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 36cpu lists: 37---------- 38 39Some kernel parameters take a list of CPUs as a value, e.g. isolcpus, 40nohz_full, irqaffinity, rcu_nocbs. The format of this list is: 41 42 <cpu number>,...,<cpu number> 43 44or 45 46 <cpu number>-<cpu number> 47 (must be a positive range in ascending order) 48 49or a mixture 50 51<cpu number>,...,<cpu number>-<cpu number> 52 53Note that for the special case of a range one can split the range into equal 54sized groups and for each group use some amount from the beginning of that 55group: 56 57 <cpu number>-cpu number>:<used size>/<group size> 58 59For example one can add to the command line following parameter: 60 61 isolcpus=1,2,10-20,100-2000:2/25 62 63where the final item represents CPUs 100,101,125,126,150,151,... 64 65 66 67This document may not be entirely up to date and comprehensive. The command 68"modinfo -p ${modulename}" shows a current list of all parameters of a loadable 69module. Loadable modules, after being loaded into the running kernel, also 70reveal their parameters in /sys/module/${modulename}/parameters/. Some of these 71parameters may be changed at runtime by the command 72"echo -n ${value} > /sys/module/${modulename}/parameters/${parm}". 73 74The parameters listed below are only valid if certain kernel build options were 75enabled and if respective hardware is present. The text in square brackets at 76the beginning of each description states the restrictions within which a 77parameter is applicable: 78 79 ACPI ACPI support is enabled. 80 AGP AGP (Accelerated Graphics Port) is enabled. 81 ALSA ALSA sound support is enabled. 82 APIC APIC support is enabled. 83 APM Advanced Power Management support is enabled. 84 ARM ARM architecture is enabled. 85 AVR32 AVR32 architecture is enabled. 86 AX25 Appropriate AX.25 support is enabled. 87 BLACKFIN Blackfin architecture is enabled. 88 CLK Common clock infrastructure is enabled. 89 CMA Contiguous Memory Area support is enabled. 90 DM Device mapper support is enabled. 91 DRM Direct Rendering Management support is enabled. 92 DYNAMIC_DEBUG Build in debug messages and enable them at runtime 93 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled 94 EFI EFI Partitioning (GPT) is enabled 95 EIDE EIDE/ATAPI support is enabled. 96 EVM Extended Verification Module 97 FB The frame buffer device is enabled. 98 FTRACE Function tracing enabled. 99 GCOV GCOV profiling is enabled. 100 HW Appropriate hardware is enabled. 101 IA-64 IA-64 architecture is enabled. 102 IMA Integrity measurement architecture is enabled. 103 IOSCHED More than one I/O scheduler is enabled. 104 IP_PNP IP DHCP, BOOTP, or RARP is enabled. 105 IPV6 IPv6 support is enabled. 106 ISAPNP ISA PnP code is enabled. 107 ISDN Appropriate ISDN support is enabled. 108 JOY Appropriate joystick support is enabled. 109 KGDB Kernel debugger support is enabled. 110 KVM Kernel Virtual Machine support is enabled. 111 LIBATA Libata driver is enabled 112 LP Printer support is enabled. 113 LOOP Loopback device support is enabled. 114 M68k M68k architecture is enabled. 115 These options have more detailed description inside of 116 Documentation/m68k/kernel-options.txt. 117 MDA MDA console support is enabled. 118 MIPS MIPS architecture is enabled. 119 MOUSE Appropriate mouse support is enabled. 120 MSI Message Signaled Interrupts (PCI). 121 MTD MTD (Memory Technology Device) support is enabled. 122 NET Appropriate network support is enabled. 123 NUMA NUMA support is enabled. 124 NFS Appropriate NFS support is enabled. 125 OSS OSS sound support is enabled. 126 PV_OPS A paravirtualized kernel is enabled. 127 PARIDE The ParIDE (parallel port IDE) subsystem is enabled. 128 PARISC The PA-RISC architecture is enabled. 129 PCI PCI bus support is enabled. 130 PCIE PCI Express support is enabled. 131 PCMCIA The PCMCIA subsystem is enabled. 132 PNP Plug & Play support is enabled. 133 PPC PowerPC architecture is enabled. 134 PPT Parallel port support is enabled. 135 PS2 Appropriate PS/2 support is enabled. 136 RAM RAM disk support is enabled. 137 S390 S390 architecture is enabled. 138 SCSI Appropriate SCSI support is enabled. 139 A lot of drivers have their options described inside 140 the Documentation/scsi/ sub-directory. 141 SECURITY Different security models are enabled. 142 SELINUX SELinux support is enabled. 143 APPARMOR AppArmor support is enabled. 144 SERIAL Serial support is enabled. 145 SH SuperH architecture is enabled. 146 SMP The kernel is an SMP kernel. 147 SPARC Sparc architecture is enabled. 148 SWSUSP Software suspend (hibernation) is enabled. 149 SUSPEND System suspend states are enabled. 150 TPM TPM drivers are enabled. 151 TS Appropriate touchscreen support is enabled. 152 UMS USB Mass Storage support is enabled. 153 USB USB support is enabled. 154 USBHID USB Human Interface Device support is enabled. 155 V4L Video For Linux support is enabled. 156 VMMIO Driver for memory mapped virtio devices is enabled. 157 VGA The VGA console has been enabled. 158 VT Virtual terminal support is enabled. 159 WDT Watchdog support is enabled. 160 XT IBM PC/XT MFM hard disk support is enabled. 161 X86-32 X86-32, aka i386 architecture is enabled. 162 X86-64 X86-64 architecture is enabled. 163 More X86-64 boot options can be found in 164 Documentation/x86/x86_64/boot-options.txt . 165 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64) 166 X86_UV SGI UV support is enabled. 167 XEN Xen support is enabled 168 169In addition, the following text indicates that the option: 170 171 BUGS= Relates to possible processor bugs on the said processor. 172 KNL Is a kernel start-up parameter. 173 BOOT Is a boot loader parameter. 174 175Parameters denoted with BOOT are actually interpreted by the boot 176loader, and have no meaning to the kernel directly. 177Do not modify the syntax of boot loader parameters without extreme 178need or coordination with <Documentation/x86/boot.txt>. 179 180There are also arch-specific kernel-parameters not documented here. 181See for example <Documentation/x86/x86_64/boot-options.txt>. 182 183Note that ALL kernel parameters listed below are CASE SENSITIVE, and that 184a trailing = on the name of any parameter states that that parameter will 185be entered as an environment variable, whereas its absence indicates that 186it will appear as a kernel argument readable via /proc/cmdline by programs 187running once the system is up. 188 189The number of kernel parameters is not limited, but the length of the 190complete command line (parameters including spaces etc.) is limited to 191a fixed number of characters. This limit depends on the architecture 192and is between 256 and 4096 characters. It is defined in the file 193./include/asm/setup.h as COMMAND_LINE_SIZE. 194 195Finally, the [KMG] suffix is commonly described after a number of kernel 196parameter values. These 'K', 'M', and 'G' letters represent the _binary_ 197multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30 198bytes respectively. Such letter suffixes can also be entirely omitted. 199 200 201 acpi= [HW,ACPI,X86,ARM64] 202 Advanced Configuration and Power Interface 203 Format: { force | on | off | strict | noirq | rsdt | 204 copy_dsdt } 205 force -- enable ACPI if default was off 206 on -- enable ACPI but allow fallback to DT [arm64] 207 off -- disable ACPI if default was on 208 noirq -- do not use ACPI for IRQ routing 209 strict -- Be less tolerant of platforms that are not 210 strictly ACPI specification compliant. 211 rsdt -- prefer RSDT over (default) XSDT 212 copy_dsdt -- copy DSDT to memory 213 For ARM64, ONLY "acpi=off", "acpi=on" or "acpi=force" 214 are available 215 216 See also Documentation/power/runtime_pm.txt, pci=noacpi 217 218 acpi_apic_instance= [ACPI, IOAPIC] 219 Format: <int> 220 2: use 2nd APIC table, if available 221 1,0: use 1st APIC table 222 default: 0 223 224 acpi_backlight= [HW,ACPI] 225 acpi_backlight=vendor 226 acpi_backlight=video 227 If set to vendor, prefer vendor specific driver 228 (e.g. thinkpad_acpi, sony_acpi, etc.) instead 229 of the ACPI video.ko driver. 230 231 acpi_force_32bit_fadt_addr 232 force FADT to use 32 bit addresses rather than the 233 64 bit X_* addresses. Some firmware have broken 64 234 bit addresses for force ACPI ignore these and use 235 the older legacy 32 bit addresses. 236 237 acpica_no_return_repair [HW, ACPI] 238 Disable AML predefined validation mechanism 239 This mechanism can repair the evaluation result to make 240 the return objects more ACPI specification compliant. 241 This option is useful for developers to identify the 242 root cause of an AML interpreter issue when the issue 243 has something to do with the repair mechanism. 244 245 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG] 246 acpi.debug_level= [HW,ACPI,ACPI_DEBUG] 247 Format: <int> 248 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI 249 debug output. Bits in debug_layer correspond to a 250 _COMPONENT in an ACPI source file, e.g., 251 #define _COMPONENT ACPI_PCI_COMPONENT 252 Bits in debug_level correspond to a level in 253 ACPI_DEBUG_PRINT statements, e.g., 254 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ... 255 The debug_level mask defaults to "info". See 256 Documentation/acpi/debug.txt for more information about 257 debug layers and levels. 258 259 Enable processor driver info messages: 260 acpi.debug_layer=0x20000000 261 Enable PCI/PCI interrupt routing info messages: 262 acpi.debug_layer=0x400000 263 Enable AML "Debug" output, i.e., stores to the Debug 264 object while interpreting AML: 265 acpi.debug_layer=0xffffffff acpi.debug_level=0x2 266 Enable all messages related to ACPI hardware: 267 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff 268 269 Some values produce so much output that the system is 270 unusable. The "log_buf_len" parameter may be useful 271 if you need to capture more output. 272 273 acpi_enforce_resources= [ACPI] 274 { strict | lax | no } 275 Check for resource conflicts between native drivers 276 and ACPI OperationRegions (SystemIO and SystemMemory 277 only). IO ports and memory declared in ACPI might be 278 used by the ACPI subsystem in arbitrary AML code and 279 can interfere with legacy drivers. 280 strict (default): access to resources claimed by ACPI 281 is denied; legacy drivers trying to access reserved 282 resources will fail to bind to device using them. 283 lax: access to resources claimed by ACPI is allowed; 284 legacy drivers trying to access reserved resources 285 will bind successfully but a warning message is logged. 286 no: ACPI OperationRegions are not marked as reserved, 287 no further checks are performed. 288 289 acpi_force_table_verification [HW,ACPI] 290 Enable table checksum verification during early stage. 291 By default, this is disabled due to x86 early mapping 292 size limitation. 293 294 acpi_irq_balance [HW,ACPI] 295 ACPI will balance active IRQs 296 default in APIC mode 297 298 acpi_irq_nobalance [HW,ACPI] 299 ACPI will not move active IRQs (default) 300 default in PIC mode 301 302 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA 303 Format: <irq>,<irq>... 304 305 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for 306 use by PCI 307 Format: <irq>,<irq>... 308 309 acpi_mask_gpe= [HW,ACPI] 310 Due to the existence of _Lxx/_Exx, some GPEs triggered 311 by unsupported hardware/firmware features can result in 312 GPE floodings that cannot be automatically disabled by 313 the GPE dispatcher. 314 This facility can be used to prevent such uncontrolled 315 GPE floodings. 316 Format: <int> 317 Support masking of GPEs numbered from 0x00 to 0x7f. 318 319 acpi_no_auto_serialize [HW,ACPI] 320 Disable auto-serialization of AML methods 321 AML control methods that contain the opcodes to create 322 named objects will be marked as "Serialized" by the 323 auto-serialization feature. 324 This feature is enabled by default. 325 This option allows to turn off the feature. 326 327 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump 328 kernels. 329 330 acpi_no_static_ssdt [HW,ACPI] 331 Disable installation of static SSDTs at early boot time 332 By default, SSDTs contained in the RSDT/XSDT will be 333 installed automatically and they will appear under 334 /sys/firmware/acpi/tables. 335 This option turns off this feature. 336 Note that specifying this option does not affect 337 dynamic table installation which will install SSDT 338 tables to /sys/firmware/acpi/tables/dynamic. 339 340 acpi_rsdp= [ACPI,EFI,KEXEC] 341 Pass the RSDP address to the kernel, mostly used 342 on machines running EFI runtime service to boot the 343 second kernel for kdump. 344 345 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS 346 Format: To spoof as Windows 98: ="Microsoft Windows" 347 348 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead 349 of 2 which is mandated by ACPI 6) as the supported ACPI 350 specification revision (when using this switch, it may 351 be necessary to carry out a cold reboot _twice_ in a 352 row to make it take effect on the platform firmware). 353 354 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings 355 acpi_osi="string1" # add string1 356 acpi_osi="!string2" # remove string2 357 acpi_osi=!* # remove all strings 358 acpi_osi=! # disable all built-in OS vendor 359 strings 360 acpi_osi=!! # enable all built-in OS vendor 361 strings 362 acpi_osi= # disable all strings 363 364 'acpi_osi=!' can be used in combination with single or 365 multiple 'acpi_osi="string1"' to support specific OS 366 vendor string(s). Note that such command can only 367 affect the default state of the OS vendor strings, thus 368 it cannot affect the default state of the feature group 369 strings and the current state of the OS vendor strings, 370 specifying it multiple times through kernel command line 371 is meaningless. This command is useful when one do not 372 care about the state of the feature group strings which 373 should be controlled by the OSPM. 374 Examples: 375 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent 376 to 'acpi_osi="Windows 2000" acpi_osi=!', they all 377 can make '_OSI("Windows 2000")' TRUE. 378 379 'acpi_osi=' cannot be used in combination with other 380 'acpi_osi=' command lines, the _OSI method will not 381 exist in the ACPI namespace. NOTE that such command can 382 only affect the _OSI support state, thus specifying it 383 multiple times through kernel command line is also 384 meaningless. 385 Examples: 386 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)' 387 FALSE. 388 389 'acpi_osi=!*' can be used in combination with single or 390 multiple 'acpi_osi="string1"' to support specific 391 string(s). Note that such command can affect the 392 current state of both the OS vendor strings and the 393 feature group strings, thus specifying it multiple times 394 through kernel command line is meaningful. But it may 395 still not able to affect the final state of a string if 396 there are quirks related to this string. This command 397 is useful when one want to control the state of the 398 feature group strings to debug BIOS issues related to 399 the OSPM features. 400 Examples: 401 1. 'acpi_osi="Module Device" acpi_osi=!*' can make 402 '_OSI("Module Device")' FALSE. 403 2. 'acpi_osi=!* acpi_osi="Module Device"' can make 404 '_OSI("Module Device")' TRUE. 405 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is 406 equivalent to 407 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"' 408 and 409 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!', 410 they all will make '_OSI("Windows 2000")' TRUE. 411 412 acpi_pm_good [X86] 413 Override the pmtimer bug detection: force the kernel 414 to assume that this machine's pmtimer latches its value 415 and always returns good values. 416 417 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode 418 Format: { level | edge | high | low } 419 420 acpi_skip_timer_override [HW,ACPI] 421 Recognize and ignore IRQ0/pin2 Interrupt Override. 422 For broken nForce2 BIOS resulting in XT-PIC timer. 423 424 acpi_sleep= [HW,ACPI] Sleep options 425 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig, 426 old_ordering, nonvs, sci_force_enable } 427 See Documentation/power/video.txt for information on 428 s3_bios and s3_mode. 429 s3_beep is for debugging; it makes the PC's speaker beep 430 as soon as the kernel's real-mode entry point is called. 431 s4_nohwsig prevents ACPI hardware signature from being 432 used during resume from hibernation. 433 old_ordering causes the ACPI 1.0 ordering of the _PTS 434 control method, with respect to putting devices into 435 low power states, to be enforced (the ACPI 2.0 ordering 436 of _PTS is used by default). 437 nonvs prevents the kernel from saving/restoring the 438 ACPI NVS memory during suspend/hibernation and resume. 439 sci_force_enable causes the kernel to set SCI_EN directly 440 on resume from S1/S3 (which is against the ACPI spec, 441 but some broken systems don't work without it). 442 443 acpi_use_timer_override [HW,ACPI] 444 Use timer override. For some broken Nvidia NF5 boards 445 that require a timer override, but don't have HPET 446 447 add_efi_memmap [EFI; X86] Include EFI memory map in 448 kernel's map of available physical RAM. 449 450 agp= [AGP] 451 { off | try_unsupported } 452 off: disable AGP support 453 try_unsupported: try to drive unsupported chipsets 454 (may crash computer or cause data corruption) 455 456 ALSA [HW,ALSA] 457 See Documentation/sound/alsa/alsa-parameters.txt 458 459 alignment= [KNL,ARM] 460 Allow the default userspace alignment fault handler 461 behaviour to be specified. Bit 0 enables warnings, 462 bit 1 enables fixups, and bit 2 sends a segfault. 463 464 align_va_addr= [X86-64] 465 Align virtual addresses by clearing slice [14:12] when 466 allocating a VMA at process creation time. This option 467 gives you up to 3% performance improvement on AMD F15h 468 machines (where it is enabled by default) for a 469 CPU-intensive style benchmark, and it can vary highly in 470 a microbenchmark depending on workload and compiler. 471 472 32: only for 32-bit processes 473 64: only for 64-bit processes 474 on: enable for both 32- and 64-bit processes 475 off: disable for both 32- and 64-bit processes 476 477 alloc_snapshot [FTRACE] 478 Allocate the ftrace snapshot buffer on boot up when the 479 main buffer is allocated. This is handy if debugging 480 and you need to use tracing_snapshot() on boot up, and 481 do not want to use tracing_snapshot_alloc() as it needs 482 to be done where GFP_KERNEL allocations are allowed. 483 484 amd_iommu= [HW,X86-64] 485 Pass parameters to the AMD IOMMU driver in the system. 486 Possible values are: 487 fullflush - enable flushing of IO/TLB entries when 488 they are unmapped. Otherwise they are 489 flushed before they will be reused, which 490 is a lot of faster 491 off - do not initialize any AMD IOMMU found in 492 the system 493 force_isolation - Force device isolation for all 494 devices. The IOMMU driver is not 495 allowed anymore to lift isolation 496 requirements as needed. This option 497 does not override iommu=pt 498 499 amd_iommu_dump= [HW,X86-64] 500 Enable AMD IOMMU driver option to dump the ACPI table 501 for AMD IOMMU. With this option enabled, AMD IOMMU 502 driver will print ACPI tables for AMD IOMMU during 503 IOMMU initialization. 504 505 amd_iommu_intr= [HW,X86-64] 506 Specifies one of the following AMD IOMMU interrupt 507 remapping modes: 508 legacy - Use legacy interrupt remapping mode. 509 vapic - Use virtual APIC mode, which allows IOMMU 510 to inject interrupts directly into guest. 511 This mode requires kvm-amd.avic=1. 512 (Default when IOMMU HW support is present.) 513 514 amijoy.map= [HW,JOY] Amiga joystick support 515 Map of devices attached to JOY0DAT and JOY1DAT 516 Format: <a>,<b> 517 See also Documentation/input/joystick.txt 518 519 analog.map= [HW,JOY] Analog joystick and gamepad support 520 Specifies type or capabilities of an analog joystick 521 connected to one of 16 gameports 522 Format: <type1>,<type2>,..<type16> 523 524 apc= [HW,SPARC] 525 Power management functions (SPARCstation-4/5 + deriv.) 526 Format: noidle 527 Disable APC CPU standby support. SPARCstation-Fox does 528 not play well with APC CPU idle - disable it if you have 529 APC and your system crashes randomly. 530 531 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller 532 Change the output verbosity whilst booting 533 Format: { quiet (default) | verbose | debug } 534 Change the amount of debugging information output 535 when initialising the APIC and IO-APIC components. 536 537 apic_extnmi= [APIC,X86] External NMI delivery setting 538 Format: { bsp (default) | all | none } 539 bsp: External NMI is delivered only to CPU 0 540 all: External NMIs are broadcast to all CPUs as a 541 backup of CPU 0 542 none: External NMI is masked for all CPUs. This is 543 useful so that a dump capture kernel won't be 544 shot down by NMI 545 546 autoconf= [IPV6] 547 See Documentation/networking/ipv6.txt. 548 549 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller 550 Limit apic dumping. The parameter defines the maximal 551 number of local apics being dumped. Also it is possible 552 to set it to "all" by meaning -- no limit here. 553 Format: { 1 (default) | 2 | ... | all }. 554 The parameter valid if only apic=debug or 555 apic=verbose is specified. 556 Example: apic=debug show_lapic=all 557 558 apm= [APM] Advanced Power Management 559 See header of arch/x86/kernel/apm_32.c. 560 561 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards 562 Format: <io>,<irq>,<nodeID> 563 564 ataflop= [HW,M68k] 565 566 atarimouse= [HW,MOUSE] Atari Mouse 567 568 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess, 569 EzKey and similar keyboards 570 571 atkbd.reset= [HW] Reset keyboard during initialization 572 573 atkbd.set= [HW] Select keyboard code set 574 Format: <int> (2 = AT (default), 3 = PS/2) 575 576 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar 577 keyboards 578 579 atkbd.softraw= [HW] Choose between synthetic and real raw mode 580 Format: <bool> (0 = real, 1 = synthetic (default)) 581 582 atkbd.softrepeat= [HW] 583 Use software keyboard repeat 584 585 audit= [KNL] Enable the audit sub-system 586 Format: { "0" | "1" } (0 = disabled, 1 = enabled) 587 0 - kernel audit is disabled and can not be enabled 588 until the next reboot 589 unset - kernel audit is initialized but disabled and 590 will be fully enabled by the userspace auditd. 591 1 - kernel audit is initialized and partially enabled, 592 storing at most audit_backlog_limit messages in 593 RAM until it is fully enabled by the userspace 594 auditd. 595 Default: unset 596 597 audit_backlog_limit= [KNL] Set the audit queue size limit. 598 Format: <int> (must be >=0) 599 Default: 64 600 601 bau= [X86_UV] Enable the BAU on SGI UV. The default 602 behavior is to disable the BAU (i.e. bau=0). 603 Format: { "0" | "1" } 604 0 - Disable the BAU. 605 1 - Enable the BAU. 606 unset - Disable the BAU. 607 608 baycom_epp= [HW,AX25] 609 Format: <io>,<mode> 610 611 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem 612 Format: <io>,<mode> 613 See header of drivers/net/hamradio/baycom_par.c. 614 615 baycom_ser_fdx= [HW,AX25] 616 BayCom Serial Port AX.25 Modem (Full Duplex Mode) 617 Format: <io>,<irq>,<mode>[,<baud>] 618 See header of drivers/net/hamradio/baycom_ser_fdx.c. 619 620 baycom_ser_hdx= [HW,AX25] 621 BayCom Serial Port AX.25 Modem (Half Duplex Mode) 622 Format: <io>,<irq>,<mode> 623 See header of drivers/net/hamradio/baycom_ser_hdx.c. 624 625 blkdevparts= Manual partition parsing of block device(s) for 626 embedded devices based on command line input. 627 See Documentation/block/cmdline-partition.txt 628 629 boot_delay= Milliseconds to delay each printk during boot. 630 Values larger than 10 seconds (10000) are changed to 631 no delay (0). 632 Format: integer 633 634 bootmem_debug [KNL] Enable bootmem allocator debug messages. 635 636 bert_disable [ACPI] 637 Disable BERT OS support on buggy BIOSes. 638 639 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards) 640 bttv.radio= Most important insmod options are available as 641 kernel args too. 642 bttv.pll= See Documentation/video4linux/bttv/Insmod-options 643 bttv.tuner= 644 645 bulk_remove=off [PPC] This parameter disables the use of the pSeries 646 firmware feature for flushing multiple hpte entries 647 at a time. 648 649 c101= [NET] Moxa C101 synchronous serial card 650 651 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection. 652 Sometimes CPU hardware bugs make them report the cache 653 size incorrectly. The kernel will attempt work arounds 654 to fix known problems, but for some CPUs it is not 655 possible to determine what the correct size should be. 656 This option provides an override for these situations. 657 658 ca_keys= [KEYS] This parameter identifies a specific key(s) on 659 the system trusted keyring to be used for certificate 660 trust validation. 661 format: { id:<keyid> | builtin } 662 663 cca= [MIPS] Override the kernel pages' cache coherency 664 algorithm. Accepted values range from 0 to 7 665 inclusive. See arch/mips/include/asm/pgtable-bits.h 666 for platform specific values (SB1, Loongson3 and 667 others). 668 669 ccw_timeout_log [S390] 670 See Documentation/s390/CommonIO for details. 671 672 cgroup_disable= [KNL] Disable a particular controller 673 Format: {name of the controller(s) to disable} 674 The effects of cgroup_disable=foo are: 675 - foo isn't auto-mounted if you mount all cgroups in 676 a single hierarchy 677 - foo isn't visible as an individually mountable 678 subsystem 679 {Currently only "memory" controller deal with this and 680 cut the overhead, others just disable the usage. So 681 only cgroup_disable=memory is actually worthy} 682 683 cgroup_no_v1= [KNL] Disable one, multiple, all cgroup controllers in v1 684 Format: { controller[,controller...] | "all" } 685 Like cgroup_disable, but only applies to cgroup v1; 686 the blacklisted controllers remain available in cgroup2. 687 688 cgroup.memory= [KNL] Pass options to the cgroup memory controller. 689 Format: <string> 690 nosocket -- Disable socket memory accounting. 691 nokmem -- Disable kernel memory accounting. 692 693 checkreqprot [SELINUX] Set initial checkreqprot flag value. 694 Format: { "0" | "1" } 695 See security/selinux/Kconfig help text. 696 0 -- check protection applied by kernel (includes 697 any implied execute protection). 698 1 -- check protection requested by application. 699 Default value is set via a kernel config option. 700 Value can be changed at runtime via 701 /selinux/checkreqprot. 702 703 cio_ignore= [S390] 704 See Documentation/s390/CommonIO for details. 705 clk_ignore_unused 706 [CLK] 707 Prevents the clock framework from automatically gating 708 clocks that have not been explicitly enabled by a Linux 709 device driver but are enabled in hardware at reset or 710 by the bootloader/firmware. Note that this does not 711 force such clocks to be always-on nor does it reserve 712 those clocks in any way. This parameter is useful for 713 debug and development, but should not be needed on a 714 platform with proper driver support. For more 715 information, see Documentation/clk.txt. 716 717 clock= [BUGS=X86-32, HW] gettimeofday clocksource override. 718 [Deprecated] 719 Forces specified clocksource (if available) to be used 720 when calculating gettimeofday(). If specified 721 clocksource is not available, it defaults to PIT. 722 Format: { pit | tsc | cyclone | pmtmr } 723 724 clocksource= Override the default clocksource 725 Format: <string> 726 Override the default clocksource and use the clocksource 727 with the name specified. 728 Some clocksource names to choose from, depending on 729 the platform: 730 [all] jiffies (this is the base, fallback clocksource) 731 [ACPI] acpi_pm 732 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2, 733 pxa_timer,timer3,32k_counter,timer0_1 734 [AVR32] avr32 735 [X86-32] pit,hpet,tsc; 736 scx200_hrt on Geode; cyclone on IBM x440 737 [MIPS] MIPS 738 [PARISC] cr16 739 [S390] tod 740 [SH] SuperH 741 [SPARC64] tick 742 [X86-64] hpet,tsc 743 744 clocksource.arm_arch_timer.evtstrm= 745 [ARM,ARM64] 746 Format: <bool> 747 Enable/disable the eventstream feature of the ARM 748 architected timer so that code using WFE-based polling 749 loops can be debugged more effectively on production 750 systems. 751 752 clocksource.arm_arch_timer.fsl-a008585= 753 [ARM64] 754 Format: <bool> 755 Enable/disable the workaround of Freescale/NXP 756 erratum A-008585. This can be useful for KVM 757 guests, if the guest device tree doesn't show the 758 erratum. If unspecified, the workaround is 759 enabled based on the device tree. 760 761 clearcpuid=BITNUM [X86] 762 Disable CPUID feature X for the kernel. See 763 arch/x86/include/asm/cpufeatures.h for the valid bit 764 numbers. Note the Linux specific bits are not necessarily 765 stable over kernel options, but the vendor specific 766 ones should be. 767 Also note that user programs calling CPUID directly 768 or using the feature without checking anything 769 will still see it. This just prevents it from 770 being used by the kernel or shown in /proc/cpuinfo. 771 Also note the kernel might malfunction if you disable 772 some critical bits. 773 774 cma=nn[MG]@[start[MG][-end[MG]]] 775 [ARM,X86,KNL] 776 Sets the size of kernel global memory area for 777 contiguous memory allocations and optionally the 778 placement constraint by the physical address range of 779 memory allocations. A value of 0 disables CMA 780 altogether. For more information, see 781 include/linux/dma-contiguous.h 782 783 cmo_free_hint= [PPC] Format: { yes | no } 784 Specify whether pages are marked as being inactive 785 when they are freed. This is used in CMO environments 786 to determine OS memory pressure for page stealing by 787 a hypervisor. 788 Default: yes 789 790 coherent_pool=nn[KMG] [ARM,KNL] 791 Sets the size of memory pool for coherent, atomic dma 792 allocations, by default set to 256K. 793 794 code_bytes [X86] How many bytes of object code to print 795 in an oops report. 796 Range: 0 - 8192 797 Default: 64 798 799 com20020= [HW,NET] ARCnet - COM20020 chipset 800 Format: 801 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]] 802 803 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers) 804 Format: <io>[,<irq>] 805 806 com90xx= [HW,NET] 807 ARCnet - COM90xx chipset (memory-mapped buffers) 808 Format: <io>[,<irq>[,<memstart>]] 809 810 condev= [HW,S390] console device 811 conmode= 812 813 console= [KNL] Output console device and options. 814 815 tty<n> Use the virtual console device <n>. 816 817 ttyS<n>[,options] 818 ttyUSB0[,options] 819 Use the specified serial port. The options are of 820 the form "bbbbpnf", where "bbbb" is the baud rate, 821 "p" is parity ("n", "o", or "e"), "n" is number of 822 bits, and "f" is flow control ("r" for RTS or 823 omit it). Default is "9600n8". 824 825 See Documentation/serial-console.txt for more 826 information. See 827 Documentation/networking/netconsole.txt for an 828 alternative. 829 830 uart[8250],io,<addr>[,options] 831 uart[8250],mmio,<addr>[,options] 832 uart[8250],mmio16,<addr>[,options] 833 uart[8250],mmio32,<addr>[,options] 834 uart[8250],0x<addr>[,options] 835 Start an early, polled-mode console on the 8250/16550 836 UART at the specified I/O port or MMIO address, 837 switching to the matching ttyS device later. 838 MMIO inter-register address stride is either 8-bit 839 (mmio), 16-bit (mmio16), or 32-bit (mmio32). 840 If none of [io|mmio|mmio16|mmio32], <addr> is assumed 841 to be equivalent to 'mmio'. 'options' are specified in 842 the same format described for ttyS above; if unspecified, 843 the h/w is not re-initialized. 844 845 hvc<n> Use the hypervisor console device <n>. This is for 846 both Xen and PowerPC hypervisors. 847 848 If the device connected to the port is not a TTY but a braille 849 device, prepend "brl," before the device type, for instance 850 console=brl,ttyS0 851 For now, only VisioBraille is supported. 852 853 consoleblank= [KNL] The console blank (screen saver) timeout in 854 seconds. Defaults to 10*60 = 10mins. A value of 0 855 disables the blank timer. 856 857 coredump_filter= 858 [KNL] Change the default value for 859 /proc/<pid>/coredump_filter. 860 See also Documentation/filesystems/proc.txt. 861 862 cpuidle.off=1 [CPU_IDLE] 863 disable the cpuidle sub-system 864 865 cpu_init_udelay=N 866 [X86] Delay for N microsec between assert and de-assert 867 of APIC INIT to start processors. This delay occurs 868 on every CPU online, such as boot, and resume from suspend. 869 Default: 10000 870 871 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver 872 Format: 873 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] 874 875 crashkernel=size[KMG][@offset[KMG]] 876 [KNL] Using kexec, Linux can switch to a 'crash kernel' 877 upon panic. This parameter reserves the physical 878 memory region [offset, offset + size] for that kernel 879 image. If '@offset' is omitted, then a suitable offset 880 is selected automatically. Check 881 Documentation/kdump/kdump.txt for further details. 882 883 crashkernel=range1:size1[,range2:size2,...][@offset] 884 [KNL] Same as above, but depends on the memory 885 in the running system. The syntax of range is 886 start-[end] where start and end are both 887 a memory unit (amount[KMG]). See also 888 Documentation/kdump/kdump.txt for an example. 889 890 crashkernel=size[KMG],high 891 [KNL, x86_64] range could be above 4G. Allow kernel 892 to allocate physical memory region from top, so could 893 be above 4G if system have more than 4G ram installed. 894 Otherwise memory region will be allocated below 4G, if 895 available. 896 It will be ignored if crashkernel=X is specified. 897 crashkernel=size[KMG],low 898 [KNL, x86_64] range under 4G. When crashkernel=X,high 899 is passed, kernel could allocate physical memory region 900 above 4G, that cause second kernel crash on system 901 that require some amount of low memory, e.g. swiotlb 902 requires at least 64M+32K low memory, also enough extra 903 low memory is needed to make sure DMA buffers for 32-bit 904 devices won't run out. Kernel would try to allocate at 905 at least 256M below 4G automatically. 906 This one let user to specify own low range under 4G 907 for second kernel instead. 908 0: to disable low allocation. 909 It will be ignored when crashkernel=X,high is not used 910 or memory reserved is below 4G. 911 912 cryptomgr.notests 913 [KNL] Disable crypto self-tests 914 915 cs89x0_dma= [HW,NET] 916 Format: <dma> 917 918 cs89x0_media= [HW,NET] 919 Format: { rj45 | aui | bnc } 920 921 dasd= [HW,NET] 922 See header of drivers/s390/block/dasd_devmap.c. 923 924 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port 925 (one device per port) 926 Format: <port#>,<type> 927 See also Documentation/input/joystick-parport.txt 928 929 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot 930 time. See Documentation/dynamic-debug-howto.txt for 931 details. Deprecated, see dyndbg. 932 933 debug [KNL] Enable kernel debugging (events log level). 934 935 debug_locks_verbose= 936 [KNL] verbose self-tests 937 Format=<0|1> 938 Print debugging info while doing the locking API 939 self-tests. 940 We default to 0 (no extra messages), setting it to 941 1 will print _a lot_ more information - normally 942 only useful to kernel developers. 943 944 debug_objects [KNL] Enable object debugging 945 946 no_debug_objects 947 [KNL] Disable object debugging 948 949 debug_guardpage_minorder= 950 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this 951 parameter allows control of the order of pages that will 952 be intentionally kept free (and hence protected) by the 953 buddy allocator. Bigger value increase the probability 954 of catching random memory corruption, but reduce the 955 amount of memory for normal system use. The maximum 956 possible value is MAX_ORDER/2. Setting this parameter 957 to 1 or 2 should be enough to identify most random 958 memory corruption problems caused by bugs in kernel or 959 driver code when a CPU writes to (or reads from) a 960 random memory location. Note that there exists a class 961 of memory corruptions problems caused by buggy H/W or 962 F/W or by drivers badly programing DMA (basically when 963 memory is written at bus level and the CPU MMU is 964 bypassed) which are not detectable by 965 CONFIG_DEBUG_PAGEALLOC, hence this option will not help 966 tracking down these problems. 967 968 debug_pagealloc= 969 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this 970 parameter enables the feature at boot time. In 971 default, it is disabled. We can avoid allocating huge 972 chunk of memory for debug pagealloc if we don't enable 973 it at boot time and the system will work mostly same 974 with the kernel built without CONFIG_DEBUG_PAGEALLOC. 975 on: enable the feature 976 977 debugpat [X86] Enable PAT debugging 978 979 decnet.addr= [HW,NET] 980 Format: <area>[,<node>] 981 See also Documentation/networking/decnet.txt. 982 983 default_hugepagesz= 984 [same as hugepagesz=] The size of the default 985 HugeTLB page size. This is the size represented by 986 the legacy /proc/ hugepages APIs, used for SHM, and 987 default size when mounting hugetlbfs filesystems. 988 Defaults to the default architecture's huge page size 989 if not specified. 990 991 dhash_entries= [KNL] 992 Set number of hash buckets for dentry cache. 993 994 disable_1tb_segments [PPC] 995 Disables the use of 1TB hash page table segments. This 996 causes the kernel to fall back to 256MB segments which 997 can be useful when debugging issues that require an SLB 998 miss to occur. 999 1000 disable= [IPV6] 1001 See Documentation/networking/ipv6.txt. 1002 1003 disable_radix [PPC] 1004 Disable RADIX MMU mode on POWER9 1005 1006 disable_cpu_apicid= [X86,APIC,SMP] 1007 Format: <int> 1008 The number of initial APIC ID for the 1009 corresponding CPU to be disabled at boot, 1010 mostly used for the kdump 2nd kernel to 1011 disable BSP to wake up multiple CPUs without 1012 causing system reset or hang due to sending 1013 INIT from AP to BSP. 1014 1015 disable_ddw [PPC/PSERIES] 1016 Disable Dynamic DMA Window support. Use this if 1017 to workaround buggy firmware. 1018 1019 disable_ipv6= [IPV6] 1020 See Documentation/networking/ipv6.txt. 1021 1022 disable_mtrr_cleanup [X86] 1023 The kernel tries to adjust MTRR layout from continuous 1024 to discrete, to make X server driver able to add WB 1025 entry later. This parameter disables that. 1026 1027 disable_mtrr_trim [X86, Intel and AMD only] 1028 By default the kernel will trim any uncacheable 1029 memory out of your available memory pool based on 1030 MTRR settings. This parameter disables that behavior, 1031 possibly causing your machine to run very slowly. 1032 1033 disable_timer_pin_1 [X86] 1034 Disable PIN 1 of APIC timer 1035 Can be useful to work around chipset bugs. 1036 1037 dis_ucode_ldr [X86] Disable the microcode loader. 1038 1039 dm= [DM] Allows early creation of a device-mapper device. 1040 See Documentation/device-mapper/boot.txt. 1041 1042 dmasound= [HW,OSS] Sound subsystem buff 1043 1044 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, 1045 this option disables the debugging code at boot. 1046 1047 dma_debug_entries=<number> 1048 This option allows to tune the number of preallocated 1049 entries for DMA-API debugging code. One entry is 1050 required per DMA-API allocation. Use this if the 1051 DMA-API debugging code disables itself because the 1052 architectural default is too low. 1053 1054 dma_debug_driver=<driver_name> 1055 With this option the DMA-API debugging driver 1056 filter feature can be enabled at boot time. Just 1057 pass the driver to filter for as the parameter. 1058 The filter can be disabled or changed to another 1059 driver later using sysfs. 1060 1061 drm_kms_helper.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>] 1062 Broken monitors, graphic adapters, KVMs and EDIDless 1063 panels may send no or incorrect EDID data sets. 1064 This parameter allows to specify an EDID data sets 1065 in the /lib/firmware directory that are used instead. 1066 Generic built-in EDID data sets are used, if one of 1067 edid/1024x768.bin, edid/1280x1024.bin, 1068 edid/1680x1050.bin, or edid/1920x1080.bin is given 1069 and no file with the same name exists. Details and 1070 instructions how to build your own EDID data are 1071 available in Documentation/EDID/HOWTO.txt. An EDID 1072 data set will only be used for a particular connector, 1073 if its name and a colon are prepended to the EDID 1074 name. Each connector may use a unique EDID data 1075 set by separating the files with a comma. An EDID 1076 data set with no connector name will be used for 1077 any connectors not explicitly specified. 1078 1079 dscc4.setup= [NET] 1080 1081 dyndbg[="val"] [KNL,DYNAMIC_DEBUG] 1082 module.dyndbg[="val"] 1083 Enable debug messages at boot time. See 1084 Documentation/dynamic-debug-howto.txt for details. 1085 1086 nompx [X86] Disables Intel Memory Protection Extensions. 1087 See Documentation/x86/intel_mpx.txt for more 1088 information about the feature. 1089 1090 nopku [X86] Disable Memory Protection Keys CPU feature found 1091 in some Intel CPUs. 1092 1093 eagerfpu= [X86] 1094 on enable eager fpu restore 1095 off disable eager fpu restore 1096 auto selects the default scheme, which automatically 1097 enables eagerfpu restore for xsaveopt. 1098 1099 module.async_probe [KNL] 1100 Enable asynchronous probe on this module. 1101 1102 early_ioremap_debug [KNL] 1103 Enable debug messages in early_ioremap support. This 1104 is useful for tracking down temporary early mappings 1105 which are not unmapped. 1106 1107 earlycon= [KNL] Output early console device and options. 1108 1109 When used with no options, the early console is 1110 determined by the stdout-path property in device 1111 tree's chosen node. 1112 1113 cdns,<addr>[,options] 1114 Start an early, polled-mode console on a Cadence 1115 (xuartps) serial port at the specified address. Only 1116 supported option is baud rate. If baud rate is not 1117 specified, the serial port must already be setup and 1118 configured. 1119 1120 uart[8250],io,<addr>[,options] 1121 uart[8250],mmio,<addr>[,options] 1122 uart[8250],mmio32,<addr>[,options] 1123 uart[8250],mmio32be,<addr>[,options] 1124 uart[8250],0x<addr>[,options] 1125 Start an early, polled-mode console on the 8250/16550 1126 UART at the specified I/O port or MMIO address. 1127 MMIO inter-register address stride is either 8-bit 1128 (mmio) or 32-bit (mmio32 or mmio32be). 1129 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed 1130 to be equivalent to 'mmio'. 'options' are specified 1131 in the same format described for "console=ttyS<n>"; if 1132 unspecified, the h/w is not initialized. 1133 1134 pl011,<addr> 1135 pl011,mmio32,<addr> 1136 Start an early, polled-mode console on a pl011 serial 1137 port at the specified address. The pl011 serial port 1138 must already be setup and configured. Options are not 1139 yet supported. If 'mmio32' is specified, then only 1140 the driver will use only 32-bit accessors to read/write 1141 the device registers. 1142 1143 meson,<addr> 1144 Start an early, polled-mode console on a meson serial 1145 port at the specified address. The serial port must 1146 already be setup and configured. Options are not yet 1147 supported. 1148 1149 msm_serial,<addr> 1150 Start an early, polled-mode console on an msm serial 1151 port at the specified address. The serial port 1152 must already be setup and configured. Options are not 1153 yet supported. 1154 1155 msm_serial_dm,<addr> 1156 Start an early, polled-mode console on an msm serial 1157 dm port at the specified address. The serial port 1158 must already be setup and configured. Options are not 1159 yet supported. 1160 1161 smh Use ARM semihosting calls for early console. 1162 1163 s3c2410,<addr> 1164 s3c2412,<addr> 1165 s3c2440,<addr> 1166 s3c6400,<addr> 1167 s5pv210,<addr> 1168 exynos4210,<addr> 1169 Use early console provided by serial driver available 1170 on Samsung SoCs, requires selecting proper type and 1171 a correct base address of the selected UART port. The 1172 serial port must already be setup and configured. 1173 Options are not yet supported. 1174 1175 lpuart,<addr> 1176 lpuart32,<addr> 1177 Use early console provided by Freescale LP UART driver 1178 found on Freescale Vybrid and QorIQ LS1021A processors. 1179 A valid base address must be provided, and the serial 1180 port must already be setup and configured. 1181 1182 armada3700_uart,<addr> 1183 Start an early, polled-mode console on the 1184 Armada 3700 serial port at the specified 1185 address. The serial port must already be setup 1186 and configured. Options are not yet supported. 1187 1188 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k] 1189 earlyprintk=vga 1190 earlyprintk=efi 1191 earlyprintk=xen 1192 earlyprintk=serial[,ttySn[,baudrate]] 1193 earlyprintk=serial[,0x...[,baudrate]] 1194 earlyprintk=ttySn[,baudrate] 1195 earlyprintk=dbgp[debugController#] 1196 earlyprintk=pciserial,bus:device.function[,baudrate] 1197 1198 earlyprintk is useful when the kernel crashes before 1199 the normal console is initialized. It is not enabled by 1200 default because it has some cosmetic problems. 1201 1202 Append ",keep" to not disable it when the real console 1203 takes over. 1204 1205 Only one of vga, efi, serial, or usb debug port can 1206 be used at a time. 1207 1208 Currently only ttyS0 and ttyS1 may be specified by 1209 name. Other I/O ports may be explicitly specified 1210 on some architectures (x86 and arm at least) by 1211 replacing ttySn with an I/O port address, like this: 1212 earlyprintk=serial,0x1008,115200 1213 You can find the port for a given device in 1214 /proc/tty/driver/serial: 1215 2: uart:ST16650V2 port:00001008 irq:18 ... 1216 1217 Interaction with the standard serial driver is not 1218 very good. 1219 1220 The VGA and EFI output is eventually overwritten by 1221 the real console. 1222 1223 The xen output can only be used by Xen PV guests. 1224 1225 edac_report= [HW,EDAC] Control how to report EDAC event 1226 Format: {"on" | "off" | "force"} 1227 on: enable EDAC to report H/W event. May be overridden 1228 by other higher priority error reporting module. 1229 off: disable H/W event reporting through EDAC. 1230 force: enforce the use of EDAC to report H/W event. 1231 default: on. 1232 1233 ekgdboc= [X86,KGDB] Allow early kernel console debugging 1234 ekgdboc=kbd 1235 1236 This is designed to be used in conjunction with 1237 the boot argument: earlyprintk=vga 1238 1239 edd= [EDD] 1240 Format: {"off" | "on" | "skip[mbr]"} 1241 1242 efi= [EFI] 1243 Format: { "old_map", "nochunk", "noruntime", "debug" } 1244 old_map [X86-64]: switch to the old ioremap-based EFI 1245 runtime services mapping. 32-bit still uses this one by 1246 default. 1247 nochunk: disable reading files in "chunks" in the EFI 1248 boot stub, as chunking can cause problems with some 1249 firmware implementations. 1250 noruntime : disable EFI runtime services support 1251 debug: enable misc debug output 1252 1253 efi_no_storage_paranoia [EFI; X86] 1254 Using this parameter you can use more than 50% of 1255 your efi variable storage. Use this parameter only if 1256 you are really sure that your UEFI does sane gc and 1257 fulfills the spec otherwise your board may brick. 1258 1259 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86] 1260 Add arbitrary attribute to specific memory range by 1261 updating original EFI memory map. 1262 Region of memory which aa attribute is added to is 1263 from ss to ss+nn. 1264 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000 1265 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000) 1266 attribute is added to range 0x100000000-0x180000000 and 1267 0x10a0000000-0x1120000000. 1268 1269 Using this parameter you can do debugging of EFI memmap 1270 related feature. For example, you can do debugging of 1271 Address Range Mirroring feature even if your box 1272 doesn't support it. 1273 1274 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT 1275 that is to be dynamically loaded by Linux. If there are 1276 multiple variables with the same name but with different 1277 vendor GUIDs, all of them will be loaded. See 1278 Documentation/acpi/ssdt-overlays.txt for details. 1279 1280 1281 eisa_irq_edge= [PARISC,HW] 1282 See header of drivers/parisc/eisa.c. 1283 1284 elanfreq= [X86-32] 1285 See comment before function elanfreq_setup() in 1286 arch/x86/kernel/cpu/cpufreq/elanfreq.c. 1287 1288 elevator= [IOSCHED] 1289 Format: {"cfq" | "deadline" | "noop"} 1290 See Documentation/block/cfq-iosched.txt and 1291 Documentation/block/deadline-iosched.txt for details. 1292 1293 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390] 1294 Specifies physical address of start of kernel core 1295 image elf header and optionally the size. Generally 1296 kexec loader will pass this option to capture kernel. 1297 See Documentation/kdump/kdump.txt for details. 1298 1299 enable_mtrr_cleanup [X86] 1300 The kernel tries to adjust MTRR layout from continuous 1301 to discrete, to make X server driver able to add WB 1302 entry later. This parameter enables that. 1303 1304 enable_timer_pin_1 [X86] 1305 Enable PIN 1 of APIC timer 1306 Can be useful to work around chipset bugs 1307 (in particular on some ATI chipsets). 1308 The kernel tries to set a reasonable default. 1309 1310 enforcing [SELINUX] Set initial enforcing status. 1311 Format: {"0" | "1"} 1312 See security/selinux/Kconfig help text. 1313 0 -- permissive (log only, no denials). 1314 1 -- enforcing (deny and log). 1315 Default value is 0. 1316 Value can be changed at runtime via /selinux/enforce. 1317 1318 erst_disable [ACPI] 1319 Disable Error Record Serialization Table (ERST) 1320 support. 1321 1322 ether= [HW,NET] Ethernet cards parameters 1323 This option is obsoleted by the "netdev=" option, which 1324 has equivalent usage. See its documentation for details. 1325 1326 evm= [EVM] 1327 Format: { "fix" } 1328 Permit 'security.evm' to be updated regardless of 1329 current integrity status. 1330 1331 failslab= 1332 fail_page_alloc= 1333 fail_make_request=[KNL] 1334 General fault injection mechanism. 1335 Format: <interval>,<probability>,<space>,<times> 1336 See also Documentation/fault-injection/. 1337 1338 floppy= [HW] 1339 See Documentation/blockdev/floppy.txt. 1340 1341 force_pal_cache_flush 1342 [IA-64] Avoid check_sal_cache_flush which may hang on 1343 buggy SAL_CACHE_FLUSH implementations. Using this 1344 parameter will force ia64_sal_cache_flush to call 1345 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH. 1346 1347 forcepae [X86-32] 1348 Forcefully enable Physical Address Extension (PAE). 1349 Many Pentium M systems disable PAE but may have a 1350 functionally usable PAE implementation. 1351 Warning: use of this parameter will taint the kernel 1352 and may cause unknown problems. 1353 1354 ftrace=[tracer] 1355 [FTRACE] will set and start the specified tracer 1356 as early as possible in order to facilitate early 1357 boot debugging. 1358 1359 ftrace_dump_on_oops[=orig_cpu] 1360 [FTRACE] will dump the trace buffers on oops. 1361 If no parameter is passed, ftrace will dump 1362 buffers of all CPUs, but if you pass orig_cpu, it will 1363 dump only the buffer of the CPU that triggered the 1364 oops. 1365 1366 ftrace_filter=[function-list] 1367 [FTRACE] Limit the functions traced by the function 1368 tracer at boot up. function-list is a comma separated 1369 list of functions. This list can be changed at run 1370 time by the set_ftrace_filter file in the debugfs 1371 tracing directory. 1372 1373 ftrace_notrace=[function-list] 1374 [FTRACE] Do not trace the functions specified in 1375 function-list. This list can be changed at run time 1376 by the set_ftrace_notrace file in the debugfs 1377 tracing directory. 1378 1379 ftrace_graph_filter=[function-list] 1380 [FTRACE] Limit the top level callers functions traced 1381 by the function graph tracer at boot up. 1382 function-list is a comma separated list of functions 1383 that can be changed at run time by the 1384 set_graph_function file in the debugfs tracing directory. 1385 1386 ftrace_graph_notrace=[function-list] 1387 [FTRACE] Do not trace from the functions specified in 1388 function-list. This list is a comma separated list of 1389 functions that can be changed at run time by the 1390 set_graph_notrace file in the debugfs tracing directory. 1391 1392 gamecon.map[2|3]= 1393 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 1394 support via parallel port (up to 5 devices per port) 1395 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 1396 See also Documentation/input/joystick-parport.txt 1397 1398 gamma= [HW,DRM] 1399 1400 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART 1401 Format: off | on 1402 default: on 1403 1404 gcov_persist= [GCOV] When non-zero (default), profiling data for 1405 kernel modules is saved and remains accessible via 1406 debugfs, even when the module is unloaded/reloaded. 1407 When zero, profiling data is discarded and associated 1408 debugfs files are removed at module unload time. 1409 1410 goldfish [X86] Enable the goldfish android emulator platform. 1411 Don't use this when you are not running on the 1412 android emulator 1413 1414 gpt [EFI] Forces disk with valid GPT signature but 1415 invalid Protective MBR to be treated as GPT. If the 1416 primary GPT is corrupted, it enables the backup/alternate 1417 GPT to be used instead. 1418 1419 grcan.enable0= [HW] Configuration of physical interface 0. Determines 1420 the "Enable 0" bit of the configuration register. 1421 Format: 0 | 1 1422 Default: 0 1423 grcan.enable1= [HW] Configuration of physical interface 1. Determines 1424 the "Enable 0" bit of the configuration register. 1425 Format: 0 | 1 1426 Default: 0 1427 grcan.select= [HW] Select which physical interface to use. 1428 Format: 0 | 1 1429 Default: 0 1430 grcan.txsize= [HW] Sets the size of the tx buffer. 1431 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. 1432 Default: 1024 1433 grcan.rxsize= [HW] Sets the size of the rx buffer. 1434 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. 1435 Default: 1024 1436 1437 gpio-mockup.gpio_mockup_ranges 1438 [HW] Sets the ranges of gpiochip of for this device. 1439 Format: <start1>,<end1>,<start2>,<end2>... 1440 1441 hardlockup_all_cpu_backtrace= 1442 [KNL] Should the hard-lockup detector generate 1443 backtraces on all cpus. 1444 Format: <integer> 1445 1446 hashdist= [KNL,NUMA] Large hashes allocated during boot 1447 are distributed across NUMA nodes. Defaults on 1448 for 64-bit NUMA, off otherwise. 1449 Format: 0 | 1 (for off | on) 1450 1451 hcl= [IA-64] SGI's Hardware Graph compatibility layer 1452 1453 hd= [EIDE] (E)IDE hard drive subsystem geometry 1454 Format: <cyl>,<head>,<sect> 1455 1456 hest_disable [ACPI] 1457 Disable Hardware Error Source Table (HEST) support; 1458 corresponding firmware-first mode error processing 1459 logic will be disabled. 1460 1461 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact 1462 size of <nn>. This works even on boxes that have no 1463 highmem otherwise. This also works to reduce highmem 1464 size on bigger boxes. 1465 1466 highres= [KNL] Enable/disable high resolution timer mode. 1467 Valid parameters: "on", "off" 1468 Default: "on" 1469 1470 hisax= [HW,ISDN] 1471 See Documentation/isdn/README.HiSax. 1472 1473 hlt [BUGS=ARM,SH] 1474 1475 hpet= [X86-32,HPET] option to control HPET usage 1476 Format: { enable (default) | disable | force | 1477 verbose } 1478 disable: disable HPET and use PIT instead 1479 force: allow force enabled of undocumented chips (ICH4, 1480 VIA, nVidia) 1481 verbose: show contents of HPET registers during setup 1482 1483 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET 1484 registers. Default set by CONFIG_HPET_MMAP_DEFAULT. 1485 1486 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot. 1487 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages. 1488 On x86-64 and powerpc, this option can be specified 1489 multiple times interleaved with hugepages= to reserve 1490 huge pages of different sizes. Valid pages sizes on 1491 x86-64 are 2M (when the CPU supports "pse") and 1G 1492 (when the CPU supports the "pdpe1gb" cpuinfo flag). 1493 1494 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 1495 terminal devices. Valid values: 0..8 1496 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 1497 If specified, z/VM IUCV HVC accepts connections 1498 from listed z/VM user IDs only. 1499 1500 hwthread_map= [METAG] Comma-separated list of Linux cpu id to 1501 hardware thread id mappings. 1502 Format: <cpu>:<hwthread> 1503 1504 keep_bootcon [KNL] 1505 Do not unregister boot console at start. This is only 1506 useful for debugging when something happens in the window 1507 between unregistering the boot console and initializing 1508 the real console. 1509 1510 i2c_bus= [HW] Override the default board specific I2C bus speed 1511 or register an additional I2C bus that is not 1512 registered from board initialization code. 1513 Format: 1514 <bus_id>,<clkrate> 1515 1516 i8042.debug [HW] Toggle i8042 debug mode 1517 i8042.unmask_kbd_data 1518 [HW] Enable printing of interrupt data from the KBD port 1519 (disabled by default, and as a pre-condition 1520 requires that i8042.debug=1 be enabled) 1521 i8042.direct [HW] Put keyboard port into non-translated mode 1522 i8042.dumbkbd [HW] Pretend that controller can only read data from 1523 keyboard and cannot control its state 1524 (Don't attempt to blink the leds) 1525 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 1526 i8042.nokbd [HW] Don't check/create keyboard port 1527 i8042.noloop [HW] Disable the AUX Loopback command while probing 1528 for the AUX port 1529 i8042.nomux [HW] Don't check presence of an active multiplexing 1530 controller 1531 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 1532 controllers 1533 i8042.notimeout [HW] Ignore timeout condition signalled by controller 1534 i8042.reset [HW] Reset the controller during init, cleanup and 1535 suspend-to-ram transitions, only during s2r 1536 transitions, or never reset 1537 Format: { 1 | Y | y | 0 | N | n } 1538 1, Y, y: always reset controller 1539 0, N, n: don't ever reset controller 1540 Default: only on s2r transitions on x86; most other 1541 architectures force reset to be always executed 1542 i8042.unlock [HW] Unlock (ignore) the keylock 1543 i8042.kbdreset [HW] Reset device connected to KBD port 1544 1545 i810= [HW,DRM] 1546 1547 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data 1548 indicates that the driver is running on unsupported 1549 hardware. 1550 i8k.force [HW] Activate i8k driver even if SMM BIOS signature 1551 does not match list of supported models. 1552 i8k.power_status 1553 [HW] Report power status in /proc/i8k 1554 (disabled by default) 1555 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN 1556 capability is set. 1557 1558 i915.invert_brightness= 1559 [DRM] Invert the sense of the variable that is used to 1560 set the brightness of the panel backlight. Normally a 1561 brightness value of 0 indicates backlight switched off, 1562 and the maximum of the brightness value sets the backlight 1563 to maximum brightness. If this parameter is set to 0 1564 (default) and the machine requires it, or this parameter 1565 is set to 1, a brightness value of 0 sets the backlight 1566 to maximum brightness, and the maximum of the brightness 1567 value switches the backlight off. 1568 -1 -- never invert brightness 1569 0 -- machine default 1570 1 -- force brightness inversion 1571 1572 icn= [HW,ISDN] 1573 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]] 1574 1575 ide-core.nodma= [HW] (E)IDE subsystem 1576 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc 1577 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr 1578 .cdrom .chs .ignore_cable are additional options 1579 See Documentation/ide/ide.txt. 1580 1581 ide-generic.probe-mask= [HW] (E)IDE subsystem 1582 Format: <int> 1583 Probe mask for legacy ISA IDE ports. Depending on 1584 platform up to 6 ports are supported, enabled by 1585 setting corresponding bits in the mask to 1. The 1586 default value is 0x0, which has a special meaning. 1587 On systems that have PCI, it triggers scanning the 1588 PCI bus for the first and the second port, which 1589 are then probed. On systems without PCI the value 1590 of 0x0 enables probing the two first ports as if it 1591 was 0x3. 1592 1593 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem 1594 Claim all unknown PCI IDE storage controllers. 1595 1596 idle= [X86] 1597 Format: idle=poll, idle=halt, idle=nomwait 1598 Poll forces a polling idle loop that can slightly 1599 improve the performance of waking up a idle CPU, but 1600 will use a lot of power and make the system run hot. 1601 Not recommended. 1602 idle=halt: Halt is forced to be used for CPU idle. 1603 In such case C2/C3 won't be used again. 1604 idle=nomwait: Disable mwait for CPU C-states 1605 1606 ieee754= [MIPS] Select IEEE Std 754 conformance mode 1607 Format: { strict | legacy | 2008 | relaxed } 1608 Default: strict 1609 1610 Choose which programs will be accepted for execution 1611 based on the IEEE 754 NaN encoding(s) supported by 1612 the FPU and the NaN encoding requested with the value 1613 of an ELF file header flag individually set by each 1614 binary. Hardware implementations are permitted to 1615 support either or both of the legacy and the 2008 NaN 1616 encoding mode. 1617 1618 Available settings are as follows: 1619 strict accept binaries that request a NaN encoding 1620 supported by the FPU 1621 legacy only accept legacy-NaN binaries, if supported 1622 by the FPU 1623 2008 only accept 2008-NaN binaries, if supported 1624 by the FPU 1625 relaxed accept any binaries regardless of whether 1626 supported by the FPU 1627 1628 The FPU emulator is always able to support both NaN 1629 encodings, so if no FPU hardware is present or it has 1630 been disabled with 'nofpu', then the settings of 1631 'legacy' and '2008' strap the emulator accordingly, 1632 'relaxed' straps the emulator for both legacy-NaN and 1633 2008-NaN, whereas 'strict' enables legacy-NaN only on 1634 legacy processors and both NaN encodings on MIPS32 or 1635 MIPS64 CPUs. 1636 1637 The setting for ABS.fmt/NEG.fmt instruction execution 1638 mode generally follows that for the NaN encoding, 1639 except where unsupported by hardware. 1640 1641 ignore_loglevel [KNL] 1642 Ignore loglevel setting - this will print /all/ 1643 kernel messages to the console. Useful for debugging. 1644 We also add it as printk module parameter, so users 1645 could change it dynamically, usually by 1646 /sys/module/printk/parameters/ignore_loglevel. 1647 1648 ignore_rlimit_data 1649 Ignore RLIMIT_DATA setting for data mappings, 1650 print warning at first misuse. Can be changed via 1651 /sys/module/kernel/parameters/ignore_rlimit_data. 1652 1653 ihash_entries= [KNL] 1654 Set number of hash buckets for inode cache. 1655 1656 ima_appraise= [IMA] appraise integrity measurements 1657 Format: { "off" | "enforce" | "fix" | "log" } 1658 default: "enforce" 1659 1660 ima_appraise_tcb [IMA] 1661 The builtin appraise policy appraises all files 1662 owned by uid=0. 1663 1664 ima_hash= [IMA] 1665 Format: { md5 | sha1 | rmd160 | sha256 | sha384 1666 | sha512 | ... } 1667 default: "sha1" 1668 1669 The list of supported hash algorithms is defined 1670 in crypto/hash_info.h. 1671 1672 ima_policy= [IMA] 1673 The builtin measurement policy to load during IMA 1674 setup. Specyfing "tcb" as the value, measures all 1675 programs exec'd, files mmap'd for exec, and all files 1676 opened with the read mode bit set by either the 1677 effective uid (euid=0) or uid=0. 1678 Format: "tcb" 1679 1680 ima_tcb [IMA] Deprecated. Use ima_policy= instead. 1681 Load a policy which meets the needs of the Trusted 1682 Computing Base. This means IMA will measure all 1683 programs exec'd, files mmap'd for exec, and all files 1684 opened for read by uid=0. 1685 1686 ima_template= [IMA] 1687 Select one of defined IMA measurements template formats. 1688 Formats: { "ima" | "ima-ng" | "ima-sig" } 1689 Default: "ima-ng" 1690 1691 ima_template_fmt= 1692 [IMA] Define a custom template format. 1693 Format: { "field1|...|fieldN" } 1694 1695 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage 1696 Format: <min_file_size> 1697 Set the minimal file size for using asynchronous hash. 1698 If left unspecified, ahash usage is disabled. 1699 1700 ahash performance varies for different data sizes on 1701 different crypto accelerators. This option can be used 1702 to achieve the best performance for a particular HW. 1703 1704 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size 1705 Format: <bufsize> 1706 Set hashing buffer size. Default: 4k. 1707 1708 ahash performance varies for different chunk sizes on 1709 different crypto accelerators. This option can be used 1710 to achieve best performance for particular HW. 1711 1712 init= [KNL] 1713 Format: <full_path> 1714 Run specified binary instead of /sbin/init as init 1715 process. 1716 1717 initcall_debug [KNL] Trace initcalls as they are executed. Useful 1718 for working out where the kernel is dying during 1719 startup. 1720 1721 initcall_blacklist= [KNL] Do not execute a comma-separated list of 1722 initcall functions. Useful for debugging built-in 1723 modules and initcalls. 1724 1725 initrd= [BOOT] Specify the location of the initial ramdisk 1726 1727 init_pkru= [x86] Specify the default memory protection keys rights 1728 register contents for all processes. 0x55555554 by 1729 default (disallow access to all but pkey 0). Can 1730 override in debugfs after boot. 1731 1732 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 1733 Format: <irq> 1734 1735 int_pln_enable [x86] Enable power limit notification interrupt 1736 1737 integrity_audit=[IMA] 1738 Format: { "0" | "1" } 1739 0 -- basic integrity auditing messages. (Default) 1740 1 -- additional integrity auditing messages. 1741 1742 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 1743 on 1744 Enable intel iommu driver. 1745 off 1746 Disable intel iommu driver. 1747 igfx_off [Default Off] 1748 By default, gfx is mapped as normal device. If a gfx 1749 device has a dedicated DMAR unit, the DMAR unit is 1750 bypassed by not enabling DMAR with this option. In 1751 this case, gfx device will use physical address for 1752 DMA. 1753 forcedac [x86_64] 1754 With this option iommu will not optimize to look 1755 for io virtual address below 32-bit forcing dual 1756 address cycle on pci bus for cards supporting greater 1757 than 32-bit addressing. The default is to look 1758 for translation below 32-bit and if not available 1759 then look in the higher range. 1760 strict [Default Off] 1761 With this option on every unmap_single operation will 1762 result in a hardware IOTLB flush operation as opposed 1763 to batching them for performance. 1764 sp_off [Default Off] 1765 By default, super page will be supported if Intel IOMMU 1766 has the capability. With this option, super page will 1767 not be supported. 1768 ecs_off [Default Off] 1769 By default, extended context tables will be supported if 1770 the hardware advertises that it has support both for the 1771 extended tables themselves, and also PASID support. With 1772 this option set, extended tables will not be used even 1773 on hardware which claims to support them. 1774 1775 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 1776 0 disables intel_idle and fall back on acpi_idle. 1777 1 to 9 specify maximum depth of C-state. 1778 1779 intel_pstate= [X86] 1780 disable 1781 Do not enable intel_pstate as the default 1782 scaling driver for the supported processors 1783 force 1784 Enable intel_pstate on systems that prohibit it by default 1785 in favor of acpi-cpufreq. Forcing the intel_pstate driver 1786 instead of acpi-cpufreq may disable platform features, such 1787 as thermal controls and power capping, that rely on ACPI 1788 P-States information being indicated to OSPM and therefore 1789 should be used with caution. This option does not work with 1790 processors that aren't supported by the intel_pstate driver 1791 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 1792 no_hwp 1793 Do not enable hardware P state control (HWP) 1794 if available. 1795 hwp_only 1796 Only load intel_pstate on systems which support 1797 hardware P state control (HWP) if available. 1798 support_acpi_ppc 1799 Enforce ACPI _PPC performance limits. If the Fixed ACPI 1800 Description Table, specifies preferred power management 1801 profile as "Enterprise Server" or "Performance Server", 1802 then this feature is turned on by default. 1803 1804 intremap= [X86-64, Intel-IOMMU] 1805 on enable Interrupt Remapping (default) 1806 off disable Interrupt Remapping 1807 nosid disable Source ID checking 1808 no_x2apic_optout 1809 BIOS x2APIC opt-out request will be ignored 1810 nopost disable Interrupt Posting 1811 1812 iomem= Disable strict checking of access to MMIO memory 1813 strict regions from userspace. 1814 relaxed 1815 1816 iommu= [x86] 1817 off 1818 force 1819 noforce 1820 biomerge 1821 panic 1822 nopanic 1823 merge 1824 nomerge 1825 forcesac 1826 soft 1827 pt [x86, IA-64] 1828 nobypass [PPC/POWERNV] 1829 Disable IOMMU bypass, using IOMMU for PCI devices. 1830 1831 1832 io7= [HW] IO7 for Marvel based alpha systems 1833 See comment before marvel_specify_io7 in 1834 arch/alpha/kernel/core_marvel.c. 1835 1836 io_delay= [X86] I/O delay method 1837 0x80 1838 Standard port 0x80 based delay 1839 0xed 1840 Alternate port 0xed based delay (needed on some systems) 1841 udelay 1842 Simple two microseconds delay 1843 none 1844 No delay 1845 1846 ip= [IP_PNP] 1847 See Documentation/filesystems/nfs/nfsroot.txt. 1848 1849 irqaffinity= [SMP] Set the default irq affinity mask 1850 The argument is a cpu list, as described above. 1851 1852 irqfixup [HW] 1853 When an interrupt is not handled search all handlers 1854 for it. Intended to get systems with badly broken 1855 firmware running. 1856 1857 irqpoll [HW] 1858 When an interrupt is not handled search all handlers 1859 for it. Also check all handlers each timer 1860 interrupt. Intended to get systems with badly broken 1861 firmware running. 1862 1863 isapnp= [ISAPNP] 1864 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 1865 1866 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler. 1867 The argument is a cpu list, as described above. 1868 1869 This option can be used to specify one or more CPUs 1870 to isolate from the general SMP balancing and scheduling 1871 algorithms. You can move a process onto or off an 1872 "isolated" CPU via the CPU affinity syscalls or cpuset. 1873 <cpu number> begins at 0 and the maximum value is 1874 "number of CPUs in system - 1". 1875 1876 This option is the preferred way to isolate CPUs. The 1877 alternative -- manually setting the CPU mask of all 1878 tasks in the system -- can cause problems and 1879 suboptimal load balancer performance. 1880 1881 iucv= [HW,NET] 1882 1883 ivrs_ioapic [HW,X86_64] 1884 Provide an override to the IOAPIC-ID<->DEVICE-ID 1885 mapping provided in the IVRS ACPI table. For 1886 example, to map IOAPIC-ID decimal 10 to 1887 PCI device 00:14.0 write the parameter as: 1888 ivrs_ioapic[10]=00:14.0 1889 1890 ivrs_hpet [HW,X86_64] 1891 Provide an override to the HPET-ID<->DEVICE-ID 1892 mapping provided in the IVRS ACPI table. For 1893 example, to map HPET-ID decimal 0 to 1894 PCI device 00:14.0 write the parameter as: 1895 ivrs_hpet[0]=00:14.0 1896 1897 ivrs_acpihid [HW,X86_64] 1898 Provide an override to the ACPI-HID:UID<->DEVICE-ID 1899 mapping provided in the IVRS ACPI table. For 1900 example, to map UART-HID:UID AMD0020:0 to 1901 PCI device 00:14.5 write the parameter as: 1902 ivrs_acpihid[00:14.5]=AMD0020:0 1903 1904 js= [HW,JOY] Analog joystick 1905 See Documentation/input/joystick.txt. 1906 1907 nokaslr [KNL] 1908 When CONFIG_RANDOMIZE_BASE is set, this disables 1909 kernel and module base offset ASLR (Address Space 1910 Layout Randomization). 1911 1912 kasan_multi_shot 1913 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print 1914 report on every invalid memory access. Without this 1915 parameter KASAN will print report only for the first 1916 invalid access. 1917 1918 keepinitrd [HW,ARM] 1919 1920 kernelcore= [KNL,X86,IA-64,PPC] 1921 Format: nn[KMGTPE] | "mirror" 1922 This parameter 1923 specifies the amount of memory usable by the kernel 1924 for non-movable allocations. The requested amount is 1925 spread evenly throughout all nodes in the system. The 1926 remaining memory in each node is used for Movable 1927 pages. In the event, a node is too small to have both 1928 kernelcore and Movable pages, kernelcore pages will 1929 take priority and other nodes will have a larger number 1930 of Movable pages. The Movable zone is used for the 1931 allocation of pages that may be reclaimed or moved 1932 by the page migration subsystem. This means that 1933 HugeTLB pages may not be allocated from this zone. 1934 Note that allocations like PTEs-from-HighMem still 1935 use the HighMem zone if it exists, and the Normal 1936 zone if it does not. 1937 1938 Instead of specifying the amount of memory (nn[KMGTPE]), 1939 you can specify "mirror" option. In case "mirror" 1940 option is specified, mirrored (reliable) memory is used 1941 for non-movable allocations and remaining memory is used 1942 for Movable pages. nn[KMGTPE] and "mirror" are exclusive, 1943 so you can NOT specify nn[KMGTPE] and "mirror" at the same 1944 time. 1945 1946 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port. 1947 Format: <Controller#>[,poll interval] 1948 The controller # is the number of the ehci usb debug 1949 port as it is probed via PCI. The poll interval is 1950 optional and is the number seconds in between 1951 each poll cycle to the debug port in case you need 1952 the functionality for interrupting the kernel with 1953 gdb or control-c on the dbgp connection. When 1954 not using this parameter you use sysrq-g to break into 1955 the kernel debugger. 1956 1957 kgdboc= [KGDB,HW] kgdb over consoles. 1958 Requires a tty driver that supports console polling, 1959 or a supported polling keyboard driver (non-usb). 1960 Serial only format: <serial_device>[,baud] 1961 keyboard only format: kbd 1962 keyboard and serial format: kbd,<serial_device>[,baud] 1963 Optional Kernel mode setting: 1964 kms, kbd format: kms,kbd 1965 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 1966 1967 kgdbwait [KGDB] Stop kernel execution and enter the 1968 kernel debugger at the earliest opportunity. 1969 1970 kmac= [MIPS] korina ethernet MAC address. 1971 Configure the RouterBoard 532 series on-chip 1972 Ethernet adapter MAC address. 1973 1974 kmemleak= [KNL] Boot-time kmemleak enable/disable 1975 Valid arguments: on, off 1976 Default: on 1977 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 1978 the default is off. 1979 1980 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode 1981 Valid arguments: 0, 1, 2 1982 kmemcheck=0 (disabled) 1983 kmemcheck=1 (enabled) 1984 kmemcheck=2 (one-shot mode) 1985 Default: 2 (one-shot mode) 1986 1987 kstack=N [X86] Print N words from the kernel stack 1988 in oops dumps. 1989 1990 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 1991 Default is 0 (don't ignore, but inject #GP) 1992 1993 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit 1994 KVM MMU at runtime. 1995 Default is 0 (off) 1996 1997 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM. 1998 Default is 1 (enabled) 1999 2000 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU) 2001 for all guests. 2002 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode. 2003 2004 kvm-intel.ept= [KVM,Intel] Disable extended page tables 2005 (virtualized MMU) support on capable Intel chips. 2006 Default is 1 (enabled) 2007 2008 kvm-intel.emulate_invalid_guest_state= 2009 [KVM,Intel] Enable emulation of invalid guest states 2010 Default is 0 (disabled) 2011 2012 kvm-intel.flexpriority= 2013 [KVM,Intel] Disable FlexPriority feature (TPR shadow). 2014 Default is 1 (enabled) 2015 2016 kvm-intel.nested= 2017 [KVM,Intel] Enable VMX nesting (nVMX). 2018 Default is 0 (disabled) 2019 2020 kvm-intel.unrestricted_guest= 2021 [KVM,Intel] Disable unrestricted guest feature 2022 (virtualized real and unpaged mode) on capable 2023 Intel chips. Default is 1 (enabled) 2024 2025 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification 2026 feature (tagged TLBs) on capable Intel chips. 2027 Default is 1 (enabled) 2028 2029 l2cr= [PPC] 2030 2031 l3cr= [PPC] 2032 2033 lapic [X86-32,APIC] Enable the local APIC even if BIOS 2034 disabled it. 2035 2036 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline 2037 value for LAPIC timer one-shot implementation. Default 2038 back to the programmable timer unit in the LAPIC. 2039 2040 lapic_timer_c2_ok [X86,APIC] trust the local apic timer 2041 in C2 power state. 2042 2043 libata.dma= [LIBATA] DMA control 2044 libata.dma=0 Disable all PATA and SATA DMA 2045 libata.dma=1 PATA and SATA Disk DMA only 2046 libata.dma=2 ATAPI (CDROM) DMA only 2047 libata.dma=4 Compact Flash DMA only 2048 Combinations also work, so libata.dma=3 enables DMA 2049 for disks and CDROMs, but not CFs. 2050 2051 libata.ignore_hpa= [LIBATA] Ignore HPA limit 2052 libata.ignore_hpa=0 keep BIOS limits (default) 2053 libata.ignore_hpa=1 ignore limits, using full disk 2054 2055 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 2056 when set. 2057 Format: <int> 2058 2059 libata.force= [LIBATA] Force configurations. The format is comma 2060 separated list of "[ID:]VAL" where ID is 2061 PORT[.DEVICE]. PORT and DEVICE are decimal numbers 2062 matching port, link or device. Basically, it matches 2063 the ATA ID string printed on console by libata. If 2064 the whole ID part is omitted, the last PORT and DEVICE 2065 values are used. If ID hasn't been specified yet, the 2066 configuration applies to all ports, links and devices. 2067 2068 If only DEVICE is omitted, the parameter applies to 2069 the port and all links and devices behind it. DEVICE 2070 number of 0 either selects the first device or the 2071 first fan-out link behind PMP device. It does not 2072 select the host link. DEVICE number of 15 selects the 2073 host link and device attached to it. 2074 2075 The VAL specifies the configuration to force. As long 2076 as there's no ambiguity shortcut notation is allowed. 2077 For example, both 1.5 and 1.5G would work for 1.5Gbps. 2078 The following configurations can be forced. 2079 2080 * Cable type: 40c, 80c, short40c, unk, ign or sata. 2081 Any ID with matching PORT is used. 2082 2083 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 2084 2085 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 2086 udma[/][16,25,33,44,66,100,133] notation is also 2087 allowed. 2088 2089 * [no]ncq: Turn on or off NCQ. 2090 2091 * [no]ncqtrim: Turn off queued DSM TRIM. 2092 2093 * nohrst, nosrst, norst: suppress hard, soft 2094 and both resets. 2095 2096 * rstonce: only attempt one reset during 2097 hot-unplug link recovery 2098 2099 * dump_id: dump IDENTIFY data. 2100 2101 * atapi_dmadir: Enable ATAPI DMADIR bridge support 2102 2103 * disable: Disable this device. 2104 2105 If there are multiple matching configurations changing 2106 the same attribute, the last one is used. 2107 2108 memblock=debug [KNL] Enable memblock debug messages. 2109 2110 load_ramdisk= [RAM] List of ramdisks to load from floppy 2111 See Documentation/blockdev/ramdisk.txt. 2112 2113 lockd.nlm_grace_period=P [NFS] Assign grace period. 2114 Format: <integer> 2115 2116 lockd.nlm_tcpport=N [NFS] Assign TCP port. 2117 Format: <integer> 2118 2119 lockd.nlm_timeout=T [NFS] Assign timeout value. 2120 Format: <integer> 2121 2122 lockd.nlm_udpport=M [NFS] Assign UDP port. 2123 Format: <integer> 2124 2125 locktorture.nreaders_stress= [KNL] 2126 Set the number of locking read-acquisition kthreads. 2127 Defaults to being automatically set based on the 2128 number of online CPUs. 2129 2130 locktorture.nwriters_stress= [KNL] 2131 Set the number of locking write-acquisition kthreads. 2132 2133 locktorture.onoff_holdoff= [KNL] 2134 Set time (s) after boot for CPU-hotplug testing. 2135 2136 locktorture.onoff_interval= [KNL] 2137 Set time (s) between CPU-hotplug operations, or 2138 zero to disable CPU-hotplug testing. 2139 2140 locktorture.shuffle_interval= [KNL] 2141 Set task-shuffle interval (jiffies). Shuffling 2142 tasks allows some CPUs to go into dyntick-idle 2143 mode during the locktorture test. 2144 2145 locktorture.shutdown_secs= [KNL] 2146 Set time (s) after boot system shutdown. This 2147 is useful for hands-off automated testing. 2148 2149 locktorture.stat_interval= [KNL] 2150 Time (s) between statistics printk()s. 2151 2152 locktorture.stutter= [KNL] 2153 Time (s) to stutter testing, for example, 2154 specifying five seconds causes the test to run for 2155 five seconds, wait for five seconds, and so on. 2156 This tests the locking primitive's ability to 2157 transition abruptly to and from idle. 2158 2159 locktorture.torture_runnable= [BOOT] 2160 Start locktorture running at boot time. 2161 2162 locktorture.torture_type= [KNL] 2163 Specify the locking implementation to test. 2164 2165 locktorture.verbose= [KNL] 2166 Enable additional printk() statements. 2167 2168 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 2169 Format: <irq> 2170 2171 loglevel= All Kernel Messages with a loglevel smaller than the 2172 console loglevel will be printed to the console. It can 2173 also be changed with klogd or other programs. The 2174 loglevels are defined as follows: 2175 2176 0 (KERN_EMERG) system is unusable 2177 1 (KERN_ALERT) action must be taken immediately 2178 2 (KERN_CRIT) critical conditions 2179 3 (KERN_ERR) error conditions 2180 4 (KERN_WARNING) warning conditions 2181 5 (KERN_NOTICE) normal but significant condition 2182 6 (KERN_INFO) informational 2183 7 (KERN_DEBUG) debug-level messages 2184 2185 log_buf_len=n[KMG] Sets the size of the printk ring buffer, 2186 in bytes. n must be a power of two and greater 2187 than the minimal size. The minimal size is defined 2188 by LOG_BUF_SHIFT kernel config parameter. There is 2189 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter 2190 that allows to increase the default size depending on 2191 the number of CPUs. See init/Kconfig for more details. 2192 2193 logo.nologo [FB] Disables display of the built-in Linux logo. 2194 This may be used to provide more screen space for 2195 kernel log messages and is useful when debugging 2196 kernel boot problems. 2197 2198 lp=0 [LP] Specify parallel ports to use, e.g, 2199 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 2200 lp=reset first parallel port). 'lp=0' disables the 2201 lp=auto printer driver. 'lp=reset' (which can be 2202 specified in addition to the ports) causes 2203 attached printers to be reset. Using 2204 lp=port1,port2,... specifies the parallel ports 2205 to associate lp devices with, starting with 2206 lp0. A port specification may be 'none' to skip 2207 that lp device, or a parport name such as 2208 'parport0'. Specifying 'lp=auto' instead of a 2209 port specification list means that device IDs 2210 from each port should be examined, to see if 2211 an IEEE 1284-compliant printer is attached; if 2212 so, the driver will manage that printer. 2213 See also header of drivers/char/lp.c. 2214 2215 lpj=n [KNL] 2216 Sets loops_per_jiffy to given constant, thus avoiding 2217 time-consuming boot-time autodetection (up to 250 ms per 2218 CPU). 0 enables autodetection (default). To determine 2219 the correct value for your kernel, boot with normal 2220 autodetection and see what value is printed. Note that 2221 on SMP systems the preset will be applied to all CPUs, 2222 which is likely to cause problems if your CPUs need 2223 significantly divergent settings. An incorrect value 2224 will cause delays in the kernel to be wrong, leading to 2225 unpredictable I/O errors and other breakage. Although 2226 unlikely, in the extreme case this might damage your 2227 hardware. 2228 2229 ltpc= [NET] 2230 Format: <io>,<irq>,<dma> 2231 2232 machvec= [IA-64] Force the use of a particular machine-vector 2233 (machvec) in a generic kernel. 2234 Example: machvec=hpzx1_swiotlb 2235 2236 machtype= [Loongson] Share the same kernel image file between different 2237 yeeloong laptop. 2238 Example: machtype=lemote-yeeloong-2f-7inch 2239 2240 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater 2241 than or equal to this physical address is ignored. 2242 2243 maxcpus= [SMP] Maximum number of processors that an SMP kernel 2244 will bring up during bootup. maxcpus=n : n >= 0 limits 2245 the kernel to bring up 'n' processors. Surely after 2246 bootup you can bring up the other plugged cpu by executing 2247 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 2248 only takes effect during system bootup. 2249 While n=0 is a special case, it is equivalent to "nosmp", 2250 which also disables the IO APIC. 2251 2252 max_loop= [LOOP] The number of loop block devices that get 2253 (loop.max_loop) unconditionally pre-created at init time. The default 2254 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 2255 of statically allocating a predefined number, loop 2256 devices can be requested on-demand with the 2257 /dev/loop-control interface. 2258 2259 mce [X86-32] Machine Check Exception 2260 2261 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt 2262 2263 md= [HW] RAID subsystems devices and level 2264 See Documentation/md.txt. 2265 2266 mdacon= [MDA] 2267 Format: <first>,<last> 2268 Specifies range of consoles to be captured by the MDA. 2269 2270 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory 2271 Amount of memory to be used when the kernel is not able 2272 to see the whole system memory or for test. 2273 [X86] Work as limiting max address. Use together 2274 with memmap= to avoid physical address space collisions. 2275 Without memmap= PCI devices could be placed at addresses 2276 belonging to unused RAM. 2277 2278 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 2279 memory. 2280 2281 memchunk=nn[KMG] 2282 [KNL,SH] Allow user to override the default size for 2283 per-device physically contiguous DMA buffers. 2284 2285 memhp_default_state=online/offline 2286 [KNL] Set the initial state for the memory hotplug 2287 onlining policy. If not specified, the default value is 2288 set according to the 2289 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config 2290 option. 2291 See Documentation/memory-hotplug.txt. 2292 2293 memmap=exactmap [KNL,X86] Enable setting of an exact 2294 E820 memory map, as specified by the user. 2295 Such memmap=exactmap lines can be constructed based on 2296 BIOS output or other requirements. See the memmap=nn@ss 2297 option description. 2298 2299 memmap=nn[KMG]@ss[KMG] 2300 [KNL] Force usage of a specific region of memory. 2301 Region of memory to be used is from ss to ss+nn. 2302 2303 memmap=nn[KMG]#ss[KMG] 2304 [KNL,ACPI] Mark specific memory as ACPI data. 2305 Region of memory to be marked is from ss to ss+nn. 2306 2307 memmap=nn[KMG]$ss[KMG] 2308 [KNL,ACPI] Mark specific memory as reserved. 2309 Region of memory to be reserved is from ss to ss+nn. 2310 Example: Exclude memory from 0x18690000-0x1869ffff 2311 memmap=64K$0x18690000 2312 or 2313 memmap=0x10000$0x18690000 2314 2315 memmap=nn[KMG]!ss[KMG] 2316 [KNL,X86] Mark specific memory as protected. 2317 Region of memory to be used, from ss to ss+nn. 2318 The memory region may be marked as e820 type 12 (0xc) 2319 and is NVDIMM or ADR memory. 2320 2321 memory_corruption_check=0/1 [X86] 2322 Some BIOSes seem to corrupt the first 64k of 2323 memory when doing things like suspend/resume. 2324 Setting this option will scan the memory 2325 looking for corruption. Enabling this will 2326 both detect corruption and prevent the kernel 2327 from using the memory being corrupted. 2328 However, its intended as a diagnostic tool; if 2329 repeatable BIOS-originated corruption always 2330 affects the same memory, you can use memmap= 2331 to prevent the kernel from using that memory. 2332 2333 memory_corruption_check_size=size [X86] 2334 By default it checks for corruption in the low 2335 64k, making this memory unavailable for normal 2336 use. Use this parameter to scan for 2337 corruption in more or less memory. 2338 2339 memory_corruption_check_period=seconds [X86] 2340 By default it checks for corruption every 60 2341 seconds. Use this parameter to check at some 2342 other rate. 0 disables periodic checking. 2343 2344 memtest= [KNL,X86,ARM] Enable memtest 2345 Format: <integer> 2346 default : 0 <disable> 2347 Specifies the number of memtest passes to be 2348 performed. Each pass selects another test 2349 pattern from a given set of patterns. Memtest 2350 fills the memory with this pattern, validates 2351 memory contents and reserves bad memory 2352 regions that are detected. 2353 2354 meye.*= [HW] Set MotionEye Camera parameters 2355 See Documentation/video4linux/meye.txt. 2356 2357 mfgpt_irq= [IA-32] Specify the IRQ to use for the 2358 Multi-Function General Purpose Timers on AMD Geode 2359 platforms. 2360 2361 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 2362 the BIOS has incorrectly applied a workaround. TinyBIOS 2363 version 0.98 is known to be affected, 0.99 fixes the 2364 problem by letting the user disable the workaround. 2365 2366 mga= [HW,DRM] 2367 2368 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this 2369 physical address is ignored. 2370 2371 mini2440= [ARM,HW,KNL] 2372 Format:[0..2][b][c][t] 2373 Default: "0tb" 2374 MINI2440 configuration specification: 2375 0 - The attached screen is the 3.5" TFT 2376 1 - The attached screen is the 7" TFT 2377 2 - The VGA Shield is attached (1024x768) 2378 Leaving out the screen size parameter will not load 2379 the TFT driver, and the framebuffer will be left 2380 unconfigured. 2381 b - Enable backlight. The TFT backlight pin will be 2382 linked to the kernel VESA blanking code and a GPIO 2383 LED. This parameter is not necessary when using the 2384 VGA shield. 2385 c - Enable the s3c camera interface. 2386 t - Reserved for enabling touchscreen support. The 2387 touchscreen support is not enabled in the mainstream 2388 kernel as of 2.6.30, a preliminary port can be found 2389 in the "bleeding edge" mini2440 support kernel at 2390 http://repo.or.cz/w/linux-2.6/mini2440.git 2391 2392 mminit_loglevel= 2393 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this 2394 parameter allows control of the logging verbosity for 2395 the additional memory initialisation checks. A value 2396 of 0 disables mminit logging and a level of 4 will 2397 log everything. Information is printed at KERN_DEBUG 2398 so loglevel=8 may also need to be specified. 2399 2400 module.sig_enforce 2401 [KNL] When CONFIG_MODULE_SIG is set, this means that 2402 modules without (valid) signatures will fail to load. 2403 Note that if CONFIG_MODULE_SIG_FORCE is set, that 2404 is always true, so this option does nothing. 2405 2406 module_blacklist= [KNL] Do not load a comma-separated list of 2407 modules. Useful for debugging problem modules. 2408 2409 mousedev.tap_time= 2410 [MOUSE] Maximum time between finger touching and 2411 leaving touchpad surface for touch to be considered 2412 a tap and be reported as a left button click (for 2413 touchpads working in absolute mode only). 2414 Format: <msecs> 2415 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 2416 reporting absolute coordinates, such as tablets 2417 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 2418 reporting absolute coordinates, such as tablets 2419 2420 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter 2421 is similar to kernelcore except it specifies the 2422 amount of memory used for migratable allocations. 2423 If both kernelcore and movablecore is specified, 2424 then kernelcore will be at *least* the specified 2425 value but may be more. If movablecore on its own 2426 is specified, the administrator must be careful 2427 that the amount of memory usable for all allocations 2428 is not too small. 2429 2430 movable_node [KNL,X86] Boot-time switch to enable the effects 2431 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details. 2432 2433 MTD_Partition= [MTD] 2434 Format: <name>,<region-number>,<size>,<offset> 2435 2436 MTD_Region= [MTD] Format: 2437 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 2438 2439 mtdparts= [MTD] 2440 See drivers/mtd/cmdlinepart.c. 2441 2442 multitce=off [PPC] This parameter disables the use of the pSeries 2443 firmware feature for updating multiple TCE entries 2444 at a time. 2445 2446 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 2447 2448 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 2449 2450 boundary - index of last SLC block on Flex-OneNAND. 2451 The remaining blocks are configured as MLC blocks. 2452 lock - Configure if Flex-OneNAND boundary should be locked. 2453 Once locked, the boundary cannot be changed. 2454 1 indicates lock status, 0 indicates unlock status. 2455 2456 mtdset= [ARM] 2457 ARM/S3C2412 JIVE boot control 2458 2459 See arch/arm/mach-s3c2412/mach-jive.c 2460 2461 mtouchusb.raw_coordinates= 2462 [HW] Make the MicroTouch USB driver use raw coordinates 2463 ('y', default) or cooked coordinates ('n') 2464 2465 mtrr_chunk_size=nn[KMG] [X86] 2466 used for mtrr cleanup. It is largest continuous chunk 2467 that could hold holes aka. UC entries. 2468 2469 mtrr_gran_size=nn[KMG] [X86] 2470 Used for mtrr cleanup. It is granularity of mtrr block. 2471 Default is 1. 2472 Large value could prevent small alignment from 2473 using up MTRRs. 2474 2475 mtrr_spare_reg_nr=n [X86] 2476 Format: <integer> 2477 Range: 0,7 : spare reg number 2478 Default : 1 2479 Used for mtrr cleanup. It is spare mtrr entries number. 2480 Set to 2 or more if your graphical card needs more. 2481 2482 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 2483 2484 netdev= [NET] Network devices parameters 2485 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 2486 Note that mem_start is often overloaded to mean 2487 something different and driver-specific. 2488 This usage is only documented in each driver source 2489 file if at all. 2490 2491 nf_conntrack.acct= 2492 [NETFILTER] Enable connection tracking flow accounting 2493 0 to disable accounting 2494 1 to enable accounting 2495 Default value is 0. 2496 2497 nfsaddrs= [NFS] Deprecated. Use ip= instead. 2498 See Documentation/filesystems/nfs/nfsroot.txt. 2499 2500 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 2501 See Documentation/filesystems/nfs/nfsroot.txt. 2502 2503 nfsrootdebug [NFS] enable nfsroot debugging messages. 2504 See Documentation/filesystems/nfs/nfsroot.txt. 2505 2506 nfs.callback_nr_threads= 2507 [NFSv4] set the total number of threads that the 2508 NFS client will assign to service NFSv4 callback 2509 requests. 2510 2511 nfs.callback_tcpport= 2512 [NFS] set the TCP port on which the NFSv4 callback 2513 channel should listen. 2514 2515 nfs.cache_getent= 2516 [NFS] sets the pathname to the program which is used 2517 to update the NFS client cache entries. 2518 2519 nfs.cache_getent_timeout= 2520 [NFS] sets the timeout after which an attempt to 2521 update a cache entry is deemed to have failed. 2522 2523 nfs.idmap_cache_timeout= 2524 [NFS] set the maximum lifetime for idmapper cache 2525 entries. 2526 2527 nfs.enable_ino64= 2528 [NFS] enable 64-bit inode numbers. 2529 If zero, the NFS client will fake up a 32-bit inode 2530 number for the readdir() and stat() syscalls instead 2531 of returning the full 64-bit number. 2532 The default is to return 64-bit inode numbers. 2533 2534 nfs.max_session_cb_slots= 2535 [NFSv4.1] Sets the maximum number of session 2536 slots the client will assign to the callback 2537 channel. This determines the maximum number of 2538 callbacks the client will process in parallel for 2539 a particular server. 2540 2541 nfs.max_session_slots= 2542 [NFSv4.1] Sets the maximum number of session slots 2543 the client will attempt to negotiate with the server. 2544 This limits the number of simultaneous RPC requests 2545 that the client can send to the NFSv4.1 server. 2546 Note that there is little point in setting this 2547 value higher than the max_tcp_slot_table_limit. 2548 2549 nfs.nfs4_disable_idmapping= 2550 [NFSv4] When set to the default of '1', this option 2551 ensures that both the RPC level authentication 2552 scheme and the NFS level operations agree to use 2553 numeric uids/gids if the mount is using the 2554 'sec=sys' security flavour. In effect it is 2555 disabling idmapping, which can make migration from 2556 legacy NFSv2/v3 systems to NFSv4 easier. 2557 Servers that do not support this mode of operation 2558 will be autodetected by the client, and it will fall 2559 back to using the idmapper. 2560 To turn off this behaviour, set the value to '0'. 2561 nfs.nfs4_unique_id= 2562 [NFS4] Specify an additional fixed unique ident- 2563 ification string that NFSv4 clients can insert into 2564 their nfs_client_id4 string. This is typically a 2565 UUID that is generated at system install time. 2566 2567 nfs.send_implementation_id = 2568 [NFSv4.1] Send client implementation identification 2569 information in exchange_id requests. 2570 If zero, no implementation identification information 2571 will be sent. 2572 The default is to send the implementation identification 2573 information. 2574 2575 nfs.recover_lost_locks = 2576 [NFSv4] Attempt to recover locks that were lost due 2577 to a lease timeout on the server. Please note that 2578 doing this risks data corruption, since there are 2579 no guarantees that the file will remain unchanged 2580 after the locks are lost. 2581 If you want to enable the kernel legacy behaviour of 2582 attempting to recover these locks, then set this 2583 parameter to '1'. 2584 The default parameter value of '0' causes the kernel 2585 not to attempt recovery of lost locks. 2586 2587 nfs4.layoutstats_timer = 2588 [NFSv4.2] Change the rate at which the kernel sends 2589 layoutstats to the pNFS metadata server. 2590 2591 Setting this to value to 0 causes the kernel to use 2592 whatever value is the default set by the layout 2593 driver. A non-zero value sets the minimum interval 2594 in seconds between layoutstats transmissions. 2595 2596 nfsd.nfs4_disable_idmapping= 2597 [NFSv4] When set to the default of '1', the NFSv4 2598 server will return only numeric uids and gids to 2599 clients using auth_sys, and will accept numeric uids 2600 and gids from such clients. This is intended to ease 2601 migration from NFSv2/v3. 2602 2603 objlayoutdriver.osd_login_prog= 2604 [NFS] [OBJLAYOUT] sets the pathname to the program which 2605 is used to automatically discover and login into new 2606 osd-targets. Please see: 2607 Documentation/filesystems/pnfs.txt for more explanations 2608 2609 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take 2610 when a NMI is triggered. 2611 Format: [state][,regs][,debounce][,die] 2612 2613 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 2614 Format: [panic,][nopanic,][num] 2615 Valid num: 0 or 1 2616 0 - turn hardlockup detector in nmi_watchdog off 2617 1 - turn hardlockup detector in nmi_watchdog on 2618 When panic is specified, panic when an NMI watchdog 2619 timeout occurs (or 'nopanic' to override the opposite 2620 default). To disable both hard and soft lockup detectors, 2621 please see 'nowatchdog'. 2622 This is useful when you use a panic=... timeout and 2623 need the box quickly up again. 2624 2625 netpoll.carrier_timeout= 2626 [NET] Specifies amount of time (in seconds) that 2627 netpoll should wait for a carrier. By default netpoll 2628 waits 4 seconds. 2629 2630 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 2631 emulation library even if a 387 maths coprocessor 2632 is present. 2633 2634 no_console_suspend 2635 [HW] Never suspend the console 2636 Disable suspending of consoles during suspend and 2637 hibernate operations. Once disabled, debugging 2638 messages can reach various consoles while the rest 2639 of the system is being put to sleep (ie, while 2640 debugging driver suspend/resume hooks). This may 2641 not work reliably with all consoles, but is known 2642 to work with serial and VGA consoles. 2643 To facilitate more flexible debugging, we also add 2644 console_suspend, a printk module parameter to control 2645 it. Users could use console_suspend (usually 2646 /sys/module/printk/parameters/console_suspend) to 2647 turn on/off it dynamically. 2648 2649 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien 2650 caches in the slab allocator. Saves per-node memory, 2651 but will impact performance. 2652 2653 noalign [KNL,ARM] 2654 2655 noaltinstr [S390] Disables alternative instructions patching 2656 (CPU alternatives feature). 2657 2658 noapic [SMP,APIC] Tells the kernel to not make use of any 2659 IOAPICs that may be present in the system. 2660 2661 noautogroup Disable scheduler automatic task group creation. 2662 2663 nobats [PPC] Do not use BATs for mapping kernel lowmem 2664 on "Classic" PPC cores. 2665 2666 nocache [ARM] 2667 2668 noclflush [BUGS=X86] Don't use the CLFLUSH instruction 2669 2670 nodelayacct [KNL] Disable per-task delay accounting 2671 2672 nodsp [SH] Disable hardware DSP at boot time. 2673 2674 noefi Disable EFI runtime services support. 2675 2676 noexec [IA-64] 2677 2678 noexec [X86] 2679 On X86-32 available only on PAE configured kernels. 2680 noexec=on: enable non-executable mappings (default) 2681 noexec=off: disable non-executable mappings 2682 2683 nosmap [X86] 2684 Disable SMAP (Supervisor Mode Access Prevention) 2685 even if it is supported by processor. 2686 2687 nosmep [X86] 2688 Disable SMEP (Supervisor Mode Execution Prevention) 2689 even if it is supported by processor. 2690 2691 noexec32 [X86-64] 2692 This affects only 32-bit executables. 2693 noexec32=on: enable non-executable mappings (default) 2694 read doesn't imply executable mappings 2695 noexec32=off: disable non-executable mappings 2696 read implies executable mappings 2697 2698 nofpu [MIPS,SH] Disable hardware FPU at boot time. 2699 2700 nofxsr [BUGS=X86-32] Disables x86 floating point extended 2701 register save and restore. The kernel will only save 2702 legacy floating-point registers on task switch. 2703 2704 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings. 2705 2706 nosmt [KNL,S390] Disable symmetric multithreading (SMT). 2707 Equivalent to smt=1. 2708 2709 nospectre_v2 [X86] Disable all mitigations for the Spectre variant 2 2710 (indirect branch prediction) vulnerability. System may 2711 allow data leaks with this option, which is equivalent 2712 to spectre_v2=off. 2713 2714 noxsave [BUGS=X86] Disables x86 extended register state save 2715 and restore using xsave. The kernel will fallback to 2716 enabling legacy floating-point and sse state. 2717 2718 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 2719 register states. The kernel will fall back to use 2720 xsave to save the states. By using this parameter, 2721 performance of saving the states is degraded because 2722 xsave doesn't support modified optimization while 2723 xsaveopt supports it on xsaveopt enabled systems. 2724 2725 noxsaves [X86] Disables xsaves and xrstors used in saving and 2726 restoring x86 extended register state in compacted 2727 form of xsave area. The kernel will fall back to use 2728 xsaveopt and xrstor to save and restore the states 2729 in standard form of xsave area. By using this 2730 parameter, xsave area per process might occupy more 2731 memory on xsaves enabled systems. 2732 2733 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or 2734 wfi(ARM) instruction doesn't work correctly and not to 2735 use it. This is also useful when using JTAG debugger. 2736 2737 no_file_caps Tells the kernel not to honor file capabilities. The 2738 only way then for a file to be executed with privilege 2739 is to be setuid root or executed by root. 2740 2741 nohalt [IA-64] Tells the kernel not to use the power saving 2742 function PAL_HALT_LIGHT when idle. This increases 2743 power-consumption. On the positive side, it reduces 2744 interrupt wake-up latency, which may improve performance 2745 in certain environments such as networked servers or 2746 real-time systems. 2747 2748 nohibernate [HIBERNATION] Disable hibernation and resume. 2749 2750 nohz= [KNL] Boottime enable/disable dynamic ticks 2751 Valid arguments: on, off 2752 Default: on 2753 2754 nohz_full= [KNL,BOOT] 2755 The argument is a cpu list, as described above. 2756 In kernels built with CONFIG_NO_HZ_FULL=y, set 2757 the specified list of CPUs whose tick will be stopped 2758 whenever possible. The boot CPU will be forced outside 2759 the range to maintain the timekeeping. 2760 The CPUs in this range must also be included in the 2761 rcu_nocbs= set. 2762 2763 noiotrap [SH] Disables trapped I/O port accesses. 2764 2765 noirqdebug [X86-32] Disables the code which attempts to detect and 2766 disable unhandled interrupt sources. 2767 2768 no_timer_check [X86,APIC] Disables the code which tests for 2769 broken timer IRQ sources. 2770 2771 noisapnp [ISAPNP] Disables ISA PnP code. 2772 2773 noinitrd [RAM] Tells the kernel not to load any configured 2774 initial RAM disk. 2775 2776 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt 2777 remapping. 2778 [Deprecated - use intremap=off] 2779 2780 nointroute [IA-64] 2781 2782 noinvpcid [X86] Disable the INVPCID cpu feature. 2783 2784 nojitter [IA-64] Disables jitter checking for ITC timers. 2785 2786 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver 2787 2788 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page 2789 fault handling. 2790 2791 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting. 2792 steal time is computed, but won't influence scheduler 2793 behaviour 2794 2795 nolapic [X86-32,APIC] Do not enable or use the local APIC. 2796 2797 nolapic_timer [X86-32,APIC] Do not use the local APIC timer. 2798 2799 noltlbs [PPC] Do not use large page/tlb entries for kernel 2800 lowmem mapping on PPC40x and PPC8xx 2801 2802 nomca [IA-64] Disable machine check abort handling 2803 2804 nomce [X86-32] Disable Machine Check Exception 2805 2806 nomfgpt [X86-32] Disable Multi-Function General Purpose 2807 Timer usage (for AMD Geode machines). 2808 2809 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 2810 shutdown the other cpus. Instead use the REBOOT_VECTOR 2811 irq. 2812 2813 nomodule Disable module load 2814 2815 nopat [X86] Disable PAT (page attribute table extension of 2816 pagetables) support. 2817 2818 nopcid [X86-64] Disable the PCID cpu feature. 2819 2820 norandmaps Don't use address space randomization. Equivalent to 2821 echo 0 > /proc/sys/kernel/randomize_va_space 2822 2823 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 2824 with UP alternatives 2825 2826 nordrand [X86] Disable kernel use of the RDRAND and 2827 RDSEED instructions even if they are supported 2828 by the processor. RDRAND and RDSEED are still 2829 available to user space applications. 2830 2831 noresume [SWSUSP] Disables resume and restores original swap 2832 space. 2833 2834 no-scroll [VGA] Disables scrollback. 2835 This is required for the Braillex ib80-piezo Braille 2836 reader made by F.H. Papenmeier (Germany). 2837 2838 nosbagart [IA-64] 2839 2840 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support. 2841 2842 nosmp [SMP] Tells an SMP kernel to act as a UP kernel, 2843 and disable the IO APIC. legacy for "maxcpus=0". 2844 2845 nosoftlockup [KNL] Disable the soft-lockup detector. 2846 2847 nosync [HW,M68K] Disables sync negotiation for all devices. 2848 2849 notsc [BUGS=X86-32] Disable Time Stamp Counter 2850 2851 nowatchdog [KNL] Disable both lockup detectors, i.e. 2852 soft-lockup and NMI watchdog (hard-lockup). 2853 2854 nowb [ARM] 2855 2856 nox2apic [X86-64,APIC] Do not enable x2APIC mode. 2857 2858 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when 2859 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off. 2860 Some features depend on CPU0. Known dependencies are: 2861 1. Resume from suspend/hibernate depends on CPU0. 2862 Suspend/hibernate will fail if CPU0 is offline and you 2863 need to online CPU0 before suspend/hibernate. 2864 2. PIC interrupts also depend on CPU0. CPU0 can't be 2865 removed if a PIC interrupt is detected. 2866 It's said poweroff/reboot may depend on CPU0 on some 2867 machines although I haven't seen such issues so far 2868 after CPU0 is offline on a few tested machines. 2869 If the dependencies are under your control, you can 2870 turn on cpu0_hotplug. 2871 2872 nptcg= [IA-64] Override max number of concurrent global TLB 2873 purges which is reported from either PAL_VM_SUMMARY or 2874 SAL PALO. 2875 2876 nr_cpus= [SMP] Maximum number of processors that an SMP kernel 2877 could support. nr_cpus=n : n >= 1 limits the kernel to 2878 support 'n' processors. It could be larger than the 2879 number of already plugged CPU during bootup, later in 2880 runtime you can physically add extra cpu until it reaches 2881 n. So during boot up some boot time memory for per-cpu 2882 variables need be pre-allocated for later physical cpu 2883 hot plugging. 2884 2885 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 2886 2887 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing. 2888 Allowed values are enable and disable 2889 2890 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 2891 one of ['zone', 'node', 'default'] can be specified 2892 This can be set from sysctl after boot. 2893 See Documentation/sysctl/vm.txt for details. 2894 2895 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver. 2896 See Documentation/debugging-via-ohci1394.txt for more 2897 info. 2898 2899 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 2900 Rather than timing out after 20 ms if an EC 2901 command is not properly ACKed, override the length 2902 of the timeout. We have interrupts disabled while 2903 waiting for the ACK, so if this is set too high 2904 interrupts *may* be lost! 2905 2906 omap_mux= [OMAP] Override bootloader pin multiplexing. 2907 Format: <mux_mode0.mode_name=value>... 2908 For example, to override I2C bus2: 2909 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 2910 2911 oprofile.timer= [HW] 2912 Use timer interrupt instead of performance counters 2913 2914 oprofile.cpu_type= Force an oprofile cpu type 2915 This might be useful if you have an older oprofile 2916 userland or if you want common events. 2917 Format: { arch_perfmon } 2918 arch_perfmon: [X86] Force use of architectural 2919 perfmon on Intel CPUs instead of the 2920 CPU specific event set. 2921 timer: [X86] Force use of architectural NMI 2922 timer mode (see also oprofile.timer 2923 for generic hr timer mode) 2924 2925 oops=panic Always panic on oopses. Default is to just kill the 2926 process, but there is a small probability of 2927 deadlocking the machine. 2928 This will also cause panics on machine check exceptions. 2929 Useful together with panic=30 to trigger a reboot. 2930 2931 OSS [HW,OSS] 2932 See Documentation/sound/oss/oss-parameters.txt 2933 2934 page_owner= [KNL] Boot-time page_owner enabling option. 2935 Storage of the information about who allocated 2936 each page is disabled in default. With this switch, 2937 we can turn it on. 2938 on: enable the feature 2939 2940 page_poison= [KNL] Boot-time parameter changing the state of 2941 poisoning on the buddy allocator. 2942 off: turn off poisoning 2943 on: turn on poisoning 2944 2945 panic= [KNL] Kernel behaviour on panic: delay <timeout> 2946 timeout > 0: seconds before rebooting 2947 timeout = 0: wait forever 2948 timeout < 0: reboot immediately 2949 Format: <timeout> 2950 2951 panic_on_warn panic() instead of WARN(). Useful to cause kdump 2952 on a WARN(). 2953 2954 crash_kexec_post_notifiers 2955 Run kdump after running panic-notifiers and dumping 2956 kmsg. This only for the users who doubt kdump always 2957 succeeds in any situation. 2958 Note that this also increases risks of kdump failure, 2959 because some panic notifiers can make the crashed 2960 kernel more unstable. 2961 2962 parkbd.port= [HW] Parallel port number the keyboard adapter is 2963 connected to, default is 0. 2964 Format: <parport#> 2965 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 2966 0 for XT, 1 for AT (default is AT). 2967 Format: <mode> 2968 2969 parport= [HW,PPT] Specify parallel ports. 0 disables. 2970 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 2971 Use 'auto' to force the driver to use any 2972 IRQ/DMA settings detected (the default is to 2973 ignore detected IRQ/DMA settings because of 2974 possible conflicts). You can specify the base 2975 address, IRQ, and DMA settings; IRQ and DMA 2976 should be numbers, or 'auto' (for using detected 2977 settings on that particular port), or 'nofifo' 2978 (to avoid using a FIFO even if it is detected). 2979 Parallel ports are assigned in the order they 2980 are specified on the command line, starting 2981 with parport0. 2982 2983 parport_init_mode= [HW,PPT] 2984 Configure VIA parallel port to operate in 2985 a specific mode. This is necessary on Pegasos 2986 computer where firmware has no options for setting 2987 up parallel port mode and sets it to spp. 2988 Currently this function knows 686a and 8231 chips. 2989 Format: [spp|ps2|epp|ecp|ecpepp] 2990 2991 pause_on_oops= 2992 Halt all CPUs after the first oops has been printed for 2993 the specified number of seconds. This is to be used if 2994 your oopses keep scrolling off the screen. 2995 2996 pcbit= [HW,ISDN] 2997 2998 pcd. [PARIDE] 2999 See header of drivers/block/paride/pcd.c. 3000 See also Documentation/blockdev/paride.txt. 3001 3002 pci=option[,option...] [PCI] various PCI subsystem options: 3003 earlydump [X86] dump PCI config space before the kernel 3004 changes anything 3005 off [X86] don't probe for the PCI bus 3006 bios [X86-32] force use of PCI BIOS, don't access 3007 the hardware directly. Use this if your machine 3008 has a non-standard PCI host bridge. 3009 nobios [X86-32] disallow use of PCI BIOS, only direct 3010 hardware access methods are allowed. Use this 3011 if you experience crashes upon bootup and you 3012 suspect they are caused by the BIOS. 3013 conf1 [X86] Force use of PCI Configuration Access 3014 Mechanism 1 (config address in IO port 0xCF8, 3015 data in IO port 0xCFC, both 32-bit). 3016 conf2 [X86] Force use of PCI Configuration Access 3017 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 3018 the function, IO port 0xCFA, also 8-bit, sets 3019 bus number. The config space is then accessed 3020 through ports 0xC000-0xCFFF). 3021 See http://wiki.osdev.org/PCI for more info 3022 on the configuration access mechanisms. 3023 noaer [PCIE] If the PCIEAER kernel config parameter is 3024 enabled, this kernel boot option can be used to 3025 disable the use of PCIE advanced error reporting. 3026 nodomains [PCI] Disable support for multiple PCI 3027 root domains (aka PCI segments, in ACPI-speak). 3028 nommconf [X86] Disable use of MMCONFIG for PCI 3029 Configuration 3030 check_enable_amd_mmconf [X86] check for and enable 3031 properly configured MMIO access to PCI 3032 config space on AMD family 10h CPU 3033 nomsi [MSI] If the PCI_MSI kernel config parameter is 3034 enabled, this kernel boot option can be used to 3035 disable the use of MSI interrupts system-wide. 3036 noioapicquirk [APIC] Disable all boot interrupt quirks. 3037 Safety option to keep boot IRQs enabled. This 3038 should never be necessary. 3039 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 3040 primary IO-APIC for bridges that cannot disable 3041 boot IRQs. This fixes a source of spurious IRQs 3042 when the system masks IRQs. 3043 noioapicreroute [APIC] Disable workaround that uses the 3044 boot IRQ equivalent of an IRQ that connects to 3045 a chipset where boot IRQs cannot be disabled. 3046 The opposite of ioapicreroute. 3047 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 3048 routing table. These calls are known to be buggy 3049 on several machines and they hang the machine 3050 when used, but on other computers it's the only 3051 way to get the interrupt routing table. Try 3052 this option if the kernel is unable to allocate 3053 IRQs or discover secondary PCI buses on your 3054 motherboard. 3055 rom [X86] Assign address space to expansion ROMs. 3056 Use with caution as certain devices share 3057 address decoders between ROMs and other 3058 resources. 3059 norom [X86] Do not assign address space to 3060 expansion ROMs that do not already have 3061 BIOS assigned address ranges. 3062 nobar [X86] Do not assign address space to the 3063 BARs that weren't assigned by the BIOS. 3064 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 3065 assigned automatically to PCI devices. You can 3066 make the kernel exclude IRQs of your ISA cards 3067 this way. 3068 pirqaddr=0xAAAAA [X86] Specify the physical address 3069 of the PIRQ table (normally generated 3070 by the BIOS) if it is outside the 3071 F0000h-100000h range. 3072 lastbus=N [X86] Scan all buses thru bus #N. Can be 3073 useful if the kernel is unable to find your 3074 secondary buses and you want to tell it 3075 explicitly which ones they are. 3076 assign-busses [X86] Always assign all PCI bus 3077 numbers ourselves, overriding 3078 whatever the firmware may have done. 3079 usepirqmask [X86] Honor the possible IRQ mask stored 3080 in the BIOS $PIR table. This is needed on 3081 some systems with broken BIOSes, notably 3082 some HP Pavilion N5400 and Omnibook XE3 3083 notebooks. This will have no effect if ACPI 3084 IRQ routing is enabled. 3085 noacpi [X86] Do not use ACPI for IRQ routing 3086 or for PCI scanning. 3087 use_crs [X86] Use PCI host bridge window information 3088 from ACPI. On BIOSes from 2008 or later, this 3089 is enabled by default. If you need to use this, 3090 please report a bug. 3091 nocrs [X86] Ignore PCI host bridge windows from ACPI. 3092 If you need to use this, please report a bug. 3093 routeirq Do IRQ routing for all PCI devices. 3094 This is normally done in pci_enable_device(), 3095 so this option is a temporary workaround 3096 for broken drivers that don't call it. 3097 skip_isa_align [X86] do not align io start addr, so can 3098 handle more pci cards 3099 noearly [X86] Don't do any early type 1 scanning. 3100 This might help on some broken boards which 3101 machine check when some devices' config space 3102 is read. But various workarounds are disabled 3103 and some IOMMU drivers will not work. 3104 bfsort Sort PCI devices into breadth-first order. 3105 This sorting is done to get a device 3106 order compatible with older (<= 2.4) kernels. 3107 nobfsort Don't sort PCI devices into breadth-first order. 3108 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 3109 tuning and use the BIOS-configured MPS defaults. 3110 pcie_bus_safe Set every device's MPS to the largest value 3111 supported by all devices below the root complex. 3112 pcie_bus_perf Set device MPS to the largest allowable MPS 3113 based on its parent bus. Also set MRRS (Max 3114 Read Request Size) to the largest supported 3115 value (no larger than the MPS that the device 3116 or bus can support) for best performance. 3117 pcie_bus_peer2peer Set every device's MPS to 128B, which 3118 every device is guaranteed to support. This 3119 configuration allows peer-to-peer DMA between 3120 any pair of devices, possibly at the cost of 3121 reduced performance. This also guarantees 3122 that hot-added devices will work. 3123 cbiosize=nn[KMG] The fixed amount of bus space which is 3124 reserved for the CardBus bridge's IO window. 3125 The default value is 256 bytes. 3126 cbmemsize=nn[KMG] The fixed amount of bus space which is 3127 reserved for the CardBus bridge's memory 3128 window. The default value is 64 megabytes. 3129 resource_alignment= 3130 Format: 3131 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...] 3132 [<order of align>@]pci:<vendor>:<device>\ 3133 [:<subvendor>:<subdevice>][; ...] 3134 Specifies alignment and device to reassign 3135 aligned memory resources. 3136 If <order of align> is not specified, 3137 PAGE_SIZE is used as alignment. 3138 PCI-PCI bridge can be specified, if resource 3139 windows need to be expanded. 3140 To specify the alignment for several 3141 instances of a device, the PCI vendor, 3142 device, subvendor, and subdevice may be 3143 specified, e.g., 4096@pci:8086:9c22:103c:198f 3144 ecrc= Enable/disable PCIe ECRC (transaction layer 3145 end-to-end CRC checking). 3146 bios: Use BIOS/firmware settings. This is the 3147 the default. 3148 off: Turn ECRC off 3149 on: Turn ECRC on. 3150 hpiosize=nn[KMG] The fixed amount of bus space which is 3151 reserved for hotplug bridge's IO window. 3152 Default size is 256 bytes. 3153 hpmemsize=nn[KMG] The fixed amount of bus space which is 3154 reserved for hotplug bridge's memory window. 3155 Default size is 2 megabytes. 3156 hpbussize=nn The minimum amount of additional bus numbers 3157 reserved for buses below a hotplug bridge. 3158 Default is 1. 3159 realloc= Enable/disable reallocating PCI bridge resources 3160 if allocations done by BIOS are too small to 3161 accommodate resources required by all child 3162 devices. 3163 off: Turn realloc off 3164 on: Turn realloc on 3165 realloc same as realloc=on 3166 noari do not use PCIe ARI. 3167 pcie_scan_all Scan all possible PCIe devices. Otherwise we 3168 only look for one device below a PCIe downstream 3169 port. 3170 3171 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power 3172 Management. 3173 off Disable ASPM. 3174 force Enable ASPM even on devices that claim not to support it. 3175 WARNING: Forcing ASPM on may cause system lockups. 3176 3177 pcie_hp= [PCIE] PCI Express Hotplug driver options: 3178 nomsi Do not use MSI for PCI Express Native Hotplug (this 3179 makes all PCIe ports use INTx for hotplug services). 3180 3181 pcie_ports= [PCIE] PCIe ports handling: 3182 auto Ask the BIOS whether or not to use native PCIe services 3183 associated with PCIe ports (PME, hot-plug, AER). Use 3184 them only if that is allowed by the BIOS. 3185 native Use native PCIe services associated with PCIe ports 3186 unconditionally. 3187 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe 3188 ports driver. 3189 3190 pcie_port_pm= [PCIE] PCIe port power management handling: 3191 off Disable power management of all PCIe ports 3192 force Forcibly enable power management of all PCIe ports 3193 3194 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 3195 nomsi Do not use MSI for native PCIe PME signaling (this makes 3196 all PCIe root ports use INTx for all services). 3197 3198 pcmv= [HW,PCMCIA] BadgePAD 4 3199 3200 pd_ignore_unused 3201 [PM] 3202 Keep all power-domains already enabled by bootloader on, 3203 even if no driver has claimed them. This is useful 3204 for debug and development, but should not be 3205 needed on a platform with proper driver support. 3206 3207 pd. [PARIDE] 3208 See Documentation/blockdev/paride.txt. 3209 3210 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 3211 boot time. 3212 Format: { 0 | 1 } 3213 See arch/parisc/kernel/pdc_chassis.c 3214 3215 percpu_alloc= Select which percpu first chunk allocator to use. 3216 Currently supported values are "embed" and "page". 3217 Archs may support subset or none of the selections. 3218 See comments in mm/percpu.c for details on each 3219 allocator. This parameter is primarily for debugging 3220 and performance comparison. 3221 3222 pf. [PARIDE] 3223 See Documentation/blockdev/paride.txt. 3224 3225 pg. [PARIDE] 3226 See Documentation/blockdev/paride.txt. 3227 3228 pirq= [SMP,APIC] Manual mp-table setup 3229 See Documentation/x86/i386/IO-APIC.txt. 3230 3231 plip= [PPT,NET] Parallel port network link 3232 Format: { parport<nr> | timid | 0 } 3233 See also Documentation/parport.txt. 3234 3235 pmtmr= [X86] Manual setup of pmtmr I/O Port. 3236 Override pmtimer IOPort with a hex value. 3237 e.g. pmtmr=0x508 3238 3239 pnp.debug=1 [PNP] 3240 Enable PNP debug messages (depends on the 3241 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 3242 via /sys/module/pnp/parameters/debug. We always show 3243 current resource usage; turning this on also shows 3244 possible settings and some assignment information. 3245 3246 pnpacpi= [ACPI] 3247 { off } 3248 3249 pnpbios= [ISAPNP] 3250 { on | off | curr | res | no-curr | no-res } 3251 3252 pnp_reserve_irq= 3253 [ISAPNP] Exclude IRQs for the autoconfiguration 3254 3255 pnp_reserve_dma= 3256 [ISAPNP] Exclude DMAs for the autoconfiguration 3257 3258 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 3259 Ranges are in pairs (I/O port base and size). 3260 3261 pnp_reserve_mem= 3262 [ISAPNP] Exclude memory regions for the 3263 autoconfiguration. 3264 Ranges are in pairs (memory base and size). 3265 3266 ports= [IP_VS_FTP] IPVS ftp helper module 3267 Default is 21. 3268 Up to 8 (IP_VS_APP_MAX_PORTS) ports 3269 may be specified. 3270 Format: <port>,<port>.... 3271 3272 ppc_strict_facility_enable 3273 [PPC] This option catches any kernel floating point, 3274 Altivec, VSX and SPE outside of regions specifically 3275 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 3276 There is some performance impact when enabling this. 3277 3278 print-fatal-signals= 3279 [KNL] debug: print fatal signals 3280 3281 If enabled, warn about various signal handling 3282 related application anomalies: too many signals, 3283 too many POSIX.1 timers, fatal signals causing a 3284 coredump - etc. 3285 3286 If you hit the warning due to signal overflow, 3287 you might want to try "ulimit -i unlimited". 3288 3289 default: off. 3290 3291 printk.always_kmsg_dump= 3292 Trigger kmsg_dump for cases other than kernel oops or 3293 panics 3294 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3295 default: disabled 3296 3297 printk.devkmsg={on,off,ratelimit} 3298 Control writing to /dev/kmsg. 3299 on - unlimited logging to /dev/kmsg from userspace 3300 off - logging to /dev/kmsg disabled 3301 ratelimit - ratelimit the logging 3302 Default: ratelimit 3303 3304 printk.time= Show timing data prefixed to each printk message line 3305 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3306 3307 processor.max_cstate= [HW,ACPI] 3308 Limit processor to maximum C-state 3309 max_cstate=9 overrides any DMI blacklist limit. 3310 3311 processor.nocst [HW,ACPI] 3312 Ignore the _CST method to determine C-states, 3313 instead using the legacy FADT method 3314 3315 profile= [KNL] Enable kernel profiling via /proc/profile 3316 Format: [schedule,]<number> 3317 Param: "schedule" - profile schedule points. 3318 Param: <number> - step/bucket size as a power of 2 for 3319 statistical time based profiling. 3320 Param: "sleep" - profile D-state sleeping (millisecs). 3321 Requires CONFIG_SCHEDSTATS 3322 Param: "kvm" - profile VM exits. 3323 3324 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk 3325 before loading. 3326 See Documentation/blockdev/ramdisk.txt. 3327 3328 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 3329 probe for; one of (bare|imps|exps|lifebook|any). 3330 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 3331 per second. 3332 psmouse.resetafter= [HW,MOUSE] 3333 Try to reset the device after so many bad packets 3334 (0 = never). 3335 psmouse.resolution= 3336 [HW,MOUSE] Set desired mouse resolution, in dpi. 3337 psmouse.smartscroll= 3338 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 3339 0 = disabled, 1 = enabled (default). 3340 3341 pstore.backend= Specify the name of the pstore backend to use 3342 3343 pt. [PARIDE] 3344 See Documentation/blockdev/paride.txt. 3345 3346 pti= [X86_64] Control Page Table Isolation of user and 3347 kernel address spaces. Disabling this feature 3348 removes hardening, but improves performance of 3349 system calls and interrupts. 3350 3351 on - unconditionally enable 3352 off - unconditionally disable 3353 auto - kernel detects whether your CPU model is 3354 vulnerable to issues that PTI mitigates 3355 3356 Not specifying this option is equivalent to pti=auto. 3357 3358 nopti [X86_64] 3359 Equivalent to pti=off 3360 3361 pty.legacy_count= 3362 [KNL] Number of legacy pty's. Overwrites compiled-in 3363 default number. 3364 3365 quiet [KNL] Disable most log messages 3366 3367 r128= [HW,DRM] 3368 3369 raid= [HW,RAID] 3370 See Documentation/md.txt. 3371 3372 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 3373 See Documentation/blockdev/ramdisk.txt. 3374 3375 rcu_nocbs= [KNL] 3376 The argument is a cpu list, as described above. 3377 3378 In kernels built with CONFIG_RCU_NOCB_CPU=y, set 3379 the specified list of CPUs to be no-callback CPUs. 3380 Invocation of these CPUs' RCU callbacks will 3381 be offloaded to "rcuox/N" kthreads created for 3382 that purpose, where "x" is "b" for RCU-bh, "p" 3383 for RCU-preempt, and "s" for RCU-sched, and "N" 3384 is the CPU number. This reduces OS jitter on the 3385 offloaded CPUs, which can be useful for HPC and 3386 real-time workloads. It can also improve energy 3387 efficiency for asymmetric multiprocessors. 3388 3389 rcu_nocb_poll [KNL] 3390 Rather than requiring that offloaded CPUs 3391 (specified by rcu_nocbs= above) explicitly 3392 awaken the corresponding "rcuoN" kthreads, 3393 make these kthreads poll for callbacks. 3394 This improves the real-time response for the 3395 offloaded CPUs by relieving them of the need to 3396 wake up the corresponding kthread, but degrades 3397 energy efficiency by requiring that the kthreads 3398 periodically wake up to do the polling. 3399 3400 rcutree.blimit= [KNL] 3401 Set maximum number of finished RCU callbacks to 3402 process in one batch. 3403 3404 rcutree.dump_tree= [KNL] 3405 Dump the structure of the rcu_node combining tree 3406 out at early boot. This is used for diagnostic 3407 purposes, to verify correct tree setup. 3408 3409 rcutree.gp_cleanup_delay= [KNL] 3410 Set the number of jiffies to delay each step of 3411 RCU grace-period cleanup. This only has effect 3412 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set. 3413 3414 rcutree.gp_init_delay= [KNL] 3415 Set the number of jiffies to delay each step of 3416 RCU grace-period initialization. This only has 3417 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT 3418 is set. 3419 3420 rcutree.gp_preinit_delay= [KNL] 3421 Set the number of jiffies to delay each step of 3422 RCU grace-period pre-initialization, that is, 3423 the propagation of recent CPU-hotplug changes up 3424 the rcu_node combining tree. This only has effect 3425 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set. 3426 3427 rcutree.rcu_fanout_exact= [KNL] 3428 Disable autobalancing of the rcu_node combining 3429 tree. This is used by rcutorture, and might 3430 possibly be useful for architectures having high 3431 cache-to-cache transfer latencies. 3432 3433 rcutree.rcu_fanout_leaf= [KNL] 3434 Change the number of CPUs assigned to each 3435 leaf rcu_node structure. Useful for very 3436 large systems, which will choose the value 64, 3437 and for NUMA systems with large remote-access 3438 latencies, which will choose a value aligned 3439 with the appropriate hardware boundaries. 3440 3441 rcutree.jiffies_till_sched_qs= [KNL] 3442 Set required age in jiffies for a 3443 given grace period before RCU starts 3444 soliciting quiescent-state help from 3445 rcu_note_context_switch(). 3446 3447 rcutree.jiffies_till_first_fqs= [KNL] 3448 Set delay from grace-period initialization to 3449 first attempt to force quiescent states. 3450 Units are jiffies, minimum value is zero, 3451 and maximum value is HZ. 3452 3453 rcutree.jiffies_till_next_fqs= [KNL] 3454 Set delay between subsequent attempts to force 3455 quiescent states. Units are jiffies, minimum 3456 value is one, and maximum value is HZ. 3457 3458 rcutree.kthread_prio= [KNL,BOOT] 3459 Set the SCHED_FIFO priority of the RCU per-CPU 3460 kthreads (rcuc/N). This value is also used for 3461 the priority of the RCU boost threads (rcub/N) 3462 and for the RCU grace-period kthreads (rcu_bh, 3463 rcu_preempt, and rcu_sched). If RCU_BOOST is 3464 set, valid values are 1-99 and the default is 1 3465 (the least-favored priority). Otherwise, when 3466 RCU_BOOST is not set, valid values are 0-99 and 3467 the default is zero (non-realtime operation). 3468 3469 rcutree.rcu_nocb_leader_stride= [KNL] 3470 Set the number of NOCB kthread groups, which 3471 defaults to the square root of the number of 3472 CPUs. Larger numbers reduces the wakeup overhead 3473 on the per-CPU grace-period kthreads, but increases 3474 that same overhead on each group's leader. 3475 3476 rcutree.qhimark= [KNL] 3477 Set threshold of queued RCU callbacks beyond which 3478 batch limiting is disabled. 3479 3480 rcutree.qlowmark= [KNL] 3481 Set threshold of queued RCU callbacks below which 3482 batch limiting is re-enabled. 3483 3484 rcutree.rcu_idle_gp_delay= [KNL] 3485 Set wakeup interval for idle CPUs that have 3486 RCU callbacks (RCU_FAST_NO_HZ=y). 3487 3488 rcutree.rcu_idle_lazy_gp_delay= [KNL] 3489 Set wakeup interval for idle CPUs that have 3490 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y). 3491 Lazy RCU callbacks are those which RCU can 3492 prove do nothing more than free memory. 3493 3494 rcuperf.gp_exp= [KNL] 3495 Measure performance of expedited synchronous 3496 grace-period primitives. 3497 3498 rcuperf.holdoff= [KNL] 3499 Set test-start holdoff period. The purpose of 3500 this parameter is to delay the start of the 3501 test until boot completes in order to avoid 3502 interference. 3503 3504 rcuperf.nreaders= [KNL] 3505 Set number of RCU readers. The value -1 selects 3506 N, where N is the number of CPUs. A value 3507 "n" less than -1 selects N-n+1, where N is again 3508 the number of CPUs. For example, -2 selects N 3509 (the number of CPUs), -3 selects N+1, and so on. 3510 A value of "n" less than or equal to -N selects 3511 a single reader. 3512 3513 rcuperf.nwriters= [KNL] 3514 Set number of RCU writers. The values operate 3515 the same as for rcuperf.nreaders. 3516 N, where N is the number of CPUs 3517 3518 rcuperf.perf_runnable= [BOOT] 3519 Start rcuperf running at boot time. 3520 3521 rcuperf.shutdown= [KNL] 3522 Shut the system down after performance tests 3523 complete. This is useful for hands-off automated 3524 testing. 3525 3526 rcuperf.perf_type= [KNL] 3527 Specify the RCU implementation to test. 3528 3529 rcuperf.verbose= [KNL] 3530 Enable additional printk() statements. 3531 3532 rcutorture.cbflood_inter_holdoff= [KNL] 3533 Set holdoff time (jiffies) between successive 3534 callback-flood tests. 3535 3536 rcutorture.cbflood_intra_holdoff= [KNL] 3537 Set holdoff time (jiffies) between successive 3538 bursts of callbacks within a given callback-flood 3539 test. 3540 3541 rcutorture.cbflood_n_burst= [KNL] 3542 Set the number of bursts making up a given 3543 callback-flood test. Set this to zero to 3544 disable callback-flood testing. 3545 3546 rcutorture.cbflood_n_per_burst= [KNL] 3547 Set the number of callbacks to be registered 3548 in a given burst of a callback-flood test. 3549 3550 rcutorture.fqs_duration= [KNL] 3551 Set duration of force_quiescent_state bursts 3552 in microseconds. 3553 3554 rcutorture.fqs_holdoff= [KNL] 3555 Set holdoff time within force_quiescent_state bursts 3556 in microseconds. 3557 3558 rcutorture.fqs_stutter= [KNL] 3559 Set wait time between force_quiescent_state bursts 3560 in seconds. 3561 3562 rcutorture.gp_cond= [KNL] 3563 Use conditional/asynchronous update-side 3564 primitives, if available. 3565 3566 rcutorture.gp_exp= [KNL] 3567 Use expedited update-side primitives, if available. 3568 3569 rcutorture.gp_normal= [KNL] 3570 Use normal (non-expedited) asynchronous 3571 update-side primitives, if available. 3572 3573 rcutorture.gp_sync= [KNL] 3574 Use normal (non-expedited) synchronous 3575 update-side primitives, if available. If all 3576 of rcutorture.gp_cond=, rcutorture.gp_exp=, 3577 rcutorture.gp_normal=, and rcutorture.gp_sync= 3578 are zero, rcutorture acts as if is interpreted 3579 they are all non-zero. 3580 3581 rcutorture.n_barrier_cbs= [KNL] 3582 Set callbacks/threads for rcu_barrier() testing. 3583 3584 rcutorture.nfakewriters= [KNL] 3585 Set number of concurrent RCU writers. These just 3586 stress RCU, they don't participate in the actual 3587 test, hence the "fake". 3588 3589 rcutorture.nreaders= [KNL] 3590 Set number of RCU readers. The value -1 selects 3591 N-1, where N is the number of CPUs. A value 3592 "n" less than -1 selects N-n-2, where N is again 3593 the number of CPUs. For example, -2 selects N 3594 (the number of CPUs), -3 selects N+1, and so on. 3595 3596 rcutorture.object_debug= [KNL] 3597 Enable debug-object double-call_rcu() testing. 3598 3599 rcutorture.onoff_holdoff= [KNL] 3600 Set time (s) after boot for CPU-hotplug testing. 3601 3602 rcutorture.onoff_interval= [KNL] 3603 Set time (s) between CPU-hotplug operations, or 3604 zero to disable CPU-hotplug testing. 3605 3606 rcutorture.shuffle_interval= [KNL] 3607 Set task-shuffle interval (s). Shuffling tasks 3608 allows some CPUs to go into dyntick-idle mode 3609 during the rcutorture test. 3610 3611 rcutorture.shutdown_secs= [KNL] 3612 Set time (s) after boot system shutdown. This 3613 is useful for hands-off automated testing. 3614 3615 rcutorture.stall_cpu= [KNL] 3616 Duration of CPU stall (s) to test RCU CPU stall 3617 warnings, zero to disable. 3618 3619 rcutorture.stall_cpu_holdoff= [KNL] 3620 Time to wait (s) after boot before inducing stall. 3621 3622 rcutorture.stat_interval= [KNL] 3623 Time (s) between statistics printk()s. 3624 3625 rcutorture.stutter= [KNL] 3626 Time (s) to stutter testing, for example, specifying 3627 five seconds causes the test to run for five seconds, 3628 wait for five seconds, and so on. This tests RCU's 3629 ability to transition abruptly to and from idle. 3630 3631 rcutorture.test_boost= [KNL] 3632 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 3633 "Maybe" means test if the RCU implementation 3634 under test support RCU priority boosting. 3635 3636 rcutorture.test_boost_duration= [KNL] 3637 Duration (s) of each individual boost test. 3638 3639 rcutorture.test_boost_interval= [KNL] 3640 Interval (s) between each boost test. 3641 3642 rcutorture.test_no_idle_hz= [KNL] 3643 Test RCU's dyntick-idle handling. See also the 3644 rcutorture.shuffle_interval parameter. 3645 3646 rcutorture.torture_runnable= [BOOT] 3647 Start rcutorture running at boot time. 3648 3649 rcutorture.torture_type= [KNL] 3650 Specify the RCU implementation to test. 3651 3652 rcutorture.verbose= [KNL] 3653 Enable additional printk() statements. 3654 3655 rcupdate.rcu_cpu_stall_suppress= [KNL] 3656 Suppress RCU CPU stall warning messages. 3657 3658 rcupdate.rcu_cpu_stall_timeout= [KNL] 3659 Set timeout for RCU CPU stall warning messages. 3660 3661 rcupdate.rcu_expedited= [KNL] 3662 Use expedited grace-period primitives, for 3663 example, synchronize_rcu_expedited() instead 3664 of synchronize_rcu(). This reduces latency, 3665 but can increase CPU utilization, degrade 3666 real-time latency, and degrade energy efficiency. 3667 No effect on CONFIG_TINY_RCU kernels. 3668 3669 rcupdate.rcu_normal= [KNL] 3670 Use only normal grace-period primitives, 3671 for example, synchronize_rcu() instead of 3672 synchronize_rcu_expedited(). This improves 3673 real-time latency, CPU utilization, and 3674 energy efficiency, but can expose users to 3675 increased grace-period latency. This parameter 3676 overrides rcupdate.rcu_expedited. No effect on 3677 CONFIG_TINY_RCU kernels. 3678 3679 rcupdate.rcu_normal_after_boot= [KNL] 3680 Once boot has completed (that is, after 3681 rcu_end_inkernel_boot() has been invoked), use 3682 only normal grace-period primitives. No effect 3683 on CONFIG_TINY_RCU kernels. 3684 3685 rcupdate.rcu_task_stall_timeout= [KNL] 3686 Set timeout in jiffies for RCU task stall warning 3687 messages. Disable with a value less than or equal 3688 to zero. 3689 3690 rcupdate.rcu_self_test= [KNL] 3691 Run the RCU early boot self tests 3692 3693 rcupdate.rcu_self_test_bh= [KNL] 3694 Run the RCU bh early boot self tests 3695 3696 rcupdate.rcu_self_test_sched= [KNL] 3697 Run the RCU sched early boot self tests 3698 3699 rdinit= [KNL] 3700 Format: <full_path> 3701 Run specified binary instead of /init from the ramdisk, 3702 used for early userspace startup. See initrd. 3703 3704 reboot= [KNL] 3705 Format (x86 or x86_64): 3706 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \ 3707 [[,]s[mp]#### \ 3708 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 3709 [[,]f[orce] 3710 Where reboot_mode is one of warm (soft) or cold (hard) or gpio, 3711 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 3712 reboot_force is either force or not specified, 3713 reboot_cpu is s[mp]#### with #### being the processor 3714 to be used for rebooting. 3715 3716 relax_domain_level= 3717 [KNL, SMP] Set scheduler's default relax_domain_level. 3718 See Documentation/cgroup-v1/cpusets.txt. 3719 3720 relative_sleep_states= 3721 [SUSPEND] Use sleep state labeling where the deepest 3722 state available other than hibernation is always "mem". 3723 Format: { "0" | "1" } 3724 0 -- Traditional sleep state labels. 3725 1 -- Relative sleep state labels. 3726 3727 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area 3728 3729 reservetop= [X86-32] 3730 Format: nn[KMG] 3731 Reserves a hole at the top of the kernel virtual 3732 address space. 3733 3734 reservelow= [X86] 3735 Format: nn[K] 3736 Set the amount of memory to reserve for BIOS at 3737 the bottom of the address space. 3738 3739 reset_devices [KNL] Force drivers to reset the underlying device 3740 during initialization. 3741 3742 resume= [SWSUSP] 3743 Specify the partition device for software suspend 3744 Format: 3745 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 3746 3747 resume_offset= [SWSUSP] 3748 Specify the offset from the beginning of the partition 3749 given by "resume=" at which the swap header is located, 3750 in <PAGE_SIZE> units (needed only for swap files). 3751 See Documentation/power/swsusp-and-swap-files.txt 3752 3753 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 3754 read the resume files 3755 3756 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 3757 Useful for devices that are detected asynchronously 3758 (e.g. USB and MMC devices). 3759 3760 hibernate= [HIBERNATION] 3761 noresume Don't check if there's a hibernation image 3762 present during boot. 3763 nocompress Don't compress/decompress hibernation images. 3764 no Disable hibernation and resume. 3765 protect_image Turn on image protection during restoration 3766 (that will set all pages holding image data 3767 during restoration read-only). 3768 3769 retain_initrd [RAM] Keep initrd memory after extraction 3770 3771 rfkill.default_state= 3772 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 3773 etc. communication is blocked by default. 3774 1 Unblocked. 3775 3776 rfkill.master_switch_mode= 3777 0 The "airplane mode" button does nothing. 3778 1 The "airplane mode" button toggles between everything 3779 blocked and the previous configuration. 3780 2 The "airplane mode" button toggles between everything 3781 blocked and everything unblocked. 3782 3783 rhash_entries= [KNL,NET] 3784 Set number of hash buckets for route cache 3785 3786 ro [KNL] Mount root device read-only on boot 3787 3788 rodata= [KNL] 3789 on Mark read-only kernel memory as read-only (default). 3790 off Leave read-only kernel memory writable for debugging. 3791 3792 rockchip.usb_uart 3793 Enable the uart passthrough on the designated usb port 3794 on Rockchip SoCs. When active, the signals of the 3795 debug-uart get routed to the D+ and D- pins of the usb 3796 port and the regular usb controller gets disabled. 3797 3798 root= [KNL] Root filesystem 3799 See name_to_dev_t comment in init/do_mounts.c. 3800 3801 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 3802 mount the root filesystem 3803 3804 rootflags= [KNL] Set root filesystem mount option string 3805 3806 rootfstype= [KNL] Set root filesystem type 3807 3808 rootwait [KNL] Wait (indefinitely) for root device to show up. 3809 Useful for devices that are detected asynchronously 3810 (e.g. USB and MMC devices). 3811 3812 rproc_mem=nn[KMG][@address] 3813 [KNL,ARM,CMA] Remoteproc physical memory block. 3814 Memory area to be used by remote processor image, 3815 managed by CMA. 3816 3817 rw [KNL] Mount root device read-write on boot 3818 3819 S [KNL] Run init in single mode 3820 3821 s390_iommu= [HW,S390] 3822 Set s390 IOTLB flushing mode 3823 strict 3824 With strict flushing every unmap operation will result in 3825 an IOTLB flush. Default is lazy flushing before reuse, 3826 which is faster. 3827 3828 sa1100ir [NET] 3829 See drivers/net/irda/sa1100_ir.c. 3830 3831 sbni= [NET] Granch SBNI12 leased line adapter 3832 3833 sched_debug [KNL] Enables verbose scheduler debug messages. 3834 3835 schedstats= [KNL,X86] Enable or disable scheduled statistics. 3836 Allowed values are enable and disable. This feature 3837 incurs a small amount of overhead in the scheduler 3838 but is useful for debugging and performance tuning. 3839 3840 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate 3841 xtime_lock contention on larger systems, and/or RCU lock 3842 contention on all systems with CONFIG_MAXSMP set. 3843 Format: { "0" | "1" } 3844 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 3845 1 -- enable. 3846 Note: increases power consumption, thus should only be 3847 enabled if running jitter sensitive (HPC/RT) workloads. 3848 3849 security= [SECURITY] Choose a security module to enable at boot. 3850 If this boot parameter is not specified, only the first 3851 security module asking for security registration will be 3852 loaded. An invalid security module name will be treated 3853 as if no module has been chosen. 3854 3855 selinux= [SELINUX] Disable or enable SELinux at boot time. 3856 Format: { "0" | "1" } 3857 See security/selinux/Kconfig help text. 3858 0 -- disable. 3859 1 -- enable. 3860 Default value is set via kernel config option. 3861 If enabled at boot time, /selinux/disable can be used 3862 later to disable prior to initial policy load. 3863 3864 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 3865 Format: { "0" | "1" } 3866 See security/apparmor/Kconfig help text 3867 0 -- disable. 3868 1 -- enable. 3869 Default value is set via kernel config option. 3870 3871 serialnumber [BUGS=X86-32] 3872 3873 shapers= [NET] 3874 Maximal number of shapers. 3875 3876 show_msr= [x86] show boot-time MSR settings 3877 Format: { <integer> } 3878 Show boot-time (BIOS-initialized) MSR settings. 3879 The parameter means the number of CPUs to show, 3880 for example 1 means boot CPU only. 3881 3882 simeth= [IA-64] 3883 simscsi= 3884 3885 slram= [HW,MTD] 3886 3887 slab_nomerge [MM] 3888 Disable merging of slabs with similar size. May be 3889 necessary if there is some reason to distinguish 3890 allocs to different slabs. Debug options disable 3891 merging on their own. 3892 For more information see Documentation/vm/slub.txt. 3893 3894 slab_max_order= [MM, SLAB] 3895 Determines the maximum allowed order for slabs. 3896 A high setting may cause OOMs due to memory 3897 fragmentation. Defaults to 1 for systems with 3898 more than 32MB of RAM, 0 otherwise. 3899 3900 slub_debug[=options[,slabs]] [MM, SLUB] 3901 Enabling slub_debug allows one to determine the 3902 culprit if slab objects become corrupted. Enabling 3903 slub_debug can create guard zones around objects and 3904 may poison objects when not in use. Also tracks the 3905 last alloc / free. For more information see 3906 Documentation/vm/slub.txt. 3907 3908 slub_max_order= [MM, SLUB] 3909 Determines the maximum allowed order for slabs. 3910 A high setting may cause OOMs due to memory 3911 fragmentation. For more information see 3912 Documentation/vm/slub.txt. 3913 3914 slub_min_objects= [MM, SLUB] 3915 The minimum number of objects per slab. SLUB will 3916 increase the slab order up to slub_max_order to 3917 generate a sufficiently large slab able to contain 3918 the number of objects indicated. The higher the number 3919 of objects the smaller the overhead of tracking slabs 3920 and the less frequently locks need to be acquired. 3921 For more information see Documentation/vm/slub.txt. 3922 3923 slub_min_order= [MM, SLUB] 3924 Determines the minimum page order for slabs. Must be 3925 lower than slub_max_order. 3926 For more information see Documentation/vm/slub.txt. 3927 3928 slub_nomerge [MM, SLUB] 3929 Same with slab_nomerge. This is supported for legacy. 3930 See slab_nomerge for more information. 3931 3932 smart2= [HW] 3933 Format: <io1>[,<io2>[,...,<io8>]] 3934 3935 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 3936 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 3937 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 3938 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 3939 smsc-ircc2.ircc_irq= [HW] IRQ line 3940 smsc-ircc2.ircc_dma= [HW] DMA channel 3941 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 3942 0: Toshiba Satellite 1800 (GP data pin select) 3943 1: Fast pin select (default) 3944 2: ATC IRMode 3945 3946 smt [KNL,S390] Set the maximum number of threads (logical 3947 CPUs) to use per physical CPU on systems capable of 3948 symmetric multithreading (SMT). Will be capped to the 3949 actual hardware limit. 3950 Format: <integer> 3951 Default: -1 (no limit) 3952 3953 softlockup_panic= 3954 [KNL] Should the soft-lockup detector generate panics. 3955 Format: <integer> 3956 3957 softlockup_all_cpu_backtrace= 3958 [KNL] Should the soft-lockup detector generate 3959 backtraces on all cpus. 3960 Format: <integer> 3961 3962 sonypi.*= [HW] Sony Programmable I/O Control Device driver 3963 See Documentation/laptops/sonypi.txt 3964 3965 spectre_v2= [X86] Control mitigation of Spectre variant 2 3966 (indirect branch speculation) vulnerability. 3967 3968 on - unconditionally enable 3969 off - unconditionally disable 3970 auto - kernel detects whether your CPU model is 3971 vulnerable 3972 3973 Selecting 'on' will, and 'auto' may, choose a 3974 mitigation method at run time according to the 3975 CPU, the available microcode, the setting of the 3976 CONFIG_RETPOLINE configuration option, and the 3977 compiler with which the kernel was built. 3978 3979 Specific mitigations can also be selected manually: 3980 3981 retpoline - replace indirect branches 3982 retpoline,generic - google's original retpoline 3983 retpoline,amd - AMD-specific minimal thunk 3984 3985 Not specifying this option is equivalent to 3986 spectre_v2=auto. 3987 3988 spia_io_base= [HW,MTD] 3989 spia_fio_base= 3990 spia_pedr= 3991 spia_peddr= 3992 3993 stack_guard_gap= [MM] 3994 override the default stack gap protection. The value 3995 is in page units and it defines how many pages prior 3996 to (for stacks growing down) resp. after (for stacks 3997 growing up) the main stack are reserved for no other 3998 mapping. Default value is 256 pages. 3999 4000 stacktrace [FTRACE] 4001 Enabled the stack tracer on boot up. 4002 4003 stacktrace_filter=[function-list] 4004 [FTRACE] Limit the functions that the stack tracer 4005 will trace at boot up. function-list is a comma separated 4006 list of functions. This list can be changed at run 4007 time by the stack_trace_filter file in the debugfs 4008 tracing directory. Note, this enables stack tracing 4009 and the stacktrace above is not needed. 4010 4011 sti= [PARISC,HW] 4012 Format: <num> 4013 Set the STI (builtin display/keyboard on the HP-PARISC 4014 machines) console (graphic card) which should be used 4015 as the initial boot-console. 4016 See also comment in drivers/video/console/sticore.c. 4017 4018 sti_font= [HW] 4019 See comment in drivers/video/console/sticore.c. 4020 4021 stifb= [HW] 4022 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 4023 4024 sunrpc.min_resvport= 4025 sunrpc.max_resvport= 4026 [NFS,SUNRPC] 4027 SunRPC servers often require that client requests 4028 originate from a privileged port (i.e. a port in the 4029 range 0 < portnr < 1024). 4030 An administrator who wishes to reserve some of these 4031 ports for other uses may adjust the range that the 4032 kernel's sunrpc client considers to be privileged 4033 using these two parameters to set the minimum and 4034 maximum port values. 4035 4036 sunrpc.svc_rpc_per_connection_limit= 4037 [NFS,SUNRPC] 4038 Limit the number of requests that the server will 4039 process in parallel from a single connection. 4040 The default value is 0 (no limit). 4041 4042 sunrpc.pool_mode= 4043 [NFS] 4044 Control how the NFS server code allocates CPUs to 4045 service thread pools. Depending on how many NICs 4046 you have and where their interrupts are bound, this 4047 option will affect which CPUs will do NFS serving. 4048 Note: this parameter cannot be changed while the 4049 NFS server is running. 4050 4051 auto the server chooses an appropriate mode 4052 automatically using heuristics 4053 global a single global pool contains all CPUs 4054 percpu one pool for each CPU 4055 pernode one pool for each NUMA node (equivalent 4056 to global on non-NUMA machines) 4057 4058 sunrpc.tcp_slot_table_entries= 4059 sunrpc.udp_slot_table_entries= 4060 [NFS,SUNRPC] 4061 Sets the upper limit on the number of simultaneous 4062 RPC calls that can be sent from the client to a 4063 server. Increasing these values may allow you to 4064 improve throughput, but will also increase the 4065 amount of memory reserved for use by the client. 4066 4067 suspend.pm_test_delay= 4068 [SUSPEND] 4069 Sets the number of seconds to remain in a suspend test 4070 mode before resuming the system (see 4071 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 4072 is set. Default value is 5. 4073 4074 swapaccount=[0|1] 4075 [KNL] Enable accounting of swap in memory resource 4076 controller if no parameter or 1 is given or disable 4077 it if 0 is given (See Documentation/cgroup-v1/memory.txt) 4078 4079 swiotlb= [ARM,IA-64,PPC,MIPS,X86] 4080 Format: { <int> | force | noforce } 4081 <int> -- Number of I/O TLB slabs 4082 force -- force using of bounce buffers even if they 4083 wouldn't be automatically used by the kernel 4084 noforce -- Never use bounce buffers (for debugging) 4085 4086 switches= [HW,M68k] 4087 4088 sysfs.deprecated=0|1 [KNL] 4089 Enable/disable old style sysfs layout for old udev 4090 on older distributions. When this option is enabled 4091 very new udev will not work anymore. When this option 4092 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled) 4093 in older udev will not work anymore. 4094 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in 4095 the kernel configuration. 4096 4097 sysrq_always_enabled 4098 [KNL] 4099 Ignore sysrq setting - this boot parameter will 4100 neutralize any effect of /proc/sys/kernel/sysrq. 4101 Useful for debugging. 4102 4103 tcpmhash_entries= [KNL,NET] 4104 Set the number of tcp_metrics_hash slots. 4105 Default value is 8192 or 16384 depending on total 4106 ram pages. This is used to specify the TCP metrics 4107 cache size. See Documentation/networking/ip-sysctl.txt 4108 "tcp_no_metrics_save" section for more details. 4109 4110 tdfx= [HW,DRM] 4111 4112 test_suspend= [SUSPEND][,N] 4113 Specify "mem" (for Suspend-to-RAM) or "standby" (for 4114 standby suspend) or "freeze" (for suspend type freeze) 4115 as the system sleep state during system startup with 4116 the optional capability to repeat N number of times. 4117 The system is woken from this state using a 4118 wakeup-capable RTC alarm. 4119 4120 thash_entries= [KNL,NET] 4121 Set number of hash buckets for TCP connection 4122 4123 thermal.act= [HW,ACPI] 4124 -1: disable all active trip points in all thermal zones 4125 <degrees C>: override all lowest active trip points 4126 4127 thermal.crt= [HW,ACPI] 4128 -1: disable all critical trip points in all thermal zones 4129 <degrees C>: override all critical trip points 4130 4131 thermal.nocrt= [HW,ACPI] 4132 Set to disable actions on ACPI thermal zone 4133 critical and hot trip points. 4134 4135 thermal.off= [HW,ACPI] 4136 1: disable ACPI thermal control 4137 4138 thermal.psv= [HW,ACPI] 4139 -1: disable all passive trip points 4140 <degrees C>: override all passive trip points to this 4141 value 4142 4143 thermal.tzp= [HW,ACPI] 4144 Specify global default ACPI thermal zone polling rate 4145 <deci-seconds>: poll all this frequency 4146 0: no polling (default) 4147 4148 threadirqs [KNL] 4149 Force threading of all interrupt handlers except those 4150 marked explicitly IRQF_NO_THREAD. 4151 4152 tmem [KNL,XEN] 4153 Enable the Transcendent memory driver if built-in. 4154 4155 tmem.cleancache=0|1 [KNL, XEN] 4156 Default is on (1). Disable the usage of the cleancache 4157 API to send anonymous pages to the hypervisor. 4158 4159 tmem.frontswap=0|1 [KNL, XEN] 4160 Default is on (1). Disable the usage of the frontswap 4161 API to send swap pages to the hypervisor. If disabled 4162 the selfballooning and selfshrinking are force disabled. 4163 4164 tmem.selfballooning=0|1 [KNL, XEN] 4165 Default is on (1). Disable the driving of swap pages 4166 to the hypervisor. 4167 4168 tmem.selfshrinking=0|1 [KNL, XEN] 4169 Default is on (1). Partial swapoff that immediately 4170 transfers pages from Xen hypervisor back to the 4171 kernel based on different criteria. 4172 4173 topology= [S390] 4174 Format: {off | on} 4175 Specify if the kernel should make use of the cpu 4176 topology information if the hardware supports this. 4177 The scheduler will make use of this information and 4178 e.g. base its process migration decisions on it. 4179 Default is on. 4180 4181 topology_updates= [KNL, PPC, NUMA] 4182 Format: {off} 4183 Specify if the kernel should ignore (off) 4184 topology updates sent by the hypervisor to this 4185 LPAR. 4186 4187 tp720= [HW,PS2] 4188 4189 tpm_suspend_pcr=[HW,TPM] 4190 Format: integer pcr id 4191 Specify that at suspend time, the tpm driver 4192 should extend the specified pcr with zeros, 4193 as a workaround for some chips which fail to 4194 flush the last written pcr on TPM_SaveState. 4195 This will guarantee that all the other pcrs 4196 are saved. 4197 4198 trace_buf_size=nn[KMG] 4199 [FTRACE] will set tracing buffer size on each cpu. 4200 4201 trace_event=[event-list] 4202 [FTRACE] Set and start specified trace events in order 4203 to facilitate early boot debugging. The event-list is a 4204 comma separated list of trace events to enable. See 4205 also Documentation/trace/events.txt 4206 4207 trace_options=[option-list] 4208 [FTRACE] Enable or disable tracer options at boot. 4209 The option-list is a comma delimited list of options 4210 that can be enabled or disabled just as if you were 4211 to echo the option name into 4212 4213 /sys/kernel/debug/tracing/trace_options 4214 4215 For example, to enable stacktrace option (to dump the 4216 stack trace of each event), add to the command line: 4217 4218 trace_options=stacktrace 4219 4220 See also Documentation/trace/ftrace.txt "trace options" 4221 section. 4222 4223 tp_printk[FTRACE] 4224 Have the tracepoints sent to printk as well as the 4225 tracing ring buffer. This is useful for early boot up 4226 where the system hangs or reboots and does not give the 4227 option for reading the tracing buffer or performing a 4228 ftrace_dump_on_oops. 4229 4230 To turn off having tracepoints sent to printk, 4231 echo 0 > /proc/sys/kernel/tracepoint_printk 4232 Note, echoing 1 into this file without the 4233 tracepoint_printk kernel cmdline option has no effect. 4234 4235 ** CAUTION ** 4236 4237 Having tracepoints sent to printk() and activating high 4238 frequency tracepoints such as irq or sched, can cause 4239 the system to live lock. 4240 4241 traceoff_on_warning 4242 [FTRACE] enable this option to disable tracing when a 4243 warning is hit. This turns off "tracing_on". Tracing can 4244 be enabled again by echoing '1' into the "tracing_on" 4245 file located in /sys/kernel/debug/tracing/ 4246 4247 This option is useful, as it disables the trace before 4248 the WARNING dump is called, which prevents the trace to 4249 be filled with content caused by the warning output. 4250 4251 This option can also be set at run time via the sysctl 4252 option: kernel/traceoff_on_warning 4253 4254 transparent_hugepage= 4255 [KNL] 4256 Format: [always|madvise|never] 4257 Can be used to control the default behavior of the system 4258 with respect to transparent hugepages. 4259 See Documentation/vm/transhuge.txt for more details. 4260 4261 tsc= Disable clocksource stability checks for TSC. 4262 Format: <string> 4263 [x86] reliable: mark tsc clocksource as reliable, this 4264 disables clocksource verification at runtime, as well 4265 as the stability checks done at bootup. Used to enable 4266 high-resolution timer mode on older hardware, and in 4267 virtualized environment. 4268 [x86] noirqtime: Do not use TSC to do irq accounting. 4269 Used to run time disable IRQ_TIME_ACCOUNTING on any 4270 platforms where RDTSC is slow and this accounting 4271 can add overhead. 4272 4273 turbografx.map[2|3]= [HW,JOY] 4274 TurboGraFX parallel port interface 4275 Format: 4276 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 4277 See also Documentation/input/joystick-parport.txt 4278 4279 udbg-immortal [PPC] When debugging early kernel crashes that 4280 happen after console_init() and before a proper 4281 console driver takes over, this boot options might 4282 help "seeing" what's going on. 4283 4284 uhash_entries= [KNL,NET] 4285 Set number of hash buckets for UDP/UDP-Lite connections 4286 4287 uhci-hcd.ignore_oc= 4288 [USB] Ignore overcurrent events (default N). 4289 Some badly-designed motherboards generate lots of 4290 bogus events, for ports that aren't wired to 4291 anything. Set this parameter to avoid log spamming. 4292 Note that genuine overcurrent events won't be 4293 reported either. 4294 4295 unknown_nmi_panic 4296 [X86] Cause panic on unknown NMI. 4297 4298 usbcore.authorized_default= 4299 [USB] Default USB device authorization: 4300 (default -1 = authorized except for wireless USB, 4301 0 = not authorized, 1 = authorized) 4302 4303 usbcore.autosuspend= 4304 [USB] The autosuspend time delay (in seconds) used 4305 for newly-detected USB devices (default 2). This 4306 is the time required before an idle device will be 4307 autosuspended. Devices for which the delay is set 4308 to a negative value won't be autosuspended at all. 4309 4310 usbcore.usbfs_snoop= 4311 [USB] Set to log all usbfs traffic (default 0 = off). 4312 4313 usbcore.usbfs_snoop_max= 4314 [USB] Maximum number of bytes to snoop in each URB 4315 (default = 65536). 4316 4317 usbcore.blinkenlights= 4318 [USB] Set to cycle leds on hubs (default 0 = off). 4319 4320 usbcore.old_scheme_first= 4321 [USB] Start with the old device initialization 4322 scheme (default 0 = off). 4323 4324 usbcore.usbfs_memory_mb= 4325 [USB] Memory limit (in MB) for buffers allocated by 4326 usbfs (default = 16, 0 = max = 2047). 4327 4328 usbcore.use_both_schemes= 4329 [USB] Try the other device initialization scheme 4330 if the first one fails (default 1 = enabled). 4331 4332 usbcore.initial_descriptor_timeout= 4333 [USB] Specifies timeout for the initial 64-byte 4334 USB_REQ_GET_DESCRIPTOR request in milliseconds 4335 (default 5000 = 5.0 seconds). 4336 4337 usbcore.nousb [USB] Disable the USB subsystem 4338 4339 usbhid.mousepoll= 4340 [USBHID] The interval which mice are to be polled at. 4341 4342 usb-storage.delay_use= 4343 [UMS] The delay in seconds before a new device is 4344 scanned for Logical Units (default 1). 4345 4346 usb-storage.quirks= 4347 [UMS] A list of quirks entries to supplement or 4348 override the built-in unusual_devs list. List 4349 entries are separated by commas. Each entry has 4350 the form VID:PID:Flags where VID and PID are Vendor 4351 and Product ID values (4-digit hex numbers) and 4352 Flags is a set of characters, each corresponding 4353 to a common usb-storage quirk flag as follows: 4354 a = SANE_SENSE (collect more than 18 bytes 4355 of sense data); 4356 b = BAD_SENSE (don't collect more than 18 4357 bytes of sense data); 4358 c = FIX_CAPACITY (decrease the reported 4359 device capacity by one sector); 4360 d = NO_READ_DISC_INFO (don't use 4361 READ_DISC_INFO command); 4362 e = NO_READ_CAPACITY_16 (don't use 4363 READ_CAPACITY_16 command); 4364 f = NO_REPORT_OPCODES (don't use report opcodes 4365 command, uas only); 4366 g = MAX_SECTORS_240 (don't transfer more than 4367 240 sectors at a time, uas only); 4368 h = CAPACITY_HEURISTICS (decrease the 4369 reported device capacity by one 4370 sector if the number is odd); 4371 i = IGNORE_DEVICE (don't bind to this 4372 device); 4373 j = NO_REPORT_LUNS (don't use report luns 4374 command, uas only); 4375 l = NOT_LOCKABLE (don't try to lock and 4376 unlock ejectable media); 4377 m = MAX_SECTORS_64 (don't transfer more 4378 than 64 sectors = 32 KB at a time); 4379 n = INITIAL_READ10 (force a retry of the 4380 initial READ(10) command); 4381 o = CAPACITY_OK (accept the capacity 4382 reported by the device); 4383 p = WRITE_CACHE (the device cache is ON 4384 by default); 4385 r = IGNORE_RESIDUE (the device reports 4386 bogus residue values); 4387 s = SINGLE_LUN (the device has only one 4388 Logical Unit); 4389 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 4390 commands, uas only); 4391 u = IGNORE_UAS (don't bind to the uas driver); 4392 w = NO_WP_DETECT (don't test whether the 4393 medium is write-protected). 4394 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 4395 even if the device claims no cache) 4396 Example: quirks=0419:aaf5:rl,0421:0433:rc 4397 4398 user_debug= [KNL,ARM] 4399 Format: <int> 4400 See arch/arm/Kconfig.debug help text. 4401 1 - undefined instruction events 4402 2 - system calls 4403 4 - invalid data aborts 4404 8 - SIGSEGV faults 4405 16 - SIGBUS faults 4406 Example: user_debug=31 4407 4408 userpte= 4409 [X86] Flags controlling user PTE allocations. 4410 4411 nohigh = do not allocate PTE pages in 4412 HIGHMEM regardless of setting 4413 of CONFIG_HIGHPTE. 4414 4415 vdso= [X86,SH] 4416 On X86_32, this is an alias for vdso32=. Otherwise: 4417 4418 vdso=1: enable VDSO (the default) 4419 vdso=0: disable VDSO mapping 4420 4421 vdso32= [X86] Control the 32-bit vDSO 4422 vdso32=1: enable 32-bit VDSO 4423 vdso32=0 or vdso32=2: disable 32-bit VDSO 4424 4425 See the help text for CONFIG_COMPAT_VDSO for more 4426 details. If CONFIG_COMPAT_VDSO is set, the default is 4427 vdso32=0; otherwise, the default is vdso32=1. 4428 4429 For compatibility with older kernels, vdso32=2 is an 4430 alias for vdso32=0. 4431 4432 Try vdso32=0 if you encounter an error that says: 4433 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 4434 4435 vector= [IA-64,SMP] 4436 vector=percpu: enable percpu vector domain 4437 4438 video= [FB] Frame buffer configuration 4439 See Documentation/fb/modedb.txt. 4440 4441 video.brightness_switch_enabled= [0,1] 4442 If set to 1, on receiving an ACPI notify event 4443 generated by hotkey, video driver will adjust brightness 4444 level and then send out the event to user space through 4445 the allocated input device; If set to 0, video driver 4446 will only send out the event without touching backlight 4447 brightness level. 4448 default: 1 4449 4450 virtio_mmio.device= 4451 [VMMIO] Memory mapped virtio (platform) device. 4452 4453 <size>@<baseaddr>:<irq>[:<id>] 4454 where: 4455 <size> := size (can use standard suffixes 4456 like K, M and G) 4457 <baseaddr> := physical base address 4458 <irq> := interrupt number (as passed to 4459 request_irq()) 4460 <id> := (optional) platform device id 4461 example: 4462 virtio_mmio.device=1K@0x100b0000:48:7 4463 4464 Can be used multiple times for multiple devices. 4465 4466 vga= [BOOT,X86-32] Select a particular video mode 4467 See Documentation/x86/boot.txt and 4468 Documentation/svga.txt. 4469 Use vga=ask for menu. 4470 This is actually a boot loader parameter; the value is 4471 passed to the kernel using a special protocol. 4472 4473 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact 4474 size of <nn>. This can be used to increase the 4475 minimum size (128MB on x86). It can also be used to 4476 decrease the size and leave more room for directly 4477 mapped kernel RAM. 4478 4479 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 4480 Format: <command> 4481 4482 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 4483 Format: <command> 4484 4485 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 4486 Format: <command> 4487 4488 vsyscall= [X86-64] 4489 Controls the behavior of vsyscalls (i.e. calls to 4490 fixed addresses of 0xffffffffff600x00 from legacy 4491 code). Most statically-linked binaries and older 4492 versions of glibc use these calls. Because these 4493 functions are at fixed addresses, they make nice 4494 targets for exploits that can control RIP. 4495 4496 emulate [default] Vsyscalls turn into traps and are 4497 emulated reasonably safely. 4498 4499 native Vsyscalls are native syscall instructions. 4500 This is a little bit faster than trapping 4501 and makes a few dynamic recompilers work 4502 better than they would in emulation mode. 4503 It also makes exploits much easier to write. 4504 4505 none Vsyscalls don't work at all. This makes 4506 them quite hard to use for exploits but 4507 might break your system. 4508 4509 vt.color= [VT] Default text color. 4510 Format: 0xYX, X = foreground, Y = background. 4511 Default: 0x07 = light gray on black. 4512 4513 vt.cur_default= [VT] Default cursor shape. 4514 Format: 0xCCBBAA, where AA, BB, and CC are the same as 4515 the parameters of the <Esc>[?A;B;Cc escape sequence; 4516 see VGA-softcursor.txt. Default: 2 = underline. 4517 4518 vt.default_blu= [VT] 4519 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 4520 Change the default blue palette of the console. 4521 This is a 16-member array composed of values 4522 ranging from 0-255. 4523 4524 vt.default_grn= [VT] 4525 Format: <green0>,<green1>,<green2>,...,<green15> 4526 Change the default green palette of the console. 4527 This is a 16-member array composed of values 4528 ranging from 0-255. 4529 4530 vt.default_red= [VT] 4531 Format: <red0>,<red1>,<red2>,...,<red15> 4532 Change the default red palette of the console. 4533 This is a 16-member array composed of values 4534 ranging from 0-255. 4535 4536 vt.default_utf8= 4537 [VT] 4538 Format=<0|1> 4539 Set system-wide default UTF-8 mode for all tty's. 4540 Default is 1, i.e. UTF-8 mode is enabled for all 4541 newly opened terminals. 4542 4543 vt.global_cursor_default= 4544 [VT] 4545 Format=<-1|0|1> 4546 Set system-wide default for whether a cursor 4547 is shown on new VTs. Default is -1, 4548 i.e. cursors will be created by default unless 4549 overridden by individual drivers. 0 will hide 4550 cursors, 1 will display them. 4551 4552 vt.italic= [VT] Default color for italic text; 0-15. 4553 Default: 2 = green. 4554 4555 vt.underline= [VT] Default color for underlined text; 0-15. 4556 Default: 3 = cyan. 4557 4558 watchdog timers [HW,WDT] For information on watchdog timers, 4559 see Documentation/watchdog/watchdog-parameters.txt 4560 or other driver-specific files in the 4561 Documentation/watchdog/ directory. 4562 4563 workqueue.watchdog_thresh= 4564 If CONFIG_WQ_WATCHDOG is configured, workqueue can 4565 warn stall conditions and dump internal state to 4566 help debugging. 0 disables workqueue stall 4567 detection; otherwise, it's the stall threshold 4568 duration in seconds. The default value is 30 and 4569 it can be updated at runtime by writing to the 4570 corresponding sysfs file. 4571 4572 workqueue.disable_numa 4573 By default, all work items queued to unbound 4574 workqueues are affine to the NUMA nodes they're 4575 issued on, which results in better behavior in 4576 general. If NUMA affinity needs to be disabled for 4577 whatever reason, this option can be used. Note 4578 that this also can be controlled per-workqueue for 4579 workqueues visible under /sys/bus/workqueue/. 4580 4581 workqueue.power_efficient 4582 Per-cpu workqueues are generally preferred because 4583 they show better performance thanks to cache 4584 locality; unfortunately, per-cpu workqueues tend to 4585 be more power hungry than unbound workqueues. 4586 4587 Enabling this makes the per-cpu workqueues which 4588 were observed to contribute significantly to power 4589 consumption unbound, leading to measurably lower 4590 power usage at the cost of small performance 4591 overhead. 4592 4593 The default value of this parameter is determined by 4594 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 4595 4596 workqueue.debug_force_rr_cpu 4597 Workqueue used to implicitly guarantee that work 4598 items queued without explicit CPU specified are put 4599 on the local CPU. This guarantee is no longer true 4600 and while local CPU is still preferred work items 4601 may be put on foreign CPUs. This debug option 4602 forces round-robin CPU selection to flush out 4603 usages which depend on the now broken guarantee. 4604 When enabled, memory and cache locality will be 4605 impacted. 4606 4607 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of 4608 default x2apic cluster mode on platforms 4609 supporting x2apic. 4610 4611 x86_intel_mid_timer= [X86-32,APBT] 4612 Choose timer option for x86 Intel MID platform. 4613 Two valid options are apbt timer only and lapic timer 4614 plus one apbt timer for broadcast timer. 4615 x86_intel_mid_timer=apbt_only | lapic_and_apbt 4616 4617 xen_512gb_limit [KNL,X86-64,XEN] 4618 Restricts the kernel running paravirtualized under Xen 4619 to use only up to 512 GB of RAM. The reason to do so is 4620 crash analysis tools and Xen tools for doing domain 4621 save/restore/migration must be enabled to handle larger 4622 domains. 4623 4624 xen_emul_unplug= [HW,X86,XEN] 4625 Unplug Xen emulated devices 4626 Format: [unplug0,][unplug1] 4627 ide-disks -- unplug primary master IDE devices 4628 aux-ide-disks -- unplug non-primary-master IDE devices 4629 nics -- unplug network devices 4630 all -- unplug all emulated devices (NICs and IDE disks) 4631 unnecessary -- unplugging emulated devices is 4632 unnecessary even if the host did not respond to 4633 the unplug protocol 4634 never -- do not unplug even if version check succeeds 4635 4636 xen_nopvspin [X86,XEN] 4637 Disables the ticketlock slowpath using Xen PV 4638 optimizations. 4639 4640 xen_nopv [X86] 4641 Disables the PV optimizations forcing the HVM guest to 4642 run as generic HVM guest with no PV drivers. 4643 4644 xirc2ps_cs= [NET,PCMCIA] 4645 Format: 4646 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 4647 4648______________________________________________________________________ 4649 4650TODO: 4651 4652 Add more DRM drivers. 4653