1 Kernel Parameters 2 ~~~~~~~~~~~~~~~~~ 3 4The following is a consolidated list of the kernel parameters as 5implemented by the __setup(), core_param() and module_param() macros 6and sorted into English Dictionary order (defined as ignoring all 7punctuation and sorting digits before letters in a case insensitive 8manner), and with descriptions where known. 9 10The kernel parses parameters from the kernel command line up to "--"; 11if it doesn't recognize a parameter and it doesn't contain a '.', the 12parameter gets passed to init: parameters with '=' go into init's 13environment, others are passed as command line arguments to init. 14Everything after "--" is passed as an argument to init. 15 16Module parameters can be specified in two ways: via the kernel command 17line with a module name prefix, or via modprobe, e.g.: 18 19 (kernel command line) usbcore.blinkenlights=1 20 (modprobe command line) modprobe usbcore blinkenlights=1 21 22Parameters for modules which are built into the kernel need to be 23specified on the kernel command line. modprobe looks through the 24kernel command line (/proc/cmdline) and collects module parameters 25when it loads a module, so the kernel command line can be used for 26loadable modules too. 27 28Hyphens (dashes) and underscores are equivalent in parameter names, so 29 log_buf_len=1M print-fatal-signals=1 30can also be entered as 31 log-buf-len=1M print_fatal_signals=1 32 33Double-quotes can be used to protect spaces in values, e.g.: 34 param="spaces in here" 35 36This document may not be entirely up to date and comprehensive. The command 37"modinfo -p ${modulename}" shows a current list of all parameters of a loadable 38module. Loadable modules, after being loaded into the running kernel, also 39reveal their parameters in /sys/module/${modulename}/parameters/. Some of these 40parameters may be changed at runtime by the command 41"echo -n ${value} > /sys/module/${modulename}/parameters/${parm}". 42 43The parameters listed below are only valid if certain kernel build options were 44enabled and if respective hardware is present. The text in square brackets at 45the beginning of each description states the restrictions within which a 46parameter is applicable: 47 48 ACPI ACPI support is enabled. 49 AGP AGP (Accelerated Graphics Port) is enabled. 50 ALSA ALSA sound support is enabled. 51 APIC APIC support is enabled. 52 APM Advanced Power Management support is enabled. 53 ARM ARM architecture is enabled. 54 AVR32 AVR32 architecture is enabled. 55 AX25 Appropriate AX.25 support is enabled. 56 BLACKFIN Blackfin architecture is enabled. 57 CLK Common clock infrastructure is enabled. 58 CMA Contiguous Memory Area support is enabled. 59 DRM Direct Rendering Management support is enabled. 60 DYNAMIC_DEBUG Build in debug messages and enable them at runtime 61 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled 62 EFI EFI Partitioning (GPT) is enabled 63 EIDE EIDE/ATAPI support is enabled. 64 EVM Extended Verification Module 65 FB The frame buffer device is enabled. 66 FTRACE Function tracing enabled. 67 GCOV GCOV profiling is enabled. 68 HW Appropriate hardware is enabled. 69 IA-64 IA-64 architecture is enabled. 70 IMA Integrity measurement architecture is enabled. 71 IOSCHED More than one I/O scheduler is enabled. 72 IP_PNP IP DHCP, BOOTP, or RARP is enabled. 73 IPV6 IPv6 support is enabled. 74 ISAPNP ISA PnP code is enabled. 75 ISDN Appropriate ISDN support is enabled. 76 JOY Appropriate joystick support is enabled. 77 KGDB Kernel debugger support is enabled. 78 KVM Kernel Virtual Machine support is enabled. 79 LIBATA Libata driver is enabled 80 LP Printer support is enabled. 81 LOOP Loopback device support is enabled. 82 M68k M68k architecture is enabled. 83 These options have more detailed description inside of 84 Documentation/m68k/kernel-options.txt. 85 MDA MDA console support is enabled. 86 MIPS MIPS architecture is enabled. 87 MOUSE Appropriate mouse support is enabled. 88 MSI Message Signaled Interrupts (PCI). 89 MTD MTD (Memory Technology Device) support is enabled. 90 NET Appropriate network support is enabled. 91 NUMA NUMA support is enabled. 92 NFS Appropriate NFS support is enabled. 93 OSS OSS sound support is enabled. 94 PV_OPS A paravirtualized kernel is enabled. 95 PARIDE The ParIDE (parallel port IDE) subsystem is enabled. 96 PARISC The PA-RISC architecture is enabled. 97 PCI PCI bus support is enabled. 98 PCIE PCI Express support is enabled. 99 PCMCIA The PCMCIA subsystem is enabled. 100 PNP Plug & Play support is enabled. 101 PPC PowerPC architecture is enabled. 102 PPT Parallel port support is enabled. 103 PS2 Appropriate PS/2 support is enabled. 104 RAM RAM disk support is enabled. 105 S390 S390 architecture is enabled. 106 SCSI Appropriate SCSI support is enabled. 107 A lot of drivers have their options described inside 108 the Documentation/scsi/ sub-directory. 109 SECURITY Different security models are enabled. 110 SELINUX SELinux support is enabled. 111 APPARMOR AppArmor support is enabled. 112 SERIAL Serial support is enabled. 113 SH SuperH architecture is enabled. 114 SMP The kernel is an SMP kernel. 115 SPARC Sparc architecture is enabled. 116 SWSUSP Software suspend (hibernation) is enabled. 117 SUSPEND System suspend states are enabled. 118 TPM TPM drivers are enabled. 119 TS Appropriate touchscreen support is enabled. 120 UMS USB Mass Storage support is enabled. 121 USB USB support is enabled. 122 USBHID USB Human Interface Device support is enabled. 123 V4L Video For Linux support is enabled. 124 VMMIO Driver for memory mapped virtio devices is enabled. 125 VGA The VGA console has been enabled. 126 VT Virtual terminal support is enabled. 127 WDT Watchdog support is enabled. 128 XT IBM PC/XT MFM hard disk support is enabled. 129 X86-32 X86-32, aka i386 architecture is enabled. 130 X86-64 X86-64 architecture is enabled. 131 More X86-64 boot options can be found in 132 Documentation/x86/x86_64/boot-options.txt . 133 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64) 134 XEN Xen support is enabled 135 136In addition, the following text indicates that the option: 137 138 BUGS= Relates to possible processor bugs on the said processor. 139 KNL Is a kernel start-up parameter. 140 BOOT Is a boot loader parameter. 141 142Parameters denoted with BOOT are actually interpreted by the boot 143loader, and have no meaning to the kernel directly. 144Do not modify the syntax of boot loader parameters without extreme 145need or coordination with <Documentation/x86/boot.txt>. 146 147There are also arch-specific kernel-parameters not documented here. 148See for example <Documentation/x86/x86_64/boot-options.txt>. 149 150Note that ALL kernel parameters listed below are CASE SENSITIVE, and that 151a trailing = on the name of any parameter states that that parameter will 152be entered as an environment variable, whereas its absence indicates that 153it will appear as a kernel argument readable via /proc/cmdline by programs 154running once the system is up. 155 156The number of kernel parameters is not limited, but the length of the 157complete command line (parameters including spaces etc.) is limited to 158a fixed number of characters. This limit depends on the architecture 159and is between 256 and 4096 characters. It is defined in the file 160./include/asm/setup.h as COMMAND_LINE_SIZE. 161 162Finally, the [KMG] suffix is commonly described after a number of kernel 163parameter values. These 'K', 'M', and 'G' letters represent the _binary_ 164multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30 165bytes respectively. Such letter suffixes can also be entirely omitted. 166 167 168 acpi= [HW,ACPI,X86,ARM64] 169 Advanced Configuration and Power Interface 170 Format: { force | off | strict | noirq | rsdt | 171 copy_dsdt } 172 force -- enable ACPI if default was off 173 off -- disable ACPI if default was on 174 noirq -- do not use ACPI for IRQ routing 175 strict -- Be less tolerant of platforms that are not 176 strictly ACPI specification compliant. 177 rsdt -- prefer RSDT over (default) XSDT 178 copy_dsdt -- copy DSDT to memory 179 For ARM64, ONLY "acpi=off" or "acpi=force" are available 180 181 See also Documentation/power/runtime_pm.txt, pci=noacpi 182 183 acpi_apic_instance= [ACPI, IOAPIC] 184 Format: <int> 185 2: use 2nd APIC table, if available 186 1,0: use 1st APIC table 187 default: 0 188 189 acpi_backlight= [HW,ACPI] 190 acpi_backlight=vendor 191 acpi_backlight=video 192 If set to vendor, prefer vendor specific driver 193 (e.g. thinkpad_acpi, sony_acpi, etc.) instead 194 of the ACPI video.ko driver. 195 196 acpica_no_return_repair [HW, ACPI] 197 Disable AML predefined validation mechanism 198 This mechanism can repair the evaluation result to make 199 the return objects more ACPI specification compliant. 200 This option is useful for developers to identify the 201 root cause of an AML interpreter issue when the issue 202 has something to do with the repair mechanism. 203 204 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG] 205 acpi.debug_level= [HW,ACPI,ACPI_DEBUG] 206 Format: <int> 207 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI 208 debug output. Bits in debug_layer correspond to a 209 _COMPONENT in an ACPI source file, e.g., 210 #define _COMPONENT ACPI_PCI_COMPONENT 211 Bits in debug_level correspond to a level in 212 ACPI_DEBUG_PRINT statements, e.g., 213 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ... 214 The debug_level mask defaults to "info". See 215 Documentation/acpi/debug.txt for more information about 216 debug layers and levels. 217 218 Enable processor driver info messages: 219 acpi.debug_layer=0x20000000 220 Enable PCI/PCI interrupt routing info messages: 221 acpi.debug_layer=0x400000 222 Enable AML "Debug" output, i.e., stores to the Debug 223 object while interpreting AML: 224 acpi.debug_layer=0xffffffff acpi.debug_level=0x2 225 Enable all messages related to ACPI hardware: 226 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff 227 228 Some values produce so much output that the system is 229 unusable. The "log_buf_len" parameter may be useful 230 if you need to capture more output. 231 232 acpi_enforce_resources= [ACPI] 233 { strict | lax | no } 234 Check for resource conflicts between native drivers 235 and ACPI OperationRegions (SystemIO and SystemMemory 236 only). IO ports and memory declared in ACPI might be 237 used by the ACPI subsystem in arbitrary AML code and 238 can interfere with legacy drivers. 239 strict (default): access to resources claimed by ACPI 240 is denied; legacy drivers trying to access reserved 241 resources will fail to bind to device using them. 242 lax: access to resources claimed by ACPI is allowed; 243 legacy drivers trying to access reserved resources 244 will bind successfully but a warning message is logged. 245 no: ACPI OperationRegions are not marked as reserved, 246 no further checks are performed. 247 248 acpi_force_table_verification [HW,ACPI] 249 Enable table checksum verification during early stage. 250 By default, this is disabled due to x86 early mapping 251 size limitation. 252 253 acpi_irq_balance [HW,ACPI] 254 ACPI will balance active IRQs 255 default in APIC mode 256 257 acpi_irq_nobalance [HW,ACPI] 258 ACPI will not move active IRQs (default) 259 default in PIC mode 260 261 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA 262 Format: <irq>,<irq>... 263 264 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for 265 use by PCI 266 Format: <irq>,<irq>... 267 268 acpi_no_auto_serialize [HW,ACPI] 269 Disable auto-serialization of AML methods 270 AML control methods that contain the opcodes to create 271 named objects will be marked as "Serialized" by the 272 auto-serialization feature. 273 This feature is enabled by default. 274 This option allows to turn off the feature. 275 276 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump 277 kernels. 278 279 acpi_no_static_ssdt [HW,ACPI] 280 Disable installation of static SSDTs at early boot time 281 By default, SSDTs contained in the RSDT/XSDT will be 282 installed automatically and they will appear under 283 /sys/firmware/acpi/tables. 284 This option turns off this feature. 285 Note that specifying this option does not affect 286 dynamic table installation which will install SSDT 287 tables to /sys/firmware/acpi/tables/dynamic. 288 289 acpi_rsdp= [ACPI,EFI,KEXEC] 290 Pass the RSDP address to the kernel, mostly used 291 on machines running EFI runtime service to boot the 292 second kernel for kdump. 293 294 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS 295 Format: To spoof as Windows 98: ="Microsoft Windows" 296 297 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead 298 of 2 which is mandated by ACPI 6) as the supported ACPI 299 specification revision (when using this switch, it may 300 be necessary to carry out a cold reboot _twice_ in a 301 row to make it take effect on the platform firmware). 302 303 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings 304 acpi_osi="string1" # add string1 305 acpi_osi="!string2" # remove string2 306 acpi_osi=!* # remove all strings 307 acpi_osi=! # disable all built-in OS vendor 308 strings 309 acpi_osi= # disable all strings 310 311 'acpi_osi=!' can be used in combination with single or 312 multiple 'acpi_osi="string1"' to support specific OS 313 vendor string(s). Note that such command can only 314 affect the default state of the OS vendor strings, thus 315 it cannot affect the default state of the feature group 316 strings and the current state of the OS vendor strings, 317 specifying it multiple times through kernel command line 318 is meaningless. This command is useful when one do not 319 care about the state of the feature group strings which 320 should be controlled by the OSPM. 321 Examples: 322 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent 323 to 'acpi_osi="Windows 2000" acpi_osi=!', they all 324 can make '_OSI("Windows 2000")' TRUE. 325 326 'acpi_osi=' cannot be used in combination with other 327 'acpi_osi=' command lines, the _OSI method will not 328 exist in the ACPI namespace. NOTE that such command can 329 only affect the _OSI support state, thus specifying it 330 multiple times through kernel command line is also 331 meaningless. 332 Examples: 333 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)' 334 FALSE. 335 336 'acpi_osi=!*' can be used in combination with single or 337 multiple 'acpi_osi="string1"' to support specific 338 string(s). Note that such command can affect the 339 current state of both the OS vendor strings and the 340 feature group strings, thus specifying it multiple times 341 through kernel command line is meaningful. But it may 342 still not able to affect the final state of a string if 343 there are quirks related to this string. This command 344 is useful when one want to control the state of the 345 feature group strings to debug BIOS issues related to 346 the OSPM features. 347 Examples: 348 1. 'acpi_osi="Module Device" acpi_osi=!*' can make 349 '_OSI("Module Device")' FALSE. 350 2. 'acpi_osi=!* acpi_osi="Module Device"' can make 351 '_OSI("Module Device")' TRUE. 352 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is 353 equivalent to 354 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"' 355 and 356 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!', 357 they all will make '_OSI("Windows 2000")' TRUE. 358 359 acpi_pm_good [X86] 360 Override the pmtimer bug detection: force the kernel 361 to assume that this machine's pmtimer latches its value 362 and always returns good values. 363 364 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode 365 Format: { level | edge | high | low } 366 367 acpi_skip_timer_override [HW,ACPI] 368 Recognize and ignore IRQ0/pin2 Interrupt Override. 369 For broken nForce2 BIOS resulting in XT-PIC timer. 370 371 acpi_sleep= [HW,ACPI] Sleep options 372 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig, 373 old_ordering, nonvs, sci_force_enable } 374 See Documentation/power/video.txt for information on 375 s3_bios and s3_mode. 376 s3_beep is for debugging; it makes the PC's speaker beep 377 as soon as the kernel's real-mode entry point is called. 378 s4_nohwsig prevents ACPI hardware signature from being 379 used during resume from hibernation. 380 old_ordering causes the ACPI 1.0 ordering of the _PTS 381 control method, with respect to putting devices into 382 low power states, to be enforced (the ACPI 2.0 ordering 383 of _PTS is used by default). 384 nonvs prevents the kernel from saving/restoring the 385 ACPI NVS memory during suspend/hibernation and resume. 386 sci_force_enable causes the kernel to set SCI_EN directly 387 on resume from S1/S3 (which is against the ACPI spec, 388 but some broken systems don't work without it). 389 390 acpi_use_timer_override [HW,ACPI] 391 Use timer override. For some broken Nvidia NF5 boards 392 that require a timer override, but don't have HPET 393 394 add_efi_memmap [EFI; X86] Include EFI memory map in 395 kernel's map of available physical RAM. 396 397 agp= [AGP] 398 { off | try_unsupported } 399 off: disable AGP support 400 try_unsupported: try to drive unsupported chipsets 401 (may crash computer or cause data corruption) 402 403 ALSA [HW,ALSA] 404 See Documentation/sound/alsa/alsa-parameters.txt 405 406 alignment= [KNL,ARM] 407 Allow the default userspace alignment fault handler 408 behaviour to be specified. Bit 0 enables warnings, 409 bit 1 enables fixups, and bit 2 sends a segfault. 410 411 align_va_addr= [X86-64] 412 Align virtual addresses by clearing slice [14:12] when 413 allocating a VMA at process creation time. This option 414 gives you up to 3% performance improvement on AMD F15h 415 machines (where it is enabled by default) for a 416 CPU-intensive style benchmark, and it can vary highly in 417 a microbenchmark depending on workload and compiler. 418 419 32: only for 32-bit processes 420 64: only for 64-bit processes 421 on: enable for both 32- and 64-bit processes 422 off: disable for both 32- and 64-bit processes 423 424 alloc_snapshot [FTRACE] 425 Allocate the ftrace snapshot buffer on boot up when the 426 main buffer is allocated. This is handy if debugging 427 and you need to use tracing_snapshot() on boot up, and 428 do not want to use tracing_snapshot_alloc() as it needs 429 to be done where GFP_KERNEL allocations are allowed. 430 431 amd_iommu= [HW,X86-64] 432 Pass parameters to the AMD IOMMU driver in the system. 433 Possible values are: 434 fullflush - enable flushing of IO/TLB entries when 435 they are unmapped. Otherwise they are 436 flushed before they will be reused, which 437 is a lot of faster 438 off - do not initialize any AMD IOMMU found in 439 the system 440 force_isolation - Force device isolation for all 441 devices. The IOMMU driver is not 442 allowed anymore to lift isolation 443 requirements as needed. This option 444 does not override iommu=pt 445 446 amd_iommu_dump= [HW,X86-64] 447 Enable AMD IOMMU driver option to dump the ACPI table 448 for AMD IOMMU. With this option enabled, AMD IOMMU 449 driver will print ACPI tables for AMD IOMMU during 450 IOMMU initialization. 451 452 amijoy.map= [HW,JOY] Amiga joystick support 453 Map of devices attached to JOY0DAT and JOY1DAT 454 Format: <a>,<b> 455 See also Documentation/input/joystick.txt 456 457 analog.map= [HW,JOY] Analog joystick and gamepad support 458 Specifies type or capabilities of an analog joystick 459 connected to one of 16 gameports 460 Format: <type1>,<type2>,..<type16> 461 462 apc= [HW,SPARC] 463 Power management functions (SPARCstation-4/5 + deriv.) 464 Format: noidle 465 Disable APC CPU standby support. SPARCstation-Fox does 466 not play well with APC CPU idle - disable it if you have 467 APC and your system crashes randomly. 468 469 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller 470 Change the output verbosity whilst booting 471 Format: { quiet (default) | verbose | debug } 472 Change the amount of debugging information output 473 when initialising the APIC and IO-APIC components. 474 475 autoconf= [IPV6] 476 See Documentation/networking/ipv6.txt. 477 478 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller 479 Limit apic dumping. The parameter defines the maximal 480 number of local apics being dumped. Also it is possible 481 to set it to "all" by meaning -- no limit here. 482 Format: { 1 (default) | 2 | ... | all }. 483 The parameter valid if only apic=debug or 484 apic=verbose is specified. 485 Example: apic=debug show_lapic=all 486 487 apm= [APM] Advanced Power Management 488 See header of arch/x86/kernel/apm_32.c. 489 490 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards 491 Format: <io>,<irq>,<nodeID> 492 493 ataflop= [HW,M68k] 494 495 atarimouse= [HW,MOUSE] Atari Mouse 496 497 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess, 498 EzKey and similar keyboards 499 500 atkbd.reset= [HW] Reset keyboard during initialization 501 502 atkbd.set= [HW] Select keyboard code set 503 Format: <int> (2 = AT (default), 3 = PS/2) 504 505 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar 506 keyboards 507 508 atkbd.softraw= [HW] Choose between synthetic and real raw mode 509 Format: <bool> (0 = real, 1 = synthetic (default)) 510 511 atkbd.softrepeat= [HW] 512 Use software keyboard repeat 513 514 audit= [KNL] Enable the audit sub-system 515 Format: { "0" | "1" } (0 = disabled, 1 = enabled) 516 0 - kernel audit is disabled and can not be enabled 517 until the next reboot 518 unset - kernel audit is initialized but disabled and 519 will be fully enabled by the userspace auditd. 520 1 - kernel audit is initialized and partially enabled, 521 storing at most audit_backlog_limit messages in 522 RAM until it is fully enabled by the userspace 523 auditd. 524 Default: unset 525 526 audit_backlog_limit= [KNL] Set the audit queue size limit. 527 Format: <int> (must be >=0) 528 Default: 64 529 530 baycom_epp= [HW,AX25] 531 Format: <io>,<mode> 532 533 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem 534 Format: <io>,<mode> 535 See header of drivers/net/hamradio/baycom_par.c. 536 537 baycom_ser_fdx= [HW,AX25] 538 BayCom Serial Port AX.25 Modem (Full Duplex Mode) 539 Format: <io>,<irq>,<mode>[,<baud>] 540 See header of drivers/net/hamradio/baycom_ser_fdx.c. 541 542 baycom_ser_hdx= [HW,AX25] 543 BayCom Serial Port AX.25 Modem (Half Duplex Mode) 544 Format: <io>,<irq>,<mode> 545 See header of drivers/net/hamradio/baycom_ser_hdx.c. 546 547 blkdevparts= Manual partition parsing of block device(s) for 548 embedded devices based on command line input. 549 See Documentation/block/cmdline-partition.txt 550 551 boot_delay= Milliseconds to delay each printk during boot. 552 Values larger than 10 seconds (10000) are changed to 553 no delay (0). 554 Format: integer 555 556 bootmem_debug [KNL] Enable bootmem allocator debug messages. 557 558 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards) 559 bttv.radio= Most important insmod options are available as 560 kernel args too. 561 bttv.pll= See Documentation/video4linux/bttv/Insmod-options 562 bttv.tuner= 563 564 bulk_remove=off [PPC] This parameter disables the use of the pSeries 565 firmware feature for flushing multiple hpte entries 566 at a time. 567 568 c101= [NET] Moxa C101 synchronous serial card 569 570 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection. 571 Sometimes CPU hardware bugs make them report the cache 572 size incorrectly. The kernel will attempt work arounds 573 to fix known problems, but for some CPUs it is not 574 possible to determine what the correct size should be. 575 This option provides an override for these situations. 576 577 ca_keys= [KEYS] This parameter identifies a specific key(s) on 578 the system trusted keyring to be used for certificate 579 trust validation. 580 format: { id:<keyid> | builtin } 581 582 cca= [MIPS] Override the kernel pages' cache coherency 583 algorithm. Accepted values range from 0 to 7 584 inclusive. See arch/mips/include/asm/pgtable-bits.h 585 for platform specific values (SB1, Loongson3 and 586 others). 587 588 ccw_timeout_log [S390] 589 See Documentation/s390/CommonIO for details. 590 591 cgroup_disable= [KNL] Disable a particular controller 592 Format: {name of the controller(s) to disable} 593 The effects of cgroup_disable=foo are: 594 - foo isn't auto-mounted if you mount all cgroups in 595 a single hierarchy 596 - foo isn't visible as an individually mountable 597 subsystem 598 {Currently only "memory" controller deal with this and 599 cut the overhead, others just disable the usage. So 600 only cgroup_disable=memory is actually worthy} 601 602 checkreqprot [SELINUX] Set initial checkreqprot flag value. 603 Format: { "0" | "1" } 604 See security/selinux/Kconfig help text. 605 0 -- check protection applied by kernel (includes 606 any implied execute protection). 607 1 -- check protection requested by application. 608 Default value is set via a kernel config option. 609 Value can be changed at runtime via 610 /selinux/checkreqprot. 611 612 cio_ignore= [S390] 613 See Documentation/s390/CommonIO for details. 614 clk_ignore_unused 615 [CLK] 616 Prevents the clock framework from automatically gating 617 clocks that have not been explicitly enabled by a Linux 618 device driver but are enabled in hardware at reset or 619 by the bootloader/firmware. Note that this does not 620 force such clocks to be always-on nor does it reserve 621 those clocks in any way. This parameter is useful for 622 debug and development, but should not be needed on a 623 platform with proper driver support. For more 624 information, see Documentation/clk.txt. 625 626 clock= [BUGS=X86-32, HW] gettimeofday clocksource override. 627 [Deprecated] 628 Forces specified clocksource (if available) to be used 629 when calculating gettimeofday(). If specified 630 clocksource is not available, it defaults to PIT. 631 Format: { pit | tsc | cyclone | pmtmr } 632 633 clocksource= Override the default clocksource 634 Format: <string> 635 Override the default clocksource and use the clocksource 636 with the name specified. 637 Some clocksource names to choose from, depending on 638 the platform: 639 [all] jiffies (this is the base, fallback clocksource) 640 [ACPI] acpi_pm 641 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2, 642 pxa_timer,timer3,32k_counter,timer0_1 643 [AVR32] avr32 644 [X86-32] pit,hpet,tsc; 645 scx200_hrt on Geode; cyclone on IBM x440 646 [MIPS] MIPS 647 [PARISC] cr16 648 [S390] tod 649 [SH] SuperH 650 [SPARC64] tick 651 [X86-64] hpet,tsc 652 653 clearcpuid=BITNUM [X86] 654 Disable CPUID feature X for the kernel. See 655 arch/x86/include/asm/cpufeature.h for the valid bit 656 numbers. Note the Linux specific bits are not necessarily 657 stable over kernel options, but the vendor specific 658 ones should be. 659 Also note that user programs calling CPUID directly 660 or using the feature without checking anything 661 will still see it. This just prevents it from 662 being used by the kernel or shown in /proc/cpuinfo. 663 Also note the kernel might malfunction if you disable 664 some critical bits. 665 666 cma=nn[MG]@[start[MG][-end[MG]]] 667 [ARM,X86,KNL] 668 Sets the size of kernel global memory area for 669 contiguous memory allocations and optionally the 670 placement constraint by the physical address range of 671 memory allocations. A value of 0 disables CMA 672 altogether. For more information, see 673 include/linux/dma-contiguous.h 674 675 cmo_free_hint= [PPC] Format: { yes | no } 676 Specify whether pages are marked as being inactive 677 when they are freed. This is used in CMO environments 678 to determine OS memory pressure for page stealing by 679 a hypervisor. 680 Default: yes 681 682 coherent_pool=nn[KMG] [ARM,KNL] 683 Sets the size of memory pool for coherent, atomic dma 684 allocations, by default set to 256K. 685 686 code_bytes [X86] How many bytes of object code to print 687 in an oops report. 688 Range: 0 - 8192 689 Default: 64 690 691 com20020= [HW,NET] ARCnet - COM20020 chipset 692 Format: 693 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]] 694 695 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers) 696 Format: <io>[,<irq>] 697 698 com90xx= [HW,NET] 699 ARCnet - COM90xx chipset (memory-mapped buffers) 700 Format: <io>[,<irq>[,<memstart>]] 701 702 condev= [HW,S390] console device 703 conmode= 704 705 console= [KNL] Output console device and options. 706 707 tty<n> Use the virtual console device <n>. 708 709 ttyS<n>[,options] 710 ttyUSB0[,options] 711 Use the specified serial port. The options are of 712 the form "bbbbpnf", where "bbbb" is the baud rate, 713 "p" is parity ("n", "o", or "e"), "n" is number of 714 bits, and "f" is flow control ("r" for RTS or 715 omit it). Default is "9600n8". 716 717 See Documentation/serial-console.txt for more 718 information. See 719 Documentation/networking/netconsole.txt for an 720 alternative. 721 722 uart[8250],io,<addr>[,options] 723 uart[8250],mmio,<addr>[,options] 724 uart[8250],mmio32,<addr>[,options] 725 uart[8250],0x<addr>[,options] 726 Start an early, polled-mode console on the 8250/16550 727 UART at the specified I/O port or MMIO address, 728 switching to the matching ttyS device later. 729 MMIO inter-register address stride is either 8-bit 730 (mmio) or 32-bit (mmio32). 731 If none of [io|mmio|mmio32], <addr> is assumed to be 732 equivalent to 'mmio'. 'options' are specified in the 733 same format described for ttyS above; if unspecified, 734 the h/w is not re-initialized. 735 736 hvc<n> Use the hypervisor console device <n>. This is for 737 both Xen and PowerPC hypervisors. 738 739 If the device connected to the port is not a TTY but a braille 740 device, prepend "brl," before the device type, for instance 741 console=brl,ttyS0 742 For now, only VisioBraille is supported. 743 744 consoleblank= [KNL] The console blank (screen saver) timeout in 745 seconds. Defaults to 10*60 = 10mins. A value of 0 746 disables the blank timer. 747 748 coredump_filter= 749 [KNL] Change the default value for 750 /proc/<pid>/coredump_filter. 751 See also Documentation/filesystems/proc.txt. 752 753 cpuidle.off=1 [CPU_IDLE] 754 disable the cpuidle sub-system 755 756 cpu_init_udelay=N 757 [X86] Delay for N microsec between assert and de-assert 758 of APIC INIT to start processors. This delay occurs 759 on every CPU online, such as boot, and resume from suspend. 760 Default: 10000 761 762 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver 763 Format: 764 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] 765 766 crashkernel=size[KMG][@offset[KMG]] 767 [KNL] Using kexec, Linux can switch to a 'crash kernel' 768 upon panic. This parameter reserves the physical 769 memory region [offset, offset + size] for that kernel 770 image. If '@offset' is omitted, then a suitable offset 771 is selected automatically. Check 772 Documentation/kdump/kdump.txt for further details. 773 774 crashkernel=range1:size1[,range2:size2,...][@offset] 775 [KNL] Same as above, but depends on the memory 776 in the running system. The syntax of range is 777 start-[end] where start and end are both 778 a memory unit (amount[KMG]). See also 779 Documentation/kdump/kdump.txt for an example. 780 781 crashkernel=size[KMG],high 782 [KNL, x86_64] range could be above 4G. Allow kernel 783 to allocate physical memory region from top, so could 784 be above 4G if system have more than 4G ram installed. 785 Otherwise memory region will be allocated below 4G, if 786 available. 787 It will be ignored if crashkernel=X is specified. 788 crashkernel=size[KMG],low 789 [KNL, x86_64] range under 4G. When crashkernel=X,high 790 is passed, kernel could allocate physical memory region 791 above 4G, that cause second kernel crash on system 792 that require some amount of low memory, e.g. swiotlb 793 requires at least 64M+32K low memory, also enough extra 794 low memory is needed to make sure DMA buffers for 32-bit 795 devices won't run out. Kernel would try to allocate at 796 at least 256M below 4G automatically. 797 This one let user to specify own low range under 4G 798 for second kernel instead. 799 0: to disable low allocation. 800 It will be ignored when crashkernel=X,high is not used 801 or memory reserved is below 4G. 802 803 cs89x0_dma= [HW,NET] 804 Format: <dma> 805 806 cs89x0_media= [HW,NET] 807 Format: { rj45 | aui | bnc } 808 809 dasd= [HW,NET] 810 See header of drivers/s390/block/dasd_devmap.c. 811 812 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port 813 (one device per port) 814 Format: <port#>,<type> 815 See also Documentation/input/joystick-parport.txt 816 817 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot 818 time. See Documentation/dynamic-debug-howto.txt for 819 details. Deprecated, see dyndbg. 820 821 debug [KNL] Enable kernel debugging (events log level). 822 823 debug_locks_verbose= 824 [KNL] verbose self-tests 825 Format=<0|1> 826 Print debugging info while doing the locking API 827 self-tests. 828 We default to 0 (no extra messages), setting it to 829 1 will print _a lot_ more information - normally 830 only useful to kernel developers. 831 832 debug_objects [KNL] Enable object debugging 833 834 no_debug_objects 835 [KNL] Disable object debugging 836 837 debug_guardpage_minorder= 838 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this 839 parameter allows control of the order of pages that will 840 be intentionally kept free (and hence protected) by the 841 buddy allocator. Bigger value increase the probability 842 of catching random memory corruption, but reduce the 843 amount of memory for normal system use. The maximum 844 possible value is MAX_ORDER/2. Setting this parameter 845 to 1 or 2 should be enough to identify most random 846 memory corruption problems caused by bugs in kernel or 847 driver code when a CPU writes to (or reads from) a 848 random memory location. Note that there exists a class 849 of memory corruptions problems caused by buggy H/W or 850 F/W or by drivers badly programing DMA (basically when 851 memory is written at bus level and the CPU MMU is 852 bypassed) which are not detectable by 853 CONFIG_DEBUG_PAGEALLOC, hence this option will not help 854 tracking down these problems. 855 856 debug_pagealloc= 857 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this 858 parameter enables the feature at boot time. In 859 default, it is disabled. We can avoid allocating huge 860 chunk of memory for debug pagealloc if we don't enable 861 it at boot time and the system will work mostly same 862 with the kernel built without CONFIG_DEBUG_PAGEALLOC. 863 on: enable the feature 864 865 debugpat [X86] Enable PAT debugging 866 867 decnet.addr= [HW,NET] 868 Format: <area>[,<node>] 869 See also Documentation/networking/decnet.txt. 870 871 default_hugepagesz= 872 [same as hugepagesz=] The size of the default 873 HugeTLB page size. This is the size represented by 874 the legacy /proc/ hugepages APIs, used for SHM, and 875 default size when mounting hugetlbfs filesystems. 876 Defaults to the default architecture's huge page size 877 if not specified. 878 879 dhash_entries= [KNL] 880 Set number of hash buckets for dentry cache. 881 882 disable= [IPV6] 883 See Documentation/networking/ipv6.txt. 884 885 disable_cpu_apicid= [X86,APIC,SMP] 886 Format: <int> 887 The number of initial APIC ID for the 888 corresponding CPU to be disabled at boot, 889 mostly used for the kdump 2nd kernel to 890 disable BSP to wake up multiple CPUs without 891 causing system reset or hang due to sending 892 INIT from AP to BSP. 893 894 disable_ddw [PPC/PSERIES] 895 Disable Dynamic DMA Window support. Use this if 896 to workaround buggy firmware. 897 898 disable_ipv6= [IPV6] 899 See Documentation/networking/ipv6.txt. 900 901 disable_mtrr_cleanup [X86] 902 The kernel tries to adjust MTRR layout from continuous 903 to discrete, to make X server driver able to add WB 904 entry later. This parameter disables that. 905 906 disable_mtrr_trim [X86, Intel and AMD only] 907 By default the kernel will trim any uncacheable 908 memory out of your available memory pool based on 909 MTRR settings. This parameter disables that behavior, 910 possibly causing your machine to run very slowly. 911 912 disable_timer_pin_1 [X86] 913 Disable PIN 1 of APIC timer 914 Can be useful to work around chipset bugs. 915 916 dis_ucode_ldr [X86] Disable the microcode loader. 917 918 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, 919 this option disables the debugging code at boot. 920 921 dma_debug_entries=<number> 922 This option allows to tune the number of preallocated 923 entries for DMA-API debugging code. One entry is 924 required per DMA-API allocation. Use this if the 925 DMA-API debugging code disables itself because the 926 architectural default is too low. 927 928 dma_debug_driver=<driver_name> 929 With this option the DMA-API debugging driver 930 filter feature can be enabled at boot time. Just 931 pass the driver to filter for as the parameter. 932 The filter can be disabled or changed to another 933 driver later using sysfs. 934 935 drm_kms_helper.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>] 936 Broken monitors, graphic adapters, KVMs and EDIDless 937 panels may send no or incorrect EDID data sets. 938 This parameter allows to specify an EDID data sets 939 in the /lib/firmware directory that are used instead. 940 Generic built-in EDID data sets are used, if one of 941 edid/1024x768.bin, edid/1280x1024.bin, 942 edid/1680x1050.bin, or edid/1920x1080.bin is given 943 and no file with the same name exists. Details and 944 instructions how to build your own EDID data are 945 available in Documentation/EDID/HOWTO.txt. An EDID 946 data set will only be used for a particular connector, 947 if its name and a colon are prepended to the EDID 948 name. Each connector may use a unique EDID data 949 set by separating the files with a comma. An EDID 950 data set with no connector name will be used for 951 any connectors not explicitly specified. 952 953 dscc4.setup= [NET] 954 955 dyndbg[="val"] [KNL,DYNAMIC_DEBUG] 956 module.dyndbg[="val"] 957 Enable debug messages at boot time. See 958 Documentation/dynamic-debug-howto.txt for details. 959 960 nompx [X86] Disables Intel Memory Protection Extensions. 961 See Documentation/x86/intel_mpx.txt for more 962 information about the feature. 963 964 eagerfpu= [X86] 965 on enable eager fpu restore 966 off disable eager fpu restore 967 auto selects the default scheme, which automatically 968 enables eagerfpu restore for xsaveopt. 969 970 module.async_probe [KNL] 971 Enable asynchronous probe on this module. 972 973 early_ioremap_debug [KNL] 974 Enable debug messages in early_ioremap support. This 975 is useful for tracking down temporary early mappings 976 which are not unmapped. 977 978 earlycon= [KNL] Output early console device and options. 979 980 When used with no options, the early console is 981 determined by the stdout-path property in device 982 tree's chosen node. 983 984 cdns,<addr> 985 Start an early, polled-mode console on a cadence serial 986 port at the specified address. The cadence serial port 987 must already be setup and configured. Options are not 988 yet supported. 989 990 uart[8250],io,<addr>[,options] 991 uart[8250],mmio,<addr>[,options] 992 uart[8250],mmio32,<addr>[,options] 993 uart[8250],mmio32be,<addr>[,options] 994 uart[8250],0x<addr>[,options] 995 Start an early, polled-mode console on the 8250/16550 996 UART at the specified I/O port or MMIO address. 997 MMIO inter-register address stride is either 8-bit 998 (mmio) or 32-bit (mmio32 or mmio32be). 999 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed 1000 to be equivalent to 'mmio'. 'options' are specified 1001 in the same format described for "console=ttyS<n>"; if 1002 unspecified, the h/w is not initialized. 1003 1004 pl011,<addr> 1005 Start an early, polled-mode console on a pl011 serial 1006 port at the specified address. The pl011 serial port 1007 must already be setup and configured. Options are not 1008 yet supported. 1009 1010 msm_serial,<addr> 1011 Start an early, polled-mode console on an msm serial 1012 port at the specified address. The serial port 1013 must already be setup and configured. Options are not 1014 yet supported. 1015 1016 msm_serial_dm,<addr> 1017 Start an early, polled-mode console on an msm serial 1018 dm port at the specified address. The serial port 1019 must already be setup and configured. Options are not 1020 yet supported. 1021 1022 smh Use ARM semihosting calls for early console. 1023 1024 s3c2410,<addr> 1025 s3c2412,<addr> 1026 s3c2440,<addr> 1027 s3c6400,<addr> 1028 s5pv210,<addr> 1029 exynos4210,<addr> 1030 Use early console provided by serial driver available 1031 on Samsung SoCs, requires selecting proper type and 1032 a correct base address of the selected UART port. The 1033 serial port must already be setup and configured. 1034 Options are not yet supported. 1035 1036 lpuart,<addr> 1037 lpuart32,<addr> 1038 Use early console provided by Freescale LP UART driver 1039 found on Freescale Vybrid and QorIQ LS1021A processors. 1040 A valid base address must be provided, and the serial 1041 port must already be setup and configured. 1042 1043 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k] 1044 earlyprintk=vga 1045 earlyprintk=efi 1046 earlyprintk=xen 1047 earlyprintk=serial[,ttySn[,baudrate]] 1048 earlyprintk=serial[,0x...[,baudrate]] 1049 earlyprintk=ttySn[,baudrate] 1050 earlyprintk=dbgp[debugController#] 1051 earlyprintk=pciserial,bus:device.function[,baudrate] 1052 1053 earlyprintk is useful when the kernel crashes before 1054 the normal console is initialized. It is not enabled by 1055 default because it has some cosmetic problems. 1056 1057 Append ",keep" to not disable it when the real console 1058 takes over. 1059 1060 Only one of vga, efi, serial, or usb debug port can 1061 be used at a time. 1062 1063 Currently only ttyS0 and ttyS1 may be specified by 1064 name. Other I/O ports may be explicitly specified 1065 on some architectures (x86 and arm at least) by 1066 replacing ttySn with an I/O port address, like this: 1067 earlyprintk=serial,0x1008,115200 1068 You can find the port for a given device in 1069 /proc/tty/driver/serial: 1070 2: uart:ST16650V2 port:00001008 irq:18 ... 1071 1072 Interaction with the standard serial driver is not 1073 very good. 1074 1075 The VGA and EFI output is eventually overwritten by 1076 the real console. 1077 1078 The xen output can only be used by Xen PV guests. 1079 1080 edac_report= [HW,EDAC] Control how to report EDAC event 1081 Format: {"on" | "off" | "force"} 1082 on: enable EDAC to report H/W event. May be overridden 1083 by other higher priority error reporting module. 1084 off: disable H/W event reporting through EDAC. 1085 force: enforce the use of EDAC to report H/W event. 1086 default: on. 1087 1088 ekgdboc= [X86,KGDB] Allow early kernel console debugging 1089 ekgdboc=kbd 1090 1091 This is designed to be used in conjunction with 1092 the boot argument: earlyprintk=vga 1093 1094 edd= [EDD] 1095 Format: {"off" | "on" | "skip[mbr]"} 1096 1097 efi= [EFI] 1098 Format: { "old_map", "nochunk", "noruntime", "debug" } 1099 old_map [X86-64]: switch to the old ioremap-based EFI 1100 runtime services mapping. 32-bit still uses this one by 1101 default. 1102 nochunk: disable reading files in "chunks" in the EFI 1103 boot stub, as chunking can cause problems with some 1104 firmware implementations. 1105 noruntime : disable EFI runtime services support 1106 debug: enable misc debug output 1107 1108 efi_no_storage_paranoia [EFI; X86] 1109 Using this parameter you can use more than 50% of 1110 your efi variable storage. Use this parameter only if 1111 you are really sure that your UEFI does sane gc and 1112 fulfills the spec otherwise your board may brick. 1113 1114 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86] 1115 Add arbitrary attribute to specific memory range by 1116 updating original EFI memory map. 1117 Region of memory which aa attribute is added to is 1118 from ss to ss+nn. 1119 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000 1120 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000) 1121 attribute is added to range 0x100000000-0x180000000 and 1122 0x10a0000000-0x1120000000. 1123 1124 Using this parameter you can do debugging of EFI memmap 1125 related feature. For example, you can do debugging of 1126 Address Range Mirroring feature even if your box 1127 doesn't support it. 1128 1129 eisa_irq_edge= [PARISC,HW] 1130 See header of drivers/parisc/eisa.c. 1131 1132 elanfreq= [X86-32] 1133 See comment before function elanfreq_setup() in 1134 arch/x86/kernel/cpu/cpufreq/elanfreq.c. 1135 1136 elevator= [IOSCHED] 1137 Format: {"cfq" | "deadline" | "noop"} 1138 See Documentation/block/cfq-iosched.txt and 1139 Documentation/block/deadline-iosched.txt for details. 1140 1141 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390] 1142 Specifies physical address of start of kernel core 1143 image elf header and optionally the size. Generally 1144 kexec loader will pass this option to capture kernel. 1145 See Documentation/kdump/kdump.txt for details. 1146 1147 enable_mtrr_cleanup [X86] 1148 The kernel tries to adjust MTRR layout from continuous 1149 to discrete, to make X server driver able to add WB 1150 entry later. This parameter enables that. 1151 1152 enable_timer_pin_1 [X86] 1153 Enable PIN 1 of APIC timer 1154 Can be useful to work around chipset bugs 1155 (in particular on some ATI chipsets). 1156 The kernel tries to set a reasonable default. 1157 1158 enforcing [SELINUX] Set initial enforcing status. 1159 Format: {"0" | "1"} 1160 See security/selinux/Kconfig help text. 1161 0 -- permissive (log only, no denials). 1162 1 -- enforcing (deny and log). 1163 Default value is 0. 1164 Value can be changed at runtime via /selinux/enforce. 1165 1166 erst_disable [ACPI] 1167 Disable Error Record Serialization Table (ERST) 1168 support. 1169 1170 ether= [HW,NET] Ethernet cards parameters 1171 This option is obsoleted by the "netdev=" option, which 1172 has equivalent usage. See its documentation for details. 1173 1174 evm= [EVM] 1175 Format: { "fix" } 1176 Permit 'security.evm' to be updated regardless of 1177 current integrity status. 1178 1179 failslab= 1180 fail_page_alloc= 1181 fail_make_request=[KNL] 1182 General fault injection mechanism. 1183 Format: <interval>,<probability>,<space>,<times> 1184 See also Documentation/fault-injection/. 1185 1186 floppy= [HW] 1187 See Documentation/blockdev/floppy.txt. 1188 1189 force_pal_cache_flush 1190 [IA-64] Avoid check_sal_cache_flush which may hang on 1191 buggy SAL_CACHE_FLUSH implementations. Using this 1192 parameter will force ia64_sal_cache_flush to call 1193 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH. 1194 1195 forcepae [X86-32] 1196 Forcefully enable Physical Address Extension (PAE). 1197 Many Pentium M systems disable PAE but may have a 1198 functionally usable PAE implementation. 1199 Warning: use of this parameter will taint the kernel 1200 and may cause unknown problems. 1201 1202 ftrace=[tracer] 1203 [FTRACE] will set and start the specified tracer 1204 as early as possible in order to facilitate early 1205 boot debugging. 1206 1207 ftrace_dump_on_oops[=orig_cpu] 1208 [FTRACE] will dump the trace buffers on oops. 1209 If no parameter is passed, ftrace will dump 1210 buffers of all CPUs, but if you pass orig_cpu, it will 1211 dump only the buffer of the CPU that triggered the 1212 oops. 1213 1214 ftrace_filter=[function-list] 1215 [FTRACE] Limit the functions traced by the function 1216 tracer at boot up. function-list is a comma separated 1217 list of functions. This list can be changed at run 1218 time by the set_ftrace_filter file in the debugfs 1219 tracing directory. 1220 1221 ftrace_notrace=[function-list] 1222 [FTRACE] Do not trace the functions specified in 1223 function-list. This list can be changed at run time 1224 by the set_ftrace_notrace file in the debugfs 1225 tracing directory. 1226 1227 ftrace_graph_filter=[function-list] 1228 [FTRACE] Limit the top level callers functions traced 1229 by the function graph tracer at boot up. 1230 function-list is a comma separated list of functions 1231 that can be changed at run time by the 1232 set_graph_function file in the debugfs tracing directory. 1233 1234 ftrace_graph_notrace=[function-list] 1235 [FTRACE] Do not trace from the functions specified in 1236 function-list. This list is a comma separated list of 1237 functions that can be changed at run time by the 1238 set_graph_notrace file in the debugfs tracing directory. 1239 1240 gamecon.map[2|3]= 1241 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 1242 support via parallel port (up to 5 devices per port) 1243 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 1244 See also Documentation/input/joystick-parport.txt 1245 1246 gamma= [HW,DRM] 1247 1248 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART 1249 Format: off | on 1250 default: on 1251 1252 gcov_persist= [GCOV] When non-zero (default), profiling data for 1253 kernel modules is saved and remains accessible via 1254 debugfs, even when the module is unloaded/reloaded. 1255 When zero, profiling data is discarded and associated 1256 debugfs files are removed at module unload time. 1257 1258 gpt [EFI] Forces disk with valid GPT signature but 1259 invalid Protective MBR to be treated as GPT. If the 1260 primary GPT is corrupted, it enables the backup/alternate 1261 GPT to be used instead. 1262 1263 grcan.enable0= [HW] Configuration of physical interface 0. Determines 1264 the "Enable 0" bit of the configuration register. 1265 Format: 0 | 1 1266 Default: 0 1267 grcan.enable1= [HW] Configuration of physical interface 1. Determines 1268 the "Enable 0" bit of the configuration register. 1269 Format: 0 | 1 1270 Default: 0 1271 grcan.select= [HW] Select which physical interface to use. 1272 Format: 0 | 1 1273 Default: 0 1274 grcan.txsize= [HW] Sets the size of the tx buffer. 1275 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. 1276 Default: 1024 1277 grcan.rxsize= [HW] Sets the size of the rx buffer. 1278 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. 1279 Default: 1024 1280 1281 hardlockup_all_cpu_backtrace= 1282 [KNL] Should the hard-lockup detector generate 1283 backtraces on all cpus. 1284 Format: <integer> 1285 1286 hashdist= [KNL,NUMA] Large hashes allocated during boot 1287 are distributed across NUMA nodes. Defaults on 1288 for 64-bit NUMA, off otherwise. 1289 Format: 0 | 1 (for off | on) 1290 1291 hcl= [IA-64] SGI's Hardware Graph compatibility layer 1292 1293 hd= [EIDE] (E)IDE hard drive subsystem geometry 1294 Format: <cyl>,<head>,<sect> 1295 1296 hest_disable [ACPI] 1297 Disable Hardware Error Source Table (HEST) support; 1298 corresponding firmware-first mode error processing 1299 logic will be disabled. 1300 1301 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact 1302 size of <nn>. This works even on boxes that have no 1303 highmem otherwise. This also works to reduce highmem 1304 size on bigger boxes. 1305 1306 highres= [KNL] Enable/disable high resolution timer mode. 1307 Valid parameters: "on", "off" 1308 Default: "on" 1309 1310 hisax= [HW,ISDN] 1311 See Documentation/isdn/README.HiSax. 1312 1313 hlt [BUGS=ARM,SH] 1314 1315 hpet= [X86-32,HPET] option to control HPET usage 1316 Format: { enable (default) | disable | force | 1317 verbose } 1318 disable: disable HPET and use PIT instead 1319 force: allow force enabled of undocumented chips (ICH4, 1320 VIA, nVidia) 1321 verbose: show contents of HPET registers during setup 1322 1323 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET 1324 registers. Default set by CONFIG_HPET_MMAP_DEFAULT. 1325 1326 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot. 1327 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages. 1328 On x86-64 and powerpc, this option can be specified 1329 multiple times interleaved with hugepages= to reserve 1330 huge pages of different sizes. Valid pages sizes on 1331 x86-64 are 2M (when the CPU supports "pse") and 1G 1332 (when the CPU supports the "pdpe1gb" cpuinfo flag). 1333 1334 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 1335 terminal devices. Valid values: 0..8 1336 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 1337 If specified, z/VM IUCV HVC accepts connections 1338 from listed z/VM user IDs only. 1339 1340 hwthread_map= [METAG] Comma-separated list of Linux cpu id to 1341 hardware thread id mappings. 1342 Format: <cpu>:<hwthread> 1343 1344 keep_bootcon [KNL] 1345 Do not unregister boot console at start. This is only 1346 useful for debugging when something happens in the window 1347 between unregistering the boot console and initializing 1348 the real console. 1349 1350 i2c_bus= [HW] Override the default board specific I2C bus speed 1351 or register an additional I2C bus that is not 1352 registered from board initialization code. 1353 Format: 1354 <bus_id>,<clkrate> 1355 1356 i8042.debug [HW] Toggle i8042 debug mode 1357 i8042.unmask_kbd_data 1358 [HW] Enable printing of interrupt data from the KBD port 1359 (disabled by default, and as a pre-condition 1360 requires that i8042.debug=1 be enabled) 1361 i8042.direct [HW] Put keyboard port into non-translated mode 1362 i8042.dumbkbd [HW] Pretend that controller can only read data from 1363 keyboard and cannot control its state 1364 (Don't attempt to blink the leds) 1365 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 1366 i8042.nokbd [HW] Don't check/create keyboard port 1367 i8042.noloop [HW] Disable the AUX Loopback command while probing 1368 for the AUX port 1369 i8042.nomux [HW] Don't check presence of an active multiplexing 1370 controller 1371 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 1372 controllers 1373 i8042.notimeout [HW] Ignore timeout condition signalled by controller 1374 i8042.reset [HW] Reset the controller during init and cleanup 1375 i8042.unlock [HW] Unlock (ignore) the keylock 1376 i8042.kbdreset [HW] Reset device connected to KBD port 1377 1378 i810= [HW,DRM] 1379 1380 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data 1381 indicates that the driver is running on unsupported 1382 hardware. 1383 i8k.force [HW] Activate i8k driver even if SMM BIOS signature 1384 does not match list of supported models. 1385 i8k.power_status 1386 [HW] Report power status in /proc/i8k 1387 (disabled by default) 1388 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN 1389 capability is set. 1390 1391 i915.invert_brightness= 1392 [DRM] Invert the sense of the variable that is used to 1393 set the brightness of the panel backlight. Normally a 1394 brightness value of 0 indicates backlight switched off, 1395 and the maximum of the brightness value sets the backlight 1396 to maximum brightness. If this parameter is set to 0 1397 (default) and the machine requires it, or this parameter 1398 is set to 1, a brightness value of 0 sets the backlight 1399 to maximum brightness, and the maximum of the brightness 1400 value switches the backlight off. 1401 -1 -- never invert brightness 1402 0 -- machine default 1403 1 -- force brightness inversion 1404 1405 icn= [HW,ISDN] 1406 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]] 1407 1408 ide-core.nodma= [HW] (E)IDE subsystem 1409 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc 1410 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr 1411 .cdrom .chs .ignore_cable are additional options 1412 See Documentation/ide/ide.txt. 1413 1414 ide-generic.probe-mask= [HW] (E)IDE subsystem 1415 Format: <int> 1416 Probe mask for legacy ISA IDE ports. Depending on 1417 platform up to 6 ports are supported, enabled by 1418 setting corresponding bits in the mask to 1. The 1419 default value is 0x0, which has a special meaning. 1420 On systems that have PCI, it triggers scanning the 1421 PCI bus for the first and the second port, which 1422 are then probed. On systems without PCI the value 1423 of 0x0 enables probing the two first ports as if it 1424 was 0x3. 1425 1426 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem 1427 Claim all unknown PCI IDE storage controllers. 1428 1429 idle= [X86] 1430 Format: idle=poll, idle=halt, idle=nomwait 1431 Poll forces a polling idle loop that can slightly 1432 improve the performance of waking up a idle CPU, but 1433 will use a lot of power and make the system run hot. 1434 Not recommended. 1435 idle=halt: Halt is forced to be used for CPU idle. 1436 In such case C2/C3 won't be used again. 1437 idle=nomwait: Disable mwait for CPU C-states 1438 1439 ignore_loglevel [KNL] 1440 Ignore loglevel setting - this will print /all/ 1441 kernel messages to the console. Useful for debugging. 1442 We also add it as printk module parameter, so users 1443 could change it dynamically, usually by 1444 /sys/module/printk/parameters/ignore_loglevel. 1445 1446 ihash_entries= [KNL] 1447 Set number of hash buckets for inode cache. 1448 1449 ima_appraise= [IMA] appraise integrity measurements 1450 Format: { "off" | "enforce" | "fix" | "log" } 1451 default: "enforce" 1452 1453 ima_appraise_tcb [IMA] 1454 The builtin appraise policy appraises all files 1455 owned by uid=0. 1456 1457 ima_hash= [IMA] 1458 Format: { md5 | sha1 | rmd160 | sha256 | sha384 1459 | sha512 | ... } 1460 default: "sha1" 1461 1462 The list of supported hash algorithms is defined 1463 in crypto/hash_info.h. 1464 1465 ima_policy= [IMA] 1466 The builtin measurement policy to load during IMA 1467 setup. Specyfing "tcb" as the value, measures all 1468 programs exec'd, files mmap'd for exec, and all files 1469 opened with the read mode bit set by either the 1470 effective uid (euid=0) or uid=0. 1471 Format: "tcb" 1472 1473 ima_tcb [IMA] Deprecated. Use ima_policy= instead. 1474 Load a policy which meets the needs of the Trusted 1475 Computing Base. This means IMA will measure all 1476 programs exec'd, files mmap'd for exec, and all files 1477 opened for read by uid=0. 1478 1479 ima_template= [IMA] 1480 Select one of defined IMA measurements template formats. 1481 Formats: { "ima" | "ima-ng" | "ima-sig" } 1482 Default: "ima-ng" 1483 1484 ima_template_fmt= 1485 [IMA] Define a custom template format. 1486 Format: { "field1|...|fieldN" } 1487 1488 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage 1489 Format: <min_file_size> 1490 Set the minimal file size for using asynchronous hash. 1491 If left unspecified, ahash usage is disabled. 1492 1493 ahash performance varies for different data sizes on 1494 different crypto accelerators. This option can be used 1495 to achieve the best performance for a particular HW. 1496 1497 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size 1498 Format: <bufsize> 1499 Set hashing buffer size. Default: 4k. 1500 1501 ahash performance varies for different chunk sizes on 1502 different crypto accelerators. This option can be used 1503 to achieve best performance for particular HW. 1504 1505 init= [KNL] 1506 Format: <full_path> 1507 Run specified binary instead of /sbin/init as init 1508 process. 1509 1510 initcall_debug [KNL] Trace initcalls as they are executed. Useful 1511 for working out where the kernel is dying during 1512 startup. 1513 1514 initcall_blacklist= [KNL] Do not execute a comma-separated list of 1515 initcall functions. Useful for debugging built-in 1516 modules and initcalls. 1517 1518 initrd= [BOOT] Specify the location of the initial ramdisk 1519 1520 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 1521 Format: <irq> 1522 1523 int_pln_enable [x86] Enable power limit notification interrupt 1524 1525 integrity_audit=[IMA] 1526 Format: { "0" | "1" } 1527 0 -- basic integrity auditing messages. (Default) 1528 1 -- additional integrity auditing messages. 1529 1530 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 1531 on 1532 Enable intel iommu driver. 1533 off 1534 Disable intel iommu driver. 1535 igfx_off [Default Off] 1536 By default, gfx is mapped as normal device. If a gfx 1537 device has a dedicated DMAR unit, the DMAR unit is 1538 bypassed by not enabling DMAR with this option. In 1539 this case, gfx device will use physical address for 1540 DMA. 1541 forcedac [x86_64] 1542 With this option iommu will not optimize to look 1543 for io virtual address below 32-bit forcing dual 1544 address cycle on pci bus for cards supporting greater 1545 than 32-bit addressing. The default is to look 1546 for translation below 32-bit and if not available 1547 then look in the higher range. 1548 strict [Default Off] 1549 With this option on every unmap_single operation will 1550 result in a hardware IOTLB flush operation as opposed 1551 to batching them for performance. 1552 sp_off [Default Off] 1553 By default, super page will be supported if Intel IOMMU 1554 has the capability. With this option, super page will 1555 not be supported. 1556 ecs_off [Default Off] 1557 By default, extended context tables will be supported if 1558 the hardware advertises that it has support both for the 1559 extended tables themselves, and also PASID support. With 1560 this option set, extended tables will not be used even 1561 on hardware which claims to support them. 1562 1563 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 1564 0 disables intel_idle and fall back on acpi_idle. 1565 1 to 6 specify maximum depth of C-state. 1566 1567 intel_pstate= [X86] 1568 disable 1569 Do not enable intel_pstate as the default 1570 scaling driver for the supported processors 1571 force 1572 Enable intel_pstate on systems that prohibit it by default 1573 in favor of acpi-cpufreq. Forcing the intel_pstate driver 1574 instead of acpi-cpufreq may disable platform features, such 1575 as thermal controls and power capping, that rely on ACPI 1576 P-States information being indicated to OSPM and therefore 1577 should be used with caution. This option does not work with 1578 processors that aren't supported by the intel_pstate driver 1579 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 1580 no_hwp 1581 Do not enable hardware P state control (HWP) 1582 if available. 1583 hwp_only 1584 Only load intel_pstate on systems which support 1585 hardware P state control (HWP) if available. 1586 1587 intremap= [X86-64, Intel-IOMMU] 1588 on enable Interrupt Remapping (default) 1589 off disable Interrupt Remapping 1590 nosid disable Source ID checking 1591 no_x2apic_optout 1592 BIOS x2APIC opt-out request will be ignored 1593 nopost disable Interrupt Posting 1594 1595 iomem= Disable strict checking of access to MMIO memory 1596 strict regions from userspace. 1597 relaxed 1598 1599 iommu= [x86] 1600 off 1601 force 1602 noforce 1603 biomerge 1604 panic 1605 nopanic 1606 merge 1607 nomerge 1608 forcesac 1609 soft 1610 pt [x86, IA-64] 1611 nobypass [PPC/POWERNV] 1612 Disable IOMMU bypass, using IOMMU for PCI devices. 1613 1614 1615 io7= [HW] IO7 for Marvel based alpha systems 1616 See comment before marvel_specify_io7 in 1617 arch/alpha/kernel/core_marvel.c. 1618 1619 io_delay= [X86] I/O delay method 1620 0x80 1621 Standard port 0x80 based delay 1622 0xed 1623 Alternate port 0xed based delay (needed on some systems) 1624 udelay 1625 Simple two microseconds delay 1626 none 1627 No delay 1628 1629 ip= [IP_PNP] 1630 See Documentation/filesystems/nfs/nfsroot.txt. 1631 1632 irqfixup [HW] 1633 When an interrupt is not handled search all handlers 1634 for it. Intended to get systems with badly broken 1635 firmware running. 1636 1637 irqpoll [HW] 1638 When an interrupt is not handled search all handlers 1639 for it. Also check all handlers each timer 1640 interrupt. Intended to get systems with badly broken 1641 firmware running. 1642 1643 isapnp= [ISAPNP] 1644 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 1645 1646 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler. 1647 Format: 1648 <cpu number>,...,<cpu number> 1649 or 1650 <cpu number>-<cpu number> 1651 (must be a positive range in ascending order) 1652 or a mixture 1653 <cpu number>,...,<cpu number>-<cpu number> 1654 1655 This option can be used to specify one or more CPUs 1656 to isolate from the general SMP balancing and scheduling 1657 algorithms. You can move a process onto or off an 1658 "isolated" CPU via the CPU affinity syscalls or cpuset. 1659 <cpu number> begins at 0 and the maximum value is 1660 "number of CPUs in system - 1". 1661 1662 This option is the preferred way to isolate CPUs. The 1663 alternative -- manually setting the CPU mask of all 1664 tasks in the system -- can cause problems and 1665 suboptimal load balancer performance. 1666 1667 iucv= [HW,NET] 1668 1669 ivrs_ioapic [HW,X86_64] 1670 Provide an override to the IOAPIC-ID<->DEVICE-ID 1671 mapping provided in the IVRS ACPI table. For 1672 example, to map IOAPIC-ID decimal 10 to 1673 PCI device 00:14.0 write the parameter as: 1674 ivrs_ioapic[10]=00:14.0 1675 1676 ivrs_hpet [HW,X86_64] 1677 Provide an override to the HPET-ID<->DEVICE-ID 1678 mapping provided in the IVRS ACPI table. For 1679 example, to map HPET-ID decimal 0 to 1680 PCI device 00:14.0 write the parameter as: 1681 ivrs_hpet[0]=00:14.0 1682 1683 js= [HW,JOY] Analog joystick 1684 See Documentation/input/joystick.txt. 1685 1686 kaslr/nokaslr [X86] 1687 Enable/disable kernel and module base offset ASLR 1688 (Address Space Layout Randomization) if built into 1689 the kernel. When CONFIG_HIBERNATION is selected, 1690 kASLR is disabled by default. When kASLR is enabled, 1691 hibernation will be disabled. 1692 1693 keepinitrd [HW,ARM] 1694 1695 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter 1696 specifies the amount of memory usable by the kernel 1697 for non-movable allocations. The requested amount is 1698 spread evenly throughout all nodes in the system. The 1699 remaining memory in each node is used for Movable 1700 pages. In the event, a node is too small to have both 1701 kernelcore and Movable pages, kernelcore pages will 1702 take priority and other nodes will have a larger number 1703 of Movable pages. The Movable zone is used for the 1704 allocation of pages that may be reclaimed or moved 1705 by the page migration subsystem. This means that 1706 HugeTLB pages may not be allocated from this zone. 1707 Note that allocations like PTEs-from-HighMem still 1708 use the HighMem zone if it exists, and the Normal 1709 zone if it does not. 1710 1711 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port. 1712 Format: <Controller#>[,poll interval] 1713 The controller # is the number of the ehci usb debug 1714 port as it is probed via PCI. The poll interval is 1715 optional and is the number seconds in between 1716 each poll cycle to the debug port in case you need 1717 the functionality for interrupting the kernel with 1718 gdb or control-c on the dbgp connection. When 1719 not using this parameter you use sysrq-g to break into 1720 the kernel debugger. 1721 1722 kgdboc= [KGDB,HW] kgdb over consoles. 1723 Requires a tty driver that supports console polling, 1724 or a supported polling keyboard driver (non-usb). 1725 Serial only format: <serial_device>[,baud] 1726 keyboard only format: kbd 1727 keyboard and serial format: kbd,<serial_device>[,baud] 1728 Optional Kernel mode setting: 1729 kms, kbd format: kms,kbd 1730 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 1731 1732 kgdbwait [KGDB] Stop kernel execution and enter the 1733 kernel debugger at the earliest opportunity. 1734 1735 kmac= [MIPS] korina ethernet MAC address. 1736 Configure the RouterBoard 532 series on-chip 1737 Ethernet adapter MAC address. 1738 1739 kmemleak= [KNL] Boot-time kmemleak enable/disable 1740 Valid arguments: on, off 1741 Default: on 1742 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 1743 the default is off. 1744 1745 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode 1746 Valid arguments: 0, 1, 2 1747 kmemcheck=0 (disabled) 1748 kmemcheck=1 (enabled) 1749 kmemcheck=2 (one-shot mode) 1750 Default: 2 (one-shot mode) 1751 1752 kstack=N [X86] Print N words from the kernel stack 1753 in oops dumps. 1754 1755 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 1756 Default is 0 (don't ignore, but inject #GP) 1757 1758 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit 1759 KVM MMU at runtime. 1760 Default is 0 (off) 1761 1762 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM. 1763 Default is 1 (enabled) 1764 1765 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU) 1766 for all guests. 1767 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode. 1768 1769 kvm-intel.ept= [KVM,Intel] Disable extended page tables 1770 (virtualized MMU) support on capable Intel chips. 1771 Default is 1 (enabled) 1772 1773 kvm-intel.emulate_invalid_guest_state= 1774 [KVM,Intel] Enable emulation of invalid guest states 1775 Default is 0 (disabled) 1776 1777 kvm-intel.flexpriority= 1778 [KVM,Intel] Disable FlexPriority feature (TPR shadow). 1779 Default is 1 (enabled) 1780 1781 kvm-intel.nested= 1782 [KVM,Intel] Enable VMX nesting (nVMX). 1783 Default is 0 (disabled) 1784 1785 kvm-intel.unrestricted_guest= 1786 [KVM,Intel] Disable unrestricted guest feature 1787 (virtualized real and unpaged mode) on capable 1788 Intel chips. Default is 1 (enabled) 1789 1790 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification 1791 feature (tagged TLBs) on capable Intel chips. 1792 Default is 1 (enabled) 1793 1794 l2cr= [PPC] 1795 1796 l3cr= [PPC] 1797 1798 lapic [X86-32,APIC] Enable the local APIC even if BIOS 1799 disabled it. 1800 1801 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline 1802 value for LAPIC timer one-shot implementation. Default 1803 back to the programmable timer unit in the LAPIC. 1804 1805 lapic_timer_c2_ok [X86,APIC] trust the local apic timer 1806 in C2 power state. 1807 1808 libata.dma= [LIBATA] DMA control 1809 libata.dma=0 Disable all PATA and SATA DMA 1810 libata.dma=1 PATA and SATA Disk DMA only 1811 libata.dma=2 ATAPI (CDROM) DMA only 1812 libata.dma=4 Compact Flash DMA only 1813 Combinations also work, so libata.dma=3 enables DMA 1814 for disks and CDROMs, but not CFs. 1815 1816 libata.ignore_hpa= [LIBATA] Ignore HPA limit 1817 libata.ignore_hpa=0 keep BIOS limits (default) 1818 libata.ignore_hpa=1 ignore limits, using full disk 1819 1820 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 1821 when set. 1822 Format: <int> 1823 1824 libata.force= [LIBATA] Force configurations. The format is comma 1825 separated list of "[ID:]VAL" where ID is 1826 PORT[.DEVICE]. PORT and DEVICE are decimal numbers 1827 matching port, link or device. Basically, it matches 1828 the ATA ID string printed on console by libata. If 1829 the whole ID part is omitted, the last PORT and DEVICE 1830 values are used. If ID hasn't been specified yet, the 1831 configuration applies to all ports, links and devices. 1832 1833 If only DEVICE is omitted, the parameter applies to 1834 the port and all links and devices behind it. DEVICE 1835 number of 0 either selects the first device or the 1836 first fan-out link behind PMP device. It does not 1837 select the host link. DEVICE number of 15 selects the 1838 host link and device attached to it. 1839 1840 The VAL specifies the configuration to force. As long 1841 as there's no ambiguity shortcut notation is allowed. 1842 For example, both 1.5 and 1.5G would work for 1.5Gbps. 1843 The following configurations can be forced. 1844 1845 * Cable type: 40c, 80c, short40c, unk, ign or sata. 1846 Any ID with matching PORT is used. 1847 1848 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 1849 1850 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 1851 udma[/][16,25,33,44,66,100,133] notation is also 1852 allowed. 1853 1854 * [no]ncq: Turn on or off NCQ. 1855 1856 * [no]ncqtrim: Turn off queued DSM TRIM. 1857 1858 * nohrst, nosrst, norst: suppress hard, soft 1859 and both resets. 1860 1861 * rstonce: only attempt one reset during 1862 hot-unplug link recovery 1863 1864 * dump_id: dump IDENTIFY data. 1865 1866 * atapi_dmadir: Enable ATAPI DMADIR bridge support 1867 1868 * disable: Disable this device. 1869 1870 If there are multiple matching configurations changing 1871 the same attribute, the last one is used. 1872 1873 memblock=debug [KNL] Enable memblock debug messages. 1874 1875 load_ramdisk= [RAM] List of ramdisks to load from floppy 1876 See Documentation/blockdev/ramdisk.txt. 1877 1878 lockd.nlm_grace_period=P [NFS] Assign grace period. 1879 Format: <integer> 1880 1881 lockd.nlm_tcpport=N [NFS] Assign TCP port. 1882 Format: <integer> 1883 1884 lockd.nlm_timeout=T [NFS] Assign timeout value. 1885 Format: <integer> 1886 1887 lockd.nlm_udpport=M [NFS] Assign UDP port. 1888 Format: <integer> 1889 1890 locktorture.nreaders_stress= [KNL] 1891 Set the number of locking read-acquisition kthreads. 1892 Defaults to being automatically set based on the 1893 number of online CPUs. 1894 1895 locktorture.nwriters_stress= [KNL] 1896 Set the number of locking write-acquisition kthreads. 1897 1898 locktorture.onoff_holdoff= [KNL] 1899 Set time (s) after boot for CPU-hotplug testing. 1900 1901 locktorture.onoff_interval= [KNL] 1902 Set time (s) between CPU-hotplug operations, or 1903 zero to disable CPU-hotplug testing. 1904 1905 locktorture.shuffle_interval= [KNL] 1906 Set task-shuffle interval (jiffies). Shuffling 1907 tasks allows some CPUs to go into dyntick-idle 1908 mode during the locktorture test. 1909 1910 locktorture.shutdown_secs= [KNL] 1911 Set time (s) after boot system shutdown. This 1912 is useful for hands-off automated testing. 1913 1914 locktorture.stat_interval= [KNL] 1915 Time (s) between statistics printk()s. 1916 1917 locktorture.stutter= [KNL] 1918 Time (s) to stutter testing, for example, 1919 specifying five seconds causes the test to run for 1920 five seconds, wait for five seconds, and so on. 1921 This tests the locking primitive's ability to 1922 transition abruptly to and from idle. 1923 1924 locktorture.torture_runnable= [BOOT] 1925 Start locktorture running at boot time. 1926 1927 locktorture.torture_type= [KNL] 1928 Specify the locking implementation to test. 1929 1930 locktorture.verbose= [KNL] 1931 Enable additional printk() statements. 1932 1933 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 1934 Format: <irq> 1935 1936 loglevel= All Kernel Messages with a loglevel smaller than the 1937 console loglevel will be printed to the console. It can 1938 also be changed with klogd or other programs. The 1939 loglevels are defined as follows: 1940 1941 0 (KERN_EMERG) system is unusable 1942 1 (KERN_ALERT) action must be taken immediately 1943 2 (KERN_CRIT) critical conditions 1944 3 (KERN_ERR) error conditions 1945 4 (KERN_WARNING) warning conditions 1946 5 (KERN_NOTICE) normal but significant condition 1947 6 (KERN_INFO) informational 1948 7 (KERN_DEBUG) debug-level messages 1949 1950 log_buf_len=n[KMG] Sets the size of the printk ring buffer, 1951 in bytes. n must be a power of two and greater 1952 than the minimal size. The minimal size is defined 1953 by LOG_BUF_SHIFT kernel config parameter. There is 1954 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter 1955 that allows to increase the default size depending on 1956 the number of CPUs. See init/Kconfig for more details. 1957 1958 logo.nologo [FB] Disables display of the built-in Linux logo. 1959 This may be used to provide more screen space for 1960 kernel log messages and is useful when debugging 1961 kernel boot problems. 1962 1963 lp=0 [LP] Specify parallel ports to use, e.g, 1964 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 1965 lp=reset first parallel port). 'lp=0' disables the 1966 lp=auto printer driver. 'lp=reset' (which can be 1967 specified in addition to the ports) causes 1968 attached printers to be reset. Using 1969 lp=port1,port2,... specifies the parallel ports 1970 to associate lp devices with, starting with 1971 lp0. A port specification may be 'none' to skip 1972 that lp device, or a parport name such as 1973 'parport0'. Specifying 'lp=auto' instead of a 1974 port specification list means that device IDs 1975 from each port should be examined, to see if 1976 an IEEE 1284-compliant printer is attached; if 1977 so, the driver will manage that printer. 1978 See also header of drivers/char/lp.c. 1979 1980 lpj=n [KNL] 1981 Sets loops_per_jiffy to given constant, thus avoiding 1982 time-consuming boot-time autodetection (up to 250 ms per 1983 CPU). 0 enables autodetection (default). To determine 1984 the correct value for your kernel, boot with normal 1985 autodetection and see what value is printed. Note that 1986 on SMP systems the preset will be applied to all CPUs, 1987 which is likely to cause problems if your CPUs need 1988 significantly divergent settings. An incorrect value 1989 will cause delays in the kernel to be wrong, leading to 1990 unpredictable I/O errors and other breakage. Although 1991 unlikely, in the extreme case this might damage your 1992 hardware. 1993 1994 ltpc= [NET] 1995 Format: <io>,<irq>,<dma> 1996 1997 machvec= [IA-64] Force the use of a particular machine-vector 1998 (machvec) in a generic kernel. 1999 Example: machvec=hpzx1_swiotlb 2000 2001 machtype= [Loongson] Share the same kernel image file between different 2002 yeeloong laptop. 2003 Example: machtype=lemote-yeeloong-2f-7inch 2004 2005 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater 2006 than or equal to this physical address is ignored. 2007 2008 maxcpus= [SMP] Maximum number of processors that an SMP kernel 2009 should make use of. maxcpus=n : n >= 0 limits the 2010 kernel to using 'n' processors. n=0 is a special case, 2011 it is equivalent to "nosmp", which also disables 2012 the IO APIC. 2013 2014 max_loop= [LOOP] The number of loop block devices that get 2015 (loop.max_loop) unconditionally pre-created at init time. The default 2016 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 2017 of statically allocating a predefined number, loop 2018 devices can be requested on-demand with the 2019 /dev/loop-control interface. 2020 2021 mce [X86-32] Machine Check Exception 2022 2023 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt 2024 2025 md= [HW] RAID subsystems devices and level 2026 See Documentation/md.txt. 2027 2028 mdacon= [MDA] 2029 Format: <first>,<last> 2030 Specifies range of consoles to be captured by the MDA. 2031 2032 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory 2033 Amount of memory to be used when the kernel is not able 2034 to see the whole system memory or for test. 2035 [X86] Work as limiting max address. Use together 2036 with memmap= to avoid physical address space collisions. 2037 Without memmap= PCI devices could be placed at addresses 2038 belonging to unused RAM. 2039 2040 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 2041 memory. 2042 2043 memchunk=nn[KMG] 2044 [KNL,SH] Allow user to override the default size for 2045 per-device physically contiguous DMA buffers. 2046 2047 memmap=exactmap [KNL,X86] Enable setting of an exact 2048 E820 memory map, as specified by the user. 2049 Such memmap=exactmap lines can be constructed based on 2050 BIOS output or other requirements. See the memmap=nn@ss 2051 option description. 2052 2053 memmap=nn[KMG]@ss[KMG] 2054 [KNL] Force usage of a specific region of memory. 2055 Region of memory to be used is from ss to ss+nn. 2056 2057 memmap=nn[KMG]#ss[KMG] 2058 [KNL,ACPI] Mark specific memory as ACPI data. 2059 Region of memory to be marked is from ss to ss+nn. 2060 2061 memmap=nn[KMG]$ss[KMG] 2062 [KNL,ACPI] Mark specific memory as reserved. 2063 Region of memory to be reserved is from ss to ss+nn. 2064 Example: Exclude memory from 0x18690000-0x1869ffff 2065 memmap=64K$0x18690000 2066 or 2067 memmap=0x10000$0x18690000 2068 2069 memmap=nn[KMG]!ss[KMG] 2070 [KNL,X86] Mark specific memory as protected. 2071 Region of memory to be used, from ss to ss+nn. 2072 The memory region may be marked as e820 type 12 (0xc) 2073 and is NVDIMM or ADR memory. 2074 2075 memory_corruption_check=0/1 [X86] 2076 Some BIOSes seem to corrupt the first 64k of 2077 memory when doing things like suspend/resume. 2078 Setting this option will scan the memory 2079 looking for corruption. Enabling this will 2080 both detect corruption and prevent the kernel 2081 from using the memory being corrupted. 2082 However, its intended as a diagnostic tool; if 2083 repeatable BIOS-originated corruption always 2084 affects the same memory, you can use memmap= 2085 to prevent the kernel from using that memory. 2086 2087 memory_corruption_check_size=size [X86] 2088 By default it checks for corruption in the low 2089 64k, making this memory unavailable for normal 2090 use. Use this parameter to scan for 2091 corruption in more or less memory. 2092 2093 memory_corruption_check_period=seconds [X86] 2094 By default it checks for corruption every 60 2095 seconds. Use this parameter to check at some 2096 other rate. 0 disables periodic checking. 2097 2098 memtest= [KNL,X86,ARM] Enable memtest 2099 Format: <integer> 2100 default : 0 <disable> 2101 Specifies the number of memtest passes to be 2102 performed. Each pass selects another test 2103 pattern from a given set of patterns. Memtest 2104 fills the memory with this pattern, validates 2105 memory contents and reserves bad memory 2106 regions that are detected. 2107 2108 meye.*= [HW] Set MotionEye Camera parameters 2109 See Documentation/video4linux/meye.txt. 2110 2111 mfgpt_irq= [IA-32] Specify the IRQ to use for the 2112 Multi-Function General Purpose Timers on AMD Geode 2113 platforms. 2114 2115 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 2116 the BIOS has incorrectly applied a workaround. TinyBIOS 2117 version 0.98 is known to be affected, 0.99 fixes the 2118 problem by letting the user disable the workaround. 2119 2120 mga= [HW,DRM] 2121 2122 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this 2123 physical address is ignored. 2124 2125 mini2440= [ARM,HW,KNL] 2126 Format:[0..2][b][c][t] 2127 Default: "0tb" 2128 MINI2440 configuration specification: 2129 0 - The attached screen is the 3.5" TFT 2130 1 - The attached screen is the 7" TFT 2131 2 - The VGA Shield is attached (1024x768) 2132 Leaving out the screen size parameter will not load 2133 the TFT driver, and the framebuffer will be left 2134 unconfigured. 2135 b - Enable backlight. The TFT backlight pin will be 2136 linked to the kernel VESA blanking code and a GPIO 2137 LED. This parameter is not necessary when using the 2138 VGA shield. 2139 c - Enable the s3c camera interface. 2140 t - Reserved for enabling touchscreen support. The 2141 touchscreen support is not enabled in the mainstream 2142 kernel as of 2.6.30, a preliminary port can be found 2143 in the "bleeding edge" mini2440 support kernel at 2144 http://repo.or.cz/w/linux-2.6/mini2440.git 2145 2146 mminit_loglevel= 2147 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this 2148 parameter allows control of the logging verbosity for 2149 the additional memory initialisation checks. A value 2150 of 0 disables mminit logging and a level of 4 will 2151 log everything. Information is printed at KERN_DEBUG 2152 so loglevel=8 may also need to be specified. 2153 2154 module.sig_enforce 2155 [KNL] When CONFIG_MODULE_SIG is set, this means that 2156 modules without (valid) signatures will fail to load. 2157 Note that if CONFIG_MODULE_SIG_FORCE is set, that 2158 is always true, so this option does nothing. 2159 2160 mousedev.tap_time= 2161 [MOUSE] Maximum time between finger touching and 2162 leaving touchpad surface for touch to be considered 2163 a tap and be reported as a left button click (for 2164 touchpads working in absolute mode only). 2165 Format: <msecs> 2166 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 2167 reporting absolute coordinates, such as tablets 2168 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 2169 reporting absolute coordinates, such as tablets 2170 2171 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter 2172 is similar to kernelcore except it specifies the 2173 amount of memory used for migratable allocations. 2174 If both kernelcore and movablecore is specified, 2175 then kernelcore will be at *least* the specified 2176 value but may be more. If movablecore on its own 2177 is specified, the administrator must be careful 2178 that the amount of memory usable for all allocations 2179 is not too small. 2180 2181 movable_node [KNL,X86] Boot-time switch to enable the effects 2182 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details. 2183 2184 MTD_Partition= [MTD] 2185 Format: <name>,<region-number>,<size>,<offset> 2186 2187 MTD_Region= [MTD] Format: 2188 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 2189 2190 mtdparts= [MTD] 2191 See drivers/mtd/cmdlinepart.c. 2192 2193 multitce=off [PPC] This parameter disables the use of the pSeries 2194 firmware feature for updating multiple TCE entries 2195 at a time. 2196 2197 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 2198 2199 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 2200 2201 boundary - index of last SLC block on Flex-OneNAND. 2202 The remaining blocks are configured as MLC blocks. 2203 lock - Configure if Flex-OneNAND boundary should be locked. 2204 Once locked, the boundary cannot be changed. 2205 1 indicates lock status, 0 indicates unlock status. 2206 2207 mtdset= [ARM] 2208 ARM/S3C2412 JIVE boot control 2209 2210 See arch/arm/mach-s3c2412/mach-jive.c 2211 2212 mtouchusb.raw_coordinates= 2213 [HW] Make the MicroTouch USB driver use raw coordinates 2214 ('y', default) or cooked coordinates ('n') 2215 2216 mtrr_chunk_size=nn[KMG] [X86] 2217 used for mtrr cleanup. It is largest continuous chunk 2218 that could hold holes aka. UC entries. 2219 2220 mtrr_gran_size=nn[KMG] [X86] 2221 Used for mtrr cleanup. It is granularity of mtrr block. 2222 Default is 1. 2223 Large value could prevent small alignment from 2224 using up MTRRs. 2225 2226 mtrr_spare_reg_nr=n [X86] 2227 Format: <integer> 2228 Range: 0,7 : spare reg number 2229 Default : 1 2230 Used for mtrr cleanup. It is spare mtrr entries number. 2231 Set to 2 or more if your graphical card needs more. 2232 2233 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 2234 2235 netdev= [NET] Network devices parameters 2236 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 2237 Note that mem_start is often overloaded to mean 2238 something different and driver-specific. 2239 This usage is only documented in each driver source 2240 file if at all. 2241 2242 nf_conntrack.acct= 2243 [NETFILTER] Enable connection tracking flow accounting 2244 0 to disable accounting 2245 1 to enable accounting 2246 Default value is 0. 2247 2248 nfsaddrs= [NFS] Deprecated. Use ip= instead. 2249 See Documentation/filesystems/nfs/nfsroot.txt. 2250 2251 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 2252 See Documentation/filesystems/nfs/nfsroot.txt. 2253 2254 nfsrootdebug [NFS] enable nfsroot debugging messages. 2255 See Documentation/filesystems/nfs/nfsroot.txt. 2256 2257 nfs.callback_tcpport= 2258 [NFS] set the TCP port on which the NFSv4 callback 2259 channel should listen. 2260 2261 nfs.cache_getent= 2262 [NFS] sets the pathname to the program which is used 2263 to update the NFS client cache entries. 2264 2265 nfs.cache_getent_timeout= 2266 [NFS] sets the timeout after which an attempt to 2267 update a cache entry is deemed to have failed. 2268 2269 nfs.idmap_cache_timeout= 2270 [NFS] set the maximum lifetime for idmapper cache 2271 entries. 2272 2273 nfs.enable_ino64= 2274 [NFS] enable 64-bit inode numbers. 2275 If zero, the NFS client will fake up a 32-bit inode 2276 number for the readdir() and stat() syscalls instead 2277 of returning the full 64-bit number. 2278 The default is to return 64-bit inode numbers. 2279 2280 nfs.max_session_slots= 2281 [NFSv4.1] Sets the maximum number of session slots 2282 the client will attempt to negotiate with the server. 2283 This limits the number of simultaneous RPC requests 2284 that the client can send to the NFSv4.1 server. 2285 Note that there is little point in setting this 2286 value higher than the max_tcp_slot_table_limit. 2287 2288 nfs.nfs4_disable_idmapping= 2289 [NFSv4] When set to the default of '1', this option 2290 ensures that both the RPC level authentication 2291 scheme and the NFS level operations agree to use 2292 numeric uids/gids if the mount is using the 2293 'sec=sys' security flavour. In effect it is 2294 disabling idmapping, which can make migration from 2295 legacy NFSv2/v3 systems to NFSv4 easier. 2296 Servers that do not support this mode of operation 2297 will be autodetected by the client, and it will fall 2298 back to using the idmapper. 2299 To turn off this behaviour, set the value to '0'. 2300 nfs.nfs4_unique_id= 2301 [NFS4] Specify an additional fixed unique ident- 2302 ification string that NFSv4 clients can insert into 2303 their nfs_client_id4 string. This is typically a 2304 UUID that is generated at system install time. 2305 2306 nfs.send_implementation_id = 2307 [NFSv4.1] Send client implementation identification 2308 information in exchange_id requests. 2309 If zero, no implementation identification information 2310 will be sent. 2311 The default is to send the implementation identification 2312 information. 2313 2314 nfs.recover_lost_locks = 2315 [NFSv4] Attempt to recover locks that were lost due 2316 to a lease timeout on the server. Please note that 2317 doing this risks data corruption, since there are 2318 no guarantees that the file will remain unchanged 2319 after the locks are lost. 2320 If you want to enable the kernel legacy behaviour of 2321 attempting to recover these locks, then set this 2322 parameter to '1'. 2323 The default parameter value of '0' causes the kernel 2324 not to attempt recovery of lost locks. 2325 2326 nfs4.layoutstats_timer = 2327 [NFSv4.2] Change the rate at which the kernel sends 2328 layoutstats to the pNFS metadata server. 2329 2330 Setting this to value to 0 causes the kernel to use 2331 whatever value is the default set by the layout 2332 driver. A non-zero value sets the minimum interval 2333 in seconds between layoutstats transmissions. 2334 2335 nfsd.nfs4_disable_idmapping= 2336 [NFSv4] When set to the default of '1', the NFSv4 2337 server will return only numeric uids and gids to 2338 clients using auth_sys, and will accept numeric uids 2339 and gids from such clients. This is intended to ease 2340 migration from NFSv2/v3. 2341 2342 objlayoutdriver.osd_login_prog= 2343 [NFS] [OBJLAYOUT] sets the pathname to the program which 2344 is used to automatically discover and login into new 2345 osd-targets. Please see: 2346 Documentation/filesystems/pnfs.txt for more explanations 2347 2348 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take 2349 when a NMI is triggered. 2350 Format: [state][,regs][,debounce][,die] 2351 2352 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 2353 Format: [panic,][nopanic,][num] 2354 Valid num: 0 or 1 2355 0 - turn hardlockup detector in nmi_watchdog off 2356 1 - turn hardlockup detector in nmi_watchdog on 2357 When panic is specified, panic when an NMI watchdog 2358 timeout occurs (or 'nopanic' to override the opposite 2359 default). To disable both hard and soft lockup detectors, 2360 please see 'nowatchdog'. 2361 This is useful when you use a panic=... timeout and 2362 need the box quickly up again. 2363 2364 netpoll.carrier_timeout= 2365 [NET] Specifies amount of time (in seconds) that 2366 netpoll should wait for a carrier. By default netpoll 2367 waits 4 seconds. 2368 2369 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 2370 emulation library even if a 387 maths coprocessor 2371 is present. 2372 2373 no_console_suspend 2374 [HW] Never suspend the console 2375 Disable suspending of consoles during suspend and 2376 hibernate operations. Once disabled, debugging 2377 messages can reach various consoles while the rest 2378 of the system is being put to sleep (ie, while 2379 debugging driver suspend/resume hooks). This may 2380 not work reliably with all consoles, but is known 2381 to work with serial and VGA consoles. 2382 To facilitate more flexible debugging, we also add 2383 console_suspend, a printk module parameter to control 2384 it. Users could use console_suspend (usually 2385 /sys/module/printk/parameters/console_suspend) to 2386 turn on/off it dynamically. 2387 2388 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien 2389 caches in the slab allocator. Saves per-node memory, 2390 but will impact performance. 2391 2392 noalign [KNL,ARM] 2393 2394 noapic [SMP,APIC] Tells the kernel to not make use of any 2395 IOAPICs that may be present in the system. 2396 2397 noautogroup Disable scheduler automatic task group creation. 2398 2399 nobats [PPC] Do not use BATs for mapping kernel lowmem 2400 on "Classic" PPC cores. 2401 2402 nocache [ARM] 2403 2404 noclflush [BUGS=X86] Don't use the CLFLUSH instruction 2405 2406 nodelayacct [KNL] Disable per-task delay accounting 2407 2408 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects. 2409 2410 nodsp [SH] Disable hardware DSP at boot time. 2411 2412 noefi Disable EFI runtime services support. 2413 2414 noexec [IA-64] 2415 2416 noexec [X86] 2417 On X86-32 available only on PAE configured kernels. 2418 noexec=on: enable non-executable mappings (default) 2419 noexec=off: disable non-executable mappings 2420 2421 nosmap [X86] 2422 Disable SMAP (Supervisor Mode Access Prevention) 2423 even if it is supported by processor. 2424 2425 nosmep [X86] 2426 Disable SMEP (Supervisor Mode Execution Prevention) 2427 even if it is supported by processor. 2428 2429 noexec32 [X86-64] 2430 This affects only 32-bit executables. 2431 noexec32=on: enable non-executable mappings (default) 2432 read doesn't imply executable mappings 2433 noexec32=off: disable non-executable mappings 2434 read implies executable mappings 2435 2436 nofpu [MIPS,SH] Disable hardware FPU at boot time. 2437 2438 nofxsr [BUGS=X86-32] Disables x86 floating point extended 2439 register save and restore. The kernel will only save 2440 legacy floating-point registers on task switch. 2441 2442 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings. 2443 2444 noxsave [BUGS=X86] Disables x86 extended register state save 2445 and restore using xsave. The kernel will fallback to 2446 enabling legacy floating-point and sse state. 2447 2448 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 2449 register states. The kernel will fall back to use 2450 xsave to save the states. By using this parameter, 2451 performance of saving the states is degraded because 2452 xsave doesn't support modified optimization while 2453 xsaveopt supports it on xsaveopt enabled systems. 2454 2455 noxsaves [X86] Disables xsaves and xrstors used in saving and 2456 restoring x86 extended register state in compacted 2457 form of xsave area. The kernel will fall back to use 2458 xsaveopt and xrstor to save and restore the states 2459 in standard form of xsave area. By using this 2460 parameter, xsave area per process might occupy more 2461 memory on xsaves enabled systems. 2462 2463 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or 2464 wfi(ARM) instruction doesn't work correctly and not to 2465 use it. This is also useful when using JTAG debugger. 2466 2467 no_file_caps Tells the kernel not to honor file capabilities. The 2468 only way then for a file to be executed with privilege 2469 is to be setuid root or executed by root. 2470 2471 nohalt [IA-64] Tells the kernel not to use the power saving 2472 function PAL_HALT_LIGHT when idle. This increases 2473 power-consumption. On the positive side, it reduces 2474 interrupt wake-up latency, which may improve performance 2475 in certain environments such as networked servers or 2476 real-time systems. 2477 2478 nohibernate [HIBERNATION] Disable hibernation and resume. 2479 2480 nohz= [KNL] Boottime enable/disable dynamic ticks 2481 Valid arguments: on, off 2482 Default: on 2483 2484 nohz_full= [KNL,BOOT] 2485 In kernels built with CONFIG_NO_HZ_FULL=y, set 2486 the specified list of CPUs whose tick will be stopped 2487 whenever possible. The boot CPU will be forced outside 2488 the range to maintain the timekeeping. 2489 The CPUs in this range must also be included in the 2490 rcu_nocbs= set. 2491 2492 noiotrap [SH] Disables trapped I/O port accesses. 2493 2494 noirqdebug [X86-32] Disables the code which attempts to detect and 2495 disable unhandled interrupt sources. 2496 2497 no_timer_check [X86,APIC] Disables the code which tests for 2498 broken timer IRQ sources. 2499 2500 noisapnp [ISAPNP] Disables ISA PnP code. 2501 2502 noinitrd [RAM] Tells the kernel not to load any configured 2503 initial RAM disk. 2504 2505 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt 2506 remapping. 2507 [Deprecated - use intremap=off] 2508 2509 nointroute [IA-64] 2510 2511 nojitter [IA-64] Disables jitter checking for ITC timers. 2512 2513 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver 2514 2515 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page 2516 fault handling. 2517 2518 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting. 2519 steal time is computed, but won't influence scheduler 2520 behaviour 2521 2522 nolapic [X86-32,APIC] Do not enable or use the local APIC. 2523 2524 nolapic_timer [X86-32,APIC] Do not use the local APIC timer. 2525 2526 noltlbs [PPC] Do not use large page/tlb entries for kernel 2527 lowmem mapping on PPC40x. 2528 2529 nomca [IA-64] Disable machine check abort handling 2530 2531 nomce [X86-32] Disable Machine Check Exception 2532 2533 nomfgpt [X86-32] Disable Multi-Function General Purpose 2534 Timer usage (for AMD Geode machines). 2535 2536 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 2537 shutdown the other cpus. Instead use the REBOOT_VECTOR 2538 irq. 2539 2540 nomodule Disable module load 2541 2542 nopat [X86] Disable PAT (page attribute table extension of 2543 pagetables) support. 2544 2545 norandmaps Don't use address space randomization. Equivalent to 2546 echo 0 > /proc/sys/kernel/randomize_va_space 2547 2548 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops 2549 2550 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 2551 with UP alternatives 2552 2553 nordrand [X86] Disable kernel use of the RDRAND and 2554 RDSEED instructions even if they are supported 2555 by the processor. RDRAND and RDSEED are still 2556 available to user space applications. 2557 2558 noresume [SWSUSP] Disables resume and restores original swap 2559 space. 2560 2561 no-scroll [VGA] Disables scrollback. 2562 This is required for the Braillex ib80-piezo Braille 2563 reader made by F.H. Papenmeier (Germany). 2564 2565 nosbagart [IA-64] 2566 2567 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support. 2568 2569 nosmp [SMP] Tells an SMP kernel to act as a UP kernel, 2570 and disable the IO APIC. legacy for "maxcpus=0". 2571 2572 nosoftlockup [KNL] Disable the soft-lockup detector. 2573 2574 nosync [HW,M68K] Disables sync negotiation for all devices. 2575 2576 notsc [BUGS=X86-32] Disable Time Stamp Counter 2577 2578 nousb [USB] Disable the USB subsystem 2579 2580 nowatchdog [KNL] Disable both lockup detectors, i.e. 2581 soft-lockup and NMI watchdog (hard-lockup). 2582 2583 nowb [ARM] 2584 2585 nox2apic [X86-64,APIC] Do not enable x2APIC mode. 2586 2587 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when 2588 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off. 2589 Some features depend on CPU0. Known dependencies are: 2590 1. Resume from suspend/hibernate depends on CPU0. 2591 Suspend/hibernate will fail if CPU0 is offline and you 2592 need to online CPU0 before suspend/hibernate. 2593 2. PIC interrupts also depend on CPU0. CPU0 can't be 2594 removed if a PIC interrupt is detected. 2595 It's said poweroff/reboot may depend on CPU0 on some 2596 machines although I haven't seen such issues so far 2597 after CPU0 is offline on a few tested machines. 2598 If the dependencies are under your control, you can 2599 turn on cpu0_hotplug. 2600 2601 nptcg= [IA-64] Override max number of concurrent global TLB 2602 purges which is reported from either PAL_VM_SUMMARY or 2603 SAL PALO. 2604 2605 nr_cpus= [SMP] Maximum number of processors that an SMP kernel 2606 could support. nr_cpus=n : n >= 1 limits the kernel to 2607 supporting 'n' processors. Later in runtime you can not 2608 use hotplug cpu feature to put more cpu back to online. 2609 just like you compile the kernel NR_CPUS=n 2610 2611 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 2612 2613 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing. 2614 Allowed values are enable and disable 2615 2616 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 2617 one of ['zone', 'node', 'default'] can be specified 2618 This can be set from sysctl after boot. 2619 See Documentation/sysctl/vm.txt for details. 2620 2621 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver. 2622 See Documentation/debugging-via-ohci1394.txt for more 2623 info. 2624 2625 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 2626 Rather than timing out after 20 ms if an EC 2627 command is not properly ACKed, override the length 2628 of the timeout. We have interrupts disabled while 2629 waiting for the ACK, so if this is set too high 2630 interrupts *may* be lost! 2631 2632 omap_mux= [OMAP] Override bootloader pin multiplexing. 2633 Format: <mux_mode0.mode_name=value>... 2634 For example, to override I2C bus2: 2635 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 2636 2637 oprofile.timer= [HW] 2638 Use timer interrupt instead of performance counters 2639 2640 oprofile.cpu_type= Force an oprofile cpu type 2641 This might be useful if you have an older oprofile 2642 userland or if you want common events. 2643 Format: { arch_perfmon } 2644 arch_perfmon: [X86] Force use of architectural 2645 perfmon on Intel CPUs instead of the 2646 CPU specific event set. 2647 timer: [X86] Force use of architectural NMI 2648 timer mode (see also oprofile.timer 2649 for generic hr timer mode) 2650 [s390] Force legacy basic mode sampling 2651 (report cpu_type "timer") 2652 2653 oops=panic Always panic on oopses. Default is to just kill the 2654 process, but there is a small probability of 2655 deadlocking the machine. 2656 This will also cause panics on machine check exceptions. 2657 Useful together with panic=30 to trigger a reboot. 2658 2659 OSS [HW,OSS] 2660 See Documentation/sound/oss/oss-parameters.txt 2661 2662 page_owner= [KNL] Boot-time page_owner enabling option. 2663 Storage of the information about who allocated 2664 each page is disabled in default. With this switch, 2665 we can turn it on. 2666 on: enable the feature 2667 2668 panic= [KNL] Kernel behaviour on panic: delay <timeout> 2669 timeout > 0: seconds before rebooting 2670 timeout = 0: wait forever 2671 timeout < 0: reboot immediately 2672 Format: <timeout> 2673 2674 panic_on_warn panic() instead of WARN(). Useful to cause kdump 2675 on a WARN(). 2676 2677 crash_kexec_post_notifiers 2678 Run kdump after running panic-notifiers and dumping 2679 kmsg. This only for the users who doubt kdump always 2680 succeeds in any situation. 2681 Note that this also increases risks of kdump failure, 2682 because some panic notifiers can make the crashed 2683 kernel more unstable. 2684 2685 parkbd.port= [HW] Parallel port number the keyboard adapter is 2686 connected to, default is 0. 2687 Format: <parport#> 2688 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 2689 0 for XT, 1 for AT (default is AT). 2690 Format: <mode> 2691 2692 parport= [HW,PPT] Specify parallel ports. 0 disables. 2693 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 2694 Use 'auto' to force the driver to use any 2695 IRQ/DMA settings detected (the default is to 2696 ignore detected IRQ/DMA settings because of 2697 possible conflicts). You can specify the base 2698 address, IRQ, and DMA settings; IRQ and DMA 2699 should be numbers, or 'auto' (for using detected 2700 settings on that particular port), or 'nofifo' 2701 (to avoid using a FIFO even if it is detected). 2702 Parallel ports are assigned in the order they 2703 are specified on the command line, starting 2704 with parport0. 2705 2706 parport_init_mode= [HW,PPT] 2707 Configure VIA parallel port to operate in 2708 a specific mode. This is necessary on Pegasos 2709 computer where firmware has no options for setting 2710 up parallel port mode and sets it to spp. 2711 Currently this function knows 686a and 8231 chips. 2712 Format: [spp|ps2|epp|ecp|ecpepp] 2713 2714 pause_on_oops= 2715 Halt all CPUs after the first oops has been printed for 2716 the specified number of seconds. This is to be used if 2717 your oopses keep scrolling off the screen. 2718 2719 pcbit= [HW,ISDN] 2720 2721 pcd. [PARIDE] 2722 See header of drivers/block/paride/pcd.c. 2723 See also Documentation/blockdev/paride.txt. 2724 2725 pci=option[,option...] [PCI] various PCI subsystem options: 2726 earlydump [X86] dump PCI config space before the kernel 2727 changes anything 2728 off [X86] don't probe for the PCI bus 2729 bios [X86-32] force use of PCI BIOS, don't access 2730 the hardware directly. Use this if your machine 2731 has a non-standard PCI host bridge. 2732 nobios [X86-32] disallow use of PCI BIOS, only direct 2733 hardware access methods are allowed. Use this 2734 if you experience crashes upon bootup and you 2735 suspect they are caused by the BIOS. 2736 conf1 [X86] Force use of PCI Configuration 2737 Mechanism 1. 2738 conf2 [X86] Force use of PCI Configuration 2739 Mechanism 2. 2740 noaer [PCIE] If the PCIEAER kernel config parameter is 2741 enabled, this kernel boot option can be used to 2742 disable the use of PCIE advanced error reporting. 2743 nodomains [PCI] Disable support for multiple PCI 2744 root domains (aka PCI segments, in ACPI-speak). 2745 nommconf [X86] Disable use of MMCONFIG for PCI 2746 Configuration 2747 check_enable_amd_mmconf [X86] check for and enable 2748 properly configured MMIO access to PCI 2749 config space on AMD family 10h CPU 2750 nomsi [MSI] If the PCI_MSI kernel config parameter is 2751 enabled, this kernel boot option can be used to 2752 disable the use of MSI interrupts system-wide. 2753 noioapicquirk [APIC] Disable all boot interrupt quirks. 2754 Safety option to keep boot IRQs enabled. This 2755 should never be necessary. 2756 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 2757 primary IO-APIC for bridges that cannot disable 2758 boot IRQs. This fixes a source of spurious IRQs 2759 when the system masks IRQs. 2760 noioapicreroute [APIC] Disable workaround that uses the 2761 boot IRQ equivalent of an IRQ that connects to 2762 a chipset where boot IRQs cannot be disabled. 2763 The opposite of ioapicreroute. 2764 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 2765 routing table. These calls are known to be buggy 2766 on several machines and they hang the machine 2767 when used, but on other computers it's the only 2768 way to get the interrupt routing table. Try 2769 this option if the kernel is unable to allocate 2770 IRQs or discover secondary PCI buses on your 2771 motherboard. 2772 rom [X86] Assign address space to expansion ROMs. 2773 Use with caution as certain devices share 2774 address decoders between ROMs and other 2775 resources. 2776 norom [X86] Do not assign address space to 2777 expansion ROMs that do not already have 2778 BIOS assigned address ranges. 2779 nobar [X86] Do not assign address space to the 2780 BARs that weren't assigned by the BIOS. 2781 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 2782 assigned automatically to PCI devices. You can 2783 make the kernel exclude IRQs of your ISA cards 2784 this way. 2785 pirqaddr=0xAAAAA [X86] Specify the physical address 2786 of the PIRQ table (normally generated 2787 by the BIOS) if it is outside the 2788 F0000h-100000h range. 2789 lastbus=N [X86] Scan all buses thru bus #N. Can be 2790 useful if the kernel is unable to find your 2791 secondary buses and you want to tell it 2792 explicitly which ones they are. 2793 assign-busses [X86] Always assign all PCI bus 2794 numbers ourselves, overriding 2795 whatever the firmware may have done. 2796 usepirqmask [X86] Honor the possible IRQ mask stored 2797 in the BIOS $PIR table. This is needed on 2798 some systems with broken BIOSes, notably 2799 some HP Pavilion N5400 and Omnibook XE3 2800 notebooks. This will have no effect if ACPI 2801 IRQ routing is enabled. 2802 noacpi [X86] Do not use ACPI for IRQ routing 2803 or for PCI scanning. 2804 use_crs [X86] Use PCI host bridge window information 2805 from ACPI. On BIOSes from 2008 or later, this 2806 is enabled by default. If you need to use this, 2807 please report a bug. 2808 nocrs [X86] Ignore PCI host bridge windows from ACPI. 2809 If you need to use this, please report a bug. 2810 routeirq Do IRQ routing for all PCI devices. 2811 This is normally done in pci_enable_device(), 2812 so this option is a temporary workaround 2813 for broken drivers that don't call it. 2814 skip_isa_align [X86] do not align io start addr, so can 2815 handle more pci cards 2816 firmware [ARM] Do not re-enumerate the bus but instead 2817 just use the configuration from the 2818 bootloader. This is currently used on 2819 IXP2000 systems where the bus has to be 2820 configured a certain way for adjunct CPUs. 2821 noearly [X86] Don't do any early type 1 scanning. 2822 This might help on some broken boards which 2823 machine check when some devices' config space 2824 is read. But various workarounds are disabled 2825 and some IOMMU drivers will not work. 2826 bfsort Sort PCI devices into breadth-first order. 2827 This sorting is done to get a device 2828 order compatible with older (<= 2.4) kernels. 2829 nobfsort Don't sort PCI devices into breadth-first order. 2830 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 2831 tuning and use the BIOS-configured MPS defaults. 2832 pcie_bus_safe Set every device's MPS to the largest value 2833 supported by all devices below the root complex. 2834 pcie_bus_perf Set device MPS to the largest allowable MPS 2835 based on its parent bus. Also set MRRS (Max 2836 Read Request Size) to the largest supported 2837 value (no larger than the MPS that the device 2838 or bus can support) for best performance. 2839 pcie_bus_peer2peer Set every device's MPS to 128B, which 2840 every device is guaranteed to support. This 2841 configuration allows peer-to-peer DMA between 2842 any pair of devices, possibly at the cost of 2843 reduced performance. This also guarantees 2844 that hot-added devices will work. 2845 cbiosize=nn[KMG] The fixed amount of bus space which is 2846 reserved for the CardBus bridge's IO window. 2847 The default value is 256 bytes. 2848 cbmemsize=nn[KMG] The fixed amount of bus space which is 2849 reserved for the CardBus bridge's memory 2850 window. The default value is 64 megabytes. 2851 resource_alignment= 2852 Format: 2853 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...] 2854 Specifies alignment and device to reassign 2855 aligned memory resources. 2856 If <order of align> is not specified, 2857 PAGE_SIZE is used as alignment. 2858 PCI-PCI bridge can be specified, if resource 2859 windows need to be expanded. 2860 ecrc= Enable/disable PCIe ECRC (transaction layer 2861 end-to-end CRC checking). 2862 bios: Use BIOS/firmware settings. This is the 2863 the default. 2864 off: Turn ECRC off 2865 on: Turn ECRC on. 2866 hpiosize=nn[KMG] The fixed amount of bus space which is 2867 reserved for hotplug bridge's IO window. 2868 Default size is 256 bytes. 2869 hpmemsize=nn[KMG] The fixed amount of bus space which is 2870 reserved for hotplug bridge's memory window. 2871 Default size is 2 megabytes. 2872 realloc= Enable/disable reallocating PCI bridge resources 2873 if allocations done by BIOS are too small to 2874 accommodate resources required by all child 2875 devices. 2876 off: Turn realloc off 2877 on: Turn realloc on 2878 realloc same as realloc=on 2879 noari do not use PCIe ARI. 2880 pcie_scan_all Scan all possible PCIe devices. Otherwise we 2881 only look for one device below a PCIe downstream 2882 port. 2883 2884 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power 2885 Management. 2886 off Disable ASPM. 2887 force Enable ASPM even on devices that claim not to support it. 2888 WARNING: Forcing ASPM on may cause system lockups. 2889 2890 pcie_hp= [PCIE] PCI Express Hotplug driver options: 2891 nomsi Do not use MSI for PCI Express Native Hotplug (this 2892 makes all PCIe ports use INTx for hotplug services). 2893 2894 pcie_ports= [PCIE] PCIe ports handling: 2895 auto Ask the BIOS whether or not to use native PCIe services 2896 associated with PCIe ports (PME, hot-plug, AER). Use 2897 them only if that is allowed by the BIOS. 2898 native Use native PCIe services associated with PCIe ports 2899 unconditionally. 2900 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe 2901 ports driver. 2902 2903 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 2904 nomsi Do not use MSI for native PCIe PME signaling (this makes 2905 all PCIe root ports use INTx for all services). 2906 2907 pcmv= [HW,PCMCIA] BadgePAD 4 2908 2909 pd_ignore_unused 2910 [PM] 2911 Keep all power-domains already enabled by bootloader on, 2912 even if no driver has claimed them. This is useful 2913 for debug and development, but should not be 2914 needed on a platform with proper driver support. 2915 2916 pd. [PARIDE] 2917 See Documentation/blockdev/paride.txt. 2918 2919 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 2920 boot time. 2921 Format: { 0 | 1 } 2922 See arch/parisc/kernel/pdc_chassis.c 2923 2924 percpu_alloc= Select which percpu first chunk allocator to use. 2925 Currently supported values are "embed" and "page". 2926 Archs may support subset or none of the selections. 2927 See comments in mm/percpu.c for details on each 2928 allocator. This parameter is primarily for debugging 2929 and performance comparison. 2930 2931 pf. [PARIDE] 2932 See Documentation/blockdev/paride.txt. 2933 2934 pg. [PARIDE] 2935 See Documentation/blockdev/paride.txt. 2936 2937 pirq= [SMP,APIC] Manual mp-table setup 2938 See Documentation/x86/i386/IO-APIC.txt. 2939 2940 plip= [PPT,NET] Parallel port network link 2941 Format: { parport<nr> | timid | 0 } 2942 See also Documentation/parport.txt. 2943 2944 pmtmr= [X86] Manual setup of pmtmr I/O Port. 2945 Override pmtimer IOPort with a hex value. 2946 e.g. pmtmr=0x508 2947 2948 pnp.debug=1 [PNP] 2949 Enable PNP debug messages (depends on the 2950 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 2951 via /sys/module/pnp/parameters/debug. We always show 2952 current resource usage; turning this on also shows 2953 possible settings and some assignment information. 2954 2955 pnpacpi= [ACPI] 2956 { off } 2957 2958 pnpbios= [ISAPNP] 2959 { on | off | curr | res | no-curr | no-res } 2960 2961 pnp_reserve_irq= 2962 [ISAPNP] Exclude IRQs for the autoconfiguration 2963 2964 pnp_reserve_dma= 2965 [ISAPNP] Exclude DMAs for the autoconfiguration 2966 2967 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 2968 Ranges are in pairs (I/O port base and size). 2969 2970 pnp_reserve_mem= 2971 [ISAPNP] Exclude memory regions for the 2972 autoconfiguration. 2973 Ranges are in pairs (memory base and size). 2974 2975 ports= [IP_VS_FTP] IPVS ftp helper module 2976 Default is 21. 2977 Up to 8 (IP_VS_APP_MAX_PORTS) ports 2978 may be specified. 2979 Format: <port>,<port>.... 2980 2981 print-fatal-signals= 2982 [KNL] debug: print fatal signals 2983 2984 If enabled, warn about various signal handling 2985 related application anomalies: too many signals, 2986 too many POSIX.1 timers, fatal signals causing a 2987 coredump - etc. 2988 2989 If you hit the warning due to signal overflow, 2990 you might want to try "ulimit -i unlimited". 2991 2992 default: off. 2993 2994 printk.always_kmsg_dump= 2995 Trigger kmsg_dump for cases other than kernel oops or 2996 panics 2997 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 2998 default: disabled 2999 3000 printk.time= Show timing data prefixed to each printk message line 3001 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3002 3003 processor.max_cstate= [HW,ACPI] 3004 Limit processor to maximum C-state 3005 max_cstate=9 overrides any DMI blacklist limit. 3006 3007 processor.nocst [HW,ACPI] 3008 Ignore the _CST method to determine C-states, 3009 instead using the legacy FADT method 3010 3011 profile= [KNL] Enable kernel profiling via /proc/profile 3012 Format: [schedule,]<number> 3013 Param: "schedule" - profile schedule points. 3014 Param: <number> - step/bucket size as a power of 2 for 3015 statistical time based profiling. 3016 Param: "sleep" - profile D-state sleeping (millisecs). 3017 Requires CONFIG_SCHEDSTATS 3018 Param: "kvm" - profile VM exits. 3019 3020 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk 3021 before loading. 3022 See Documentation/blockdev/ramdisk.txt. 3023 3024 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 3025 probe for; one of (bare|imps|exps|lifebook|any). 3026 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 3027 per second. 3028 psmouse.resetafter= [HW,MOUSE] 3029 Try to reset the device after so many bad packets 3030 (0 = never). 3031 psmouse.resolution= 3032 [HW,MOUSE] Set desired mouse resolution, in dpi. 3033 psmouse.smartscroll= 3034 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 3035 0 = disabled, 1 = enabled (default). 3036 3037 pstore.backend= Specify the name of the pstore backend to use 3038 3039 pt. [PARIDE] 3040 See Documentation/blockdev/paride.txt. 3041 3042 pty.legacy_count= 3043 [KNL] Number of legacy pty's. Overwrites compiled-in 3044 default number. 3045 3046 quiet [KNL] Disable most log messages 3047 3048 r128= [HW,DRM] 3049 3050 raid= [HW,RAID] 3051 See Documentation/md.txt. 3052 3053 ramdisk_blocksize= [RAM] 3054 See Documentation/blockdev/ramdisk.txt. 3055 3056 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 3057 See Documentation/blockdev/ramdisk.txt. 3058 3059 rcu_nocbs= [KNL] 3060 In kernels built with CONFIG_RCU_NOCB_CPU=y, set 3061 the specified list of CPUs to be no-callback CPUs. 3062 Invocation of these CPUs' RCU callbacks will 3063 be offloaded to "rcuox/N" kthreads created for 3064 that purpose, where "x" is "b" for RCU-bh, "p" 3065 for RCU-preempt, and "s" for RCU-sched, and "N" 3066 is the CPU number. This reduces OS jitter on the 3067 offloaded CPUs, which can be useful for HPC and 3068 real-time workloads. It can also improve energy 3069 efficiency for asymmetric multiprocessors. 3070 3071 rcu_nocb_poll [KNL] 3072 Rather than requiring that offloaded CPUs 3073 (specified by rcu_nocbs= above) explicitly 3074 awaken the corresponding "rcuoN" kthreads, 3075 make these kthreads poll for callbacks. 3076 This improves the real-time response for the 3077 offloaded CPUs by relieving them of the need to 3078 wake up the corresponding kthread, but degrades 3079 energy efficiency by requiring that the kthreads 3080 periodically wake up to do the polling. 3081 3082 rcutree.blimit= [KNL] 3083 Set maximum number of finished RCU callbacks to 3084 process in one batch. 3085 3086 rcutree.dump_tree= [KNL] 3087 Dump the structure of the rcu_node combining tree 3088 out at early boot. This is used for diagnostic 3089 purposes, to verify correct tree setup. 3090 3091 rcutree.gp_cleanup_delay= [KNL] 3092 Set the number of jiffies to delay each step of 3093 RCU grace-period cleanup. This only has effect 3094 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set. 3095 3096 rcutree.gp_init_delay= [KNL] 3097 Set the number of jiffies to delay each step of 3098 RCU grace-period initialization. This only has 3099 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT 3100 is set. 3101 3102 rcutree.gp_preinit_delay= [KNL] 3103 Set the number of jiffies to delay each step of 3104 RCU grace-period pre-initialization, that is, 3105 the propagation of recent CPU-hotplug changes up 3106 the rcu_node combining tree. This only has effect 3107 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set. 3108 3109 rcutree.rcu_fanout_exact= [KNL] 3110 Disable autobalancing of the rcu_node combining 3111 tree. This is used by rcutorture, and might 3112 possibly be useful for architectures having high 3113 cache-to-cache transfer latencies. 3114 3115 rcutree.rcu_fanout_leaf= [KNL] 3116 Change the number of CPUs assigned to each 3117 leaf rcu_node structure. Useful for very 3118 large systems, which will choose the value 64, 3119 and for NUMA systems with large remote-access 3120 latencies, which will choose a value aligned 3121 with the appropriate hardware boundaries. 3122 3123 rcutree.jiffies_till_sched_qs= [KNL] 3124 Set required age in jiffies for a 3125 given grace period before RCU starts 3126 soliciting quiescent-state help from 3127 rcu_note_context_switch(). 3128 3129 rcutree.jiffies_till_first_fqs= [KNL] 3130 Set delay from grace-period initialization to 3131 first attempt to force quiescent states. 3132 Units are jiffies, minimum value is zero, 3133 and maximum value is HZ. 3134 3135 rcutree.jiffies_till_next_fqs= [KNL] 3136 Set delay between subsequent attempts to force 3137 quiescent states. Units are jiffies, minimum 3138 value is one, and maximum value is HZ. 3139 3140 rcutree.kthread_prio= [KNL,BOOT] 3141 Set the SCHED_FIFO priority of the RCU per-CPU 3142 kthreads (rcuc/N). This value is also used for 3143 the priority of the RCU boost threads (rcub/N) 3144 and for the RCU grace-period kthreads (rcu_bh, 3145 rcu_preempt, and rcu_sched). If RCU_BOOST is 3146 set, valid values are 1-99 and the default is 1 3147 (the least-favored priority). Otherwise, when 3148 RCU_BOOST is not set, valid values are 0-99 and 3149 the default is zero (non-realtime operation). 3150 3151 rcutree.rcu_nocb_leader_stride= [KNL] 3152 Set the number of NOCB kthread groups, which 3153 defaults to the square root of the number of 3154 CPUs. Larger numbers reduces the wakeup overhead 3155 on the per-CPU grace-period kthreads, but increases 3156 that same overhead on each group's leader. 3157 3158 rcutree.qhimark= [KNL] 3159 Set threshold of queued RCU callbacks beyond which 3160 batch limiting is disabled. 3161 3162 rcutree.qlowmark= [KNL] 3163 Set threshold of queued RCU callbacks below which 3164 batch limiting is re-enabled. 3165 3166 rcutree.rcu_idle_gp_delay= [KNL] 3167 Set wakeup interval for idle CPUs that have 3168 RCU callbacks (RCU_FAST_NO_HZ=y). 3169 3170 rcutree.rcu_idle_lazy_gp_delay= [KNL] 3171 Set wakeup interval for idle CPUs that have 3172 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y). 3173 Lazy RCU callbacks are those which RCU can 3174 prove do nothing more than free memory. 3175 3176 rcutorture.cbflood_inter_holdoff= [KNL] 3177 Set holdoff time (jiffies) between successive 3178 callback-flood tests. 3179 3180 rcutorture.cbflood_intra_holdoff= [KNL] 3181 Set holdoff time (jiffies) between successive 3182 bursts of callbacks within a given callback-flood 3183 test. 3184 3185 rcutorture.cbflood_n_burst= [KNL] 3186 Set the number of bursts making up a given 3187 callback-flood test. Set this to zero to 3188 disable callback-flood testing. 3189 3190 rcutorture.cbflood_n_per_burst= [KNL] 3191 Set the number of callbacks to be registered 3192 in a given burst of a callback-flood test. 3193 3194 rcutorture.fqs_duration= [KNL] 3195 Set duration of force_quiescent_state bursts 3196 in microseconds. 3197 3198 rcutorture.fqs_holdoff= [KNL] 3199 Set holdoff time within force_quiescent_state bursts 3200 in microseconds. 3201 3202 rcutorture.fqs_stutter= [KNL] 3203 Set wait time between force_quiescent_state bursts 3204 in seconds. 3205 3206 rcutorture.gp_cond= [KNL] 3207 Use conditional/asynchronous update-side 3208 primitives, if available. 3209 3210 rcutorture.gp_exp= [KNL] 3211 Use expedited update-side primitives, if available. 3212 3213 rcutorture.gp_normal= [KNL] 3214 Use normal (non-expedited) asynchronous 3215 update-side primitives, if available. 3216 3217 rcutorture.gp_sync= [KNL] 3218 Use normal (non-expedited) synchronous 3219 update-side primitives, if available. If all 3220 of rcutorture.gp_cond=, rcutorture.gp_exp=, 3221 rcutorture.gp_normal=, and rcutorture.gp_sync= 3222 are zero, rcutorture acts as if is interpreted 3223 they are all non-zero. 3224 3225 rcutorture.n_barrier_cbs= [KNL] 3226 Set callbacks/threads for rcu_barrier() testing. 3227 3228 rcutorture.nfakewriters= [KNL] 3229 Set number of concurrent RCU writers. These just 3230 stress RCU, they don't participate in the actual 3231 test, hence the "fake". 3232 3233 rcutorture.nreaders= [KNL] 3234 Set number of RCU readers. The value -1 selects 3235 N-1, where N is the number of CPUs. A value 3236 "n" less than -1 selects N-n-2, where N is again 3237 the number of CPUs. For example, -2 selects N 3238 (the number of CPUs), -3 selects N+1, and so on. 3239 3240 rcutorture.object_debug= [KNL] 3241 Enable debug-object double-call_rcu() testing. 3242 3243 rcutorture.onoff_holdoff= [KNL] 3244 Set time (s) after boot for CPU-hotplug testing. 3245 3246 rcutorture.onoff_interval= [KNL] 3247 Set time (s) between CPU-hotplug operations, or 3248 zero to disable CPU-hotplug testing. 3249 3250 rcutorture.shuffle_interval= [KNL] 3251 Set task-shuffle interval (s). Shuffling tasks 3252 allows some CPUs to go into dyntick-idle mode 3253 during the rcutorture test. 3254 3255 rcutorture.shutdown_secs= [KNL] 3256 Set time (s) after boot system shutdown. This 3257 is useful for hands-off automated testing. 3258 3259 rcutorture.stall_cpu= [KNL] 3260 Duration of CPU stall (s) to test RCU CPU stall 3261 warnings, zero to disable. 3262 3263 rcutorture.stall_cpu_holdoff= [KNL] 3264 Time to wait (s) after boot before inducing stall. 3265 3266 rcutorture.stat_interval= [KNL] 3267 Time (s) between statistics printk()s. 3268 3269 rcutorture.stutter= [KNL] 3270 Time (s) to stutter testing, for example, specifying 3271 five seconds causes the test to run for five seconds, 3272 wait for five seconds, and so on. This tests RCU's 3273 ability to transition abruptly to and from idle. 3274 3275 rcutorture.test_boost= [KNL] 3276 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 3277 "Maybe" means test if the RCU implementation 3278 under test support RCU priority boosting. 3279 3280 rcutorture.test_boost_duration= [KNL] 3281 Duration (s) of each individual boost test. 3282 3283 rcutorture.test_boost_interval= [KNL] 3284 Interval (s) between each boost test. 3285 3286 rcutorture.test_no_idle_hz= [KNL] 3287 Test RCU's dyntick-idle handling. See also the 3288 rcutorture.shuffle_interval parameter. 3289 3290 rcutorture.torture_runnable= [BOOT] 3291 Start rcutorture running at boot time. 3292 3293 rcutorture.torture_type= [KNL] 3294 Specify the RCU implementation to test. 3295 3296 rcutorture.verbose= [KNL] 3297 Enable additional printk() statements. 3298 3299 rcupdate.rcu_expedited= [KNL] 3300 Use expedited grace-period primitives, for 3301 example, synchronize_rcu_expedited() instead 3302 of synchronize_rcu(). This reduces latency, 3303 but can increase CPU utilization, degrade 3304 real-time latency, and degrade energy efficiency. 3305 3306 rcupdate.rcu_cpu_stall_suppress= [KNL] 3307 Suppress RCU CPU stall warning messages. 3308 3309 rcupdate.rcu_cpu_stall_timeout= [KNL] 3310 Set timeout for RCU CPU stall warning messages. 3311 3312 rcupdate.rcu_task_stall_timeout= [KNL] 3313 Set timeout in jiffies for RCU task stall warning 3314 messages. Disable with a value less than or equal 3315 to zero. 3316 3317 rcupdate.rcu_self_test= [KNL] 3318 Run the RCU early boot self tests 3319 3320 rcupdate.rcu_self_test_bh= [KNL] 3321 Run the RCU bh early boot self tests 3322 3323 rcupdate.rcu_self_test_sched= [KNL] 3324 Run the RCU sched early boot self tests 3325 3326 rdinit= [KNL] 3327 Format: <full_path> 3328 Run specified binary instead of /init from the ramdisk, 3329 used for early userspace startup. See initrd. 3330 3331 reboot= [KNL] 3332 Format (x86 or x86_64): 3333 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \ 3334 [[,]s[mp]#### \ 3335 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 3336 [[,]f[orce] 3337 Where reboot_mode is one of warm (soft) or cold (hard) or gpio, 3338 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 3339 reboot_force is either force or not specified, 3340 reboot_cpu is s[mp]#### with #### being the processor 3341 to be used for rebooting. 3342 3343 relax_domain_level= 3344 [KNL, SMP] Set scheduler's default relax_domain_level. 3345 See Documentation/cgroups/cpusets.txt. 3346 3347 relative_sleep_states= 3348 [SUSPEND] Use sleep state labeling where the deepest 3349 state available other than hibernation is always "mem". 3350 Format: { "0" | "1" } 3351 0 -- Traditional sleep state labels. 3352 1 -- Relative sleep state labels. 3353 3354 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area 3355 3356 reservetop= [X86-32] 3357 Format: nn[KMG] 3358 Reserves a hole at the top of the kernel virtual 3359 address space. 3360 3361 reservelow= [X86] 3362 Format: nn[K] 3363 Set the amount of memory to reserve for BIOS at 3364 the bottom of the address space. 3365 3366 reset_devices [KNL] Force drivers to reset the underlying device 3367 during initialization. 3368 3369 resume= [SWSUSP] 3370 Specify the partition device for software suspend 3371 Format: 3372 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 3373 3374 resume_offset= [SWSUSP] 3375 Specify the offset from the beginning of the partition 3376 given by "resume=" at which the swap header is located, 3377 in <PAGE_SIZE> units (needed only for swap files). 3378 See Documentation/power/swsusp-and-swap-files.txt 3379 3380 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 3381 read the resume files 3382 3383 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 3384 Useful for devices that are detected asynchronously 3385 (e.g. USB and MMC devices). 3386 3387 hibernate= [HIBERNATION] 3388 noresume Don't check if there's a hibernation image 3389 present during boot. 3390 nocompress Don't compress/decompress hibernation images. 3391 no Disable hibernation and resume. 3392 3393 retain_initrd [RAM] Keep initrd memory after extraction 3394 3395 rfkill.default_state= 3396 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 3397 etc. communication is blocked by default. 3398 1 Unblocked. 3399 3400 rfkill.master_switch_mode= 3401 0 The "airplane mode" button does nothing. 3402 1 The "airplane mode" button toggles between everything 3403 blocked and the previous configuration. 3404 2 The "airplane mode" button toggles between everything 3405 blocked and everything unblocked. 3406 3407 rhash_entries= [KNL,NET] 3408 Set number of hash buckets for route cache 3409 3410 ro [KNL] Mount root device read-only on boot 3411 3412 root= [KNL] Root filesystem 3413 See name_to_dev_t comment in init/do_mounts.c. 3414 3415 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 3416 mount the root filesystem 3417 3418 rootflags= [KNL] Set root filesystem mount option string 3419 3420 rootfstype= [KNL] Set root filesystem type 3421 3422 rootwait [KNL] Wait (indefinitely) for root device to show up. 3423 Useful for devices that are detected asynchronously 3424 (e.g. USB and MMC devices). 3425 3426 rproc_mem=nn[KMG][@address] 3427 [KNL,ARM,CMA] Remoteproc physical memory block. 3428 Memory area to be used by remote processor image, 3429 managed by CMA. 3430 3431 rw [KNL] Mount root device read-write on boot 3432 3433 S [KNL] Run init in single mode 3434 3435 s390_iommu= [HW,S390] 3436 Set s390 IOTLB flushing mode 3437 strict 3438 With strict flushing every unmap operation will result in 3439 an IOTLB flush. Default is lazy flushing before reuse, 3440 which is faster. 3441 3442 sa1100ir [NET] 3443 See drivers/net/irda/sa1100_ir.c. 3444 3445 sbni= [NET] Granch SBNI12 leased line adapter 3446 3447 sched_debug [KNL] Enables verbose scheduler debug messages. 3448 3449 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate 3450 xtime_lock contention on larger systems, and/or RCU lock 3451 contention on all systems with CONFIG_MAXSMP set. 3452 Format: { "0" | "1" } 3453 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 3454 1 -- enable. 3455 Note: increases power consumption, thus should only be 3456 enabled if running jitter sensitive (HPC/RT) workloads. 3457 3458 security= [SECURITY] Choose a security module to enable at boot. 3459 If this boot parameter is not specified, only the first 3460 security module asking for security registration will be 3461 loaded. An invalid security module name will be treated 3462 as if no module has been chosen. 3463 3464 selinux= [SELINUX] Disable or enable SELinux at boot time. 3465 Format: { "0" | "1" } 3466 See security/selinux/Kconfig help text. 3467 0 -- disable. 3468 1 -- enable. 3469 Default value is set via kernel config option. 3470 If enabled at boot time, /selinux/disable can be used 3471 later to disable prior to initial policy load. 3472 3473 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 3474 Format: { "0" | "1" } 3475 See security/apparmor/Kconfig help text 3476 0 -- disable. 3477 1 -- enable. 3478 Default value is set via kernel config option. 3479 3480 serialnumber [BUGS=X86-32] 3481 3482 shapers= [NET] 3483 Maximal number of shapers. 3484 3485 show_msr= [x86] show boot-time MSR settings 3486 Format: { <integer> } 3487 Show boot-time (BIOS-initialized) MSR settings. 3488 The parameter means the number of CPUs to show, 3489 for example 1 means boot CPU only. 3490 3491 simeth= [IA-64] 3492 simscsi= 3493 3494 slram= [HW,MTD] 3495 3496 slab_nomerge [MM] 3497 Disable merging of slabs with similar size. May be 3498 necessary if there is some reason to distinguish 3499 allocs to different slabs. Debug options disable 3500 merging on their own. 3501 For more information see Documentation/vm/slub.txt. 3502 3503 slab_max_order= [MM, SLAB] 3504 Determines the maximum allowed order for slabs. 3505 A high setting may cause OOMs due to memory 3506 fragmentation. Defaults to 1 for systems with 3507 more than 32MB of RAM, 0 otherwise. 3508 3509 slub_debug[=options[,slabs]] [MM, SLUB] 3510 Enabling slub_debug allows one to determine the 3511 culprit if slab objects become corrupted. Enabling 3512 slub_debug can create guard zones around objects and 3513 may poison objects when not in use. Also tracks the 3514 last alloc / free. For more information see 3515 Documentation/vm/slub.txt. 3516 3517 slub_max_order= [MM, SLUB] 3518 Determines the maximum allowed order for slabs. 3519 A high setting may cause OOMs due to memory 3520 fragmentation. For more information see 3521 Documentation/vm/slub.txt. 3522 3523 slub_min_objects= [MM, SLUB] 3524 The minimum number of objects per slab. SLUB will 3525 increase the slab order up to slub_max_order to 3526 generate a sufficiently large slab able to contain 3527 the number of objects indicated. The higher the number 3528 of objects the smaller the overhead of tracking slabs 3529 and the less frequently locks need to be acquired. 3530 For more information see Documentation/vm/slub.txt. 3531 3532 slub_min_order= [MM, SLUB] 3533 Determines the minimum page order for slabs. Must be 3534 lower than slub_max_order. 3535 For more information see Documentation/vm/slub.txt. 3536 3537 slub_nomerge [MM, SLUB] 3538 Same with slab_nomerge. This is supported for legacy. 3539 See slab_nomerge for more information. 3540 3541 smart2= [HW] 3542 Format: <io1>[,<io2>[,...,<io8>]] 3543 3544 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 3545 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 3546 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 3547 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 3548 smsc-ircc2.ircc_irq= [HW] IRQ line 3549 smsc-ircc2.ircc_dma= [HW] DMA channel 3550 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 3551 0: Toshiba Satellite 1800 (GP data pin select) 3552 1: Fast pin select (default) 3553 2: ATC IRMode 3554 3555 softlockup_panic= 3556 [KNL] Should the soft-lockup detector generate panics. 3557 Format: <integer> 3558 3559 softlockup_all_cpu_backtrace= 3560 [KNL] Should the soft-lockup detector generate 3561 backtraces on all cpus. 3562 Format: <integer> 3563 3564 sonypi.*= [HW] Sony Programmable I/O Control Device driver 3565 See Documentation/laptops/sonypi.txt 3566 3567 spia_io_base= [HW,MTD] 3568 spia_fio_base= 3569 spia_pedr= 3570 spia_peddr= 3571 3572 stacktrace [FTRACE] 3573 Enabled the stack tracer on boot up. 3574 3575 stacktrace_filter=[function-list] 3576 [FTRACE] Limit the functions that the stack tracer 3577 will trace at boot up. function-list is a comma separated 3578 list of functions. This list can be changed at run 3579 time by the stack_trace_filter file in the debugfs 3580 tracing directory. Note, this enables stack tracing 3581 and the stacktrace above is not needed. 3582 3583 sti= [PARISC,HW] 3584 Format: <num> 3585 Set the STI (builtin display/keyboard on the HP-PARISC 3586 machines) console (graphic card) which should be used 3587 as the initial boot-console. 3588 See also comment in drivers/video/console/sticore.c. 3589 3590 sti_font= [HW] 3591 See comment in drivers/video/console/sticore.c. 3592 3593 stifb= [HW] 3594 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 3595 3596 sunrpc.min_resvport= 3597 sunrpc.max_resvport= 3598 [NFS,SUNRPC] 3599 SunRPC servers often require that client requests 3600 originate from a privileged port (i.e. a port in the 3601 range 0 < portnr < 1024). 3602 An administrator who wishes to reserve some of these 3603 ports for other uses may adjust the range that the 3604 kernel's sunrpc client considers to be privileged 3605 using these two parameters to set the minimum and 3606 maximum port values. 3607 3608 sunrpc.pool_mode= 3609 [NFS] 3610 Control how the NFS server code allocates CPUs to 3611 service thread pools. Depending on how many NICs 3612 you have and where their interrupts are bound, this 3613 option will affect which CPUs will do NFS serving. 3614 Note: this parameter cannot be changed while the 3615 NFS server is running. 3616 3617 auto the server chooses an appropriate mode 3618 automatically using heuristics 3619 global a single global pool contains all CPUs 3620 percpu one pool for each CPU 3621 pernode one pool for each NUMA node (equivalent 3622 to global on non-NUMA machines) 3623 3624 sunrpc.tcp_slot_table_entries= 3625 sunrpc.udp_slot_table_entries= 3626 [NFS,SUNRPC] 3627 Sets the upper limit on the number of simultaneous 3628 RPC calls that can be sent from the client to a 3629 server. Increasing these values may allow you to 3630 improve throughput, but will also increase the 3631 amount of memory reserved for use by the client. 3632 3633 suspend.pm_test_delay= 3634 [SUSPEND] 3635 Sets the number of seconds to remain in a suspend test 3636 mode before resuming the system (see 3637 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 3638 is set. Default value is 5. 3639 3640 swapaccount=[0|1] 3641 [KNL] Enable accounting of swap in memory resource 3642 controller if no parameter or 1 is given or disable 3643 it if 0 is given (See Documentation/cgroups/memory.txt) 3644 3645 swiotlb= [ARM,IA-64,PPC,MIPS,X86] 3646 Format: { <int> | force } 3647 <int> -- Number of I/O TLB slabs 3648 force -- force using of bounce buffers even if they 3649 wouldn't be automatically used by the kernel 3650 3651 switches= [HW,M68k] 3652 3653 sysfs.deprecated=0|1 [KNL] 3654 Enable/disable old style sysfs layout for old udev 3655 on older distributions. When this option is enabled 3656 very new udev will not work anymore. When this option 3657 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled) 3658 in older udev will not work anymore. 3659 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in 3660 the kernel configuration. 3661 3662 sysrq_always_enabled 3663 [KNL] 3664 Ignore sysrq setting - this boot parameter will 3665 neutralize any effect of /proc/sys/kernel/sysrq. 3666 Useful for debugging. 3667 3668 tcpmhash_entries= [KNL,NET] 3669 Set the number of tcp_metrics_hash slots. 3670 Default value is 8192 or 16384 depending on total 3671 ram pages. This is used to specify the TCP metrics 3672 cache size. See Documentation/networking/ip-sysctl.txt 3673 "tcp_no_metrics_save" section for more details. 3674 3675 tdfx= [HW,DRM] 3676 3677 test_suspend= [SUSPEND][,N] 3678 Specify "mem" (for Suspend-to-RAM) or "standby" (for 3679 standby suspend) or "freeze" (for suspend type freeze) 3680 as the system sleep state during system startup with 3681 the optional capability to repeat N number of times. 3682 The system is woken from this state using a 3683 wakeup-capable RTC alarm. 3684 3685 thash_entries= [KNL,NET] 3686 Set number of hash buckets for TCP connection 3687 3688 thermal.act= [HW,ACPI] 3689 -1: disable all active trip points in all thermal zones 3690 <degrees C>: override all lowest active trip points 3691 3692 thermal.crt= [HW,ACPI] 3693 -1: disable all critical trip points in all thermal zones 3694 <degrees C>: override all critical trip points 3695 3696 thermal.nocrt= [HW,ACPI] 3697 Set to disable actions on ACPI thermal zone 3698 critical and hot trip points. 3699 3700 thermal.off= [HW,ACPI] 3701 1: disable ACPI thermal control 3702 3703 thermal.psv= [HW,ACPI] 3704 -1: disable all passive trip points 3705 <degrees C>: override all passive trip points to this 3706 value 3707 3708 thermal.tzp= [HW,ACPI] 3709 Specify global default ACPI thermal zone polling rate 3710 <deci-seconds>: poll all this frequency 3711 0: no polling (default) 3712 3713 threadirqs [KNL] 3714 Force threading of all interrupt handlers except those 3715 marked explicitly IRQF_NO_THREAD. 3716 3717 tmem [KNL,XEN] 3718 Enable the Transcendent memory driver if built-in. 3719 3720 tmem.cleancache=0|1 [KNL, XEN] 3721 Default is on (1). Disable the usage of the cleancache 3722 API to send anonymous pages to the hypervisor. 3723 3724 tmem.frontswap=0|1 [KNL, XEN] 3725 Default is on (1). Disable the usage of the frontswap 3726 API to send swap pages to the hypervisor. If disabled 3727 the selfballooning and selfshrinking are force disabled. 3728 3729 tmem.selfballooning=0|1 [KNL, XEN] 3730 Default is on (1). Disable the driving of swap pages 3731 to the hypervisor. 3732 3733 tmem.selfshrinking=0|1 [KNL, XEN] 3734 Default is on (1). Partial swapoff that immediately 3735 transfers pages from Xen hypervisor back to the 3736 kernel based on different criteria. 3737 3738 topology= [S390] 3739 Format: {off | on} 3740 Specify if the kernel should make use of the cpu 3741 topology information if the hardware supports this. 3742 The scheduler will make use of this information and 3743 e.g. base its process migration decisions on it. 3744 Default is on. 3745 3746 topology_updates= [KNL, PPC, NUMA] 3747 Format: {off} 3748 Specify if the kernel should ignore (off) 3749 topology updates sent by the hypervisor to this 3750 LPAR. 3751 3752 tp720= [HW,PS2] 3753 3754 tpm_suspend_pcr=[HW,TPM] 3755 Format: integer pcr id 3756 Specify that at suspend time, the tpm driver 3757 should extend the specified pcr with zeros, 3758 as a workaround for some chips which fail to 3759 flush the last written pcr on TPM_SaveState. 3760 This will guarantee that all the other pcrs 3761 are saved. 3762 3763 trace_buf_size=nn[KMG] 3764 [FTRACE] will set tracing buffer size on each cpu. 3765 3766 trace_event=[event-list] 3767 [FTRACE] Set and start specified trace events in order 3768 to facilitate early boot debugging. 3769 See also Documentation/trace/events.txt 3770 3771 trace_options=[option-list] 3772 [FTRACE] Enable or disable tracer options at boot. 3773 The option-list is a comma delimited list of options 3774 that can be enabled or disabled just as if you were 3775 to echo the option name into 3776 3777 /sys/kernel/debug/tracing/trace_options 3778 3779 For example, to enable stacktrace option (to dump the 3780 stack trace of each event), add to the command line: 3781 3782 trace_options=stacktrace 3783 3784 See also Documentation/trace/ftrace.txt "trace options" 3785 section. 3786 3787 tp_printk[FTRACE] 3788 Have the tracepoints sent to printk as well as the 3789 tracing ring buffer. This is useful for early boot up 3790 where the system hangs or reboots and does not give the 3791 option for reading the tracing buffer or performing a 3792 ftrace_dump_on_oops. 3793 3794 To turn off having tracepoints sent to printk, 3795 echo 0 > /proc/sys/kernel/tracepoint_printk 3796 Note, echoing 1 into this file without the 3797 tracepoint_printk kernel cmdline option has no effect. 3798 3799 ** CAUTION ** 3800 3801 Having tracepoints sent to printk() and activating high 3802 frequency tracepoints such as irq or sched, can cause 3803 the system to live lock. 3804 3805 traceoff_on_warning 3806 [FTRACE] enable this option to disable tracing when a 3807 warning is hit. This turns off "tracing_on". Tracing can 3808 be enabled again by echoing '1' into the "tracing_on" 3809 file located in /sys/kernel/debug/tracing/ 3810 3811 This option is useful, as it disables the trace before 3812 the WARNING dump is called, which prevents the trace to 3813 be filled with content caused by the warning output. 3814 3815 This option can also be set at run time via the sysctl 3816 option: kernel/traceoff_on_warning 3817 3818 transparent_hugepage= 3819 [KNL] 3820 Format: [always|madvise|never] 3821 Can be used to control the default behavior of the system 3822 with respect to transparent hugepages. 3823 See Documentation/vm/transhuge.txt for more details. 3824 3825 tsc= Disable clocksource stability checks for TSC. 3826 Format: <string> 3827 [x86] reliable: mark tsc clocksource as reliable, this 3828 disables clocksource verification at runtime, as well 3829 as the stability checks done at bootup. Used to enable 3830 high-resolution timer mode on older hardware, and in 3831 virtualized environment. 3832 [x86] noirqtime: Do not use TSC to do irq accounting. 3833 Used to run time disable IRQ_TIME_ACCOUNTING on any 3834 platforms where RDTSC is slow and this accounting 3835 can add overhead. 3836 3837 turbografx.map[2|3]= [HW,JOY] 3838 TurboGraFX parallel port interface 3839 Format: 3840 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 3841 See also Documentation/input/joystick-parport.txt 3842 3843 udbg-immortal [PPC] When debugging early kernel crashes that 3844 happen after console_init() and before a proper 3845 console driver takes over, this boot options might 3846 help "seeing" what's going on. 3847 3848 uhash_entries= [KNL,NET] 3849 Set number of hash buckets for UDP/UDP-Lite connections 3850 3851 uhci-hcd.ignore_oc= 3852 [USB] Ignore overcurrent events (default N). 3853 Some badly-designed motherboards generate lots of 3854 bogus events, for ports that aren't wired to 3855 anything. Set this parameter to avoid log spamming. 3856 Note that genuine overcurrent events won't be 3857 reported either. 3858 3859 unknown_nmi_panic 3860 [X86] Cause panic on unknown NMI. 3861 3862 usbcore.authorized_default= 3863 [USB] Default USB device authorization: 3864 (default -1 = authorized except for wireless USB, 3865 0 = not authorized, 1 = authorized) 3866 3867 usbcore.autosuspend= 3868 [USB] The autosuspend time delay (in seconds) used 3869 for newly-detected USB devices (default 2). This 3870 is the time required before an idle device will be 3871 autosuspended. Devices for which the delay is set 3872 to a negative value won't be autosuspended at all. 3873 3874 usbcore.usbfs_snoop= 3875 [USB] Set to log all usbfs traffic (default 0 = off). 3876 3877 usbcore.blinkenlights= 3878 [USB] Set to cycle leds on hubs (default 0 = off). 3879 3880 usbcore.old_scheme_first= 3881 [USB] Start with the old device initialization 3882 scheme (default 0 = off). 3883 3884 usbcore.usbfs_memory_mb= 3885 [USB] Memory limit (in MB) for buffers allocated by 3886 usbfs (default = 16, 0 = max = 2047). 3887 3888 usbcore.use_both_schemes= 3889 [USB] Try the other device initialization scheme 3890 if the first one fails (default 1 = enabled). 3891 3892 usbcore.initial_descriptor_timeout= 3893 [USB] Specifies timeout for the initial 64-byte 3894 USB_REQ_GET_DESCRIPTOR request in milliseconds 3895 (default 5000 = 5.0 seconds). 3896 3897 usbhid.mousepoll= 3898 [USBHID] The interval which mice are to be polled at. 3899 3900 usb-storage.delay_use= 3901 [UMS] The delay in seconds before a new device is 3902 scanned for Logical Units (default 1). 3903 3904 usb-storage.quirks= 3905 [UMS] A list of quirks entries to supplement or 3906 override the built-in unusual_devs list. List 3907 entries are separated by commas. Each entry has 3908 the form VID:PID:Flags where VID and PID are Vendor 3909 and Product ID values (4-digit hex numbers) and 3910 Flags is a set of characters, each corresponding 3911 to a common usb-storage quirk flag as follows: 3912 a = SANE_SENSE (collect more than 18 bytes 3913 of sense data); 3914 b = BAD_SENSE (don't collect more than 18 3915 bytes of sense data); 3916 c = FIX_CAPACITY (decrease the reported 3917 device capacity by one sector); 3918 d = NO_READ_DISC_INFO (don't use 3919 READ_DISC_INFO command); 3920 e = NO_READ_CAPACITY_16 (don't use 3921 READ_CAPACITY_16 command); 3922 f = NO_REPORT_OPCODES (don't use report opcodes 3923 command, uas only); 3924 g = MAX_SECTORS_240 (don't transfer more than 3925 240 sectors at a time, uas only); 3926 h = CAPACITY_HEURISTICS (decrease the 3927 reported device capacity by one 3928 sector if the number is odd); 3929 i = IGNORE_DEVICE (don't bind to this 3930 device); 3931 j = NO_REPORT_LUNS (don't use report luns 3932 command, uas only); 3933 l = NOT_LOCKABLE (don't try to lock and 3934 unlock ejectable media); 3935 m = MAX_SECTORS_64 (don't transfer more 3936 than 64 sectors = 32 KB at a time); 3937 n = INITIAL_READ10 (force a retry of the 3938 initial READ(10) command); 3939 o = CAPACITY_OK (accept the capacity 3940 reported by the device); 3941 p = WRITE_CACHE (the device cache is ON 3942 by default); 3943 r = IGNORE_RESIDUE (the device reports 3944 bogus residue values); 3945 s = SINGLE_LUN (the device has only one 3946 Logical Unit); 3947 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 3948 commands, uas only); 3949 u = IGNORE_UAS (don't bind to the uas driver); 3950 w = NO_WP_DETECT (don't test whether the 3951 medium is write-protected). 3952 Example: quirks=0419:aaf5:rl,0421:0433:rc 3953 3954 user_debug= [KNL,ARM] 3955 Format: <int> 3956 See arch/arm/Kconfig.debug help text. 3957 1 - undefined instruction events 3958 2 - system calls 3959 4 - invalid data aborts 3960 8 - SIGSEGV faults 3961 16 - SIGBUS faults 3962 Example: user_debug=31 3963 3964 userpte= 3965 [X86] Flags controlling user PTE allocations. 3966 3967 nohigh = do not allocate PTE pages in 3968 HIGHMEM regardless of setting 3969 of CONFIG_HIGHPTE. 3970 3971 vdso= [X86,SH] 3972 On X86_32, this is an alias for vdso32=. Otherwise: 3973 3974 vdso=1: enable VDSO (the default) 3975 vdso=0: disable VDSO mapping 3976 3977 vdso32= [X86] Control the 32-bit vDSO 3978 vdso32=1: enable 32-bit VDSO 3979 vdso32=0 or vdso32=2: disable 32-bit VDSO 3980 3981 See the help text for CONFIG_COMPAT_VDSO for more 3982 details. If CONFIG_COMPAT_VDSO is set, the default is 3983 vdso32=0; otherwise, the default is vdso32=1. 3984 3985 For compatibility with older kernels, vdso32=2 is an 3986 alias for vdso32=0. 3987 3988 Try vdso32=0 if you encounter an error that says: 3989 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 3990 3991 vector= [IA-64,SMP] 3992 vector=percpu: enable percpu vector domain 3993 3994 video= [FB] Frame buffer configuration 3995 See Documentation/fb/modedb.txt. 3996 3997 video.brightness_switch_enabled= [0,1] 3998 If set to 1, on receiving an ACPI notify event 3999 generated by hotkey, video driver will adjust brightness 4000 level and then send out the event to user space through 4001 the allocated input device; If set to 0, video driver 4002 will only send out the event without touching backlight 4003 brightness level. 4004 default: 1 4005 4006 virtio_mmio.device= 4007 [VMMIO] Memory mapped virtio (platform) device. 4008 4009 <size>@<baseaddr>:<irq>[:<id>] 4010 where: 4011 <size> := size (can use standard suffixes 4012 like K, M and G) 4013 <baseaddr> := physical base address 4014 <irq> := interrupt number (as passed to 4015 request_irq()) 4016 <id> := (optional) platform device id 4017 example: 4018 virtio_mmio.device=1K@0x100b0000:48:7 4019 4020 Can be used multiple times for multiple devices. 4021 4022 vga= [BOOT,X86-32] Select a particular video mode 4023 See Documentation/x86/boot.txt and 4024 Documentation/svga.txt. 4025 Use vga=ask for menu. 4026 This is actually a boot loader parameter; the value is 4027 passed to the kernel using a special protocol. 4028 4029 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact 4030 size of <nn>. This can be used to increase the 4031 minimum size (128MB on x86). It can also be used to 4032 decrease the size and leave more room for directly 4033 mapped kernel RAM. 4034 4035 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 4036 Format: <command> 4037 4038 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 4039 Format: <command> 4040 4041 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 4042 Format: <command> 4043 4044 vsyscall= [X86-64] 4045 Controls the behavior of vsyscalls (i.e. calls to 4046 fixed addresses of 0xffffffffff600x00 from legacy 4047 code). Most statically-linked binaries and older 4048 versions of glibc use these calls. Because these 4049 functions are at fixed addresses, they make nice 4050 targets for exploits that can control RIP. 4051 4052 emulate [default] Vsyscalls turn into traps and are 4053 emulated reasonably safely. 4054 4055 native Vsyscalls are native syscall instructions. 4056 This is a little bit faster than trapping 4057 and makes a few dynamic recompilers work 4058 better than they would in emulation mode. 4059 It also makes exploits much easier to write. 4060 4061 none Vsyscalls don't work at all. This makes 4062 them quite hard to use for exploits but 4063 might break your system. 4064 4065 vt.color= [VT] Default text color. 4066 Format: 0xYX, X = foreground, Y = background. 4067 Default: 0x07 = light gray on black. 4068 4069 vt.cur_default= [VT] Default cursor shape. 4070 Format: 0xCCBBAA, where AA, BB, and CC are the same as 4071 the parameters of the <Esc>[?A;B;Cc escape sequence; 4072 see VGA-softcursor.txt. Default: 2 = underline. 4073 4074 vt.default_blu= [VT] 4075 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 4076 Change the default blue palette of the console. 4077 This is a 16-member array composed of values 4078 ranging from 0-255. 4079 4080 vt.default_grn= [VT] 4081 Format: <green0>,<green1>,<green2>,...,<green15> 4082 Change the default green palette of the console. 4083 This is a 16-member array composed of values 4084 ranging from 0-255. 4085 4086 vt.default_red= [VT] 4087 Format: <red0>,<red1>,<red2>,...,<red15> 4088 Change the default red palette of the console. 4089 This is a 16-member array composed of values 4090 ranging from 0-255. 4091 4092 vt.default_utf8= 4093 [VT] 4094 Format=<0|1> 4095 Set system-wide default UTF-8 mode for all tty's. 4096 Default is 1, i.e. UTF-8 mode is enabled for all 4097 newly opened terminals. 4098 4099 vt.global_cursor_default= 4100 [VT] 4101 Format=<-1|0|1> 4102 Set system-wide default for whether a cursor 4103 is shown on new VTs. Default is -1, 4104 i.e. cursors will be created by default unless 4105 overridden by individual drivers. 0 will hide 4106 cursors, 1 will display them. 4107 4108 vt.italic= [VT] Default color for italic text; 0-15. 4109 Default: 2 = green. 4110 4111 vt.underline= [VT] Default color for underlined text; 0-15. 4112 Default: 3 = cyan. 4113 4114 watchdog timers [HW,WDT] For information on watchdog timers, 4115 see Documentation/watchdog/watchdog-parameters.txt 4116 or other driver-specific files in the 4117 Documentation/watchdog/ directory. 4118 4119 workqueue.disable_numa 4120 By default, all work items queued to unbound 4121 workqueues are affine to the NUMA nodes they're 4122 issued on, which results in better behavior in 4123 general. If NUMA affinity needs to be disabled for 4124 whatever reason, this option can be used. Note 4125 that this also can be controlled per-workqueue for 4126 workqueues visible under /sys/bus/workqueue/. 4127 4128 workqueue.power_efficient 4129 Per-cpu workqueues are generally preferred because 4130 they show better performance thanks to cache 4131 locality; unfortunately, per-cpu workqueues tend to 4132 be more power hungry than unbound workqueues. 4133 4134 Enabling this makes the per-cpu workqueues which 4135 were observed to contribute significantly to power 4136 consumption unbound, leading to measurably lower 4137 power usage at the cost of small performance 4138 overhead. 4139 4140 The default value of this parameter is determined by 4141 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 4142 4143 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of 4144 default x2apic cluster mode on platforms 4145 supporting x2apic. 4146 4147 x86_intel_mid_timer= [X86-32,APBT] 4148 Choose timer option for x86 Intel MID platform. 4149 Two valid options are apbt timer only and lapic timer 4150 plus one apbt timer for broadcast timer. 4151 x86_intel_mid_timer=apbt_only | lapic_and_apbt 4152 4153 xen_512gb_limit [KNL,X86-64,XEN] 4154 Restricts the kernel running paravirtualized under Xen 4155 to use only up to 512 GB of RAM. The reason to do so is 4156 crash analysis tools and Xen tools for doing domain 4157 save/restore/migration must be enabled to handle larger 4158 domains. 4159 4160 xen_emul_unplug= [HW,X86,XEN] 4161 Unplug Xen emulated devices 4162 Format: [unplug0,][unplug1] 4163 ide-disks -- unplug primary master IDE devices 4164 aux-ide-disks -- unplug non-primary-master IDE devices 4165 nics -- unplug network devices 4166 all -- unplug all emulated devices (NICs and IDE disks) 4167 unnecessary -- unplugging emulated devices is 4168 unnecessary even if the host did not respond to 4169 the unplug protocol 4170 never -- do not unplug even if version check succeeds 4171 4172 xen_nopvspin [X86,XEN] 4173 Disables the ticketlock slowpath using Xen PV 4174 optimizations. 4175 4176 xen_nopv [X86] 4177 Disables the PV optimizations forcing the HVM guest to 4178 run as generic HVM guest with no PV drivers. 4179 4180 xirc2ps_cs= [NET,PCMCIA] 4181 Format: 4182 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 4183 4184______________________________________________________________________ 4185 4186TODO: 4187 4188 Add more DRM drivers. 4189