1 Kernel Parameters 2 ~~~~~~~~~~~~~~~~~ 3 4The following is a consolidated list of the kernel parameters as implemented 5(mostly) by the __setup() macro and sorted into English Dictionary order 6(defined as ignoring all punctuation and sorting digits before letters in a 7case insensitive manner), and with descriptions where known. 8 9Module parameters for loadable modules are specified only as the 10parameter name with optional '=' and value as appropriate, such as: 11 12 modprobe usbcore blinkenlights=1 13 14Module parameters for modules that are built into the kernel image 15are specified on the kernel command line with the module name plus 16'.' plus parameter name, with '=' and value if appropriate, such as: 17 18 usbcore.blinkenlights=1 19 20Hyphens (dashes) and underscores are equivalent in parameter names, so 21 log_buf_len=1M print-fatal-signals=1 22can also be entered as 23 log-buf-len=1M print_fatal_signals=1 24 25 26This document may not be entirely up to date and comprehensive. The command 27"modinfo -p ${modulename}" shows a current list of all parameters of a loadable 28module. Loadable modules, after being loaded into the running kernel, also 29reveal their parameters in /sys/module/${modulename}/parameters/. Some of these 30parameters may be changed at runtime by the command 31"echo -n ${value} > /sys/module/${modulename}/parameters/${parm}". 32 33The parameters listed below are only valid if certain kernel build options were 34enabled and if respective hardware is present. The text in square brackets at 35the beginning of each description states the restrictions within which a 36parameter is applicable: 37 38 ACPI ACPI support is enabled. 39 AGP AGP (Accelerated Graphics Port) is enabled. 40 ALSA ALSA sound support is enabled. 41 APIC APIC support is enabled. 42 APM Advanced Power Management support is enabled. 43 ARM ARM architecture is enabled. 44 AVR32 AVR32 architecture is enabled. 45 AX25 Appropriate AX.25 support is enabled. 46 BLACKFIN Blackfin architecture is enabled. 47 DRM Direct Rendering Management support is enabled. 48 DYNAMIC_DEBUG Build in debug messages and enable them at runtime 49 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled 50 EFI EFI Partitioning (GPT) is enabled 51 EIDE EIDE/ATAPI support is enabled. 52 EVM Extended Verification Module 53 FB The frame buffer device is enabled. 54 FTRACE Function tracing enabled. 55 GCOV GCOV profiling is enabled. 56 HW Appropriate hardware is enabled. 57 IA-64 IA-64 architecture is enabled. 58 IMA Integrity measurement architecture is enabled. 59 IOSCHED More than one I/O scheduler is enabled. 60 IP_PNP IP DHCP, BOOTP, or RARP is enabled. 61 IPV6 IPv6 support is enabled. 62 ISAPNP ISA PnP code is enabled. 63 ISDN Appropriate ISDN support is enabled. 64 JOY Appropriate joystick support is enabled. 65 KGDB Kernel debugger support is enabled. 66 KVM Kernel Virtual Machine support is enabled. 67 LIBATA Libata driver is enabled 68 LP Printer support is enabled. 69 LOOP Loopback device support is enabled. 70 M68k M68k architecture is enabled. 71 These options have more detailed description inside of 72 Documentation/m68k/kernel-options.txt. 73 MCA MCA bus support is enabled. 74 MDA MDA console support is enabled. 75 MIPS MIPS architecture is enabled. 76 MOUSE Appropriate mouse support is enabled. 77 MSI Message Signaled Interrupts (PCI). 78 MTD MTD (Memory Technology Device) support is enabled. 79 NET Appropriate network support is enabled. 80 NUMA NUMA support is enabled. 81 NFS Appropriate NFS support is enabled. 82 OSS OSS sound support is enabled. 83 PV_OPS A paravirtualized kernel is enabled. 84 PARIDE The ParIDE (parallel port IDE) subsystem is enabled. 85 PARISC The PA-RISC architecture is enabled. 86 PCI PCI bus support is enabled. 87 PCIE PCI Express support is enabled. 88 PCMCIA The PCMCIA subsystem is enabled. 89 PNP Plug & Play support is enabled. 90 PPC PowerPC architecture is enabled. 91 PPT Parallel port support is enabled. 92 PS2 Appropriate PS/2 support is enabled. 93 RAM RAM disk support is enabled. 94 S390 S390 architecture is enabled. 95 SCSI Appropriate SCSI support is enabled. 96 A lot of drivers have their options described inside 97 the Documentation/scsi/ sub-directory. 98 SECURITY Different security models are enabled. 99 SELINUX SELinux support is enabled. 100 APPARMOR AppArmor support is enabled. 101 SERIAL Serial support is enabled. 102 SH SuperH architecture is enabled. 103 SMP The kernel is an SMP kernel. 104 SPARC Sparc architecture is enabled. 105 SWSUSP Software suspend (hibernation) is enabled. 106 SUSPEND System suspend states are enabled. 107 TPM TPM drivers are enabled. 108 TS Appropriate touchscreen support is enabled. 109 UMS USB Mass Storage support is enabled. 110 USB USB support is enabled. 111 USBHID USB Human Interface Device support is enabled. 112 V4L Video For Linux support is enabled. 113 VGA The VGA console has been enabled. 114 VT Virtual terminal support is enabled. 115 WDT Watchdog support is enabled. 116 XT IBM PC/XT MFM hard disk support is enabled. 117 X86-32 X86-32, aka i386 architecture is enabled. 118 X86-64 X86-64 architecture is enabled. 119 More X86-64 boot options can be found in 120 Documentation/x86/x86_64/boot-options.txt . 121 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64) 122 XEN Xen support is enabled 123 124In addition, the following text indicates that the option: 125 126 BUGS= Relates to possible processor bugs on the said processor. 127 KNL Is a kernel start-up parameter. 128 BOOT Is a boot loader parameter. 129 130Parameters denoted with BOOT are actually interpreted by the boot 131loader, and have no meaning to the kernel directly. 132Do not modify the syntax of boot loader parameters without extreme 133need or coordination with <Documentation/x86/boot.txt>. 134 135There are also arch-specific kernel-parameters not documented here. 136See for example <Documentation/x86/x86_64/boot-options.txt>. 137 138Note that ALL kernel parameters listed below are CASE SENSITIVE, and that 139a trailing = on the name of any parameter states that that parameter will 140be entered as an environment variable, whereas its absence indicates that 141it will appear as a kernel argument readable via /proc/cmdline by programs 142running once the system is up. 143 144The number of kernel parameters is not limited, but the length of the 145complete command line (parameters including spaces etc.) is limited to 146a fixed number of characters. This limit depends on the architecture 147and is between 256 and 4096 characters. It is defined in the file 148./include/asm/setup.h as COMMAND_LINE_SIZE. 149 150Finally, the [KMG] suffix is commonly described after a number of kernel 151parameter values. These 'K', 'M', and 'G' letters represent the _binary_ 152multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30 153bytes respectively. Such letter suffixes can also be entirely omitted. 154 155 156 acpi= [HW,ACPI,X86] 157 Advanced Configuration and Power Interface 158 Format: { force | off | strict | noirq | rsdt } 159 force -- enable ACPI if default was off 160 off -- disable ACPI if default was on 161 noirq -- do not use ACPI for IRQ routing 162 strict -- Be less tolerant of platforms that are not 163 strictly ACPI specification compliant. 164 rsdt -- prefer RSDT over (default) XSDT 165 copy_dsdt -- copy DSDT to memory 166 167 See also Documentation/power/runtime_pm.txt, pci=noacpi 168 169 acpi_rsdp= [ACPI,EFI,KEXEC] 170 Pass the RSDP address to the kernel, mostly used 171 on machines running EFI runtime service to boot the 172 second kernel for kdump. 173 174 acpi_apic_instance= [ACPI, IOAPIC] 175 Format: <int> 176 2: use 2nd APIC table, if available 177 1,0: use 1st APIC table 178 default: 0 179 180 acpi_backlight= [HW,ACPI] 181 acpi_backlight=vendor 182 acpi_backlight=video 183 If set to vendor, prefer vendor specific driver 184 (e.g. thinkpad_acpi, sony_acpi, etc.) instead 185 of the ACPI video.ko driver. 186 187 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG] 188 acpi.debug_level= [HW,ACPI,ACPI_DEBUG] 189 Format: <int> 190 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI 191 debug output. Bits in debug_layer correspond to a 192 _COMPONENT in an ACPI source file, e.g., 193 #define _COMPONENT ACPI_PCI_COMPONENT 194 Bits in debug_level correspond to a level in 195 ACPI_DEBUG_PRINT statements, e.g., 196 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ... 197 The debug_level mask defaults to "info". See 198 Documentation/acpi/debug.txt for more information about 199 debug layers and levels. 200 201 Enable processor driver info messages: 202 acpi.debug_layer=0x20000000 203 Enable PCI/PCI interrupt routing info messages: 204 acpi.debug_layer=0x400000 205 Enable AML "Debug" output, i.e., stores to the Debug 206 object while interpreting AML: 207 acpi.debug_layer=0xffffffff acpi.debug_level=0x2 208 Enable all messages related to ACPI hardware: 209 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff 210 211 Some values produce so much output that the system is 212 unusable. The "log_buf_len" parameter may be useful 213 if you need to capture more output. 214 215 acpi_irq_balance [HW,ACPI] 216 ACPI will balance active IRQs 217 default in APIC mode 218 219 acpi_irq_nobalance [HW,ACPI] 220 ACPI will not move active IRQs (default) 221 default in PIC mode 222 223 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA 224 Format: <irq>,<irq>... 225 226 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for 227 use by PCI 228 Format: <irq>,<irq>... 229 230 acpi_no_auto_ssdt [HW,ACPI] Disable automatic loading of SSDT 231 232 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS 233 Format: To spoof as Windows 98: ="Microsoft Windows" 234 235 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings 236 acpi_osi="string1" # add string1 -- only one string 237 acpi_osi="!string2" # remove built-in string2 238 acpi_osi= # disable all strings 239 240 acpi_pm_good [X86] 241 Override the pmtimer bug detection: force the kernel 242 to assume that this machine's pmtimer latches its value 243 and always returns good values. 244 245 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode 246 Format: { level | edge | high | low } 247 248 acpi_serialize [HW,ACPI] force serialization of AML methods 249 250 acpi_skip_timer_override [HW,ACPI] 251 Recognize and ignore IRQ0/pin2 Interrupt Override. 252 For broken nForce2 BIOS resulting in XT-PIC timer. 253 254 acpi_sleep= [HW,ACPI] Sleep options 255 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig, 256 old_ordering, nonvs, sci_force_enable } 257 See Documentation/power/video.txt for information on 258 s3_bios and s3_mode. 259 s3_beep is for debugging; it makes the PC's speaker beep 260 as soon as the kernel's real-mode entry point is called. 261 s4_nohwsig prevents ACPI hardware signature from being 262 used during resume from hibernation. 263 old_ordering causes the ACPI 1.0 ordering of the _PTS 264 control method, with respect to putting devices into 265 low power states, to be enforced (the ACPI 2.0 ordering 266 of _PTS is used by default). 267 nonvs prevents the kernel from saving/restoring the 268 ACPI NVS memory during suspend/hibernation and resume. 269 sci_force_enable causes the kernel to set SCI_EN directly 270 on resume from S1/S3 (which is against the ACPI spec, 271 but some broken systems don't work without it). 272 273 acpi_use_timer_override [HW,ACPI] 274 Use timer override. For some broken Nvidia NF5 boards 275 that require a timer override, but don't have HPET 276 277 acpi_enforce_resources= [ACPI] 278 { strict | lax | no } 279 Check for resource conflicts between native drivers 280 and ACPI OperationRegions (SystemIO and SystemMemory 281 only). IO ports and memory declared in ACPI might be 282 used by the ACPI subsystem in arbitrary AML code and 283 can interfere with legacy drivers. 284 strict (default): access to resources claimed by ACPI 285 is denied; legacy drivers trying to access reserved 286 resources will fail to bind to device using them. 287 lax: access to resources claimed by ACPI is allowed; 288 legacy drivers trying to access reserved resources 289 will bind successfully but a warning message is logged. 290 no: ACPI OperationRegions are not marked as reserved, 291 no further checks are performed. 292 293 add_efi_memmap [EFI; X86] Include EFI memory map in 294 kernel's map of available physical RAM. 295 296 agp= [AGP] 297 { off | try_unsupported } 298 off: disable AGP support 299 try_unsupported: try to drive unsupported chipsets 300 (may crash computer or cause data corruption) 301 302 ALSA [HW,ALSA] 303 See Documentation/sound/alsa/alsa-parameters.txt 304 305 alignment= [KNL,ARM] 306 Allow the default userspace alignment fault handler 307 behaviour to be specified. Bit 0 enables warnings, 308 bit 1 enables fixups, and bit 2 sends a segfault. 309 310 align_va_addr= [X86-64] 311 Align virtual addresses by clearing slice [14:12] when 312 allocating a VMA at process creation time. This option 313 gives you up to 3% performance improvement on AMD F15h 314 machines (where it is enabled by default) for a 315 CPU-intensive style benchmark, and it can vary highly in 316 a microbenchmark depending on workload and compiler. 317 318 32: only for 32-bit processes 319 64: only for 64-bit processes 320 on: enable for both 32- and 64-bit processes 321 off: disable for both 32- and 64-bit processes 322 323 amd_iommu= [HW,X86-64] 324 Pass parameters to the AMD IOMMU driver in the system. 325 Possible values are: 326 fullflush - enable flushing of IO/TLB entries when 327 they are unmapped. Otherwise they are 328 flushed before they will be reused, which 329 is a lot of faster 330 off - do not initialize any AMD IOMMU found in 331 the system 332 force_isolation - Force device isolation for all 333 devices. The IOMMU driver is not 334 allowed anymore to lift isolation 335 requirements as needed. This option 336 does not override iommu=pt 337 338 amijoy.map= [HW,JOY] Amiga joystick support 339 Map of devices attached to JOY0DAT and JOY1DAT 340 Format: <a>,<b> 341 See also Documentation/input/joystick.txt 342 343 analog.map= [HW,JOY] Analog joystick and gamepad support 344 Specifies type or capabilities of an analog joystick 345 connected to one of 16 gameports 346 Format: <type1>,<type2>,..<type16> 347 348 apc= [HW,SPARC] 349 Power management functions (SPARCstation-4/5 + deriv.) 350 Format: noidle 351 Disable APC CPU standby support. SPARCstation-Fox does 352 not play well with APC CPU idle - disable it if you have 353 APC and your system crashes randomly. 354 355 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller 356 Change the output verbosity whilst booting 357 Format: { quiet (default) | verbose | debug } 358 Change the amount of debugging information output 359 when initialising the APIC and IO-APIC components. 360 361 autoconf= [IPV6] 362 See Documentation/networking/ipv6.txt. 363 364 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller 365 Limit apic dumping. The parameter defines the maximal 366 number of local apics being dumped. Also it is possible 367 to set it to "all" by meaning -- no limit here. 368 Format: { 1 (default) | 2 | ... | all }. 369 The parameter valid if only apic=debug or 370 apic=verbose is specified. 371 Example: apic=debug show_lapic=all 372 373 apm= [APM] Advanced Power Management 374 See header of arch/x86/kernel/apm_32.c. 375 376 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards 377 Format: <io>,<irq>,<nodeID> 378 379 ataflop= [HW,M68k] 380 381 atarimouse= [HW,MOUSE] Atari Mouse 382 383 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess, 384 EzKey and similar keyboards 385 386 atkbd.reset= [HW] Reset keyboard during initialization 387 388 atkbd.set= [HW] Select keyboard code set 389 Format: <int> (2 = AT (default), 3 = PS/2) 390 391 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar 392 keyboards 393 394 atkbd.softraw= [HW] Choose between synthetic and real raw mode 395 Format: <bool> (0 = real, 1 = synthetic (default)) 396 397 atkbd.softrepeat= [HW] 398 Use software keyboard repeat 399 400 autotest [IA-64] 401 402 baycom_epp= [HW,AX25] 403 Format: <io>,<mode> 404 405 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem 406 Format: <io>,<mode> 407 See header of drivers/net/hamradio/baycom_par.c. 408 409 baycom_ser_fdx= [HW,AX25] 410 BayCom Serial Port AX.25 Modem (Full Duplex Mode) 411 Format: <io>,<irq>,<mode>[,<baud>] 412 See header of drivers/net/hamradio/baycom_ser_fdx.c. 413 414 baycom_ser_hdx= [HW,AX25] 415 BayCom Serial Port AX.25 Modem (Half Duplex Mode) 416 Format: <io>,<irq>,<mode> 417 See header of drivers/net/hamradio/baycom_ser_hdx.c. 418 419 boot_delay= Milliseconds to delay each printk during boot. 420 Values larger than 10 seconds (10000) are changed to 421 no delay (0). 422 Format: integer 423 424 bootmem_debug [KNL] Enable bootmem allocator debug messages. 425 426 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards) 427 bttv.radio= Most important insmod options are available as 428 kernel args too. 429 bttv.pll= See Documentation/video4linux/bttv/Insmod-options 430 bttv.tuner= 431 432 bulk_remove=off [PPC] This parameter disables the use of the pSeries 433 firmware feature for flushing multiple hpte entries 434 at a time. 435 436 c101= [NET] Moxa C101 synchronous serial card 437 438 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection. 439 Sometimes CPU hardware bugs make them report the cache 440 size incorrectly. The kernel will attempt work arounds 441 to fix known problems, but for some CPUs it is not 442 possible to determine what the correct size should be. 443 This option provides an override for these situations. 444 445 capability.disable= 446 [SECURITY] Disable capabilities. This would normally 447 be used only if an alternative security model is to be 448 configured. Potentially dangerous and should only be 449 used if you are entirely sure of the consequences. 450 451 ccw_timeout_log [S390] 452 See Documentation/s390/CommonIO for details. 453 454 cgroup_disable= [KNL] Disable a particular controller 455 Format: {name of the controller(s) to disable} 456 {Currently supported controllers - "memory"} 457 458 checkreqprot [SELINUX] Set initial checkreqprot flag value. 459 Format: { "0" | "1" } 460 See security/selinux/Kconfig help text. 461 0 -- check protection applied by kernel (includes 462 any implied execute protection). 463 1 -- check protection requested by application. 464 Default value is set via a kernel config option. 465 Value can be changed at runtime via 466 /selinux/checkreqprot. 467 468 cio_ignore= [S390] 469 See Documentation/s390/CommonIO for details. 470 471 clock= [BUGS=X86-32, HW] gettimeofday clocksource override. 472 [Deprecated] 473 Forces specified clocksource (if available) to be used 474 when calculating gettimeofday(). If specified 475 clocksource is not available, it defaults to PIT. 476 Format: { pit | tsc | cyclone | pmtmr } 477 478 clocksource= Override the default clocksource 479 Format: <string> 480 Override the default clocksource and use the clocksource 481 with the name specified. 482 Some clocksource names to choose from, depending on 483 the platform: 484 [all] jiffies (this is the base, fallback clocksource) 485 [ACPI] acpi_pm 486 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2, 487 pxa_timer,timer3,32k_counter,timer0_1 488 [AVR32] avr32 489 [X86-32] pit,hpet,tsc; 490 scx200_hrt on Geode; cyclone on IBM x440 491 [MIPS] MIPS 492 [PARISC] cr16 493 [S390] tod 494 [SH] SuperH 495 [SPARC64] tick 496 [X86-64] hpet,tsc 497 498 clearcpuid=BITNUM [X86] 499 Disable CPUID feature X for the kernel. See 500 arch/x86/include/asm/cpufeature.h for the valid bit 501 numbers. Note the Linux specific bits are not necessarily 502 stable over kernel options, but the vendor specific 503 ones should be. 504 Also note that user programs calling CPUID directly 505 or using the feature without checking anything 506 will still see it. This just prevents it from 507 being used by the kernel or shown in /proc/cpuinfo. 508 Also note the kernel might malfunction if you disable 509 some critical bits. 510 511 cmo_free_hint= [PPC] Format: { yes | no } 512 Specify whether pages are marked as being inactive 513 when they are freed. This is used in CMO environments 514 to determine OS memory pressure for page stealing by 515 a hypervisor. 516 Default: yes 517 518 code_bytes [X86] How many bytes of object code to print 519 in an oops report. 520 Range: 0 - 8192 521 Default: 64 522 523 com20020= [HW,NET] ARCnet - COM20020 chipset 524 Format: 525 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]] 526 527 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers) 528 Format: <io>[,<irq>] 529 530 com90xx= [HW,NET] 531 ARCnet - COM90xx chipset (memory-mapped buffers) 532 Format: <io>[,<irq>[,<memstart>]] 533 534 condev= [HW,S390] console device 535 conmode= 536 537 console= [KNL] Output console device and options. 538 539 tty<n> Use the virtual console device <n>. 540 541 ttyS<n>[,options] 542 ttyUSB0[,options] 543 Use the specified serial port. The options are of 544 the form "bbbbpnf", where "bbbb" is the baud rate, 545 "p" is parity ("n", "o", or "e"), "n" is number of 546 bits, and "f" is flow control ("r" for RTS or 547 omit it). Default is "9600n8". 548 549 See Documentation/serial-console.txt for more 550 information. See 551 Documentation/networking/netconsole.txt for an 552 alternative. 553 554 uart[8250],io,<addr>[,options] 555 uart[8250],mmio,<addr>[,options] 556 Start an early, polled-mode console on the 8250/16550 557 UART at the specified I/O port or MMIO address, 558 switching to the matching ttyS device later. The 559 options are the same as for ttyS, above. 560 hvc<n> Use the hypervisor console device <n>. This is for 561 both Xen and PowerPC hypervisors. 562 563 If the device connected to the port is not a TTY but a braille 564 device, prepend "brl," before the device type, for instance 565 console=brl,ttyS0 566 For now, only VisioBraille is supported. 567 568 consoleblank= [KNL] The console blank (screen saver) timeout in 569 seconds. Defaults to 10*60 = 10mins. A value of 0 570 disables the blank timer. 571 572 coredump_filter= 573 [KNL] Change the default value for 574 /proc/<pid>/coredump_filter. 575 See also Documentation/filesystems/proc.txt. 576 577 cpuidle.off=1 [CPU_IDLE] 578 disable the cpuidle sub-system 579 580 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver 581 Format: 582 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] 583 584 crashkernel=size[KMG][@offset[KMG]] 585 [KNL] Using kexec, Linux can switch to a 'crash kernel' 586 upon panic. This parameter reserves the physical 587 memory region [offset, offset + size] for that kernel 588 image. If '@offset' is omitted, then a suitable offset 589 is selected automatically. Check 590 Documentation/kdump/kdump.txt for further details. 591 592 crashkernel=range1:size1[,range2:size2,...][@offset] 593 [KNL] Same as above, but depends on the memory 594 in the running system. The syntax of range is 595 start-[end] where start and end are both 596 a memory unit (amount[KMG]). See also 597 Documentation/kdump/kdump.txt for an example. 598 599 cs89x0_dma= [HW,NET] 600 Format: <dma> 601 602 cs89x0_media= [HW,NET] 603 Format: { rj45 | aui | bnc } 604 605 dasd= [HW,NET] 606 See header of drivers/s390/block/dasd_devmap.c. 607 608 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port 609 (one device per port) 610 Format: <port#>,<type> 611 See also Documentation/input/joystick-parport.txt 612 613 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot 614 time. See Documentation/dynamic-debug-howto.txt for 615 details. 616 617 debug [KNL] Enable kernel debugging (events log level). 618 619 debug_locks_verbose= 620 [KNL] verbose self-tests 621 Format=<0|1> 622 Print debugging info while doing the locking API 623 self-tests. 624 We default to 0 (no extra messages), setting it to 625 1 will print _a lot_ more information - normally 626 only useful to kernel developers. 627 628 debug_objects [KNL] Enable object debugging 629 630 no_debug_objects 631 [KNL] Disable object debugging 632 633 debug_guardpage_minorder= 634 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this 635 parameter allows control of the order of pages that will 636 be intentionally kept free (and hence protected) by the 637 buddy allocator. Bigger value increase the probability 638 of catching random memory corruption, but reduce the 639 amount of memory for normal system use. The maximum 640 possible value is MAX_ORDER/2. Setting this parameter 641 to 1 or 2 should be enough to identify most random 642 memory corruption problems caused by bugs in kernel or 643 driver code when a CPU writes to (or reads from) a 644 random memory location. Note that there exists a class 645 of memory corruptions problems caused by buggy H/W or 646 F/W or by drivers badly programing DMA (basically when 647 memory is written at bus level and the CPU MMU is 648 bypassed) which are not detectable by 649 CONFIG_DEBUG_PAGEALLOC, hence this option will not help 650 tracking down these problems. 651 652 debugpat [X86] Enable PAT debugging 653 654 decnet.addr= [HW,NET] 655 Format: <area>[,<node>] 656 See also Documentation/networking/decnet.txt. 657 658 default_hugepagesz= 659 [same as hugepagesz=] The size of the default 660 HugeTLB page size. This is the size represented by 661 the legacy /proc/ hugepages APIs, used for SHM, and 662 default size when mounting hugetlbfs filesystems. 663 Defaults to the default architecture's huge page size 664 if not specified. 665 666 dhash_entries= [KNL] 667 Set number of hash buckets for dentry cache. 668 669 digi= [HW,SERIAL] 670 IO parameters + enable/disable command. 671 672 digiepca= [HW,SERIAL] 673 See drivers/char/README.epca and 674 Documentation/serial/digiepca.txt. 675 676 disable= [IPV6] 677 See Documentation/networking/ipv6.txt. 678 679 disable_ddw [PPC/PSERIES] 680 Disable Dynamic DMA Window support. Use this if 681 to workaround buggy firmware. 682 683 disable_ipv6= [IPV6] 684 See Documentation/networking/ipv6.txt. 685 686 disable_mtrr_cleanup [X86] 687 The kernel tries to adjust MTRR layout from continuous 688 to discrete, to make X server driver able to add WB 689 entry later. This parameter disables that. 690 691 disable_mtrr_trim [X86, Intel and AMD only] 692 By default the kernel will trim any uncacheable 693 memory out of your available memory pool based on 694 MTRR settings. This parameter disables that behavior, 695 possibly causing your machine to run very slowly. 696 697 disable_timer_pin_1 [X86] 698 Disable PIN 1 of APIC timer 699 Can be useful to work around chipset bugs. 700 701 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, 702 this option disables the debugging code at boot. 703 704 dma_debug_entries=<number> 705 This option allows to tune the number of preallocated 706 entries for DMA-API debugging code. One entry is 707 required per DMA-API allocation. Use this if the 708 DMA-API debugging code disables itself because the 709 architectural default is too low. 710 711 dma_debug_driver=<driver_name> 712 With this option the DMA-API debugging driver 713 filter feature can be enabled at boot time. Just 714 pass the driver to filter for as the parameter. 715 The filter can be disabled or changed to another 716 driver later using sysfs. 717 718 drm_kms_helper.edid_firmware=[<connector>:]<file> 719 Broken monitors, graphic adapters and KVMs may 720 send no or incorrect EDID data sets. This parameter 721 allows to specify an EDID data set in the 722 /lib/firmware directory that is used instead. 723 Generic built-in EDID data sets are used, if one of 724 edid/1024x768.bin, edid/1280x1024.bin, 725 edid/1680x1050.bin, or edid/1920x1080.bin is given 726 and no file with the same name exists. Details and 727 instructions how to build your own EDID data are 728 available in Documentation/EDID/HOWTO.txt. An EDID 729 data set will only be used for a particular connector, 730 if its name and a colon are prepended to the EDID 731 name. 732 733 dscc4.setup= [NET] 734 735 earlycon= [KNL] Output early console device and options. 736 uart[8250],io,<addr>[,options] 737 uart[8250],mmio,<addr>[,options] 738 uart[8250],mmio32,<addr>[,options] 739 Start an early, polled-mode console on the 8250/16550 740 UART at the specified I/O port or MMIO address. 741 MMIO inter-register address stride is either 8-bit 742 (mmio) or 32-bit (mmio32). 743 The options are the same as for ttyS, above. 744 745 earlyprintk= [X86,SH,BLACKFIN] 746 earlyprintk=vga 747 earlyprintk=xen 748 earlyprintk=serial[,ttySn[,baudrate]] 749 earlyprintk=ttySn[,baudrate] 750 earlyprintk=dbgp[debugController#] 751 752 Append ",keep" to not disable it when the real console 753 takes over. 754 755 Only vga or serial or usb debug port at a time. 756 757 Currently only ttyS0 and ttyS1 are supported. 758 759 Interaction with the standard serial driver is not 760 very good. 761 762 The VGA output is eventually overwritten by the real 763 console. 764 765 The xen output can only be used by Xen PV guests. 766 767 ekgdboc= [X86,KGDB] Allow early kernel console debugging 768 ekgdboc=kbd 769 770 This is designed to be used in conjunction with 771 the boot argument: earlyprintk=vga 772 773 edd= [EDD] 774 Format: {"off" | "on" | "skip[mbr]"} 775 776 eisa_irq_edge= [PARISC,HW] 777 See header of drivers/parisc/eisa.c. 778 779 elanfreq= [X86-32] 780 See comment before function elanfreq_setup() in 781 arch/x86/kernel/cpu/cpufreq/elanfreq.c. 782 783 elevator= [IOSCHED] 784 Format: {"cfq" | "deadline" | "noop"} 785 See Documentation/block/cfq-iosched.txt and 786 Documentation/block/deadline-iosched.txt for details. 787 788 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390] 789 Specifies physical address of start of kernel core 790 image elf header and optionally the size. Generally 791 kexec loader will pass this option to capture kernel. 792 See Documentation/kdump/kdump.txt for details. 793 794 enable_mtrr_cleanup [X86] 795 The kernel tries to adjust MTRR layout from continuous 796 to discrete, to make X server driver able to add WB 797 entry later. This parameter enables that. 798 799 enable_timer_pin_1 [X86] 800 Enable PIN 1 of APIC timer 801 Can be useful to work around chipset bugs 802 (in particular on some ATI chipsets). 803 The kernel tries to set a reasonable default. 804 805 enforcing [SELINUX] Set initial enforcing status. 806 Format: {"0" | "1"} 807 See security/selinux/Kconfig help text. 808 0 -- permissive (log only, no denials). 809 1 -- enforcing (deny and log). 810 Default value is 0. 811 Value can be changed at runtime via /selinux/enforce. 812 813 erst_disable [ACPI] 814 Disable Error Record Serialization Table (ERST) 815 support. 816 817 ether= [HW,NET] Ethernet cards parameters 818 This option is obsoleted by the "netdev=" option, which 819 has equivalent usage. See its documentation for details. 820 821 evm= [EVM] 822 Format: { "fix" } 823 Permit 'security.evm' to be updated regardless of 824 current integrity status. 825 826 failslab= 827 fail_page_alloc= 828 fail_make_request=[KNL] 829 General fault injection mechanism. 830 Format: <interval>,<probability>,<space>,<times> 831 See also Documentation/fault-injection/. 832 833 floppy= [HW] 834 See Documentation/blockdev/floppy.txt. 835 836 force_pal_cache_flush 837 [IA-64] Avoid check_sal_cache_flush which may hang on 838 buggy SAL_CACHE_FLUSH implementations. Using this 839 parameter will force ia64_sal_cache_flush to call 840 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH. 841 842 ftrace=[tracer] 843 [FTRACE] will set and start the specified tracer 844 as early as possible in order to facilitate early 845 boot debugging. 846 847 ftrace_dump_on_oops[=orig_cpu] 848 [FTRACE] will dump the trace buffers on oops. 849 If no parameter is passed, ftrace will dump 850 buffers of all CPUs, but if you pass orig_cpu, it will 851 dump only the buffer of the CPU that triggered the 852 oops. 853 854 ftrace_filter=[function-list] 855 [FTRACE] Limit the functions traced by the function 856 tracer at boot up. function-list is a comma separated 857 list of functions. This list can be changed at run 858 time by the set_ftrace_filter file in the debugfs 859 tracing directory. 860 861 ftrace_notrace=[function-list] 862 [FTRACE] Do not trace the functions specified in 863 function-list. This list can be changed at run time 864 by the set_ftrace_notrace file in the debugfs 865 tracing directory. 866 867 ftrace_graph_filter=[function-list] 868 [FTRACE] Limit the top level callers functions traced 869 by the function graph tracer at boot up. 870 function-list is a comma separated list of functions 871 that can be changed at run time by the 872 set_graph_function file in the debugfs tracing directory. 873 874 gamecon.map[2|3]= 875 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 876 support via parallel port (up to 5 devices per port) 877 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 878 See also Documentation/input/joystick-parport.txt 879 880 gamma= [HW,DRM] 881 882 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART 883 Format: off | on 884 default: on 885 886 gcov_persist= [GCOV] When non-zero (default), profiling data for 887 kernel modules is saved and remains accessible via 888 debugfs, even when the module is unloaded/reloaded. 889 When zero, profiling data is discarded and associated 890 debugfs files are removed at module unload time. 891 892 gpt [EFI] Forces disk with valid GPT signature but 893 invalid Protective MBR to be treated as GPT. 894 895 hashdist= [KNL,NUMA] Large hashes allocated during boot 896 are distributed across NUMA nodes. Defaults on 897 for 64-bit NUMA, off otherwise. 898 Format: 0 | 1 (for off | on) 899 900 hcl= [IA-64] SGI's Hardware Graph compatibility layer 901 902 hd= [EIDE] (E)IDE hard drive subsystem geometry 903 Format: <cyl>,<head>,<sect> 904 905 hest_disable [ACPI] 906 Disable Hardware Error Source Table (HEST) support; 907 corresponding firmware-first mode error processing 908 logic will be disabled. 909 910 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact 911 size of <nn>. This works even on boxes that have no 912 highmem otherwise. This also works to reduce highmem 913 size on bigger boxes. 914 915 highres= [KNL] Enable/disable high resolution timer mode. 916 Valid parameters: "on", "off" 917 Default: "on" 918 919 hisax= [HW,ISDN] 920 See Documentation/isdn/README.HiSax. 921 922 hlt [BUGS=ARM,SH] 923 924 hpet= [X86-32,HPET] option to control HPET usage 925 Format: { enable (default) | disable | force | 926 verbose } 927 disable: disable HPET and use PIT instead 928 force: allow force enabled of undocumented chips (ICH4, 929 VIA, nVidia) 930 verbose: show contents of HPET registers during setup 931 932 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot. 933 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages. 934 On x86-64 and powerpc, this option can be specified 935 multiple times interleaved with hugepages= to reserve 936 huge pages of different sizes. Valid pages sizes on 937 x86-64 are 2M (when the CPU supports "pse") and 1G 938 (when the CPU supports the "pdpe1gb" cpuinfo flag) 939 Note that 1GB pages can only be allocated at boot time 940 using hugepages= and not freed afterwards. 941 942 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 943 terminal devices. Valid values: 0..8 944 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 945 If specified, z/VM IUCV HVC accepts connections 946 from listed z/VM user IDs only. 947 948 keep_bootcon [KNL] 949 Do not unregister boot console at start. This is only 950 useful for debugging when something happens in the window 951 between unregistering the boot console and initializing 952 the real console. 953 954 i2c_bus= [HW] Override the default board specific I2C bus speed 955 or register an additional I2C bus that is not 956 registered from board initialization code. 957 Format: 958 <bus_id>,<clkrate> 959 960 i8042.debug [HW] Toggle i8042 debug mode 961 i8042.direct [HW] Put keyboard port into non-translated mode 962 i8042.dumbkbd [HW] Pretend that controller can only read data from 963 keyboard and cannot control its state 964 (Don't attempt to blink the leds) 965 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 966 i8042.nokbd [HW] Don't check/create keyboard port 967 i8042.noloop [HW] Disable the AUX Loopback command while probing 968 for the AUX port 969 i8042.nomux [HW] Don't check presence of an active multiplexing 970 controller 971 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 972 controllers 973 i8042.notimeout [HW] Ignore timeout condition signalled by controller 974 i8042.reset [HW] Reset the controller during init and cleanup 975 i8042.unlock [HW] Unlock (ignore) the keylock 976 977 i810= [HW,DRM] 978 979 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data 980 indicates that the driver is running on unsupported 981 hardware. 982 i8k.force [HW] Activate i8k driver even if SMM BIOS signature 983 does not match list of supported models. 984 i8k.power_status 985 [HW] Report power status in /proc/i8k 986 (disabled by default) 987 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN 988 capability is set. 989 990 icn= [HW,ISDN] 991 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]] 992 993 ide-core.nodma= [HW] (E)IDE subsystem 994 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc 995 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr 996 .cdrom .chs .ignore_cable are additional options 997 See Documentation/ide/ide.txt. 998 999 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem 1000 Claim all unknown PCI IDE storage controllers. 1001 1002 idle= [X86] 1003 Format: idle=poll, idle=mwait, idle=halt, idle=nomwait 1004 Poll forces a polling idle loop that can slightly 1005 improve the performance of waking up a idle CPU, but 1006 will use a lot of power and make the system run hot. 1007 Not recommended. 1008 idle=mwait: On systems which support MONITOR/MWAIT but 1009 the kernel chose to not use it because it doesn't save 1010 as much power as a normal idle loop, use the 1011 MONITOR/MWAIT idle loop anyways. Performance should be 1012 the same as idle=poll. 1013 idle=halt: Halt is forced to be used for CPU idle. 1014 In such case C2/C3 won't be used again. 1015 idle=nomwait: Disable mwait for CPU C-states 1016 1017 ignore_loglevel [KNL] 1018 Ignore loglevel setting - this will print /all/ 1019 kernel messages to the console. Useful for debugging. 1020 We also add it as printk module parameter, so users 1021 could change it dynamically, usually by 1022 /sys/module/printk/parameters/ignore_loglevel. 1023 1024 ihash_entries= [KNL] 1025 Set number of hash buckets for inode cache. 1026 1027 ima_audit= [IMA] 1028 Format: { "0" | "1" } 1029 0 -- integrity auditing messages. (Default) 1030 1 -- enable informational integrity auditing messages. 1031 1032 ima_hash= [IMA] 1033 Format: { "sha1" | "md5" } 1034 default: "sha1" 1035 1036 ima_tcb [IMA] 1037 Load a policy which meets the needs of the Trusted 1038 Computing Base. This means IMA will measure all 1039 programs exec'd, files mmap'd for exec, and all files 1040 opened for read by uid=0. 1041 1042 init= [KNL] 1043 Format: <full_path> 1044 Run specified binary instead of /sbin/init as init 1045 process. 1046 1047 initcall_debug [KNL] Trace initcalls as they are executed. Useful 1048 for working out where the kernel is dying during 1049 startup. 1050 1051 initrd= [BOOT] Specify the location of the initial ramdisk 1052 1053 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 1054 Format: <irq> 1055 1056 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 1057 on 1058 Enable intel iommu driver. 1059 off 1060 Disable intel iommu driver. 1061 igfx_off [Default Off] 1062 By default, gfx is mapped as normal device. If a gfx 1063 device has a dedicated DMAR unit, the DMAR unit is 1064 bypassed by not enabling DMAR with this option. In 1065 this case, gfx device will use physical address for 1066 DMA. 1067 forcedac [x86_64] 1068 With this option iommu will not optimize to look 1069 for io virtual address below 32-bit forcing dual 1070 address cycle on pci bus for cards supporting greater 1071 than 32-bit addressing. The default is to look 1072 for translation below 32-bit and if not available 1073 then look in the higher range. 1074 strict [Default Off] 1075 With this option on every unmap_single operation will 1076 result in a hardware IOTLB flush operation as opposed 1077 to batching them for performance. 1078 sp_off [Default Off] 1079 By default, super page will be supported if Intel IOMMU 1080 has the capability. With this option, super page will 1081 not be supported. 1082 1083 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 1084 0 disables intel_idle and fall back on acpi_idle. 1085 1 to 6 specify maximum depth of C-state. 1086 1087 intremap= [X86-64, Intel-IOMMU] 1088 on enable Interrupt Remapping (default) 1089 off disable Interrupt Remapping 1090 nosid disable Source ID checking 1091 no_x2apic_optout 1092 BIOS x2APIC opt-out request will be ignored 1093 1094 iomem= Disable strict checking of access to MMIO memory 1095 strict regions from userspace. 1096 relaxed 1097 1098 iommu= [x86] 1099 off 1100 force 1101 noforce 1102 biomerge 1103 panic 1104 nopanic 1105 merge 1106 nomerge 1107 forcesac 1108 soft 1109 pt [x86, IA-64] 1110 group_mf [x86, IA-64] 1111 1112 1113 io7= [HW] IO7 for Marvel based alpha systems 1114 See comment before marvel_specify_io7 in 1115 arch/alpha/kernel/core_marvel.c. 1116 1117 io_delay= [X86] I/O delay method 1118 0x80 1119 Standard port 0x80 based delay 1120 0xed 1121 Alternate port 0xed based delay (needed on some systems) 1122 udelay 1123 Simple two microseconds delay 1124 none 1125 No delay 1126 1127 ip= [IP_PNP] 1128 See Documentation/filesystems/nfs/nfsroot.txt. 1129 1130 ip2= [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards 1131 See comment before ip2_setup() in 1132 drivers/char/ip2/ip2base.c. 1133 1134 irqfixup [HW] 1135 When an interrupt is not handled search all handlers 1136 for it. Intended to get systems with badly broken 1137 firmware running. 1138 1139 irqpoll [HW] 1140 When an interrupt is not handled search all handlers 1141 for it. Also check all handlers each timer 1142 interrupt. Intended to get systems with badly broken 1143 firmware running. 1144 1145 isapnp= [ISAPNP] 1146 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 1147 1148 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler. 1149 Format: 1150 <cpu number>,...,<cpu number> 1151 or 1152 <cpu number>-<cpu number> 1153 (must be a positive range in ascending order) 1154 or a mixture 1155 <cpu number>,...,<cpu number>-<cpu number> 1156 1157 This option can be used to specify one or more CPUs 1158 to isolate from the general SMP balancing and scheduling 1159 algorithms. You can move a process onto or off an 1160 "isolated" CPU via the CPU affinity syscalls or cpuset. 1161 <cpu number> begins at 0 and the maximum value is 1162 "number of CPUs in system - 1". 1163 1164 This option is the preferred way to isolate CPUs. The 1165 alternative -- manually setting the CPU mask of all 1166 tasks in the system -- can cause problems and 1167 suboptimal load balancer performance. 1168 1169 iucv= [HW,NET] 1170 1171 js= [HW,JOY] Analog joystick 1172 See Documentation/input/joystick.txt. 1173 1174 keepinitrd [HW,ARM] 1175 1176 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter 1177 specifies the amount of memory usable by the kernel 1178 for non-movable allocations. The requested amount is 1179 spread evenly throughout all nodes in the system. The 1180 remaining memory in each node is used for Movable 1181 pages. In the event, a node is too small to have both 1182 kernelcore and Movable pages, kernelcore pages will 1183 take priority and other nodes will have a larger number 1184 of kernelcore pages. The Movable zone is used for the 1185 allocation of pages that may be reclaimed or moved 1186 by the page migration subsystem. This means that 1187 HugeTLB pages may not be allocated from this zone. 1188 Note that allocations like PTEs-from-HighMem still 1189 use the HighMem zone if it exists, and the Normal 1190 zone if it does not. 1191 1192 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port. 1193 Format: <Controller#>[,poll interval] 1194 The controller # is the number of the ehci usb debug 1195 port as it is probed via PCI. The poll interval is 1196 optional and is the number seconds in between 1197 each poll cycle to the debug port in case you need 1198 the functionality for interrupting the kernel with 1199 gdb or control-c on the dbgp connection. When 1200 not using this parameter you use sysrq-g to break into 1201 the kernel debugger. 1202 1203 kgdboc= [KGDB,HW] kgdb over consoles. 1204 Requires a tty driver that supports console polling, 1205 or a supported polling keyboard driver (non-usb). 1206 Serial only format: <serial_device>[,baud] 1207 keyboard only format: kbd 1208 keyboard and serial format: kbd,<serial_device>[,baud] 1209 Optional Kernel mode setting: 1210 kms, kbd format: kms,kbd 1211 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 1212 1213 kgdbwait [KGDB] Stop kernel execution and enter the 1214 kernel debugger at the earliest opportunity. 1215 1216 kmac= [MIPS] korina ethernet MAC address. 1217 Configure the RouterBoard 532 series on-chip 1218 Ethernet adapter MAC address. 1219 1220 kmemleak= [KNL] Boot-time kmemleak enable/disable 1221 Valid arguments: on, off 1222 Default: on 1223 1224 kstack=N [X86] Print N words from the kernel stack 1225 in oops dumps. 1226 1227 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 1228 Default is 0 (don't ignore, but inject #GP) 1229 1230 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit 1231 KVM MMU at runtime. 1232 Default is 0 (off) 1233 1234 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM. 1235 Default is 1 (enabled) 1236 1237 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU) 1238 for all guests. 1239 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode. 1240 1241 kvm-intel.ept= [KVM,Intel] Disable extended page tables 1242 (virtualized MMU) support on capable Intel chips. 1243 Default is 1 (enabled) 1244 1245 kvm-intel.emulate_invalid_guest_state= 1246 [KVM,Intel] Enable emulation of invalid guest states 1247 Default is 0 (disabled) 1248 1249 kvm-intel.flexpriority= 1250 [KVM,Intel] Disable FlexPriority feature (TPR shadow). 1251 Default is 1 (enabled) 1252 1253 kvm-intel.nested= 1254 [KVM,Intel] Enable VMX nesting (nVMX). 1255 Default is 0 (disabled) 1256 1257 kvm-intel.unrestricted_guest= 1258 [KVM,Intel] Disable unrestricted guest feature 1259 (virtualized real and unpaged mode) on capable 1260 Intel chips. Default is 1 (enabled) 1261 1262 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification 1263 feature (tagged TLBs) on capable Intel chips. 1264 Default is 1 (enabled) 1265 1266 l2cr= [PPC] 1267 1268 l3cr= [PPC] 1269 1270 lapic [X86-32,APIC] Enable the local APIC even if BIOS 1271 disabled it. 1272 1273 lapic_timer_c2_ok [X86,APIC] trust the local apic timer 1274 in C2 power state. 1275 1276 libata.dma= [LIBATA] DMA control 1277 libata.dma=0 Disable all PATA and SATA DMA 1278 libata.dma=1 PATA and SATA Disk DMA only 1279 libata.dma=2 ATAPI (CDROM) DMA only 1280 libata.dma=4 Compact Flash DMA only 1281 Combinations also work, so libata.dma=3 enables DMA 1282 for disks and CDROMs, but not CFs. 1283 1284 libata.ignore_hpa= [LIBATA] Ignore HPA limit 1285 libata.ignore_hpa=0 keep BIOS limits (default) 1286 libata.ignore_hpa=1 ignore limits, using full disk 1287 1288 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 1289 when set. 1290 Format: <int> 1291 1292 libata.force= [LIBATA] Force configurations. The format is comma 1293 separated list of "[ID:]VAL" where ID is 1294 PORT[.DEVICE]. PORT and DEVICE are decimal numbers 1295 matching port, link or device. Basically, it matches 1296 the ATA ID string printed on console by libata. If 1297 the whole ID part is omitted, the last PORT and DEVICE 1298 values are used. If ID hasn't been specified yet, the 1299 configuration applies to all ports, links and devices. 1300 1301 If only DEVICE is omitted, the parameter applies to 1302 the port and all links and devices behind it. DEVICE 1303 number of 0 either selects the first device or the 1304 first fan-out link behind PMP device. It does not 1305 select the host link. DEVICE number of 15 selects the 1306 host link and device attached to it. 1307 1308 The VAL specifies the configuration to force. As long 1309 as there's no ambiguity shortcut notation is allowed. 1310 For example, both 1.5 and 1.5G would work for 1.5Gbps. 1311 The following configurations can be forced. 1312 1313 * Cable type: 40c, 80c, short40c, unk, ign or sata. 1314 Any ID with matching PORT is used. 1315 1316 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 1317 1318 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 1319 udma[/][16,25,33,44,66,100,133] notation is also 1320 allowed. 1321 1322 * [no]ncq: Turn on or off NCQ. 1323 1324 * nohrst, nosrst, norst: suppress hard, soft 1325 and both resets. 1326 1327 * dump_id: dump IDENTIFY data. 1328 1329 If there are multiple matching configurations changing 1330 the same attribute, the last one is used. 1331 1332 memblock=debug [KNL] Enable memblock debug messages. 1333 1334 load_ramdisk= [RAM] List of ramdisks to load from floppy 1335 See Documentation/blockdev/ramdisk.txt. 1336 1337 lockd.nlm_grace_period=P [NFS] Assign grace period. 1338 Format: <integer> 1339 1340 lockd.nlm_tcpport=N [NFS] Assign TCP port. 1341 Format: <integer> 1342 1343 lockd.nlm_timeout=T [NFS] Assign timeout value. 1344 Format: <integer> 1345 1346 lockd.nlm_udpport=M [NFS] Assign UDP port. 1347 Format: <integer> 1348 1349 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 1350 Format: <irq> 1351 1352 loglevel= All Kernel Messages with a loglevel smaller than the 1353 console loglevel will be printed to the console. It can 1354 also be changed with klogd or other programs. The 1355 loglevels are defined as follows: 1356 1357 0 (KERN_EMERG) system is unusable 1358 1 (KERN_ALERT) action must be taken immediately 1359 2 (KERN_CRIT) critical conditions 1360 3 (KERN_ERR) error conditions 1361 4 (KERN_WARNING) warning conditions 1362 5 (KERN_NOTICE) normal but significant condition 1363 6 (KERN_INFO) informational 1364 7 (KERN_DEBUG) debug-level messages 1365 1366 log_buf_len=n[KMG] Sets the size of the printk ring buffer, 1367 in bytes. n must be a power of two. The default 1368 size is set in the kernel config file. 1369 1370 logo.nologo [FB] Disables display of the built-in Linux logo. 1371 This may be used to provide more screen space for 1372 kernel log messages and is useful when debugging 1373 kernel boot problems. 1374 1375 lp=0 [LP] Specify parallel ports to use, e.g, 1376 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 1377 lp=reset first parallel port). 'lp=0' disables the 1378 lp=auto printer driver. 'lp=reset' (which can be 1379 specified in addition to the ports) causes 1380 attached printers to be reset. Using 1381 lp=port1,port2,... specifies the parallel ports 1382 to associate lp devices with, starting with 1383 lp0. A port specification may be 'none' to skip 1384 that lp device, or a parport name such as 1385 'parport0'. Specifying 'lp=auto' instead of a 1386 port specification list means that device IDs 1387 from each port should be examined, to see if 1388 an IEEE 1284-compliant printer is attached; if 1389 so, the driver will manage that printer. 1390 See also header of drivers/char/lp.c. 1391 1392 lpj=n [KNL] 1393 Sets loops_per_jiffy to given constant, thus avoiding 1394 time-consuming boot-time autodetection (up to 250 ms per 1395 CPU). 0 enables autodetection (default). To determine 1396 the correct value for your kernel, boot with normal 1397 autodetection and see what value is printed. Note that 1398 on SMP systems the preset will be applied to all CPUs, 1399 which is likely to cause problems if your CPUs need 1400 significantly divergent settings. An incorrect value 1401 will cause delays in the kernel to be wrong, leading to 1402 unpredictable I/O errors and other breakage. Although 1403 unlikely, in the extreme case this might damage your 1404 hardware. 1405 1406 ltpc= [NET] 1407 Format: <io>,<irq>,<dma> 1408 1409 machvec= [IA-64] Force the use of a particular machine-vector 1410 (machvec) in a generic kernel. 1411 Example: machvec=hpzx1_swiotlb 1412 1413 machtype= [Loongson] Share the same kernel image file between different 1414 yeeloong laptop. 1415 Example: machtype=lemote-yeeloong-2f-7inch 1416 1417 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater 1418 than or equal to this physical address is ignored. 1419 1420 maxcpus= [SMP] Maximum number of processors that an SMP kernel 1421 should make use of. maxcpus=n : n >= 0 limits the 1422 kernel to using 'n' processors. n=0 is a special case, 1423 it is equivalent to "nosmp", which also disables 1424 the IO APIC. 1425 1426 max_loop= [LOOP] The number of loop block devices that get 1427 (loop.max_loop) unconditionally pre-created at init time. The default 1428 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 1429 of statically allocating a predefined number, loop 1430 devices can be requested on-demand with the 1431 /dev/loop-control interface. 1432 1433 mcatest= [IA-64] 1434 1435 mce [X86-32] Machine Check Exception 1436 1437 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt 1438 1439 md= [HW] RAID subsystems devices and level 1440 See Documentation/md.txt. 1441 1442 mdacon= [MDA] 1443 Format: <first>,<last> 1444 Specifies range of consoles to be captured by the MDA. 1445 1446 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory 1447 Amount of memory to be used when the kernel is not able 1448 to see the whole system memory or for test. 1449 [X86-32] Use together with memmap= to avoid physical 1450 address space collisions. Without memmap= PCI devices 1451 could be placed at addresses belonging to unused RAM. 1452 1453 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 1454 memory. 1455 1456 memchunk=nn[KMG] 1457 [KNL,SH] Allow user to override the default size for 1458 per-device physically contiguous DMA buffers. 1459 1460 memmap=exactmap [KNL,X86] Enable setting of an exact 1461 E820 memory map, as specified by the user. 1462 Such memmap=exactmap lines can be constructed based on 1463 BIOS output or other requirements. See the memmap=nn@ss 1464 option description. 1465 1466 memmap=nn[KMG]@ss[KMG] 1467 [KNL] Force usage of a specific region of memory 1468 Region of memory to be used, from ss to ss+nn. 1469 1470 memmap=nn[KMG]#ss[KMG] 1471 [KNL,ACPI] Mark specific memory as ACPI data. 1472 Region of memory to be used, from ss to ss+nn. 1473 1474 memmap=nn[KMG]$ss[KMG] 1475 [KNL,ACPI] Mark specific memory as reserved. 1476 Region of memory to be used, from ss to ss+nn. 1477 Example: Exclude memory from 0x18690000-0x1869ffff 1478 memmap=64K$0x18690000 1479 or 1480 memmap=0x10000$0x18690000 1481 1482 memory_corruption_check=0/1 [X86] 1483 Some BIOSes seem to corrupt the first 64k of 1484 memory when doing things like suspend/resume. 1485 Setting this option will scan the memory 1486 looking for corruption. Enabling this will 1487 both detect corruption and prevent the kernel 1488 from using the memory being corrupted. 1489 However, its intended as a diagnostic tool; if 1490 repeatable BIOS-originated corruption always 1491 affects the same memory, you can use memmap= 1492 to prevent the kernel from using that memory. 1493 1494 memory_corruption_check_size=size [X86] 1495 By default it checks for corruption in the low 1496 64k, making this memory unavailable for normal 1497 use. Use this parameter to scan for 1498 corruption in more or less memory. 1499 1500 memory_corruption_check_period=seconds [X86] 1501 By default it checks for corruption every 60 1502 seconds. Use this parameter to check at some 1503 other rate. 0 disables periodic checking. 1504 1505 memtest= [KNL,X86] Enable memtest 1506 Format: <integer> 1507 default : 0 <disable> 1508 Specifies the number of memtest passes to be 1509 performed. Each pass selects another test 1510 pattern from a given set of patterns. Memtest 1511 fills the memory with this pattern, validates 1512 memory contents and reserves bad memory 1513 regions that are detected. 1514 1515 meye.*= [HW] Set MotionEye Camera parameters 1516 See Documentation/video4linux/meye.txt. 1517 1518 mfgpt_irq= [IA-32] Specify the IRQ to use for the 1519 Multi-Function General Purpose Timers on AMD Geode 1520 platforms. 1521 1522 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 1523 the BIOS has incorrectly applied a workaround. TinyBIOS 1524 version 0.98 is known to be affected, 0.99 fixes the 1525 problem by letting the user disable the workaround. 1526 1527 mga= [HW,DRM] 1528 1529 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this 1530 physical address is ignored. 1531 1532 mini2440= [ARM,HW,KNL] 1533 Format:[0..2][b][c][t] 1534 Default: "0tb" 1535 MINI2440 configuration specification: 1536 0 - The attached screen is the 3.5" TFT 1537 1 - The attached screen is the 7" TFT 1538 2 - The VGA Shield is attached (1024x768) 1539 Leaving out the screen size parameter will not load 1540 the TFT driver, and the framebuffer will be left 1541 unconfigured. 1542 b - Enable backlight. The TFT backlight pin will be 1543 linked to the kernel VESA blanking code and a GPIO 1544 LED. This parameter is not necessary when using the 1545 VGA shield. 1546 c - Enable the s3c camera interface. 1547 t - Reserved for enabling touchscreen support. The 1548 touchscreen support is not enabled in the mainstream 1549 kernel as of 2.6.30, a preliminary port can be found 1550 in the "bleeding edge" mini2440 support kernel at 1551 http://repo.or.cz/w/linux-2.6/mini2440.git 1552 1553 mminit_loglevel= 1554 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this 1555 parameter allows control of the logging verbosity for 1556 the additional memory initialisation checks. A value 1557 of 0 disables mminit logging and a level of 4 will 1558 log everything. Information is printed at KERN_DEBUG 1559 so loglevel=8 may also need to be specified. 1560 1561 mousedev.tap_time= 1562 [MOUSE] Maximum time between finger touching and 1563 leaving touchpad surface for touch to be considered 1564 a tap and be reported as a left button click (for 1565 touchpads working in absolute mode only). 1566 Format: <msecs> 1567 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 1568 reporting absolute coordinates, such as tablets 1569 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 1570 reporting absolute coordinates, such as tablets 1571 1572 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter 1573 is similar to kernelcore except it specifies the 1574 amount of memory used for migratable allocations. 1575 If both kernelcore and movablecore is specified, 1576 then kernelcore will be at *least* the specified 1577 value but may be more. If movablecore on its own 1578 is specified, the administrator must be careful 1579 that the amount of memory usable for all allocations 1580 is not too small. 1581 1582 MTD_Partition= [MTD] 1583 Format: <name>,<region-number>,<size>,<offset> 1584 1585 MTD_Region= [MTD] Format: 1586 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 1587 1588 mtdparts= [MTD] 1589 See drivers/mtd/cmdlinepart.c. 1590 1591 multitce=off [PPC] This parameter disables the use of the pSeries 1592 firmware feature for updating multiple TCE entries 1593 at a time. 1594 1595 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 1596 1597 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 1598 1599 boundary - index of last SLC block on Flex-OneNAND. 1600 The remaining blocks are configured as MLC blocks. 1601 lock - Configure if Flex-OneNAND boundary should be locked. 1602 Once locked, the boundary cannot be changed. 1603 1 indicates lock status, 0 indicates unlock status. 1604 1605 mtdset= [ARM] 1606 ARM/S3C2412 JIVE boot control 1607 1608 See arch/arm/mach-s3c2412/mach-jive.c 1609 1610 mtouchusb.raw_coordinates= 1611 [HW] Make the MicroTouch USB driver use raw coordinates 1612 ('y', default) or cooked coordinates ('n') 1613 1614 mtrr_chunk_size=nn[KMG] [X86] 1615 used for mtrr cleanup. It is largest continuous chunk 1616 that could hold holes aka. UC entries. 1617 1618 mtrr_gran_size=nn[KMG] [X86] 1619 Used for mtrr cleanup. It is granularity of mtrr block. 1620 Default is 1. 1621 Large value could prevent small alignment from 1622 using up MTRRs. 1623 1624 mtrr_spare_reg_nr=n [X86] 1625 Format: <integer> 1626 Range: 0,7 : spare reg number 1627 Default : 1 1628 Used for mtrr cleanup. It is spare mtrr entries number. 1629 Set to 2 or more if your graphical card needs more. 1630 1631 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 1632 1633 netdev= [NET] Network devices parameters 1634 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 1635 Note that mem_start is often overloaded to mean 1636 something different and driver-specific. 1637 This usage is only documented in each driver source 1638 file if at all. 1639 1640 nf_conntrack.acct= 1641 [NETFILTER] Enable connection tracking flow accounting 1642 0 to disable accounting 1643 1 to enable accounting 1644 Default value is 0. 1645 1646 nfsaddrs= [NFS] Deprecated. Use ip= instead. 1647 See Documentation/filesystems/nfs/nfsroot.txt. 1648 1649 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 1650 See Documentation/filesystems/nfs/nfsroot.txt. 1651 1652 nfsrootdebug [NFS] enable nfsroot debugging messages. 1653 See Documentation/filesystems/nfs/nfsroot.txt. 1654 1655 nfs.callback_tcpport= 1656 [NFS] set the TCP port on which the NFSv4 callback 1657 channel should listen. 1658 1659 nfs.cache_getent= 1660 [NFS] sets the pathname to the program which is used 1661 to update the NFS client cache entries. 1662 1663 nfs.cache_getent_timeout= 1664 [NFS] sets the timeout after which an attempt to 1665 update a cache entry is deemed to have failed. 1666 1667 nfs.idmap_cache_timeout= 1668 [NFS] set the maximum lifetime for idmapper cache 1669 entries. 1670 1671 nfs.enable_ino64= 1672 [NFS] enable 64-bit inode numbers. 1673 If zero, the NFS client will fake up a 32-bit inode 1674 number for the readdir() and stat() syscalls instead 1675 of returning the full 64-bit number. 1676 The default is to return 64-bit inode numbers. 1677 1678 nfs.max_session_slots= 1679 [NFSv4.1] Sets the maximum number of session slots 1680 the client will attempt to negotiate with the server. 1681 This limits the number of simultaneous RPC requests 1682 that the client can send to the NFSv4.1 server. 1683 Note that there is little point in setting this 1684 value higher than the max_tcp_slot_table_limit. 1685 1686 nfs.nfs4_disable_idmapping= 1687 [NFSv4] When set to the default of '1', this option 1688 ensures that both the RPC level authentication 1689 scheme and the NFS level operations agree to use 1690 numeric uids/gids if the mount is using the 1691 'sec=sys' security flavour. In effect it is 1692 disabling idmapping, which can make migration from 1693 legacy NFSv2/v3 systems to NFSv4 easier. 1694 Servers that do not support this mode of operation 1695 will be autodetected by the client, and it will fall 1696 back to using the idmapper. 1697 To turn off this behaviour, set the value to '0'. 1698 1699 nfs.send_implementation_id = 1700 [NFSv4.1] Send client implementation identification 1701 information in exchange_id requests. 1702 If zero, no implementation identification information 1703 will be sent. 1704 The default is to send the implementation identification 1705 information. 1706 1707 nfsd.nfs4_disable_idmapping= 1708 [NFSv4] When set to the default of '1', the NFSv4 1709 server will return only numeric uids and gids to 1710 clients using auth_sys, and will accept numeric uids 1711 and gids from such clients. This is intended to ease 1712 migration from NFSv2/v3. 1713 1714 objlayoutdriver.osd_login_prog= 1715 [NFS] [OBJLAYOUT] sets the pathname to the program which 1716 is used to automatically discover and login into new 1717 osd-targets. Please see: 1718 Documentation/filesystems/pnfs.txt for more explanations 1719 1720 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take 1721 when a NMI is triggered. 1722 Format: [state][,regs][,debounce][,die] 1723 1724 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 1725 Format: [panic,][nopanic,][num] 1726 Valid num: 0 1727 0 - turn nmi_watchdog off 1728 When panic is specified, panic when an NMI watchdog 1729 timeout occurs (or 'nopanic' to override the opposite 1730 default). 1731 This is useful when you use a panic=... timeout and 1732 need the box quickly up again. 1733 1734 netpoll.carrier_timeout= 1735 [NET] Specifies amount of time (in seconds) that 1736 netpoll should wait for a carrier. By default netpoll 1737 waits 4 seconds. 1738 1739 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 1740 emulation library even if a 387 maths coprocessor 1741 is present. 1742 1743 no_console_suspend 1744 [HW] Never suspend the console 1745 Disable suspending of consoles during suspend and 1746 hibernate operations. Once disabled, debugging 1747 messages can reach various consoles while the rest 1748 of the system is being put to sleep (ie, while 1749 debugging driver suspend/resume hooks). This may 1750 not work reliably with all consoles, but is known 1751 to work with serial and VGA consoles. 1752 To facilitate more flexible debugging, we also add 1753 console_suspend, a printk module parameter to control 1754 it. Users could use console_suspend (usually 1755 /sys/module/printk/parameters/console_suspend) to 1756 turn on/off it dynamically. 1757 1758 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien 1759 caches in the slab allocator. Saves per-node memory, 1760 but will impact performance. 1761 1762 noalign [KNL,ARM] 1763 1764 noapic [SMP,APIC] Tells the kernel to not make use of any 1765 IOAPICs that may be present in the system. 1766 1767 noautogroup Disable scheduler automatic task group creation. 1768 1769 nobats [PPC] Do not use BATs for mapping kernel lowmem 1770 on "Classic" PPC cores. 1771 1772 nocache [ARM] 1773 1774 noclflush [BUGS=X86] Don't use the CLFLUSH instruction 1775 1776 nodelayacct [KNL] Disable per-task delay accounting 1777 1778 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects. 1779 1780 nodsp [SH] Disable hardware DSP at boot time. 1781 1782 noefi [X86] Disable EFI runtime services support. 1783 1784 noexec [IA-64] 1785 1786 noexec [X86] 1787 On X86-32 available only on PAE configured kernels. 1788 noexec=on: enable non-executable mappings (default) 1789 noexec=off: disable non-executable mappings 1790 1791 nosmep [X86] 1792 Disable SMEP (Supervisor Mode Execution Protection) 1793 even if it is supported by processor. 1794 1795 noexec32 [X86-64] 1796 This affects only 32-bit executables. 1797 noexec32=on: enable non-executable mappings (default) 1798 read doesn't imply executable mappings 1799 noexec32=off: disable non-executable mappings 1800 read implies executable mappings 1801 1802 nofpu [SH] Disable hardware FPU at boot time. 1803 1804 nofxsr [BUGS=X86-32] Disables x86 floating point extended 1805 register save and restore. The kernel will only save 1806 legacy floating-point registers on task switch. 1807 1808 noxsave [BUGS=X86] Disables x86 extended register state save 1809 and restore using xsave. The kernel will fallback to 1810 enabling legacy floating-point and sse state. 1811 1812 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or 1813 wfi(ARM) instruction doesn't work correctly and not to 1814 use it. This is also useful when using JTAG debugger. 1815 1816 no-hlt [BUGS=X86-32] Tells the kernel that the hlt 1817 instruction doesn't work correctly and not to 1818 use it. 1819 1820 no_file_caps Tells the kernel not to honor file capabilities. The 1821 only way then for a file to be executed with privilege 1822 is to be setuid root or executed by root. 1823 1824 nohalt [IA-64] Tells the kernel not to use the power saving 1825 function PAL_HALT_LIGHT when idle. This increases 1826 power-consumption. On the positive side, it reduces 1827 interrupt wake-up latency, which may improve performance 1828 in certain environments such as networked servers or 1829 real-time systems. 1830 1831 nohz= [KNL] Boottime enable/disable dynamic ticks 1832 Valid arguments: on, off 1833 Default: on 1834 1835 noiotrap [SH] Disables trapped I/O port accesses. 1836 1837 noirqdebug [X86-32] Disables the code which attempts to detect and 1838 disable unhandled interrupt sources. 1839 1840 no_timer_check [X86,APIC] Disables the code which tests for 1841 broken timer IRQ sources. 1842 1843 noisapnp [ISAPNP] Disables ISA PnP code. 1844 1845 noinitrd [RAM] Tells the kernel not to load any configured 1846 initial RAM disk. 1847 1848 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt 1849 remapping. 1850 [Deprecated - use intremap=off] 1851 1852 nointroute [IA-64] 1853 1854 nojitter [IA-64] Disables jitter checking for ITC timers. 1855 1856 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver 1857 1858 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page 1859 fault handling. 1860 1861 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting. 1862 steal time is computed, but won't influence scheduler 1863 behaviour 1864 1865 nolapic [X86-32,APIC] Do not enable or use the local APIC. 1866 1867 nolapic_timer [X86-32,APIC] Do not use the local APIC timer. 1868 1869 noltlbs [PPC] Do not use large page/tlb entries for kernel 1870 lowmem mapping on PPC40x. 1871 1872 nomca [IA-64] Disable machine check abort handling 1873 1874 nomce [X86-32] Machine Check Exception 1875 1876 nomfgpt [X86-32] Disable Multi-Function General Purpose 1877 Timer usage (for AMD Geode machines). 1878 1879 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 1880 shutdown the other cpus. Instead use the REBOOT_VECTOR 1881 irq. 1882 1883 nomodule Disable module load 1884 1885 nopat [X86] Disable PAT (page attribute table extension of 1886 pagetables) support. 1887 1888 norandmaps Don't use address space randomization. Equivalent to 1889 echo 0 > /proc/sys/kernel/randomize_va_space 1890 1891 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops 1892 1893 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 1894 with UP alternatives 1895 1896 noresidual [PPC] Don't use residual data on PReP machines. 1897 1898 nordrand [X86] Disable the direct use of the RDRAND 1899 instruction even if it is supported by the 1900 processor. RDRAND is still available to user 1901 space applications. 1902 1903 noresume [SWSUSP] Disables resume and restores original swap 1904 space. 1905 1906 no-scroll [VGA] Disables scrollback. 1907 This is required for the Braillex ib80-piezo Braille 1908 reader made by F.H. Papenmeier (Germany). 1909 1910 nosbagart [IA-64] 1911 1912 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support. 1913 1914 nosmp [SMP] Tells an SMP kernel to act as a UP kernel, 1915 and disable the IO APIC. legacy for "maxcpus=0". 1916 1917 nosoftlockup [KNL] Disable the soft-lockup detector. 1918 1919 nosync [HW,M68K] Disables sync negotiation for all devices. 1920 1921 notsc [BUGS=X86-32] Disable Time Stamp Counter 1922 1923 nousb [USB] Disable the USB subsystem 1924 1925 nowatchdog [KNL] Disable the lockup detector (NMI watchdog). 1926 1927 nowb [ARM] 1928 1929 nox2apic [X86-64,APIC] Do not enable x2APIC mode. 1930 1931 nptcg= [IA-64] Override max number of concurrent global TLB 1932 purges which is reported from either PAL_VM_SUMMARY or 1933 SAL PALO. 1934 1935 nr_cpus= [SMP] Maximum number of processors that an SMP kernel 1936 could support. nr_cpus=n : n >= 1 limits the kernel to 1937 supporting 'n' processors. Later in runtime you can not 1938 use hotplug cpu feature to put more cpu back to online. 1939 just like you compile the kernel NR_CPUS=n 1940 1941 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 1942 1943 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 1944 one of ['zone', 'node', 'default'] can be specified 1945 This can be set from sysctl after boot. 1946 See Documentation/sysctl/vm.txt for details. 1947 1948 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver. 1949 See Documentation/debugging-via-ohci1394.txt for more 1950 info. 1951 1952 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 1953 Rather than timing out after 20 ms if an EC 1954 command is not properly ACKed, override the length 1955 of the timeout. We have interrupts disabled while 1956 waiting for the ACK, so if this is set too high 1957 interrupts *may* be lost! 1958 1959 omap_mux= [OMAP] Override bootloader pin multiplexing. 1960 Format: <mux_mode0.mode_name=value>... 1961 For example, to override I2C bus2: 1962 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 1963 1964 oprofile.timer= [HW] 1965 Use timer interrupt instead of performance counters 1966 1967 oprofile.cpu_type= Force an oprofile cpu type 1968 This might be useful if you have an older oprofile 1969 userland or if you want common events. 1970 Format: { arch_perfmon } 1971 arch_perfmon: [X86] Force use of architectural 1972 perfmon on Intel CPUs instead of the 1973 CPU specific event set. 1974 timer: [X86] Force use of architectural NMI 1975 timer mode (see also oprofile.timer 1976 for generic hr timer mode) 1977 [s390] Force legacy basic mode sampling 1978 (report cpu_type "timer") 1979 1980 oops=panic Always panic on oopses. Default is to just kill the 1981 process, but there is a small probability of 1982 deadlocking the machine. 1983 This will also cause panics on machine check exceptions. 1984 Useful together with panic=30 to trigger a reboot. 1985 1986 OSS [HW,OSS] 1987 See Documentation/sound/oss/oss-parameters.txt 1988 1989 panic= [KNL] Kernel behaviour on panic: delay <timeout> 1990 timeout > 0: seconds before rebooting 1991 timeout = 0: wait forever 1992 timeout < 0: reboot immediately 1993 Format: <timeout> 1994 1995 parkbd.port= [HW] Parallel port number the keyboard adapter is 1996 connected to, default is 0. 1997 Format: <parport#> 1998 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 1999 0 for XT, 1 for AT (default is AT). 2000 Format: <mode> 2001 2002 parport= [HW,PPT] Specify parallel ports. 0 disables. 2003 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 2004 Use 'auto' to force the driver to use any 2005 IRQ/DMA settings detected (the default is to 2006 ignore detected IRQ/DMA settings because of 2007 possible conflicts). You can specify the base 2008 address, IRQ, and DMA settings; IRQ and DMA 2009 should be numbers, or 'auto' (for using detected 2010 settings on that particular port), or 'nofifo' 2011 (to avoid using a FIFO even if it is detected). 2012 Parallel ports are assigned in the order they 2013 are specified on the command line, starting 2014 with parport0. 2015 2016 parport_init_mode= [HW,PPT] 2017 Configure VIA parallel port to operate in 2018 a specific mode. This is necessary on Pegasos 2019 computer where firmware has no options for setting 2020 up parallel port mode and sets it to spp. 2021 Currently this function knows 686a and 8231 chips. 2022 Format: [spp|ps2|epp|ecp|ecpepp] 2023 2024 pause_on_oops= 2025 Halt all CPUs after the first oops has been printed for 2026 the specified number of seconds. This is to be used if 2027 your oopses keep scrolling off the screen. 2028 2029 pcbit= [HW,ISDN] 2030 2031 pcd. [PARIDE] 2032 See header of drivers/block/paride/pcd.c. 2033 See also Documentation/blockdev/paride.txt. 2034 2035 pci=option[,option...] [PCI] various PCI subsystem options: 2036 earlydump [X86] dump PCI config space before the kernel 2037 changes anything 2038 off [X86] don't probe for the PCI bus 2039 bios [X86-32] force use of PCI BIOS, don't access 2040 the hardware directly. Use this if your machine 2041 has a non-standard PCI host bridge. 2042 nobios [X86-32] disallow use of PCI BIOS, only direct 2043 hardware access methods are allowed. Use this 2044 if you experience crashes upon bootup and you 2045 suspect they are caused by the BIOS. 2046 conf1 [X86] Force use of PCI Configuration 2047 Mechanism 1. 2048 conf2 [X86] Force use of PCI Configuration 2049 Mechanism 2. 2050 noaer [PCIE] If the PCIEAER kernel config parameter is 2051 enabled, this kernel boot option can be used to 2052 disable the use of PCIE advanced error reporting. 2053 nodomains [PCI] Disable support for multiple PCI 2054 root domains (aka PCI segments, in ACPI-speak). 2055 nommconf [X86] Disable use of MMCONFIG for PCI 2056 Configuration 2057 check_enable_amd_mmconf [X86] check for and enable 2058 properly configured MMIO access to PCI 2059 config space on AMD family 10h CPU 2060 nomsi [MSI] If the PCI_MSI kernel config parameter is 2061 enabled, this kernel boot option can be used to 2062 disable the use of MSI interrupts system-wide. 2063 noioapicquirk [APIC] Disable all boot interrupt quirks. 2064 Safety option to keep boot IRQs enabled. This 2065 should never be necessary. 2066 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 2067 primary IO-APIC for bridges that cannot disable 2068 boot IRQs. This fixes a source of spurious IRQs 2069 when the system masks IRQs. 2070 noioapicreroute [APIC] Disable workaround that uses the 2071 boot IRQ equivalent of an IRQ that connects to 2072 a chipset where boot IRQs cannot be disabled. 2073 The opposite of ioapicreroute. 2074 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 2075 routing table. These calls are known to be buggy 2076 on several machines and they hang the machine 2077 when used, but on other computers it's the only 2078 way to get the interrupt routing table. Try 2079 this option if the kernel is unable to allocate 2080 IRQs or discover secondary PCI buses on your 2081 motherboard. 2082 rom [X86] Assign address space to expansion ROMs. 2083 Use with caution as certain devices share 2084 address decoders between ROMs and other 2085 resources. 2086 norom [X86] Do not assign address space to 2087 expansion ROMs that do not already have 2088 BIOS assigned address ranges. 2089 nobar [X86] Do not assign address space to the 2090 BARs that weren't assigned by the BIOS. 2091 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 2092 assigned automatically to PCI devices. You can 2093 make the kernel exclude IRQs of your ISA cards 2094 this way. 2095 pirqaddr=0xAAAAA [X86] Specify the physical address 2096 of the PIRQ table (normally generated 2097 by the BIOS) if it is outside the 2098 F0000h-100000h range. 2099 lastbus=N [X86] Scan all buses thru bus #N. Can be 2100 useful if the kernel is unable to find your 2101 secondary buses and you want to tell it 2102 explicitly which ones they are. 2103 assign-busses [X86] Always assign all PCI bus 2104 numbers ourselves, overriding 2105 whatever the firmware may have done. 2106 usepirqmask [X86] Honor the possible IRQ mask stored 2107 in the BIOS $PIR table. This is needed on 2108 some systems with broken BIOSes, notably 2109 some HP Pavilion N5400 and Omnibook XE3 2110 notebooks. This will have no effect if ACPI 2111 IRQ routing is enabled. 2112 noacpi [X86] Do not use ACPI for IRQ routing 2113 or for PCI scanning. 2114 use_crs [X86] Use PCI host bridge window information 2115 from ACPI. On BIOSes from 2008 or later, this 2116 is enabled by default. If you need to use this, 2117 please report a bug. 2118 nocrs [X86] Ignore PCI host bridge windows from ACPI. 2119 If you need to use this, please report a bug. 2120 routeirq Do IRQ routing for all PCI devices. 2121 This is normally done in pci_enable_device(), 2122 so this option is a temporary workaround 2123 for broken drivers that don't call it. 2124 skip_isa_align [X86] do not align io start addr, so can 2125 handle more pci cards 2126 firmware [ARM] Do not re-enumerate the bus but instead 2127 just use the configuration from the 2128 bootloader. This is currently used on 2129 IXP2000 systems where the bus has to be 2130 configured a certain way for adjunct CPUs. 2131 noearly [X86] Don't do any early type 1 scanning. 2132 This might help on some broken boards which 2133 machine check when some devices' config space 2134 is read. But various workarounds are disabled 2135 and some IOMMU drivers will not work. 2136 bfsort Sort PCI devices into breadth-first order. 2137 This sorting is done to get a device 2138 order compatible with older (<= 2.4) kernels. 2139 nobfsort Don't sort PCI devices into breadth-first order. 2140 cbiosize=nn[KMG] The fixed amount of bus space which is 2141 reserved for the CardBus bridge's IO window. 2142 The default value is 256 bytes. 2143 cbmemsize=nn[KMG] The fixed amount of bus space which is 2144 reserved for the CardBus bridge's memory 2145 window. The default value is 64 megabytes. 2146 resource_alignment= 2147 Format: 2148 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...] 2149 Specifies alignment and device to reassign 2150 aligned memory resources. 2151 If <order of align> is not specified, 2152 PAGE_SIZE is used as alignment. 2153 PCI-PCI bridge can be specified, if resource 2154 windows need to be expanded. 2155 ecrc= Enable/disable PCIe ECRC (transaction layer 2156 end-to-end CRC checking). 2157 bios: Use BIOS/firmware settings. This is the 2158 the default. 2159 off: Turn ECRC off 2160 on: Turn ECRC on. 2161 realloc= Enable/disable reallocating PCI bridge resources 2162 if allocations done by BIOS are too small to 2163 accommodate resources required by all child 2164 devices. 2165 off: Turn realloc off 2166 on: Turn realloc on 2167 realloc same as realloc=on 2168 noari do not use PCIe ARI. 2169 2170 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power 2171 Management. 2172 off Disable ASPM. 2173 force Enable ASPM even on devices that claim not to support it. 2174 WARNING: Forcing ASPM on may cause system lockups. 2175 2176 pcie_hp= [PCIE] PCI Express Hotplug driver options: 2177 nomsi Do not use MSI for PCI Express Native Hotplug (this 2178 makes all PCIe ports use INTx for hotplug services). 2179 2180 pcie_ports= [PCIE] PCIe ports handling: 2181 auto Ask the BIOS whether or not to use native PCIe services 2182 associated with PCIe ports (PME, hot-plug, AER). Use 2183 them only if that is allowed by the BIOS. 2184 native Use native PCIe services associated with PCIe ports 2185 unconditionally. 2186 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe 2187 ports driver. 2188 2189 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 2190 nomsi Do not use MSI for native PCIe PME signaling (this makes 2191 all PCIe root ports use INTx for all services). 2192 2193 pcmv= [HW,PCMCIA] BadgePAD 4 2194 2195 pd. [PARIDE] 2196 See Documentation/blockdev/paride.txt. 2197 2198 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 2199 boot time. 2200 Format: { 0 | 1 } 2201 See arch/parisc/kernel/pdc_chassis.c 2202 2203 percpu_alloc= Select which percpu first chunk allocator to use. 2204 Currently supported values are "embed" and "page". 2205 Archs may support subset or none of the selections. 2206 See comments in mm/percpu.c for details on each 2207 allocator. This parameter is primarily for debugging 2208 and performance comparison. 2209 2210 pf. [PARIDE] 2211 See Documentation/blockdev/paride.txt. 2212 2213 pg. [PARIDE] 2214 See Documentation/blockdev/paride.txt. 2215 2216 pirq= [SMP,APIC] Manual mp-table setup 2217 See Documentation/x86/i386/IO-APIC.txt. 2218 2219 plip= [PPT,NET] Parallel port network link 2220 Format: { parport<nr> | timid | 0 } 2221 See also Documentation/parport.txt. 2222 2223 pmtmr= [X86] Manual setup of pmtmr I/O Port. 2224 Override pmtimer IOPort with a hex value. 2225 e.g. pmtmr=0x508 2226 2227 pnp.debug=1 [PNP] 2228 Enable PNP debug messages (depends on the 2229 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 2230 via /sys/module/pnp/parameters/debug. We always show 2231 current resource usage; turning this on also shows 2232 possible settings and some assignment information. 2233 2234 pnpacpi= [ACPI] 2235 { off } 2236 2237 pnpbios= [ISAPNP] 2238 { on | off | curr | res | no-curr | no-res } 2239 2240 pnp_reserve_irq= 2241 [ISAPNP] Exclude IRQs for the autoconfiguration 2242 2243 pnp_reserve_dma= 2244 [ISAPNP] Exclude DMAs for the autoconfiguration 2245 2246 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 2247 Ranges are in pairs (I/O port base and size). 2248 2249 pnp_reserve_mem= 2250 [ISAPNP] Exclude memory regions for the 2251 autoconfiguration. 2252 Ranges are in pairs (memory base and size). 2253 2254 ports= [IP_VS_FTP] IPVS ftp helper module 2255 Default is 21. 2256 Up to 8 (IP_VS_APP_MAX_PORTS) ports 2257 may be specified. 2258 Format: <port>,<port>.... 2259 2260 print-fatal-signals= 2261 [KNL] debug: print fatal signals 2262 2263 If enabled, warn about various signal handling 2264 related application anomalies: too many signals, 2265 too many POSIX.1 timers, fatal signals causing a 2266 coredump - etc. 2267 2268 If you hit the warning due to signal overflow, 2269 you might want to try "ulimit -i unlimited". 2270 2271 default: off. 2272 2273 printk.always_kmsg_dump= 2274 Trigger kmsg_dump for cases other than kernel oops or 2275 panics 2276 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 2277 default: disabled 2278 2279 printk.time= Show timing data prefixed to each printk message line 2280 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 2281 2282 processor.max_cstate= [HW,ACPI] 2283 Limit processor to maximum C-state 2284 max_cstate=9 overrides any DMI blacklist limit. 2285 2286 processor.nocst [HW,ACPI] 2287 Ignore the _CST method to determine C-states, 2288 instead using the legacy FADT method 2289 2290 profile= [KNL] Enable kernel profiling via /proc/profile 2291 Format: [schedule,]<number> 2292 Param: "schedule" - profile schedule points. 2293 Param: <number> - step/bucket size as a power of 2 for 2294 statistical time based profiling. 2295 Param: "sleep" - profile D-state sleeping (millisecs). 2296 Requires CONFIG_SCHEDSTATS 2297 Param: "kvm" - profile VM exits. 2298 2299 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk 2300 before loading. 2301 See Documentation/blockdev/ramdisk.txt. 2302 2303 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 2304 probe for; one of (bare|imps|exps|lifebook|any). 2305 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 2306 per second. 2307 psmouse.resetafter= [HW,MOUSE] 2308 Try to reset the device after so many bad packets 2309 (0 = never). 2310 psmouse.resolution= 2311 [HW,MOUSE] Set desired mouse resolution, in dpi. 2312 psmouse.smartscroll= 2313 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 2314 0 = disabled, 1 = enabled (default). 2315 2316 pstore.backend= Specify the name of the pstore backend to use 2317 2318 pt. [PARIDE] 2319 See Documentation/blockdev/paride.txt. 2320 2321 pty.legacy_count= 2322 [KNL] Number of legacy pty's. Overwrites compiled-in 2323 default number. 2324 2325 quiet [KNL] Disable most log messages 2326 2327 r128= [HW,DRM] 2328 2329 raid= [HW,RAID] 2330 See Documentation/md.txt. 2331 2332 ramdisk_blocksize= [RAM] 2333 See Documentation/blockdev/ramdisk.txt. 2334 2335 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 2336 See Documentation/blockdev/ramdisk.txt. 2337 2338 rcupdate.blimit= [KNL,BOOT] 2339 Set maximum number of finished RCU callbacks to process 2340 in one batch. 2341 2342 rcupdate.qhimark= [KNL,BOOT] 2343 Set threshold of queued 2344 RCU callbacks over which batch limiting is disabled. 2345 2346 rcupdate.qlowmark= [KNL,BOOT] 2347 Set threshold of queued RCU callbacks below which 2348 batch limiting is re-enabled. 2349 2350 rdinit= [KNL] 2351 Format: <full_path> 2352 Run specified binary instead of /init from the ramdisk, 2353 used for early userspace startup. See initrd. 2354 2355 reboot= [BUGS=X86-32,BUGS=ARM,BUGS=IA-64] Rebooting mode 2356 Format: <reboot_mode>[,<reboot_mode2>[,...]] 2357 See arch/*/kernel/reboot.c or arch/*/kernel/process.c 2358 2359 relax_domain_level= 2360 [KNL, SMP] Set scheduler's default relax_domain_level. 2361 See Documentation/cgroups/cpusets.txt. 2362 2363 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area 2364 2365 reservetop= [X86-32] 2366 Format: nn[KMG] 2367 Reserves a hole at the top of the kernel virtual 2368 address space. 2369 2370 reservelow= [X86] 2371 Format: nn[K] 2372 Set the amount of memory to reserve for BIOS at 2373 the bottom of the address space. 2374 2375 reset_devices [KNL] Force drivers to reset the underlying device 2376 during initialization. 2377 2378 resume= [SWSUSP] 2379 Specify the partition device for software suspend 2380 Format: 2381 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 2382 2383 resume_offset= [SWSUSP] 2384 Specify the offset from the beginning of the partition 2385 given by "resume=" at which the swap header is located, 2386 in <PAGE_SIZE> units (needed only for swap files). 2387 See Documentation/power/swsusp-and-swap-files.txt 2388 2389 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 2390 read the resume files 2391 2392 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 2393 Useful for devices that are detected asynchronously 2394 (e.g. USB and MMC devices). 2395 2396 hibernate= [HIBERNATION] 2397 noresume Don't check if there's a hibernation image 2398 present during boot. 2399 nocompress Don't compress/decompress hibernation images. 2400 2401 retain_initrd [RAM] Keep initrd memory after extraction 2402 2403 rhash_entries= [KNL,NET] 2404 Set number of hash buckets for route cache 2405 2406 riscom8= [HW,SERIAL] 2407 Format: <io_board1>[,<io_board2>[,...<io_boardN>]] 2408 2409 ro [KNL] Mount root device read-only on boot 2410 2411 root= [KNL] Root filesystem 2412 See name_to_dev_t comment in init/do_mounts.c. 2413 2414 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 2415 mount the root filesystem 2416 2417 rootflags= [KNL] Set root filesystem mount option string 2418 2419 rootfstype= [KNL] Set root filesystem type 2420 2421 rootwait [KNL] Wait (indefinitely) for root device to show up. 2422 Useful for devices that are detected asynchronously 2423 (e.g. USB and MMC devices). 2424 2425 rw [KNL] Mount root device read-write on boot 2426 2427 S [KNL] Run init in single mode 2428 2429 sa1100ir [NET] 2430 See drivers/net/irda/sa1100_ir.c. 2431 2432 sbni= [NET] Granch SBNI12 leased line adapter 2433 2434 sched_debug [KNL] Enables verbose scheduler debug messages. 2435 2436 security= [SECURITY] Choose a security module to enable at boot. 2437 If this boot parameter is not specified, only the first 2438 security module asking for security registration will be 2439 loaded. An invalid security module name will be treated 2440 as if no module has been chosen. 2441 2442 selinux= [SELINUX] Disable or enable SELinux at boot time. 2443 Format: { "0" | "1" } 2444 See security/selinux/Kconfig help text. 2445 0 -- disable. 2446 1 -- enable. 2447 Default value is set via kernel config option. 2448 If enabled at boot time, /selinux/disable can be used 2449 later to disable prior to initial policy load. 2450 2451 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 2452 Format: { "0" | "1" } 2453 See security/apparmor/Kconfig help text 2454 0 -- disable. 2455 1 -- enable. 2456 Default value is set via kernel config option. 2457 2458 serialnumber [BUGS=X86-32] 2459 2460 shapers= [NET] 2461 Maximal number of shapers. 2462 2463 show_msr= [x86] show boot-time MSR settings 2464 Format: { <integer> } 2465 Show boot-time (BIOS-initialized) MSR settings. 2466 The parameter means the number of CPUs to show, 2467 for example 1 means boot CPU only. 2468 2469 simeth= [IA-64] 2470 simscsi= 2471 2472 slram= [HW,MTD] 2473 2474 slab_max_order= [MM, SLAB] 2475 Determines the maximum allowed order for slabs. 2476 A high setting may cause OOMs due to memory 2477 fragmentation. Defaults to 1 for systems with 2478 more than 32MB of RAM, 0 otherwise. 2479 2480 slub_debug[=options[,slabs]] [MM, SLUB] 2481 Enabling slub_debug allows one to determine the 2482 culprit if slab objects become corrupted. Enabling 2483 slub_debug can create guard zones around objects and 2484 may poison objects when not in use. Also tracks the 2485 last alloc / free. For more information see 2486 Documentation/vm/slub.txt. 2487 2488 slub_max_order= [MM, SLUB] 2489 Determines the maximum allowed order for slabs. 2490 A high setting may cause OOMs due to memory 2491 fragmentation. For more information see 2492 Documentation/vm/slub.txt. 2493 2494 slub_min_objects= [MM, SLUB] 2495 The minimum number of objects per slab. SLUB will 2496 increase the slab order up to slub_max_order to 2497 generate a sufficiently large slab able to contain 2498 the number of objects indicated. The higher the number 2499 of objects the smaller the overhead of tracking slabs 2500 and the less frequently locks need to be acquired. 2501 For more information see Documentation/vm/slub.txt. 2502 2503 slub_min_order= [MM, SLUB] 2504 Determines the minimum page order for slabs. Must be 2505 lower than slub_max_order. 2506 For more information see Documentation/vm/slub.txt. 2507 2508 slub_nomerge [MM, SLUB] 2509 Disable merging of slabs with similar size. May be 2510 necessary if there is some reason to distinguish 2511 allocs to different slabs. Debug options disable 2512 merging on their own. 2513 For more information see Documentation/vm/slub.txt. 2514 2515 smart2= [HW] 2516 Format: <io1>[,<io2>[,...,<io8>]] 2517 2518 smp-alt-once [X86-32,SMP] On a hotplug CPU system, only 2519 attempt to substitute SMP alternatives once at boot. 2520 2521 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 2522 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 2523 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 2524 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 2525 smsc-ircc2.ircc_irq= [HW] IRQ line 2526 smsc-ircc2.ircc_dma= [HW] DMA channel 2527 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 2528 0: Toshiba Satellite 1800 (GP data pin select) 2529 1: Fast pin select (default) 2530 2: ATC IRMode 2531 2532 softlockup_panic= 2533 [KNL] Should the soft-lockup detector generate panics. 2534 Format: <integer> 2535 2536 sonypi.*= [HW] Sony Programmable I/O Control Device driver 2537 See Documentation/laptops/sonypi.txt 2538 2539 specialix= [HW,SERIAL] Specialix multi-serial port adapter 2540 See Documentation/serial/specialix.txt. 2541 2542 spia_io_base= [HW,MTD] 2543 spia_fio_base= 2544 spia_pedr= 2545 spia_peddr= 2546 2547 stacktrace [FTRACE] 2548 Enabled the stack tracer on boot up. 2549 2550 stacktrace_filter=[function-list] 2551 [FTRACE] Limit the functions that the stack tracer 2552 will trace at boot up. function-list is a comma separated 2553 list of functions. This list can be changed at run 2554 time by the stack_trace_filter file in the debugfs 2555 tracing directory. Note, this enables stack tracing 2556 and the stacktrace above is not needed. 2557 2558 sti= [PARISC,HW] 2559 Format: <num> 2560 Set the STI (builtin display/keyboard on the HP-PARISC 2561 machines) console (graphic card) which should be used 2562 as the initial boot-console. 2563 See also comment in drivers/video/console/sticore.c. 2564 2565 sti_font= [HW] 2566 See comment in drivers/video/console/sticore.c. 2567 2568 stifb= [HW] 2569 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 2570 2571 sunrpc.min_resvport= 2572 sunrpc.max_resvport= 2573 [NFS,SUNRPC] 2574 SunRPC servers often require that client requests 2575 originate from a privileged port (i.e. a port in the 2576 range 0 < portnr < 1024). 2577 An administrator who wishes to reserve some of these 2578 ports for other uses may adjust the range that the 2579 kernel's sunrpc client considers to be privileged 2580 using these two parameters to set the minimum and 2581 maximum port values. 2582 2583 sunrpc.pool_mode= 2584 [NFS] 2585 Control how the NFS server code allocates CPUs to 2586 service thread pools. Depending on how many NICs 2587 you have and where their interrupts are bound, this 2588 option will affect which CPUs will do NFS serving. 2589 Note: this parameter cannot be changed while the 2590 NFS server is running. 2591 2592 auto the server chooses an appropriate mode 2593 automatically using heuristics 2594 global a single global pool contains all CPUs 2595 percpu one pool for each CPU 2596 pernode one pool for each NUMA node (equivalent 2597 to global on non-NUMA machines) 2598 2599 sunrpc.tcp_slot_table_entries= 2600 sunrpc.udp_slot_table_entries= 2601 [NFS,SUNRPC] 2602 Sets the upper limit on the number of simultaneous 2603 RPC calls that can be sent from the client to a 2604 server. Increasing these values may allow you to 2605 improve throughput, but will also increase the 2606 amount of memory reserved for use by the client. 2607 2608 swapaccount[=0|1] 2609 [KNL] Enable accounting of swap in memory resource 2610 controller if no parameter or 1 is given or disable 2611 it if 0 is given (See Documentation/cgroups/memory.txt) 2612 2613 swiotlb= [IA-64] Number of I/O TLB slabs 2614 2615 switches= [HW,M68k] 2616 2617 sysfs.deprecated=0|1 [KNL] 2618 Enable/disable old style sysfs layout for old udev 2619 on older distributions. When this option is enabled 2620 very new udev will not work anymore. When this option 2621 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled) 2622 in older udev will not work anymore. 2623 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in 2624 the kernel configuration. 2625 2626 sysrq_always_enabled 2627 [KNL] 2628 Ignore sysrq setting - this boot parameter will 2629 neutralize any effect of /proc/sys/kernel/sysrq. 2630 Useful for debugging. 2631 2632 tdfx= [HW,DRM] 2633 2634 test_suspend= [SUSPEND] 2635 Specify "mem" (for Suspend-to-RAM) or "standby" (for 2636 standby suspend) as the system sleep state to briefly 2637 enter during system startup. The system is woken from 2638 this state using a wakeup-capable RTC alarm. 2639 2640 thash_entries= [KNL,NET] 2641 Set number of hash buckets for TCP connection 2642 2643 thermal.act= [HW,ACPI] 2644 -1: disable all active trip points in all thermal zones 2645 <degrees C>: override all lowest active trip points 2646 2647 thermal.crt= [HW,ACPI] 2648 -1: disable all critical trip points in all thermal zones 2649 <degrees C>: override all critical trip points 2650 2651 thermal.nocrt= [HW,ACPI] 2652 Set to disable actions on ACPI thermal zone 2653 critical and hot trip points. 2654 2655 thermal.off= [HW,ACPI] 2656 1: disable ACPI thermal control 2657 2658 thermal.psv= [HW,ACPI] 2659 -1: disable all passive trip points 2660 <degrees C>: override all passive trip points to this 2661 value 2662 2663 thermal.tzp= [HW,ACPI] 2664 Specify global default ACPI thermal zone polling rate 2665 <deci-seconds>: poll all this frequency 2666 0: no polling (default) 2667 2668 threadirqs [KNL] 2669 Force threading of all interrupt handlers except those 2670 marked explicitly IRQF_NO_THREAD. 2671 2672 topology= [S390] 2673 Format: {off | on} 2674 Specify if the kernel should make use of the cpu 2675 topology information if the hardware supports this. 2676 The scheduler will make use of this information and 2677 e.g. base its process migration decisions on it. 2678 Default is on. 2679 2680 tp720= [HW,PS2] 2681 2682 tpm_suspend_pcr=[HW,TPM] 2683 Format: integer pcr id 2684 Specify that at suspend time, the tpm driver 2685 should extend the specified pcr with zeros, 2686 as a workaround for some chips which fail to 2687 flush the last written pcr on TPM_SaveState. 2688 This will guarantee that all the other pcrs 2689 are saved. 2690 2691 trace_buf_size=nn[KMG] 2692 [FTRACE] will set tracing buffer size. 2693 2694 trace_event=[event-list] 2695 [FTRACE] Set and start specified trace events in order 2696 to facilitate early boot debugging. 2697 See also Documentation/trace/events.txt 2698 2699 transparent_hugepage= 2700 [KNL] 2701 Format: [always|madvise|never] 2702 Can be used to control the default behavior of the system 2703 with respect to transparent hugepages. 2704 See Documentation/vm/transhuge.txt for more details. 2705 2706 tsc= Disable clocksource stability checks for TSC. 2707 Format: <string> 2708 [x86] reliable: mark tsc clocksource as reliable, this 2709 disables clocksource verification at runtime, as well 2710 as the stability checks done at bootup. Used to enable 2711 high-resolution timer mode on older hardware, and in 2712 virtualized environment. 2713 [x86] noirqtime: Do not use TSC to do irq accounting. 2714 Used to run time disable IRQ_TIME_ACCOUNTING on any 2715 platforms where RDTSC is slow and this accounting 2716 can add overhead. 2717 2718 turbografx.map[2|3]= [HW,JOY] 2719 TurboGraFX parallel port interface 2720 Format: 2721 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 2722 See also Documentation/input/joystick-parport.txt 2723 2724 udbg-immortal [PPC] When debugging early kernel crashes that 2725 happen after console_init() and before a proper 2726 console driver takes over, this boot options might 2727 help "seeing" what's going on. 2728 2729 uhash_entries= [KNL,NET] 2730 Set number of hash buckets for UDP/UDP-Lite connections 2731 2732 uhci-hcd.ignore_oc= 2733 [USB] Ignore overcurrent events (default N). 2734 Some badly-designed motherboards generate lots of 2735 bogus events, for ports that aren't wired to 2736 anything. Set this parameter to avoid log spamming. 2737 Note that genuine overcurrent events won't be 2738 reported either. 2739 2740 unknown_nmi_panic 2741 [X86] Cause panic on unknown NMI. 2742 2743 usbcore.authorized_default= 2744 [USB] Default USB device authorization: 2745 (default -1 = authorized except for wireless USB, 2746 0 = not authorized, 1 = authorized) 2747 2748 usbcore.autosuspend= 2749 [USB] The autosuspend time delay (in seconds) used 2750 for newly-detected USB devices (default 2). This 2751 is the time required before an idle device will be 2752 autosuspended. Devices for which the delay is set 2753 to a negative value won't be autosuspended at all. 2754 2755 usbcore.usbfs_snoop= 2756 [USB] Set to log all usbfs traffic (default 0 = off). 2757 2758 usbcore.blinkenlights= 2759 [USB] Set to cycle leds on hubs (default 0 = off). 2760 2761 usbcore.old_scheme_first= 2762 [USB] Start with the old device initialization 2763 scheme (default 0 = off). 2764 2765 usbcore.usbfs_memory_mb= 2766 [USB] Memory limit (in MB) for buffers allocated by 2767 usbfs (default = 16, 0 = max = 2047). 2768 2769 usbcore.use_both_schemes= 2770 [USB] Try the other device initialization scheme 2771 if the first one fails (default 1 = enabled). 2772 2773 usbcore.initial_descriptor_timeout= 2774 [USB] Specifies timeout for the initial 64-byte 2775 USB_REQ_GET_DESCRIPTOR request in milliseconds 2776 (default 5000 = 5.0 seconds). 2777 2778 usbhid.mousepoll= 2779 [USBHID] The interval which mice are to be polled at. 2780 2781 usb-storage.delay_use= 2782 [UMS] The delay in seconds before a new device is 2783 scanned for Logical Units (default 5). 2784 2785 usb-storage.quirks= 2786 [UMS] A list of quirks entries to supplement or 2787 override the built-in unusual_devs list. List 2788 entries are separated by commas. Each entry has 2789 the form VID:PID:Flags where VID and PID are Vendor 2790 and Product ID values (4-digit hex numbers) and 2791 Flags is a set of characters, each corresponding 2792 to a common usb-storage quirk flag as follows: 2793 a = SANE_SENSE (collect more than 18 bytes 2794 of sense data); 2795 b = BAD_SENSE (don't collect more than 18 2796 bytes of sense data); 2797 c = FIX_CAPACITY (decrease the reported 2798 device capacity by one sector); 2799 d = NO_READ_DISC_INFO (don't use 2800 READ_DISC_INFO command); 2801 e = NO_READ_CAPACITY_16 (don't use 2802 READ_CAPACITY_16 command); 2803 h = CAPACITY_HEURISTICS (decrease the 2804 reported device capacity by one 2805 sector if the number is odd); 2806 i = IGNORE_DEVICE (don't bind to this 2807 device); 2808 l = NOT_LOCKABLE (don't try to lock and 2809 unlock ejectable media); 2810 m = MAX_SECTORS_64 (don't transfer more 2811 than 64 sectors = 32 KB at a time); 2812 n = INITIAL_READ10 (force a retry of the 2813 initial READ(10) command); 2814 o = CAPACITY_OK (accept the capacity 2815 reported by the device); 2816 r = IGNORE_RESIDUE (the device reports 2817 bogus residue values); 2818 s = SINGLE_LUN (the device has only one 2819 Logical Unit); 2820 w = NO_WP_DETECT (don't test whether the 2821 medium is write-protected). 2822 Example: quirks=0419:aaf5:rl,0421:0433:rc 2823 2824 user_debug= [KNL,ARM] 2825 Format: <int> 2826 See arch/arm/Kconfig.debug help text. 2827 1 - undefined instruction events 2828 2 - system calls 2829 4 - invalid data aborts 2830 8 - SIGSEGV faults 2831 16 - SIGBUS faults 2832 Example: user_debug=31 2833 2834 userpte= 2835 [X86] Flags controlling user PTE allocations. 2836 2837 nohigh = do not allocate PTE pages in 2838 HIGHMEM regardless of setting 2839 of CONFIG_HIGHPTE. 2840 2841 vdso= [X86,SH] 2842 vdso=2: enable compat VDSO (default with COMPAT_VDSO) 2843 vdso=1: enable VDSO (default) 2844 vdso=0: disable VDSO mapping 2845 2846 vdso32= [X86] 2847 vdso32=2: enable compat VDSO (default with COMPAT_VDSO) 2848 vdso32=1: enable 32-bit VDSO (default) 2849 vdso32=0: disable 32-bit VDSO mapping 2850 2851 vector= [IA-64,SMP] 2852 vector=percpu: enable percpu vector domain 2853 2854 video= [FB] Frame buffer configuration 2855 See Documentation/fb/modedb.txt. 2856 2857 vga= [BOOT,X86-32] Select a particular video mode 2858 See Documentation/x86/boot.txt and 2859 Documentation/svga.txt. 2860 Use vga=ask for menu. 2861 This is actually a boot loader parameter; the value is 2862 passed to the kernel using a special protocol. 2863 2864 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact 2865 size of <nn>. This can be used to increase the 2866 minimum size (128MB on x86). It can also be used to 2867 decrease the size and leave more room for directly 2868 mapped kernel RAM. 2869 2870 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 2871 Format: <command> 2872 2873 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 2874 Format: <command> 2875 2876 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 2877 Format: <command> 2878 2879 vsyscall= [X86-64] 2880 Controls the behavior of vsyscalls (i.e. calls to 2881 fixed addresses of 0xffffffffff600x00 from legacy 2882 code). Most statically-linked binaries and older 2883 versions of glibc use these calls. Because these 2884 functions are at fixed addresses, they make nice 2885 targets for exploits that can control RIP. 2886 2887 emulate [default] Vsyscalls turn into traps and are 2888 emulated reasonably safely. 2889 2890 native Vsyscalls are native syscall instructions. 2891 This is a little bit faster than trapping 2892 and makes a few dynamic recompilers work 2893 better than they would in emulation mode. 2894 It also makes exploits much easier to write. 2895 2896 none Vsyscalls don't work at all. This makes 2897 them quite hard to use for exploits but 2898 might break your system. 2899 2900 vt.cur_default= [VT] Default cursor shape. 2901 Format: 0xCCBBAA, where AA, BB, and CC are the same as 2902 the parameters of the <Esc>[?A;B;Cc escape sequence; 2903 see VGA-softcursor.txt. Default: 2 = underline. 2904 2905 vt.default_blu= [VT] 2906 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 2907 Change the default blue palette of the console. 2908 This is a 16-member array composed of values 2909 ranging from 0-255. 2910 2911 vt.default_grn= [VT] 2912 Format: <green0>,<green1>,<green2>,...,<green15> 2913 Change the default green palette of the console. 2914 This is a 16-member array composed of values 2915 ranging from 0-255. 2916 2917 vt.default_red= [VT] 2918 Format: <red0>,<red1>,<red2>,...,<red15> 2919 Change the default red palette of the console. 2920 This is a 16-member array composed of values 2921 ranging from 0-255. 2922 2923 vt.default_utf8= 2924 [VT] 2925 Format=<0|1> 2926 Set system-wide default UTF-8 mode for all tty's. 2927 Default is 1, i.e. UTF-8 mode is enabled for all 2928 newly opened terminals. 2929 2930 vt.global_cursor_default= 2931 [VT] 2932 Format=<-1|0|1> 2933 Set system-wide default for whether a cursor 2934 is shown on new VTs. Default is -1, 2935 i.e. cursors will be created by default unless 2936 overridden by individual drivers. 0 will hide 2937 cursors, 1 will display them. 2938 2939 watchdog timers [HW,WDT] For information on watchdog timers, 2940 see Documentation/watchdog/watchdog-parameters.txt 2941 or other driver-specific files in the 2942 Documentation/watchdog/ directory. 2943 2944 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of 2945 default x2apic cluster mode on platforms 2946 supporting x2apic. 2947 2948 x86_mrst_timer= [X86-32,APBT] 2949 Choose timer option for x86 Moorestown MID platform. 2950 Two valid options are apbt timer only and lapic timer 2951 plus one apbt timer for broadcast timer. 2952 x86_mrst_timer=apbt_only | lapic_and_apbt 2953 2954 xd= [HW,XT] Original XT pre-IDE (RLL encoded) disks. 2955 xd_geo= See header of drivers/block/xd.c. 2956 2957 xen_emul_unplug= [HW,X86,XEN] 2958 Unplug Xen emulated devices 2959 Format: [unplug0,][unplug1] 2960 ide-disks -- unplug primary master IDE devices 2961 aux-ide-disks -- unplug non-primary-master IDE devices 2962 nics -- unplug network devices 2963 all -- unplug all emulated devices (NICs and IDE disks) 2964 unnecessary -- unplugging emulated devices is 2965 unnecessary even if the host did not respond to 2966 the unplug protocol 2967 never -- do not unplug even if version check succeeds 2968 2969 xirc2ps_cs= [NET,PCMCIA] 2970 Format: 2971 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 2972 2973______________________________________________________________________ 2974 2975TODO: 2976 2977 Add more DRM drivers. 2978