1 acpi= [HW,ACPI,X86,ARM64] 2 Advanced Configuration and Power Interface 3 Format: { force | on | off | strict | noirq | rsdt | 4 copy_dsdt } 5 force -- enable ACPI if default was off 6 on -- enable ACPI but allow fallback to DT [arm64] 7 off -- disable ACPI if default was on 8 noirq -- do not use ACPI for IRQ routing 9 strict -- Be less tolerant of platforms that are not 10 strictly ACPI specification compliant. 11 rsdt -- prefer RSDT over (default) XSDT 12 copy_dsdt -- copy DSDT to memory 13 For ARM64, ONLY "acpi=off", "acpi=on" or "acpi=force" 14 are available 15 16 See also Documentation/power/runtime_pm.txt, pci=noacpi 17 18 acpi_apic_instance= [ACPI, IOAPIC] 19 Format: <int> 20 2: use 2nd APIC table, if available 21 1,0: use 1st APIC table 22 default: 0 23 24 acpi_backlight= [HW,ACPI] 25 acpi_backlight=vendor 26 acpi_backlight=video 27 If set to vendor, prefer vendor specific driver 28 (e.g. thinkpad_acpi, sony_acpi, etc.) instead 29 of the ACPI video.ko driver. 30 31 acpi_force_32bit_fadt_addr 32 force FADT to use 32 bit addresses rather than the 33 64 bit X_* addresses. Some firmware have broken 64 34 bit addresses for force ACPI ignore these and use 35 the older legacy 32 bit addresses. 36 37 acpica_no_return_repair [HW, ACPI] 38 Disable AML predefined validation mechanism 39 This mechanism can repair the evaluation result to make 40 the return objects more ACPI specification compliant. 41 This option is useful for developers to identify the 42 root cause of an AML interpreter issue when the issue 43 has something to do with the repair mechanism. 44 45 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG] 46 acpi.debug_level= [HW,ACPI,ACPI_DEBUG] 47 Format: <int> 48 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI 49 debug output. Bits in debug_layer correspond to a 50 _COMPONENT in an ACPI source file, e.g., 51 #define _COMPONENT ACPI_PCI_COMPONENT 52 Bits in debug_level correspond to a level in 53 ACPI_DEBUG_PRINT statements, e.g., 54 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ... 55 The debug_level mask defaults to "info". See 56 Documentation/acpi/debug.txt for more information about 57 debug layers and levels. 58 59 Enable processor driver info messages: 60 acpi.debug_layer=0x20000000 61 Enable PCI/PCI interrupt routing info messages: 62 acpi.debug_layer=0x400000 63 Enable AML "Debug" output, i.e., stores to the Debug 64 object while interpreting AML: 65 acpi.debug_layer=0xffffffff acpi.debug_level=0x2 66 Enable all messages related to ACPI hardware: 67 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff 68 69 Some values produce so much output that the system is 70 unusable. The "log_buf_len" parameter may be useful 71 if you need to capture more output. 72 73 acpi_enforce_resources= [ACPI] 74 { strict | lax | no } 75 Check for resource conflicts between native drivers 76 and ACPI OperationRegions (SystemIO and SystemMemory 77 only). IO ports and memory declared in ACPI might be 78 used by the ACPI subsystem in arbitrary AML code and 79 can interfere with legacy drivers. 80 strict (default): access to resources claimed by ACPI 81 is denied; legacy drivers trying to access reserved 82 resources will fail to bind to device using them. 83 lax: access to resources claimed by ACPI is allowed; 84 legacy drivers trying to access reserved resources 85 will bind successfully but a warning message is logged. 86 no: ACPI OperationRegions are not marked as reserved, 87 no further checks are performed. 88 89 acpi_force_table_verification [HW,ACPI] 90 Enable table checksum verification during early stage. 91 By default, this is disabled due to x86 early mapping 92 size limitation. 93 94 acpi_irq_balance [HW,ACPI] 95 ACPI will balance active IRQs 96 default in APIC mode 97 98 acpi_irq_nobalance [HW,ACPI] 99 ACPI will not move active IRQs (default) 100 default in PIC mode 101 102 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA 103 Format: <irq>,<irq>... 104 105 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for 106 use by PCI 107 Format: <irq>,<irq>... 108 109 acpi_mask_gpe= [HW,ACPI] 110 Due to the existence of _Lxx/_Exx, some GPEs triggered 111 by unsupported hardware/firmware features can result in 112 GPE floodings that cannot be automatically disabled by 113 the GPE dispatcher. 114 This facility can be used to prevent such uncontrolled 115 GPE floodings. 116 Format: <int> 117 Support masking of GPEs numbered from 0x00 to 0x7f. 118 119 acpi_no_auto_serialize [HW,ACPI] 120 Disable auto-serialization of AML methods 121 AML control methods that contain the opcodes to create 122 named objects will be marked as "Serialized" by the 123 auto-serialization feature. 124 This feature is enabled by default. 125 This option allows to turn off the feature. 126 127 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump 128 kernels. 129 130 acpi_no_static_ssdt [HW,ACPI] 131 Disable installation of static SSDTs at early boot time 132 By default, SSDTs contained in the RSDT/XSDT will be 133 installed automatically and they will appear under 134 /sys/firmware/acpi/tables. 135 This option turns off this feature. 136 Note that specifying this option does not affect 137 dynamic table installation which will install SSDT 138 tables to /sys/firmware/acpi/tables/dynamic. 139 140 acpi_rsdp= [ACPI,EFI,KEXEC] 141 Pass the RSDP address to the kernel, mostly used 142 on machines running EFI runtime service to boot the 143 second kernel for kdump. 144 145 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS 146 Format: To spoof as Windows 98: ="Microsoft Windows" 147 148 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead 149 of 2 which is mandated by ACPI 6) as the supported ACPI 150 specification revision (when using this switch, it may 151 be necessary to carry out a cold reboot _twice_ in a 152 row to make it take effect on the platform firmware). 153 154 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings 155 acpi_osi="string1" # add string1 156 acpi_osi="!string2" # remove string2 157 acpi_osi=!* # remove all strings 158 acpi_osi=! # disable all built-in OS vendor 159 strings 160 acpi_osi=!! # enable all built-in OS vendor 161 strings 162 acpi_osi= # disable all strings 163 164 'acpi_osi=!' can be used in combination with single or 165 multiple 'acpi_osi="string1"' to support specific OS 166 vendor string(s). Note that such command can only 167 affect the default state of the OS vendor strings, thus 168 it cannot affect the default state of the feature group 169 strings and the current state of the OS vendor strings, 170 specifying it multiple times through kernel command line 171 is meaningless. This command is useful when one do not 172 care about the state of the feature group strings which 173 should be controlled by the OSPM. 174 Examples: 175 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent 176 to 'acpi_osi="Windows 2000" acpi_osi=!', they all 177 can make '_OSI("Windows 2000")' TRUE. 178 179 'acpi_osi=' cannot be used in combination with other 180 'acpi_osi=' command lines, the _OSI method will not 181 exist in the ACPI namespace. NOTE that such command can 182 only affect the _OSI support state, thus specifying it 183 multiple times through kernel command line is also 184 meaningless. 185 Examples: 186 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)' 187 FALSE. 188 189 'acpi_osi=!*' can be used in combination with single or 190 multiple 'acpi_osi="string1"' to support specific 191 string(s). Note that such command can affect the 192 current state of both the OS vendor strings and the 193 feature group strings, thus specifying it multiple times 194 through kernel command line is meaningful. But it may 195 still not able to affect the final state of a string if 196 there are quirks related to this string. This command 197 is useful when one want to control the state of the 198 feature group strings to debug BIOS issues related to 199 the OSPM features. 200 Examples: 201 1. 'acpi_osi="Module Device" acpi_osi=!*' can make 202 '_OSI("Module Device")' FALSE. 203 2. 'acpi_osi=!* acpi_osi="Module Device"' can make 204 '_OSI("Module Device")' TRUE. 205 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is 206 equivalent to 207 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"' 208 and 209 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!', 210 they all will make '_OSI("Windows 2000")' TRUE. 211 212 acpi_pm_good [X86] 213 Override the pmtimer bug detection: force the kernel 214 to assume that this machine's pmtimer latches its value 215 and always returns good values. 216 217 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode 218 Format: { level | edge | high | low } 219 220 acpi_skip_timer_override [HW,ACPI] 221 Recognize and ignore IRQ0/pin2 Interrupt Override. 222 For broken nForce2 BIOS resulting in XT-PIC timer. 223 224 acpi_sleep= [HW,ACPI] Sleep options 225 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig, 226 old_ordering, nonvs, sci_force_enable } 227 See Documentation/power/video.txt for information on 228 s3_bios and s3_mode. 229 s3_beep is for debugging; it makes the PC's speaker beep 230 as soon as the kernel's real-mode entry point is called. 231 s4_nohwsig prevents ACPI hardware signature from being 232 used during resume from hibernation. 233 old_ordering causes the ACPI 1.0 ordering of the _PTS 234 control method, with respect to putting devices into 235 low power states, to be enforced (the ACPI 2.0 ordering 236 of _PTS is used by default). 237 nonvs prevents the kernel from saving/restoring the 238 ACPI NVS memory during suspend/hibernation and resume. 239 sci_force_enable causes the kernel to set SCI_EN directly 240 on resume from S1/S3 (which is against the ACPI spec, 241 but some broken systems don't work without it). 242 243 acpi_use_timer_override [HW,ACPI] 244 Use timer override. For some broken Nvidia NF5 boards 245 that require a timer override, but don't have HPET 246 247 add_efi_memmap [EFI; X86] Include EFI memory map in 248 kernel's map of available physical RAM. 249 250 agp= [AGP] 251 { off | try_unsupported } 252 off: disable AGP support 253 try_unsupported: try to drive unsupported chipsets 254 (may crash computer or cause data corruption) 255 256 ALSA [HW,ALSA] 257 See Documentation/sound/alsa/alsa-parameters.txt 258 259 alignment= [KNL,ARM] 260 Allow the default userspace alignment fault handler 261 behaviour to be specified. Bit 0 enables warnings, 262 bit 1 enables fixups, and bit 2 sends a segfault. 263 264 align_va_addr= [X86-64] 265 Align virtual addresses by clearing slice [14:12] when 266 allocating a VMA at process creation time. This option 267 gives you up to 3% performance improvement on AMD F15h 268 machines (where it is enabled by default) for a 269 CPU-intensive style benchmark, and it can vary highly in 270 a microbenchmark depending on workload and compiler. 271 272 32: only for 32-bit processes 273 64: only for 64-bit processes 274 on: enable for both 32- and 64-bit processes 275 off: disable for both 32- and 64-bit processes 276 277 alloc_snapshot [FTRACE] 278 Allocate the ftrace snapshot buffer on boot up when the 279 main buffer is allocated. This is handy if debugging 280 and you need to use tracing_snapshot() on boot up, and 281 do not want to use tracing_snapshot_alloc() as it needs 282 to be done where GFP_KERNEL allocations are allowed. 283 284 amd_iommu= [HW,X86-64] 285 Pass parameters to the AMD IOMMU driver in the system. 286 Possible values are: 287 fullflush - enable flushing of IO/TLB entries when 288 they are unmapped. Otherwise they are 289 flushed before they will be reused, which 290 is a lot of faster 291 off - do not initialize any AMD IOMMU found in 292 the system 293 force_isolation - Force device isolation for all 294 devices. The IOMMU driver is not 295 allowed anymore to lift isolation 296 requirements as needed. This option 297 does not override iommu=pt 298 299 amd_iommu_dump= [HW,X86-64] 300 Enable AMD IOMMU driver option to dump the ACPI table 301 for AMD IOMMU. With this option enabled, AMD IOMMU 302 driver will print ACPI tables for AMD IOMMU during 303 IOMMU initialization. 304 305 amd_iommu_intr= [HW,X86-64] 306 Specifies one of the following AMD IOMMU interrupt 307 remapping modes: 308 legacy - Use legacy interrupt remapping mode. 309 vapic - Use virtual APIC mode, which allows IOMMU 310 to inject interrupts directly into guest. 311 This mode requires kvm-amd.avic=1. 312 (Default when IOMMU HW support is present.) 313 314 amijoy.map= [HW,JOY] Amiga joystick support 315 Map of devices attached to JOY0DAT and JOY1DAT 316 Format: <a>,<b> 317 See also Documentation/input/joystick.txt 318 319 analog.map= [HW,JOY] Analog joystick and gamepad support 320 Specifies type or capabilities of an analog joystick 321 connected to one of 16 gameports 322 Format: <type1>,<type2>,..<type16> 323 324 apc= [HW,SPARC] 325 Power management functions (SPARCstation-4/5 + deriv.) 326 Format: noidle 327 Disable APC CPU standby support. SPARCstation-Fox does 328 not play well with APC CPU idle - disable it if you have 329 APC and your system crashes randomly. 330 331 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller 332 Change the output verbosity whilst booting 333 Format: { quiet (default) | verbose | debug } 334 Change the amount of debugging information output 335 when initialising the APIC and IO-APIC components. 336 337 apic_extnmi= [APIC,X86] External NMI delivery setting 338 Format: { bsp (default) | all | none } 339 bsp: External NMI is delivered only to CPU 0 340 all: External NMIs are broadcast to all CPUs as a 341 backup of CPU 0 342 none: External NMI is masked for all CPUs. This is 343 useful so that a dump capture kernel won't be 344 shot down by NMI 345 346 autoconf= [IPV6] 347 See Documentation/networking/ipv6.txt. 348 349 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller 350 Limit apic dumping. The parameter defines the maximal 351 number of local apics being dumped. Also it is possible 352 to set it to "all" by meaning -- no limit here. 353 Format: { 1 (default) | 2 | ... | all }. 354 The parameter valid if only apic=debug or 355 apic=verbose is specified. 356 Example: apic=debug show_lapic=all 357 358 apm= [APM] Advanced Power Management 359 See header of arch/x86/kernel/apm_32.c. 360 361 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards 362 Format: <io>,<irq>,<nodeID> 363 364 ataflop= [HW,M68k] 365 366 atarimouse= [HW,MOUSE] Atari Mouse 367 368 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess, 369 EzKey and similar keyboards 370 371 atkbd.reset= [HW] Reset keyboard during initialization 372 373 atkbd.set= [HW] Select keyboard code set 374 Format: <int> (2 = AT (default), 3 = PS/2) 375 376 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar 377 keyboards 378 379 atkbd.softraw= [HW] Choose between synthetic and real raw mode 380 Format: <bool> (0 = real, 1 = synthetic (default)) 381 382 atkbd.softrepeat= [HW] 383 Use software keyboard repeat 384 385 audit= [KNL] Enable the audit sub-system 386 Format: { "0" | "1" } (0 = disabled, 1 = enabled) 387 0 - kernel audit is disabled and can not be enabled 388 until the next reboot 389 unset - kernel audit is initialized but disabled and 390 will be fully enabled by the userspace auditd. 391 1 - kernel audit is initialized and partially enabled, 392 storing at most audit_backlog_limit messages in 393 RAM until it is fully enabled by the userspace 394 auditd. 395 Default: unset 396 397 audit_backlog_limit= [KNL] Set the audit queue size limit. 398 Format: <int> (must be >=0) 399 Default: 64 400 401 bau= [X86_UV] Enable the BAU on SGI UV. The default 402 behavior is to disable the BAU (i.e. bau=0). 403 Format: { "0" | "1" } 404 0 - Disable the BAU. 405 1 - Enable the BAU. 406 unset - Disable the BAU. 407 408 baycom_epp= [HW,AX25] 409 Format: <io>,<mode> 410 411 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem 412 Format: <io>,<mode> 413 See header of drivers/net/hamradio/baycom_par.c. 414 415 baycom_ser_fdx= [HW,AX25] 416 BayCom Serial Port AX.25 Modem (Full Duplex Mode) 417 Format: <io>,<irq>,<mode>[,<baud>] 418 See header of drivers/net/hamradio/baycom_ser_fdx.c. 419 420 baycom_ser_hdx= [HW,AX25] 421 BayCom Serial Port AX.25 Modem (Half Duplex Mode) 422 Format: <io>,<irq>,<mode> 423 See header of drivers/net/hamradio/baycom_ser_hdx.c. 424 425 blkdevparts= Manual partition parsing of block device(s) for 426 embedded devices based on command line input. 427 See Documentation/block/cmdline-partition.txt 428 429 boot_delay= Milliseconds to delay each printk during boot. 430 Values larger than 10 seconds (10000) are changed to 431 no delay (0). 432 Format: integer 433 434 bootmem_debug [KNL] Enable bootmem allocator debug messages. 435 436 bert_disable [ACPI] 437 Disable BERT OS support on buggy BIOSes. 438 439 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards) 440 bttv.radio= Most important insmod options are available as 441 kernel args too. 442 bttv.pll= See Documentation/video4linux/bttv/Insmod-options 443 bttv.tuner= 444 445 bulk_remove=off [PPC] This parameter disables the use of the pSeries 446 firmware feature for flushing multiple hpte entries 447 at a time. 448 449 c101= [NET] Moxa C101 synchronous serial card 450 451 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection. 452 Sometimes CPU hardware bugs make them report the cache 453 size incorrectly. The kernel will attempt work arounds 454 to fix known problems, but for some CPUs it is not 455 possible to determine what the correct size should be. 456 This option provides an override for these situations. 457 458 ca_keys= [KEYS] This parameter identifies a specific key(s) on 459 the system trusted keyring to be used for certificate 460 trust validation. 461 format: { id:<keyid> | builtin } 462 463 cca= [MIPS] Override the kernel pages' cache coherency 464 algorithm. Accepted values range from 0 to 7 465 inclusive. See arch/mips/include/asm/pgtable-bits.h 466 for platform specific values (SB1, Loongson3 and 467 others). 468 469 ccw_timeout_log [S390] 470 See Documentation/s390/CommonIO for details. 471 472 cgroup_disable= [KNL] Disable a particular controller 473 Format: {name of the controller(s) to disable} 474 The effects of cgroup_disable=foo are: 475 - foo isn't auto-mounted if you mount all cgroups in 476 a single hierarchy 477 - foo isn't visible as an individually mountable 478 subsystem 479 {Currently only "memory" controller deal with this and 480 cut the overhead, others just disable the usage. So 481 only cgroup_disable=memory is actually worthy} 482 483 cgroup_no_v1= [KNL] Disable one, multiple, all cgroup controllers in v1 484 Format: { controller[,controller...] | "all" } 485 Like cgroup_disable, but only applies to cgroup v1; 486 the blacklisted controllers remain available in cgroup2. 487 488 cgroup.memory= [KNL] Pass options to the cgroup memory controller. 489 Format: <string> 490 nosocket -- Disable socket memory accounting. 491 nokmem -- Disable kernel memory accounting. 492 493 checkreqprot [SELINUX] Set initial checkreqprot flag value. 494 Format: { "0" | "1" } 495 See security/selinux/Kconfig help text. 496 0 -- check protection applied by kernel (includes 497 any implied execute protection). 498 1 -- check protection requested by application. 499 Default value is set via a kernel config option. 500 Value can be changed at runtime via 501 /selinux/checkreqprot. 502 503 cio_ignore= [S390] 504 See Documentation/s390/CommonIO for details. 505 clk_ignore_unused 506 [CLK] 507 Prevents the clock framework from automatically gating 508 clocks that have not been explicitly enabled by a Linux 509 device driver but are enabled in hardware at reset or 510 by the bootloader/firmware. Note that this does not 511 force such clocks to be always-on nor does it reserve 512 those clocks in any way. This parameter is useful for 513 debug and development, but should not be needed on a 514 platform with proper driver support. For more 515 information, see Documentation/clk.txt. 516 517 clock= [BUGS=X86-32, HW] gettimeofday clocksource override. 518 [Deprecated] 519 Forces specified clocksource (if available) to be used 520 when calculating gettimeofday(). If specified 521 clocksource is not available, it defaults to PIT. 522 Format: { pit | tsc | cyclone | pmtmr } 523 524 clocksource= Override the default clocksource 525 Format: <string> 526 Override the default clocksource and use the clocksource 527 with the name specified. 528 Some clocksource names to choose from, depending on 529 the platform: 530 [all] jiffies (this is the base, fallback clocksource) 531 [ACPI] acpi_pm 532 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2, 533 pxa_timer,timer3,32k_counter,timer0_1 534 [X86-32] pit,hpet,tsc; 535 scx200_hrt on Geode; cyclone on IBM x440 536 [MIPS] MIPS 537 [PARISC] cr16 538 [S390] tod 539 [SH] SuperH 540 [SPARC64] tick 541 [X86-64] hpet,tsc 542 543 clocksource.arm_arch_timer.evtstrm= 544 [ARM,ARM64] 545 Format: <bool> 546 Enable/disable the eventstream feature of the ARM 547 architected timer so that code using WFE-based polling 548 loops can be debugged more effectively on production 549 systems. 550 551 clearcpuid=BITNUM [X86] 552 Disable CPUID feature X for the kernel. See 553 arch/x86/include/asm/cpufeatures.h for the valid bit 554 numbers. Note the Linux specific bits are not necessarily 555 stable over kernel options, but the vendor specific 556 ones should be. 557 Also note that user programs calling CPUID directly 558 or using the feature without checking anything 559 will still see it. This just prevents it from 560 being used by the kernel or shown in /proc/cpuinfo. 561 Also note the kernel might malfunction if you disable 562 some critical bits. 563 564 cma=nn[MG]@[start[MG][-end[MG]]] 565 [ARM,X86,KNL] 566 Sets the size of kernel global memory area for 567 contiguous memory allocations and optionally the 568 placement constraint by the physical address range of 569 memory allocations. A value of 0 disables CMA 570 altogether. For more information, see 571 include/linux/dma-contiguous.h 572 573 cmo_free_hint= [PPC] Format: { yes | no } 574 Specify whether pages are marked as being inactive 575 when they are freed. This is used in CMO environments 576 to determine OS memory pressure for page stealing by 577 a hypervisor. 578 Default: yes 579 580 coherent_pool=nn[KMG] [ARM,KNL] 581 Sets the size of memory pool for coherent, atomic dma 582 allocations, by default set to 256K. 583 584 code_bytes [X86] How many bytes of object code to print 585 in an oops report. 586 Range: 0 - 8192 587 Default: 64 588 589 com20020= [HW,NET] ARCnet - COM20020 chipset 590 Format: 591 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]] 592 593 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers) 594 Format: <io>[,<irq>] 595 596 com90xx= [HW,NET] 597 ARCnet - COM90xx chipset (memory-mapped buffers) 598 Format: <io>[,<irq>[,<memstart>]] 599 600 condev= [HW,S390] console device 601 conmode= 602 603 console= [KNL] Output console device and options. 604 605 tty<n> Use the virtual console device <n>. 606 607 ttyS<n>[,options] 608 ttyUSB0[,options] 609 Use the specified serial port. The options are of 610 the form "bbbbpnf", where "bbbb" is the baud rate, 611 "p" is parity ("n", "o", or "e"), "n" is number of 612 bits, and "f" is flow control ("r" for RTS or 613 omit it). Default is "9600n8". 614 615 See Documentation/admin-guide/serial-console.rst for more 616 information. See 617 Documentation/networking/netconsole.txt for an 618 alternative. 619 620 uart[8250],io,<addr>[,options] 621 uart[8250],mmio,<addr>[,options] 622 uart[8250],mmio16,<addr>[,options] 623 uart[8250],mmio32,<addr>[,options] 624 uart[8250],0x<addr>[,options] 625 Start an early, polled-mode console on the 8250/16550 626 UART at the specified I/O port or MMIO address, 627 switching to the matching ttyS device later. 628 MMIO inter-register address stride is either 8-bit 629 (mmio), 16-bit (mmio16), or 32-bit (mmio32). 630 If none of [io|mmio|mmio16|mmio32], <addr> is assumed 631 to be equivalent to 'mmio'. 'options' are specified in 632 the same format described for ttyS above; if unspecified, 633 the h/w is not re-initialized. 634 635 hvc<n> Use the hypervisor console device <n>. This is for 636 both Xen and PowerPC hypervisors. 637 638 If the device connected to the port is not a TTY but a braille 639 device, prepend "brl," before the device type, for instance 640 console=brl,ttyS0 641 For now, only VisioBraille is supported. 642 643 consoleblank= [KNL] The console blank (screen saver) timeout in 644 seconds. Defaults to 10*60 = 10mins. A value of 0 645 disables the blank timer. 646 647 coredump_filter= 648 [KNL] Change the default value for 649 /proc/<pid>/coredump_filter. 650 See also Documentation/filesystems/proc.txt. 651 652 cpuidle.off=1 [CPU_IDLE] 653 disable the cpuidle sub-system 654 655 cpufreq.off=1 [CPU_FREQ] 656 disable the cpufreq sub-system 657 658 cpu_init_udelay=N 659 [X86] Delay for N microsec between assert and de-assert 660 of APIC INIT to start processors. This delay occurs 661 on every CPU online, such as boot, and resume from suspend. 662 Default: 10000 663 664 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver 665 Format: 666 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] 667 668 crashkernel=size[KMG][@offset[KMG]] 669 [KNL] Using kexec, Linux can switch to a 'crash kernel' 670 upon panic. This parameter reserves the physical 671 memory region [offset, offset + size] for that kernel 672 image. If '@offset' is omitted, then a suitable offset 673 is selected automatically. Check 674 Documentation/kdump/kdump.txt for further details. 675 676 crashkernel=range1:size1[,range2:size2,...][@offset] 677 [KNL] Same as above, but depends on the memory 678 in the running system. The syntax of range is 679 start-[end] where start and end are both 680 a memory unit (amount[KMG]). See also 681 Documentation/kdump/kdump.txt for an example. 682 683 crashkernel=size[KMG],high 684 [KNL, x86_64] range could be above 4G. Allow kernel 685 to allocate physical memory region from top, so could 686 be above 4G if system have more than 4G ram installed. 687 Otherwise memory region will be allocated below 4G, if 688 available. 689 It will be ignored if crashkernel=X is specified. 690 crashkernel=size[KMG],low 691 [KNL, x86_64] range under 4G. When crashkernel=X,high 692 is passed, kernel could allocate physical memory region 693 above 4G, that cause second kernel crash on system 694 that require some amount of low memory, e.g. swiotlb 695 requires at least 64M+32K low memory, also enough extra 696 low memory is needed to make sure DMA buffers for 32-bit 697 devices won't run out. Kernel would try to allocate at 698 at least 256M below 4G automatically. 699 This one let user to specify own low range under 4G 700 for second kernel instead. 701 0: to disable low allocation. 702 It will be ignored when crashkernel=X,high is not used 703 or memory reserved is below 4G. 704 705 cryptomgr.notests 706 [KNL] Disable crypto self-tests 707 708 cs89x0_dma= [HW,NET] 709 Format: <dma> 710 711 cs89x0_media= [HW,NET] 712 Format: { rj45 | aui | bnc } 713 714 dasd= [HW,NET] 715 See header of drivers/s390/block/dasd_devmap.c. 716 717 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port 718 (one device per port) 719 Format: <port#>,<type> 720 See also Documentation/input/joystick-parport.txt 721 722 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot 723 time. See Documentation/dynamic-debug-howto.txt for 724 details. Deprecated, see dyndbg. 725 726 debug [KNL] Enable kernel debugging (events log level). 727 728 debug_locks_verbose= 729 [KNL] verbose self-tests 730 Format=<0|1> 731 Print debugging info while doing the locking API 732 self-tests. 733 We default to 0 (no extra messages), setting it to 734 1 will print _a lot_ more information - normally 735 only useful to kernel developers. 736 737 debug_objects [KNL] Enable object debugging 738 739 no_debug_objects 740 [KNL] Disable object debugging 741 742 debug_guardpage_minorder= 743 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this 744 parameter allows control of the order of pages that will 745 be intentionally kept free (and hence protected) by the 746 buddy allocator. Bigger value increase the probability 747 of catching random memory corruption, but reduce the 748 amount of memory for normal system use. The maximum 749 possible value is MAX_ORDER/2. Setting this parameter 750 to 1 or 2 should be enough to identify most random 751 memory corruption problems caused by bugs in kernel or 752 driver code when a CPU writes to (or reads from) a 753 random memory location. Note that there exists a class 754 of memory corruptions problems caused by buggy H/W or 755 F/W or by drivers badly programing DMA (basically when 756 memory is written at bus level and the CPU MMU is 757 bypassed) which are not detectable by 758 CONFIG_DEBUG_PAGEALLOC, hence this option will not help 759 tracking down these problems. 760 761 debug_pagealloc= 762 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this 763 parameter enables the feature at boot time. In 764 default, it is disabled. We can avoid allocating huge 765 chunk of memory for debug pagealloc if we don't enable 766 it at boot time and the system will work mostly same 767 with the kernel built without CONFIG_DEBUG_PAGEALLOC. 768 on: enable the feature 769 770 debugpat [X86] Enable PAT debugging 771 772 decnet.addr= [HW,NET] 773 Format: <area>[,<node>] 774 See also Documentation/networking/decnet.txt. 775 776 default_hugepagesz= 777 [same as hugepagesz=] The size of the default 778 HugeTLB page size. This is the size represented by 779 the legacy /proc/ hugepages APIs, used for SHM, and 780 default size when mounting hugetlbfs filesystems. 781 Defaults to the default architecture's huge page size 782 if not specified. 783 784 dhash_entries= [KNL] 785 Set number of hash buckets for dentry cache. 786 787 disable_1tb_segments [PPC] 788 Disables the use of 1TB hash page table segments. This 789 causes the kernel to fall back to 256MB segments which 790 can be useful when debugging issues that require an SLB 791 miss to occur. 792 793 disable= [IPV6] 794 See Documentation/networking/ipv6.txt. 795 796 disable_radix [PPC] 797 Disable RADIX MMU mode on POWER9 798 799 disable_cpu_apicid= [X86,APIC,SMP] 800 Format: <int> 801 The number of initial APIC ID for the 802 corresponding CPU to be disabled at boot, 803 mostly used for the kdump 2nd kernel to 804 disable BSP to wake up multiple CPUs without 805 causing system reset or hang due to sending 806 INIT from AP to BSP. 807 808 disable_ddw [PPC/PSERIES] 809 Disable Dynamic DMA Window support. Use this if 810 to workaround buggy firmware. 811 812 disable_ipv6= [IPV6] 813 See Documentation/networking/ipv6.txt. 814 815 disable_mtrr_cleanup [X86] 816 The kernel tries to adjust MTRR layout from continuous 817 to discrete, to make X server driver able to add WB 818 entry later. This parameter disables that. 819 820 disable_mtrr_trim [X86, Intel and AMD only] 821 By default the kernel will trim any uncacheable 822 memory out of your available memory pool based on 823 MTRR settings. This parameter disables that behavior, 824 possibly causing your machine to run very slowly. 825 826 disable_timer_pin_1 [X86] 827 Disable PIN 1 of APIC timer 828 Can be useful to work around chipset bugs. 829 830 dis_ucode_ldr [X86] Disable the microcode loader. 831 832 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, 833 this option disables the debugging code at boot. 834 835 dma_debug_entries=<number> 836 This option allows to tune the number of preallocated 837 entries for DMA-API debugging code. One entry is 838 required per DMA-API allocation. Use this if the 839 DMA-API debugging code disables itself because the 840 architectural default is too low. 841 842 dma_debug_driver=<driver_name> 843 With this option the DMA-API debugging driver 844 filter feature can be enabled at boot time. Just 845 pass the driver to filter for as the parameter. 846 The filter can be disabled or changed to another 847 driver later using sysfs. 848 849 drm_kms_helper.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>] 850 Broken monitors, graphic adapters, KVMs and EDIDless 851 panels may send no or incorrect EDID data sets. 852 This parameter allows to specify an EDID data sets 853 in the /lib/firmware directory that are used instead. 854 Generic built-in EDID data sets are used, if one of 855 edid/1024x768.bin, edid/1280x1024.bin, 856 edid/1680x1050.bin, or edid/1920x1080.bin is given 857 and no file with the same name exists. Details and 858 instructions how to build your own EDID data are 859 available in Documentation/EDID/HOWTO.txt. An EDID 860 data set will only be used for a particular connector, 861 if its name and a colon are prepended to the EDID 862 name. Each connector may use a unique EDID data 863 set by separating the files with a comma. An EDID 864 data set with no connector name will be used for 865 any connectors not explicitly specified. 866 867 dscc4.setup= [NET] 868 869 dt_cpu_ftrs= [PPC] 870 Format: {"off" | "known"} 871 Control how the dt_cpu_ftrs device-tree binding is 872 used for CPU feature discovery and setup (if it 873 exists). 874 off: Do not use it, fall back to legacy cpu table. 875 known: Do not pass through unknown features to guests 876 or userspace, only those that the kernel is aware of. 877 878 dump_apple_properties [X86] 879 Dump name and content of EFI device properties on 880 x86 Macs. Useful for driver authors to determine 881 what data is available or for reverse-engineering. 882 883 dyndbg[="val"] [KNL,DYNAMIC_DEBUG] 884 module.dyndbg[="val"] 885 Enable debug messages at boot time. See 886 Documentation/dynamic-debug-howto.txt for details. 887 888 nompx [X86] Disables Intel Memory Protection Extensions. 889 See Documentation/x86/intel_mpx.txt for more 890 information about the feature. 891 892 nopku [X86] Disable Memory Protection Keys CPU feature found 893 in some Intel CPUs. 894 895 module.async_probe [KNL] 896 Enable asynchronous probe on this module. 897 898 early_ioremap_debug [KNL] 899 Enable debug messages in early_ioremap support. This 900 is useful for tracking down temporary early mappings 901 which are not unmapped. 902 903 earlycon= [KNL] Output early console device and options. 904 905 When used with no options, the early console is 906 determined by the stdout-path property in device 907 tree's chosen node. 908 909 cdns,<addr>[,options] 910 Start an early, polled-mode console on a Cadence 911 (xuartps) serial port at the specified address. Only 912 supported option is baud rate. If baud rate is not 913 specified, the serial port must already be setup and 914 configured. 915 916 uart[8250],io,<addr>[,options] 917 uart[8250],mmio,<addr>[,options] 918 uart[8250],mmio32,<addr>[,options] 919 uart[8250],mmio32be,<addr>[,options] 920 uart[8250],0x<addr>[,options] 921 Start an early, polled-mode console on the 8250/16550 922 UART at the specified I/O port or MMIO address. 923 MMIO inter-register address stride is either 8-bit 924 (mmio) or 32-bit (mmio32 or mmio32be). 925 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed 926 to be equivalent to 'mmio'. 'options' are specified 927 in the same format described for "console=ttyS<n>"; if 928 unspecified, the h/w is not initialized. 929 930 pl011,<addr> 931 pl011,mmio32,<addr> 932 Start an early, polled-mode console on a pl011 serial 933 port at the specified address. The pl011 serial port 934 must already be setup and configured. Options are not 935 yet supported. If 'mmio32' is specified, then only 936 the driver will use only 32-bit accessors to read/write 937 the device registers. 938 939 meson,<addr> 940 Start an early, polled-mode console on a meson serial 941 port at the specified address. The serial port must 942 already be setup and configured. Options are not yet 943 supported. 944 945 msm_serial,<addr> 946 Start an early, polled-mode console on an msm serial 947 port at the specified address. The serial port 948 must already be setup and configured. Options are not 949 yet supported. 950 951 msm_serial_dm,<addr> 952 Start an early, polled-mode console on an msm serial 953 dm port at the specified address. The serial port 954 must already be setup and configured. Options are not 955 yet supported. 956 957 smh Use ARM semihosting calls for early console. 958 959 s3c2410,<addr> 960 s3c2412,<addr> 961 s3c2440,<addr> 962 s3c6400,<addr> 963 s5pv210,<addr> 964 exynos4210,<addr> 965 Use early console provided by serial driver available 966 on Samsung SoCs, requires selecting proper type and 967 a correct base address of the selected UART port. The 968 serial port must already be setup and configured. 969 Options are not yet supported. 970 971 lantiq,<addr> 972 Start an early, polled-mode console on a lantiq serial 973 (lqasc) port at the specified address. The serial port 974 must already be setup and configured. Options are not 975 yet supported. 976 977 lpuart,<addr> 978 lpuart32,<addr> 979 Use early console provided by Freescale LP UART driver 980 found on Freescale Vybrid and QorIQ LS1021A processors. 981 A valid base address must be provided, and the serial 982 port must already be setup and configured. 983 984 ar3700_uart,<addr> 985 Start an early, polled-mode console on the 986 Armada 3700 serial port at the specified 987 address. The serial port must already be setup 988 and configured. Options are not yet supported. 989 990 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k,S390] 991 earlyprintk=vga 992 earlyprintk=efi 993 earlyprintk=sclp 994 earlyprintk=xen 995 earlyprintk=serial[,ttySn[,baudrate]] 996 earlyprintk=serial[,0x...[,baudrate]] 997 earlyprintk=ttySn[,baudrate] 998 earlyprintk=dbgp[debugController#] 999 earlyprintk=pciserial,bus:device.function[,baudrate] 1000 earlyprintk=xdbc[xhciController#] 1001 1002 earlyprintk is useful when the kernel crashes before 1003 the normal console is initialized. It is not enabled by 1004 default because it has some cosmetic problems. 1005 1006 Append ",keep" to not disable it when the real console 1007 takes over. 1008 1009 Only one of vga, efi, serial, or usb debug port can 1010 be used at a time. 1011 1012 Currently only ttyS0 and ttyS1 may be specified by 1013 name. Other I/O ports may be explicitly specified 1014 on some architectures (x86 and arm at least) by 1015 replacing ttySn with an I/O port address, like this: 1016 earlyprintk=serial,0x1008,115200 1017 You can find the port for a given device in 1018 /proc/tty/driver/serial: 1019 2: uart:ST16650V2 port:00001008 irq:18 ... 1020 1021 Interaction with the standard serial driver is not 1022 very good. 1023 1024 The VGA and EFI output is eventually overwritten by 1025 the real console. 1026 1027 The xen output can only be used by Xen PV guests. 1028 1029 The sclp output can only be used on s390. 1030 1031 edac_report= [HW,EDAC] Control how to report EDAC event 1032 Format: {"on" | "off" | "force"} 1033 on: enable EDAC to report H/W event. May be overridden 1034 by other higher priority error reporting module. 1035 off: disable H/W event reporting through EDAC. 1036 force: enforce the use of EDAC to report H/W event. 1037 default: on. 1038 1039 ekgdboc= [X86,KGDB] Allow early kernel console debugging 1040 ekgdboc=kbd 1041 1042 This is designed to be used in conjunction with 1043 the boot argument: earlyprintk=vga 1044 1045 edd= [EDD] 1046 Format: {"off" | "on" | "skip[mbr]"} 1047 1048 efi= [EFI] 1049 Format: { "old_map", "nochunk", "noruntime", "debug" } 1050 old_map [X86-64]: switch to the old ioremap-based EFI 1051 runtime services mapping. 32-bit still uses this one by 1052 default. 1053 nochunk: disable reading files in "chunks" in the EFI 1054 boot stub, as chunking can cause problems with some 1055 firmware implementations. 1056 noruntime : disable EFI runtime services support 1057 debug: enable misc debug output 1058 1059 efi_no_storage_paranoia [EFI; X86] 1060 Using this parameter you can use more than 50% of 1061 your efi variable storage. Use this parameter only if 1062 you are really sure that your UEFI does sane gc and 1063 fulfills the spec otherwise your board may brick. 1064 1065 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86] 1066 Add arbitrary attribute to specific memory range by 1067 updating original EFI memory map. 1068 Region of memory which aa attribute is added to is 1069 from ss to ss+nn. 1070 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000 1071 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000) 1072 attribute is added to range 0x100000000-0x180000000 and 1073 0x10a0000000-0x1120000000. 1074 1075 Using this parameter you can do debugging of EFI memmap 1076 related feature. For example, you can do debugging of 1077 Address Range Mirroring feature even if your box 1078 doesn't support it. 1079 1080 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT 1081 that is to be dynamically loaded by Linux. If there are 1082 multiple variables with the same name but with different 1083 vendor GUIDs, all of them will be loaded. See 1084 Documentation/acpi/ssdt-overlays.txt for details. 1085 1086 1087 eisa_irq_edge= [PARISC,HW] 1088 See header of drivers/parisc/eisa.c. 1089 1090 elanfreq= [X86-32] 1091 See comment before function elanfreq_setup() in 1092 arch/x86/kernel/cpu/cpufreq/elanfreq.c. 1093 1094 elevator= [IOSCHED] 1095 Format: {"cfq" | "deadline" | "noop"} 1096 See Documentation/block/cfq-iosched.txt and 1097 Documentation/block/deadline-iosched.txt for details. 1098 1099 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390] 1100 Specifies physical address of start of kernel core 1101 image elf header and optionally the size. Generally 1102 kexec loader will pass this option to capture kernel. 1103 See Documentation/kdump/kdump.txt for details. 1104 1105 enable_mtrr_cleanup [X86] 1106 The kernel tries to adjust MTRR layout from continuous 1107 to discrete, to make X server driver able to add WB 1108 entry later. This parameter enables that. 1109 1110 enable_timer_pin_1 [X86] 1111 Enable PIN 1 of APIC timer 1112 Can be useful to work around chipset bugs 1113 (in particular on some ATI chipsets). 1114 The kernel tries to set a reasonable default. 1115 1116 enforcing [SELINUX] Set initial enforcing status. 1117 Format: {"0" | "1"} 1118 See security/selinux/Kconfig help text. 1119 0 -- permissive (log only, no denials). 1120 1 -- enforcing (deny and log). 1121 Default value is 0. 1122 Value can be changed at runtime via /selinux/enforce. 1123 1124 erst_disable [ACPI] 1125 Disable Error Record Serialization Table (ERST) 1126 support. 1127 1128 ether= [HW,NET] Ethernet cards parameters 1129 This option is obsoleted by the "netdev=" option, which 1130 has equivalent usage. See its documentation for details. 1131 1132 evm= [EVM] 1133 Format: { "fix" } 1134 Permit 'security.evm' to be updated regardless of 1135 current integrity status. 1136 1137 failslab= 1138 fail_page_alloc= 1139 fail_make_request=[KNL] 1140 General fault injection mechanism. 1141 Format: <interval>,<probability>,<space>,<times> 1142 See also Documentation/fault-injection/. 1143 1144 floppy= [HW] 1145 See Documentation/blockdev/floppy.txt. 1146 1147 force_pal_cache_flush 1148 [IA-64] Avoid check_sal_cache_flush which may hang on 1149 buggy SAL_CACHE_FLUSH implementations. Using this 1150 parameter will force ia64_sal_cache_flush to call 1151 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH. 1152 1153 forcepae [X86-32] 1154 Forcefully enable Physical Address Extension (PAE). 1155 Many Pentium M systems disable PAE but may have a 1156 functionally usable PAE implementation. 1157 Warning: use of this parameter will taint the kernel 1158 and may cause unknown problems. 1159 1160 ftrace=[tracer] 1161 [FTRACE] will set and start the specified tracer 1162 as early as possible in order to facilitate early 1163 boot debugging. 1164 1165 ftrace_dump_on_oops[=orig_cpu] 1166 [FTRACE] will dump the trace buffers on oops. 1167 If no parameter is passed, ftrace will dump 1168 buffers of all CPUs, but if you pass orig_cpu, it will 1169 dump only the buffer of the CPU that triggered the 1170 oops. 1171 1172 ftrace_filter=[function-list] 1173 [FTRACE] Limit the functions traced by the function 1174 tracer at boot up. function-list is a comma separated 1175 list of functions. This list can be changed at run 1176 time by the set_ftrace_filter file in the debugfs 1177 tracing directory. 1178 1179 ftrace_notrace=[function-list] 1180 [FTRACE] Do not trace the functions specified in 1181 function-list. This list can be changed at run time 1182 by the set_ftrace_notrace file in the debugfs 1183 tracing directory. 1184 1185 ftrace_graph_filter=[function-list] 1186 [FTRACE] Limit the top level callers functions traced 1187 by the function graph tracer at boot up. 1188 function-list is a comma separated list of functions 1189 that can be changed at run time by the 1190 set_graph_function file in the debugfs tracing directory. 1191 1192 ftrace_graph_notrace=[function-list] 1193 [FTRACE] Do not trace from the functions specified in 1194 function-list. This list is a comma separated list of 1195 functions that can be changed at run time by the 1196 set_graph_notrace file in the debugfs tracing directory. 1197 1198 ftrace_graph_max_depth=<uint> 1199 [FTRACE] Used with the function graph tracer. This is 1200 the max depth it will trace into a function. This value 1201 can be changed at run time by the max_graph_depth file 1202 in the tracefs tracing directory. default: 0 (no limit) 1203 1204 gamecon.map[2|3]= 1205 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 1206 support via parallel port (up to 5 devices per port) 1207 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 1208 See also Documentation/input/joystick-parport.txt 1209 1210 gamma= [HW,DRM] 1211 1212 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART 1213 Format: off | on 1214 default: on 1215 1216 gcov_persist= [GCOV] When non-zero (default), profiling data for 1217 kernel modules is saved and remains accessible via 1218 debugfs, even when the module is unloaded/reloaded. 1219 When zero, profiling data is discarded and associated 1220 debugfs files are removed at module unload time. 1221 1222 goldfish [X86] Enable the goldfish android emulator platform. 1223 Don't use this when you are not running on the 1224 android emulator 1225 1226 gpt [EFI] Forces disk with valid GPT signature but 1227 invalid Protective MBR to be treated as GPT. If the 1228 primary GPT is corrupted, it enables the backup/alternate 1229 GPT to be used instead. 1230 1231 grcan.enable0= [HW] Configuration of physical interface 0. Determines 1232 the "Enable 0" bit of the configuration register. 1233 Format: 0 | 1 1234 Default: 0 1235 grcan.enable1= [HW] Configuration of physical interface 1. Determines 1236 the "Enable 0" bit of the configuration register. 1237 Format: 0 | 1 1238 Default: 0 1239 grcan.select= [HW] Select which physical interface to use. 1240 Format: 0 | 1 1241 Default: 0 1242 grcan.txsize= [HW] Sets the size of the tx buffer. 1243 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. 1244 Default: 1024 1245 grcan.rxsize= [HW] Sets the size of the rx buffer. 1246 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. 1247 Default: 1024 1248 1249 gpio-mockup.gpio_mockup_ranges 1250 [HW] Sets the ranges of gpiochip of for this device. 1251 Format: <start1>,<end1>,<start2>,<end2>... 1252 1253 hardlockup_all_cpu_backtrace= 1254 [KNL] Should the hard-lockup detector generate 1255 backtraces on all cpus. 1256 Format: <integer> 1257 1258 hashdist= [KNL,NUMA] Large hashes allocated during boot 1259 are distributed across NUMA nodes. Defaults on 1260 for 64-bit NUMA, off otherwise. 1261 Format: 0 | 1 (for off | on) 1262 1263 hcl= [IA-64] SGI's Hardware Graph compatibility layer 1264 1265 hd= [EIDE] (E)IDE hard drive subsystem geometry 1266 Format: <cyl>,<head>,<sect> 1267 1268 hest_disable [ACPI] 1269 Disable Hardware Error Source Table (HEST) support; 1270 corresponding firmware-first mode error processing 1271 logic will be disabled. 1272 1273 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact 1274 size of <nn>. This works even on boxes that have no 1275 highmem otherwise. This also works to reduce highmem 1276 size on bigger boxes. 1277 1278 highres= [KNL] Enable/disable high resolution timer mode. 1279 Valid parameters: "on", "off" 1280 Default: "on" 1281 1282 hisax= [HW,ISDN] 1283 See Documentation/isdn/README.HiSax. 1284 1285 hlt [BUGS=ARM,SH] 1286 1287 hpet= [X86-32,HPET] option to control HPET usage 1288 Format: { enable (default) | disable | force | 1289 verbose } 1290 disable: disable HPET and use PIT instead 1291 force: allow force enabled of undocumented chips (ICH4, 1292 VIA, nVidia) 1293 verbose: show contents of HPET registers during setup 1294 1295 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET 1296 registers. Default set by CONFIG_HPET_MMAP_DEFAULT. 1297 1298 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot. 1299 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages. 1300 On x86-64 and powerpc, this option can be specified 1301 multiple times interleaved with hugepages= to reserve 1302 huge pages of different sizes. Valid pages sizes on 1303 x86-64 are 2M (when the CPU supports "pse") and 1G 1304 (when the CPU supports the "pdpe1gb" cpuinfo flag). 1305 1306 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 1307 terminal devices. Valid values: 0..8 1308 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 1309 If specified, z/VM IUCV HVC accepts connections 1310 from listed z/VM user IDs only. 1311 1312 hwthread_map= [METAG] Comma-separated list of Linux cpu id to 1313 hardware thread id mappings. 1314 Format: <cpu>:<hwthread> 1315 1316 keep_bootcon [KNL] 1317 Do not unregister boot console at start. This is only 1318 useful for debugging when something happens in the window 1319 between unregistering the boot console and initializing 1320 the real console. 1321 1322 i2c_bus= [HW] Override the default board specific I2C bus speed 1323 or register an additional I2C bus that is not 1324 registered from board initialization code. 1325 Format: 1326 <bus_id>,<clkrate> 1327 1328 i8042.debug [HW] Toggle i8042 debug mode 1329 i8042.unmask_kbd_data 1330 [HW] Enable printing of interrupt data from the KBD port 1331 (disabled by default, and as a pre-condition 1332 requires that i8042.debug=1 be enabled) 1333 i8042.direct [HW] Put keyboard port into non-translated mode 1334 i8042.dumbkbd [HW] Pretend that controller can only read data from 1335 keyboard and cannot control its state 1336 (Don't attempt to blink the leds) 1337 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 1338 i8042.nokbd [HW] Don't check/create keyboard port 1339 i8042.noloop [HW] Disable the AUX Loopback command while probing 1340 for the AUX port 1341 i8042.nomux [HW] Don't check presence of an active multiplexing 1342 controller 1343 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 1344 controllers 1345 i8042.notimeout [HW] Ignore timeout condition signalled by controller 1346 i8042.reset [HW] Reset the controller during init, cleanup and 1347 suspend-to-ram transitions, only during s2r 1348 transitions, or never reset 1349 Format: { 1 | Y | y | 0 | N | n } 1350 1, Y, y: always reset controller 1351 0, N, n: don't ever reset controller 1352 Default: only on s2r transitions on x86; most other 1353 architectures force reset to be always executed 1354 i8042.unlock [HW] Unlock (ignore) the keylock 1355 i8042.kbdreset [HW] Reset device connected to KBD port 1356 1357 i810= [HW,DRM] 1358 1359 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data 1360 indicates that the driver is running on unsupported 1361 hardware. 1362 i8k.force [HW] Activate i8k driver even if SMM BIOS signature 1363 does not match list of supported models. 1364 i8k.power_status 1365 [HW] Report power status in /proc/i8k 1366 (disabled by default) 1367 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN 1368 capability is set. 1369 1370 i915.invert_brightness= 1371 [DRM] Invert the sense of the variable that is used to 1372 set the brightness of the panel backlight. Normally a 1373 brightness value of 0 indicates backlight switched off, 1374 and the maximum of the brightness value sets the backlight 1375 to maximum brightness. If this parameter is set to 0 1376 (default) and the machine requires it, or this parameter 1377 is set to 1, a brightness value of 0 sets the backlight 1378 to maximum brightness, and the maximum of the brightness 1379 value switches the backlight off. 1380 -1 -- never invert brightness 1381 0 -- machine default 1382 1 -- force brightness inversion 1383 1384 icn= [HW,ISDN] 1385 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]] 1386 1387 ide-core.nodma= [HW] (E)IDE subsystem 1388 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc 1389 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr 1390 .cdrom .chs .ignore_cable are additional options 1391 See Documentation/ide/ide.txt. 1392 1393 ide-generic.probe-mask= [HW] (E)IDE subsystem 1394 Format: <int> 1395 Probe mask for legacy ISA IDE ports. Depending on 1396 platform up to 6 ports are supported, enabled by 1397 setting corresponding bits in the mask to 1. The 1398 default value is 0x0, which has a special meaning. 1399 On systems that have PCI, it triggers scanning the 1400 PCI bus for the first and the second port, which 1401 are then probed. On systems without PCI the value 1402 of 0x0 enables probing the two first ports as if it 1403 was 0x3. 1404 1405 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem 1406 Claim all unknown PCI IDE storage controllers. 1407 1408 idle= [X86] 1409 Format: idle=poll, idle=halt, idle=nomwait 1410 Poll forces a polling idle loop that can slightly 1411 improve the performance of waking up a idle CPU, but 1412 will use a lot of power and make the system run hot. 1413 Not recommended. 1414 idle=halt: Halt is forced to be used for CPU idle. 1415 In such case C2/C3 won't be used again. 1416 idle=nomwait: Disable mwait for CPU C-states 1417 1418 ieee754= [MIPS] Select IEEE Std 754 conformance mode 1419 Format: { strict | legacy | 2008 | relaxed } 1420 Default: strict 1421 1422 Choose which programs will be accepted for execution 1423 based on the IEEE 754 NaN encoding(s) supported by 1424 the FPU and the NaN encoding requested with the value 1425 of an ELF file header flag individually set by each 1426 binary. Hardware implementations are permitted to 1427 support either or both of the legacy and the 2008 NaN 1428 encoding mode. 1429 1430 Available settings are as follows: 1431 strict accept binaries that request a NaN encoding 1432 supported by the FPU 1433 legacy only accept legacy-NaN binaries, if supported 1434 by the FPU 1435 2008 only accept 2008-NaN binaries, if supported 1436 by the FPU 1437 relaxed accept any binaries regardless of whether 1438 supported by the FPU 1439 1440 The FPU emulator is always able to support both NaN 1441 encodings, so if no FPU hardware is present or it has 1442 been disabled with 'nofpu', then the settings of 1443 'legacy' and '2008' strap the emulator accordingly, 1444 'relaxed' straps the emulator for both legacy-NaN and 1445 2008-NaN, whereas 'strict' enables legacy-NaN only on 1446 legacy processors and both NaN encodings on MIPS32 or 1447 MIPS64 CPUs. 1448 1449 The setting for ABS.fmt/NEG.fmt instruction execution 1450 mode generally follows that for the NaN encoding, 1451 except where unsupported by hardware. 1452 1453 ignore_loglevel [KNL] 1454 Ignore loglevel setting - this will print /all/ 1455 kernel messages to the console. Useful for debugging. 1456 We also add it as printk module parameter, so users 1457 could change it dynamically, usually by 1458 /sys/module/printk/parameters/ignore_loglevel. 1459 1460 ignore_rlimit_data 1461 Ignore RLIMIT_DATA setting for data mappings, 1462 print warning at first misuse. Can be changed via 1463 /sys/module/kernel/parameters/ignore_rlimit_data. 1464 1465 ihash_entries= [KNL] 1466 Set number of hash buckets for inode cache. 1467 1468 ima_appraise= [IMA] appraise integrity measurements 1469 Format: { "off" | "enforce" | "fix" | "log" } 1470 default: "enforce" 1471 1472 ima_appraise_tcb [IMA] 1473 The builtin appraise policy appraises all files 1474 owned by uid=0. 1475 1476 ima_canonical_fmt [IMA] 1477 Use the canonical format for the binary runtime 1478 measurements, instead of host native format. 1479 1480 ima_hash= [IMA] 1481 Format: { md5 | sha1 | rmd160 | sha256 | sha384 1482 | sha512 | ... } 1483 default: "sha1" 1484 1485 The list of supported hash algorithms is defined 1486 in crypto/hash_info.h. 1487 1488 ima_policy= [IMA] 1489 The builtin measurement policy to load during IMA 1490 setup. Specyfing "tcb" as the value, measures all 1491 programs exec'd, files mmap'd for exec, and all files 1492 opened with the read mode bit set by either the 1493 effective uid (euid=0) or uid=0. 1494 Format: "tcb" 1495 1496 ima_tcb [IMA] Deprecated. Use ima_policy= instead. 1497 Load a policy which meets the needs of the Trusted 1498 Computing Base. This means IMA will measure all 1499 programs exec'd, files mmap'd for exec, and all files 1500 opened for read by uid=0. 1501 1502 ima_template= [IMA] 1503 Select one of defined IMA measurements template formats. 1504 Formats: { "ima" | "ima-ng" | "ima-sig" } 1505 Default: "ima-ng" 1506 1507 ima_template_fmt= 1508 [IMA] Define a custom template format. 1509 Format: { "field1|...|fieldN" } 1510 1511 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage 1512 Format: <min_file_size> 1513 Set the minimal file size for using asynchronous hash. 1514 If left unspecified, ahash usage is disabled. 1515 1516 ahash performance varies for different data sizes on 1517 different crypto accelerators. This option can be used 1518 to achieve the best performance for a particular HW. 1519 1520 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size 1521 Format: <bufsize> 1522 Set hashing buffer size. Default: 4k. 1523 1524 ahash performance varies for different chunk sizes on 1525 different crypto accelerators. This option can be used 1526 to achieve best performance for particular HW. 1527 1528 init= [KNL] 1529 Format: <full_path> 1530 Run specified binary instead of /sbin/init as init 1531 process. 1532 1533 initcall_debug [KNL] Trace initcalls as they are executed. Useful 1534 for working out where the kernel is dying during 1535 startup. 1536 1537 initcall_blacklist= [KNL] Do not execute a comma-separated list of 1538 initcall functions. Useful for debugging built-in 1539 modules and initcalls. 1540 1541 initrd= [BOOT] Specify the location of the initial ramdisk 1542 1543 init_pkru= [x86] Specify the default memory protection keys rights 1544 register contents for all processes. 0x55555554 by 1545 default (disallow access to all but pkey 0). Can 1546 override in debugfs after boot. 1547 1548 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 1549 Format: <irq> 1550 1551 int_pln_enable [x86] Enable power limit notification interrupt 1552 1553 integrity_audit=[IMA] 1554 Format: { "0" | "1" } 1555 0 -- basic integrity auditing messages. (Default) 1556 1 -- additional integrity auditing messages. 1557 1558 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 1559 on 1560 Enable intel iommu driver. 1561 off 1562 Disable intel iommu driver. 1563 igfx_off [Default Off] 1564 By default, gfx is mapped as normal device. If a gfx 1565 device has a dedicated DMAR unit, the DMAR unit is 1566 bypassed by not enabling DMAR with this option. In 1567 this case, gfx device will use physical address for 1568 DMA. 1569 forcedac [x86_64] 1570 With this option iommu will not optimize to look 1571 for io virtual address below 32-bit forcing dual 1572 address cycle on pci bus for cards supporting greater 1573 than 32-bit addressing. The default is to look 1574 for translation below 32-bit and if not available 1575 then look in the higher range. 1576 strict [Default Off] 1577 With this option on every unmap_single operation will 1578 result in a hardware IOTLB flush operation as opposed 1579 to batching them for performance. 1580 sp_off [Default Off] 1581 By default, super page will be supported if Intel IOMMU 1582 has the capability. With this option, super page will 1583 not be supported. 1584 ecs_off [Default Off] 1585 By default, extended context tables will be supported if 1586 the hardware advertises that it has support both for the 1587 extended tables themselves, and also PASID support. With 1588 this option set, extended tables will not be used even 1589 on hardware which claims to support them. 1590 tboot_noforce [Default Off] 1591 Do not force the Intel IOMMU enabled under tboot. 1592 By default, tboot will force Intel IOMMU on, which 1593 could harm performance of some high-throughput 1594 devices like 40GBit network cards, even if identity 1595 mapping is enabled. 1596 Note that using this option lowers the security 1597 provided by tboot because it makes the system 1598 vulnerable to DMA attacks. 1599 1600 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 1601 0 disables intel_idle and fall back on acpi_idle. 1602 1 to 9 specify maximum depth of C-state. 1603 1604 intel_pstate= [X86] 1605 disable 1606 Do not enable intel_pstate as the default 1607 scaling driver for the supported processors 1608 passive 1609 Use intel_pstate as a scaling driver, but configure it 1610 to work with generic cpufreq governors (instead of 1611 enabling its internal governor). This mode cannot be 1612 used along with the hardware-managed P-states (HWP) 1613 feature. 1614 force 1615 Enable intel_pstate on systems that prohibit it by default 1616 in favor of acpi-cpufreq. Forcing the intel_pstate driver 1617 instead of acpi-cpufreq may disable platform features, such 1618 as thermal controls and power capping, that rely on ACPI 1619 P-States information being indicated to OSPM and therefore 1620 should be used with caution. This option does not work with 1621 processors that aren't supported by the intel_pstate driver 1622 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 1623 no_hwp 1624 Do not enable hardware P state control (HWP) 1625 if available. 1626 hwp_only 1627 Only load intel_pstate on systems which support 1628 hardware P state control (HWP) if available. 1629 support_acpi_ppc 1630 Enforce ACPI _PPC performance limits. If the Fixed ACPI 1631 Description Table, specifies preferred power management 1632 profile as "Enterprise Server" or "Performance Server", 1633 then this feature is turned on by default. 1634 per_cpu_perf_limits 1635 Allow per-logical-CPU P-State performance control limits using 1636 cpufreq sysfs interface 1637 1638 intremap= [X86-64, Intel-IOMMU] 1639 on enable Interrupt Remapping (default) 1640 off disable Interrupt Remapping 1641 nosid disable Source ID checking 1642 no_x2apic_optout 1643 BIOS x2APIC opt-out request will be ignored 1644 nopost disable Interrupt Posting 1645 1646 iomem= Disable strict checking of access to MMIO memory 1647 strict regions from userspace. 1648 relaxed 1649 1650 iommu= [x86] 1651 off 1652 force 1653 noforce 1654 biomerge 1655 panic 1656 nopanic 1657 merge 1658 nomerge 1659 forcesac 1660 soft 1661 pt [x86, IA-64] 1662 nobypass [PPC/POWERNV] 1663 Disable IOMMU bypass, using IOMMU for PCI devices. 1664 1665 iommu.passthrough= 1666 [ARM64] Configure DMA to bypass the IOMMU by default. 1667 Format: { "0" | "1" } 1668 0 - Use IOMMU translation for DMA. 1669 1 - Bypass the IOMMU for DMA. 1670 unset - Use IOMMU translation for DMA. 1671 1672 io7= [HW] IO7 for Marvel based alpha systems 1673 See comment before marvel_specify_io7 in 1674 arch/alpha/kernel/core_marvel.c. 1675 1676 io_delay= [X86] I/O delay method 1677 0x80 1678 Standard port 0x80 based delay 1679 0xed 1680 Alternate port 0xed based delay (needed on some systems) 1681 udelay 1682 Simple two microseconds delay 1683 none 1684 No delay 1685 1686 ip= [IP_PNP] 1687 See Documentation/filesystems/nfs/nfsroot.txt. 1688 1689 irqaffinity= [SMP] Set the default irq affinity mask 1690 The argument is a cpu list, as described above. 1691 1692 irqfixup [HW] 1693 When an interrupt is not handled search all handlers 1694 for it. Intended to get systems with badly broken 1695 firmware running. 1696 1697 irqpoll [HW] 1698 When an interrupt is not handled search all handlers 1699 for it. Also check all handlers each timer 1700 interrupt. Intended to get systems with badly broken 1701 firmware running. 1702 1703 isapnp= [ISAPNP] 1704 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 1705 1706 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler. 1707 The argument is a cpu list, as described above. 1708 1709 This option can be used to specify one or more CPUs 1710 to isolate from the general SMP balancing and scheduling 1711 algorithms. You can move a process onto or off an 1712 "isolated" CPU via the CPU affinity syscalls or cpuset. 1713 <cpu number> begins at 0 and the maximum value is 1714 "number of CPUs in system - 1". 1715 1716 This option is the preferred way to isolate CPUs. The 1717 alternative -- manually setting the CPU mask of all 1718 tasks in the system -- can cause problems and 1719 suboptimal load balancer performance. 1720 1721 iucv= [HW,NET] 1722 1723 ivrs_ioapic [HW,X86_64] 1724 Provide an override to the IOAPIC-ID<->DEVICE-ID 1725 mapping provided in the IVRS ACPI table. For 1726 example, to map IOAPIC-ID decimal 10 to 1727 PCI device 00:14.0 write the parameter as: 1728 ivrs_ioapic[10]=00:14.0 1729 1730 ivrs_hpet [HW,X86_64] 1731 Provide an override to the HPET-ID<->DEVICE-ID 1732 mapping provided in the IVRS ACPI table. For 1733 example, to map HPET-ID decimal 0 to 1734 PCI device 00:14.0 write the parameter as: 1735 ivrs_hpet[0]=00:14.0 1736 1737 ivrs_acpihid [HW,X86_64] 1738 Provide an override to the ACPI-HID:UID<->DEVICE-ID 1739 mapping provided in the IVRS ACPI table. For 1740 example, to map UART-HID:UID AMD0020:0 to 1741 PCI device 00:14.5 write the parameter as: 1742 ivrs_acpihid[00:14.5]=AMD0020:0 1743 1744 js= [HW,JOY] Analog joystick 1745 See Documentation/input/joystick.txt. 1746 1747 nokaslr [KNL] 1748 When CONFIG_RANDOMIZE_BASE is set, this disables 1749 kernel and module base offset ASLR (Address Space 1750 Layout Randomization). 1751 1752 kasan_multi_shot 1753 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print 1754 report on every invalid memory access. Without this 1755 parameter KASAN will print report only for the first 1756 invalid access. 1757 1758 keepinitrd [HW,ARM] 1759 1760 kernelcore= [KNL,X86,IA-64,PPC] 1761 Format: nn[KMGTPE] | "mirror" 1762 This parameter 1763 specifies the amount of memory usable by the kernel 1764 for non-movable allocations. The requested amount is 1765 spread evenly throughout all nodes in the system. The 1766 remaining memory in each node is used for Movable 1767 pages. In the event, a node is too small to have both 1768 kernelcore and Movable pages, kernelcore pages will 1769 take priority and other nodes will have a larger number 1770 of Movable pages. The Movable zone is used for the 1771 allocation of pages that may be reclaimed or moved 1772 by the page migration subsystem. This means that 1773 HugeTLB pages may not be allocated from this zone. 1774 Note that allocations like PTEs-from-HighMem still 1775 use the HighMem zone if it exists, and the Normal 1776 zone if it does not. 1777 1778 Instead of specifying the amount of memory (nn[KMGTPE]), 1779 you can specify "mirror" option. In case "mirror" 1780 option is specified, mirrored (reliable) memory is used 1781 for non-movable allocations and remaining memory is used 1782 for Movable pages. nn[KMGTPE] and "mirror" are exclusive, 1783 so you can NOT specify nn[KMGTPE] and "mirror" at the same 1784 time. 1785 1786 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port. 1787 Format: <Controller#>[,poll interval] 1788 The controller # is the number of the ehci usb debug 1789 port as it is probed via PCI. The poll interval is 1790 optional and is the number seconds in between 1791 each poll cycle to the debug port in case you need 1792 the functionality for interrupting the kernel with 1793 gdb or control-c on the dbgp connection. When 1794 not using this parameter you use sysrq-g to break into 1795 the kernel debugger. 1796 1797 kgdboc= [KGDB,HW] kgdb over consoles. 1798 Requires a tty driver that supports console polling, 1799 or a supported polling keyboard driver (non-usb). 1800 Serial only format: <serial_device>[,baud] 1801 keyboard only format: kbd 1802 keyboard and serial format: kbd,<serial_device>[,baud] 1803 Optional Kernel mode setting: 1804 kms, kbd format: kms,kbd 1805 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 1806 1807 kgdbwait [KGDB] Stop kernel execution and enter the 1808 kernel debugger at the earliest opportunity. 1809 1810 kmac= [MIPS] korina ethernet MAC address. 1811 Configure the RouterBoard 532 series on-chip 1812 Ethernet adapter MAC address. 1813 1814 kmemleak= [KNL] Boot-time kmemleak enable/disable 1815 Valid arguments: on, off 1816 Default: on 1817 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 1818 the default is off. 1819 1820 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode 1821 Valid arguments: 0, 1, 2 1822 kmemcheck=0 (disabled) 1823 kmemcheck=1 (enabled) 1824 kmemcheck=2 (one-shot mode) 1825 Default: 2 (one-shot mode) 1826 1827 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 1828 Default is 0 (don't ignore, but inject #GP) 1829 1830 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit 1831 KVM MMU at runtime. 1832 Default is 0 (off) 1833 1834 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM. 1835 Default is 1 (enabled) 1836 1837 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU) 1838 for all guests. 1839 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode. 1840 1841 kvm-intel.ept= [KVM,Intel] Disable extended page tables 1842 (virtualized MMU) support on capable Intel chips. 1843 Default is 1 (enabled) 1844 1845 kvm-intel.emulate_invalid_guest_state= 1846 [KVM,Intel] Enable emulation of invalid guest states 1847 Default is 0 (disabled) 1848 1849 kvm-intel.flexpriority= 1850 [KVM,Intel] Disable FlexPriority feature (TPR shadow). 1851 Default is 1 (enabled) 1852 1853 kvm-intel.nested= 1854 [KVM,Intel] Enable VMX nesting (nVMX). 1855 Default is 0 (disabled) 1856 1857 kvm-intel.unrestricted_guest= 1858 [KVM,Intel] Disable unrestricted guest feature 1859 (virtualized real and unpaged mode) on capable 1860 Intel chips. Default is 1 (enabled) 1861 1862 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification 1863 feature (tagged TLBs) on capable Intel chips. 1864 Default is 1 (enabled) 1865 1866 l2cr= [PPC] 1867 1868 l3cr= [PPC] 1869 1870 lapic [X86-32,APIC] Enable the local APIC even if BIOS 1871 disabled it. 1872 1873 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline 1874 value for LAPIC timer one-shot implementation. Default 1875 back to the programmable timer unit in the LAPIC. 1876 1877 lapic_timer_c2_ok [X86,APIC] trust the local apic timer 1878 in C2 power state. 1879 1880 libata.dma= [LIBATA] DMA control 1881 libata.dma=0 Disable all PATA and SATA DMA 1882 libata.dma=1 PATA and SATA Disk DMA only 1883 libata.dma=2 ATAPI (CDROM) DMA only 1884 libata.dma=4 Compact Flash DMA only 1885 Combinations also work, so libata.dma=3 enables DMA 1886 for disks and CDROMs, but not CFs. 1887 1888 libata.ignore_hpa= [LIBATA] Ignore HPA limit 1889 libata.ignore_hpa=0 keep BIOS limits (default) 1890 libata.ignore_hpa=1 ignore limits, using full disk 1891 1892 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 1893 when set. 1894 Format: <int> 1895 1896 libata.force= [LIBATA] Force configurations. The format is comma 1897 separated list of "[ID:]VAL" where ID is 1898 PORT[.DEVICE]. PORT and DEVICE are decimal numbers 1899 matching port, link or device. Basically, it matches 1900 the ATA ID string printed on console by libata. If 1901 the whole ID part is omitted, the last PORT and DEVICE 1902 values are used. If ID hasn't been specified yet, the 1903 configuration applies to all ports, links and devices. 1904 1905 If only DEVICE is omitted, the parameter applies to 1906 the port and all links and devices behind it. DEVICE 1907 number of 0 either selects the first device or the 1908 first fan-out link behind PMP device. It does not 1909 select the host link. DEVICE number of 15 selects the 1910 host link and device attached to it. 1911 1912 The VAL specifies the configuration to force. As long 1913 as there's no ambiguity shortcut notation is allowed. 1914 For example, both 1.5 and 1.5G would work for 1.5Gbps. 1915 The following configurations can be forced. 1916 1917 * Cable type: 40c, 80c, short40c, unk, ign or sata. 1918 Any ID with matching PORT is used. 1919 1920 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 1921 1922 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 1923 udma[/][16,25,33,44,66,100,133] notation is also 1924 allowed. 1925 1926 * [no]ncq: Turn on or off NCQ. 1927 1928 * [no]ncqtrim: Turn off queued DSM TRIM. 1929 1930 * nohrst, nosrst, norst: suppress hard, soft 1931 and both resets. 1932 1933 * rstonce: only attempt one reset during 1934 hot-unplug link recovery 1935 1936 * dump_id: dump IDENTIFY data. 1937 1938 * atapi_dmadir: Enable ATAPI DMADIR bridge support 1939 1940 * disable: Disable this device. 1941 1942 If there are multiple matching configurations changing 1943 the same attribute, the last one is used. 1944 1945 memblock=debug [KNL] Enable memblock debug messages. 1946 1947 load_ramdisk= [RAM] List of ramdisks to load from floppy 1948 See Documentation/blockdev/ramdisk.txt. 1949 1950 lockd.nlm_grace_period=P [NFS] Assign grace period. 1951 Format: <integer> 1952 1953 lockd.nlm_tcpport=N [NFS] Assign TCP port. 1954 Format: <integer> 1955 1956 lockd.nlm_timeout=T [NFS] Assign timeout value. 1957 Format: <integer> 1958 1959 lockd.nlm_udpport=M [NFS] Assign UDP port. 1960 Format: <integer> 1961 1962 locktorture.nreaders_stress= [KNL] 1963 Set the number of locking read-acquisition kthreads. 1964 Defaults to being automatically set based on the 1965 number of online CPUs. 1966 1967 locktorture.nwriters_stress= [KNL] 1968 Set the number of locking write-acquisition kthreads. 1969 1970 locktorture.onoff_holdoff= [KNL] 1971 Set time (s) after boot for CPU-hotplug testing. 1972 1973 locktorture.onoff_interval= [KNL] 1974 Set time (s) between CPU-hotplug operations, or 1975 zero to disable CPU-hotplug testing. 1976 1977 locktorture.shuffle_interval= [KNL] 1978 Set task-shuffle interval (jiffies). Shuffling 1979 tasks allows some CPUs to go into dyntick-idle 1980 mode during the locktorture test. 1981 1982 locktorture.shutdown_secs= [KNL] 1983 Set time (s) after boot system shutdown. This 1984 is useful for hands-off automated testing. 1985 1986 locktorture.stat_interval= [KNL] 1987 Time (s) between statistics printk()s. 1988 1989 locktorture.stutter= [KNL] 1990 Time (s) to stutter testing, for example, 1991 specifying five seconds causes the test to run for 1992 five seconds, wait for five seconds, and so on. 1993 This tests the locking primitive's ability to 1994 transition abruptly to and from idle. 1995 1996 locktorture.torture_runnable= [BOOT] 1997 Start locktorture running at boot time. 1998 1999 locktorture.torture_type= [KNL] 2000 Specify the locking implementation to test. 2001 2002 locktorture.verbose= [KNL] 2003 Enable additional printk() statements. 2004 2005 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 2006 Format: <irq> 2007 2008 loglevel= All Kernel Messages with a loglevel smaller than the 2009 console loglevel will be printed to the console. It can 2010 also be changed with klogd or other programs. The 2011 loglevels are defined as follows: 2012 2013 0 (KERN_EMERG) system is unusable 2014 1 (KERN_ALERT) action must be taken immediately 2015 2 (KERN_CRIT) critical conditions 2016 3 (KERN_ERR) error conditions 2017 4 (KERN_WARNING) warning conditions 2018 5 (KERN_NOTICE) normal but significant condition 2019 6 (KERN_INFO) informational 2020 7 (KERN_DEBUG) debug-level messages 2021 2022 log_buf_len=n[KMG] Sets the size of the printk ring buffer, 2023 in bytes. n must be a power of two and greater 2024 than the minimal size. The minimal size is defined 2025 by LOG_BUF_SHIFT kernel config parameter. There is 2026 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter 2027 that allows to increase the default size depending on 2028 the number of CPUs. See init/Kconfig for more details. 2029 2030 logo.nologo [FB] Disables display of the built-in Linux logo. 2031 This may be used to provide more screen space for 2032 kernel log messages and is useful when debugging 2033 kernel boot problems. 2034 2035 lp=0 [LP] Specify parallel ports to use, e.g, 2036 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 2037 lp=reset first parallel port). 'lp=0' disables the 2038 lp=auto printer driver. 'lp=reset' (which can be 2039 specified in addition to the ports) causes 2040 attached printers to be reset. Using 2041 lp=port1,port2,... specifies the parallel ports 2042 to associate lp devices with, starting with 2043 lp0. A port specification may be 'none' to skip 2044 that lp device, or a parport name such as 2045 'parport0'. Specifying 'lp=auto' instead of a 2046 port specification list means that device IDs 2047 from each port should be examined, to see if 2048 an IEEE 1284-compliant printer is attached; if 2049 so, the driver will manage that printer. 2050 See also header of drivers/char/lp.c. 2051 2052 lpj=n [KNL] 2053 Sets loops_per_jiffy to given constant, thus avoiding 2054 time-consuming boot-time autodetection (up to 250 ms per 2055 CPU). 0 enables autodetection (default). To determine 2056 the correct value for your kernel, boot with normal 2057 autodetection and see what value is printed. Note that 2058 on SMP systems the preset will be applied to all CPUs, 2059 which is likely to cause problems if your CPUs need 2060 significantly divergent settings. An incorrect value 2061 will cause delays in the kernel to be wrong, leading to 2062 unpredictable I/O errors and other breakage. Although 2063 unlikely, in the extreme case this might damage your 2064 hardware. 2065 2066 ltpc= [NET] 2067 Format: <io>,<irq>,<dma> 2068 2069 machvec= [IA-64] Force the use of a particular machine-vector 2070 (machvec) in a generic kernel. 2071 Example: machvec=hpzx1_swiotlb 2072 2073 machtype= [Loongson] Share the same kernel image file between different 2074 yeeloong laptop. 2075 Example: machtype=lemote-yeeloong-2f-7inch 2076 2077 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater 2078 than or equal to this physical address is ignored. 2079 2080 maxcpus= [SMP] Maximum number of processors that an SMP kernel 2081 will bring up during bootup. maxcpus=n : n >= 0 limits 2082 the kernel to bring up 'n' processors. Surely after 2083 bootup you can bring up the other plugged cpu by executing 2084 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 2085 only takes effect during system bootup. 2086 While n=0 is a special case, it is equivalent to "nosmp", 2087 which also disables the IO APIC. 2088 2089 max_loop= [LOOP] The number of loop block devices that get 2090 (loop.max_loop) unconditionally pre-created at init time. The default 2091 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 2092 of statically allocating a predefined number, loop 2093 devices can be requested on-demand with the 2094 /dev/loop-control interface. 2095 2096 mce [X86-32] Machine Check Exception 2097 2098 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt 2099 2100 md= [HW] RAID subsystems devices and level 2101 See Documentation/admin-guide/md.rst. 2102 2103 mdacon= [MDA] 2104 Format: <first>,<last> 2105 Specifies range of consoles to be captured by the MDA. 2106 2107 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory 2108 Amount of memory to be used when the kernel is not able 2109 to see the whole system memory or for test. 2110 [X86] Work as limiting max address. Use together 2111 with memmap= to avoid physical address space collisions. 2112 Without memmap= PCI devices could be placed at addresses 2113 belonging to unused RAM. 2114 2115 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 2116 memory. 2117 2118 memchunk=nn[KMG] 2119 [KNL,SH] Allow user to override the default size for 2120 per-device physically contiguous DMA buffers. 2121 2122 memhp_default_state=online/offline 2123 [KNL] Set the initial state for the memory hotplug 2124 onlining policy. If not specified, the default value is 2125 set according to the 2126 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config 2127 option. 2128 See Documentation/memory-hotplug.txt. 2129 2130 memmap=exactmap [KNL,X86] Enable setting of an exact 2131 E820 memory map, as specified by the user. 2132 Such memmap=exactmap lines can be constructed based on 2133 BIOS output or other requirements. See the memmap=nn@ss 2134 option description. 2135 2136 memmap=nn[KMG]@ss[KMG] 2137 [KNL] Force usage of a specific region of memory. 2138 Region of memory to be used is from ss to ss+nn. 2139 2140 memmap=nn[KMG]#ss[KMG] 2141 [KNL,ACPI] Mark specific memory as ACPI data. 2142 Region of memory to be marked is from ss to ss+nn. 2143 2144 memmap=nn[KMG]$ss[KMG] 2145 [KNL,ACPI] Mark specific memory as reserved. 2146 Region of memory to be reserved is from ss to ss+nn. 2147 Example: Exclude memory from 0x18690000-0x1869ffff 2148 memmap=64K$0x18690000 2149 or 2150 memmap=0x10000$0x18690000 2151 2152 memmap=nn[KMG]!ss[KMG] 2153 [KNL,X86] Mark specific memory as protected. 2154 Region of memory to be used, from ss to ss+nn. 2155 The memory region may be marked as e820 type 12 (0xc) 2156 and is NVDIMM or ADR memory. 2157 2158 memory_corruption_check=0/1 [X86] 2159 Some BIOSes seem to corrupt the first 64k of 2160 memory when doing things like suspend/resume. 2161 Setting this option will scan the memory 2162 looking for corruption. Enabling this will 2163 both detect corruption and prevent the kernel 2164 from using the memory being corrupted. 2165 However, its intended as a diagnostic tool; if 2166 repeatable BIOS-originated corruption always 2167 affects the same memory, you can use memmap= 2168 to prevent the kernel from using that memory. 2169 2170 memory_corruption_check_size=size [X86] 2171 By default it checks for corruption in the low 2172 64k, making this memory unavailable for normal 2173 use. Use this parameter to scan for 2174 corruption in more or less memory. 2175 2176 memory_corruption_check_period=seconds [X86] 2177 By default it checks for corruption every 60 2178 seconds. Use this parameter to check at some 2179 other rate. 0 disables periodic checking. 2180 2181 memtest= [KNL,X86,ARM] Enable memtest 2182 Format: <integer> 2183 default : 0 <disable> 2184 Specifies the number of memtest passes to be 2185 performed. Each pass selects another test 2186 pattern from a given set of patterns. Memtest 2187 fills the memory with this pattern, validates 2188 memory contents and reserves bad memory 2189 regions that are detected. 2190 2191 mem_sleep_default= [SUSPEND] Default system suspend mode: 2192 s2idle - Suspend-To-Idle 2193 shallow - Power-On Suspend or equivalent (if supported) 2194 deep - Suspend-To-RAM or equivalent (if supported) 2195 See Documentation/power/states.txt. 2196 2197 meye.*= [HW] Set MotionEye Camera parameters 2198 See Documentation/video4linux/meye.txt. 2199 2200 mfgpt_irq= [IA-32] Specify the IRQ to use for the 2201 Multi-Function General Purpose Timers on AMD Geode 2202 platforms. 2203 2204 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 2205 the BIOS has incorrectly applied a workaround. TinyBIOS 2206 version 0.98 is known to be affected, 0.99 fixes the 2207 problem by letting the user disable the workaround. 2208 2209 mga= [HW,DRM] 2210 2211 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this 2212 physical address is ignored. 2213 2214 mini2440= [ARM,HW,KNL] 2215 Format:[0..2][b][c][t] 2216 Default: "0tb" 2217 MINI2440 configuration specification: 2218 0 - The attached screen is the 3.5" TFT 2219 1 - The attached screen is the 7" TFT 2220 2 - The VGA Shield is attached (1024x768) 2221 Leaving out the screen size parameter will not load 2222 the TFT driver, and the framebuffer will be left 2223 unconfigured. 2224 b - Enable backlight. The TFT backlight pin will be 2225 linked to the kernel VESA blanking code and a GPIO 2226 LED. This parameter is not necessary when using the 2227 VGA shield. 2228 c - Enable the s3c camera interface. 2229 t - Reserved for enabling touchscreen support. The 2230 touchscreen support is not enabled in the mainstream 2231 kernel as of 2.6.30, a preliminary port can be found 2232 in the "bleeding edge" mini2440 support kernel at 2233 http://repo.or.cz/w/linux-2.6/mini2440.git 2234 2235 mminit_loglevel= 2236 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this 2237 parameter allows control of the logging verbosity for 2238 the additional memory initialisation checks. A value 2239 of 0 disables mminit logging and a level of 4 will 2240 log everything. Information is printed at KERN_DEBUG 2241 so loglevel=8 may also need to be specified. 2242 2243 module.sig_enforce 2244 [KNL] When CONFIG_MODULE_SIG is set, this means that 2245 modules without (valid) signatures will fail to load. 2246 Note that if CONFIG_MODULE_SIG_FORCE is set, that 2247 is always true, so this option does nothing. 2248 2249 module_blacklist= [KNL] Do not load a comma-separated list of 2250 modules. Useful for debugging problem modules. 2251 2252 mousedev.tap_time= 2253 [MOUSE] Maximum time between finger touching and 2254 leaving touchpad surface for touch to be considered 2255 a tap and be reported as a left button click (for 2256 touchpads working in absolute mode only). 2257 Format: <msecs> 2258 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 2259 reporting absolute coordinates, such as tablets 2260 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 2261 reporting absolute coordinates, such as tablets 2262 2263 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter 2264 is similar to kernelcore except it specifies the 2265 amount of memory used for migratable allocations. 2266 If both kernelcore and movablecore is specified, 2267 then kernelcore will be at *least* the specified 2268 value but may be more. If movablecore on its own 2269 is specified, the administrator must be careful 2270 that the amount of memory usable for all allocations 2271 is not too small. 2272 2273 movable_node [KNL] Boot-time switch to enable the effects 2274 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details. 2275 2276 MTD_Partition= [MTD] 2277 Format: <name>,<region-number>,<size>,<offset> 2278 2279 MTD_Region= [MTD] Format: 2280 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 2281 2282 mtdparts= [MTD] 2283 See drivers/mtd/cmdlinepart.c. 2284 2285 multitce=off [PPC] This parameter disables the use of the pSeries 2286 firmware feature for updating multiple TCE entries 2287 at a time. 2288 2289 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 2290 2291 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 2292 2293 boundary - index of last SLC block on Flex-OneNAND. 2294 The remaining blocks are configured as MLC blocks. 2295 lock - Configure if Flex-OneNAND boundary should be locked. 2296 Once locked, the boundary cannot be changed. 2297 1 indicates lock status, 0 indicates unlock status. 2298 2299 mtdset= [ARM] 2300 ARM/S3C2412 JIVE boot control 2301 2302 See arch/arm/mach-s3c2412/mach-jive.c 2303 2304 mtouchusb.raw_coordinates= 2305 [HW] Make the MicroTouch USB driver use raw coordinates 2306 ('y', default) or cooked coordinates ('n') 2307 2308 mtrr_chunk_size=nn[KMG] [X86] 2309 used for mtrr cleanup. It is largest continuous chunk 2310 that could hold holes aka. UC entries. 2311 2312 mtrr_gran_size=nn[KMG] [X86] 2313 Used for mtrr cleanup. It is granularity of mtrr block. 2314 Default is 1. 2315 Large value could prevent small alignment from 2316 using up MTRRs. 2317 2318 mtrr_spare_reg_nr=n [X86] 2319 Format: <integer> 2320 Range: 0,7 : spare reg number 2321 Default : 1 2322 Used for mtrr cleanup. It is spare mtrr entries number. 2323 Set to 2 or more if your graphical card needs more. 2324 2325 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 2326 2327 netdev= [NET] Network devices parameters 2328 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 2329 Note that mem_start is often overloaded to mean 2330 something different and driver-specific. 2331 This usage is only documented in each driver source 2332 file if at all. 2333 2334 nf_conntrack.acct= 2335 [NETFILTER] Enable connection tracking flow accounting 2336 0 to disable accounting 2337 1 to enable accounting 2338 Default value is 0. 2339 2340 nfsaddrs= [NFS] Deprecated. Use ip= instead. 2341 See Documentation/filesystems/nfs/nfsroot.txt. 2342 2343 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 2344 See Documentation/filesystems/nfs/nfsroot.txt. 2345 2346 nfsrootdebug [NFS] enable nfsroot debugging messages. 2347 See Documentation/filesystems/nfs/nfsroot.txt. 2348 2349 nfs.callback_nr_threads= 2350 [NFSv4] set the total number of threads that the 2351 NFS client will assign to service NFSv4 callback 2352 requests. 2353 2354 nfs.callback_tcpport= 2355 [NFS] set the TCP port on which the NFSv4 callback 2356 channel should listen. 2357 2358 nfs.cache_getent= 2359 [NFS] sets the pathname to the program which is used 2360 to update the NFS client cache entries. 2361 2362 nfs.cache_getent_timeout= 2363 [NFS] sets the timeout after which an attempt to 2364 update a cache entry is deemed to have failed. 2365 2366 nfs.idmap_cache_timeout= 2367 [NFS] set the maximum lifetime for idmapper cache 2368 entries. 2369 2370 nfs.enable_ino64= 2371 [NFS] enable 64-bit inode numbers. 2372 If zero, the NFS client will fake up a 32-bit inode 2373 number for the readdir() and stat() syscalls instead 2374 of returning the full 64-bit number. 2375 The default is to return 64-bit inode numbers. 2376 2377 nfs.max_session_cb_slots= 2378 [NFSv4.1] Sets the maximum number of session 2379 slots the client will assign to the callback 2380 channel. This determines the maximum number of 2381 callbacks the client will process in parallel for 2382 a particular server. 2383 2384 nfs.max_session_slots= 2385 [NFSv4.1] Sets the maximum number of session slots 2386 the client will attempt to negotiate with the server. 2387 This limits the number of simultaneous RPC requests 2388 that the client can send to the NFSv4.1 server. 2389 Note that there is little point in setting this 2390 value higher than the max_tcp_slot_table_limit. 2391 2392 nfs.nfs4_disable_idmapping= 2393 [NFSv4] When set to the default of '1', this option 2394 ensures that both the RPC level authentication 2395 scheme and the NFS level operations agree to use 2396 numeric uids/gids if the mount is using the 2397 'sec=sys' security flavour. In effect it is 2398 disabling idmapping, which can make migration from 2399 legacy NFSv2/v3 systems to NFSv4 easier. 2400 Servers that do not support this mode of operation 2401 will be autodetected by the client, and it will fall 2402 back to using the idmapper. 2403 To turn off this behaviour, set the value to '0'. 2404 nfs.nfs4_unique_id= 2405 [NFS4] Specify an additional fixed unique ident- 2406 ification string that NFSv4 clients can insert into 2407 their nfs_client_id4 string. This is typically a 2408 UUID that is generated at system install time. 2409 2410 nfs.send_implementation_id = 2411 [NFSv4.1] Send client implementation identification 2412 information in exchange_id requests. 2413 If zero, no implementation identification information 2414 will be sent. 2415 The default is to send the implementation identification 2416 information. 2417 2418 nfs.recover_lost_locks = 2419 [NFSv4] Attempt to recover locks that were lost due 2420 to a lease timeout on the server. Please note that 2421 doing this risks data corruption, since there are 2422 no guarantees that the file will remain unchanged 2423 after the locks are lost. 2424 If you want to enable the kernel legacy behaviour of 2425 attempting to recover these locks, then set this 2426 parameter to '1'. 2427 The default parameter value of '0' causes the kernel 2428 not to attempt recovery of lost locks. 2429 2430 nfs4.layoutstats_timer = 2431 [NFSv4.2] Change the rate at which the kernel sends 2432 layoutstats to the pNFS metadata server. 2433 2434 Setting this to value to 0 causes the kernel to use 2435 whatever value is the default set by the layout 2436 driver. A non-zero value sets the minimum interval 2437 in seconds between layoutstats transmissions. 2438 2439 nfsd.nfs4_disable_idmapping= 2440 [NFSv4] When set to the default of '1', the NFSv4 2441 server will return only numeric uids and gids to 2442 clients using auth_sys, and will accept numeric uids 2443 and gids from such clients. This is intended to ease 2444 migration from NFSv2/v3. 2445 2446 nmi_debug= [KNL,SH] Specify one or more actions to take 2447 when a NMI is triggered. 2448 Format: [state][,regs][,debounce][,die] 2449 2450 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 2451 Format: [panic,][nopanic,][num] 2452 Valid num: 0 or 1 2453 0 - turn hardlockup detector in nmi_watchdog off 2454 1 - turn hardlockup detector in nmi_watchdog on 2455 When panic is specified, panic when an NMI watchdog 2456 timeout occurs (or 'nopanic' to override the opposite 2457 default). To disable both hard and soft lockup detectors, 2458 please see 'nowatchdog'. 2459 This is useful when you use a panic=... timeout and 2460 need the box quickly up again. 2461 2462 netpoll.carrier_timeout= 2463 [NET] Specifies amount of time (in seconds) that 2464 netpoll should wait for a carrier. By default netpoll 2465 waits 4 seconds. 2466 2467 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 2468 emulation library even if a 387 maths coprocessor 2469 is present. 2470 2471 no_console_suspend 2472 [HW] Never suspend the console 2473 Disable suspending of consoles during suspend and 2474 hibernate operations. Once disabled, debugging 2475 messages can reach various consoles while the rest 2476 of the system is being put to sleep (ie, while 2477 debugging driver suspend/resume hooks). This may 2478 not work reliably with all consoles, but is known 2479 to work with serial and VGA consoles. 2480 To facilitate more flexible debugging, we also add 2481 console_suspend, a printk module parameter to control 2482 it. Users could use console_suspend (usually 2483 /sys/module/printk/parameters/console_suspend) to 2484 turn on/off it dynamically. 2485 2486 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien 2487 caches in the slab allocator. Saves per-node memory, 2488 but will impact performance. 2489 2490 noalign [KNL,ARM] 2491 2492 noapic [SMP,APIC] Tells the kernel to not make use of any 2493 IOAPICs that may be present in the system. 2494 2495 noautogroup Disable scheduler automatic task group creation. 2496 2497 nobats [PPC] Do not use BATs for mapping kernel lowmem 2498 on "Classic" PPC cores. 2499 2500 nocache [ARM] 2501 2502 noclflush [BUGS=X86] Don't use the CLFLUSH instruction 2503 2504 nodelayacct [KNL] Disable per-task delay accounting 2505 2506 nodsp [SH] Disable hardware DSP at boot time. 2507 2508 noefi Disable EFI runtime services support. 2509 2510 noexec [IA-64] 2511 2512 noexec [X86] 2513 On X86-32 available only on PAE configured kernels. 2514 noexec=on: enable non-executable mappings (default) 2515 noexec=off: disable non-executable mappings 2516 2517 nosmap [X86] 2518 Disable SMAP (Supervisor Mode Access Prevention) 2519 even if it is supported by processor. 2520 2521 nosmep [X86] 2522 Disable SMEP (Supervisor Mode Execution Prevention) 2523 even if it is supported by processor. 2524 2525 noexec32 [X86-64] 2526 This affects only 32-bit executables. 2527 noexec32=on: enable non-executable mappings (default) 2528 read doesn't imply executable mappings 2529 noexec32=off: disable non-executable mappings 2530 read implies executable mappings 2531 2532 nofpu [MIPS,SH] Disable hardware FPU at boot time. 2533 2534 nofxsr [BUGS=X86-32] Disables x86 floating point extended 2535 register save and restore. The kernel will only save 2536 legacy floating-point registers on task switch. 2537 2538 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings. 2539 2540 nosmt [KNL,S390] Disable symmetric multithreading (SMT). 2541 Equivalent to smt=1. 2542 2543 noxsave [BUGS=X86] Disables x86 extended register state save 2544 and restore using xsave. The kernel will fallback to 2545 enabling legacy floating-point and sse state. 2546 2547 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 2548 register states. The kernel will fall back to use 2549 xsave to save the states. By using this parameter, 2550 performance of saving the states is degraded because 2551 xsave doesn't support modified optimization while 2552 xsaveopt supports it on xsaveopt enabled systems. 2553 2554 noxsaves [X86] Disables xsaves and xrstors used in saving and 2555 restoring x86 extended register state in compacted 2556 form of xsave area. The kernel will fall back to use 2557 xsaveopt and xrstor to save and restore the states 2558 in standard form of xsave area. By using this 2559 parameter, xsave area per process might occupy more 2560 memory on xsaves enabled systems. 2561 2562 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or 2563 wfi(ARM) instruction doesn't work correctly and not to 2564 use it. This is also useful when using JTAG debugger. 2565 2566 no_file_caps Tells the kernel not to honor file capabilities. The 2567 only way then for a file to be executed with privilege 2568 is to be setuid root or executed by root. 2569 2570 nohalt [IA-64] Tells the kernel not to use the power saving 2571 function PAL_HALT_LIGHT when idle. This increases 2572 power-consumption. On the positive side, it reduces 2573 interrupt wake-up latency, which may improve performance 2574 in certain environments such as networked servers or 2575 real-time systems. 2576 2577 nohibernate [HIBERNATION] Disable hibernation and resume. 2578 2579 nohz= [KNL] Boottime enable/disable dynamic ticks 2580 Valid arguments: on, off 2581 Default: on 2582 2583 nohz_full= [KNL,BOOT] 2584 The argument is a cpu list, as described above. 2585 In kernels built with CONFIG_NO_HZ_FULL=y, set 2586 the specified list of CPUs whose tick will be stopped 2587 whenever possible. The boot CPU will be forced outside 2588 the range to maintain the timekeeping. 2589 The CPUs in this range must also be included in the 2590 rcu_nocbs= set. 2591 2592 noiotrap [SH] Disables trapped I/O port accesses. 2593 2594 noirqdebug [X86-32] Disables the code which attempts to detect and 2595 disable unhandled interrupt sources. 2596 2597 no_timer_check [X86,APIC] Disables the code which tests for 2598 broken timer IRQ sources. 2599 2600 noisapnp [ISAPNP] Disables ISA PnP code. 2601 2602 noinitrd [RAM] Tells the kernel not to load any configured 2603 initial RAM disk. 2604 2605 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt 2606 remapping. 2607 [Deprecated - use intremap=off] 2608 2609 nointroute [IA-64] 2610 2611 noinvpcid [X86] Disable the INVPCID cpu feature. 2612 2613 nojitter [IA-64] Disables jitter checking for ITC timers. 2614 2615 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver 2616 2617 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page 2618 fault handling. 2619 2620 no-vmw-sched-clock 2621 [X86,PV_OPS] Disable paravirtualized VMware scheduler 2622 clock and use the default one. 2623 2624 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting. 2625 steal time is computed, but won't influence scheduler 2626 behaviour 2627 2628 nolapic [X86-32,APIC] Do not enable or use the local APIC. 2629 2630 nolapic_timer [X86-32,APIC] Do not use the local APIC timer. 2631 2632 noltlbs [PPC] Do not use large page/tlb entries for kernel 2633 lowmem mapping on PPC40x and PPC8xx 2634 2635 nomca [IA-64] Disable machine check abort handling 2636 2637 nomce [X86-32] Disable Machine Check Exception 2638 2639 nomfgpt [X86-32] Disable Multi-Function General Purpose 2640 Timer usage (for AMD Geode machines). 2641 2642 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 2643 shutdown the other cpus. Instead use the REBOOT_VECTOR 2644 irq. 2645 2646 nomodule Disable module load 2647 2648 nopat [X86] Disable PAT (page attribute table extension of 2649 pagetables) support. 2650 2651 norandmaps Don't use address space randomization. Equivalent to 2652 echo 0 > /proc/sys/kernel/randomize_va_space 2653 2654 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops 2655 2656 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 2657 with UP alternatives 2658 2659 nordrand [X86] Disable kernel use of the RDRAND and 2660 RDSEED instructions even if they are supported 2661 by the processor. RDRAND and RDSEED are still 2662 available to user space applications. 2663 2664 noresume [SWSUSP] Disables resume and restores original swap 2665 space. 2666 2667 no-scroll [VGA] Disables scrollback. 2668 This is required for the Braillex ib80-piezo Braille 2669 reader made by F.H. Papenmeier (Germany). 2670 2671 nosbagart [IA-64] 2672 2673 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support. 2674 2675 nosmp [SMP] Tells an SMP kernel to act as a UP kernel, 2676 and disable the IO APIC. legacy for "maxcpus=0". 2677 2678 nosoftlockup [KNL] Disable the soft-lockup detector. 2679 2680 nosync [HW,M68K] Disables sync negotiation for all devices. 2681 2682 notsc [BUGS=X86-32] Disable Time Stamp Counter 2683 2684 nowatchdog [KNL] Disable both lockup detectors, i.e. 2685 soft-lockup and NMI watchdog (hard-lockup). 2686 2687 nowb [ARM] 2688 2689 nox2apic [X86-64,APIC] Do not enable x2APIC mode. 2690 2691 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when 2692 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off. 2693 Some features depend on CPU0. Known dependencies are: 2694 1. Resume from suspend/hibernate depends on CPU0. 2695 Suspend/hibernate will fail if CPU0 is offline and you 2696 need to online CPU0 before suspend/hibernate. 2697 2. PIC interrupts also depend on CPU0. CPU0 can't be 2698 removed if a PIC interrupt is detected. 2699 It's said poweroff/reboot may depend on CPU0 on some 2700 machines although I haven't seen such issues so far 2701 after CPU0 is offline on a few tested machines. 2702 If the dependencies are under your control, you can 2703 turn on cpu0_hotplug. 2704 2705 nptcg= [IA-64] Override max number of concurrent global TLB 2706 purges which is reported from either PAL_VM_SUMMARY or 2707 SAL PALO. 2708 2709 nr_cpus= [SMP] Maximum number of processors that an SMP kernel 2710 could support. nr_cpus=n : n >= 1 limits the kernel to 2711 support 'n' processors. It could be larger than the 2712 number of already plugged CPU during bootup, later in 2713 runtime you can physically add extra cpu until it reaches 2714 n. So during boot up some boot time memory for per-cpu 2715 variables need be pre-allocated for later physical cpu 2716 hot plugging. 2717 2718 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 2719 2720 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing. 2721 Allowed values are enable and disable 2722 2723 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 2724 one of ['zone', 'node', 'default'] can be specified 2725 This can be set from sysctl after boot. 2726 See Documentation/sysctl/vm.txt for details. 2727 2728 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver. 2729 See Documentation/debugging-via-ohci1394.txt for more 2730 info. 2731 2732 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 2733 Rather than timing out after 20 ms if an EC 2734 command is not properly ACKed, override the length 2735 of the timeout. We have interrupts disabled while 2736 waiting for the ACK, so if this is set too high 2737 interrupts *may* be lost! 2738 2739 omap_mux= [OMAP] Override bootloader pin multiplexing. 2740 Format: <mux_mode0.mode_name=value>... 2741 For example, to override I2C bus2: 2742 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 2743 2744 oprofile.timer= [HW] 2745 Use timer interrupt instead of performance counters 2746 2747 oprofile.cpu_type= Force an oprofile cpu type 2748 This might be useful if you have an older oprofile 2749 userland or if you want common events. 2750 Format: { arch_perfmon } 2751 arch_perfmon: [X86] Force use of architectural 2752 perfmon on Intel CPUs instead of the 2753 CPU specific event set. 2754 timer: [X86] Force use of architectural NMI 2755 timer mode (see also oprofile.timer 2756 for generic hr timer mode) 2757 2758 oops=panic Always panic on oopses. Default is to just kill the 2759 process, but there is a small probability of 2760 deadlocking the machine. 2761 This will also cause panics on machine check exceptions. 2762 Useful together with panic=30 to trigger a reboot. 2763 2764 OSS [HW,OSS] 2765 See Documentation/sound/oss/oss-parameters.txt 2766 2767 page_owner= [KNL] Boot-time page_owner enabling option. 2768 Storage of the information about who allocated 2769 each page is disabled in default. With this switch, 2770 we can turn it on. 2771 on: enable the feature 2772 2773 page_poison= [KNL] Boot-time parameter changing the state of 2774 poisoning on the buddy allocator. 2775 off: turn off poisoning 2776 on: turn on poisoning 2777 2778 panic= [KNL] Kernel behaviour on panic: delay <timeout> 2779 timeout > 0: seconds before rebooting 2780 timeout = 0: wait forever 2781 timeout < 0: reboot immediately 2782 Format: <timeout> 2783 2784 panic_on_warn panic() instead of WARN(). Useful to cause kdump 2785 on a WARN(). 2786 2787 crash_kexec_post_notifiers 2788 Run kdump after running panic-notifiers and dumping 2789 kmsg. This only for the users who doubt kdump always 2790 succeeds in any situation. 2791 Note that this also increases risks of kdump failure, 2792 because some panic notifiers can make the crashed 2793 kernel more unstable. 2794 2795 parkbd.port= [HW] Parallel port number the keyboard adapter is 2796 connected to, default is 0. 2797 Format: <parport#> 2798 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 2799 0 for XT, 1 for AT (default is AT). 2800 Format: <mode> 2801 2802 parport= [HW,PPT] Specify parallel ports. 0 disables. 2803 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 2804 Use 'auto' to force the driver to use any 2805 IRQ/DMA settings detected (the default is to 2806 ignore detected IRQ/DMA settings because of 2807 possible conflicts). You can specify the base 2808 address, IRQ, and DMA settings; IRQ and DMA 2809 should be numbers, or 'auto' (for using detected 2810 settings on that particular port), or 'nofifo' 2811 (to avoid using a FIFO even if it is detected). 2812 Parallel ports are assigned in the order they 2813 are specified on the command line, starting 2814 with parport0. 2815 2816 parport_init_mode= [HW,PPT] 2817 Configure VIA parallel port to operate in 2818 a specific mode. This is necessary on Pegasos 2819 computer where firmware has no options for setting 2820 up parallel port mode and sets it to spp. 2821 Currently this function knows 686a and 8231 chips. 2822 Format: [spp|ps2|epp|ecp|ecpepp] 2823 2824 pause_on_oops= 2825 Halt all CPUs after the first oops has been printed for 2826 the specified number of seconds. This is to be used if 2827 your oopses keep scrolling off the screen. 2828 2829 pcbit= [HW,ISDN] 2830 2831 pcd. [PARIDE] 2832 See header of drivers/block/paride/pcd.c. 2833 See also Documentation/blockdev/paride.txt. 2834 2835 pci=option[,option...] [PCI] various PCI subsystem options: 2836 earlydump [X86] dump PCI config space before the kernel 2837 changes anything 2838 off [X86] don't probe for the PCI bus 2839 bios [X86-32] force use of PCI BIOS, don't access 2840 the hardware directly. Use this if your machine 2841 has a non-standard PCI host bridge. 2842 nobios [X86-32] disallow use of PCI BIOS, only direct 2843 hardware access methods are allowed. Use this 2844 if you experience crashes upon bootup and you 2845 suspect they are caused by the BIOS. 2846 conf1 [X86] Force use of PCI Configuration Access 2847 Mechanism 1 (config address in IO port 0xCF8, 2848 data in IO port 0xCFC, both 32-bit). 2849 conf2 [X86] Force use of PCI Configuration Access 2850 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 2851 the function, IO port 0xCFA, also 8-bit, sets 2852 bus number. The config space is then accessed 2853 through ports 0xC000-0xCFFF). 2854 See http://wiki.osdev.org/PCI for more info 2855 on the configuration access mechanisms. 2856 noaer [PCIE] If the PCIEAER kernel config parameter is 2857 enabled, this kernel boot option can be used to 2858 disable the use of PCIE advanced error reporting. 2859 nodomains [PCI] Disable support for multiple PCI 2860 root domains (aka PCI segments, in ACPI-speak). 2861 nommconf [X86] Disable use of MMCONFIG for PCI 2862 Configuration 2863 check_enable_amd_mmconf [X86] check for and enable 2864 properly configured MMIO access to PCI 2865 config space on AMD family 10h CPU 2866 nomsi [MSI] If the PCI_MSI kernel config parameter is 2867 enabled, this kernel boot option can be used to 2868 disable the use of MSI interrupts system-wide. 2869 noioapicquirk [APIC] Disable all boot interrupt quirks. 2870 Safety option to keep boot IRQs enabled. This 2871 should never be necessary. 2872 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 2873 primary IO-APIC for bridges that cannot disable 2874 boot IRQs. This fixes a source of spurious IRQs 2875 when the system masks IRQs. 2876 noioapicreroute [APIC] Disable workaround that uses the 2877 boot IRQ equivalent of an IRQ that connects to 2878 a chipset where boot IRQs cannot be disabled. 2879 The opposite of ioapicreroute. 2880 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 2881 routing table. These calls are known to be buggy 2882 on several machines and they hang the machine 2883 when used, but on other computers it's the only 2884 way to get the interrupt routing table. Try 2885 this option if the kernel is unable to allocate 2886 IRQs or discover secondary PCI buses on your 2887 motherboard. 2888 rom [X86] Assign address space to expansion ROMs. 2889 Use with caution as certain devices share 2890 address decoders between ROMs and other 2891 resources. 2892 norom [X86] Do not assign address space to 2893 expansion ROMs that do not already have 2894 BIOS assigned address ranges. 2895 nobar [X86] Do not assign address space to the 2896 BARs that weren't assigned by the BIOS. 2897 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 2898 assigned automatically to PCI devices. You can 2899 make the kernel exclude IRQs of your ISA cards 2900 this way. 2901 pirqaddr=0xAAAAA [X86] Specify the physical address 2902 of the PIRQ table (normally generated 2903 by the BIOS) if it is outside the 2904 F0000h-100000h range. 2905 lastbus=N [X86] Scan all buses thru bus #N. Can be 2906 useful if the kernel is unable to find your 2907 secondary buses and you want to tell it 2908 explicitly which ones they are. 2909 assign-busses [X86] Always assign all PCI bus 2910 numbers ourselves, overriding 2911 whatever the firmware may have done. 2912 usepirqmask [X86] Honor the possible IRQ mask stored 2913 in the BIOS $PIR table. This is needed on 2914 some systems with broken BIOSes, notably 2915 some HP Pavilion N5400 and Omnibook XE3 2916 notebooks. This will have no effect if ACPI 2917 IRQ routing is enabled. 2918 noacpi [X86] Do not use ACPI for IRQ routing 2919 or for PCI scanning. 2920 use_crs [X86] Use PCI host bridge window information 2921 from ACPI. On BIOSes from 2008 or later, this 2922 is enabled by default. If you need to use this, 2923 please report a bug. 2924 nocrs [X86] Ignore PCI host bridge windows from ACPI. 2925 If you need to use this, please report a bug. 2926 routeirq Do IRQ routing for all PCI devices. 2927 This is normally done in pci_enable_device(), 2928 so this option is a temporary workaround 2929 for broken drivers that don't call it. 2930 skip_isa_align [X86] do not align io start addr, so can 2931 handle more pci cards 2932 noearly [X86] Don't do any early type 1 scanning. 2933 This might help on some broken boards which 2934 machine check when some devices' config space 2935 is read. But various workarounds are disabled 2936 and some IOMMU drivers will not work. 2937 bfsort Sort PCI devices into breadth-first order. 2938 This sorting is done to get a device 2939 order compatible with older (<= 2.4) kernels. 2940 nobfsort Don't sort PCI devices into breadth-first order. 2941 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 2942 tuning and use the BIOS-configured MPS defaults. 2943 pcie_bus_safe Set every device's MPS to the largest value 2944 supported by all devices below the root complex. 2945 pcie_bus_perf Set device MPS to the largest allowable MPS 2946 based on its parent bus. Also set MRRS (Max 2947 Read Request Size) to the largest supported 2948 value (no larger than the MPS that the device 2949 or bus can support) for best performance. 2950 pcie_bus_peer2peer Set every device's MPS to 128B, which 2951 every device is guaranteed to support. This 2952 configuration allows peer-to-peer DMA between 2953 any pair of devices, possibly at the cost of 2954 reduced performance. This also guarantees 2955 that hot-added devices will work. 2956 cbiosize=nn[KMG] The fixed amount of bus space which is 2957 reserved for the CardBus bridge's IO window. 2958 The default value is 256 bytes. 2959 cbmemsize=nn[KMG] The fixed amount of bus space which is 2960 reserved for the CardBus bridge's memory 2961 window. The default value is 64 megabytes. 2962 resource_alignment= 2963 Format: 2964 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...] 2965 [<order of align>@]pci:<vendor>:<device>\ 2966 [:<subvendor>:<subdevice>][; ...] 2967 Specifies alignment and device to reassign 2968 aligned memory resources. 2969 If <order of align> is not specified, 2970 PAGE_SIZE is used as alignment. 2971 PCI-PCI bridge can be specified, if resource 2972 windows need to be expanded. 2973 To specify the alignment for several 2974 instances of a device, the PCI vendor, 2975 device, subvendor, and subdevice may be 2976 specified, e.g., 4096@pci:8086:9c22:103c:198f 2977 ecrc= Enable/disable PCIe ECRC (transaction layer 2978 end-to-end CRC checking). 2979 bios: Use BIOS/firmware settings. This is the 2980 the default. 2981 off: Turn ECRC off 2982 on: Turn ECRC on. 2983 hpiosize=nn[KMG] The fixed amount of bus space which is 2984 reserved for hotplug bridge's IO window. 2985 Default size is 256 bytes. 2986 hpmemsize=nn[KMG] The fixed amount of bus space which is 2987 reserved for hotplug bridge's memory window. 2988 Default size is 2 megabytes. 2989 hpbussize=nn The minimum amount of additional bus numbers 2990 reserved for buses below a hotplug bridge. 2991 Default is 1. 2992 realloc= Enable/disable reallocating PCI bridge resources 2993 if allocations done by BIOS are too small to 2994 accommodate resources required by all child 2995 devices. 2996 off: Turn realloc off 2997 on: Turn realloc on 2998 realloc same as realloc=on 2999 noari do not use PCIe ARI. 3000 pcie_scan_all Scan all possible PCIe devices. Otherwise we 3001 only look for one device below a PCIe downstream 3002 port. 3003 3004 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power 3005 Management. 3006 off Disable ASPM. 3007 force Enable ASPM even on devices that claim not to support it. 3008 WARNING: Forcing ASPM on may cause system lockups. 3009 3010 pcie_hp= [PCIE] PCI Express Hotplug driver options: 3011 nomsi Do not use MSI for PCI Express Native Hotplug (this 3012 makes all PCIe ports use INTx for hotplug services). 3013 3014 pcie_ports= [PCIE] PCIe ports handling: 3015 auto Ask the BIOS whether or not to use native PCIe services 3016 associated with PCIe ports (PME, hot-plug, AER). Use 3017 them only if that is allowed by the BIOS. 3018 native Use native PCIe services associated with PCIe ports 3019 unconditionally. 3020 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe 3021 ports driver. 3022 3023 pcie_port_pm= [PCIE] PCIe port power management handling: 3024 off Disable power management of all PCIe ports 3025 force Forcibly enable power management of all PCIe ports 3026 3027 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 3028 nomsi Do not use MSI for native PCIe PME signaling (this makes 3029 all PCIe root ports use INTx for all services). 3030 3031 pcmv= [HW,PCMCIA] BadgePAD 4 3032 3033 pd_ignore_unused 3034 [PM] 3035 Keep all power-domains already enabled by bootloader on, 3036 even if no driver has claimed them. This is useful 3037 for debug and development, but should not be 3038 needed on a platform with proper driver support. 3039 3040 pd. [PARIDE] 3041 See Documentation/blockdev/paride.txt. 3042 3043 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 3044 boot time. 3045 Format: { 0 | 1 } 3046 See arch/parisc/kernel/pdc_chassis.c 3047 3048 percpu_alloc= Select which percpu first chunk allocator to use. 3049 Currently supported values are "embed" and "page". 3050 Archs may support subset or none of the selections. 3051 See comments in mm/percpu.c for details on each 3052 allocator. This parameter is primarily for debugging 3053 and performance comparison. 3054 3055 pf. [PARIDE] 3056 See Documentation/blockdev/paride.txt. 3057 3058 pg. [PARIDE] 3059 See Documentation/blockdev/paride.txt. 3060 3061 pirq= [SMP,APIC] Manual mp-table setup 3062 See Documentation/x86/i386/IO-APIC.txt. 3063 3064 plip= [PPT,NET] Parallel port network link 3065 Format: { parport<nr> | timid | 0 } 3066 See also Documentation/parport.txt. 3067 3068 pmtmr= [X86] Manual setup of pmtmr I/O Port. 3069 Override pmtimer IOPort with a hex value. 3070 e.g. pmtmr=0x508 3071 3072 pnp.debug=1 [PNP] 3073 Enable PNP debug messages (depends on the 3074 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 3075 via /sys/module/pnp/parameters/debug. We always show 3076 current resource usage; turning this on also shows 3077 possible settings and some assignment information. 3078 3079 pnpacpi= [ACPI] 3080 { off } 3081 3082 pnpbios= [ISAPNP] 3083 { on | off | curr | res | no-curr | no-res } 3084 3085 pnp_reserve_irq= 3086 [ISAPNP] Exclude IRQs for the autoconfiguration 3087 3088 pnp_reserve_dma= 3089 [ISAPNP] Exclude DMAs for the autoconfiguration 3090 3091 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 3092 Ranges are in pairs (I/O port base and size). 3093 3094 pnp_reserve_mem= 3095 [ISAPNP] Exclude memory regions for the 3096 autoconfiguration. 3097 Ranges are in pairs (memory base and size). 3098 3099 ports= [IP_VS_FTP] IPVS ftp helper module 3100 Default is 21. 3101 Up to 8 (IP_VS_APP_MAX_PORTS) ports 3102 may be specified. 3103 Format: <port>,<port>.... 3104 3105 powersave=off [PPC] This option disables power saving features. 3106 It specifically disables cpuidle and sets the 3107 platform machine description specific power_save 3108 function to NULL. On Idle the CPU just reduces 3109 execution priority. 3110 3111 ppc_strict_facility_enable 3112 [PPC] This option catches any kernel floating point, 3113 Altivec, VSX and SPE outside of regions specifically 3114 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 3115 There is some performance impact when enabling this. 3116 3117 print-fatal-signals= 3118 [KNL] debug: print fatal signals 3119 3120 If enabled, warn about various signal handling 3121 related application anomalies: too many signals, 3122 too many POSIX.1 timers, fatal signals causing a 3123 coredump - etc. 3124 3125 If you hit the warning due to signal overflow, 3126 you might want to try "ulimit -i unlimited". 3127 3128 default: off. 3129 3130 printk.always_kmsg_dump= 3131 Trigger kmsg_dump for cases other than kernel oops or 3132 panics 3133 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3134 default: disabled 3135 3136 printk.devkmsg={on,off,ratelimit} 3137 Control writing to /dev/kmsg. 3138 on - unlimited logging to /dev/kmsg from userspace 3139 off - logging to /dev/kmsg disabled 3140 ratelimit - ratelimit the logging 3141 Default: ratelimit 3142 3143 printk.time= Show timing data prefixed to each printk message line 3144 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3145 3146 processor.max_cstate= [HW,ACPI] 3147 Limit processor to maximum C-state 3148 max_cstate=9 overrides any DMI blacklist limit. 3149 3150 processor.nocst [HW,ACPI] 3151 Ignore the _CST method to determine C-states, 3152 instead using the legacy FADT method 3153 3154 profile= [KNL] Enable kernel profiling via /proc/profile 3155 Format: [schedule,]<number> 3156 Param: "schedule" - profile schedule points. 3157 Param: <number> - step/bucket size as a power of 2 for 3158 statistical time based profiling. 3159 Param: "sleep" - profile D-state sleeping (millisecs). 3160 Requires CONFIG_SCHEDSTATS 3161 Param: "kvm" - profile VM exits. 3162 3163 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk 3164 before loading. 3165 See Documentation/blockdev/ramdisk.txt. 3166 3167 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 3168 probe for; one of (bare|imps|exps|lifebook|any). 3169 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 3170 per second. 3171 psmouse.resetafter= [HW,MOUSE] 3172 Try to reset the device after so many bad packets 3173 (0 = never). 3174 psmouse.resolution= 3175 [HW,MOUSE] Set desired mouse resolution, in dpi. 3176 psmouse.smartscroll= 3177 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 3178 0 = disabled, 1 = enabled (default). 3179 3180 pstore.backend= Specify the name of the pstore backend to use 3181 3182 pt. [PARIDE] 3183 See Documentation/blockdev/paride.txt. 3184 3185 pty.legacy_count= 3186 [KNL] Number of legacy pty's. Overwrites compiled-in 3187 default number. 3188 3189 quiet [KNL] Disable most log messages 3190 3191 r128= [HW,DRM] 3192 3193 raid= [HW,RAID] 3194 See Documentation/admin-guide/md.rst. 3195 3196 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 3197 See Documentation/blockdev/ramdisk.txt. 3198 3199 ras=option[,option,...] [KNL] RAS-specific options 3200 3201 cec_disable [X86] 3202 Disable the Correctable Errors Collector, 3203 see CONFIG_RAS_CEC help text. 3204 3205 rcu_nocbs= [KNL] 3206 The argument is a cpu list, as described above. 3207 3208 In kernels built with CONFIG_RCU_NOCB_CPU=y, set 3209 the specified list of CPUs to be no-callback CPUs. 3210 Invocation of these CPUs' RCU callbacks will 3211 be offloaded to "rcuox/N" kthreads created for 3212 that purpose, where "x" is "b" for RCU-bh, "p" 3213 for RCU-preempt, and "s" for RCU-sched, and "N" 3214 is the CPU number. This reduces OS jitter on the 3215 offloaded CPUs, which can be useful for HPC and 3216 real-time workloads. It can also improve energy 3217 efficiency for asymmetric multiprocessors. 3218 3219 rcu_nocb_poll [KNL] 3220 Rather than requiring that offloaded CPUs 3221 (specified by rcu_nocbs= above) explicitly 3222 awaken the corresponding "rcuoN" kthreads, 3223 make these kthreads poll for callbacks. 3224 This improves the real-time response for the 3225 offloaded CPUs by relieving them of the need to 3226 wake up the corresponding kthread, but degrades 3227 energy efficiency by requiring that the kthreads 3228 periodically wake up to do the polling. 3229 3230 rcutree.blimit= [KNL] 3231 Set maximum number of finished RCU callbacks to 3232 process in one batch. 3233 3234 rcutree.dump_tree= [KNL] 3235 Dump the structure of the rcu_node combining tree 3236 out at early boot. This is used for diagnostic 3237 purposes, to verify correct tree setup. 3238 3239 rcutree.gp_cleanup_delay= [KNL] 3240 Set the number of jiffies to delay each step of 3241 RCU grace-period cleanup. This only has effect 3242 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set. 3243 3244 rcutree.gp_init_delay= [KNL] 3245 Set the number of jiffies to delay each step of 3246 RCU grace-period initialization. This only has 3247 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT 3248 is set. 3249 3250 rcutree.gp_preinit_delay= [KNL] 3251 Set the number of jiffies to delay each step of 3252 RCU grace-period pre-initialization, that is, 3253 the propagation of recent CPU-hotplug changes up 3254 the rcu_node combining tree. This only has effect 3255 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set. 3256 3257 rcutree.rcu_fanout_exact= [KNL] 3258 Disable autobalancing of the rcu_node combining 3259 tree. This is used by rcutorture, and might 3260 possibly be useful for architectures having high 3261 cache-to-cache transfer latencies. 3262 3263 rcutree.rcu_fanout_leaf= [KNL] 3264 Change the number of CPUs assigned to each 3265 leaf rcu_node structure. Useful for very 3266 large systems, which will choose the value 64, 3267 and for NUMA systems with large remote-access 3268 latencies, which will choose a value aligned 3269 with the appropriate hardware boundaries. 3270 3271 rcutree.jiffies_till_sched_qs= [KNL] 3272 Set required age in jiffies for a 3273 given grace period before RCU starts 3274 soliciting quiescent-state help from 3275 rcu_note_context_switch(). 3276 3277 rcutree.jiffies_till_first_fqs= [KNL] 3278 Set delay from grace-period initialization to 3279 first attempt to force quiescent states. 3280 Units are jiffies, minimum value is zero, 3281 and maximum value is HZ. 3282 3283 rcutree.jiffies_till_next_fqs= [KNL] 3284 Set delay between subsequent attempts to force 3285 quiescent states. Units are jiffies, minimum 3286 value is one, and maximum value is HZ. 3287 3288 rcutree.kthread_prio= [KNL,BOOT] 3289 Set the SCHED_FIFO priority of the RCU per-CPU 3290 kthreads (rcuc/N). This value is also used for 3291 the priority of the RCU boost threads (rcub/N) 3292 and for the RCU grace-period kthreads (rcu_bh, 3293 rcu_preempt, and rcu_sched). If RCU_BOOST is 3294 set, valid values are 1-99 and the default is 1 3295 (the least-favored priority). Otherwise, when 3296 RCU_BOOST is not set, valid values are 0-99 and 3297 the default is zero (non-realtime operation). 3298 3299 rcutree.rcu_nocb_leader_stride= [KNL] 3300 Set the number of NOCB kthread groups, which 3301 defaults to the square root of the number of 3302 CPUs. Larger numbers reduces the wakeup overhead 3303 on the per-CPU grace-period kthreads, but increases 3304 that same overhead on each group's leader. 3305 3306 rcutree.qhimark= [KNL] 3307 Set threshold of queued RCU callbacks beyond which 3308 batch limiting is disabled. 3309 3310 rcutree.qlowmark= [KNL] 3311 Set threshold of queued RCU callbacks below which 3312 batch limiting is re-enabled. 3313 3314 rcutree.rcu_idle_gp_delay= [KNL] 3315 Set wakeup interval for idle CPUs that have 3316 RCU callbacks (RCU_FAST_NO_HZ=y). 3317 3318 rcutree.rcu_idle_lazy_gp_delay= [KNL] 3319 Set wakeup interval for idle CPUs that have 3320 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y). 3321 Lazy RCU callbacks are those which RCU can 3322 prove do nothing more than free memory. 3323 3324 rcutree.rcu_kick_kthreads= [KNL] 3325 Cause the grace-period kthread to get an extra 3326 wake_up() if it sleeps three times longer than 3327 it should at force-quiescent-state time. 3328 This wake_up() will be accompanied by a 3329 WARN_ONCE() splat and an ftrace_dump(). 3330 3331 rcuperf.gp_exp= [KNL] 3332 Measure performance of expedited synchronous 3333 grace-period primitives. 3334 3335 rcuperf.holdoff= [KNL] 3336 Set test-start holdoff period. The purpose of 3337 this parameter is to delay the start of the 3338 test until boot completes in order to avoid 3339 interference. 3340 3341 rcuperf.nreaders= [KNL] 3342 Set number of RCU readers. The value -1 selects 3343 N, where N is the number of CPUs. A value 3344 "n" less than -1 selects N-n+1, where N is again 3345 the number of CPUs. For example, -2 selects N 3346 (the number of CPUs), -3 selects N+1, and so on. 3347 A value of "n" less than or equal to -N selects 3348 a single reader. 3349 3350 rcuperf.nwriters= [KNL] 3351 Set number of RCU writers. The values operate 3352 the same as for rcuperf.nreaders. 3353 N, where N is the number of CPUs 3354 3355 rcuperf.perf_runnable= [BOOT] 3356 Start rcuperf running at boot time. 3357 3358 rcuperf.shutdown= [KNL] 3359 Shut the system down after performance tests 3360 complete. This is useful for hands-off automated 3361 testing. 3362 3363 rcuperf.perf_type= [KNL] 3364 Specify the RCU implementation to test. 3365 3366 rcuperf.verbose= [KNL] 3367 Enable additional printk() statements. 3368 3369 rcutorture.cbflood_inter_holdoff= [KNL] 3370 Set holdoff time (jiffies) between successive 3371 callback-flood tests. 3372 3373 rcutorture.cbflood_intra_holdoff= [KNL] 3374 Set holdoff time (jiffies) between successive 3375 bursts of callbacks within a given callback-flood 3376 test. 3377 3378 rcutorture.cbflood_n_burst= [KNL] 3379 Set the number of bursts making up a given 3380 callback-flood test. Set this to zero to 3381 disable callback-flood testing. 3382 3383 rcutorture.cbflood_n_per_burst= [KNL] 3384 Set the number of callbacks to be registered 3385 in a given burst of a callback-flood test. 3386 3387 rcutorture.fqs_duration= [KNL] 3388 Set duration of force_quiescent_state bursts 3389 in microseconds. 3390 3391 rcutorture.fqs_holdoff= [KNL] 3392 Set holdoff time within force_quiescent_state bursts 3393 in microseconds. 3394 3395 rcutorture.fqs_stutter= [KNL] 3396 Set wait time between force_quiescent_state bursts 3397 in seconds. 3398 3399 rcutorture.gp_cond= [KNL] 3400 Use conditional/asynchronous update-side 3401 primitives, if available. 3402 3403 rcutorture.gp_exp= [KNL] 3404 Use expedited update-side primitives, if available. 3405 3406 rcutorture.gp_normal= [KNL] 3407 Use normal (non-expedited) asynchronous 3408 update-side primitives, if available. 3409 3410 rcutorture.gp_sync= [KNL] 3411 Use normal (non-expedited) synchronous 3412 update-side primitives, if available. If all 3413 of rcutorture.gp_cond=, rcutorture.gp_exp=, 3414 rcutorture.gp_normal=, and rcutorture.gp_sync= 3415 are zero, rcutorture acts as if is interpreted 3416 they are all non-zero. 3417 3418 rcutorture.n_barrier_cbs= [KNL] 3419 Set callbacks/threads for rcu_barrier() testing. 3420 3421 rcutorture.nfakewriters= [KNL] 3422 Set number of concurrent RCU writers. These just 3423 stress RCU, they don't participate in the actual 3424 test, hence the "fake". 3425 3426 rcutorture.nreaders= [KNL] 3427 Set number of RCU readers. The value -1 selects 3428 N-1, where N is the number of CPUs. A value 3429 "n" less than -1 selects N-n-2, where N is again 3430 the number of CPUs. For example, -2 selects N 3431 (the number of CPUs), -3 selects N+1, and so on. 3432 3433 rcutorture.object_debug= [KNL] 3434 Enable debug-object double-call_rcu() testing. 3435 3436 rcutorture.onoff_holdoff= [KNL] 3437 Set time (s) after boot for CPU-hotplug testing. 3438 3439 rcutorture.onoff_interval= [KNL] 3440 Set time (s) between CPU-hotplug operations, or 3441 zero to disable CPU-hotplug testing. 3442 3443 rcutorture.shuffle_interval= [KNL] 3444 Set task-shuffle interval (s). Shuffling tasks 3445 allows some CPUs to go into dyntick-idle mode 3446 during the rcutorture test. 3447 3448 rcutorture.shutdown_secs= [KNL] 3449 Set time (s) after boot system shutdown. This 3450 is useful for hands-off automated testing. 3451 3452 rcutorture.stall_cpu= [KNL] 3453 Duration of CPU stall (s) to test RCU CPU stall 3454 warnings, zero to disable. 3455 3456 rcutorture.stall_cpu_holdoff= [KNL] 3457 Time to wait (s) after boot before inducing stall. 3458 3459 rcutorture.stat_interval= [KNL] 3460 Time (s) between statistics printk()s. 3461 3462 rcutorture.stutter= [KNL] 3463 Time (s) to stutter testing, for example, specifying 3464 five seconds causes the test to run for five seconds, 3465 wait for five seconds, and so on. This tests RCU's 3466 ability to transition abruptly to and from idle. 3467 3468 rcutorture.test_boost= [KNL] 3469 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 3470 "Maybe" means test if the RCU implementation 3471 under test support RCU priority boosting. 3472 3473 rcutorture.test_boost_duration= [KNL] 3474 Duration (s) of each individual boost test. 3475 3476 rcutorture.test_boost_interval= [KNL] 3477 Interval (s) between each boost test. 3478 3479 rcutorture.test_no_idle_hz= [KNL] 3480 Test RCU's dyntick-idle handling. See also the 3481 rcutorture.shuffle_interval parameter. 3482 3483 rcutorture.torture_runnable= [BOOT] 3484 Start rcutorture running at boot time. 3485 3486 rcutorture.torture_type= [KNL] 3487 Specify the RCU implementation to test. 3488 3489 rcutorture.verbose= [KNL] 3490 Enable additional printk() statements. 3491 3492 rcupdate.rcu_cpu_stall_suppress= [KNL] 3493 Suppress RCU CPU stall warning messages. 3494 3495 rcupdate.rcu_cpu_stall_timeout= [KNL] 3496 Set timeout for RCU CPU stall warning messages. 3497 3498 rcupdate.rcu_expedited= [KNL] 3499 Use expedited grace-period primitives, for 3500 example, synchronize_rcu_expedited() instead 3501 of synchronize_rcu(). This reduces latency, 3502 but can increase CPU utilization, degrade 3503 real-time latency, and degrade energy efficiency. 3504 No effect on CONFIG_TINY_RCU kernels. 3505 3506 rcupdate.rcu_normal= [KNL] 3507 Use only normal grace-period primitives, 3508 for example, synchronize_rcu() instead of 3509 synchronize_rcu_expedited(). This improves 3510 real-time latency, CPU utilization, and 3511 energy efficiency, but can expose users to 3512 increased grace-period latency. This parameter 3513 overrides rcupdate.rcu_expedited. No effect on 3514 CONFIG_TINY_RCU kernels. 3515 3516 rcupdate.rcu_normal_after_boot= [KNL] 3517 Once boot has completed (that is, after 3518 rcu_end_inkernel_boot() has been invoked), use 3519 only normal grace-period primitives. No effect 3520 on CONFIG_TINY_RCU kernels. 3521 3522 rcupdate.rcu_task_stall_timeout= [KNL] 3523 Set timeout in jiffies for RCU task stall warning 3524 messages. Disable with a value less than or equal 3525 to zero. 3526 3527 rcupdate.rcu_self_test= [KNL] 3528 Run the RCU early boot self tests 3529 3530 rcupdate.rcu_self_test_bh= [KNL] 3531 Run the RCU bh early boot self tests 3532 3533 rcupdate.rcu_self_test_sched= [KNL] 3534 Run the RCU sched early boot self tests 3535 3536 rdinit= [KNL] 3537 Format: <full_path> 3538 Run specified binary instead of /init from the ramdisk, 3539 used for early userspace startup. See initrd. 3540 3541 reboot= [KNL] 3542 Format (x86 or x86_64): 3543 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \ 3544 [[,]s[mp]#### \ 3545 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 3546 [[,]f[orce] 3547 Where reboot_mode is one of warm (soft) or cold (hard) or gpio, 3548 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 3549 reboot_force is either force or not specified, 3550 reboot_cpu is s[mp]#### with #### being the processor 3551 to be used for rebooting. 3552 3553 relax_domain_level= 3554 [KNL, SMP] Set scheduler's default relax_domain_level. 3555 See Documentation/cgroup-v1/cpusets.txt. 3556 3557 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area 3558 3559 reservetop= [X86-32] 3560 Format: nn[KMG] 3561 Reserves a hole at the top of the kernel virtual 3562 address space. 3563 3564 reservelow= [X86] 3565 Format: nn[K] 3566 Set the amount of memory to reserve for BIOS at 3567 the bottom of the address space. 3568 3569 reset_devices [KNL] Force drivers to reset the underlying device 3570 during initialization. 3571 3572 resume= [SWSUSP] 3573 Specify the partition device for software suspend 3574 Format: 3575 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 3576 3577 resume_offset= [SWSUSP] 3578 Specify the offset from the beginning of the partition 3579 given by "resume=" at which the swap header is located, 3580 in <PAGE_SIZE> units (needed only for swap files). 3581 See Documentation/power/swsusp-and-swap-files.txt 3582 3583 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 3584 read the resume files 3585 3586 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 3587 Useful for devices that are detected asynchronously 3588 (e.g. USB and MMC devices). 3589 3590 hibernate= [HIBERNATION] 3591 noresume Don't check if there's a hibernation image 3592 present during boot. 3593 nocompress Don't compress/decompress hibernation images. 3594 no Disable hibernation and resume. 3595 protect_image Turn on image protection during restoration 3596 (that will set all pages holding image data 3597 during restoration read-only). 3598 3599 retain_initrd [RAM] Keep initrd memory after extraction 3600 3601 rfkill.default_state= 3602 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 3603 etc. communication is blocked by default. 3604 1 Unblocked. 3605 3606 rfkill.master_switch_mode= 3607 0 The "airplane mode" button does nothing. 3608 1 The "airplane mode" button toggles between everything 3609 blocked and the previous configuration. 3610 2 The "airplane mode" button toggles between everything 3611 blocked and everything unblocked. 3612 3613 rhash_entries= [KNL,NET] 3614 Set number of hash buckets for route cache 3615 3616 ring3mwait=disable 3617 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 3618 CPUs. 3619 3620 ro [KNL] Mount root device read-only on boot 3621 3622 rodata= [KNL] 3623 on Mark read-only kernel memory as read-only (default). 3624 off Leave read-only kernel memory writable for debugging. 3625 3626 rockchip.usb_uart 3627 Enable the uart passthrough on the designated usb port 3628 on Rockchip SoCs. When active, the signals of the 3629 debug-uart get routed to the D+ and D- pins of the usb 3630 port and the regular usb controller gets disabled. 3631 3632 root= [KNL] Root filesystem 3633 See name_to_dev_t comment in init/do_mounts.c. 3634 3635 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 3636 mount the root filesystem 3637 3638 rootflags= [KNL] Set root filesystem mount option string 3639 3640 rootfstype= [KNL] Set root filesystem type 3641 3642 rootwait [KNL] Wait (indefinitely) for root device to show up. 3643 Useful for devices that are detected asynchronously 3644 (e.g. USB and MMC devices). 3645 3646 rproc_mem=nn[KMG][@address] 3647 [KNL,ARM,CMA] Remoteproc physical memory block. 3648 Memory area to be used by remote processor image, 3649 managed by CMA. 3650 3651 rw [KNL] Mount root device read-write on boot 3652 3653 S [KNL] Run init in single mode 3654 3655 s390_iommu= [HW,S390] 3656 Set s390 IOTLB flushing mode 3657 strict 3658 With strict flushing every unmap operation will result in 3659 an IOTLB flush. Default is lazy flushing before reuse, 3660 which is faster. 3661 3662 sa1100ir [NET] 3663 See drivers/net/irda/sa1100_ir.c. 3664 3665 sbni= [NET] Granch SBNI12 leased line adapter 3666 3667 sched_debug [KNL] Enables verbose scheduler debug messages. 3668 3669 schedstats= [KNL,X86] Enable or disable scheduled statistics. 3670 Allowed values are enable and disable. This feature 3671 incurs a small amount of overhead in the scheduler 3672 but is useful for debugging and performance tuning. 3673 3674 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate 3675 xtime_lock contention on larger systems, and/or RCU lock 3676 contention on all systems with CONFIG_MAXSMP set. 3677 Format: { "0" | "1" } 3678 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 3679 1 -- enable. 3680 Note: increases power consumption, thus should only be 3681 enabled if running jitter sensitive (HPC/RT) workloads. 3682 3683 security= [SECURITY] Choose a security module to enable at boot. 3684 If this boot parameter is not specified, only the first 3685 security module asking for security registration will be 3686 loaded. An invalid security module name will be treated 3687 as if no module has been chosen. 3688 3689 selinux= [SELINUX] Disable or enable SELinux at boot time. 3690 Format: { "0" | "1" } 3691 See security/selinux/Kconfig help text. 3692 0 -- disable. 3693 1 -- enable. 3694 Default value is set via kernel config option. 3695 If enabled at boot time, /selinux/disable can be used 3696 later to disable prior to initial policy load. 3697 3698 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 3699 Format: { "0" | "1" } 3700 See security/apparmor/Kconfig help text 3701 0 -- disable. 3702 1 -- enable. 3703 Default value is set via kernel config option. 3704 3705 serialnumber [BUGS=X86-32] 3706 3707 shapers= [NET] 3708 Maximal number of shapers. 3709 3710 simeth= [IA-64] 3711 simscsi= 3712 3713 slram= [HW,MTD] 3714 3715 slab_nomerge [MM] 3716 Disable merging of slabs with similar size. May be 3717 necessary if there is some reason to distinguish 3718 allocs to different slabs. Debug options disable 3719 merging on their own. 3720 For more information see Documentation/vm/slub.txt. 3721 3722 slab_max_order= [MM, SLAB] 3723 Determines the maximum allowed order for slabs. 3724 A high setting may cause OOMs due to memory 3725 fragmentation. Defaults to 1 for systems with 3726 more than 32MB of RAM, 0 otherwise. 3727 3728 slub_debug[=options[,slabs]] [MM, SLUB] 3729 Enabling slub_debug allows one to determine the 3730 culprit if slab objects become corrupted. Enabling 3731 slub_debug can create guard zones around objects and 3732 may poison objects when not in use. Also tracks the 3733 last alloc / free. For more information see 3734 Documentation/vm/slub.txt. 3735 3736 slub_memcg_sysfs= [MM, SLUB] 3737 Determines whether to enable sysfs directories for 3738 memory cgroup sub-caches. 1 to enable, 0 to disable. 3739 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON. 3740 Enabling this can lead to a very high number of debug 3741 directories and files being created under 3742 /sys/kernel/slub. 3743 3744 slub_max_order= [MM, SLUB] 3745 Determines the maximum allowed order for slabs. 3746 A high setting may cause OOMs due to memory 3747 fragmentation. For more information see 3748 Documentation/vm/slub.txt. 3749 3750 slub_min_objects= [MM, SLUB] 3751 The minimum number of objects per slab. SLUB will 3752 increase the slab order up to slub_max_order to 3753 generate a sufficiently large slab able to contain 3754 the number of objects indicated. The higher the number 3755 of objects the smaller the overhead of tracking slabs 3756 and the less frequently locks need to be acquired. 3757 For more information see Documentation/vm/slub.txt. 3758 3759 slub_min_order= [MM, SLUB] 3760 Determines the minimum page order for slabs. Must be 3761 lower than slub_max_order. 3762 For more information see Documentation/vm/slub.txt. 3763 3764 slub_nomerge [MM, SLUB] 3765 Same with slab_nomerge. This is supported for legacy. 3766 See slab_nomerge for more information. 3767 3768 smart2= [HW] 3769 Format: <io1>[,<io2>[,...,<io8>]] 3770 3771 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 3772 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 3773 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 3774 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 3775 smsc-ircc2.ircc_irq= [HW] IRQ line 3776 smsc-ircc2.ircc_dma= [HW] DMA channel 3777 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 3778 0: Toshiba Satellite 1800 (GP data pin select) 3779 1: Fast pin select (default) 3780 2: ATC IRMode 3781 3782 smt [KNL,S390] Set the maximum number of threads (logical 3783 CPUs) to use per physical CPU on systems capable of 3784 symmetric multithreading (SMT). Will be capped to the 3785 actual hardware limit. 3786 Format: <integer> 3787 Default: -1 (no limit) 3788 3789 softlockup_panic= 3790 [KNL] Should the soft-lockup detector generate panics. 3791 Format: <integer> 3792 3793 softlockup_all_cpu_backtrace= 3794 [KNL] Should the soft-lockup detector generate 3795 backtraces on all cpus. 3796 Format: <integer> 3797 3798 sonypi.*= [HW] Sony Programmable I/O Control Device driver 3799 See Documentation/laptops/sonypi.txt 3800 3801 spia_io_base= [HW,MTD] 3802 spia_fio_base= 3803 spia_pedr= 3804 spia_peddr= 3805 3806 srcutree.exp_holdoff [KNL] 3807 Specifies how many nanoseconds must elapse 3808 since the end of the last SRCU grace period for 3809 a given srcu_struct until the next normal SRCU 3810 grace period will be considered for automatic 3811 expediting. Set to zero to disable automatic 3812 expediting. 3813 3814 stack_guard_gap= [MM] 3815 override the default stack gap protection. The value 3816 is in page units and it defines how many pages prior 3817 to (for stacks growing down) resp. after (for stacks 3818 growing up) the main stack are reserved for no other 3819 mapping. Default value is 256 pages. 3820 3821 stacktrace [FTRACE] 3822 Enabled the stack tracer on boot up. 3823 3824 stacktrace_filter=[function-list] 3825 [FTRACE] Limit the functions that the stack tracer 3826 will trace at boot up. function-list is a comma separated 3827 list of functions. This list can be changed at run 3828 time by the stack_trace_filter file in the debugfs 3829 tracing directory. Note, this enables stack tracing 3830 and the stacktrace above is not needed. 3831 3832 sti= [PARISC,HW] 3833 Format: <num> 3834 Set the STI (builtin display/keyboard on the HP-PARISC 3835 machines) console (graphic card) which should be used 3836 as the initial boot-console. 3837 See also comment in drivers/video/console/sticore.c. 3838 3839 sti_font= [HW] 3840 See comment in drivers/video/console/sticore.c. 3841 3842 stifb= [HW] 3843 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 3844 3845 sunrpc.min_resvport= 3846 sunrpc.max_resvport= 3847 [NFS,SUNRPC] 3848 SunRPC servers often require that client requests 3849 originate from a privileged port (i.e. a port in the 3850 range 0 < portnr < 1024). 3851 An administrator who wishes to reserve some of these 3852 ports for other uses may adjust the range that the 3853 kernel's sunrpc client considers to be privileged 3854 using these two parameters to set the minimum and 3855 maximum port values. 3856 3857 sunrpc.svc_rpc_per_connection_limit= 3858 [NFS,SUNRPC] 3859 Limit the number of requests that the server will 3860 process in parallel from a single connection. 3861 The default value is 0 (no limit). 3862 3863 sunrpc.pool_mode= 3864 [NFS] 3865 Control how the NFS server code allocates CPUs to 3866 service thread pools. Depending on how many NICs 3867 you have and where their interrupts are bound, this 3868 option will affect which CPUs will do NFS serving. 3869 Note: this parameter cannot be changed while the 3870 NFS server is running. 3871 3872 auto the server chooses an appropriate mode 3873 automatically using heuristics 3874 global a single global pool contains all CPUs 3875 percpu one pool for each CPU 3876 pernode one pool for each NUMA node (equivalent 3877 to global on non-NUMA machines) 3878 3879 sunrpc.tcp_slot_table_entries= 3880 sunrpc.udp_slot_table_entries= 3881 [NFS,SUNRPC] 3882 Sets the upper limit on the number of simultaneous 3883 RPC calls that can be sent from the client to a 3884 server. Increasing these values may allow you to 3885 improve throughput, but will also increase the 3886 amount of memory reserved for use by the client. 3887 3888 suspend.pm_test_delay= 3889 [SUSPEND] 3890 Sets the number of seconds to remain in a suspend test 3891 mode before resuming the system (see 3892 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 3893 is set. Default value is 5. 3894 3895 swapaccount=[0|1] 3896 [KNL] Enable accounting of swap in memory resource 3897 controller if no parameter or 1 is given or disable 3898 it if 0 is given (See Documentation/cgroup-v1/memory.txt) 3899 3900 swiotlb= [ARM,IA-64,PPC,MIPS,X86] 3901 Format: { <int> | force | noforce } 3902 <int> -- Number of I/O TLB slabs 3903 force -- force using of bounce buffers even if they 3904 wouldn't be automatically used by the kernel 3905 noforce -- Never use bounce buffers (for debugging) 3906 3907 switches= [HW,M68k] 3908 3909 sysfs.deprecated=0|1 [KNL] 3910 Enable/disable old style sysfs layout for old udev 3911 on older distributions. When this option is enabled 3912 very new udev will not work anymore. When this option 3913 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled) 3914 in older udev will not work anymore. 3915 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in 3916 the kernel configuration. 3917 3918 sysrq_always_enabled 3919 [KNL] 3920 Ignore sysrq setting - this boot parameter will 3921 neutralize any effect of /proc/sys/kernel/sysrq. 3922 Useful for debugging. 3923 3924 tcpmhash_entries= [KNL,NET] 3925 Set the number of tcp_metrics_hash slots. 3926 Default value is 8192 or 16384 depending on total 3927 ram pages. This is used to specify the TCP metrics 3928 cache size. See Documentation/networking/ip-sysctl.txt 3929 "tcp_no_metrics_save" section for more details. 3930 3931 tdfx= [HW,DRM] 3932 3933 test_suspend= [SUSPEND][,N] 3934 Specify "mem" (for Suspend-to-RAM) or "standby" (for 3935 standby suspend) or "freeze" (for suspend type freeze) 3936 as the system sleep state during system startup with 3937 the optional capability to repeat N number of times. 3938 The system is woken from this state using a 3939 wakeup-capable RTC alarm. 3940 3941 thash_entries= [KNL,NET] 3942 Set number of hash buckets for TCP connection 3943 3944 thermal.act= [HW,ACPI] 3945 -1: disable all active trip points in all thermal zones 3946 <degrees C>: override all lowest active trip points 3947 3948 thermal.crt= [HW,ACPI] 3949 -1: disable all critical trip points in all thermal zones 3950 <degrees C>: override all critical trip points 3951 3952 thermal.nocrt= [HW,ACPI] 3953 Set to disable actions on ACPI thermal zone 3954 critical and hot trip points. 3955 3956 thermal.off= [HW,ACPI] 3957 1: disable ACPI thermal control 3958 3959 thermal.psv= [HW,ACPI] 3960 -1: disable all passive trip points 3961 <degrees C>: override all passive trip points to this 3962 value 3963 3964 thermal.tzp= [HW,ACPI] 3965 Specify global default ACPI thermal zone polling rate 3966 <deci-seconds>: poll all this frequency 3967 0: no polling (default) 3968 3969 threadirqs [KNL] 3970 Force threading of all interrupt handlers except those 3971 marked explicitly IRQF_NO_THREAD. 3972 3973 tmem [KNL,XEN] 3974 Enable the Transcendent memory driver if built-in. 3975 3976 tmem.cleancache=0|1 [KNL, XEN] 3977 Default is on (1). Disable the usage of the cleancache 3978 API to send anonymous pages to the hypervisor. 3979 3980 tmem.frontswap=0|1 [KNL, XEN] 3981 Default is on (1). Disable the usage of the frontswap 3982 API to send swap pages to the hypervisor. If disabled 3983 the selfballooning and selfshrinking are force disabled. 3984 3985 tmem.selfballooning=0|1 [KNL, XEN] 3986 Default is on (1). Disable the driving of swap pages 3987 to the hypervisor. 3988 3989 tmem.selfshrinking=0|1 [KNL, XEN] 3990 Default is on (1). Partial swapoff that immediately 3991 transfers pages from Xen hypervisor back to the 3992 kernel based on different criteria. 3993 3994 topology= [S390] 3995 Format: {off | on} 3996 Specify if the kernel should make use of the cpu 3997 topology information if the hardware supports this. 3998 The scheduler will make use of this information and 3999 e.g. base its process migration decisions on it. 4000 Default is on. 4001 4002 topology_updates= [KNL, PPC, NUMA] 4003 Format: {off} 4004 Specify if the kernel should ignore (off) 4005 topology updates sent by the hypervisor to this 4006 LPAR. 4007 4008 tp720= [HW,PS2] 4009 4010 tpm_suspend_pcr=[HW,TPM] 4011 Format: integer pcr id 4012 Specify that at suspend time, the tpm driver 4013 should extend the specified pcr with zeros, 4014 as a workaround for some chips which fail to 4015 flush the last written pcr on TPM_SaveState. 4016 This will guarantee that all the other pcrs 4017 are saved. 4018 4019 trace_buf_size=nn[KMG] 4020 [FTRACE] will set tracing buffer size on each cpu. 4021 4022 trace_event=[event-list] 4023 [FTRACE] Set and start specified trace events in order 4024 to facilitate early boot debugging. The event-list is a 4025 comma separated list of trace events to enable. See 4026 also Documentation/trace/events.txt 4027 4028 trace_options=[option-list] 4029 [FTRACE] Enable or disable tracer options at boot. 4030 The option-list is a comma delimited list of options 4031 that can be enabled or disabled just as if you were 4032 to echo the option name into 4033 4034 /sys/kernel/debug/tracing/trace_options 4035 4036 For example, to enable stacktrace option (to dump the 4037 stack trace of each event), add to the command line: 4038 4039 trace_options=stacktrace 4040 4041 See also Documentation/trace/ftrace.txt "trace options" 4042 section. 4043 4044 tp_printk[FTRACE] 4045 Have the tracepoints sent to printk as well as the 4046 tracing ring buffer. This is useful for early boot up 4047 where the system hangs or reboots and does not give the 4048 option for reading the tracing buffer or performing a 4049 ftrace_dump_on_oops. 4050 4051 To turn off having tracepoints sent to printk, 4052 echo 0 > /proc/sys/kernel/tracepoint_printk 4053 Note, echoing 1 into this file without the 4054 tracepoint_printk kernel cmdline option has no effect. 4055 4056 ** CAUTION ** 4057 4058 Having tracepoints sent to printk() and activating high 4059 frequency tracepoints such as irq or sched, can cause 4060 the system to live lock. 4061 4062 traceoff_on_warning 4063 [FTRACE] enable this option to disable tracing when a 4064 warning is hit. This turns off "tracing_on". Tracing can 4065 be enabled again by echoing '1' into the "tracing_on" 4066 file located in /sys/kernel/debug/tracing/ 4067 4068 This option is useful, as it disables the trace before 4069 the WARNING dump is called, which prevents the trace to 4070 be filled with content caused by the warning output. 4071 4072 This option can also be set at run time via the sysctl 4073 option: kernel/traceoff_on_warning 4074 4075 transparent_hugepage= 4076 [KNL] 4077 Format: [always|madvise|never] 4078 Can be used to control the default behavior of the system 4079 with respect to transparent hugepages. 4080 See Documentation/vm/transhuge.txt for more details. 4081 4082 tsc= Disable clocksource stability checks for TSC. 4083 Format: <string> 4084 [x86] reliable: mark tsc clocksource as reliable, this 4085 disables clocksource verification at runtime, as well 4086 as the stability checks done at bootup. Used to enable 4087 high-resolution timer mode on older hardware, and in 4088 virtualized environment. 4089 [x86] noirqtime: Do not use TSC to do irq accounting. 4090 Used to run time disable IRQ_TIME_ACCOUNTING on any 4091 platforms where RDTSC is slow and this accounting 4092 can add overhead. 4093 4094 turbografx.map[2|3]= [HW,JOY] 4095 TurboGraFX parallel port interface 4096 Format: 4097 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 4098 See also Documentation/input/joystick-parport.txt 4099 4100 udbg-immortal [PPC] When debugging early kernel crashes that 4101 happen after console_init() and before a proper 4102 console driver takes over, this boot options might 4103 help "seeing" what's going on. 4104 4105 uhash_entries= [KNL,NET] 4106 Set number of hash buckets for UDP/UDP-Lite connections 4107 4108 uhci-hcd.ignore_oc= 4109 [USB] Ignore overcurrent events (default N). 4110 Some badly-designed motherboards generate lots of 4111 bogus events, for ports that aren't wired to 4112 anything. Set this parameter to avoid log spamming. 4113 Note that genuine overcurrent events won't be 4114 reported either. 4115 4116 unknown_nmi_panic 4117 [X86] Cause panic on unknown NMI. 4118 4119 usbcore.authorized_default= 4120 [USB] Default USB device authorization: 4121 (default -1 = authorized except for wireless USB, 4122 0 = not authorized, 1 = authorized) 4123 4124 usbcore.autosuspend= 4125 [USB] The autosuspend time delay (in seconds) used 4126 for newly-detected USB devices (default 2). This 4127 is the time required before an idle device will be 4128 autosuspended. Devices for which the delay is set 4129 to a negative value won't be autosuspended at all. 4130 4131 usbcore.usbfs_snoop= 4132 [USB] Set to log all usbfs traffic (default 0 = off). 4133 4134 usbcore.usbfs_snoop_max= 4135 [USB] Maximum number of bytes to snoop in each URB 4136 (default = 65536). 4137 4138 usbcore.blinkenlights= 4139 [USB] Set to cycle leds on hubs (default 0 = off). 4140 4141 usbcore.old_scheme_first= 4142 [USB] Start with the old device initialization 4143 scheme (default 0 = off). 4144 4145 usbcore.usbfs_memory_mb= 4146 [USB] Memory limit (in MB) for buffers allocated by 4147 usbfs (default = 16, 0 = max = 2047). 4148 4149 usbcore.use_both_schemes= 4150 [USB] Try the other device initialization scheme 4151 if the first one fails (default 1 = enabled). 4152 4153 usbcore.initial_descriptor_timeout= 4154 [USB] Specifies timeout for the initial 64-byte 4155 USB_REQ_GET_DESCRIPTOR request in milliseconds 4156 (default 5000 = 5.0 seconds). 4157 4158 usbcore.nousb [USB] Disable the USB subsystem 4159 4160 usbhid.mousepoll= 4161 [USBHID] The interval which mice are to be polled at. 4162 4163 usbhid.jspoll= 4164 [USBHID] The interval which joysticks are to be polled at. 4165 4166 usb-storage.delay_use= 4167 [UMS] The delay in seconds before a new device is 4168 scanned for Logical Units (default 1). 4169 4170 usb-storage.quirks= 4171 [UMS] A list of quirks entries to supplement or 4172 override the built-in unusual_devs list. List 4173 entries are separated by commas. Each entry has 4174 the form VID:PID:Flags where VID and PID are Vendor 4175 and Product ID values (4-digit hex numbers) and 4176 Flags is a set of characters, each corresponding 4177 to a common usb-storage quirk flag as follows: 4178 a = SANE_SENSE (collect more than 18 bytes 4179 of sense data); 4180 b = BAD_SENSE (don't collect more than 18 4181 bytes of sense data); 4182 c = FIX_CAPACITY (decrease the reported 4183 device capacity by one sector); 4184 d = NO_READ_DISC_INFO (don't use 4185 READ_DISC_INFO command); 4186 e = NO_READ_CAPACITY_16 (don't use 4187 READ_CAPACITY_16 command); 4188 f = NO_REPORT_OPCODES (don't use report opcodes 4189 command, uas only); 4190 g = MAX_SECTORS_240 (don't transfer more than 4191 240 sectors at a time, uas only); 4192 h = CAPACITY_HEURISTICS (decrease the 4193 reported device capacity by one 4194 sector if the number is odd); 4195 i = IGNORE_DEVICE (don't bind to this 4196 device); 4197 j = NO_REPORT_LUNS (don't use report luns 4198 command, uas only); 4199 l = NOT_LOCKABLE (don't try to lock and 4200 unlock ejectable media); 4201 m = MAX_SECTORS_64 (don't transfer more 4202 than 64 sectors = 32 KB at a time); 4203 n = INITIAL_READ10 (force a retry of the 4204 initial READ(10) command); 4205 o = CAPACITY_OK (accept the capacity 4206 reported by the device); 4207 p = WRITE_CACHE (the device cache is ON 4208 by default); 4209 r = IGNORE_RESIDUE (the device reports 4210 bogus residue values); 4211 s = SINGLE_LUN (the device has only one 4212 Logical Unit); 4213 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 4214 commands, uas only); 4215 u = IGNORE_UAS (don't bind to the uas driver); 4216 w = NO_WP_DETECT (don't test whether the 4217 medium is write-protected). 4218 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 4219 even if the device claims no cache) 4220 Example: quirks=0419:aaf5:rl,0421:0433:rc 4221 4222 user_debug= [KNL,ARM] 4223 Format: <int> 4224 See arch/arm/Kconfig.debug help text. 4225 1 - undefined instruction events 4226 2 - system calls 4227 4 - invalid data aborts 4228 8 - SIGSEGV faults 4229 16 - SIGBUS faults 4230 Example: user_debug=31 4231 4232 userpte= 4233 [X86] Flags controlling user PTE allocations. 4234 4235 nohigh = do not allocate PTE pages in 4236 HIGHMEM regardless of setting 4237 of CONFIG_HIGHPTE. 4238 4239 vdso= [X86,SH] 4240 On X86_32, this is an alias for vdso32=. Otherwise: 4241 4242 vdso=1: enable VDSO (the default) 4243 vdso=0: disable VDSO mapping 4244 4245 vdso32= [X86] Control the 32-bit vDSO 4246 vdso32=1: enable 32-bit VDSO 4247 vdso32=0 or vdso32=2: disable 32-bit VDSO 4248 4249 See the help text for CONFIG_COMPAT_VDSO for more 4250 details. If CONFIG_COMPAT_VDSO is set, the default is 4251 vdso32=0; otherwise, the default is vdso32=1. 4252 4253 For compatibility with older kernels, vdso32=2 is an 4254 alias for vdso32=0. 4255 4256 Try vdso32=0 if you encounter an error that says: 4257 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 4258 4259 vector= [IA-64,SMP] 4260 vector=percpu: enable percpu vector domain 4261 4262 video= [FB] Frame buffer configuration 4263 See Documentation/fb/modedb.txt. 4264 4265 video.brightness_switch_enabled= [0,1] 4266 If set to 1, on receiving an ACPI notify event 4267 generated by hotkey, video driver will adjust brightness 4268 level and then send out the event to user space through 4269 the allocated input device; If set to 0, video driver 4270 will only send out the event without touching backlight 4271 brightness level. 4272 default: 1 4273 4274 virtio_mmio.device= 4275 [VMMIO] Memory mapped virtio (platform) device. 4276 4277 <size>@<baseaddr>:<irq>[:<id>] 4278 where: 4279 <size> := size (can use standard suffixes 4280 like K, M and G) 4281 <baseaddr> := physical base address 4282 <irq> := interrupt number (as passed to 4283 request_irq()) 4284 <id> := (optional) platform device id 4285 example: 4286 virtio_mmio.device=1K@0x100b0000:48:7 4287 4288 Can be used multiple times for multiple devices. 4289 4290 vga= [BOOT,X86-32] Select a particular video mode 4291 See Documentation/x86/boot.txt and 4292 Documentation/svga.txt. 4293 Use vga=ask for menu. 4294 This is actually a boot loader parameter; the value is 4295 passed to the kernel using a special protocol. 4296 4297 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact 4298 size of <nn>. This can be used to increase the 4299 minimum size (128MB on x86). It can also be used to 4300 decrease the size and leave more room for directly 4301 mapped kernel RAM. 4302 4303 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 4304 Format: <command> 4305 4306 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 4307 Format: <command> 4308 4309 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 4310 Format: <command> 4311 4312 vsyscall= [X86-64] 4313 Controls the behavior of vsyscalls (i.e. calls to 4314 fixed addresses of 0xffffffffff600x00 from legacy 4315 code). Most statically-linked binaries and older 4316 versions of glibc use these calls. Because these 4317 functions are at fixed addresses, they make nice 4318 targets for exploits that can control RIP. 4319 4320 emulate [default] Vsyscalls turn into traps and are 4321 emulated reasonably safely. 4322 4323 native Vsyscalls are native syscall instructions. 4324 This is a little bit faster than trapping 4325 and makes a few dynamic recompilers work 4326 better than they would in emulation mode. 4327 It also makes exploits much easier to write. 4328 4329 none Vsyscalls don't work at all. This makes 4330 them quite hard to use for exploits but 4331 might break your system. 4332 4333 vt.color= [VT] Default text color. 4334 Format: 0xYX, X = foreground, Y = background. 4335 Default: 0x07 = light gray on black. 4336 4337 vt.cur_default= [VT] Default cursor shape. 4338 Format: 0xCCBBAA, where AA, BB, and CC are the same as 4339 the parameters of the <Esc>[?A;B;Cc escape sequence; 4340 see VGA-softcursor.txt. Default: 2 = underline. 4341 4342 vt.default_blu= [VT] 4343 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 4344 Change the default blue palette of the console. 4345 This is a 16-member array composed of values 4346 ranging from 0-255. 4347 4348 vt.default_grn= [VT] 4349 Format: <green0>,<green1>,<green2>,...,<green15> 4350 Change the default green palette of the console. 4351 This is a 16-member array composed of values 4352 ranging from 0-255. 4353 4354 vt.default_red= [VT] 4355 Format: <red0>,<red1>,<red2>,...,<red15> 4356 Change the default red palette of the console. 4357 This is a 16-member array composed of values 4358 ranging from 0-255. 4359 4360 vt.default_utf8= 4361 [VT] 4362 Format=<0|1> 4363 Set system-wide default UTF-8 mode for all tty's. 4364 Default is 1, i.e. UTF-8 mode is enabled for all 4365 newly opened terminals. 4366 4367 vt.global_cursor_default= 4368 [VT] 4369 Format=<-1|0|1> 4370 Set system-wide default for whether a cursor 4371 is shown on new VTs. Default is -1, 4372 i.e. cursors will be created by default unless 4373 overridden by individual drivers. 0 will hide 4374 cursors, 1 will display them. 4375 4376 vt.italic= [VT] Default color for italic text; 0-15. 4377 Default: 2 = green. 4378 4379 vt.underline= [VT] Default color for underlined text; 0-15. 4380 Default: 3 = cyan. 4381 4382 watchdog timers [HW,WDT] For information on watchdog timers, 4383 see Documentation/watchdog/watchdog-parameters.txt 4384 or other driver-specific files in the 4385 Documentation/watchdog/ directory. 4386 4387 workqueue.watchdog_thresh= 4388 If CONFIG_WQ_WATCHDOG is configured, workqueue can 4389 warn stall conditions and dump internal state to 4390 help debugging. 0 disables workqueue stall 4391 detection; otherwise, it's the stall threshold 4392 duration in seconds. The default value is 30 and 4393 it can be updated at runtime by writing to the 4394 corresponding sysfs file. 4395 4396 workqueue.disable_numa 4397 By default, all work items queued to unbound 4398 workqueues are affine to the NUMA nodes they're 4399 issued on, which results in better behavior in 4400 general. If NUMA affinity needs to be disabled for 4401 whatever reason, this option can be used. Note 4402 that this also can be controlled per-workqueue for 4403 workqueues visible under /sys/bus/workqueue/. 4404 4405 workqueue.power_efficient 4406 Per-cpu workqueues are generally preferred because 4407 they show better performance thanks to cache 4408 locality; unfortunately, per-cpu workqueues tend to 4409 be more power hungry than unbound workqueues. 4410 4411 Enabling this makes the per-cpu workqueues which 4412 were observed to contribute significantly to power 4413 consumption unbound, leading to measurably lower 4414 power usage at the cost of small performance 4415 overhead. 4416 4417 The default value of this parameter is determined by 4418 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 4419 4420 workqueue.debug_force_rr_cpu 4421 Workqueue used to implicitly guarantee that work 4422 items queued without explicit CPU specified are put 4423 on the local CPU. This guarantee is no longer true 4424 and while local CPU is still preferred work items 4425 may be put on foreign CPUs. This debug option 4426 forces round-robin CPU selection to flush out 4427 usages which depend on the now broken guarantee. 4428 When enabled, memory and cache locality will be 4429 impacted. 4430 4431 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of 4432 default x2apic cluster mode on platforms 4433 supporting x2apic. 4434 4435 x86_intel_mid_timer= [X86-32,APBT] 4436 Choose timer option for x86 Intel MID platform. 4437 Two valid options are apbt timer only and lapic timer 4438 plus one apbt timer for broadcast timer. 4439 x86_intel_mid_timer=apbt_only | lapic_and_apbt 4440 4441 xen_512gb_limit [KNL,X86-64,XEN] 4442 Restricts the kernel running paravirtualized under Xen 4443 to use only up to 512 GB of RAM. The reason to do so is 4444 crash analysis tools and Xen tools for doing domain 4445 save/restore/migration must be enabled to handle larger 4446 domains. 4447 4448 xen_emul_unplug= [HW,X86,XEN] 4449 Unplug Xen emulated devices 4450 Format: [unplug0,][unplug1] 4451 ide-disks -- unplug primary master IDE devices 4452 aux-ide-disks -- unplug non-primary-master IDE devices 4453 nics -- unplug network devices 4454 all -- unplug all emulated devices (NICs and IDE disks) 4455 unnecessary -- unplugging emulated devices is 4456 unnecessary even if the host did not respond to 4457 the unplug protocol 4458 never -- do not unplug even if version check succeeds 4459 4460 xen_nopvspin [X86,XEN] 4461 Disables the ticketlock slowpath using Xen PV 4462 optimizations. 4463 4464 xen_nopv [X86] 4465 Disables the PV optimizations forcing the HVM guest to 4466 run as generic HVM guest with no PV drivers. 4467 4468 xirc2ps_cs= [NET,PCMCIA] 4469 Format: 4470 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 4471