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 coresight_cpu_debug.enable 653 [ARM,ARM64] 654 Format: <bool> 655 Enable/disable the CPU sampling based debugging. 656 0: default value, disable debugging 657 1: enable debugging at boot time 658 659 cpuidle.off=1 [CPU_IDLE] 660 disable the cpuidle sub-system 661 662 cpufreq.off=1 [CPU_FREQ] 663 disable the cpufreq sub-system 664 665 cpu_init_udelay=N 666 [X86] Delay for N microsec between assert and de-assert 667 of APIC INIT to start processors. This delay occurs 668 on every CPU online, such as boot, and resume from suspend. 669 Default: 10000 670 671 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver 672 Format: 673 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] 674 675 crashkernel=size[KMG][@offset[KMG]] 676 [KNL] Using kexec, Linux can switch to a 'crash kernel' 677 upon panic. This parameter reserves the physical 678 memory region [offset, offset + size] for that kernel 679 image. If '@offset' is omitted, then a suitable offset 680 is selected automatically. Check 681 Documentation/kdump/kdump.txt for further details. 682 683 crashkernel=range1:size1[,range2:size2,...][@offset] 684 [KNL] Same as above, but depends on the memory 685 in the running system. The syntax of range is 686 start-[end] where start and end are both 687 a memory unit (amount[KMG]). See also 688 Documentation/kdump/kdump.txt for an example. 689 690 crashkernel=size[KMG],high 691 [KNL, x86_64] range could be above 4G. Allow kernel 692 to allocate physical memory region from top, so could 693 be above 4G if system have more than 4G ram installed. 694 Otherwise memory region will be allocated below 4G, if 695 available. 696 It will be ignored if crashkernel=X is specified. 697 crashkernel=size[KMG],low 698 [KNL, x86_64] range under 4G. When crashkernel=X,high 699 is passed, kernel could allocate physical memory region 700 above 4G, that cause second kernel crash on system 701 that require some amount of low memory, e.g. swiotlb 702 requires at least 64M+32K low memory, also enough extra 703 low memory is needed to make sure DMA buffers for 32-bit 704 devices won't run out. Kernel would try to allocate at 705 at least 256M below 4G automatically. 706 This one let user to specify own low range under 4G 707 for second kernel instead. 708 0: to disable low allocation. 709 It will be ignored when crashkernel=X,high is not used 710 or memory reserved is below 4G. 711 712 cryptomgr.notests 713 [KNL] Disable crypto self-tests 714 715 cs89x0_dma= [HW,NET] 716 Format: <dma> 717 718 cs89x0_media= [HW,NET] 719 Format: { rj45 | aui | bnc } 720 721 dasd= [HW,NET] 722 See header of drivers/s390/block/dasd_devmap.c. 723 724 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port 725 (one device per port) 726 Format: <port#>,<type> 727 See also Documentation/input/joystick-parport.txt 728 729 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot 730 time. See 731 Documentation/admin-guide/dynamic-debug-howto.rst for 732 details. Deprecated, see dyndbg. 733 734 debug [KNL] Enable kernel debugging (events log level). 735 736 debug_locks_verbose= 737 [KNL] verbose self-tests 738 Format=<0|1> 739 Print debugging info while doing the locking API 740 self-tests. 741 We default to 0 (no extra messages), setting it to 742 1 will print _a lot_ more information - normally 743 only useful to kernel developers. 744 745 debug_objects [KNL] Enable object debugging 746 747 no_debug_objects 748 [KNL] Disable object debugging 749 750 debug_guardpage_minorder= 751 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this 752 parameter allows control of the order of pages that will 753 be intentionally kept free (and hence protected) by the 754 buddy allocator. Bigger value increase the probability 755 of catching random memory corruption, but reduce the 756 amount of memory for normal system use. The maximum 757 possible value is MAX_ORDER/2. Setting this parameter 758 to 1 or 2 should be enough to identify most random 759 memory corruption problems caused by bugs in kernel or 760 driver code when a CPU writes to (or reads from) a 761 random memory location. Note that there exists a class 762 of memory corruptions problems caused by buggy H/W or 763 F/W or by drivers badly programing DMA (basically when 764 memory is written at bus level and the CPU MMU is 765 bypassed) which are not detectable by 766 CONFIG_DEBUG_PAGEALLOC, hence this option will not help 767 tracking down these problems. 768 769 debug_pagealloc= 770 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this 771 parameter enables the feature at boot time. In 772 default, it is disabled. We can avoid allocating huge 773 chunk of memory for debug pagealloc if we don't enable 774 it at boot time and the system will work mostly same 775 with the kernel built without CONFIG_DEBUG_PAGEALLOC. 776 on: enable the feature 777 778 debugpat [X86] Enable PAT debugging 779 780 decnet.addr= [HW,NET] 781 Format: <area>[,<node>] 782 See also Documentation/networking/decnet.txt. 783 784 default_hugepagesz= 785 [same as hugepagesz=] The size of the default 786 HugeTLB page size. This is the size represented by 787 the legacy /proc/ hugepages APIs, used for SHM, and 788 default size when mounting hugetlbfs filesystems. 789 Defaults to the default architecture's huge page size 790 if not specified. 791 792 dhash_entries= [KNL] 793 Set number of hash buckets for dentry cache. 794 795 disable_1tb_segments [PPC] 796 Disables the use of 1TB hash page table segments. This 797 causes the kernel to fall back to 256MB segments which 798 can be useful when debugging issues that require an SLB 799 miss to occur. 800 801 disable= [IPV6] 802 See Documentation/networking/ipv6.txt. 803 804 disable_radix [PPC] 805 Disable RADIX MMU mode on POWER9 806 807 disable_cpu_apicid= [X86,APIC,SMP] 808 Format: <int> 809 The number of initial APIC ID for the 810 corresponding CPU to be disabled at boot, 811 mostly used for the kdump 2nd kernel to 812 disable BSP to wake up multiple CPUs without 813 causing system reset or hang due to sending 814 INIT from AP to BSP. 815 816 disable_ddw [PPC/PSERIES] 817 Disable Dynamic DMA Window support. Use this if 818 to workaround buggy firmware. 819 820 disable_ipv6= [IPV6] 821 See Documentation/networking/ipv6.txt. 822 823 disable_mtrr_cleanup [X86] 824 The kernel tries to adjust MTRR layout from continuous 825 to discrete, to make X server driver able to add WB 826 entry later. This parameter disables that. 827 828 disable_mtrr_trim [X86, Intel and AMD only] 829 By default the kernel will trim any uncacheable 830 memory out of your available memory pool based on 831 MTRR settings. This parameter disables that behavior, 832 possibly causing your machine to run very slowly. 833 834 disable_timer_pin_1 [X86] 835 Disable PIN 1 of APIC timer 836 Can be useful to work around chipset bugs. 837 838 dis_ucode_ldr [X86] Disable the microcode loader. 839 840 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, 841 this option disables the debugging code at boot. 842 843 dma_debug_entries=<number> 844 This option allows to tune the number of preallocated 845 entries for DMA-API debugging code. One entry is 846 required per DMA-API allocation. Use this if the 847 DMA-API debugging code disables itself because the 848 architectural default is too low. 849 850 dma_debug_driver=<driver_name> 851 With this option the DMA-API debugging driver 852 filter feature can be enabled at boot time. Just 853 pass the driver to filter for as the parameter. 854 The filter can be disabled or changed to another 855 driver later using sysfs. 856 857 drm_kms_helper.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>] 858 Broken monitors, graphic adapters, KVMs and EDIDless 859 panels may send no or incorrect EDID data sets. 860 This parameter allows to specify an EDID data sets 861 in the /lib/firmware directory that are used instead. 862 Generic built-in EDID data sets are used, if one of 863 edid/1024x768.bin, edid/1280x1024.bin, 864 edid/1680x1050.bin, or edid/1920x1080.bin is given 865 and no file with the same name exists. Details and 866 instructions how to build your own EDID data are 867 available in Documentation/EDID/HOWTO.txt. An EDID 868 data set will only be used for a particular connector, 869 if its name and a colon are prepended to the EDID 870 name. Each connector may use a unique EDID data 871 set by separating the files with a comma. An EDID 872 data set with no connector name will be used for 873 any connectors not explicitly specified. 874 875 dscc4.setup= [NET] 876 877 dt_cpu_ftrs= [PPC] 878 Format: {"off" | "known"} 879 Control how the dt_cpu_ftrs device-tree binding is 880 used for CPU feature discovery and setup (if it 881 exists). 882 off: Do not use it, fall back to legacy cpu table. 883 known: Do not pass through unknown features to guests 884 or userspace, only those that the kernel is aware of. 885 886 dump_apple_properties [X86] 887 Dump name and content of EFI device properties on 888 x86 Macs. Useful for driver authors to determine 889 what data is available or for reverse-engineering. 890 891 dyndbg[="val"] [KNL,DYNAMIC_DEBUG] 892 module.dyndbg[="val"] 893 Enable debug messages at boot time. See 894 Documentation/admin-guide/dynamic-debug-howto.rst 895 for details. 896 897 nompx [X86] Disables Intel Memory Protection Extensions. 898 See Documentation/x86/intel_mpx.txt for more 899 information about the feature. 900 901 nopku [X86] Disable Memory Protection Keys CPU feature found 902 in some Intel CPUs. 903 904 module.async_probe [KNL] 905 Enable asynchronous probe on this module. 906 907 early_ioremap_debug [KNL] 908 Enable debug messages in early_ioremap support. This 909 is useful for tracking down temporary early mappings 910 which are not unmapped. 911 912 earlycon= [KNL] Output early console device and options. 913 914 When used with no options, the early console is 915 determined by the stdout-path property in device 916 tree's chosen node. 917 918 cdns,<addr>[,options] 919 Start an early, polled-mode console on a Cadence 920 (xuartps) serial port at the specified address. Only 921 supported option is baud rate. If baud rate is not 922 specified, the serial port must already be setup and 923 configured. 924 925 uart[8250],io,<addr>[,options] 926 uart[8250],mmio,<addr>[,options] 927 uart[8250],mmio32,<addr>[,options] 928 uart[8250],mmio32be,<addr>[,options] 929 uart[8250],0x<addr>[,options] 930 Start an early, polled-mode console on the 8250/16550 931 UART at the specified I/O port or MMIO address. 932 MMIO inter-register address stride is either 8-bit 933 (mmio) or 32-bit (mmio32 or mmio32be). 934 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed 935 to be equivalent to 'mmio'. 'options' are specified 936 in the same format described for "console=ttyS<n>"; if 937 unspecified, the h/w is not initialized. 938 939 pl011,<addr> 940 pl011,mmio32,<addr> 941 Start an early, polled-mode console on a pl011 serial 942 port at the specified address. The pl011 serial port 943 must already be setup and configured. Options are not 944 yet supported. If 'mmio32' is specified, then only 945 the driver will use only 32-bit accessors to read/write 946 the device registers. 947 948 meson,<addr> 949 Start an early, polled-mode console on a meson serial 950 port at the specified address. The serial port must 951 already be setup and configured. Options are not yet 952 supported. 953 954 msm_serial,<addr> 955 Start an early, polled-mode console on an msm serial 956 port at the specified address. The serial port 957 must already be setup and configured. Options are not 958 yet supported. 959 960 msm_serial_dm,<addr> 961 Start an early, polled-mode console on an msm serial 962 dm port at the specified address. The serial port 963 must already be setup and configured. Options are not 964 yet supported. 965 966 owl,<addr> 967 Start an early, polled-mode console on a serial port 968 of an Actions Semi SoC, such as S500 or S900, at the 969 specified address. The serial port must already be 970 setup and configured. Options are not yet supported. 971 972 smh Use ARM semihosting calls for early console. 973 974 s3c2410,<addr> 975 s3c2412,<addr> 976 s3c2440,<addr> 977 s3c6400,<addr> 978 s5pv210,<addr> 979 exynos4210,<addr> 980 Use early console provided by serial driver available 981 on Samsung SoCs, requires selecting proper type and 982 a correct base address of the selected UART port. The 983 serial port must already be setup and configured. 984 Options are not yet supported. 985 986 lantiq,<addr> 987 Start an early, polled-mode console on a lantiq serial 988 (lqasc) port at the specified address. The serial port 989 must already be setup and configured. Options are not 990 yet supported. 991 992 lpuart,<addr> 993 lpuart32,<addr> 994 Use early console provided by Freescale LP UART driver 995 found on Freescale Vybrid and QorIQ LS1021A processors. 996 A valid base address must be provided, and the serial 997 port must already be setup and configured. 998 999 ar3700_uart,<addr> 1000 Start an early, polled-mode console on the 1001 Armada 3700 serial port at the specified 1002 address. The serial port must already be setup 1003 and configured. Options are not yet supported. 1004 1005 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k,S390] 1006 earlyprintk=vga 1007 earlyprintk=efi 1008 earlyprintk=sclp 1009 earlyprintk=xen 1010 earlyprintk=serial[,ttySn[,baudrate]] 1011 earlyprintk=serial[,0x...[,baudrate]] 1012 earlyprintk=ttySn[,baudrate] 1013 earlyprintk=dbgp[debugController#] 1014 earlyprintk=pciserial,bus:device.function[,baudrate] 1015 earlyprintk=xdbc[xhciController#] 1016 1017 earlyprintk is useful when the kernel crashes before 1018 the normal console is initialized. It is not enabled by 1019 default because it has some cosmetic problems. 1020 1021 Append ",keep" to not disable it when the real console 1022 takes over. 1023 1024 Only one of vga, efi, serial, or usb debug port can 1025 be used at a time. 1026 1027 Currently only ttyS0 and ttyS1 may be specified by 1028 name. Other I/O ports may be explicitly specified 1029 on some architectures (x86 and arm at least) by 1030 replacing ttySn with an I/O port address, like this: 1031 earlyprintk=serial,0x1008,115200 1032 You can find the port for a given device in 1033 /proc/tty/driver/serial: 1034 2: uart:ST16650V2 port:00001008 irq:18 ... 1035 1036 Interaction with the standard serial driver is not 1037 very good. 1038 1039 The VGA and EFI output is eventually overwritten by 1040 the real console. 1041 1042 The xen output can only be used by Xen PV guests. 1043 1044 The sclp output can only be used on s390. 1045 1046 edac_report= [HW,EDAC] Control how to report EDAC event 1047 Format: {"on" | "off" | "force"} 1048 on: enable EDAC to report H/W event. May be overridden 1049 by other higher priority error reporting module. 1050 off: disable H/W event reporting through EDAC. 1051 force: enforce the use of EDAC to report H/W event. 1052 default: on. 1053 1054 ekgdboc= [X86,KGDB] Allow early kernel console debugging 1055 ekgdboc=kbd 1056 1057 This is designed to be used in conjunction with 1058 the boot argument: earlyprintk=vga 1059 1060 edd= [EDD] 1061 Format: {"off" | "on" | "skip[mbr]"} 1062 1063 efi= [EFI] 1064 Format: { "old_map", "nochunk", "noruntime", "debug" } 1065 old_map [X86-64]: switch to the old ioremap-based EFI 1066 runtime services mapping. 32-bit still uses this one by 1067 default. 1068 nochunk: disable reading files in "chunks" in the EFI 1069 boot stub, as chunking can cause problems with some 1070 firmware implementations. 1071 noruntime : disable EFI runtime services support 1072 debug: enable misc debug output 1073 1074 efi_no_storage_paranoia [EFI; X86] 1075 Using this parameter you can use more than 50% of 1076 your efi variable storage. Use this parameter only if 1077 you are really sure that your UEFI does sane gc and 1078 fulfills the spec otherwise your board may brick. 1079 1080 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86] 1081 Add arbitrary attribute to specific memory range by 1082 updating original EFI memory map. 1083 Region of memory which aa attribute is added to is 1084 from ss to ss+nn. 1085 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000 1086 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000) 1087 attribute is added to range 0x100000000-0x180000000 and 1088 0x10a0000000-0x1120000000. 1089 1090 Using this parameter you can do debugging of EFI memmap 1091 related feature. For example, you can do debugging of 1092 Address Range Mirroring feature even if your box 1093 doesn't support it. 1094 1095 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT 1096 that is to be dynamically loaded by Linux. If there are 1097 multiple variables with the same name but with different 1098 vendor GUIDs, all of them will be loaded. See 1099 Documentation/acpi/ssdt-overlays.txt for details. 1100 1101 1102 eisa_irq_edge= [PARISC,HW] 1103 See header of drivers/parisc/eisa.c. 1104 1105 elanfreq= [X86-32] 1106 See comment before function elanfreq_setup() in 1107 arch/x86/kernel/cpu/cpufreq/elanfreq.c. 1108 1109 elevator= [IOSCHED] 1110 Format: {"cfq" | "deadline" | "noop"} 1111 See Documentation/block/cfq-iosched.txt and 1112 Documentation/block/deadline-iosched.txt for details. 1113 1114 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390] 1115 Specifies physical address of start of kernel core 1116 image elf header and optionally the size. Generally 1117 kexec loader will pass this option to capture kernel. 1118 See Documentation/kdump/kdump.txt for details. 1119 1120 enable_mtrr_cleanup [X86] 1121 The kernel tries to adjust MTRR layout from continuous 1122 to discrete, to make X server driver able to add WB 1123 entry later. This parameter enables that. 1124 1125 enable_timer_pin_1 [X86] 1126 Enable PIN 1 of APIC timer 1127 Can be useful to work around chipset bugs 1128 (in particular on some ATI chipsets). 1129 The kernel tries to set a reasonable default. 1130 1131 enforcing [SELINUX] Set initial enforcing status. 1132 Format: {"0" | "1"} 1133 See security/selinux/Kconfig help text. 1134 0 -- permissive (log only, no denials). 1135 1 -- enforcing (deny and log). 1136 Default value is 0. 1137 Value can be changed at runtime via /selinux/enforce. 1138 1139 erst_disable [ACPI] 1140 Disable Error Record Serialization Table (ERST) 1141 support. 1142 1143 ether= [HW,NET] Ethernet cards parameters 1144 This option is obsoleted by the "netdev=" option, which 1145 has equivalent usage. See its documentation for details. 1146 1147 evm= [EVM] 1148 Format: { "fix" } 1149 Permit 'security.evm' to be updated regardless of 1150 current integrity status. 1151 1152 failslab= 1153 fail_page_alloc= 1154 fail_make_request=[KNL] 1155 General fault injection mechanism. 1156 Format: <interval>,<probability>,<space>,<times> 1157 See also Documentation/fault-injection/. 1158 1159 floppy= [HW] 1160 See Documentation/blockdev/floppy.txt. 1161 1162 force_pal_cache_flush 1163 [IA-64] Avoid check_sal_cache_flush which may hang on 1164 buggy SAL_CACHE_FLUSH implementations. Using this 1165 parameter will force ia64_sal_cache_flush to call 1166 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH. 1167 1168 forcepae [X86-32] 1169 Forcefully enable Physical Address Extension (PAE). 1170 Many Pentium M systems disable PAE but may have a 1171 functionally usable PAE implementation. 1172 Warning: use of this parameter will taint the kernel 1173 and may cause unknown problems. 1174 1175 ftrace=[tracer] 1176 [FTRACE] will set and start the specified tracer 1177 as early as possible in order to facilitate early 1178 boot debugging. 1179 1180 ftrace_dump_on_oops[=orig_cpu] 1181 [FTRACE] will dump the trace buffers on oops. 1182 If no parameter is passed, ftrace will dump 1183 buffers of all CPUs, but if you pass orig_cpu, it will 1184 dump only the buffer of the CPU that triggered the 1185 oops. 1186 1187 ftrace_filter=[function-list] 1188 [FTRACE] Limit the functions traced by the function 1189 tracer at boot up. function-list is a comma separated 1190 list of functions. This list can be changed at run 1191 time by the set_ftrace_filter file in the debugfs 1192 tracing directory. 1193 1194 ftrace_notrace=[function-list] 1195 [FTRACE] Do not trace the functions specified in 1196 function-list. This list can be changed at run time 1197 by the set_ftrace_notrace file in the debugfs 1198 tracing directory. 1199 1200 ftrace_graph_filter=[function-list] 1201 [FTRACE] Limit the top level callers functions traced 1202 by the function graph tracer at boot up. 1203 function-list is a comma separated list of functions 1204 that can be changed at run time by the 1205 set_graph_function file in the debugfs tracing directory. 1206 1207 ftrace_graph_notrace=[function-list] 1208 [FTRACE] Do not trace from the functions specified in 1209 function-list. This list is a comma separated list of 1210 functions that can be changed at run time by the 1211 set_graph_notrace file in the debugfs tracing directory. 1212 1213 ftrace_graph_max_depth=<uint> 1214 [FTRACE] Used with the function graph tracer. This is 1215 the max depth it will trace into a function. This value 1216 can be changed at run time by the max_graph_depth file 1217 in the tracefs tracing directory. default: 0 (no limit) 1218 1219 gamecon.map[2|3]= 1220 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 1221 support via parallel port (up to 5 devices per port) 1222 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 1223 See also Documentation/input/joystick-parport.txt 1224 1225 gamma= [HW,DRM] 1226 1227 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART 1228 Format: off | on 1229 default: on 1230 1231 gcov_persist= [GCOV] When non-zero (default), profiling data for 1232 kernel modules is saved and remains accessible via 1233 debugfs, even when the module is unloaded/reloaded. 1234 When zero, profiling data is discarded and associated 1235 debugfs files are removed at module unload time. 1236 1237 goldfish [X86] Enable the goldfish android emulator platform. 1238 Don't use this when you are not running on the 1239 android emulator 1240 1241 gpt [EFI] Forces disk with valid GPT signature but 1242 invalid Protective MBR to be treated as GPT. If the 1243 primary GPT is corrupted, it enables the backup/alternate 1244 GPT to be used instead. 1245 1246 grcan.enable0= [HW] Configuration of physical interface 0. Determines 1247 the "Enable 0" bit of the configuration register. 1248 Format: 0 | 1 1249 Default: 0 1250 grcan.enable1= [HW] Configuration of physical interface 1. Determines 1251 the "Enable 0" bit of the configuration register. 1252 Format: 0 | 1 1253 Default: 0 1254 grcan.select= [HW] Select which physical interface to use. 1255 Format: 0 | 1 1256 Default: 0 1257 grcan.txsize= [HW] Sets the size of the tx buffer. 1258 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. 1259 Default: 1024 1260 grcan.rxsize= [HW] Sets the size of the rx buffer. 1261 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. 1262 Default: 1024 1263 1264 gpio-mockup.gpio_mockup_ranges 1265 [HW] Sets the ranges of gpiochip of for this device. 1266 Format: <start1>,<end1>,<start2>,<end2>... 1267 1268 hardlockup_all_cpu_backtrace= 1269 [KNL] Should the hard-lockup detector generate 1270 backtraces on all cpus. 1271 Format: <integer> 1272 1273 hashdist= [KNL,NUMA] Large hashes allocated during boot 1274 are distributed across NUMA nodes. Defaults on 1275 for 64-bit NUMA, off otherwise. 1276 Format: 0 | 1 (for off | on) 1277 1278 hcl= [IA-64] SGI's Hardware Graph compatibility layer 1279 1280 hd= [EIDE] (E)IDE hard drive subsystem geometry 1281 Format: <cyl>,<head>,<sect> 1282 1283 hest_disable [ACPI] 1284 Disable Hardware Error Source Table (HEST) support; 1285 corresponding firmware-first mode error processing 1286 logic will be disabled. 1287 1288 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact 1289 size of <nn>. This works even on boxes that have no 1290 highmem otherwise. This also works to reduce highmem 1291 size on bigger boxes. 1292 1293 highres= [KNL] Enable/disable high resolution timer mode. 1294 Valid parameters: "on", "off" 1295 Default: "on" 1296 1297 hisax= [HW,ISDN] 1298 See Documentation/isdn/README.HiSax. 1299 1300 hlt [BUGS=ARM,SH] 1301 1302 hpet= [X86-32,HPET] option to control HPET usage 1303 Format: { enable (default) | disable | force | 1304 verbose } 1305 disable: disable HPET and use PIT instead 1306 force: allow force enabled of undocumented chips (ICH4, 1307 VIA, nVidia) 1308 verbose: show contents of HPET registers during setup 1309 1310 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET 1311 registers. Default set by CONFIG_HPET_MMAP_DEFAULT. 1312 1313 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot. 1314 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages. 1315 On x86-64 and powerpc, this option can be specified 1316 multiple times interleaved with hugepages= to reserve 1317 huge pages of different sizes. Valid pages sizes on 1318 x86-64 are 2M (when the CPU supports "pse") and 1G 1319 (when the CPU supports the "pdpe1gb" cpuinfo flag). 1320 1321 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 1322 terminal devices. Valid values: 0..8 1323 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 1324 If specified, z/VM IUCV HVC accepts connections 1325 from listed z/VM user IDs only. 1326 1327 hwthread_map= [METAG] Comma-separated list of Linux cpu id to 1328 hardware thread id mappings. 1329 Format: <cpu>:<hwthread> 1330 1331 keep_bootcon [KNL] 1332 Do not unregister boot console at start. This is only 1333 useful for debugging when something happens in the window 1334 between unregistering the boot console and initializing 1335 the real console. 1336 1337 i2c_bus= [HW] Override the default board specific I2C bus speed 1338 or register an additional I2C bus that is not 1339 registered from board initialization code. 1340 Format: 1341 <bus_id>,<clkrate> 1342 1343 i8042.debug [HW] Toggle i8042 debug mode 1344 i8042.unmask_kbd_data 1345 [HW] Enable printing of interrupt data from the KBD port 1346 (disabled by default, and as a pre-condition 1347 requires that i8042.debug=1 be enabled) 1348 i8042.direct [HW] Put keyboard port into non-translated mode 1349 i8042.dumbkbd [HW] Pretend that controller can only read data from 1350 keyboard and cannot control its state 1351 (Don't attempt to blink the leds) 1352 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 1353 i8042.nokbd [HW] Don't check/create keyboard port 1354 i8042.noloop [HW] Disable the AUX Loopback command while probing 1355 for the AUX port 1356 i8042.nomux [HW] Don't check presence of an active multiplexing 1357 controller 1358 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 1359 controllers 1360 i8042.notimeout [HW] Ignore timeout condition signalled by controller 1361 i8042.reset [HW] Reset the controller during init, cleanup and 1362 suspend-to-ram transitions, only during s2r 1363 transitions, or never reset 1364 Format: { 1 | Y | y | 0 | N | n } 1365 1, Y, y: always reset controller 1366 0, N, n: don't ever reset controller 1367 Default: only on s2r transitions on x86; most other 1368 architectures force reset to be always executed 1369 i8042.unlock [HW] Unlock (ignore) the keylock 1370 i8042.kbdreset [HW] Reset device connected to KBD port 1371 1372 i810= [HW,DRM] 1373 1374 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data 1375 indicates that the driver is running on unsupported 1376 hardware. 1377 i8k.force [HW] Activate i8k driver even if SMM BIOS signature 1378 does not match list of supported models. 1379 i8k.power_status 1380 [HW] Report power status in /proc/i8k 1381 (disabled by default) 1382 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN 1383 capability is set. 1384 1385 i915.invert_brightness= 1386 [DRM] Invert the sense of the variable that is used to 1387 set the brightness of the panel backlight. Normally a 1388 brightness value of 0 indicates backlight switched off, 1389 and the maximum of the brightness value sets the backlight 1390 to maximum brightness. If this parameter is set to 0 1391 (default) and the machine requires it, or this parameter 1392 is set to 1, a brightness value of 0 sets the backlight 1393 to maximum brightness, and the maximum of the brightness 1394 value switches the backlight off. 1395 -1 -- never invert brightness 1396 0 -- machine default 1397 1 -- force brightness inversion 1398 1399 icn= [HW,ISDN] 1400 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]] 1401 1402 ide-core.nodma= [HW] (E)IDE subsystem 1403 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc 1404 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr 1405 .cdrom .chs .ignore_cable are additional options 1406 See Documentation/ide/ide.txt. 1407 1408 ide-generic.probe-mask= [HW] (E)IDE subsystem 1409 Format: <int> 1410 Probe mask for legacy ISA IDE ports. Depending on 1411 platform up to 6 ports are supported, enabled by 1412 setting corresponding bits in the mask to 1. The 1413 default value is 0x0, which has a special meaning. 1414 On systems that have PCI, it triggers scanning the 1415 PCI bus for the first and the second port, which 1416 are then probed. On systems without PCI the value 1417 of 0x0 enables probing the two first ports as if it 1418 was 0x3. 1419 1420 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem 1421 Claim all unknown PCI IDE storage controllers. 1422 1423 idle= [X86] 1424 Format: idle=poll, idle=halt, idle=nomwait 1425 Poll forces a polling idle loop that can slightly 1426 improve the performance of waking up a idle CPU, but 1427 will use a lot of power and make the system run hot. 1428 Not recommended. 1429 idle=halt: Halt is forced to be used for CPU idle. 1430 In such case C2/C3 won't be used again. 1431 idle=nomwait: Disable mwait for CPU C-states 1432 1433 ieee754= [MIPS] Select IEEE Std 754 conformance mode 1434 Format: { strict | legacy | 2008 | relaxed } 1435 Default: strict 1436 1437 Choose which programs will be accepted for execution 1438 based on the IEEE 754 NaN encoding(s) supported by 1439 the FPU and the NaN encoding requested with the value 1440 of an ELF file header flag individually set by each 1441 binary. Hardware implementations are permitted to 1442 support either or both of the legacy and the 2008 NaN 1443 encoding mode. 1444 1445 Available settings are as follows: 1446 strict accept binaries that request a NaN encoding 1447 supported by the FPU 1448 legacy only accept legacy-NaN binaries, if supported 1449 by the FPU 1450 2008 only accept 2008-NaN binaries, if supported 1451 by the FPU 1452 relaxed accept any binaries regardless of whether 1453 supported by the FPU 1454 1455 The FPU emulator is always able to support both NaN 1456 encodings, so if no FPU hardware is present or it has 1457 been disabled with 'nofpu', then the settings of 1458 'legacy' and '2008' strap the emulator accordingly, 1459 'relaxed' straps the emulator for both legacy-NaN and 1460 2008-NaN, whereas 'strict' enables legacy-NaN only on 1461 legacy processors and both NaN encodings on MIPS32 or 1462 MIPS64 CPUs. 1463 1464 The setting for ABS.fmt/NEG.fmt instruction execution 1465 mode generally follows that for the NaN encoding, 1466 except where unsupported by hardware. 1467 1468 ignore_loglevel [KNL] 1469 Ignore loglevel setting - this will print /all/ 1470 kernel messages to the console. Useful for debugging. 1471 We also add it as printk module parameter, so users 1472 could change it dynamically, usually by 1473 /sys/module/printk/parameters/ignore_loglevel. 1474 1475 ignore_rlimit_data 1476 Ignore RLIMIT_DATA setting for data mappings, 1477 print warning at first misuse. Can be changed via 1478 /sys/module/kernel/parameters/ignore_rlimit_data. 1479 1480 ihash_entries= [KNL] 1481 Set number of hash buckets for inode cache. 1482 1483 ima_appraise= [IMA] appraise integrity measurements 1484 Format: { "off" | "enforce" | "fix" | "log" } 1485 default: "enforce" 1486 1487 ima_appraise_tcb [IMA] 1488 The builtin appraise policy appraises all files 1489 owned by uid=0. 1490 1491 ima_canonical_fmt [IMA] 1492 Use the canonical format for the binary runtime 1493 measurements, instead of host native format. 1494 1495 ima_hash= [IMA] 1496 Format: { md5 | sha1 | rmd160 | sha256 | sha384 1497 | sha512 | ... } 1498 default: "sha1" 1499 1500 The list of supported hash algorithms is defined 1501 in crypto/hash_info.h. 1502 1503 ima_policy= [IMA] 1504 The builtin policies to load during IMA setup. 1505 Format: "tcb | appraise_tcb | secure_boot" 1506 1507 The "tcb" policy measures all programs exec'd, files 1508 mmap'd for exec, and all files opened with the read 1509 mode bit set by either the effective uid (euid=0) or 1510 uid=0. 1511 1512 The "appraise_tcb" policy appraises the integrity of 1513 all files owned by root. (This is the equivalent 1514 of ima_appraise_tcb.) 1515 1516 The "secure_boot" policy appraises the integrity 1517 of files (eg. kexec kernel image, kernel modules, 1518 firmware, policy, etc) based on file signatures. 1519 1520 ima_tcb [IMA] Deprecated. Use ima_policy= instead. 1521 Load a policy which meets the needs of the Trusted 1522 Computing Base. This means IMA will measure all 1523 programs exec'd, files mmap'd for exec, and all files 1524 opened for read by uid=0. 1525 1526 ima_template= [IMA] 1527 Select one of defined IMA measurements template formats. 1528 Formats: { "ima" | "ima-ng" | "ima-sig" } 1529 Default: "ima-ng" 1530 1531 ima_template_fmt= 1532 [IMA] Define a custom template format. 1533 Format: { "field1|...|fieldN" } 1534 1535 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage 1536 Format: <min_file_size> 1537 Set the minimal file size for using asynchronous hash. 1538 If left unspecified, ahash usage is disabled. 1539 1540 ahash performance varies for different data sizes on 1541 different crypto accelerators. This option can be used 1542 to achieve the best performance for a particular HW. 1543 1544 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size 1545 Format: <bufsize> 1546 Set hashing buffer size. Default: 4k. 1547 1548 ahash performance varies for different chunk sizes on 1549 different crypto accelerators. This option can be used 1550 to achieve best performance for particular HW. 1551 1552 init= [KNL] 1553 Format: <full_path> 1554 Run specified binary instead of /sbin/init as init 1555 process. 1556 1557 initcall_debug [KNL] Trace initcalls as they are executed. Useful 1558 for working out where the kernel is dying during 1559 startup. 1560 1561 initcall_blacklist= [KNL] Do not execute a comma-separated list of 1562 initcall functions. Useful for debugging built-in 1563 modules and initcalls. 1564 1565 initrd= [BOOT] Specify the location of the initial ramdisk 1566 1567 init_pkru= [x86] Specify the default memory protection keys rights 1568 register contents for all processes. 0x55555554 by 1569 default (disallow access to all but pkey 0). Can 1570 override in debugfs after boot. 1571 1572 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 1573 Format: <irq> 1574 1575 int_pln_enable [x86] Enable power limit notification interrupt 1576 1577 integrity_audit=[IMA] 1578 Format: { "0" | "1" } 1579 0 -- basic integrity auditing messages. (Default) 1580 1 -- additional integrity auditing messages. 1581 1582 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 1583 on 1584 Enable intel iommu driver. 1585 off 1586 Disable intel iommu driver. 1587 igfx_off [Default Off] 1588 By default, gfx is mapped as normal device. If a gfx 1589 device has a dedicated DMAR unit, the DMAR unit is 1590 bypassed by not enabling DMAR with this option. In 1591 this case, gfx device will use physical address for 1592 DMA. 1593 forcedac [x86_64] 1594 With this option iommu will not optimize to look 1595 for io virtual address below 32-bit forcing dual 1596 address cycle on pci bus for cards supporting greater 1597 than 32-bit addressing. The default is to look 1598 for translation below 32-bit and if not available 1599 then look in the higher range. 1600 strict [Default Off] 1601 With this option on every unmap_single operation will 1602 result in a hardware IOTLB flush operation as opposed 1603 to batching them for performance. 1604 sp_off [Default Off] 1605 By default, super page will be supported if Intel IOMMU 1606 has the capability. With this option, super page will 1607 not be supported. 1608 ecs_off [Default Off] 1609 By default, extended context tables will be supported if 1610 the hardware advertises that it has support both for the 1611 extended tables themselves, and also PASID support. With 1612 this option set, extended tables will not be used even 1613 on hardware which claims to support them. 1614 tboot_noforce [Default Off] 1615 Do not force the Intel IOMMU enabled under tboot. 1616 By default, tboot will force Intel IOMMU on, which 1617 could harm performance of some high-throughput 1618 devices like 40GBit network cards, even if identity 1619 mapping is enabled. 1620 Note that using this option lowers the security 1621 provided by tboot because it makes the system 1622 vulnerable to DMA attacks. 1623 1624 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 1625 0 disables intel_idle and fall back on acpi_idle. 1626 1 to 9 specify maximum depth of C-state. 1627 1628 intel_pstate= [X86] 1629 disable 1630 Do not enable intel_pstate as the default 1631 scaling driver for the supported processors 1632 passive 1633 Use intel_pstate as a scaling driver, but configure it 1634 to work with generic cpufreq governors (instead of 1635 enabling its internal governor). This mode cannot be 1636 used along with the hardware-managed P-states (HWP) 1637 feature. 1638 force 1639 Enable intel_pstate on systems that prohibit it by default 1640 in favor of acpi-cpufreq. Forcing the intel_pstate driver 1641 instead of acpi-cpufreq may disable platform features, such 1642 as thermal controls and power capping, that rely on ACPI 1643 P-States information being indicated to OSPM and therefore 1644 should be used with caution. This option does not work with 1645 processors that aren't supported by the intel_pstate driver 1646 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 1647 no_hwp 1648 Do not enable hardware P state control (HWP) 1649 if available. 1650 hwp_only 1651 Only load intel_pstate on systems which support 1652 hardware P state control (HWP) if available. 1653 support_acpi_ppc 1654 Enforce ACPI _PPC performance limits. If the Fixed ACPI 1655 Description Table, specifies preferred power management 1656 profile as "Enterprise Server" or "Performance Server", 1657 then this feature is turned on by default. 1658 per_cpu_perf_limits 1659 Allow per-logical-CPU P-State performance control limits using 1660 cpufreq sysfs interface 1661 1662 intremap= [X86-64, Intel-IOMMU] 1663 on enable Interrupt Remapping (default) 1664 off disable Interrupt Remapping 1665 nosid disable Source ID checking 1666 no_x2apic_optout 1667 BIOS x2APIC opt-out request will be ignored 1668 nopost disable Interrupt Posting 1669 1670 iomem= Disable strict checking of access to MMIO memory 1671 strict regions from userspace. 1672 relaxed 1673 1674 iommu= [x86] 1675 off 1676 force 1677 noforce 1678 biomerge 1679 panic 1680 nopanic 1681 merge 1682 nomerge 1683 forcesac 1684 soft 1685 pt [x86, IA-64] 1686 nobypass [PPC/POWERNV] 1687 Disable IOMMU bypass, using IOMMU for PCI devices. 1688 1689 iommu.passthrough= 1690 [ARM64] Configure DMA to bypass the IOMMU by default. 1691 Format: { "0" | "1" } 1692 0 - Use IOMMU translation for DMA. 1693 1 - Bypass the IOMMU for DMA. 1694 unset - Use IOMMU translation for DMA. 1695 1696 io7= [HW] IO7 for Marvel based alpha systems 1697 See comment before marvel_specify_io7 in 1698 arch/alpha/kernel/core_marvel.c. 1699 1700 io_delay= [X86] I/O delay method 1701 0x80 1702 Standard port 0x80 based delay 1703 0xed 1704 Alternate port 0xed based delay (needed on some systems) 1705 udelay 1706 Simple two microseconds delay 1707 none 1708 No delay 1709 1710 ip= [IP_PNP] 1711 See Documentation/filesystems/nfs/nfsroot.txt. 1712 1713 irqaffinity= [SMP] Set the default irq affinity mask 1714 The argument is a cpu list, as described above. 1715 1716 irqfixup [HW] 1717 When an interrupt is not handled search all handlers 1718 for it. Intended to get systems with badly broken 1719 firmware running. 1720 1721 irqpoll [HW] 1722 When an interrupt is not handled search all handlers 1723 for it. Also check all handlers each timer 1724 interrupt. Intended to get systems with badly broken 1725 firmware running. 1726 1727 isapnp= [ISAPNP] 1728 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 1729 1730 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler. 1731 The argument is a cpu list, as described above. 1732 1733 This option can be used to specify one or more CPUs 1734 to isolate from the general SMP balancing and scheduling 1735 algorithms. You can move a process onto or off an 1736 "isolated" CPU via the CPU affinity syscalls or cpuset. 1737 <cpu number> begins at 0 and the maximum value is 1738 "number of CPUs in system - 1". 1739 1740 This option is the preferred way to isolate CPUs. The 1741 alternative -- manually setting the CPU mask of all 1742 tasks in the system -- can cause problems and 1743 suboptimal load balancer performance. 1744 1745 iucv= [HW,NET] 1746 1747 ivrs_ioapic [HW,X86_64] 1748 Provide an override to the IOAPIC-ID<->DEVICE-ID 1749 mapping provided in the IVRS ACPI table. For 1750 example, to map IOAPIC-ID decimal 10 to 1751 PCI device 00:14.0 write the parameter as: 1752 ivrs_ioapic[10]=00:14.0 1753 1754 ivrs_hpet [HW,X86_64] 1755 Provide an override to the HPET-ID<->DEVICE-ID 1756 mapping provided in the IVRS ACPI table. For 1757 example, to map HPET-ID decimal 0 to 1758 PCI device 00:14.0 write the parameter as: 1759 ivrs_hpet[0]=00:14.0 1760 1761 ivrs_acpihid [HW,X86_64] 1762 Provide an override to the ACPI-HID:UID<->DEVICE-ID 1763 mapping provided in the IVRS ACPI table. For 1764 example, to map UART-HID:UID AMD0020:0 to 1765 PCI device 00:14.5 write the parameter as: 1766 ivrs_acpihid[00:14.5]=AMD0020:0 1767 1768 js= [HW,JOY] Analog joystick 1769 See Documentation/input/joystick.txt. 1770 1771 nokaslr [KNL] 1772 When CONFIG_RANDOMIZE_BASE is set, this disables 1773 kernel and module base offset ASLR (Address Space 1774 Layout Randomization). 1775 1776 kasan_multi_shot 1777 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print 1778 report on every invalid memory access. Without this 1779 parameter KASAN will print report only for the first 1780 invalid access. 1781 1782 keepinitrd [HW,ARM] 1783 1784 kernelcore= [KNL,X86,IA-64,PPC] 1785 Format: nn[KMGTPE] | "mirror" 1786 This parameter 1787 specifies the amount of memory usable by the kernel 1788 for non-movable allocations. The requested amount is 1789 spread evenly throughout all nodes in the system. The 1790 remaining memory in each node is used for Movable 1791 pages. In the event, a node is too small to have both 1792 kernelcore and Movable pages, kernelcore pages will 1793 take priority and other nodes will have a larger number 1794 of Movable pages. The Movable zone is used for the 1795 allocation of pages that may be reclaimed or moved 1796 by the page migration subsystem. This means that 1797 HugeTLB pages may not be allocated from this zone. 1798 Note that allocations like PTEs-from-HighMem still 1799 use the HighMem zone if it exists, and the Normal 1800 zone if it does not. 1801 1802 Instead of specifying the amount of memory (nn[KMGTPE]), 1803 you can specify "mirror" option. In case "mirror" 1804 option is specified, mirrored (reliable) memory is used 1805 for non-movable allocations and remaining memory is used 1806 for Movable pages. nn[KMGTPE] and "mirror" are exclusive, 1807 so you can NOT specify nn[KMGTPE] and "mirror" at the same 1808 time. 1809 1810 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port. 1811 Format: <Controller#>[,poll interval] 1812 The controller # is the number of the ehci usb debug 1813 port as it is probed via PCI. The poll interval is 1814 optional and is the number seconds in between 1815 each poll cycle to the debug port in case you need 1816 the functionality for interrupting the kernel with 1817 gdb or control-c on the dbgp connection. When 1818 not using this parameter you use sysrq-g to break into 1819 the kernel debugger. 1820 1821 kgdboc= [KGDB,HW] kgdb over consoles. 1822 Requires a tty driver that supports console polling, 1823 or a supported polling keyboard driver (non-usb). 1824 Serial only format: <serial_device>[,baud] 1825 keyboard only format: kbd 1826 keyboard and serial format: kbd,<serial_device>[,baud] 1827 Optional Kernel mode setting: 1828 kms, kbd format: kms,kbd 1829 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 1830 1831 kgdbwait [KGDB] Stop kernel execution and enter the 1832 kernel debugger at the earliest opportunity. 1833 1834 kmac= [MIPS] korina ethernet MAC address. 1835 Configure the RouterBoard 532 series on-chip 1836 Ethernet adapter MAC address. 1837 1838 kmemleak= [KNL] Boot-time kmemleak enable/disable 1839 Valid arguments: on, off 1840 Default: on 1841 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 1842 the default is off. 1843 1844 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode 1845 Valid arguments: 0, 1, 2 1846 kmemcheck=0 (disabled) 1847 kmemcheck=1 (enabled) 1848 kmemcheck=2 (one-shot mode) 1849 Default: 2 (one-shot mode) 1850 1851 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 1852 Default is 0 (don't ignore, but inject #GP) 1853 1854 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit 1855 KVM MMU at runtime. 1856 Default is 0 (off) 1857 1858 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM. 1859 Default is 1 (enabled) 1860 1861 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU) 1862 for all guests. 1863 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode. 1864 1865 kvm-arm.vgic_v3_group0_trap= 1866 [KVM,ARM] Trap guest accesses to GICv3 group-0 1867 system registers 1868 1869 kvm-arm.vgic_v3_group1_trap= 1870 [KVM,ARM] Trap guest accesses to GICv3 group-1 1871 system registers 1872 1873 kvm-arm.vgic_v3_common_trap= 1874 [KVM,ARM] Trap guest accesses to GICv3 common 1875 system registers 1876 1877 kvm-intel.ept= [KVM,Intel] Disable extended page tables 1878 (virtualized MMU) support on capable Intel chips. 1879 Default is 1 (enabled) 1880 1881 kvm-intel.emulate_invalid_guest_state= 1882 [KVM,Intel] Enable emulation of invalid guest states 1883 Default is 0 (disabled) 1884 1885 kvm-intel.flexpriority= 1886 [KVM,Intel] Disable FlexPriority feature (TPR shadow). 1887 Default is 1 (enabled) 1888 1889 kvm-intel.nested= 1890 [KVM,Intel] Enable VMX nesting (nVMX). 1891 Default is 0 (disabled) 1892 1893 kvm-intel.unrestricted_guest= 1894 [KVM,Intel] Disable unrestricted guest feature 1895 (virtualized real and unpaged mode) on capable 1896 Intel chips. Default is 1 (enabled) 1897 1898 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification 1899 feature (tagged TLBs) on capable Intel chips. 1900 Default is 1 (enabled) 1901 1902 l2cr= [PPC] 1903 1904 l3cr= [PPC] 1905 1906 lapic [X86-32,APIC] Enable the local APIC even if BIOS 1907 disabled it. 1908 1909 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline 1910 value for LAPIC timer one-shot implementation. Default 1911 back to the programmable timer unit in the LAPIC. 1912 1913 lapic_timer_c2_ok [X86,APIC] trust the local apic timer 1914 in C2 power state. 1915 1916 libata.dma= [LIBATA] DMA control 1917 libata.dma=0 Disable all PATA and SATA DMA 1918 libata.dma=1 PATA and SATA Disk DMA only 1919 libata.dma=2 ATAPI (CDROM) DMA only 1920 libata.dma=4 Compact Flash DMA only 1921 Combinations also work, so libata.dma=3 enables DMA 1922 for disks and CDROMs, but not CFs. 1923 1924 libata.ignore_hpa= [LIBATA] Ignore HPA limit 1925 libata.ignore_hpa=0 keep BIOS limits (default) 1926 libata.ignore_hpa=1 ignore limits, using full disk 1927 1928 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 1929 when set. 1930 Format: <int> 1931 1932 libata.force= [LIBATA] Force configurations. The format is comma 1933 separated list of "[ID:]VAL" where ID is 1934 PORT[.DEVICE]. PORT and DEVICE are decimal numbers 1935 matching port, link or device. Basically, it matches 1936 the ATA ID string printed on console by libata. If 1937 the whole ID part is omitted, the last PORT and DEVICE 1938 values are used. If ID hasn't been specified yet, the 1939 configuration applies to all ports, links and devices. 1940 1941 If only DEVICE is omitted, the parameter applies to 1942 the port and all links and devices behind it. DEVICE 1943 number of 0 either selects the first device or the 1944 first fan-out link behind PMP device. It does not 1945 select the host link. DEVICE number of 15 selects the 1946 host link and device attached to it. 1947 1948 The VAL specifies the configuration to force. As long 1949 as there's no ambiguity shortcut notation is allowed. 1950 For example, both 1.5 and 1.5G would work for 1.5Gbps. 1951 The following configurations can be forced. 1952 1953 * Cable type: 40c, 80c, short40c, unk, ign or sata. 1954 Any ID with matching PORT is used. 1955 1956 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 1957 1958 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 1959 udma[/][16,25,33,44,66,100,133] notation is also 1960 allowed. 1961 1962 * [no]ncq: Turn on or off NCQ. 1963 1964 * [no]ncqtrim: Turn off queued DSM TRIM. 1965 1966 * nohrst, nosrst, norst: suppress hard, soft 1967 and both resets. 1968 1969 * rstonce: only attempt one reset during 1970 hot-unplug link recovery 1971 1972 * dump_id: dump IDENTIFY data. 1973 1974 * atapi_dmadir: Enable ATAPI DMADIR bridge support 1975 1976 * disable: Disable this device. 1977 1978 If there are multiple matching configurations changing 1979 the same attribute, the last one is used. 1980 1981 memblock=debug [KNL] Enable memblock debug messages. 1982 1983 load_ramdisk= [RAM] List of ramdisks to load from floppy 1984 See Documentation/blockdev/ramdisk.txt. 1985 1986 lockd.nlm_grace_period=P [NFS] Assign grace period. 1987 Format: <integer> 1988 1989 lockd.nlm_tcpport=N [NFS] Assign TCP port. 1990 Format: <integer> 1991 1992 lockd.nlm_timeout=T [NFS] Assign timeout value. 1993 Format: <integer> 1994 1995 lockd.nlm_udpport=M [NFS] Assign UDP port. 1996 Format: <integer> 1997 1998 locktorture.nreaders_stress= [KNL] 1999 Set the number of locking read-acquisition kthreads. 2000 Defaults to being automatically set based on the 2001 number of online CPUs. 2002 2003 locktorture.nwriters_stress= [KNL] 2004 Set the number of locking write-acquisition kthreads. 2005 2006 locktorture.onoff_holdoff= [KNL] 2007 Set time (s) after boot for CPU-hotplug testing. 2008 2009 locktorture.onoff_interval= [KNL] 2010 Set time (s) between CPU-hotplug operations, or 2011 zero to disable CPU-hotplug testing. 2012 2013 locktorture.shuffle_interval= [KNL] 2014 Set task-shuffle interval (jiffies). Shuffling 2015 tasks allows some CPUs to go into dyntick-idle 2016 mode during the locktorture test. 2017 2018 locktorture.shutdown_secs= [KNL] 2019 Set time (s) after boot system shutdown. This 2020 is useful for hands-off automated testing. 2021 2022 locktorture.stat_interval= [KNL] 2023 Time (s) between statistics printk()s. 2024 2025 locktorture.stutter= [KNL] 2026 Time (s) to stutter testing, for example, 2027 specifying five seconds causes the test to run for 2028 five seconds, wait for five seconds, and so on. 2029 This tests the locking primitive's ability to 2030 transition abruptly to and from idle. 2031 2032 locktorture.torture_runnable= [BOOT] 2033 Start locktorture running at boot time. 2034 2035 locktorture.torture_type= [KNL] 2036 Specify the locking implementation to test. 2037 2038 locktorture.verbose= [KNL] 2039 Enable additional printk() statements. 2040 2041 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 2042 Format: <irq> 2043 2044 loglevel= All Kernel Messages with a loglevel smaller than the 2045 console loglevel will be printed to the console. It can 2046 also be changed with klogd or other programs. The 2047 loglevels are defined as follows: 2048 2049 0 (KERN_EMERG) system is unusable 2050 1 (KERN_ALERT) action must be taken immediately 2051 2 (KERN_CRIT) critical conditions 2052 3 (KERN_ERR) error conditions 2053 4 (KERN_WARNING) warning conditions 2054 5 (KERN_NOTICE) normal but significant condition 2055 6 (KERN_INFO) informational 2056 7 (KERN_DEBUG) debug-level messages 2057 2058 log_buf_len=n[KMG] Sets the size of the printk ring buffer, 2059 in bytes. n must be a power of two and greater 2060 than the minimal size. The minimal size is defined 2061 by LOG_BUF_SHIFT kernel config parameter. There is 2062 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter 2063 that allows to increase the default size depending on 2064 the number of CPUs. See init/Kconfig for more details. 2065 2066 logo.nologo [FB] Disables display of the built-in Linux logo. 2067 This may be used to provide more screen space for 2068 kernel log messages and is useful when debugging 2069 kernel boot problems. 2070 2071 lp=0 [LP] Specify parallel ports to use, e.g, 2072 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 2073 lp=reset first parallel port). 'lp=0' disables the 2074 lp=auto printer driver. 'lp=reset' (which can be 2075 specified in addition to the ports) causes 2076 attached printers to be reset. Using 2077 lp=port1,port2,... specifies the parallel ports 2078 to associate lp devices with, starting with 2079 lp0. A port specification may be 'none' to skip 2080 that lp device, or a parport name such as 2081 'parport0'. Specifying 'lp=auto' instead of a 2082 port specification list means that device IDs 2083 from each port should be examined, to see if 2084 an IEEE 1284-compliant printer is attached; if 2085 so, the driver will manage that printer. 2086 See also header of drivers/char/lp.c. 2087 2088 lpj=n [KNL] 2089 Sets loops_per_jiffy to given constant, thus avoiding 2090 time-consuming boot-time autodetection (up to 250 ms per 2091 CPU). 0 enables autodetection (default). To determine 2092 the correct value for your kernel, boot with normal 2093 autodetection and see what value is printed. Note that 2094 on SMP systems the preset will be applied to all CPUs, 2095 which is likely to cause problems if your CPUs need 2096 significantly divergent settings. An incorrect value 2097 will cause delays in the kernel to be wrong, leading to 2098 unpredictable I/O errors and other breakage. Although 2099 unlikely, in the extreme case this might damage your 2100 hardware. 2101 2102 ltpc= [NET] 2103 Format: <io>,<irq>,<dma> 2104 2105 machvec= [IA-64] Force the use of a particular machine-vector 2106 (machvec) in a generic kernel. 2107 Example: machvec=hpzx1_swiotlb 2108 2109 machtype= [Loongson] Share the same kernel image file between different 2110 yeeloong laptop. 2111 Example: machtype=lemote-yeeloong-2f-7inch 2112 2113 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater 2114 than or equal to this physical address is ignored. 2115 2116 maxcpus= [SMP] Maximum number of processors that an SMP kernel 2117 will bring up during bootup. maxcpus=n : n >= 0 limits 2118 the kernel to bring up 'n' processors. Surely after 2119 bootup you can bring up the other plugged cpu by executing 2120 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 2121 only takes effect during system bootup. 2122 While n=0 is a special case, it is equivalent to "nosmp", 2123 which also disables the IO APIC. 2124 2125 max_loop= [LOOP] The number of loop block devices that get 2126 (loop.max_loop) unconditionally pre-created at init time. The default 2127 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 2128 of statically allocating a predefined number, loop 2129 devices can be requested on-demand with the 2130 /dev/loop-control interface. 2131 2132 mce [X86-32] Machine Check Exception 2133 2134 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt 2135 2136 md= [HW] RAID subsystems devices and level 2137 See Documentation/admin-guide/md.rst. 2138 2139 mdacon= [MDA] 2140 Format: <first>,<last> 2141 Specifies range of consoles to be captured by the MDA. 2142 2143 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory 2144 Amount of memory to be used when the kernel is not able 2145 to see the whole system memory or for test. 2146 [X86] Work as limiting max address. Use together 2147 with memmap= to avoid physical address space collisions. 2148 Without memmap= PCI devices could be placed at addresses 2149 belonging to unused RAM. 2150 2151 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 2152 memory. 2153 2154 memchunk=nn[KMG] 2155 [KNL,SH] Allow user to override the default size for 2156 per-device physically contiguous DMA buffers. 2157 2158 memhp_default_state=online/offline 2159 [KNL] Set the initial state for the memory hotplug 2160 onlining policy. If not specified, the default value is 2161 set according to the 2162 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config 2163 option. 2164 See Documentation/memory-hotplug.txt. 2165 2166 memmap=exactmap [KNL,X86] Enable setting of an exact 2167 E820 memory map, as specified by the user. 2168 Such memmap=exactmap lines can be constructed based on 2169 BIOS output or other requirements. See the memmap=nn@ss 2170 option description. 2171 2172 memmap=nn[KMG]@ss[KMG] 2173 [KNL] Force usage of a specific region of memory. 2174 Region of memory to be used is from ss to ss+nn. 2175 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], 2176 which limits max address to nn[KMG]. 2177 Multiple different regions can be specified, 2178 comma delimited. 2179 Example: 2180 memmap=100M@2G,100M#3G,1G!1024G 2181 2182 memmap=nn[KMG]#ss[KMG] 2183 [KNL,ACPI] Mark specific memory as ACPI data. 2184 Region of memory to be marked is from ss to ss+nn. 2185 2186 memmap=nn[KMG]$ss[KMG] 2187 [KNL,ACPI] Mark specific memory as reserved. 2188 Region of memory to be reserved is from ss to ss+nn. 2189 Example: Exclude memory from 0x18690000-0x1869ffff 2190 memmap=64K$0x18690000 2191 or 2192 memmap=0x10000$0x18690000 2193 Some bootloaders may need an escape character before '$', 2194 like Grub2, otherwise '$' and the following number 2195 will be eaten. 2196 2197 memmap=nn[KMG]!ss[KMG] 2198 [KNL,X86] Mark specific memory as protected. 2199 Region of memory to be used, from ss to ss+nn. 2200 The memory region may be marked as e820 type 12 (0xc) 2201 and is NVDIMM or ADR memory. 2202 2203 memory_corruption_check=0/1 [X86] 2204 Some BIOSes seem to corrupt the first 64k of 2205 memory when doing things like suspend/resume. 2206 Setting this option will scan the memory 2207 looking for corruption. Enabling this will 2208 both detect corruption and prevent the kernel 2209 from using the memory being corrupted. 2210 However, its intended as a diagnostic tool; if 2211 repeatable BIOS-originated corruption always 2212 affects the same memory, you can use memmap= 2213 to prevent the kernel from using that memory. 2214 2215 memory_corruption_check_size=size [X86] 2216 By default it checks for corruption in the low 2217 64k, making this memory unavailable for normal 2218 use. Use this parameter to scan for 2219 corruption in more or less memory. 2220 2221 memory_corruption_check_period=seconds [X86] 2222 By default it checks for corruption every 60 2223 seconds. Use this parameter to check at some 2224 other rate. 0 disables periodic checking. 2225 2226 memtest= [KNL,X86,ARM] Enable memtest 2227 Format: <integer> 2228 default : 0 <disable> 2229 Specifies the number of memtest passes to be 2230 performed. Each pass selects another test 2231 pattern from a given set of patterns. Memtest 2232 fills the memory with this pattern, validates 2233 memory contents and reserves bad memory 2234 regions that are detected. 2235 2236 mem_sleep_default= [SUSPEND] Default system suspend mode: 2237 s2idle - Suspend-To-Idle 2238 shallow - Power-On Suspend or equivalent (if supported) 2239 deep - Suspend-To-RAM or equivalent (if supported) 2240 See Documentation/power/states.txt. 2241 2242 meye.*= [HW] Set MotionEye Camera parameters 2243 See Documentation/video4linux/meye.txt. 2244 2245 mfgpt_irq= [IA-32] Specify the IRQ to use for the 2246 Multi-Function General Purpose Timers on AMD Geode 2247 platforms. 2248 2249 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 2250 the BIOS has incorrectly applied a workaround. TinyBIOS 2251 version 0.98 is known to be affected, 0.99 fixes the 2252 problem by letting the user disable the workaround. 2253 2254 mga= [HW,DRM] 2255 2256 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this 2257 physical address is ignored. 2258 2259 mini2440= [ARM,HW,KNL] 2260 Format:[0..2][b][c][t] 2261 Default: "0tb" 2262 MINI2440 configuration specification: 2263 0 - The attached screen is the 3.5" TFT 2264 1 - The attached screen is the 7" TFT 2265 2 - The VGA Shield is attached (1024x768) 2266 Leaving out the screen size parameter will not load 2267 the TFT driver, and the framebuffer will be left 2268 unconfigured. 2269 b - Enable backlight. The TFT backlight pin will be 2270 linked to the kernel VESA blanking code and a GPIO 2271 LED. This parameter is not necessary when using the 2272 VGA shield. 2273 c - Enable the s3c camera interface. 2274 t - Reserved for enabling touchscreen support. The 2275 touchscreen support is not enabled in the mainstream 2276 kernel as of 2.6.30, a preliminary port can be found 2277 in the "bleeding edge" mini2440 support kernel at 2278 http://repo.or.cz/w/linux-2.6/mini2440.git 2279 2280 mminit_loglevel= 2281 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this 2282 parameter allows control of the logging verbosity for 2283 the additional memory initialisation checks. A value 2284 of 0 disables mminit logging and a level of 4 will 2285 log everything. Information is printed at KERN_DEBUG 2286 so loglevel=8 may also need to be specified. 2287 2288 module.sig_enforce 2289 [KNL] When CONFIG_MODULE_SIG is set, this means that 2290 modules without (valid) signatures will fail to load. 2291 Note that if CONFIG_MODULE_SIG_FORCE is set, that 2292 is always true, so this option does nothing. 2293 2294 module_blacklist= [KNL] Do not load a comma-separated list of 2295 modules. Useful for debugging problem modules. 2296 2297 mousedev.tap_time= 2298 [MOUSE] Maximum time between finger touching and 2299 leaving touchpad surface for touch to be considered 2300 a tap and be reported as a left button click (for 2301 touchpads working in absolute mode only). 2302 Format: <msecs> 2303 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 2304 reporting absolute coordinates, such as tablets 2305 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 2306 reporting absolute coordinates, such as tablets 2307 2308 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter 2309 is similar to kernelcore except it specifies the 2310 amount of memory used for migratable allocations. 2311 If both kernelcore and movablecore is specified, 2312 then kernelcore will be at *least* the specified 2313 value but may be more. If movablecore on its own 2314 is specified, the administrator must be careful 2315 that the amount of memory usable for all allocations 2316 is not too small. 2317 2318 movable_node [KNL] Boot-time switch to make hotplugable memory 2319 NUMA nodes to be movable. This means that the memory 2320 of such nodes will be usable only for movable 2321 allocations which rules out almost all kernel 2322 allocations. Use with caution! 2323 2324 MTD_Partition= [MTD] 2325 Format: <name>,<region-number>,<size>,<offset> 2326 2327 MTD_Region= [MTD] Format: 2328 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 2329 2330 mtdparts= [MTD] 2331 See drivers/mtd/cmdlinepart.c. 2332 2333 multitce=off [PPC] This parameter disables the use of the pSeries 2334 firmware feature for updating multiple TCE entries 2335 at a time. 2336 2337 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 2338 2339 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 2340 2341 boundary - index of last SLC block on Flex-OneNAND. 2342 The remaining blocks are configured as MLC blocks. 2343 lock - Configure if Flex-OneNAND boundary should be locked. 2344 Once locked, the boundary cannot be changed. 2345 1 indicates lock status, 0 indicates unlock status. 2346 2347 mtdset= [ARM] 2348 ARM/S3C2412 JIVE boot control 2349 2350 See arch/arm/mach-s3c2412/mach-jive.c 2351 2352 mtouchusb.raw_coordinates= 2353 [HW] Make the MicroTouch USB driver use raw coordinates 2354 ('y', default) or cooked coordinates ('n') 2355 2356 mtrr_chunk_size=nn[KMG] [X86] 2357 used for mtrr cleanup. It is largest continuous chunk 2358 that could hold holes aka. UC entries. 2359 2360 mtrr_gran_size=nn[KMG] [X86] 2361 Used for mtrr cleanup. It is granularity of mtrr block. 2362 Default is 1. 2363 Large value could prevent small alignment from 2364 using up MTRRs. 2365 2366 mtrr_spare_reg_nr=n [X86] 2367 Format: <integer> 2368 Range: 0,7 : spare reg number 2369 Default : 1 2370 Used for mtrr cleanup. It is spare mtrr entries number. 2371 Set to 2 or more if your graphical card needs more. 2372 2373 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 2374 2375 netdev= [NET] Network devices parameters 2376 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 2377 Note that mem_start is often overloaded to mean 2378 something different and driver-specific. 2379 This usage is only documented in each driver source 2380 file if at all. 2381 2382 nf_conntrack.acct= 2383 [NETFILTER] Enable connection tracking flow accounting 2384 0 to disable accounting 2385 1 to enable accounting 2386 Default value is 0. 2387 2388 nfsaddrs= [NFS] Deprecated. Use ip= instead. 2389 See Documentation/filesystems/nfs/nfsroot.txt. 2390 2391 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 2392 See Documentation/filesystems/nfs/nfsroot.txt. 2393 2394 nfsrootdebug [NFS] enable nfsroot debugging messages. 2395 See Documentation/filesystems/nfs/nfsroot.txt. 2396 2397 nfs.callback_nr_threads= 2398 [NFSv4] set the total number of threads that the 2399 NFS client will assign to service NFSv4 callback 2400 requests. 2401 2402 nfs.callback_tcpport= 2403 [NFS] set the TCP port on which the NFSv4 callback 2404 channel should listen. 2405 2406 nfs.cache_getent= 2407 [NFS] sets the pathname to the program which is used 2408 to update the NFS client cache entries. 2409 2410 nfs.cache_getent_timeout= 2411 [NFS] sets the timeout after which an attempt to 2412 update a cache entry is deemed to have failed. 2413 2414 nfs.idmap_cache_timeout= 2415 [NFS] set the maximum lifetime for idmapper cache 2416 entries. 2417 2418 nfs.enable_ino64= 2419 [NFS] enable 64-bit inode numbers. 2420 If zero, the NFS client will fake up a 32-bit inode 2421 number for the readdir() and stat() syscalls instead 2422 of returning the full 64-bit number. 2423 The default is to return 64-bit inode numbers. 2424 2425 nfs.max_session_cb_slots= 2426 [NFSv4.1] Sets the maximum number of session 2427 slots the client will assign to the callback 2428 channel. This determines the maximum number of 2429 callbacks the client will process in parallel for 2430 a particular server. 2431 2432 nfs.max_session_slots= 2433 [NFSv4.1] Sets the maximum number of session slots 2434 the client will attempt to negotiate with the server. 2435 This limits the number of simultaneous RPC requests 2436 that the client can send to the NFSv4.1 server. 2437 Note that there is little point in setting this 2438 value higher than the max_tcp_slot_table_limit. 2439 2440 nfs.nfs4_disable_idmapping= 2441 [NFSv4] When set to the default of '1', this option 2442 ensures that both the RPC level authentication 2443 scheme and the NFS level operations agree to use 2444 numeric uids/gids if the mount is using the 2445 'sec=sys' security flavour. In effect it is 2446 disabling idmapping, which can make migration from 2447 legacy NFSv2/v3 systems to NFSv4 easier. 2448 Servers that do not support this mode of operation 2449 will be autodetected by the client, and it will fall 2450 back to using the idmapper. 2451 To turn off this behaviour, set the value to '0'. 2452 nfs.nfs4_unique_id= 2453 [NFS4] Specify an additional fixed unique ident- 2454 ification string that NFSv4 clients can insert into 2455 their nfs_client_id4 string. This is typically a 2456 UUID that is generated at system install time. 2457 2458 nfs.send_implementation_id = 2459 [NFSv4.1] Send client implementation identification 2460 information in exchange_id requests. 2461 If zero, no implementation identification information 2462 will be sent. 2463 The default is to send the implementation identification 2464 information. 2465 2466 nfs.recover_lost_locks = 2467 [NFSv4] Attempt to recover locks that were lost due 2468 to a lease timeout on the server. Please note that 2469 doing this risks data corruption, since there are 2470 no guarantees that the file will remain unchanged 2471 after the locks are lost. 2472 If you want to enable the kernel legacy behaviour of 2473 attempting to recover these locks, then set this 2474 parameter to '1'. 2475 The default parameter value of '0' causes the kernel 2476 not to attempt recovery of lost locks. 2477 2478 nfs4.layoutstats_timer = 2479 [NFSv4.2] Change the rate at which the kernel sends 2480 layoutstats to the pNFS metadata server. 2481 2482 Setting this to value to 0 causes the kernel to use 2483 whatever value is the default set by the layout 2484 driver. A non-zero value sets the minimum interval 2485 in seconds between layoutstats transmissions. 2486 2487 nfsd.nfs4_disable_idmapping= 2488 [NFSv4] When set to the default of '1', the NFSv4 2489 server will return only numeric uids and gids to 2490 clients using auth_sys, and will accept numeric uids 2491 and gids from such clients. This is intended to ease 2492 migration from NFSv2/v3. 2493 2494 nmi_debug= [KNL,SH] Specify one or more actions to take 2495 when a NMI is triggered. 2496 Format: [state][,regs][,debounce][,die] 2497 2498 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 2499 Format: [panic,][nopanic,][num] 2500 Valid num: 0 or 1 2501 0 - turn hardlockup detector in nmi_watchdog off 2502 1 - turn hardlockup detector in nmi_watchdog on 2503 When panic is specified, panic when an NMI watchdog 2504 timeout occurs (or 'nopanic' to override the opposite 2505 default). To disable both hard and soft lockup detectors, 2506 please see 'nowatchdog'. 2507 This is useful when you use a panic=... timeout and 2508 need the box quickly up again. 2509 2510 netpoll.carrier_timeout= 2511 [NET] Specifies amount of time (in seconds) that 2512 netpoll should wait for a carrier. By default netpoll 2513 waits 4 seconds. 2514 2515 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 2516 emulation library even if a 387 maths coprocessor 2517 is present. 2518 2519 no_console_suspend 2520 [HW] Never suspend the console 2521 Disable suspending of consoles during suspend and 2522 hibernate operations. Once disabled, debugging 2523 messages can reach various consoles while the rest 2524 of the system is being put to sleep (ie, while 2525 debugging driver suspend/resume hooks). This may 2526 not work reliably with all consoles, but is known 2527 to work with serial and VGA consoles. 2528 To facilitate more flexible debugging, we also add 2529 console_suspend, a printk module parameter to control 2530 it. Users could use console_suspend (usually 2531 /sys/module/printk/parameters/console_suspend) to 2532 turn on/off it dynamically. 2533 2534 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien 2535 caches in the slab allocator. Saves per-node memory, 2536 but will impact performance. 2537 2538 noalign [KNL,ARM] 2539 2540 noapic [SMP,APIC] Tells the kernel to not make use of any 2541 IOAPICs that may be present in the system. 2542 2543 noautogroup Disable scheduler automatic task group creation. 2544 2545 nobats [PPC] Do not use BATs for mapping kernel lowmem 2546 on "Classic" PPC cores. 2547 2548 nocache [ARM] 2549 2550 noclflush [BUGS=X86] Don't use the CLFLUSH instruction 2551 2552 nodelayacct [KNL] Disable per-task delay accounting 2553 2554 nodsp [SH] Disable hardware DSP at boot time. 2555 2556 noefi Disable EFI runtime services support. 2557 2558 noexec [IA-64] 2559 2560 noexec [X86] 2561 On X86-32 available only on PAE configured kernels. 2562 noexec=on: enable non-executable mappings (default) 2563 noexec=off: disable non-executable mappings 2564 2565 nosmap [X86] 2566 Disable SMAP (Supervisor Mode Access Prevention) 2567 even if it is supported by processor. 2568 2569 nosmep [X86] 2570 Disable SMEP (Supervisor Mode Execution Prevention) 2571 even if it is supported by processor. 2572 2573 noexec32 [X86-64] 2574 This affects only 32-bit executables. 2575 noexec32=on: enable non-executable mappings (default) 2576 read doesn't imply executable mappings 2577 noexec32=off: disable non-executable mappings 2578 read implies executable mappings 2579 2580 nofpu [MIPS,SH] Disable hardware FPU at boot time. 2581 2582 nofxsr [BUGS=X86-32] Disables x86 floating point extended 2583 register save and restore. The kernel will only save 2584 legacy floating-point registers on task switch. 2585 2586 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings. 2587 2588 nosmt [KNL,S390] Disable symmetric multithreading (SMT). 2589 Equivalent to smt=1. 2590 2591 noxsave [BUGS=X86] Disables x86 extended register state save 2592 and restore using xsave. The kernel will fallback to 2593 enabling legacy floating-point and sse state. 2594 2595 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 2596 register states. The kernel will fall back to use 2597 xsave to save the states. By using this parameter, 2598 performance of saving the states is degraded because 2599 xsave doesn't support modified optimization while 2600 xsaveopt supports it on xsaveopt enabled systems. 2601 2602 noxsaves [X86] Disables xsaves and xrstors used in saving and 2603 restoring x86 extended register state in compacted 2604 form of xsave area. The kernel will fall back to use 2605 xsaveopt and xrstor to save and restore the states 2606 in standard form of xsave area. By using this 2607 parameter, xsave area per process might occupy more 2608 memory on xsaves enabled systems. 2609 2610 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or 2611 wfi(ARM) instruction doesn't work correctly and not to 2612 use it. This is also useful when using JTAG debugger. 2613 2614 no_file_caps Tells the kernel not to honor file capabilities. The 2615 only way then for a file to be executed with privilege 2616 is to be setuid root or executed by root. 2617 2618 nohalt [IA-64] Tells the kernel not to use the power saving 2619 function PAL_HALT_LIGHT when idle. This increases 2620 power-consumption. On the positive side, it reduces 2621 interrupt wake-up latency, which may improve performance 2622 in certain environments such as networked servers or 2623 real-time systems. 2624 2625 nohibernate [HIBERNATION] Disable hibernation and resume. 2626 2627 nohz= [KNL] Boottime enable/disable dynamic ticks 2628 Valid arguments: on, off 2629 Default: on 2630 2631 nohz_full= [KNL,BOOT] 2632 The argument is a cpu list, as described above. 2633 In kernels built with CONFIG_NO_HZ_FULL=y, set 2634 the specified list of CPUs whose tick will be stopped 2635 whenever possible. The boot CPU will be forced outside 2636 the range to maintain the timekeeping. 2637 The CPUs in this range must also be included in the 2638 rcu_nocbs= set. 2639 2640 noiotrap [SH] Disables trapped I/O port accesses. 2641 2642 noirqdebug [X86-32] Disables the code which attempts to detect and 2643 disable unhandled interrupt sources. 2644 2645 no_timer_check [X86,APIC] Disables the code which tests for 2646 broken timer IRQ sources. 2647 2648 noisapnp [ISAPNP] Disables ISA PnP code. 2649 2650 noinitrd [RAM] Tells the kernel not to load any configured 2651 initial RAM disk. 2652 2653 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt 2654 remapping. 2655 [Deprecated - use intremap=off] 2656 2657 nointroute [IA-64] 2658 2659 noinvpcid [X86] Disable the INVPCID cpu feature. 2660 2661 nojitter [IA-64] Disables jitter checking for ITC timers. 2662 2663 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver 2664 2665 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page 2666 fault handling. 2667 2668 no-vmw-sched-clock 2669 [X86,PV_OPS] Disable paravirtualized VMware scheduler 2670 clock and use the default one. 2671 2672 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting. 2673 steal time is computed, but won't influence scheduler 2674 behaviour 2675 2676 nolapic [X86-32,APIC] Do not enable or use the local APIC. 2677 2678 nolapic_timer [X86-32,APIC] Do not use the local APIC timer. 2679 2680 noltlbs [PPC] Do not use large page/tlb entries for kernel 2681 lowmem mapping on PPC40x and PPC8xx 2682 2683 nomca [IA-64] Disable machine check abort handling 2684 2685 nomce [X86-32] Disable Machine Check Exception 2686 2687 nomfgpt [X86-32] Disable Multi-Function General Purpose 2688 Timer usage (for AMD Geode machines). 2689 2690 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 2691 shutdown the other cpus. Instead use the REBOOT_VECTOR 2692 irq. 2693 2694 nomodule Disable module load 2695 2696 nopat [X86] Disable PAT (page attribute table extension of 2697 pagetables) support. 2698 2699 norandmaps Don't use address space randomization. Equivalent to 2700 echo 0 > /proc/sys/kernel/randomize_va_space 2701 2702 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops 2703 2704 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 2705 with UP alternatives 2706 2707 nordrand [X86] Disable kernel use of the RDRAND and 2708 RDSEED instructions even if they are supported 2709 by the processor. RDRAND and RDSEED are still 2710 available to user space applications. 2711 2712 noresume [SWSUSP] Disables resume and restores original swap 2713 space. 2714 2715 no-scroll [VGA] Disables scrollback. 2716 This is required for the Braillex ib80-piezo Braille 2717 reader made by F.H. Papenmeier (Germany). 2718 2719 nosbagart [IA-64] 2720 2721 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support. 2722 2723 nosmp [SMP] Tells an SMP kernel to act as a UP kernel, 2724 and disable the IO APIC. legacy for "maxcpus=0". 2725 2726 nosoftlockup [KNL] Disable the soft-lockup detector. 2727 2728 nosync [HW,M68K] Disables sync negotiation for all devices. 2729 2730 notsc [BUGS=X86-32] Disable Time Stamp Counter 2731 2732 nowatchdog [KNL] Disable both lockup detectors, i.e. 2733 soft-lockup and NMI watchdog (hard-lockup). 2734 2735 nowb [ARM] 2736 2737 nox2apic [X86-64,APIC] Do not enable x2APIC mode. 2738 2739 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when 2740 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off. 2741 Some features depend on CPU0. Known dependencies are: 2742 1. Resume from suspend/hibernate depends on CPU0. 2743 Suspend/hibernate will fail if CPU0 is offline and you 2744 need to online CPU0 before suspend/hibernate. 2745 2. PIC interrupts also depend on CPU0. CPU0 can't be 2746 removed if a PIC interrupt is detected. 2747 It's said poweroff/reboot may depend on CPU0 on some 2748 machines although I haven't seen such issues so far 2749 after CPU0 is offline on a few tested machines. 2750 If the dependencies are under your control, you can 2751 turn on cpu0_hotplug. 2752 2753 nptcg= [IA-64] Override max number of concurrent global TLB 2754 purges which is reported from either PAL_VM_SUMMARY or 2755 SAL PALO. 2756 2757 nr_cpus= [SMP] Maximum number of processors that an SMP kernel 2758 could support. nr_cpus=n : n >= 1 limits the kernel to 2759 support 'n' processors. It could be larger than the 2760 number of already plugged CPU during bootup, later in 2761 runtime you can physically add extra cpu until it reaches 2762 n. So during boot up some boot time memory for per-cpu 2763 variables need be pre-allocated for later physical cpu 2764 hot plugging. 2765 2766 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 2767 2768 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing. 2769 Allowed values are enable and disable 2770 2771 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 2772 one of ['zone', 'node', 'default'] can be specified 2773 This can be set from sysctl after boot. 2774 See Documentation/sysctl/vm.txt for details. 2775 2776 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver. 2777 See Documentation/debugging-via-ohci1394.txt for more 2778 info. 2779 2780 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 2781 Rather than timing out after 20 ms if an EC 2782 command is not properly ACKed, override the length 2783 of the timeout. We have interrupts disabled while 2784 waiting for the ACK, so if this is set too high 2785 interrupts *may* be lost! 2786 2787 omap_mux= [OMAP] Override bootloader pin multiplexing. 2788 Format: <mux_mode0.mode_name=value>... 2789 For example, to override I2C bus2: 2790 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 2791 2792 oprofile.timer= [HW] 2793 Use timer interrupt instead of performance counters 2794 2795 oprofile.cpu_type= Force an oprofile cpu type 2796 This might be useful if you have an older oprofile 2797 userland or if you want common events. 2798 Format: { arch_perfmon } 2799 arch_perfmon: [X86] Force use of architectural 2800 perfmon on Intel CPUs instead of the 2801 CPU specific event set. 2802 timer: [X86] Force use of architectural NMI 2803 timer mode (see also oprofile.timer 2804 for generic hr timer mode) 2805 2806 oops=panic Always panic on oopses. Default is to just kill the 2807 process, but there is a small probability of 2808 deadlocking the machine. 2809 This will also cause panics on machine check exceptions. 2810 Useful together with panic=30 to trigger a reboot. 2811 2812 OSS [HW,OSS] 2813 See Documentation/sound/oss/oss-parameters.txt 2814 2815 page_owner= [KNL] Boot-time page_owner enabling option. 2816 Storage of the information about who allocated 2817 each page is disabled in default. With this switch, 2818 we can turn it on. 2819 on: enable the feature 2820 2821 page_poison= [KNL] Boot-time parameter changing the state of 2822 poisoning on the buddy allocator. 2823 off: turn off poisoning 2824 on: turn on poisoning 2825 2826 panic= [KNL] Kernel behaviour on panic: delay <timeout> 2827 timeout > 0: seconds before rebooting 2828 timeout = 0: wait forever 2829 timeout < 0: reboot immediately 2830 Format: <timeout> 2831 2832 panic_on_warn panic() instead of WARN(). Useful to cause kdump 2833 on a WARN(). 2834 2835 crash_kexec_post_notifiers 2836 Run kdump after running panic-notifiers and dumping 2837 kmsg. This only for the users who doubt kdump always 2838 succeeds in any situation. 2839 Note that this also increases risks of kdump failure, 2840 because some panic notifiers can make the crashed 2841 kernel more unstable. 2842 2843 parkbd.port= [HW] Parallel port number the keyboard adapter is 2844 connected to, default is 0. 2845 Format: <parport#> 2846 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 2847 0 for XT, 1 for AT (default is AT). 2848 Format: <mode> 2849 2850 parport= [HW,PPT] Specify parallel ports. 0 disables. 2851 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 2852 Use 'auto' to force the driver to use any 2853 IRQ/DMA settings detected (the default is to 2854 ignore detected IRQ/DMA settings because of 2855 possible conflicts). You can specify the base 2856 address, IRQ, and DMA settings; IRQ and DMA 2857 should be numbers, or 'auto' (for using detected 2858 settings on that particular port), or 'nofifo' 2859 (to avoid using a FIFO even if it is detected). 2860 Parallel ports are assigned in the order they 2861 are specified on the command line, starting 2862 with parport0. 2863 2864 parport_init_mode= [HW,PPT] 2865 Configure VIA parallel port to operate in 2866 a specific mode. This is necessary on Pegasos 2867 computer where firmware has no options for setting 2868 up parallel port mode and sets it to spp. 2869 Currently this function knows 686a and 8231 chips. 2870 Format: [spp|ps2|epp|ecp|ecpepp] 2871 2872 pause_on_oops= 2873 Halt all CPUs after the first oops has been printed for 2874 the specified number of seconds. This is to be used if 2875 your oopses keep scrolling off the screen. 2876 2877 pcbit= [HW,ISDN] 2878 2879 pcd. [PARIDE] 2880 See header of drivers/block/paride/pcd.c. 2881 See also Documentation/blockdev/paride.txt. 2882 2883 pci=option[,option...] [PCI] various PCI subsystem options: 2884 earlydump [X86] dump PCI config space before the kernel 2885 changes anything 2886 off [X86] don't probe for the PCI bus 2887 bios [X86-32] force use of PCI BIOS, don't access 2888 the hardware directly. Use this if your machine 2889 has a non-standard PCI host bridge. 2890 nobios [X86-32] disallow use of PCI BIOS, only direct 2891 hardware access methods are allowed. Use this 2892 if you experience crashes upon bootup and you 2893 suspect they are caused by the BIOS. 2894 conf1 [X86] Force use of PCI Configuration Access 2895 Mechanism 1 (config address in IO port 0xCF8, 2896 data in IO port 0xCFC, both 32-bit). 2897 conf2 [X86] Force use of PCI Configuration Access 2898 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 2899 the function, IO port 0xCFA, also 8-bit, sets 2900 bus number. The config space is then accessed 2901 through ports 0xC000-0xCFFF). 2902 See http://wiki.osdev.org/PCI for more info 2903 on the configuration access mechanisms. 2904 noaer [PCIE] If the PCIEAER kernel config parameter is 2905 enabled, this kernel boot option can be used to 2906 disable the use of PCIE advanced error reporting. 2907 nodomains [PCI] Disable support for multiple PCI 2908 root domains (aka PCI segments, in ACPI-speak). 2909 nommconf [X86] Disable use of MMCONFIG for PCI 2910 Configuration 2911 check_enable_amd_mmconf [X86] check for and enable 2912 properly configured MMIO access to PCI 2913 config space on AMD family 10h CPU 2914 nomsi [MSI] If the PCI_MSI kernel config parameter is 2915 enabled, this kernel boot option can be used to 2916 disable the use of MSI interrupts system-wide. 2917 noioapicquirk [APIC] Disable all boot interrupt quirks. 2918 Safety option to keep boot IRQs enabled. This 2919 should never be necessary. 2920 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 2921 primary IO-APIC for bridges that cannot disable 2922 boot IRQs. This fixes a source of spurious IRQs 2923 when the system masks IRQs. 2924 noioapicreroute [APIC] Disable workaround that uses the 2925 boot IRQ equivalent of an IRQ that connects to 2926 a chipset where boot IRQs cannot be disabled. 2927 The opposite of ioapicreroute. 2928 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 2929 routing table. These calls are known to be buggy 2930 on several machines and they hang the machine 2931 when used, but on other computers it's the only 2932 way to get the interrupt routing table. Try 2933 this option if the kernel is unable to allocate 2934 IRQs or discover secondary PCI buses on your 2935 motherboard. 2936 rom [X86] Assign address space to expansion ROMs. 2937 Use with caution as certain devices share 2938 address decoders between ROMs and other 2939 resources. 2940 norom [X86] Do not assign address space to 2941 expansion ROMs that do not already have 2942 BIOS assigned address ranges. 2943 nobar [X86] Do not assign address space to the 2944 BARs that weren't assigned by the BIOS. 2945 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 2946 assigned automatically to PCI devices. You can 2947 make the kernel exclude IRQs of your ISA cards 2948 this way. 2949 pirqaddr=0xAAAAA [X86] Specify the physical address 2950 of the PIRQ table (normally generated 2951 by the BIOS) if it is outside the 2952 F0000h-100000h range. 2953 lastbus=N [X86] Scan all buses thru bus #N. Can be 2954 useful if the kernel is unable to find your 2955 secondary buses and you want to tell it 2956 explicitly which ones they are. 2957 assign-busses [X86] Always assign all PCI bus 2958 numbers ourselves, overriding 2959 whatever the firmware may have done. 2960 usepirqmask [X86] Honor the possible IRQ mask stored 2961 in the BIOS $PIR table. This is needed on 2962 some systems with broken BIOSes, notably 2963 some HP Pavilion N5400 and Omnibook XE3 2964 notebooks. This will have no effect if ACPI 2965 IRQ routing is enabled. 2966 noacpi [X86] Do not use ACPI for IRQ routing 2967 or for PCI scanning. 2968 use_crs [X86] Use PCI host bridge window information 2969 from ACPI. On BIOSes from 2008 or later, this 2970 is enabled by default. If you need to use this, 2971 please report a bug. 2972 nocrs [X86] Ignore PCI host bridge windows from ACPI. 2973 If you need to use this, please report a bug. 2974 routeirq Do IRQ routing for all PCI devices. 2975 This is normally done in pci_enable_device(), 2976 so this option is a temporary workaround 2977 for broken drivers that don't call it. 2978 skip_isa_align [X86] do not align io start addr, so can 2979 handle more pci cards 2980 noearly [X86] Don't do any early type 1 scanning. 2981 This might help on some broken boards which 2982 machine check when some devices' config space 2983 is read. But various workarounds are disabled 2984 and some IOMMU drivers will not work. 2985 bfsort Sort PCI devices into breadth-first order. 2986 This sorting is done to get a device 2987 order compatible with older (<= 2.4) kernels. 2988 nobfsort Don't sort PCI devices into breadth-first order. 2989 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 2990 tuning and use the BIOS-configured MPS defaults. 2991 pcie_bus_safe Set every device's MPS to the largest value 2992 supported by all devices below the root complex. 2993 pcie_bus_perf Set device MPS to the largest allowable MPS 2994 based on its parent bus. Also set MRRS (Max 2995 Read Request Size) to the largest supported 2996 value (no larger than the MPS that the device 2997 or bus can support) for best performance. 2998 pcie_bus_peer2peer Set every device's MPS to 128B, which 2999 every device is guaranteed to support. This 3000 configuration allows peer-to-peer DMA between 3001 any pair of devices, possibly at the cost of 3002 reduced performance. This also guarantees 3003 that hot-added devices will work. 3004 cbiosize=nn[KMG] The fixed amount of bus space which is 3005 reserved for the CardBus bridge's IO window. 3006 The default value is 256 bytes. 3007 cbmemsize=nn[KMG] The fixed amount of bus space which is 3008 reserved for the CardBus bridge's memory 3009 window. The default value is 64 megabytes. 3010 resource_alignment= 3011 Format: 3012 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...] 3013 [<order of align>@]pci:<vendor>:<device>\ 3014 [:<subvendor>:<subdevice>][; ...] 3015 Specifies alignment and device to reassign 3016 aligned memory resources. 3017 If <order of align> is not specified, 3018 PAGE_SIZE is used as alignment. 3019 PCI-PCI bridge can be specified, if resource 3020 windows need to be expanded. 3021 To specify the alignment for several 3022 instances of a device, the PCI vendor, 3023 device, subvendor, and subdevice may be 3024 specified, e.g., 4096@pci:8086:9c22:103c:198f 3025 ecrc= Enable/disable PCIe ECRC (transaction layer 3026 end-to-end CRC checking). 3027 bios: Use BIOS/firmware settings. This is the 3028 the default. 3029 off: Turn ECRC off 3030 on: Turn ECRC on. 3031 hpiosize=nn[KMG] The fixed amount of bus space which is 3032 reserved for hotplug bridge's IO window. 3033 Default size is 256 bytes. 3034 hpmemsize=nn[KMG] The fixed amount of bus space which is 3035 reserved for hotplug bridge's memory window. 3036 Default size is 2 megabytes. 3037 hpbussize=nn The minimum amount of additional bus numbers 3038 reserved for buses below a hotplug bridge. 3039 Default is 1. 3040 realloc= Enable/disable reallocating PCI bridge resources 3041 if allocations done by BIOS are too small to 3042 accommodate resources required by all child 3043 devices. 3044 off: Turn realloc off 3045 on: Turn realloc on 3046 realloc same as realloc=on 3047 noari do not use PCIe ARI. 3048 pcie_scan_all Scan all possible PCIe devices. Otherwise we 3049 only look for one device below a PCIe downstream 3050 port. 3051 3052 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power 3053 Management. 3054 off Disable ASPM. 3055 force Enable ASPM even on devices that claim not to support it. 3056 WARNING: Forcing ASPM on may cause system lockups. 3057 3058 pcie_hp= [PCIE] PCI Express Hotplug driver options: 3059 nomsi Do not use MSI for PCI Express Native Hotplug (this 3060 makes all PCIe ports use INTx for hotplug services). 3061 3062 pcie_ports= [PCIE] PCIe ports handling: 3063 auto Ask the BIOS whether or not to use native PCIe services 3064 associated with PCIe ports (PME, hot-plug, AER). Use 3065 them only if that is allowed by the BIOS. 3066 native Use native PCIe services associated with PCIe ports 3067 unconditionally. 3068 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe 3069 ports driver. 3070 3071 pcie_port_pm= [PCIE] PCIe port power management handling: 3072 off Disable power management of all PCIe ports 3073 force Forcibly enable power management of all PCIe ports 3074 3075 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 3076 nomsi Do not use MSI for native PCIe PME signaling (this makes 3077 all PCIe root ports use INTx for all services). 3078 3079 pcmv= [HW,PCMCIA] BadgePAD 4 3080 3081 pd_ignore_unused 3082 [PM] 3083 Keep all power-domains already enabled by bootloader on, 3084 even if no driver has claimed them. This is useful 3085 for debug and development, but should not be 3086 needed on a platform with proper driver support. 3087 3088 pd. [PARIDE] 3089 See Documentation/blockdev/paride.txt. 3090 3091 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 3092 boot time. 3093 Format: { 0 | 1 } 3094 See arch/parisc/kernel/pdc_chassis.c 3095 3096 percpu_alloc= Select which percpu first chunk allocator to use. 3097 Currently supported values are "embed" and "page". 3098 Archs may support subset or none of the selections. 3099 See comments in mm/percpu.c for details on each 3100 allocator. This parameter is primarily for debugging 3101 and performance comparison. 3102 3103 pf. [PARIDE] 3104 See Documentation/blockdev/paride.txt. 3105 3106 pg. [PARIDE] 3107 See Documentation/blockdev/paride.txt. 3108 3109 pirq= [SMP,APIC] Manual mp-table setup 3110 See Documentation/x86/i386/IO-APIC.txt. 3111 3112 plip= [PPT,NET] Parallel port network link 3113 Format: { parport<nr> | timid | 0 } 3114 See also Documentation/parport.txt. 3115 3116 pmtmr= [X86] Manual setup of pmtmr I/O Port. 3117 Override pmtimer IOPort with a hex value. 3118 e.g. pmtmr=0x508 3119 3120 pnp.debug=1 [PNP] 3121 Enable PNP debug messages (depends on the 3122 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 3123 via /sys/module/pnp/parameters/debug. We always show 3124 current resource usage; turning this on also shows 3125 possible settings and some assignment information. 3126 3127 pnpacpi= [ACPI] 3128 { off } 3129 3130 pnpbios= [ISAPNP] 3131 { on | off | curr | res | no-curr | no-res } 3132 3133 pnp_reserve_irq= 3134 [ISAPNP] Exclude IRQs for the autoconfiguration 3135 3136 pnp_reserve_dma= 3137 [ISAPNP] Exclude DMAs for the autoconfiguration 3138 3139 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 3140 Ranges are in pairs (I/O port base and size). 3141 3142 pnp_reserve_mem= 3143 [ISAPNP] Exclude memory regions for the 3144 autoconfiguration. 3145 Ranges are in pairs (memory base and size). 3146 3147 ports= [IP_VS_FTP] IPVS ftp helper module 3148 Default is 21. 3149 Up to 8 (IP_VS_APP_MAX_PORTS) ports 3150 may be specified. 3151 Format: <port>,<port>.... 3152 3153 powersave=off [PPC] This option disables power saving features. 3154 It specifically disables cpuidle and sets the 3155 platform machine description specific power_save 3156 function to NULL. On Idle the CPU just reduces 3157 execution priority. 3158 3159 ppc_strict_facility_enable 3160 [PPC] This option catches any kernel floating point, 3161 Altivec, VSX and SPE outside of regions specifically 3162 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 3163 There is some performance impact when enabling this. 3164 3165 print-fatal-signals= 3166 [KNL] debug: print fatal signals 3167 3168 If enabled, warn about various signal handling 3169 related application anomalies: too many signals, 3170 too many POSIX.1 timers, fatal signals causing a 3171 coredump - etc. 3172 3173 If you hit the warning due to signal overflow, 3174 you might want to try "ulimit -i unlimited". 3175 3176 default: off. 3177 3178 printk.always_kmsg_dump= 3179 Trigger kmsg_dump for cases other than kernel oops or 3180 panics 3181 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3182 default: disabled 3183 3184 printk.devkmsg={on,off,ratelimit} 3185 Control writing to /dev/kmsg. 3186 on - unlimited logging to /dev/kmsg from userspace 3187 off - logging to /dev/kmsg disabled 3188 ratelimit - ratelimit the logging 3189 Default: ratelimit 3190 3191 printk.time= Show timing data prefixed to each printk message line 3192 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3193 3194 processor.max_cstate= [HW,ACPI] 3195 Limit processor to maximum C-state 3196 max_cstate=9 overrides any DMI blacklist limit. 3197 3198 processor.nocst [HW,ACPI] 3199 Ignore the _CST method to determine C-states, 3200 instead using the legacy FADT method 3201 3202 profile= [KNL] Enable kernel profiling via /proc/profile 3203 Format: [schedule,]<number> 3204 Param: "schedule" - profile schedule points. 3205 Param: <number> - step/bucket size as a power of 2 for 3206 statistical time based profiling. 3207 Param: "sleep" - profile D-state sleeping (millisecs). 3208 Requires CONFIG_SCHEDSTATS 3209 Param: "kvm" - profile VM exits. 3210 3211 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk 3212 before loading. 3213 See Documentation/blockdev/ramdisk.txt. 3214 3215 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 3216 probe for; one of (bare|imps|exps|lifebook|any). 3217 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 3218 per second. 3219 psmouse.resetafter= [HW,MOUSE] 3220 Try to reset the device after so many bad packets 3221 (0 = never). 3222 psmouse.resolution= 3223 [HW,MOUSE] Set desired mouse resolution, in dpi. 3224 psmouse.smartscroll= 3225 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 3226 0 = disabled, 1 = enabled (default). 3227 3228 pstore.backend= Specify the name of the pstore backend to use 3229 3230 pt. [PARIDE] 3231 See Documentation/blockdev/paride.txt. 3232 3233 pty.legacy_count= 3234 [KNL] Number of legacy pty's. Overwrites compiled-in 3235 default number. 3236 3237 quiet [KNL] Disable most log messages 3238 3239 r128= [HW,DRM] 3240 3241 raid= [HW,RAID] 3242 See Documentation/admin-guide/md.rst. 3243 3244 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 3245 See Documentation/blockdev/ramdisk.txt. 3246 3247 ras=option[,option,...] [KNL] RAS-specific options 3248 3249 cec_disable [X86] 3250 Disable the Correctable Errors Collector, 3251 see CONFIG_RAS_CEC help text. 3252 3253 rcu_nocbs= [KNL] 3254 The argument is a cpu list, as described above. 3255 3256 In kernels built with CONFIG_RCU_NOCB_CPU=y, set 3257 the specified list of CPUs to be no-callback CPUs. 3258 Invocation of these CPUs' RCU callbacks will 3259 be offloaded to "rcuox/N" kthreads created for 3260 that purpose, where "x" is "b" for RCU-bh, "p" 3261 for RCU-preempt, and "s" for RCU-sched, and "N" 3262 is the CPU number. This reduces OS jitter on the 3263 offloaded CPUs, which can be useful for HPC and 3264 real-time workloads. It can also improve energy 3265 efficiency for asymmetric multiprocessors. 3266 3267 rcu_nocb_poll [KNL] 3268 Rather than requiring that offloaded CPUs 3269 (specified by rcu_nocbs= above) explicitly 3270 awaken the corresponding "rcuoN" kthreads, 3271 make these kthreads poll for callbacks. 3272 This improves the real-time response for the 3273 offloaded CPUs by relieving them of the need to 3274 wake up the corresponding kthread, but degrades 3275 energy efficiency by requiring that the kthreads 3276 periodically wake up to do the polling. 3277 3278 rcutree.blimit= [KNL] 3279 Set maximum number of finished RCU callbacks to 3280 process in one batch. 3281 3282 rcutree.dump_tree= [KNL] 3283 Dump the structure of the rcu_node combining tree 3284 out at early boot. This is used for diagnostic 3285 purposes, to verify correct tree setup. 3286 3287 rcutree.gp_cleanup_delay= [KNL] 3288 Set the number of jiffies to delay each step of 3289 RCU grace-period cleanup. 3290 3291 rcutree.gp_init_delay= [KNL] 3292 Set the number of jiffies to delay each step of 3293 RCU grace-period initialization. 3294 3295 rcutree.gp_preinit_delay= [KNL] 3296 Set the number of jiffies to delay each step of 3297 RCU grace-period pre-initialization, that is, 3298 the propagation of recent CPU-hotplug changes up 3299 the rcu_node combining tree. 3300 3301 rcutree.rcu_fanout_exact= [KNL] 3302 Disable autobalancing of the rcu_node combining 3303 tree. This is used by rcutorture, and might 3304 possibly be useful for architectures having high 3305 cache-to-cache transfer latencies. 3306 3307 rcutree.rcu_fanout_leaf= [KNL] 3308 Change the number of CPUs assigned to each 3309 leaf rcu_node structure. Useful for very 3310 large systems, which will choose the value 64, 3311 and for NUMA systems with large remote-access 3312 latencies, which will choose a value aligned 3313 with the appropriate hardware boundaries. 3314 3315 rcutree.jiffies_till_sched_qs= [KNL] 3316 Set required age in jiffies for a 3317 given grace period before RCU starts 3318 soliciting quiescent-state help from 3319 rcu_note_context_switch(). 3320 3321 rcutree.jiffies_till_first_fqs= [KNL] 3322 Set delay from grace-period initialization to 3323 first attempt to force quiescent states. 3324 Units are jiffies, minimum value is zero, 3325 and maximum value is HZ. 3326 3327 rcutree.jiffies_till_next_fqs= [KNL] 3328 Set delay between subsequent attempts to force 3329 quiescent states. Units are jiffies, minimum 3330 value is one, and maximum value is HZ. 3331 3332 rcutree.kthread_prio= [KNL,BOOT] 3333 Set the SCHED_FIFO priority of the RCU per-CPU 3334 kthreads (rcuc/N). This value is also used for 3335 the priority of the RCU boost threads (rcub/N) 3336 and for the RCU grace-period kthreads (rcu_bh, 3337 rcu_preempt, and rcu_sched). If RCU_BOOST is 3338 set, valid values are 1-99 and the default is 1 3339 (the least-favored priority). Otherwise, when 3340 RCU_BOOST is not set, valid values are 0-99 and 3341 the default is zero (non-realtime operation). 3342 3343 rcutree.rcu_nocb_leader_stride= [KNL] 3344 Set the number of NOCB kthread groups, which 3345 defaults to the square root of the number of 3346 CPUs. Larger numbers reduces the wakeup overhead 3347 on the per-CPU grace-period kthreads, but increases 3348 that same overhead on each group's leader. 3349 3350 rcutree.qhimark= [KNL] 3351 Set threshold of queued RCU callbacks beyond which 3352 batch limiting is disabled. 3353 3354 rcutree.qlowmark= [KNL] 3355 Set threshold of queued RCU callbacks below which 3356 batch limiting is re-enabled. 3357 3358 rcutree.rcu_idle_gp_delay= [KNL] 3359 Set wakeup interval for idle CPUs that have 3360 RCU callbacks (RCU_FAST_NO_HZ=y). 3361 3362 rcutree.rcu_idle_lazy_gp_delay= [KNL] 3363 Set wakeup interval for idle CPUs that have 3364 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y). 3365 Lazy RCU callbacks are those which RCU can 3366 prove do nothing more than free memory. 3367 3368 rcutree.rcu_kick_kthreads= [KNL] 3369 Cause the grace-period kthread to get an extra 3370 wake_up() if it sleeps three times longer than 3371 it should at force-quiescent-state time. 3372 This wake_up() will be accompanied by a 3373 WARN_ONCE() splat and an ftrace_dump(). 3374 3375 rcuperf.gp_async= [KNL] 3376 Measure performance of asynchronous 3377 grace-period primitives such as call_rcu(). 3378 3379 rcuperf.gp_async_max= [KNL] 3380 Specify the maximum number of outstanding 3381 callbacks per writer thread. When a writer 3382 thread exceeds this limit, it invokes the 3383 corresponding flavor of rcu_barrier() to allow 3384 previously posted callbacks to drain. 3385 3386 rcuperf.gp_exp= [KNL] 3387 Measure performance of expedited synchronous 3388 grace-period primitives. 3389 3390 rcuperf.holdoff= [KNL] 3391 Set test-start holdoff period. The purpose of 3392 this parameter is to delay the start of the 3393 test until boot completes in order to avoid 3394 interference. 3395 3396 rcuperf.nreaders= [KNL] 3397 Set number of RCU readers. The value -1 selects 3398 N, where N is the number of CPUs. A value 3399 "n" less than -1 selects N-n+1, where N is again 3400 the number of CPUs. For example, -2 selects N 3401 (the number of CPUs), -3 selects N+1, and so on. 3402 A value of "n" less than or equal to -N selects 3403 a single reader. 3404 3405 rcuperf.nwriters= [KNL] 3406 Set number of RCU writers. The values operate 3407 the same as for rcuperf.nreaders. 3408 N, where N is the number of CPUs 3409 3410 rcuperf.perf_runnable= [BOOT] 3411 Start rcuperf running at boot time. 3412 3413 rcuperf.perf_type= [KNL] 3414 Specify the RCU implementation to test. 3415 3416 rcuperf.shutdown= [KNL] 3417 Shut the system down after performance tests 3418 complete. This is useful for hands-off automated 3419 testing. 3420 3421 rcuperf.verbose= [KNL] 3422 Enable additional printk() statements. 3423 3424 rcuperf.writer_holdoff= [KNL] 3425 Write-side holdoff between grace periods, 3426 in microseconds. The default of zero says 3427 no holdoff. 3428 3429 rcutorture.cbflood_inter_holdoff= [KNL] 3430 Set holdoff time (jiffies) between successive 3431 callback-flood tests. 3432 3433 rcutorture.cbflood_intra_holdoff= [KNL] 3434 Set holdoff time (jiffies) between successive 3435 bursts of callbacks within a given callback-flood 3436 test. 3437 3438 rcutorture.cbflood_n_burst= [KNL] 3439 Set the number of bursts making up a given 3440 callback-flood test. Set this to zero to 3441 disable callback-flood testing. 3442 3443 rcutorture.cbflood_n_per_burst= [KNL] 3444 Set the number of callbacks to be registered 3445 in a given burst of a callback-flood test. 3446 3447 rcutorture.fqs_duration= [KNL] 3448 Set duration of force_quiescent_state bursts 3449 in microseconds. 3450 3451 rcutorture.fqs_holdoff= [KNL] 3452 Set holdoff time within force_quiescent_state bursts 3453 in microseconds. 3454 3455 rcutorture.fqs_stutter= [KNL] 3456 Set wait time between force_quiescent_state bursts 3457 in seconds. 3458 3459 rcutorture.gp_cond= [KNL] 3460 Use conditional/asynchronous update-side 3461 primitives, if available. 3462 3463 rcutorture.gp_exp= [KNL] 3464 Use expedited update-side primitives, if available. 3465 3466 rcutorture.gp_normal= [KNL] 3467 Use normal (non-expedited) asynchronous 3468 update-side primitives, if available. 3469 3470 rcutorture.gp_sync= [KNL] 3471 Use normal (non-expedited) synchronous 3472 update-side primitives, if available. If all 3473 of rcutorture.gp_cond=, rcutorture.gp_exp=, 3474 rcutorture.gp_normal=, and rcutorture.gp_sync= 3475 are zero, rcutorture acts as if is interpreted 3476 they are all non-zero. 3477 3478 rcutorture.n_barrier_cbs= [KNL] 3479 Set callbacks/threads for rcu_barrier() testing. 3480 3481 rcutorture.nfakewriters= [KNL] 3482 Set number of concurrent RCU writers. These just 3483 stress RCU, they don't participate in the actual 3484 test, hence the "fake". 3485 3486 rcutorture.nreaders= [KNL] 3487 Set number of RCU readers. The value -1 selects 3488 N-1, where N is the number of CPUs. A value 3489 "n" less than -1 selects N-n-2, where N is again 3490 the number of CPUs. For example, -2 selects N 3491 (the number of CPUs), -3 selects N+1, and so on. 3492 3493 rcutorture.object_debug= [KNL] 3494 Enable debug-object double-call_rcu() testing. 3495 3496 rcutorture.onoff_holdoff= [KNL] 3497 Set time (s) after boot for CPU-hotplug testing. 3498 3499 rcutorture.onoff_interval= [KNL] 3500 Set time (s) between CPU-hotplug operations, or 3501 zero to disable CPU-hotplug testing. 3502 3503 rcutorture.shuffle_interval= [KNL] 3504 Set task-shuffle interval (s). Shuffling tasks 3505 allows some CPUs to go into dyntick-idle mode 3506 during the rcutorture test. 3507 3508 rcutorture.shutdown_secs= [KNL] 3509 Set time (s) after boot system shutdown. This 3510 is useful for hands-off automated testing. 3511 3512 rcutorture.stall_cpu= [KNL] 3513 Duration of CPU stall (s) to test RCU CPU stall 3514 warnings, zero to disable. 3515 3516 rcutorture.stall_cpu_holdoff= [KNL] 3517 Time to wait (s) after boot before inducing stall. 3518 3519 rcutorture.stat_interval= [KNL] 3520 Time (s) between statistics printk()s. 3521 3522 rcutorture.stutter= [KNL] 3523 Time (s) to stutter testing, for example, specifying 3524 five seconds causes the test to run for five seconds, 3525 wait for five seconds, and so on. This tests RCU's 3526 ability to transition abruptly to and from idle. 3527 3528 rcutorture.test_boost= [KNL] 3529 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 3530 "Maybe" means test if the RCU implementation 3531 under test support RCU priority boosting. 3532 3533 rcutorture.test_boost_duration= [KNL] 3534 Duration (s) of each individual boost test. 3535 3536 rcutorture.test_boost_interval= [KNL] 3537 Interval (s) between each boost test. 3538 3539 rcutorture.test_no_idle_hz= [KNL] 3540 Test RCU's dyntick-idle handling. See also the 3541 rcutorture.shuffle_interval parameter. 3542 3543 rcutorture.torture_runnable= [BOOT] 3544 Start rcutorture running at boot time. 3545 3546 rcutorture.torture_type= [KNL] 3547 Specify the RCU implementation to test. 3548 3549 rcutorture.verbose= [KNL] 3550 Enable additional printk() statements. 3551 3552 rcupdate.rcu_cpu_stall_suppress= [KNL] 3553 Suppress RCU CPU stall warning messages. 3554 3555 rcupdate.rcu_cpu_stall_timeout= [KNL] 3556 Set timeout for RCU CPU stall warning messages. 3557 3558 rcupdate.rcu_expedited= [KNL] 3559 Use expedited grace-period primitives, for 3560 example, synchronize_rcu_expedited() instead 3561 of synchronize_rcu(). This reduces latency, 3562 but can increase CPU utilization, degrade 3563 real-time latency, and degrade energy efficiency. 3564 No effect on CONFIG_TINY_RCU kernels. 3565 3566 rcupdate.rcu_normal= [KNL] 3567 Use only normal grace-period primitives, 3568 for example, synchronize_rcu() instead of 3569 synchronize_rcu_expedited(). This improves 3570 real-time latency, CPU utilization, and 3571 energy efficiency, but can expose users to 3572 increased grace-period latency. This parameter 3573 overrides rcupdate.rcu_expedited. No effect on 3574 CONFIG_TINY_RCU kernels. 3575 3576 rcupdate.rcu_normal_after_boot= [KNL] 3577 Once boot has completed (that is, after 3578 rcu_end_inkernel_boot() has been invoked), use 3579 only normal grace-period primitives. No effect 3580 on CONFIG_TINY_RCU kernels. 3581 3582 rcupdate.rcu_task_stall_timeout= [KNL] 3583 Set timeout in jiffies for RCU task stall warning 3584 messages. Disable with a value less than or equal 3585 to zero. 3586 3587 rcupdate.rcu_self_test= [KNL] 3588 Run the RCU early boot self tests 3589 3590 rcupdate.rcu_self_test_bh= [KNL] 3591 Run the RCU bh early boot self tests 3592 3593 rcupdate.rcu_self_test_sched= [KNL] 3594 Run the RCU sched early boot self tests 3595 3596 rdinit= [KNL] 3597 Format: <full_path> 3598 Run specified binary instead of /init from the ramdisk, 3599 used for early userspace startup. See initrd. 3600 3601 reboot= [KNL] 3602 Format (x86 or x86_64): 3603 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \ 3604 [[,]s[mp]#### \ 3605 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 3606 [[,]f[orce] 3607 Where reboot_mode is one of warm (soft) or cold (hard) or gpio, 3608 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 3609 reboot_force is either force or not specified, 3610 reboot_cpu is s[mp]#### with #### being the processor 3611 to be used for rebooting. 3612 3613 relax_domain_level= 3614 [KNL, SMP] Set scheduler's default relax_domain_level. 3615 See Documentation/cgroup-v1/cpusets.txt. 3616 3617 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area 3618 3619 reservetop= [X86-32] 3620 Format: nn[KMG] 3621 Reserves a hole at the top of the kernel virtual 3622 address space. 3623 3624 reservelow= [X86] 3625 Format: nn[K] 3626 Set the amount of memory to reserve for BIOS at 3627 the bottom of the address space. 3628 3629 reset_devices [KNL] Force drivers to reset the underlying device 3630 during initialization. 3631 3632 resume= [SWSUSP] 3633 Specify the partition device for software suspend 3634 Format: 3635 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 3636 3637 resume_offset= [SWSUSP] 3638 Specify the offset from the beginning of the partition 3639 given by "resume=" at which the swap header is located, 3640 in <PAGE_SIZE> units (needed only for swap files). 3641 See Documentation/power/swsusp-and-swap-files.txt 3642 3643 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 3644 read the resume files 3645 3646 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 3647 Useful for devices that are detected asynchronously 3648 (e.g. USB and MMC devices). 3649 3650 hibernate= [HIBERNATION] 3651 noresume Don't check if there's a hibernation image 3652 present during boot. 3653 nocompress Don't compress/decompress hibernation images. 3654 no Disable hibernation and resume. 3655 protect_image Turn on image protection during restoration 3656 (that will set all pages holding image data 3657 during restoration read-only). 3658 3659 retain_initrd [RAM] Keep initrd memory after extraction 3660 3661 rfkill.default_state= 3662 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 3663 etc. communication is blocked by default. 3664 1 Unblocked. 3665 3666 rfkill.master_switch_mode= 3667 0 The "airplane mode" button does nothing. 3668 1 The "airplane mode" button toggles between everything 3669 blocked and the previous configuration. 3670 2 The "airplane mode" button toggles between everything 3671 blocked and everything unblocked. 3672 3673 rhash_entries= [KNL,NET] 3674 Set number of hash buckets for route cache 3675 3676 ring3mwait=disable 3677 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 3678 CPUs. 3679 3680 ro [KNL] Mount root device read-only on boot 3681 3682 rodata= [KNL] 3683 on Mark read-only kernel memory as read-only (default). 3684 off Leave read-only kernel memory writable for debugging. 3685 3686 rockchip.usb_uart 3687 Enable the uart passthrough on the designated usb port 3688 on Rockchip SoCs. When active, the signals of the 3689 debug-uart get routed to the D+ and D- pins of the usb 3690 port and the regular usb controller gets disabled. 3691 3692 root= [KNL] Root filesystem 3693 See name_to_dev_t comment in init/do_mounts.c. 3694 3695 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 3696 mount the root filesystem 3697 3698 rootflags= [KNL] Set root filesystem mount option string 3699 3700 rootfstype= [KNL] Set root filesystem type 3701 3702 rootwait [KNL] Wait (indefinitely) for root device to show up. 3703 Useful for devices that are detected asynchronously 3704 (e.g. USB and MMC devices). 3705 3706 rproc_mem=nn[KMG][@address] 3707 [KNL,ARM,CMA] Remoteproc physical memory block. 3708 Memory area to be used by remote processor image, 3709 managed by CMA. 3710 3711 rw [KNL] Mount root device read-write on boot 3712 3713 S [KNL] Run init in single mode 3714 3715 s390_iommu= [HW,S390] 3716 Set s390 IOTLB flushing mode 3717 strict 3718 With strict flushing every unmap operation will result in 3719 an IOTLB flush. Default is lazy flushing before reuse, 3720 which is faster. 3721 3722 sa1100ir [NET] 3723 See drivers/net/irda/sa1100_ir.c. 3724 3725 sbni= [NET] Granch SBNI12 leased line adapter 3726 3727 sched_debug [KNL] Enables verbose scheduler debug messages. 3728 3729 schedstats= [KNL,X86] Enable or disable scheduled statistics. 3730 Allowed values are enable and disable. This feature 3731 incurs a small amount of overhead in the scheduler 3732 but is useful for debugging and performance tuning. 3733 3734 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate 3735 xtime_lock contention on larger systems, and/or RCU lock 3736 contention on all systems with CONFIG_MAXSMP set. 3737 Format: { "0" | "1" } 3738 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 3739 1 -- enable. 3740 Note: increases power consumption, thus should only be 3741 enabled if running jitter sensitive (HPC/RT) workloads. 3742 3743 security= [SECURITY] Choose a security module to enable at boot. 3744 If this boot parameter is not specified, only the first 3745 security module asking for security registration will be 3746 loaded. An invalid security module name will be treated 3747 as if no module has been chosen. 3748 3749 selinux= [SELINUX] Disable or enable SELinux at boot time. 3750 Format: { "0" | "1" } 3751 See security/selinux/Kconfig help text. 3752 0 -- disable. 3753 1 -- enable. 3754 Default value is set via kernel config option. 3755 If enabled at boot time, /selinux/disable can be used 3756 later to disable prior to initial policy load. 3757 3758 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 3759 Format: { "0" | "1" } 3760 See security/apparmor/Kconfig help text 3761 0 -- disable. 3762 1 -- enable. 3763 Default value is set via kernel config option. 3764 3765 serialnumber [BUGS=X86-32] 3766 3767 shapers= [NET] 3768 Maximal number of shapers. 3769 3770 simeth= [IA-64] 3771 simscsi= 3772 3773 slram= [HW,MTD] 3774 3775 slab_nomerge [MM] 3776 Disable merging of slabs with similar size. May be 3777 necessary if there is some reason to distinguish 3778 allocs to different slabs, especially in hardened 3779 environments where the risk of heap overflows and 3780 layout control by attackers can usually be 3781 frustrated by disabling merging. This will reduce 3782 most of the exposure of a heap attack to a single 3783 cache (risks via metadata attacks are mostly 3784 unchanged). Debug options disable merging on their 3785 own. 3786 For more information see Documentation/vm/slub.txt. 3787 3788 slab_max_order= [MM, SLAB] 3789 Determines the maximum allowed order for slabs. 3790 A high setting may cause OOMs due to memory 3791 fragmentation. Defaults to 1 for systems with 3792 more than 32MB of RAM, 0 otherwise. 3793 3794 slub_debug[=options[,slabs]] [MM, SLUB] 3795 Enabling slub_debug allows one to determine the 3796 culprit if slab objects become corrupted. Enabling 3797 slub_debug can create guard zones around objects and 3798 may poison objects when not in use. Also tracks the 3799 last alloc / free. For more information see 3800 Documentation/vm/slub.txt. 3801 3802 slub_memcg_sysfs= [MM, SLUB] 3803 Determines whether to enable sysfs directories for 3804 memory cgroup sub-caches. 1 to enable, 0 to disable. 3805 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON. 3806 Enabling this can lead to a very high number of debug 3807 directories and files being created under 3808 /sys/kernel/slub. 3809 3810 slub_max_order= [MM, SLUB] 3811 Determines the maximum allowed order for slabs. 3812 A high setting may cause OOMs due to memory 3813 fragmentation. For more information see 3814 Documentation/vm/slub.txt. 3815 3816 slub_min_objects= [MM, SLUB] 3817 The minimum number of objects per slab. SLUB will 3818 increase the slab order up to slub_max_order to 3819 generate a sufficiently large slab able to contain 3820 the number of objects indicated. The higher the number 3821 of objects the smaller the overhead of tracking slabs 3822 and the less frequently locks need to be acquired. 3823 For more information see Documentation/vm/slub.txt. 3824 3825 slub_min_order= [MM, SLUB] 3826 Determines the minimum page order for slabs. Must be 3827 lower than slub_max_order. 3828 For more information see Documentation/vm/slub.txt. 3829 3830 slub_nomerge [MM, SLUB] 3831 Same with slab_nomerge. This is supported for legacy. 3832 See slab_nomerge for more information. 3833 3834 smart2= [HW] 3835 Format: <io1>[,<io2>[,...,<io8>]] 3836 3837 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 3838 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 3839 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 3840 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 3841 smsc-ircc2.ircc_irq= [HW] IRQ line 3842 smsc-ircc2.ircc_dma= [HW] DMA channel 3843 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 3844 0: Toshiba Satellite 1800 (GP data pin select) 3845 1: Fast pin select (default) 3846 2: ATC IRMode 3847 3848 smt [KNL,S390] Set the maximum number of threads (logical 3849 CPUs) to use per physical CPU on systems capable of 3850 symmetric multithreading (SMT). Will be capped to the 3851 actual hardware limit. 3852 Format: <integer> 3853 Default: -1 (no limit) 3854 3855 softlockup_panic= 3856 [KNL] Should the soft-lockup detector generate panics. 3857 Format: <integer> 3858 3859 softlockup_all_cpu_backtrace= 3860 [KNL] Should the soft-lockup detector generate 3861 backtraces on all cpus. 3862 Format: <integer> 3863 3864 sonypi.*= [HW] Sony Programmable I/O Control Device driver 3865 See Documentation/laptops/sonypi.txt 3866 3867 spia_io_base= [HW,MTD] 3868 spia_fio_base= 3869 spia_pedr= 3870 spia_peddr= 3871 3872 srcutree.counter_wrap_check [KNL] 3873 Specifies how frequently to check for 3874 grace-period sequence counter wrap for the 3875 srcu_data structure's ->srcu_gp_seq_needed field. 3876 The greater the number of bits set in this kernel 3877 parameter, the less frequently counter wrap will 3878 be checked for. Note that the bottom two bits 3879 are ignored. 3880 3881 srcutree.exp_holdoff [KNL] 3882 Specifies how many nanoseconds must elapse 3883 since the end of the last SRCU grace period for 3884 a given srcu_struct until the next normal SRCU 3885 grace period will be considered for automatic 3886 expediting. Set to zero to disable automatic 3887 expediting. 3888 3889 stack_guard_gap= [MM] 3890 override the default stack gap protection. The value 3891 is in page units and it defines how many pages prior 3892 to (for stacks growing down) resp. after (for stacks 3893 growing up) the main stack are reserved for no other 3894 mapping. Default value is 256 pages. 3895 3896 stacktrace [FTRACE] 3897 Enabled the stack tracer on boot up. 3898 3899 stacktrace_filter=[function-list] 3900 [FTRACE] Limit the functions that the stack tracer 3901 will trace at boot up. function-list is a comma separated 3902 list of functions. This list can be changed at run 3903 time by the stack_trace_filter file in the debugfs 3904 tracing directory. Note, this enables stack tracing 3905 and the stacktrace above is not needed. 3906 3907 sti= [PARISC,HW] 3908 Format: <num> 3909 Set the STI (builtin display/keyboard on the HP-PARISC 3910 machines) console (graphic card) which should be used 3911 as the initial boot-console. 3912 See also comment in drivers/video/console/sticore.c. 3913 3914 sti_font= [HW] 3915 See comment in drivers/video/console/sticore.c. 3916 3917 stifb= [HW] 3918 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 3919 3920 sunrpc.min_resvport= 3921 sunrpc.max_resvport= 3922 [NFS,SUNRPC] 3923 SunRPC servers often require that client requests 3924 originate from a privileged port (i.e. a port in the 3925 range 0 < portnr < 1024). 3926 An administrator who wishes to reserve some of these 3927 ports for other uses may adjust the range that the 3928 kernel's sunrpc client considers to be privileged 3929 using these two parameters to set the minimum and 3930 maximum port values. 3931 3932 sunrpc.svc_rpc_per_connection_limit= 3933 [NFS,SUNRPC] 3934 Limit the number of requests that the server will 3935 process in parallel from a single connection. 3936 The default value is 0 (no limit). 3937 3938 sunrpc.pool_mode= 3939 [NFS] 3940 Control how the NFS server code allocates CPUs to 3941 service thread pools. Depending on how many NICs 3942 you have and where their interrupts are bound, this 3943 option will affect which CPUs will do NFS serving. 3944 Note: this parameter cannot be changed while the 3945 NFS server is running. 3946 3947 auto the server chooses an appropriate mode 3948 automatically using heuristics 3949 global a single global pool contains all CPUs 3950 percpu one pool for each CPU 3951 pernode one pool for each NUMA node (equivalent 3952 to global on non-NUMA machines) 3953 3954 sunrpc.tcp_slot_table_entries= 3955 sunrpc.udp_slot_table_entries= 3956 [NFS,SUNRPC] 3957 Sets the upper limit on the number of simultaneous 3958 RPC calls that can be sent from the client to a 3959 server. Increasing these values may allow you to 3960 improve throughput, but will also increase the 3961 amount of memory reserved for use by the client. 3962 3963 suspend.pm_test_delay= 3964 [SUSPEND] 3965 Sets the number of seconds to remain in a suspend test 3966 mode before resuming the system (see 3967 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 3968 is set. Default value is 5. 3969 3970 swapaccount=[0|1] 3971 [KNL] Enable accounting of swap in memory resource 3972 controller if no parameter or 1 is given or disable 3973 it if 0 is given (See Documentation/cgroup-v1/memory.txt) 3974 3975 swiotlb= [ARM,IA-64,PPC,MIPS,X86] 3976 Format: { <int> | force | noforce } 3977 <int> -- Number of I/O TLB slabs 3978 force -- force using of bounce buffers even if they 3979 wouldn't be automatically used by the kernel 3980 noforce -- Never use bounce buffers (for debugging) 3981 3982 switches= [HW,M68k] 3983 3984 sysfs.deprecated=0|1 [KNL] 3985 Enable/disable old style sysfs layout for old udev 3986 on older distributions. When this option is enabled 3987 very new udev will not work anymore. When this option 3988 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled) 3989 in older udev will not work anymore. 3990 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in 3991 the kernel configuration. 3992 3993 sysrq_always_enabled 3994 [KNL] 3995 Ignore sysrq setting - this boot parameter will 3996 neutralize any effect of /proc/sys/kernel/sysrq. 3997 Useful for debugging. 3998 3999 tcpmhash_entries= [KNL,NET] 4000 Set the number of tcp_metrics_hash slots. 4001 Default value is 8192 or 16384 depending on total 4002 ram pages. This is used to specify the TCP metrics 4003 cache size. See Documentation/networking/ip-sysctl.txt 4004 "tcp_no_metrics_save" section for more details. 4005 4006 tdfx= [HW,DRM] 4007 4008 test_suspend= [SUSPEND][,N] 4009 Specify "mem" (for Suspend-to-RAM) or "standby" (for 4010 standby suspend) or "freeze" (for suspend type freeze) 4011 as the system sleep state during system startup with 4012 the optional capability to repeat N number of times. 4013 The system is woken from this state using a 4014 wakeup-capable RTC alarm. 4015 4016 thash_entries= [KNL,NET] 4017 Set number of hash buckets for TCP connection 4018 4019 thermal.act= [HW,ACPI] 4020 -1: disable all active trip points in all thermal zones 4021 <degrees C>: override all lowest active trip points 4022 4023 thermal.crt= [HW,ACPI] 4024 -1: disable all critical trip points in all thermal zones 4025 <degrees C>: override all critical trip points 4026 4027 thermal.nocrt= [HW,ACPI] 4028 Set to disable actions on ACPI thermal zone 4029 critical and hot trip points. 4030 4031 thermal.off= [HW,ACPI] 4032 1: disable ACPI thermal control 4033 4034 thermal.psv= [HW,ACPI] 4035 -1: disable all passive trip points 4036 <degrees C>: override all passive trip points to this 4037 value 4038 4039 thermal.tzp= [HW,ACPI] 4040 Specify global default ACPI thermal zone polling rate 4041 <deci-seconds>: poll all this frequency 4042 0: no polling (default) 4043 4044 threadirqs [KNL] 4045 Force threading of all interrupt handlers except those 4046 marked explicitly IRQF_NO_THREAD. 4047 4048 tmem [KNL,XEN] 4049 Enable the Transcendent memory driver if built-in. 4050 4051 tmem.cleancache=0|1 [KNL, XEN] 4052 Default is on (1). Disable the usage of the cleancache 4053 API to send anonymous pages to the hypervisor. 4054 4055 tmem.frontswap=0|1 [KNL, XEN] 4056 Default is on (1). Disable the usage of the frontswap 4057 API to send swap pages to the hypervisor. If disabled 4058 the selfballooning and selfshrinking are force disabled. 4059 4060 tmem.selfballooning=0|1 [KNL, XEN] 4061 Default is on (1). Disable the driving of swap pages 4062 to the hypervisor. 4063 4064 tmem.selfshrinking=0|1 [KNL, XEN] 4065 Default is on (1). Partial swapoff that immediately 4066 transfers pages from Xen hypervisor back to the 4067 kernel based on different criteria. 4068 4069 topology= [S390] 4070 Format: {off | on} 4071 Specify if the kernel should make use of the cpu 4072 topology information if the hardware supports this. 4073 The scheduler will make use of this information and 4074 e.g. base its process migration decisions on it. 4075 Default is on. 4076 4077 topology_updates= [KNL, PPC, NUMA] 4078 Format: {off} 4079 Specify if the kernel should ignore (off) 4080 topology updates sent by the hypervisor to this 4081 LPAR. 4082 4083 tp720= [HW,PS2] 4084 4085 tpm_suspend_pcr=[HW,TPM] 4086 Format: integer pcr id 4087 Specify that at suspend time, the tpm driver 4088 should extend the specified pcr with zeros, 4089 as a workaround for some chips which fail to 4090 flush the last written pcr on TPM_SaveState. 4091 This will guarantee that all the other pcrs 4092 are saved. 4093 4094 trace_buf_size=nn[KMG] 4095 [FTRACE] will set tracing buffer size on each cpu. 4096 4097 trace_event=[event-list] 4098 [FTRACE] Set and start specified trace events in order 4099 to facilitate early boot debugging. The event-list is a 4100 comma separated list of trace events to enable. See 4101 also Documentation/trace/events.txt 4102 4103 trace_options=[option-list] 4104 [FTRACE] Enable or disable tracer options at boot. 4105 The option-list is a comma delimited list of options 4106 that can be enabled or disabled just as if you were 4107 to echo the option name into 4108 4109 /sys/kernel/debug/tracing/trace_options 4110 4111 For example, to enable stacktrace option (to dump the 4112 stack trace of each event), add to the command line: 4113 4114 trace_options=stacktrace 4115 4116 See also Documentation/trace/ftrace.txt "trace options" 4117 section. 4118 4119 tp_printk[FTRACE] 4120 Have the tracepoints sent to printk as well as the 4121 tracing ring buffer. This is useful for early boot up 4122 where the system hangs or reboots and does not give the 4123 option for reading the tracing buffer or performing a 4124 ftrace_dump_on_oops. 4125 4126 To turn off having tracepoints sent to printk, 4127 echo 0 > /proc/sys/kernel/tracepoint_printk 4128 Note, echoing 1 into this file without the 4129 tracepoint_printk kernel cmdline option has no effect. 4130 4131 ** CAUTION ** 4132 4133 Having tracepoints sent to printk() and activating high 4134 frequency tracepoints such as irq or sched, can cause 4135 the system to live lock. 4136 4137 traceoff_on_warning 4138 [FTRACE] enable this option to disable tracing when a 4139 warning is hit. This turns off "tracing_on". Tracing can 4140 be enabled again by echoing '1' into the "tracing_on" 4141 file located in /sys/kernel/debug/tracing/ 4142 4143 This option is useful, as it disables the trace before 4144 the WARNING dump is called, which prevents the trace to 4145 be filled with content caused by the warning output. 4146 4147 This option can also be set at run time via the sysctl 4148 option: kernel/traceoff_on_warning 4149 4150 transparent_hugepage= 4151 [KNL] 4152 Format: [always|madvise|never] 4153 Can be used to control the default behavior of the system 4154 with respect to transparent hugepages. 4155 See Documentation/vm/transhuge.txt for more details. 4156 4157 tsc= Disable clocksource stability checks for TSC. 4158 Format: <string> 4159 [x86] reliable: mark tsc clocksource as reliable, this 4160 disables clocksource verification at runtime, as well 4161 as the stability checks done at bootup. Used to enable 4162 high-resolution timer mode on older hardware, and in 4163 virtualized environment. 4164 [x86] noirqtime: Do not use TSC to do irq accounting. 4165 Used to run time disable IRQ_TIME_ACCOUNTING on any 4166 platforms where RDTSC is slow and this accounting 4167 can add overhead. 4168 4169 turbografx.map[2|3]= [HW,JOY] 4170 TurboGraFX parallel port interface 4171 Format: 4172 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 4173 See also Documentation/input/joystick-parport.txt 4174 4175 udbg-immortal [PPC] When debugging early kernel crashes that 4176 happen after console_init() and before a proper 4177 console driver takes over, this boot options might 4178 help "seeing" what's going on. 4179 4180 uhash_entries= [KNL,NET] 4181 Set number of hash buckets for UDP/UDP-Lite connections 4182 4183 uhci-hcd.ignore_oc= 4184 [USB] Ignore overcurrent events (default N). 4185 Some badly-designed motherboards generate lots of 4186 bogus events, for ports that aren't wired to 4187 anything. Set this parameter to avoid log spamming. 4188 Note that genuine overcurrent events won't be 4189 reported either. 4190 4191 unknown_nmi_panic 4192 [X86] Cause panic on unknown NMI. 4193 4194 usbcore.authorized_default= 4195 [USB] Default USB device authorization: 4196 (default -1 = authorized except for wireless USB, 4197 0 = not authorized, 1 = authorized) 4198 4199 usbcore.autosuspend= 4200 [USB] The autosuspend time delay (in seconds) used 4201 for newly-detected USB devices (default 2). This 4202 is the time required before an idle device will be 4203 autosuspended. Devices for which the delay is set 4204 to a negative value won't be autosuspended at all. 4205 4206 usbcore.usbfs_snoop= 4207 [USB] Set to log all usbfs traffic (default 0 = off). 4208 4209 usbcore.usbfs_snoop_max= 4210 [USB] Maximum number of bytes to snoop in each URB 4211 (default = 65536). 4212 4213 usbcore.blinkenlights= 4214 [USB] Set to cycle leds on hubs (default 0 = off). 4215 4216 usbcore.old_scheme_first= 4217 [USB] Start with the old device initialization 4218 scheme (default 0 = off). 4219 4220 usbcore.usbfs_memory_mb= 4221 [USB] Memory limit (in MB) for buffers allocated by 4222 usbfs (default = 16, 0 = max = 2047). 4223 4224 usbcore.use_both_schemes= 4225 [USB] Try the other device initialization scheme 4226 if the first one fails (default 1 = enabled). 4227 4228 usbcore.initial_descriptor_timeout= 4229 [USB] Specifies timeout for the initial 64-byte 4230 USB_REQ_GET_DESCRIPTOR request in milliseconds 4231 (default 5000 = 5.0 seconds). 4232 4233 usbcore.nousb [USB] Disable the USB subsystem 4234 4235 usbhid.mousepoll= 4236 [USBHID] The interval which mice are to be polled at. 4237 4238 usbhid.jspoll= 4239 [USBHID] The interval which joysticks are to be polled at. 4240 4241 usb-storage.delay_use= 4242 [UMS] The delay in seconds before a new device is 4243 scanned for Logical Units (default 1). 4244 4245 usb-storage.quirks= 4246 [UMS] A list of quirks entries to supplement or 4247 override the built-in unusual_devs list. List 4248 entries are separated by commas. Each entry has 4249 the form VID:PID:Flags where VID and PID are Vendor 4250 and Product ID values (4-digit hex numbers) and 4251 Flags is a set of characters, each corresponding 4252 to a common usb-storage quirk flag as follows: 4253 a = SANE_SENSE (collect more than 18 bytes 4254 of sense data); 4255 b = BAD_SENSE (don't collect more than 18 4256 bytes of sense data); 4257 c = FIX_CAPACITY (decrease the reported 4258 device capacity by one sector); 4259 d = NO_READ_DISC_INFO (don't use 4260 READ_DISC_INFO command); 4261 e = NO_READ_CAPACITY_16 (don't use 4262 READ_CAPACITY_16 command); 4263 f = NO_REPORT_OPCODES (don't use report opcodes 4264 command, uas only); 4265 g = MAX_SECTORS_240 (don't transfer more than 4266 240 sectors at a time, uas only); 4267 h = CAPACITY_HEURISTICS (decrease the 4268 reported device capacity by one 4269 sector if the number is odd); 4270 i = IGNORE_DEVICE (don't bind to this 4271 device); 4272 j = NO_REPORT_LUNS (don't use report luns 4273 command, uas only); 4274 l = NOT_LOCKABLE (don't try to lock and 4275 unlock ejectable media); 4276 m = MAX_SECTORS_64 (don't transfer more 4277 than 64 sectors = 32 KB at a time); 4278 n = INITIAL_READ10 (force a retry of the 4279 initial READ(10) command); 4280 o = CAPACITY_OK (accept the capacity 4281 reported by the device); 4282 p = WRITE_CACHE (the device cache is ON 4283 by default); 4284 r = IGNORE_RESIDUE (the device reports 4285 bogus residue values); 4286 s = SINGLE_LUN (the device has only one 4287 Logical Unit); 4288 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 4289 commands, uas only); 4290 u = IGNORE_UAS (don't bind to the uas driver); 4291 w = NO_WP_DETECT (don't test whether the 4292 medium is write-protected). 4293 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 4294 even if the device claims no cache) 4295 Example: quirks=0419:aaf5:rl,0421:0433:rc 4296 4297 user_debug= [KNL,ARM] 4298 Format: <int> 4299 See arch/arm/Kconfig.debug help text. 4300 1 - undefined instruction events 4301 2 - system calls 4302 4 - invalid data aborts 4303 8 - SIGSEGV faults 4304 16 - SIGBUS faults 4305 Example: user_debug=31 4306 4307 userpte= 4308 [X86] Flags controlling user PTE allocations. 4309 4310 nohigh = do not allocate PTE pages in 4311 HIGHMEM regardless of setting 4312 of CONFIG_HIGHPTE. 4313 4314 vdso= [X86,SH] 4315 On X86_32, this is an alias for vdso32=. Otherwise: 4316 4317 vdso=1: enable VDSO (the default) 4318 vdso=0: disable VDSO mapping 4319 4320 vdso32= [X86] Control the 32-bit vDSO 4321 vdso32=1: enable 32-bit VDSO 4322 vdso32=0 or vdso32=2: disable 32-bit VDSO 4323 4324 See the help text for CONFIG_COMPAT_VDSO for more 4325 details. If CONFIG_COMPAT_VDSO is set, the default is 4326 vdso32=0; otherwise, the default is vdso32=1. 4327 4328 For compatibility with older kernels, vdso32=2 is an 4329 alias for vdso32=0. 4330 4331 Try vdso32=0 if you encounter an error that says: 4332 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 4333 4334 vector= [IA-64,SMP] 4335 vector=percpu: enable percpu vector domain 4336 4337 video= [FB] Frame buffer configuration 4338 See Documentation/fb/modedb.txt. 4339 4340 video.brightness_switch_enabled= [0,1] 4341 If set to 1, on receiving an ACPI notify event 4342 generated by hotkey, video driver will adjust brightness 4343 level and then send out the event to user space through 4344 the allocated input device; If set to 0, video driver 4345 will only send out the event without touching backlight 4346 brightness level. 4347 default: 1 4348 4349 virtio_mmio.device= 4350 [VMMIO] Memory mapped virtio (platform) device. 4351 4352 <size>@<baseaddr>:<irq>[:<id>] 4353 where: 4354 <size> := size (can use standard suffixes 4355 like K, M and G) 4356 <baseaddr> := physical base address 4357 <irq> := interrupt number (as passed to 4358 request_irq()) 4359 <id> := (optional) platform device id 4360 example: 4361 virtio_mmio.device=1K@0x100b0000:48:7 4362 4363 Can be used multiple times for multiple devices. 4364 4365 vga= [BOOT,X86-32] Select a particular video mode 4366 See Documentation/x86/boot.txt and 4367 Documentation/svga.txt. 4368 Use vga=ask for menu. 4369 This is actually a boot loader parameter; the value is 4370 passed to the kernel using a special protocol. 4371 4372 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact 4373 size of <nn>. This can be used to increase the 4374 minimum size (128MB on x86). It can also be used to 4375 decrease the size and leave more room for directly 4376 mapped kernel RAM. 4377 4378 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 4379 Format: <command> 4380 4381 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 4382 Format: <command> 4383 4384 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 4385 Format: <command> 4386 4387 vsyscall= [X86-64] 4388 Controls the behavior of vsyscalls (i.e. calls to 4389 fixed addresses of 0xffffffffff600x00 from legacy 4390 code). Most statically-linked binaries and older 4391 versions of glibc use these calls. Because these 4392 functions are at fixed addresses, they make nice 4393 targets for exploits that can control RIP. 4394 4395 emulate [default] Vsyscalls turn into traps and are 4396 emulated reasonably safely. 4397 4398 native Vsyscalls are native syscall instructions. 4399 This is a little bit faster than trapping 4400 and makes a few dynamic recompilers work 4401 better than they would in emulation mode. 4402 It also makes exploits much easier to write. 4403 4404 none Vsyscalls don't work at all. This makes 4405 them quite hard to use for exploits but 4406 might break your system. 4407 4408 vt.color= [VT] Default text color. 4409 Format: 0xYX, X = foreground, Y = background. 4410 Default: 0x07 = light gray on black. 4411 4412 vt.cur_default= [VT] Default cursor shape. 4413 Format: 0xCCBBAA, where AA, BB, and CC are the same as 4414 the parameters of the <Esc>[?A;B;Cc escape sequence; 4415 see VGA-softcursor.txt. Default: 2 = underline. 4416 4417 vt.default_blu= [VT] 4418 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 4419 Change the default blue palette of the console. 4420 This is a 16-member array composed of values 4421 ranging from 0-255. 4422 4423 vt.default_grn= [VT] 4424 Format: <green0>,<green1>,<green2>,...,<green15> 4425 Change the default green palette of the console. 4426 This is a 16-member array composed of values 4427 ranging from 0-255. 4428 4429 vt.default_red= [VT] 4430 Format: <red0>,<red1>,<red2>,...,<red15> 4431 Change the default red palette of the console. 4432 This is a 16-member array composed of values 4433 ranging from 0-255. 4434 4435 vt.default_utf8= 4436 [VT] 4437 Format=<0|1> 4438 Set system-wide default UTF-8 mode for all tty's. 4439 Default is 1, i.e. UTF-8 mode is enabled for all 4440 newly opened terminals. 4441 4442 vt.global_cursor_default= 4443 [VT] 4444 Format=<-1|0|1> 4445 Set system-wide default for whether a cursor 4446 is shown on new VTs. Default is -1, 4447 i.e. cursors will be created by default unless 4448 overridden by individual drivers. 0 will hide 4449 cursors, 1 will display them. 4450 4451 vt.italic= [VT] Default color for italic text; 0-15. 4452 Default: 2 = green. 4453 4454 vt.underline= [VT] Default color for underlined text; 0-15. 4455 Default: 3 = cyan. 4456 4457 watchdog timers [HW,WDT] For information on watchdog timers, 4458 see Documentation/watchdog/watchdog-parameters.txt 4459 or other driver-specific files in the 4460 Documentation/watchdog/ directory. 4461 4462 workqueue.watchdog_thresh= 4463 If CONFIG_WQ_WATCHDOG is configured, workqueue can 4464 warn stall conditions and dump internal state to 4465 help debugging. 0 disables workqueue stall 4466 detection; otherwise, it's the stall threshold 4467 duration in seconds. The default value is 30 and 4468 it can be updated at runtime by writing to the 4469 corresponding sysfs file. 4470 4471 workqueue.disable_numa 4472 By default, all work items queued to unbound 4473 workqueues are affine to the NUMA nodes they're 4474 issued on, which results in better behavior in 4475 general. If NUMA affinity needs to be disabled for 4476 whatever reason, this option can be used. Note 4477 that this also can be controlled per-workqueue for 4478 workqueues visible under /sys/bus/workqueue/. 4479 4480 workqueue.power_efficient 4481 Per-cpu workqueues are generally preferred because 4482 they show better performance thanks to cache 4483 locality; unfortunately, per-cpu workqueues tend to 4484 be more power hungry than unbound workqueues. 4485 4486 Enabling this makes the per-cpu workqueues which 4487 were observed to contribute significantly to power 4488 consumption unbound, leading to measurably lower 4489 power usage at the cost of small performance 4490 overhead. 4491 4492 The default value of this parameter is determined by 4493 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 4494 4495 workqueue.debug_force_rr_cpu 4496 Workqueue used to implicitly guarantee that work 4497 items queued without explicit CPU specified are put 4498 on the local CPU. This guarantee is no longer true 4499 and while local CPU is still preferred work items 4500 may be put on foreign CPUs. This debug option 4501 forces round-robin CPU selection to flush out 4502 usages which depend on the now broken guarantee. 4503 When enabled, memory and cache locality will be 4504 impacted. 4505 4506 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of 4507 default x2apic cluster mode on platforms 4508 supporting x2apic. 4509 4510 x86_intel_mid_timer= [X86-32,APBT] 4511 Choose timer option for x86 Intel MID platform. 4512 Two valid options are apbt timer only and lapic timer 4513 plus one apbt timer for broadcast timer. 4514 x86_intel_mid_timer=apbt_only | lapic_and_apbt 4515 4516 xen_512gb_limit [KNL,X86-64,XEN] 4517 Restricts the kernel running paravirtualized under Xen 4518 to use only up to 512 GB of RAM. The reason to do so is 4519 crash analysis tools and Xen tools for doing domain 4520 save/restore/migration must be enabled to handle larger 4521 domains. 4522 4523 xen_emul_unplug= [HW,X86,XEN] 4524 Unplug Xen emulated devices 4525 Format: [unplug0,][unplug1] 4526 ide-disks -- unplug primary master IDE devices 4527 aux-ide-disks -- unplug non-primary-master IDE devices 4528 nics -- unplug network devices 4529 all -- unplug all emulated devices (NICs and IDE disks) 4530 unnecessary -- unplugging emulated devices is 4531 unnecessary even if the host did not respond to 4532 the unplug protocol 4533 never -- do not unplug even if version check succeeds 4534 4535 xen_nopvspin [X86,XEN] 4536 Disables the ticketlock slowpath using Xen PV 4537 optimizations. 4538 4539 xen_nopv [X86] 4540 Disables the PV optimizations forcing the HVM guest to 4541 run as generic HVM guest with no PV drivers. 4542 4543 xirc2ps_cs= [NET,PCMCIA] 4544 Format: 4545 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 4546