCU starts 2962 soliciting quiescent-state help from 2963 rcu_note_context_switch(). 2964 2965 rcutree.jiffies_till_first_fqs= [KNL] 2966 Set delay from grace-period initialization to 2967 first attempt to force quiescent states. 2968 Units are jiffies, minimum value is zero, 2969 and maximum value is HZ. 2970 2971 rcutree.jiffies_till_next_fqs= [KNL] 2972 Set delay between subsequent attempts to force 2973 quiescent states. Units are jiffies, minimum 2974 value is one, and maximum value is HZ. 2975 2976 rcutree.kthread_prio= [KNL,BOOT] 2977 Set the SCHED_FIFO priority of the RCU 2978 per-CPU kthreads (rcuc/N). This value is also 2979 used for the priority of the RCU boost threads 2980 (rcub/N). Valid values are 1-99 and the default 2981 is 1 (the least-favored priority). 2982 2983 rcutree.rcu_nocb_leader_stride= [KNL] 2984 Set the number of NOCB kthread groups, which 2985 defaults to the square root of the number of 2986 CPUs. Larger numbers reduces the wakeup overhead 2987 on the per-CPU grace-period kthreads, but increases 2988 that same overhead on each group's leader. 2989 2990 rcutree.qhimark= [KNL] 2991 Set threshold of queued RCU callbacks beyond which 2992 batch limiting is disabled. 2993 2994 rcutree.qlowmark= [KNL] 2995 Set threshold of queued RCU callbacks below which 2996 batch limiting is re-enabled. 2997 2998 rcutree.rcu_idle_gp_delay= [KNL] 2999 Set wakeup interval for idle CPUs that have 3000 RCU callbacks (RCU_FAST_NO_HZ=y). 3001 3002 rcutree.rcu_idle_lazy_gp_delay= [KNL] 3003 Set wakeup interval for idle CPUs that have 3004 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y). 3005 Lazy RCU callbacks are those which RCU can 3006 prove do nothing more than free memory. 3007 3008 rcutorture.cbflood_inter_holdoff= [KNL] 3009 Set holdoff time (jiffies) between successive 3010 callback-flood tests. 3011 3012 rcutorture.cbflood_intra_holdoff= [KNL] 3013 Set holdoff time (jiffies) between successive 3014 bursts of callbacks within a given callback-flood 3015 test. 3016 3017 rcutorture.cbflood_n_burst= [KNL] 3018 Set the number of bursts making up a given 3019 callback-flood test. Set this to zero to 3020 disable callback-flood testing. 3021 3022 rcutorture.cbflood_n_per_burst= [KNL] 3023 Set the number of callbacks to be registered 3024 in a given burst of a callback-flood test. 3025 3026 rcutorture.fqs_duration= [KNL] 3027 Set duration of force_quiescent_state bursts. 3028 3029 rcutorture.fqs_holdoff= [KNL] 3030 Set holdoff time within force_quiescent_state bursts. 3031 3032 rcutorture.fqs_stutter= [KNL] 3033 Set wait time between force_quiescent_state bursts. 3034 3035 rcutorture.gp_exp= [KNL] 3036 Use expedited update-side primitives. 3037 3038 rcutorture.gp_normal= [KNL] 3039 Use normal (non-expedited) update-side primitives. 3040 If both gp_exp and gp_normal are set, do both. 3041 If neither gp_exp nor gp_normal are set, still 3042 do both. 3043 3044 rcutorture.n_barrier_cbs= [KNL] 3045 Set callbacks/threads for rcu_barrier() testing. 3046 3047 rcutorture.nfakewriters= [KNL] 3048 Set number of concurrent RCU writers. These just 3049 stress RCU, they don't participate in the actual 3050 test, hence the "fake". 3051 3052 rcutorture.nreaders= [KNL] 3053 Set number of RCU readers. 3054 3055 rcutorture.object_debug= [KNL] 3056 Enable debug-object double-call_rcu() testing. 3057 3058 rcutorture.onoff_holdoff= [KNL] 3059 Set time (s) after boot for CPU-hotplug testing. 3060 3061 rcutorture.onoff_interval= [KNL] 3062 Set time (s) between CPU-hotplug operations, or 3063 zero to disable CPU-hotplug testing. 3064 3065 rcutorture.torture_runnable= [BOOT] 3066 Start rcutorture running at boot time. 3067 3068 rcutorture.shuffle_interval= [KNL] 3069 Set task-shuffle interval (s). Shuffling tasks 3070 allows some CPUs to go into dyntick-idle mode 3071 during the rcutorture test. 3072 3073 rcutorture.shutdown_secs= [KNL] 3074 Set time (s) after boot system shutdown. This 3075 is useful for hands-off automated testing. 3076 3077 rcutorture.stall_cpu= [KNL] 3078 Duration of CPU stall (s) to test RCU CPU stall 3079 warnings, zero to disable. 3080 3081 rcutorture.stall_cpu_holdoff= [KNL] 3082 Time to wait (s) after boot before inducing stall. 3083 3084 rcutorture.stat_interval= [KNL] 3085 Time (s) between statistics printk()s. 3086 3087 rcutorture.stutter= [KNL] 3088 Time (s) to stutter testing, for example, specifying 3089 five seconds causes the test to run for five seconds, 3090 wait for five seconds, and so on. This tests RCU's 3091 ability to transition abruptly to and from idle. 3092 3093 rcutorture.test_boost= [KNL] 3094 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 3095 "Maybe" means test if the RCU implementation 3096 under test support RCU priority boosting. 3097 3098 rcutorture.test_boost_duration= [KNL] 3099 Duration (s) of each individual boost test. 3100 3101 rcutorture.test_boost_interval= [KNL] 3102 Interval (s) between each boost test. 3103 3104 rcutorture.test_no_idle_hz= [KNL] 3105 Test RCU's dyntick-idle handling. See also the 3106 rcutorture.shuffle_interval parameter. 3107 3108 rcutorture.torture_type= [KNL] 3109 Specify the RCU implementation to test. 3110 3111 rcutorture.verbose= [KNL] 3112 Enable additional printk() statements. 3113 3114 rcupdate.rcu_expedited= [KNL] 3115 Use expedited grace-period primitives, for 3116 example, synchronize_rcu_expedited() instead 3117 of synchronize_rcu(). This reduces latency, 3118 but can increase CPU utilization, degrade 3119 real-time latency, and degrade energy efficiency. 3120 3121 rcupdate.rcu_cpu_stall_suppress= [KNL] 3122 Suppress RCU CPU stall warning messages. 3123 3124 rcupdate.rcu_cpu_stall_timeout= [KNL] 3125 Set timeout for RCU CPU stall warning messages. 3126 3127 rcupdate.rcu_task_stall_timeout= [KNL] 3128 Set timeout in jiffies for RCU task stall warning 3129 messages. Disable with a value less than or equal 3130 to zero. 3131 3132 rcupdate.rcu_self_test= [KNL] 3133 Run the RCU early boot self tests 3134 3135 rcupdate.rcu_self_test_bh= [KNL] 3136 Run the RCU bh early boot self tests 3137 3138 rcupdate.rcu_self_test_sched= [KNL] 3139 Run the RCU sched early boot self tests 3140 3141 rdinit= [KNL] 3142 Format: <full_path> 3143 Run specified binary instead of /init from the ramdisk, 3144 used for early userspace startup. See initrd. 3145 3146 reboot= [KNL] 3147 Format (x86 or x86_64): 3148 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \ 3149 [[,]s[mp]#### \ 3150 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 3151 [[,]f[orce] 3152 Where reboot_mode is one of warm (soft) or cold (hard) or gpio, 3153 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 3154 reboot_force is either force or not specified, 3155 reboot_cpu is s[mp]#### with #### being the processor 3156 to be used for rebooting. 3157 3158 relax_domain_level= 3159 [KNL, SMP] Set scheduler's default relax_domain_level. 3160 See Documentation/cgroups/cpusets.txt. 3161 3162 relative_sleep_states= 3163 [SUSPEND] Use sleep state labeling where the deepest 3164 state available other than hibernation is always "mem". 3165 Format: { "0" | "1" } 3166 0 -- Traditional sleep state labels. 3167 1 -- Relative sleep state labels. 3168 3169 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area 3170 3171 reservetop= [X86-32] 3172 Format: nn[KMG] 3173 Reserves a hole at the top of the kernel virtual 3174 address space. 3175 3176 reservelow= [X86] 3177 Format: nn[K] 3178 Set the amount of memory to reserve for BIOS at 3179 the bottom of the address space. 3180 3181 reset_devices [KNL] Force drivers to reset the underlying device 3182 during initialization. 3183 3184 resume= [SWSUSP] 3185 Specify the partition device for software suspend 3186 Format: 3187 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 3188 3189 resume_offset= [SWSUSP] 3190 Specify the offset from the beginning of the partition 3191 given by "resume=" at which the swap header is located, 3192 in <PAGE_SIZE> units (needed only for swap files). 3193 See Documentation/power/swsusp-and-swap-files.txt 3194 3195 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 3196 read the resume files 3197 3198 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 3199 Useful for devices that are detected asynchronously 3200 (e.g. USB and MMC devices). 3201 3202 hibernate= [HIBERNATION] 3203 noresume Don't check if there's a hibernation image 3204 present during boot. 3205 nocompress Don't compress/decompress hibernation images. 3206 no Disable hibernation and resume. 3207 3208 retain_initrd [RAM] Keep initrd memory after extraction 3209 3210 rhash_entries= [KNL,NET] 3211 Set number of hash buckets for route cache 3212 3213 ro [KNL] Mount root device read-only on boot 3214 3215 root= [KNL] Root filesystem 3216 See name_to_dev_t comment in init/do_mounts.c. 3217 3218 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 3219 mount the root filesystem 3220 3221 rootflags= [KNL] Set root filesystem mount option string 3222 3223 rootfstype= [KNL] Set root filesystem type 3224 3225 rootwait [KNL] Wait (indefinitely) for root device to show up. 3226 Useful for devices that are detected asynchronously 3227 (e.g. USB and MMC devices). 3228 3229 rproc_mem=nn[KMG][@address] 3230 [KNL,ARM,CMA] Remoteproc physical memory block. 3231 Memory area to be used by remote processor image, 3232 managed by CMA. 3233 3234 rw [KNL] Mount root device read-write on boot 3235 3236 S [KNL] Run init in single mode 3237 3238 s390_iommu= [HW,S390] 3239 Set s390 IOTLB flushing mode 3240 strict 3241 With strict flushing every unmap operation will result in 3242 an IOTLB flush. Default is lazy flushing before reuse, 3243 which is faster. 3244 3245 sa1100ir [NET] 3246 See drivers/net/irda/sa1100_ir.c. 3247 3248 sbni= [NET] Granch SBNI12 leased line adapter 3249 3250 sched_debug [KNL] Enables verbose scheduler debug messages. 3251 3252 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate 3253 xtime_lock contention on larger systems, and/or RCU lock 3254 contention on all systems with CONFIG_MAXSMP set. 3255 Format: { "0" | "1" } 3256 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 3257 1 -- enable. 3258 Note: increases power consumption, thus should only be 3259 enabled if running jitter sensitive (HPC/RT) workloads. 3260 3261 security= [SECURITY] Choose a security module to enable at boot. 3262 If this boot parameter is not specified, only the first 3263 security module asking for security registration will be 3264 loaded. An invalid security module name will be treated 3265 as if no module has been chosen. 3266 3267 selinux= [SELINUX] Disable or enable SELinux at boot time. 3268 Format: { "0" | "1" } 3269 See security/selinux/Kconfig help text. 3270 0 -- disable. 3271 1 -- enable. 3272 Default value is set via kernel config option. 3273 If enabled at boot time, /selinux/disable can be used 3274 later to disable prior to initial policy load. 3275 3276 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 3277 Format: { "0" | "1" } 3278 See security/apparmor/Kconfig help text 3279 0 -- disable. 3280 1 -- enable. 3281 Default value is set via kernel config option. 3282 3283 serialnumber [BUGS=X86-32] 3284 3285 shapers= [NET] 3286 Maximal number of shapers. 3287 3288 show_msr= [x86] show boot-time MSR settings 3289 Format: { <integer> } 3290 Show boot-time (BIOS-initialized) MSR settings. 3291 The parameter means the number of CPUs to show, 3292 for example 1 means boot CPU only. 3293 3294 simeth= [IA-64] 3295 simscsi= 3296 3297 slram= [HW,MTD] 3298 3299 slab_nomerge [MM] 3300 Disable merging of slabs with similar size. May be 3301 necessary if there is some reason to distinguish 3302 allocs to different slabs. Debug options disable 3303 merging on their own. 3304 For more information see Documentation/vm/slub.txt. 3305 3306 slab_max_order= [MM, SLAB] 3307 Determines the maximum allowed order for slabs. 3308 A high setting may cause OOMs due to memory 3309 fragmentation. Defaults to 1 for systems with 3310 more than 32MB of RAM, 0 otherwise. 3311 3312 slub_debug[=options[,slabs]] [MM, SLUB] 3313 Enabling slub_debug allows one to determine the 3314 culprit if slab objects become corrupted. Enabling 3315 slub_debug can create guard zones around objects and 3316 may poison objects when not in use. Also tracks the 3317 last alloc / free. For more information see 3318 Documentation/vm/slub.txt. 3319 3320 slub_max_order= [MM, SLUB] 3321 Determines the maximum allowed order for slabs. 3322 A high setting may cause OOMs due to memory 3323 fragmentation. For more information see 3324 Documentation/vm/slub.txt. 3325 3326 slub_min_objects= [MM, SLUB] 3327 The minimum number of objects per slab. SLUB will 3328 increase the slab order up to slub_max_order to 3329 generate a sufficiently large slab able to contain 3330 the number of objects indicated. The higher the number 3331 of objects the smaller the overhead of tracking slabs 3332 and the less frequently locks need to be acquired. 3333 For more information see Documentation/vm/slub.txt. 3334 3335 slub_min_order= [MM, SLUB] 3336 Determines the minimum page order for slabs. Must be 3337 lower than slub_max_order. 3338 For more information see Documentation/vm/slub.txt. 3339 3340 slub_nomerge [MM, SLUB] 3341 Same with slab_nomerge. This is supported for legacy. 3342 See slab_nomerge for more information. 3343 3344 smart2= [HW] 3345 Format: <io1>[,<io2>[,...,<io8>]] 3346 3347 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 3348 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 3349 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 3350 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 3351 smsc-ircc2.ircc_irq= [HW] IRQ line 3352 smsc-ircc2.ircc_dma= [HW] DMA channel 3353 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 3354 0: Toshiba Satellite 1800 (GP data pin select) 3355 1: Fast pin select (default) 3356 2: ATC IRMode 3357 3358 softlockup_panic= 3359 [KNL] Should the soft-lockup detector generate panics. 3360 Format: <integer> 3361 3362 softlockup_all_cpu_backtrace= 3363 [KNL] Should the soft-lockup detector generate 3364 backtraces on all cpus. 3365 Format: <integer> 3366 3367 sonypi.*= [HW] Sony Programmable I/O Control Device driver 3368 See Documentation/laptops/sonypi.txt 3369 3370 spia_io_base= [HW,MTD] 3371 spia_fio_base= 3372 spia_pedr= 3373 spia_peddr= 3374 3375 stacktrace [FTRACE] 3376 Enabled the stack tracer on boot up. 3377 3378 stacktrace_filter=[function-list] 3379 [FTRACE] Limit the functions that the stack tracer 3380 will trace at boot up. function-list is a comma separated 3381 list of functions. This list can be changed at run 3382 time by the stack_trace_filter file in the debugfs 3383 tracing directory. Note, this enables stack tracing 3384 and the stacktrace above is not needed. 3385 3386 sti= [PARISC,HW] 3387 Format: <num> 3388 Set the STI (builtin display/keyboard on the HP-PARISC 3389 machines) console (graphic card) which should be used 3390 as the initial boot-console. 3391 See also comment in drivers/video/console/sticore.c. 3392 3393 sti_font= [HW] 3394 See comment in drivers/video/console/sticore.c. 3395 3396 stifb= [HW] 3397 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 3398 3399 sunrpc.min_resvport= 3400 sunrpc.max_resvport= 3401 [NFS,SUNRPC] 3402 SunRPC servers often require that client requests 3403 originate from a privileged port (i.e. a port in the 3404 range 0 < portnr < 1024). 3405 An administrator who wishes to reserve some of these 3406 ports for other uses may adjust the range that the 3407 kernel's sunrpc client considers to be privileged 3408 using these two parameters to set the minimum and 3409 maximum port values. 3410 3411 sunrpc.pool_mode= 3412 [NFS] 3413 Control how the NFS server code allocates CPUs to 3414 service thread pools. Depending on how many NICs 3415 you have and where their interrupts are bound, this 3416 option will affect which CPUs will do NFS serving. 3417 Note: this parameter cannot be changed while the 3418 NFS server is running. 3419 3420 auto the server chooses an appropriate mode 3421 automatically using heuristics 3422 global a single global pool contains all CPUs 3423 percpu one pool for each CPU 3424 pernode one pool for each NUMA node (equivalent 3425 to global on non-NUMA machines) 3426 3427 sunrpc.tcp_slot_table_entries= 3428 sunrpc.udp_slot_table_entries= 3429 [NFS,SUNRPC] 3430 Sets the upper limit on the number of simultaneous 3431 RPC calls that can be sent from the client to a 3432 server. Increasing these values may allow you to 3433 improve throughput, but will also increase the 3434 amount of memory reserved for use by the client. 3435 3436 swapaccount=[0|1] 3437 [KNL] Enable accounting of swap in memory resource 3438 controller if no parameter or 1 is given or disable 3439 it if 0 is given (See Documentation/cgroups/memory.txt) 3440 3441 swiotlb= [ARM,IA-64,PPC,MIPS,X86] 3442 Format: { <int> | force } 3443 <int> -- Number of I/O TLB slabs 3444 force -- force using of bounce buffers even if they 3445 wouldn't be automatically used by the kernel 3446 3447 switches= [HW,M68k] 3448 3449 sysfs.deprecated=0|1 [KNL] 3450 Enable/disable old style sysfs layout for old udev 3451 on older distributions. When this option is enabled 3452 very new udev will not work anymore. When this option 3453 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled) 3454 in older udev will not work anymore. 3455 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in 3456 the kernel configuration. 3457 3458 sysrq_always_enabled 3459 [KNL] 3460 Ignore sysrq setting - this boot parameter will 3461 neutralize any effect of /proc/sys/kernel/sysrq. 3462 Useful for debugging. 3463 3464 tcpmhash_entries= [KNL,NET] 3465 Set the number of tcp_metrics_hash slots. 3466 Default value is 8192 or 16384 depending on total 3467 ram pages. This is used to specify the TCP metrics 3468 cache size. See Documentation/networking/ip-sysctl.txt 3469 "tcp_no_metrics_save" section for more details. 3470 3471 tdfx= [HW,DRM] 3472 3473 test_suspend= [SUSPEND][,N] 3474 Specify "mem" (for Suspend-to-RAM) or "standby" (for 3475 standby suspend) or "freeze" (for suspend type freeze) 3476 as the system sleep state during system startup with 3477 the optional capability to repeat N number of times. 3478 The system is woken from this state using a 3479 wakeup-capable RTC alarm. 3480 3481 thash_entries= [KNL,NET] 3482 Set number of hash buckets for TCP connection 3483 3484 thermal.act= [HW,ACPI] 3485 -1: disable all active trip points in all thermal zones 3486 <degrees C>: override all lowest active trip points 3487 3488 thermal.crt= [HW,ACPI] 3489 -1: disable all critical trip points in all thermal zones 3490 <degrees C>: override all critical trip points 3491 3492 thermal.nocrt= [HW,ACPI] 3493 Set to disable actions on ACPI thermal zone 3494 critical and hot trip points. 3495 3496 thermal.off= [HW,ACPI] 3497 1: disable ACPI thermal control 3498 3499 thermal.psv= [HW,ACPI] 3500 -1: disable all passive trip points 3501 <degrees C>: override all passive trip points to this 3502 value 3503 3504 thermal.tzp= [HW,ACPI] 3505 Specify global default ACPI thermal zone polling rate 3506 <deci-seconds>: poll all this frequency 3507 0: no polling (default) 3508 3509 threadirqs [KNL] 3510 Force threading of all interrupt handlers except those 3511 marked explicitly IRQF_NO_THREAD. 3512 3513 tmem [KNL,XEN] 3514 Enable the Transcendent memory driver if built-in. 3515 3516 tmem.cleancache=0|1 [KNL, XEN] 3517 Default is on (1). Disable the usage of the cleancache 3518 API to send anonymous pages to the hypervisor. 3519 3520 tmem.frontswap=0|1 [KNL, XEN] 3521 Default is on (1). Disable the usage of the frontswap 3522 API to send swap pages to the hypervisor. If disabled 3523 the selfballooning and selfshrinking are force disabled. 3524 3525 tmem.selfballooning=0|1 [KNL, XEN] 3526 Default is on (1). Disable the driving of swap pages 3527 to the hypervisor. 3528 3529 tmem.selfshrinking=0|1 [KNL, XEN] 3530 Default is on (1). Partial swapoff that immediately 3531 transfers pages from Xen hypervisor back to the 3532 kernel based on different criteria. 3533 3534 topology= [S390] 3535 Format: {off | on} 3536 Specify if the kernel should make use of the cpu 3537 topology information if the hardware supports this. 3538 The scheduler will make use of this information and 3539 e.g. base its process migration decisions on it. 3540 Default is on. 3541 3542 topology_updates= [KNL, PPC, NUMA] 3543 Format: {off} 3544 Specify if the kernel should ignore (off) 3545 topology updates sent by the hypervisor to this 3546 LPAR. 3547 3548 tp720= [HW,PS2] 3549 3550 tpm_suspend_pcr=[HW,TPM] 3551 Format: integer pcr id 3552 Specify that at suspend time, the tpm driver 3553 should extend the specified pcr with zeros, 3554 as a workaround for some chips which fail to 3555 flush the last written pcr on TPM_SaveState. 3556 This will guarantee that all the other pcrs 3557 are saved. 3558 3559 trace_buf_size=nn[KMG] 3560 [FTRACE] will set tracing buffer size on each cpu. 3561 3562 trace_event=[event-list] 3563 [FTRACE] Set and start specified trace events in order 3564 to facilitate early boot debugging. 3565 See also Documentation/trace/events.txt 3566 3567 trace_options=[option-list] 3568 [FTRACE] Enable or disable tracer options at boot. 3569 The option-list is a comma delimited list of options 3570 that can be enabled or disabled just as if you were 3571 to echo the option name into 3572 3573 /sys/kernel/debug/tracing/trace_options 3574 3575 For example, to enable stacktrace option (to dump the 3576 stack trace of each event), add to the command line: 3577 3578 trace_options=stacktrace 3579 3580 See also Documentation/trace/ftrace.txt "trace options" 3581 section. 3582 3583 tp_printk[FTRACE] 3584 Have the tracepoints sent to printk as well as the 3585 tracing ring buffer. This is useful for early boot up 3586 where the system hangs or reboots and does not give the 3587 option for reading the tracing buffer or performing a 3588 ftrace_dump_on_oops. 3589 3590 To turn off having tracepoints sent to printk, 3591 echo 0 > /proc/sys/kernel/tracepoint_printk 3592 Note, echoing 1 into this file without the 3593 tracepoint_printk kernel cmdline option has no effect. 3594 3595 ** CAUTION ** 3596 3597 Having tracepoints sent to printk() and activating high 3598 frequency tracepoints such as irq or sched, can cause 3599 the system to live lock. 3600 3601 traceoff_on_warning 3602 [FTRACE] enable this option to disable tracing when a 3603 warning is hit. This turns off "tracing_on". Tracing can 3604 be enabled again by echoing '1' into the "tracing_on" 3605 file located in /sys/kernel/debug/tracing/ 3606 3607 This option is useful, as it disables the trace before 3608 the WARNING dump is called, which prevents the trace to 3609 be filled with content caused by the warning output. 3610 3611 This option can also be set at run time via the sysctl 3612 option: kernel/traceoff_on_warning 3613 3614 transparent_hugepage= 3615 [KNL] 3616 Format: [always|madvise|never] 3617 Can be used to control the default behavior of the system 3618 with respect to transparent hugepages. 3619 See Documentation/vm/transhuge.txt for more details. 3620 3621 tsc= Disable clocksource stability checks for TSC. 3622 Format: <string> 3623 [x86] reliable: mark tsc clocksource as reliable, this 3624 disables clocksource verification at runtime, as well 3625 as the stability checks done at bootup. Used to enable 3626 high-resolution timer mode on older hardware, and in 3627 virtualized environment. 3628 [x86] noirqtime: Do not use TSC to do irq accounting. 3629 Used to run time disable IRQ_TIME_ACCOUNTING on any 3630 platforms where RDTSC is slow and this accounting 3631 can add overhead. 3632 3633 turbografx.map[2|3]= [HW,JOY] 3634 TurboGraFX parallel port interface 3635 Format: 3636 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 3637 See also Documentation/input/joystick-parport.txt 3638 3639 udbg-immortal [PPC] When debugging early kernel crashes that 3640 happen after console_init() and before a proper 3641 console driver takes over, this boot options might 3642 help "seeing" what's going on. 3643 3644 uhash_entries= [KNL,NET] 3645 Set number of hash buckets for UDP/UDP-Lite connections 3646 3647 uhci-hcd.ignore_oc= 3648 [USB] Ignore overcurrent events (default N). 3649 Some badly-designed motherboards generate lots of 3650 bogus events, for ports that aren't wired to 3651 anything. Set this parameter to avoid log spamming. 3652 Note that genuine overcurrent events won't be 3653 reported either. 3654 3655 unknown_nmi_panic 3656 [X86] Cause panic on unknown NMI. 3657 3658 usbcore.authorized_default= 3659 [USB] Default USB device authorization: 3660 (default -1 = authorized except for wireless USB, 3661 0 = not authorized, 1 = authorized) 3662 3663 usbcore.autosuspend= 3664 [USB] The autosuspend time delay (in seconds) used 3665 for newly-detected USB devices (default 2). This 3666 is the time required before an idle device will be 3667 autosuspended. Devices for which the delay is set 3668 to a negative value won't be autosuspended at all. 3669 3670 usbcore.usbfs_snoop= 3671 [USB] Set to log all usbfs traffic (default 0 = off). 3672 3673 usbcore.blinkenlights= 3674 [USB] Set to cycle leds on hubs (default 0 = off). 3675 3676 usbcore.old_scheme_first= 3677 [USB] Start with the old device initialization 3678 scheme (default 0 = off). 3679 3680 usbcore.usbfs_memory_mb= 3681 [USB] Memory limit (in MB) for buffers allocated by 3682 usbfs (default = 16, 0 = max = 2047). 3683 3684 usbcore.use_both_schemes= 3685 [USB] Try the other device initialization scheme 3686 if the first one fails (default 1 = enabled). 3687 3688 usbcore.initial_descriptor_timeout= 3689 [USB] Specifies timeout for the initial 64-byte 3690 USB_REQ_GET_DESCRIPTOR request in milliseconds 3691 (default 5000 = 5.0 seconds). 3692 3693 usbhid.mousepoll= 3694 [USBHID] The interval which mice are to be polled at. 3695 3696 usb-storage.delay_use= 3697 [UMS] The delay in seconds before a new device is 3698 scanned for Logical Units (default 1). 3699 3700 usb-storage.quirks= 3701 [UMS] A list of quirks entries to supplement or 3702 override the built-in unusual_devs list. List 3703 entries are separated by commas. Each entry has 3704 the form VID:PID:Flags where VID and PID are Vendor 3705 and Product ID values (4-digit hex numbers) and 3706 Flags is a set of characters, each corresponding 3707 to a common usb-storage quirk flag as follows: 3708 a = SANE_SENSE (collect more than 18 bytes 3709 of sense data); 3710 b = BAD_SENSE (don't collect more than 18 3711 bytes of sense data); 3712 c = FIX_CAPACITY (decrease the reported 3713 device capacity by one sector); 3714 d = NO_READ_DISC_INFO (don't use 3715 READ_DISC_INFO command); 3716 e = NO_READ_CAPACITY_16 (don't use 3717 READ_CAPACITY_16 command); 3718 f = NO_REPORT_OPCODES (don't use report opcodes 3719 command, uas only); 3720 h = CAPACITY_HEURISTICS (decrease the 3721 reported device capacity by one 3722 sector if the number is odd); 3723 i = IGNORE_DEVICE (don't bind to this 3724 device); 3725 l = NOT_LOCKABLE (don't try to lock and 3726 unlock ejectable media); 3727 m = MAX_SECTORS_64 (don't transfer more 3728 than 64 sectors = 32 KB at a time); 3729 n = INITIAL_READ10 (force a retry of the 3730 initial READ(10) command); 3731 o = CAPACITY_OK (accept the capacity 3732 reported by the device); 3733 p = WRITE_CACHE (the device cache is ON 3734 by default); 3735 r = IGNORE_RESIDUE (the device reports 3736 bogus residue values); 3737 s = SINGLE_LUN (the device has only one 3738 Logical Unit); 3739 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 3740 commands, uas only); 3741 u = IGNORE_UAS (don't bind to the uas driver); 3742 w = NO_WP_DETECT (don't test whether the 3743 medium is write-protected). 3744 Example: quirks=0419:aaf5:rl,0421:0433:rc 3745 3746 user_debug= [KNL,ARM] 3747 Format: <int> 3748 See arch/arm/Kconfig.debug help text. 3749 1 - undefined instruction events 3750 2 - system calls 3751 4 - invalid data aborts 3752 8 - SIGSEGV faults 3753 16 - SIGBUS faults 3754 Example: user_debug=31 3755 3756 userpte= 3757 [X86] Flags controlling user PTE allocations. 3758 3759 nohigh = do not allocate PTE pages in 3760 HIGHMEM regardless of setting 3761 of CONFIG_HIGHPTE. 3762 3763 vdso= [X86,SH] 3764 On X86_32, this is an alias for vdso32=. Otherwise: 3765 3766 vdso=1: enable VDSO (the default) 3767 vdso=0: disable VDSO mapping 3768 3769 vdso32= [X86] Control the 32-bit vDSO 3770 vdso32=1: enable 32-bit VDSO 3771 vdso32=0 or vdso32=2: disable 32-bit VDSO 3772 3773 See the help text for CONFIG_COMPAT_VDSO for more 3774 details. If CONFIG_COMPAT_VDSO is set, the default is 3775 vdso32=0; otherwise, the default is vdso32=1. 3776 3777 For compatibility with older kernels, vdso32=2 is an 3778 alias for vdso32=0. 3779 3780 Try vdso32=0 if you encounter an error that says: 3781 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 3782 3783 vector= [IA-64,SMP] 3784 vector=percpu: enable percpu vector domain 3785 3786 video= [FB] Frame buffer configuration 3787 See Documentation/fb/modedb.txt. 3788 3789 video.brightness_switch_enabled= [0,1] 3790 If set to 1, on receiving an ACPI notify event 3791 generated by hotkey, video driver will adjust brightness 3792 level and then send out the event to user space through 3793 the allocated input device; If set to 0, video driver 3794 will only send out the event without touching backlight 3795 brightness level. 3796 default: 1 3797 3798 virtio_mmio.device= 3799 [VMMIO] Memory mapped virtio (platform) device. 3800 3801 <size>@<baseaddr>:<irq>[:<id>] 3802 where: 3803 <size> := size (can use standard suffixes 3804 like K, M and G) 3805 <baseaddr> := physical base address 3806 <irq> := interrupt number (as passed to 3807 request_irq()) 3808 <id> := (optional) platform device id 3809 example: 3810 virtio_mmio.device=1K@0x100b0000:48:7 3811 3812 Can be used multiple times for multiple devices. 3813 3814 vga= [BOOT,X86-32] Select a particular video mode 3815 See Documentation/x86/boot.txt and 3816 Documentation/svga.txt. 3817 Use vga=ask for menu. 3818 This is actually a boot loader parameter; the value is 3819 passed to the kernel using a special protocol. 3820 3821 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact 3822 size of <nn>. This can be used to increase the 3823 minimum size (128MB on x86). It can also be used to 3824 decrease the size and leave more room for directly 3825 mapped kernel RAM. 3826 3827 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 3828 Format: <command> 3829 3830 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 3831 Format: <command> 3832 3833 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 3834 Format: <command> 3835 3836 vsyscall= [X86-64] 3837 Controls the behavior of vsyscalls (i.e. calls to 3838 fixed addresses of 0xffffffffff600x00 from legacy 3839 code). Most statically-linked binaries and older 3840 versions of glibc use these calls. Because these 3841 functions are at fixed addresses, they make nice 3842 targets for exploits that can control RIP. 3843 3844 emulate [default] Vsyscalls turn into traps and are 3845 emulated reasonably safely. 3846 3847 native Vsyscalls are native syscall instructions. 3848 This is a little bit faster than trapping 3849 and makes a few dynamic recompilers work 3850 better than they would in emulation mode. 3851 It also makes exploits much easier to write. 3852 3853 none Vsyscalls don't work at all. This makes 3854 them quite hard to use for exploits but 3855 might break your system. 3856 3857 vt.color= [VT] Default text color. 3858 Format: 0xYX, X = foreground, Y = background. 3859 Default: 0x07 = light gray on black. 3860 3861 vt.cur_default= [VT] Default cursor shape. 3862 Format: 0xCCBBAA, where AA, BB, and CC are the same as 3863 the parameters of the <Esc>[?A;B;Cc escape sequence; 3864 see VGA-softcursor.txt. Default: 2 = underline. 3865 3866 vt.default_blu= [VT] 3867 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 3868 Change the default blue palette of the console. 3869 This is a 16-member array composed of values 3870 ranging from 0-255. 3871 3872 vt.default_grn= [VT] 3873 Format: <green0>,<green1>,<green2>,...,<green15> 3874 Change the default green palette of the console. 3875 This is a 16-member array composed of values 3876 ranging from 0-255. 3877 3878 vt.default_red= [VT] 3879 Format: <red0>,<red1>,<red2>,...,<red15> 3880 Change the default red palette of the console. 3881 This is a 16-member array composed of values 3882 ranging from 0-255. 3883 3884 vt.default_utf8= 3885 [VT] 3886 Format=<0|1> 3887 Set system-wide default UTF-8 mode for all tty's. 3888 Default is 1, i.e. UTF-8 mode is enabled for all 3889 newly opened terminals. 3890 3891 vt.global_cursor_default= 3892 [VT] 3893 Format=<-1|0|1> 3894 Set system-wide default for whether a cursor 3895 is shown on new VTs. Default is -1, 3896 i.e. cursors will be created by default unless 3897 overridden by individual drivers. 0 will hide 3898 cursors, 1 will display them. 3899 3900 vt.italic= [VT] Default color for italic text; 0-15. 3901 Default: 2 = green. 3902 3903 vt.underline= [VT] Default color for underlined text; 0-15. 3904 Default: 3 = cyan. 3905 3906 watchdog timers [HW,WDT] For information on watchdog timers, 3907 see Documentation/watchdog/watchdog-parameters.txt 3908 or other driver-specific files in the 3909 Documentation/watchdog/ directory. 3910 3911 workqueue.disable_numa 3912 By default, all work items queued to unbound 3913 workqueues are affine to the NUMA nodes they're 3914 issued on, which results in better behavior in 3915 general. If NUMA affinity needs to be disabled for 3916 whatever reason, this option can be used. Note 3917 that this also can be controlled per-workqueue for 3918 workqueues visible under /sys/bus/workqueue/. 3919 3920 workqueue.power_efficient 3921 Per-cpu workqueues are generally preferred because 3922 they show better performance thanks to cache 3923 locality; unfortunately, per-cpu workqueues tend to 3924 be more power hungry than unbound workqueues. 3925 3926 Enabling this makes the per-cpu workqueues which 3927 were observed to contribute significantly to power 3928 consumption unbound, leading to measurably lower 3929 power usage at the cost of small performance 3930 overhead. 3931 3932 The default value of this parameter is determined by 3933 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 3934 3935 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of 3936 default x2apic cluster mode on platforms 3937 supporting x2apic. 3938 3939 x86_intel_mid_timer= [X86-32,APBT] 3940 Choose timer option for x86 Intel MID platform. 3941 Two valid options are apbt timer only and lapic timer 3942 plus one apbt timer for broadcast timer. 3943 x86_intel_mid_timer=apbt_only | lapic_and_apbt 3944 3945 xen_emul_unplug= [HW,X86,XEN] 3946 Unplug Xen emulated devices 3947 Format: [unplug0,][unplug1] 3948 ide-disks -- unplug primary master IDE devices 3949 aux-ide-disks -- unplug non-primary-master IDE devices 3950 nics -- unplug network devices 3951 all -- unplug all emulated devices (NICs and IDE disks) 3952 unnecessary -- unplugging emulated devices is 3953 unnecessary even if the host did not respond to 3954 the unplug protocol 3955 never -- do not unplug even if version check succeeds 3956 3957 xen_nopvspin [X86,XEN] 3958 Disables the ticketlock slowpath using Xen PV 3959 optimizations. 3960 3961 xen_nopv [X86] 3962 Disables the PV optimizations forcing the HVM guest to 3963 run as generic HVM guest with no PV drivers. 3964 3965 xirc2ps_cs= [NET,PCMCIA] 3966 Format: 3967 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 3968 3969 ______________________________________________________________________ 3970 3971 TODO: 3972 3973 Add more DRM drivers.