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