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> 117 118 acpi_no_auto_serialize [HW,ACPI] 119 Disable auto-serialization of AML methods 120 AML control methods that contain the opcodes to create 121 named objects will be marked as "Serialized" by the 122 auto-serialization feature. 123 This feature is enabled by default. 124 This option allows to turn off the feature. 125 126 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump 127 kernels. 128 129 acpi_no_static_ssdt [HW,ACPI] 130 Disable installation of static SSDTs at early boot time 131 By default, SSDTs contained in the RSDT/XSDT will be 132 installed automatically and they will appear under 133 /sys/firmware/acpi/tables. 134 This option turns off this feature. 135 Note that specifying this option does not affect 136 dynamic table installation which will install SSDT 137 tables to /sys/firmware/acpi/tables/dynamic. 138 139 acpi_rsdp= [ACPI,EFI,KEXEC] 140 Pass the RSDP address to the kernel, mostly used 141 on machines running EFI runtime service to boot the 142 second kernel for kdump. 143 144 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS 145 Format: To spoof as Windows 98: ="Microsoft Windows" 146 147 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead 148 of 2 which is mandated by ACPI 6) as the supported ACPI 149 specification revision (when using this switch, it may 150 be necessary to carry out a cold reboot _twice_ in a 151 row to make it take effect on the platform firmware). 152 153 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings 154 acpi_osi="string1" # add string1 155 acpi_osi="!string2" # remove string2 156 acpi_osi=!* # remove all strings 157 acpi_osi=! # disable all built-in OS vendor 158 strings 159 acpi_osi=!! # enable all built-in OS vendor 160 strings 161 acpi_osi= # disable all strings 162 163 'acpi_osi=!' can be used in combination with single or 164 multiple 'acpi_osi="string1"' to support specific OS 165 vendor string(s). Note that such command can only 166 affect the default state of the OS vendor strings, thus 167 it cannot affect the default state of the feature group 168 strings and the current state of the OS vendor strings, 169 specifying it multiple times through kernel command line 170 is meaningless. This command is useful when one do not 171 care about the state of the feature group strings which 172 should be controlled by the OSPM. 173 Examples: 174 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent 175 to 'acpi_osi="Windows 2000" acpi_osi=!', they all 176 can make '_OSI("Windows 2000")' TRUE. 177 178 'acpi_osi=' cannot be used in combination with other 179 'acpi_osi=' command lines, the _OSI method will not 180 exist in the ACPI namespace. NOTE that such command can 181 only affect the _OSI support state, thus specifying it 182 multiple times through kernel command line is also 183 meaningless. 184 Examples: 185 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)' 186 FALSE. 187 188 'acpi_osi=!*' can be used in combination with single or 189 multiple 'acpi_osi="string1"' to support specific 190 string(s). Note that such command can affect the 191 current state of both the OS vendor strings and the 192 feature group strings, thus specifying it multiple times 193 through kernel command line is meaningful. But it may 194 still not able to affect the final state of a string if 195 there are quirks related to this string. This command 196 is useful when one want to control the state of the 197 feature group strings to debug BIOS issues related to 198 the OSPM features. 199 Examples: 200 1. 'acpi_osi="Module Device" acpi_osi=!*' can make 201 '_OSI("Module Device")' FALSE. 202 2. 'acpi_osi=!* acpi_osi="Module Device"' can make 203 '_OSI("Module Device")' TRUE. 204 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is 205 equivalent to 206 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"' 207 and 208 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!', 209 they all will make '_OSI("Windows 2000")' TRUE. 210 211 acpi_pm_good [X86] 212 Override the pmtimer bug detection: force the kernel 213 to assume that this machine's pmtimer latches its value 214 and always returns good values. 215 216 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode 217 Format: { level | edge | high | low } 218 219 acpi_skip_timer_override [HW,ACPI] 220 Recognize and ignore IRQ0/pin2 Interrupt Override. 221 For broken nForce2 BIOS resulting in XT-PIC timer. 222 223 acpi_sleep= [HW,ACPI] Sleep options 224 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig, 225 old_ordering, nonvs, sci_force_enable, nobl } 226 See Documentation/power/video.txt for information on 227 s3_bios and s3_mode. 228 s3_beep is for debugging; it makes the PC's speaker beep 229 as soon as the kernel's real-mode entry point is called. 230 s4_nohwsig prevents ACPI hardware signature from being 231 used during resume from hibernation. 232 old_ordering causes the ACPI 1.0 ordering of the _PTS 233 control method, with respect to putting devices into 234 low power states, to be enforced (the ACPI 2.0 ordering 235 of _PTS is used by default). 236 nonvs prevents the kernel from saving/restoring the 237 ACPI NVS memory during suspend/hibernation and resume. 238 sci_force_enable causes the kernel to set SCI_EN directly 239 on resume from S1/S3 (which is against the ACPI spec, 240 but some broken systems don't work without it). 241 nobl causes the internal blacklist of systems known to 242 behave incorrectly in some ways with respect to system 243 suspend and resume to be ignored (use wisely). 244 245 acpi_use_timer_override [HW,ACPI] 246 Use timer override. For some broken Nvidia NF5 boards 247 that require a timer override, but don't have HPET 248 249 add_efi_memmap [EFI; X86] Include EFI memory map in 250 kernel's map of available physical RAM. 251 252 agp= [AGP] 253 { off | try_unsupported } 254 off: disable AGP support 255 try_unsupported: try to drive unsupported chipsets 256 (may crash computer or cause data corruption) 257 258 ALSA [HW,ALSA] 259 See Documentation/sound/alsa-configuration.rst 260 261 alignment= [KNL,ARM] 262 Allow the default userspace alignment fault handler 263 behaviour to be specified. Bit 0 enables warnings, 264 bit 1 enables fixups, and bit 2 sends a segfault. 265 266 align_va_addr= [X86-64] 267 Align virtual addresses by clearing slice [14:12] when 268 allocating a VMA at process creation time. This option 269 gives you up to 3% performance improvement on AMD F15h 270 machines (where it is enabled by default) for a 271 CPU-intensive style benchmark, and it can vary highly in 272 a microbenchmark depending on workload and compiler. 273 274 32: only for 32-bit processes 275 64: only for 64-bit processes 276 on: enable for both 32- and 64-bit processes 277 off: disable for both 32- and 64-bit processes 278 279 alloc_snapshot [FTRACE] 280 Allocate the ftrace snapshot buffer on boot up when the 281 main buffer is allocated. This is handy if debugging 282 and you need to use tracing_snapshot() on boot up, and 283 do not want to use tracing_snapshot_alloc() as it needs 284 to be done where GFP_KERNEL allocations are allowed. 285 286 amd_iommu= [HW,X86-64] 287 Pass parameters to the AMD IOMMU driver in the system. 288 Possible values are: 289 fullflush - enable flushing of IO/TLB entries when 290 they are unmapped. Otherwise they are 291 flushed before they will be reused, which 292 is a lot of faster 293 off - do not initialize any AMD IOMMU found in 294 the system 295 force_isolation - Force device isolation for all 296 devices. The IOMMU driver is not 297 allowed anymore to lift isolation 298 requirements as needed. This option 299 does not override iommu=pt 300 301 amd_iommu_dump= [HW,X86-64] 302 Enable AMD IOMMU driver option to dump the ACPI table 303 for AMD IOMMU. With this option enabled, AMD IOMMU 304 driver will print ACPI tables for AMD IOMMU during 305 IOMMU initialization. 306 307 amd_iommu_intr= [HW,X86-64] 308 Specifies one of the following AMD IOMMU interrupt 309 remapping modes: 310 legacy - Use legacy interrupt remapping mode. 311 vapic - Use virtual APIC mode, which allows IOMMU 312 to inject interrupts directly into guest. 313 This mode requires kvm-amd.avic=1. 314 (Default when IOMMU HW support is present.) 315 316 amijoy.map= [HW,JOY] Amiga joystick support 317 Map of devices attached to JOY0DAT and JOY1DAT 318 Format: <a>,<b> 319 See also Documentation/input/joydev/joystick.rst 320 321 analog.map= [HW,JOY] Analog joystick and gamepad support 322 Specifies type or capabilities of an analog joystick 323 connected to one of 16 gameports 324 Format: <type1>,<type2>,..<type16> 325 326 apc= [HW,SPARC] 327 Power management functions (SPARCstation-4/5 + deriv.) 328 Format: noidle 329 Disable APC CPU standby support. SPARCstation-Fox does 330 not play well with APC CPU idle - disable it if you have 331 APC and your system crashes randomly. 332 333 apic= [APIC,X86] Advanced Programmable Interrupt Controller 334 Change the output verbosity while booting 335 Format: { quiet (default) | verbose | debug } 336 Change the amount of debugging information output 337 when initialising the APIC and IO-APIC components. 338 For X86-32, this can also be used to specify an APIC 339 driver name. 340 Format: apic=driver_name 341 Examples: apic=bigsmp 342 343 apic_extnmi= [APIC,X86] External NMI delivery setting 344 Format: { bsp (default) | all | none } 345 bsp: External NMI is delivered only to CPU 0 346 all: External NMIs are broadcast to all CPUs as a 347 backup of CPU 0 348 none: External NMI is masked for all CPUs. This is 349 useful so that a dump capture kernel won't be 350 shot down by NMI 351 352 autoconf= [IPV6] 353 See Documentation/networking/ipv6.txt. 354 355 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller 356 Limit apic dumping. The parameter defines the maximal 357 number of local apics being dumped. Also it is possible 358 to set it to "all" by meaning -- no limit here. 359 Format: { 1 (default) | 2 | ... | all }. 360 The parameter valid if only apic=debug or 361 apic=verbose is specified. 362 Example: apic=debug show_lapic=all 363 364 apm= [APM] Advanced Power Management 365 See header of arch/x86/kernel/apm_32.c. 366 367 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards 368 Format: <io>,<irq>,<nodeID> 369 370 ataflop= [HW,M68k] 371 372 atarimouse= [HW,MOUSE] Atari Mouse 373 374 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess, 375 EzKey and similar keyboards 376 377 atkbd.reset= [HW] Reset keyboard during initialization 378 379 atkbd.set= [HW] Select keyboard code set 380 Format: <int> (2 = AT (default), 3 = PS/2) 381 382 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar 383 keyboards 384 385 atkbd.softraw= [HW] Choose between synthetic and real raw mode 386 Format: <bool> (0 = real, 1 = synthetic (default)) 387 388 atkbd.softrepeat= [HW] 389 Use software keyboard repeat 390 391 audit= [KNL] Enable the audit sub-system 392 Format: { "0" | "1" | "off" | "on" } 393 0 | off - kernel audit is disabled and can not be 394 enabled until the next reboot 395 unset - kernel audit is initialized but disabled and 396 will be fully enabled by the userspace auditd. 397 1 | on - kernel audit is initialized and partially 398 enabled, storing at most audit_backlog_limit 399 messages in RAM until it is fully enabled by the 400 userspace auditd. 401 Default: unset 402 403 audit_backlog_limit= [KNL] Set the audit queue size limit. 404 Format: <int> (must be >=0) 405 Default: 64 406 407 bau= [X86_UV] Enable the BAU on SGI UV. The default 408 behavior is to disable the BAU (i.e. bau=0). 409 Format: { "0" | "1" } 410 0 - Disable the BAU. 411 1 - Enable the BAU. 412 unset - Disable the BAU. 413 414 baycom_epp= [HW,AX25] 415 Format: <io>,<mode> 416 417 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem 418 Format: <io>,<mode> 419 See header of drivers/net/hamradio/baycom_par.c. 420 421 baycom_ser_fdx= [HW,AX25] 422 BayCom Serial Port AX.25 Modem (Full Duplex Mode) 423 Format: <io>,<irq>,<mode>[,<baud>] 424 See header of drivers/net/hamradio/baycom_ser_fdx.c. 425 426 baycom_ser_hdx= [HW,AX25] 427 BayCom Serial Port AX.25 Modem (Half Duplex Mode) 428 Format: <io>,<irq>,<mode> 429 See header of drivers/net/hamradio/baycom_ser_hdx.c. 430 431 blkdevparts= Manual partition parsing of block device(s) for 432 embedded devices based on command line input. 433 See Documentation/block/cmdline-partition.txt 434 435 boot_delay= Milliseconds to delay each printk during boot. 436 Values larger than 10 seconds (10000) are changed to 437 no delay (0). 438 Format: integer 439 440 bootmem_debug [KNL] Enable bootmem allocator debug messages. 441 442 bert_disable [ACPI] 443 Disable BERT OS support on buggy BIOSes. 444 445 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards) 446 bttv.radio= Most important insmod options are available as 447 kernel args too. 448 bttv.pll= See Documentation/media/v4l-drivers/bttv.rst 449 bttv.tuner= 450 451 bulk_remove=off [PPC] This parameter disables the use of the pSeries 452 firmware feature for flushing multiple hpte entries 453 at a time. 454 455 c101= [NET] Moxa C101 synchronous serial card 456 457 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection. 458 Sometimes CPU hardware bugs make them report the cache 459 size incorrectly. The kernel will attempt work arounds 460 to fix known problems, but for some CPUs it is not 461 possible to determine what the correct size should be. 462 This option provides an override for these situations. 463 464 ca_keys= [KEYS] This parameter identifies a specific key(s) on 465 the system trusted keyring to be used for certificate 466 trust validation. 467 format: { id:<keyid> | builtin } 468 469 cca= [MIPS] Override the kernel pages' cache coherency 470 algorithm. Accepted values range from 0 to 7 471 inclusive. See arch/mips/include/asm/pgtable-bits.h 472 for platform specific values (SB1, Loongson3 and 473 others). 474 475 ccw_timeout_log [S390] 476 See Documentation/s390/CommonIO for details. 477 478 cgroup_disable= [KNL] Disable a particular controller 479 Format: {name of the controller(s) to disable} 480 The effects of cgroup_disable=foo are: 481 - foo isn't auto-mounted if you mount all cgroups in 482 a single hierarchy 483 - foo isn't visible as an individually mountable 484 subsystem 485 {Currently only "memory" controller deal with this and 486 cut the overhead, others just disable the usage. So 487 only cgroup_disable=memory is actually worthy} 488 489 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1 490 Format: { { controller | "all" | "named" } 491 [,{ controller | "all" | "named" }...] } 492 Like cgroup_disable, but only applies to cgroup v1; 493 the blacklisted controllers remain available in cgroup2. 494 "all" blacklists all controllers and "named" disables 495 named mounts. Specifying both "all" and "named" disables 496 all v1 hierarchies. 497 498 cgroup.memory= [KNL] Pass options to the cgroup memory controller. 499 Format: <string> 500 nosocket -- Disable socket memory accounting. 501 nokmem -- Disable kernel memory accounting. 502 503 checkreqprot [SELINUX] Set initial checkreqprot flag value. 504 Format: { "0" | "1" } 505 See security/selinux/Kconfig help text. 506 0 -- check protection applied by kernel (includes 507 any implied execute protection). 508 1 -- check protection requested by application. 509 Default value is set via a kernel config option. 510 Value can be changed at runtime via 511 /selinux/checkreqprot. 512 513 cio_ignore= [S390] 514 See Documentation/s390/CommonIO for details. 515 clk_ignore_unused 516 [CLK] 517 Prevents the clock framework from automatically gating 518 clocks that have not been explicitly enabled by a Linux 519 device driver but are enabled in hardware at reset or 520 by the bootloader/firmware. Note that this does not 521 force such clocks to be always-on nor does it reserve 522 those clocks in any way. This parameter is useful for 523 debug and development, but should not be needed on a 524 platform with proper driver support. For more 525 information, see Documentation/driver-api/clk.rst. 526 527 clock= [BUGS=X86-32, HW] gettimeofday clocksource override. 528 [Deprecated] 529 Forces specified clocksource (if available) to be used 530 when calculating gettimeofday(). If specified 531 clocksource is not available, it defaults to PIT. 532 Format: { pit | tsc | cyclone | pmtmr } 533 534 clocksource= Override the default clocksource 535 Format: <string> 536 Override the default clocksource and use the clocksource 537 with the name specified. 538 Some clocksource names to choose from, depending on 539 the platform: 540 [all] jiffies (this is the base, fallback clocksource) 541 [ACPI] acpi_pm 542 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2, 543 pxa_timer,timer3,32k_counter,timer0_1 544 [X86-32] pit,hpet,tsc; 545 scx200_hrt on Geode; cyclone on IBM x440 546 [MIPS] MIPS 547 [PARISC] cr16 548 [S390] tod 549 [SH] SuperH 550 [SPARC64] tick 551 [X86-64] hpet,tsc 552 553 clocksource.arm_arch_timer.evtstrm= 554 [ARM,ARM64] 555 Format: <bool> 556 Enable/disable the eventstream feature of the ARM 557 architected timer so that code using WFE-based polling 558 loops can be debugged more effectively on production 559 systems. 560 561 clearcpuid=BITNUM [X86] 562 Disable CPUID feature X for the kernel. See 563 arch/x86/include/asm/cpufeatures.h for the valid bit 564 numbers. Note the Linux specific bits are not necessarily 565 stable over kernel options, but the vendor specific 566 ones should be. 567 Also note that user programs calling CPUID directly 568 or using the feature without checking anything 569 will still see it. This just prevents it from 570 being used by the kernel or shown in /proc/cpuinfo. 571 Also note the kernel might malfunction if you disable 572 some critical bits. 573 574 cma=nn[MG]@[start[MG][-end[MG]]] 575 [ARM,X86,KNL] 576 Sets the size of kernel global memory area for 577 contiguous memory allocations and optionally the 578 placement constraint by the physical address range of 579 memory allocations. A value of 0 disables CMA 580 altogether. For more information, see 581 include/linux/dma-contiguous.h 582 583 cmo_free_hint= [PPC] Format: { yes | no } 584 Specify whether pages are marked as being inactive 585 when they are freed. This is used in CMO environments 586 to determine OS memory pressure for page stealing by 587 a hypervisor. 588 Default: yes 589 590 coherent_pool=nn[KMG] [ARM,KNL] 591 Sets the size of memory pool for coherent, atomic dma 592 allocations, by default set to 256K. 593 594 com20020= [HW,NET] ARCnet - COM20020 chipset 595 Format: 596 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]] 597 598 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers) 599 Format: <io>[,<irq>] 600 601 com90xx= [HW,NET] 602 ARCnet - COM90xx chipset (memory-mapped buffers) 603 Format: <io>[,<irq>[,<memstart>]] 604 605 condev= [HW,S390] console device 606 conmode= 607 608 console= [KNL] Output console device and options. 609 610 tty<n> Use the virtual console device <n>. 611 612 ttyS<n>[,options] 613 ttyUSB0[,options] 614 Use the specified serial port. The options are of 615 the form "bbbbpnf", where "bbbb" is the baud rate, 616 "p" is parity ("n", "o", or "e"), "n" is number of 617 bits, and "f" is flow control ("r" for RTS or 618 omit it). Default is "9600n8". 619 620 See Documentation/admin-guide/serial-console.rst for more 621 information. See 622 Documentation/networking/netconsole.txt for an 623 alternative. 624 625 uart[8250],io,<addr>[,options] 626 uart[8250],mmio,<addr>[,options] 627 uart[8250],mmio16,<addr>[,options] 628 uart[8250],mmio32,<addr>[,options] 629 uart[8250],0x<addr>[,options] 630 Start an early, polled-mode console on the 8250/16550 631 UART at the specified I/O port or MMIO address, 632 switching to the matching ttyS device later. 633 MMIO inter-register address stride is either 8-bit 634 (mmio), 16-bit (mmio16), or 32-bit (mmio32). 635 If none of [io|mmio|mmio16|mmio32], <addr> is assumed 636 to be equivalent to 'mmio'. 'options' are specified in 637 the same format described for ttyS above; if unspecified, 638 the h/w is not re-initialized. 639 640 hvc<n> Use the hypervisor console device <n>. This is for 641 both Xen and PowerPC hypervisors. 642 643 If the device connected to the port is not a TTY but a braille 644 device, prepend "brl," before the device type, for instance 645 console=brl,ttyS0 646 For now, only VisioBraille is supported. 647 648 console_msg_format= 649 [KNL] Change console messages format 650 default 651 By default we print messages on consoles in 652 "[time stamp] text\n" format (time stamp may not be 653 printed, depending on CONFIG_PRINTK_TIME or 654 `printk_time' param). 655 syslog 656 Switch to syslog format: "<%u>[time stamp] text\n" 657 IOW, each message will have a facility and loglevel 658 prefix. The format is similar to one used by syslog() 659 syscall, or to executing "dmesg -S --raw" or to reading 660 from /proc/kmsg. 661 662 consoleblank= [KNL] The console blank (screen saver) timeout in 663 seconds. A value of 0 disables the blank timer. 664 Defaults to 0. 665 666 coredump_filter= 667 [KNL] Change the default value for 668 /proc/<pid>/coredump_filter. 669 See also Documentation/filesystems/proc.txt. 670 671 coresight_cpu_debug.enable 672 [ARM,ARM64] 673 Format: <bool> 674 Enable/disable the CPU sampling based debugging. 675 0: default value, disable debugging 676 1: enable debugging at boot time 677 678 cpuidle.off=1 [CPU_IDLE] 679 disable the cpuidle sub-system 680 681 cpuidle.governor= 682 [CPU_IDLE] Name of the cpuidle governor to use. 683 684 cpufreq.off=1 [CPU_FREQ] 685 disable the cpufreq sub-system 686 687 cpu_init_udelay=N 688 [X86] Delay for N microsec between assert and de-assert 689 of APIC INIT to start processors. This delay occurs 690 on every CPU online, such as boot, and resume from suspend. 691 Default: 10000 692 693 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver 694 Format: 695 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] 696 697 crashkernel=size[KMG][@offset[KMG]] 698 [KNL] Using kexec, Linux can switch to a 'crash kernel' 699 upon panic. This parameter reserves the physical 700 memory region [offset, offset + size] for that kernel 701 image. If '@offset' is omitted, then a suitable offset 702 is selected automatically. Check 703 Documentation/kdump/kdump.txt for further details. 704 705 crashkernel=range1:size1[,range2:size2,...][@offset] 706 [KNL] Same as above, but depends on the memory 707 in the running system. The syntax of range is 708 start-[end] where start and end are both 709 a memory unit (amount[KMG]). See also 710 Documentation/kdump/kdump.txt for an example. 711 712 crashkernel=size[KMG],high 713 [KNL, x86_64] range could be above 4G. Allow kernel 714 to allocate physical memory region from top, so could 715 be above 4G if system have more than 4G ram installed. 716 Otherwise memory region will be allocated below 4G, if 717 available. 718 It will be ignored if crashkernel=X is specified. 719 crashkernel=size[KMG],low 720 [KNL, x86_64] range under 4G. When crashkernel=X,high 721 is passed, kernel could allocate physical memory region 722 above 4G, that cause second kernel crash on system 723 that require some amount of low memory, e.g. swiotlb 724 requires at least 64M+32K low memory, also enough extra 725 low memory is needed to make sure DMA buffers for 32-bit 726 devices won't run out. Kernel would try to allocate at 727 at least 256M below 4G automatically. 728 This one let user to specify own low range under 4G 729 for second kernel instead. 730 0: to disable low allocation. 731 It will be ignored when crashkernel=X,high is not used 732 or memory reserved is below 4G. 733 734 cryptomgr.notests 735 [KNL] Disable crypto self-tests 736 737 cs89x0_dma= [HW,NET] 738 Format: <dma> 739 740 cs89x0_media= [HW,NET] 741 Format: { rj45 | aui | bnc } 742 743 dasd= [HW,NET] 744 See header of drivers/s390/block/dasd_devmap.c. 745 746 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port 747 (one device per port) 748 Format: <port#>,<type> 749 See also Documentation/input/devices/joystick-parport.rst 750 751 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot 752 time. See 753 Documentation/admin-guide/dynamic-debug-howto.rst for 754 details. Deprecated, see dyndbg. 755 756 debug [KNL] Enable kernel debugging (events log level). 757 758 debug_boot_weak_hash 759 [KNL] Enable printing [hashed] pointers early in the 760 boot sequence. If enabled, we use a weak hash instead 761 of siphash to hash pointers. Use this option if you are 762 seeing instances of '(___ptrval___)') and need to see a 763 value (hashed pointer) instead. Cryptographically 764 insecure, please do not use on production kernels. 765 766 debug_locks_verbose= 767 [KNL] verbose self-tests 768 Format=<0|1> 769 Print debugging info while doing the locking API 770 self-tests. 771 We default to 0 (no extra messages), setting it to 772 1 will print _a lot_ more information - normally 773 only useful to kernel developers. 774 775 debug_objects [KNL] Enable object debugging 776 777 no_debug_objects 778 [KNL] Disable object debugging 779 780 debug_guardpage_minorder= 781 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this 782 parameter allows control of the order of pages that will 783 be intentionally kept free (and hence protected) by the 784 buddy allocator. Bigger value increase the probability 785 of catching random memory corruption, but reduce the 786 amount of memory for normal system use. The maximum 787 possible value is MAX_ORDER/2. Setting this parameter 788 to 1 or 2 should be enough to identify most random 789 memory corruption problems caused by bugs in kernel or 790 driver code when a CPU writes to (or reads from) a 791 random memory location. Note that there exists a class 792 of memory corruptions problems caused by buggy H/W or 793 F/W or by drivers badly programing DMA (basically when 794 memory is written at bus level and the CPU MMU is 795 bypassed) which are not detectable by 796 CONFIG_DEBUG_PAGEALLOC, hence this option will not help 797 tracking down these problems. 798 799 debug_pagealloc= 800 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this 801 parameter enables the feature at boot time. In 802 default, it is disabled. We can avoid allocating huge 803 chunk of memory for debug pagealloc if we don't enable 804 it at boot time and the system will work mostly same 805 with the kernel built without CONFIG_DEBUG_PAGEALLOC. 806 on: enable the feature 807 808 debugpat [X86] Enable PAT debugging 809 810 decnet.addr= [HW,NET] 811 Format: <area>[,<node>] 812 See also Documentation/networking/decnet.txt. 813 814 default_hugepagesz= 815 [same as hugepagesz=] The size of the default 816 HugeTLB page size. This is the size represented by 817 the legacy /proc/ hugepages APIs, used for SHM, and 818 default size when mounting hugetlbfs filesystems. 819 Defaults to the default architecture's huge page size 820 if not specified. 821 822 deferred_probe_timeout= 823 [KNL] Debugging option to set a timeout in seconds for 824 deferred probe to give up waiting on dependencies to 825 probe. Only specific dependencies (subsystems or 826 drivers) that have opted in will be ignored. A timeout of 0 827 will timeout at the end of initcalls. This option will also 828 dump out devices still on the deferred probe list after 829 retrying. 830 831 dhash_entries= [KNL] 832 Set number of hash buckets for dentry cache. 833 834 disable_1tb_segments [PPC] 835 Disables the use of 1TB hash page table segments. This 836 causes the kernel to fall back to 256MB segments which 837 can be useful when debugging issues that require an SLB 838 miss to occur. 839 840 disable= [IPV6] 841 See Documentation/networking/ipv6.txt. 842 843 hardened_usercopy= 844 [KNL] Under CONFIG_HARDENED_USERCOPY, whether 845 hardening is enabled for this boot. Hardened 846 usercopy checking is used to protect the kernel 847 from reading or writing beyond known memory 848 allocation boundaries as a proactive defense 849 against bounds-checking flaws in the kernel's 850 copy_to_user()/copy_from_user() interface. 851 on Perform hardened usercopy checks (default). 852 off Disable hardened usercopy checks. 853 854 disable_radix [PPC] 855 Disable RADIX MMU mode on POWER9 856 857 disable_cpu_apicid= [X86,APIC,SMP] 858 Format: <int> 859 The number of initial APIC ID for the 860 corresponding CPU to be disabled at boot, 861 mostly used for the kdump 2nd kernel to 862 disable BSP to wake up multiple CPUs without 863 causing system reset or hang due to sending 864 INIT from AP to BSP. 865 866 perf_v4_pmi= [X86,INTEL] 867 Format: <bool> 868 Disable Intel PMU counter freezing feature. 869 The feature only exists starting from 870 Arch Perfmon v4 (Skylake and newer). 871 872 disable_ddw [PPC/PSERIES] 873 Disable Dynamic DMA Window support. Use this if 874 to workaround buggy firmware. 875 876 disable_ipv6= [IPV6] 877 See Documentation/networking/ipv6.txt. 878 879 disable_mtrr_cleanup [X86] 880 The kernel tries to adjust MTRR layout from continuous 881 to discrete, to make X server driver able to add WB 882 entry later. This parameter disables that. 883 884 disable_mtrr_trim [X86, Intel and AMD only] 885 By default the kernel will trim any uncacheable 886 memory out of your available memory pool based on 887 MTRR settings. This parameter disables that behavior, 888 possibly causing your machine to run very slowly. 889 890 disable_timer_pin_1 [X86] 891 Disable PIN 1 of APIC timer 892 Can be useful to work around chipset bugs. 893 894 dis_ucode_ldr [X86] Disable the microcode loader. 895 896 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, 897 this option disables the debugging code at boot. 898 899 dma_debug_entries=<number> 900 This option allows to tune the number of preallocated 901 entries for DMA-API debugging code. One entry is 902 required per DMA-API allocation. Use this if the 903 DMA-API debugging code disables itself because the 904 architectural default is too low. 905 906 dma_debug_driver=<driver_name> 907 With this option the DMA-API debugging driver 908 filter feature can be enabled at boot time. Just 909 pass the driver to filter for as the parameter. 910 The filter can be disabled or changed to another 911 driver later using sysfs. 912 913 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>] 914 Broken monitors, graphic adapters, KVMs and EDIDless 915 panels may send no or incorrect EDID data sets. 916 This parameter allows to specify an EDID data sets 917 in the /lib/firmware directory that are used instead. 918 Generic built-in EDID data sets are used, if one of 919 edid/1024x768.bin, edid/1280x1024.bin, 920 edid/1680x1050.bin, or edid/1920x1080.bin is given 921 and no file with the same name exists. Details and 922 instructions how to build your own EDID data are 923 available in Documentation/EDID/HOWTO.txt. An EDID 924 data set will only be used for a particular connector, 925 if its name and a colon are prepended to the EDID 926 name. Each connector may use a unique EDID data 927 set by separating the files with a comma. An EDID 928 data set with no connector name will be used for 929 any connectors not explicitly specified. 930 931 dscc4.setup= [NET] 932 933 dt_cpu_ftrs= [PPC] 934 Format: {"off" | "known"} 935 Control how the dt_cpu_ftrs device-tree binding is 936 used for CPU feature discovery and setup (if it 937 exists). 938 off: Do not use it, fall back to legacy cpu table. 939 known: Do not pass through unknown features to guests 940 or userspace, only those that the kernel is aware of. 941 942 dump_apple_properties [X86] 943 Dump name and content of EFI device properties on 944 x86 Macs. Useful for driver authors to determine 945 what data is available or for reverse-engineering. 946 947 dyndbg[="val"] [KNL,DYNAMIC_DEBUG] 948 module.dyndbg[="val"] 949 Enable debug messages at boot time. See 950 Documentation/admin-guide/dynamic-debug-howto.rst 951 for details. 952 953 nompx [X86] Disables Intel Memory Protection Extensions. 954 See Documentation/x86/intel_mpx.txt for more 955 information about the feature. 956 957 nopku [X86] Disable Memory Protection Keys CPU feature found 958 in some Intel CPUs. 959 960 module.async_probe [KNL] 961 Enable asynchronous probe on this module. 962 963 early_ioremap_debug [KNL] 964 Enable debug messages in early_ioremap support. This 965 is useful for tracking down temporary early mappings 966 which are not unmapped. 967 968 earlycon= [KNL] Output early console device and options. 969 970 [ARM64] The early console is determined by the 971 stdout-path property in device tree's chosen node, 972 or determined by the ACPI SPCR table. 973 974 [X86] When used with no options the early console is 975 determined by the ACPI SPCR table. 976 977 cdns,<addr>[,options] 978 Start an early, polled-mode console on a Cadence 979 (xuartps) serial port at the specified address. Only 980 supported option is baud rate. If baud rate is not 981 specified, the serial port must already be setup and 982 configured. 983 984 uart[8250],io,<addr>[,options] 985 uart[8250],mmio,<addr>[,options] 986 uart[8250],mmio32,<addr>[,options] 987 uart[8250],mmio32be,<addr>[,options] 988 uart[8250],0x<addr>[,options] 989 Start an early, polled-mode console on the 8250/16550 990 UART at the specified I/O port or MMIO address. 991 MMIO inter-register address stride is either 8-bit 992 (mmio) or 32-bit (mmio32 or mmio32be). 993 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed 994 to be equivalent to 'mmio'. 'options' are specified 995 in the same format described for "console=ttyS<n>"; if 996 unspecified, the h/w is not initialized. 997 998 pl011,<addr> 999 pl011,mmio32,<addr> 1000 Start an early, polled-mode console on a pl011 serial 1001 port at the specified address. The pl011 serial port 1002 must already be setup and configured. Options are not 1003 yet supported. If 'mmio32' is specified, then only 1004 the driver will use only 32-bit accessors to read/write 1005 the device registers. 1006 1007 meson,<addr> 1008 Start an early, polled-mode console on a meson serial 1009 port at the specified address. The serial port must 1010 already be setup and configured. Options are not yet 1011 supported. 1012 1013 msm_serial,<addr> 1014 Start an early, polled-mode console on an msm serial 1015 port at the specified address. The serial port 1016 must already be setup and configured. Options are not 1017 yet supported. 1018 1019 msm_serial_dm,<addr> 1020 Start an early, polled-mode console on an msm serial 1021 dm port at the specified address. The serial port 1022 must already be setup and configured. Options are not 1023 yet supported. 1024 1025 owl,<addr> 1026 Start an early, polled-mode console on a serial port 1027 of an Actions Semi SoC, such as S500 or S900, at the 1028 specified address. The serial port must already be 1029 setup and configured. Options are not yet supported. 1030 1031 rda,<addr> 1032 Start an early, polled-mode console on a serial port 1033 of an RDA Micro SoC, such as RDA8810PL, at the 1034 specified address. The serial port must already be 1035 setup and configured. Options are not yet supported. 1036 1037 smh Use ARM semihosting calls for early console. 1038 1039 s3c2410,<addr> 1040 s3c2412,<addr> 1041 s3c2440,<addr> 1042 s3c6400,<addr> 1043 s5pv210,<addr> 1044 exynos4210,<addr> 1045 Use early console provided by serial driver available 1046 on Samsung SoCs, requires selecting proper type and 1047 a correct base address of the selected UART port. The 1048 serial port must already be setup and configured. 1049 Options are not yet supported. 1050 1051 lantiq,<addr> 1052 Start an early, polled-mode console on a lantiq serial 1053 (lqasc) port at the specified address. The serial port 1054 must already be setup and configured. Options are not 1055 yet supported. 1056 1057 lpuart,<addr> 1058 lpuart32,<addr> 1059 Use early console provided by Freescale LP UART driver 1060 found on Freescale Vybrid and QorIQ LS1021A processors. 1061 A valid base address must be provided, and the serial 1062 port must already be setup and configured. 1063 1064 ar3700_uart,<addr> 1065 Start an early, polled-mode console on the 1066 Armada 3700 serial port at the specified 1067 address. The serial port must already be setup 1068 and configured. Options are not yet supported. 1069 1070 qcom_geni,<addr> 1071 Start an early, polled-mode console on a Qualcomm 1072 Generic Interface (GENI) based serial port at the 1073 specified address. The serial port must already be 1074 setup and configured. Options are not yet supported. 1075 1076 earlyprintk= [X86,SH,ARM,M68k,S390] 1077 earlyprintk=vga 1078 earlyprintk=efi 1079 earlyprintk=sclp 1080 earlyprintk=xen 1081 earlyprintk=serial[,ttySn[,baudrate]] 1082 earlyprintk=serial[,0x...[,baudrate]] 1083 earlyprintk=ttySn[,baudrate] 1084 earlyprintk=dbgp[debugController#] 1085 earlyprintk=pciserial[,force],bus:device.function[,baudrate] 1086 earlyprintk=xdbc[xhciController#] 1087 1088 earlyprintk is useful when the kernel crashes before 1089 the normal console is initialized. It is not enabled by 1090 default because it has some cosmetic problems. 1091 1092 Append ",keep" to not disable it when the real console 1093 takes over. 1094 1095 Only one of vga, efi, serial, or usb debug port can 1096 be used at a time. 1097 1098 Currently only ttyS0 and ttyS1 may be specified by 1099 name. Other I/O ports may be explicitly specified 1100 on some architectures (x86 and arm at least) by 1101 replacing ttySn with an I/O port address, like this: 1102 earlyprintk=serial,0x1008,115200 1103 You can find the port for a given device in 1104 /proc/tty/driver/serial: 1105 2: uart:ST16650V2 port:00001008 irq:18 ... 1106 1107 Interaction with the standard serial driver is not 1108 very good. 1109 1110 The VGA and EFI output is eventually overwritten by 1111 the real console. 1112 1113 The xen output can only be used by Xen PV guests. 1114 1115 The sclp output can only be used on s390. 1116 1117 The optional "force" to "pciserial" enables use of a 1118 PCI device even when its classcode is not of the 1119 UART class. 1120 1121 edac_report= [HW,EDAC] Control how to report EDAC event 1122 Format: {"on" | "off" | "force"} 1123 on: enable EDAC to report H/W event. May be overridden 1124 by other higher priority error reporting module. 1125 off: disable H/W event reporting through EDAC. 1126 force: enforce the use of EDAC to report H/W event. 1127 default: on. 1128 1129 ekgdboc= [X86,KGDB] Allow early kernel console debugging 1130 ekgdboc=kbd 1131 1132 This is designed to be used in conjunction with 1133 the boot argument: earlyprintk=vga 1134 1135 edd= [EDD] 1136 Format: {"off" | "on" | "skip[mbr]"} 1137 1138 efi= [EFI] 1139 Format: { "old_map", "nochunk", "noruntime", "debug" } 1140 old_map [X86-64]: switch to the old ioremap-based EFI 1141 runtime services mapping. 32-bit still uses this one by 1142 default. 1143 nochunk: disable reading files in "chunks" in the EFI 1144 boot stub, as chunking can cause problems with some 1145 firmware implementations. 1146 noruntime : disable EFI runtime services support 1147 debug: enable misc debug output 1148 1149 efi_no_storage_paranoia [EFI; X86] 1150 Using this parameter you can use more than 50% of 1151 your efi variable storage. Use this parameter only if 1152 you are really sure that your UEFI does sane gc and 1153 fulfills the spec otherwise your board may brick. 1154 1155 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86] 1156 Add arbitrary attribute to specific memory range by 1157 updating original EFI memory map. 1158 Region of memory which aa attribute is added to is 1159 from ss to ss+nn. 1160 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000 1161 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000) 1162 attribute is added to range 0x100000000-0x180000000 and 1163 0x10a0000000-0x1120000000. 1164 1165 Using this parameter you can do debugging of EFI memmap 1166 related feature. For example, you can do debugging of 1167 Address Range Mirroring feature even if your box 1168 doesn't support it. 1169 1170 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT 1171 that is to be dynamically loaded by Linux. If there are 1172 multiple variables with the same name but with different 1173 vendor GUIDs, all of them will be loaded. See 1174 Documentation/acpi/ssdt-overlays.txt for details. 1175 1176 1177 eisa_irq_edge= [PARISC,HW] 1178 See header of drivers/parisc/eisa.c. 1179 1180 elanfreq= [X86-32] 1181 See comment before function elanfreq_setup() in 1182 arch/x86/kernel/cpu/cpufreq/elanfreq.c. 1183 1184 elevator= [IOSCHED] 1185 Format: {"cfq" | "deadline" | "noop"} 1186 See Documentation/block/cfq-iosched.txt and 1187 Documentation/block/deadline-iosched.txt for details. 1188 1189 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390] 1190 Specifies physical address of start of kernel core 1191 image elf header and optionally the size. Generally 1192 kexec loader will pass this option to capture kernel. 1193 See Documentation/kdump/kdump.txt for details. 1194 1195 enable_mtrr_cleanup [X86] 1196 The kernel tries to adjust MTRR layout from continuous 1197 to discrete, to make X server driver able to add WB 1198 entry later. This parameter enables that. 1199 1200 enable_timer_pin_1 [X86] 1201 Enable PIN 1 of APIC timer 1202 Can be useful to work around chipset bugs 1203 (in particular on some ATI chipsets). 1204 The kernel tries to set a reasonable default. 1205 1206 enforcing [SELINUX] Set initial enforcing status. 1207 Format: {"0" | "1"} 1208 See security/selinux/Kconfig help text. 1209 0 -- permissive (log only, no denials). 1210 1 -- enforcing (deny and log). 1211 Default value is 0. 1212 Value can be changed at runtime via /selinux/enforce. 1213 1214 erst_disable [ACPI] 1215 Disable Error Record Serialization Table (ERST) 1216 support. 1217 1218 ether= [HW,NET] Ethernet cards parameters 1219 This option is obsoleted by the "netdev=" option, which 1220 has equivalent usage. See its documentation for details. 1221 1222 evm= [EVM] 1223 Format: { "fix" } 1224 Permit 'security.evm' to be updated regardless of 1225 current integrity status. 1226 1227 failslab= 1228 fail_page_alloc= 1229 fail_make_request=[KNL] 1230 General fault injection mechanism. 1231 Format: <interval>,<probability>,<space>,<times> 1232 See also Documentation/fault-injection/. 1233 1234 floppy= [HW] 1235 See Documentation/blockdev/floppy.txt. 1236 1237 force_pal_cache_flush 1238 [IA-64] Avoid check_sal_cache_flush which may hang on 1239 buggy SAL_CACHE_FLUSH implementations. Using this 1240 parameter will force ia64_sal_cache_flush to call 1241 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH. 1242 1243 forcepae [X86-32] 1244 Forcefully enable Physical Address Extension (PAE). 1245 Many Pentium M systems disable PAE but may have a 1246 functionally usable PAE implementation. 1247 Warning: use of this parameter will taint the kernel 1248 and may cause unknown problems. 1249 1250 ftrace=[tracer] 1251 [FTRACE] will set and start the specified tracer 1252 as early as possible in order to facilitate early 1253 boot debugging. 1254 1255 ftrace_dump_on_oops[=orig_cpu] 1256 [FTRACE] will dump the trace buffers on oops. 1257 If no parameter is passed, ftrace will dump 1258 buffers of all CPUs, but if you pass orig_cpu, it will 1259 dump only the buffer of the CPU that triggered the 1260 oops. 1261 1262 ftrace_filter=[function-list] 1263 [FTRACE] Limit the functions traced by the function 1264 tracer at boot up. function-list is a comma separated 1265 list of functions. This list can be changed at run 1266 time by the set_ftrace_filter file in the debugfs 1267 tracing directory. 1268 1269 ftrace_notrace=[function-list] 1270 [FTRACE] Do not trace the functions specified in 1271 function-list. This list can be changed at run time 1272 by the set_ftrace_notrace file in the debugfs 1273 tracing directory. 1274 1275 ftrace_graph_filter=[function-list] 1276 [FTRACE] Limit the top level callers functions traced 1277 by the function graph tracer at boot up. 1278 function-list is a comma separated list of functions 1279 that can be changed at run time by the 1280 set_graph_function file in the debugfs tracing directory. 1281 1282 ftrace_graph_notrace=[function-list] 1283 [FTRACE] Do not trace from the functions specified in 1284 function-list. This list is a comma separated list of 1285 functions that can be changed at run time by the 1286 set_graph_notrace file in the debugfs tracing directory. 1287 1288 ftrace_graph_max_depth=<uint> 1289 [FTRACE] Used with the function graph tracer. This is 1290 the max depth it will trace into a function. This value 1291 can be changed at run time by the max_graph_depth file 1292 in the tracefs tracing directory. default: 0 (no limit) 1293 1294 gamecon.map[2|3]= 1295 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 1296 support via parallel port (up to 5 devices per port) 1297 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 1298 See also Documentation/input/devices/joystick-parport.rst 1299 1300 gamma= [HW,DRM] 1301 1302 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART 1303 Format: off | on 1304 default: on 1305 1306 gcov_persist= [GCOV] When non-zero (default), profiling data for 1307 kernel modules is saved and remains accessible via 1308 debugfs, even when the module is unloaded/reloaded. 1309 When zero, profiling data is discarded and associated 1310 debugfs files are removed at module unload time. 1311 1312 goldfish [X86] Enable the goldfish android emulator platform. 1313 Don't use this when you are not running on the 1314 android emulator 1315 1316 gpt [EFI] Forces disk with valid GPT signature but 1317 invalid Protective MBR to be treated as GPT. If the 1318 primary GPT is corrupted, it enables the backup/alternate 1319 GPT to be used instead. 1320 1321 grcan.enable0= [HW] Configuration of physical interface 0. Determines 1322 the "Enable 0" bit of the configuration register. 1323 Format: 0 | 1 1324 Default: 0 1325 grcan.enable1= [HW] Configuration of physical interface 1. Determines 1326 the "Enable 0" bit of the configuration register. 1327 Format: 0 | 1 1328 Default: 0 1329 grcan.select= [HW] Select which physical interface to use. 1330 Format: 0 | 1 1331 Default: 0 1332 grcan.txsize= [HW] Sets the size of the tx buffer. 1333 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. 1334 Default: 1024 1335 grcan.rxsize= [HW] Sets the size of the rx buffer. 1336 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. 1337 Default: 1024 1338 1339 gpio-mockup.gpio_mockup_ranges 1340 [HW] Sets the ranges of gpiochip of for this device. 1341 Format: <start1>,<end1>,<start2>,<end2>... 1342 1343 hardlockup_all_cpu_backtrace= 1344 [KNL] Should the hard-lockup detector generate 1345 backtraces on all cpus. 1346 Format: <integer> 1347 1348 hashdist= [KNL,NUMA] Large hashes allocated during boot 1349 are distributed across NUMA nodes. Defaults on 1350 for 64-bit NUMA, off otherwise. 1351 Format: 0 | 1 (for off | on) 1352 1353 hcl= [IA-64] SGI's Hardware Graph compatibility layer 1354 1355 hd= [EIDE] (E)IDE hard drive subsystem geometry 1356 Format: <cyl>,<head>,<sect> 1357 1358 hest_disable [ACPI] 1359 Disable Hardware Error Source Table (HEST) support; 1360 corresponding firmware-first mode error processing 1361 logic will be disabled. 1362 1363 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact 1364 size of <nn>. This works even on boxes that have no 1365 highmem otherwise. This also works to reduce highmem 1366 size on bigger boxes. 1367 1368 highres= [KNL] Enable/disable high resolution timer mode. 1369 Valid parameters: "on", "off" 1370 Default: "on" 1371 1372 hisax= [HW,ISDN] 1373 See Documentation/isdn/README.HiSax. 1374 1375 hlt [BUGS=ARM,SH] 1376 1377 hpet= [X86-32,HPET] option to control HPET usage 1378 Format: { enable (default) | disable | force | 1379 verbose } 1380 disable: disable HPET and use PIT instead 1381 force: allow force enabled of undocumented chips (ICH4, 1382 VIA, nVidia) 1383 verbose: show contents of HPET registers during setup 1384 1385 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET 1386 registers. Default set by CONFIG_HPET_MMAP_DEFAULT. 1387 1388 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot. 1389 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages. 1390 On x86-64 and powerpc, this option can be specified 1391 multiple times interleaved with hugepages= to reserve 1392 huge pages of different sizes. Valid pages sizes on 1393 x86-64 are 2M (when the CPU supports "pse") and 1G 1394 (when the CPU supports the "pdpe1gb" cpuinfo flag). 1395 1396 hung_task_panic= 1397 [KNL] Should the hung task detector generate panics. 1398 Format: <integer> 1399 1400 A nonzero value instructs the kernel to panic when a 1401 hung task is detected. The default value is controlled 1402 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time 1403 option. The value selected by this boot parameter can 1404 be changed later by the kernel.hung_task_panic sysctl. 1405 1406 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 1407 terminal devices. Valid values: 0..8 1408 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 1409 If specified, z/VM IUCV HVC accepts connections 1410 from listed z/VM user IDs only. 1411 1412 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations 1413 which allow the hypervisor to 'idle' the 1414 guest on lock contention. 1415 1416 keep_bootcon [KNL] 1417 Do not unregister boot console at start. This is only 1418 useful for debugging when something happens in the window 1419 between unregistering the boot console and initializing 1420 the real console. 1421 1422 i2c_bus= [HW] Override the default board specific I2C bus speed 1423 or register an additional I2C bus that is not 1424 registered from board initialization code. 1425 Format: 1426 <bus_id>,<clkrate> 1427 1428 i8042.debug [HW] Toggle i8042 debug mode 1429 i8042.unmask_kbd_data 1430 [HW] Enable printing of interrupt data from the KBD port 1431 (disabled by default, and as a pre-condition 1432 requires that i8042.debug=1 be enabled) 1433 i8042.direct [HW] Put keyboard port into non-translated mode 1434 i8042.dumbkbd [HW] Pretend that controller can only read data from 1435 keyboard and cannot control its state 1436 (Don't attempt to blink the leds) 1437 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 1438 i8042.nokbd [HW] Don't check/create keyboard port 1439 i8042.noloop [HW] Disable the AUX Loopback command while probing 1440 for the AUX port 1441 i8042.nomux [HW] Don't check presence of an active multiplexing 1442 controller 1443 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 1444 controllers 1445 i8042.notimeout [HW] Ignore timeout condition signalled by controller 1446 i8042.reset [HW] Reset the controller during init, cleanup and 1447 suspend-to-ram transitions, only during s2r 1448 transitions, or never reset 1449 Format: { 1 | Y | y | 0 | N | n } 1450 1, Y, y: always reset controller 1451 0, N, n: don't ever reset controller 1452 Default: only on s2r transitions on x86; most other 1453 architectures force reset to be always executed 1454 i8042.unlock [HW] Unlock (ignore) the keylock 1455 i8042.kbdreset [HW] Reset device connected to KBD port 1456 1457 i810= [HW,DRM] 1458 1459 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data 1460 indicates that the driver is running on unsupported 1461 hardware. 1462 i8k.force [HW] Activate i8k driver even if SMM BIOS signature 1463 does not match list of supported models. 1464 i8k.power_status 1465 [HW] Report power status in /proc/i8k 1466 (disabled by default) 1467 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN 1468 capability is set. 1469 1470 i915.invert_brightness= 1471 [DRM] Invert the sense of the variable that is used to 1472 set the brightness of the panel backlight. Normally a 1473 brightness value of 0 indicates backlight switched off, 1474 and the maximum of the brightness value sets the backlight 1475 to maximum brightness. If this parameter is set to 0 1476 (default) and the machine requires it, or this parameter 1477 is set to 1, a brightness value of 0 sets the backlight 1478 to maximum brightness, and the maximum of the brightness 1479 value switches the backlight off. 1480 -1 -- never invert brightness 1481 0 -- machine default 1482 1 -- force brightness inversion 1483 1484 icn= [HW,ISDN] 1485 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]] 1486 1487 ide-core.nodma= [HW] (E)IDE subsystem 1488 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc 1489 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr 1490 .cdrom .chs .ignore_cable are additional options 1491 See Documentation/ide/ide.txt. 1492 1493 ide-generic.probe-mask= [HW] (E)IDE subsystem 1494 Format: <int> 1495 Probe mask for legacy ISA IDE ports. Depending on 1496 platform up to 6 ports are supported, enabled by 1497 setting corresponding bits in the mask to 1. The 1498 default value is 0x0, which has a special meaning. 1499 On systems that have PCI, it triggers scanning the 1500 PCI bus for the first and the second port, which 1501 are then probed. On systems without PCI the value 1502 of 0x0 enables probing the two first ports as if it 1503 was 0x3. 1504 1505 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem 1506 Claim all unknown PCI IDE storage controllers. 1507 1508 idle= [X86] 1509 Format: idle=poll, idle=halt, idle=nomwait 1510 Poll forces a polling idle loop that can slightly 1511 improve the performance of waking up a idle CPU, but 1512 will use a lot of power and make the system run hot. 1513 Not recommended. 1514 idle=halt: Halt is forced to be used for CPU idle. 1515 In such case C2/C3 won't be used again. 1516 idle=nomwait: Disable mwait for CPU C-states 1517 1518 ieee754= [MIPS] Select IEEE Std 754 conformance mode 1519 Format: { strict | legacy | 2008 | relaxed } 1520 Default: strict 1521 1522 Choose which programs will be accepted for execution 1523 based on the IEEE 754 NaN encoding(s) supported by 1524 the FPU and the NaN encoding requested with the value 1525 of an ELF file header flag individually set by each 1526 binary. Hardware implementations are permitted to 1527 support either or both of the legacy and the 2008 NaN 1528 encoding mode. 1529 1530 Available settings are as follows: 1531 strict accept binaries that request a NaN encoding 1532 supported by the FPU 1533 legacy only accept legacy-NaN binaries, if supported 1534 by the FPU 1535 2008 only accept 2008-NaN binaries, if supported 1536 by the FPU 1537 relaxed accept any binaries regardless of whether 1538 supported by the FPU 1539 1540 The FPU emulator is always able to support both NaN 1541 encodings, so if no FPU hardware is present or it has 1542 been disabled with 'nofpu', then the settings of 1543 'legacy' and '2008' strap the emulator accordingly, 1544 'relaxed' straps the emulator for both legacy-NaN and 1545 2008-NaN, whereas 'strict' enables legacy-NaN only on 1546 legacy processors and both NaN encodings on MIPS32 or 1547 MIPS64 CPUs. 1548 1549 The setting for ABS.fmt/NEG.fmt instruction execution 1550 mode generally follows that for the NaN encoding, 1551 except where unsupported by hardware. 1552 1553 ignore_loglevel [KNL] 1554 Ignore loglevel setting - this will print /all/ 1555 kernel messages to the console. Useful for debugging. 1556 We also add it as printk module parameter, so users 1557 could change it dynamically, usually by 1558 /sys/module/printk/parameters/ignore_loglevel. 1559 1560 ignore_rlimit_data 1561 Ignore RLIMIT_DATA setting for data mappings, 1562 print warning at first misuse. Can be changed via 1563 /sys/module/kernel/parameters/ignore_rlimit_data. 1564 1565 ihash_entries= [KNL] 1566 Set number of hash buckets for inode cache. 1567 1568 ima_appraise= [IMA] appraise integrity measurements 1569 Format: { "off" | "enforce" | "fix" | "log" } 1570 default: "enforce" 1571 1572 ima_appraise_tcb [IMA] 1573 The builtin appraise policy appraises all files 1574 owned by uid=0. 1575 1576 ima_canonical_fmt [IMA] 1577 Use the canonical format for the binary runtime 1578 measurements, instead of host native format. 1579 1580 ima_hash= [IMA] 1581 Format: { md5 | sha1 | rmd160 | sha256 | sha384 1582 | sha512 | ... } 1583 default: "sha1" 1584 1585 The list of supported hash algorithms is defined 1586 in crypto/hash_info.h. 1587 1588 ima_policy= [IMA] 1589 The builtin policies to load during IMA setup. 1590 Format: "tcb | appraise_tcb | secure_boot | 1591 fail_securely" 1592 1593 The "tcb" policy measures all programs exec'd, files 1594 mmap'd for exec, and all files opened with the read 1595 mode bit set by either the effective uid (euid=0) or 1596 uid=0. 1597 1598 The "appraise_tcb" policy appraises the integrity of 1599 all files owned by root. (This is the equivalent 1600 of ima_appraise_tcb.) 1601 1602 The "secure_boot" policy appraises the integrity 1603 of files (eg. kexec kernel image, kernel modules, 1604 firmware, policy, etc) based on file signatures. 1605 1606 The "fail_securely" policy forces file signature 1607 verification failure also on privileged mounted 1608 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE 1609 flag. 1610 1611 ima_tcb [IMA] Deprecated. Use ima_policy= instead. 1612 Load a policy which meets the needs of the Trusted 1613 Computing Base. This means IMA will measure all 1614 programs exec'd, files mmap'd for exec, and all files 1615 opened for read by uid=0. 1616 1617 ima_template= [IMA] 1618 Select one of defined IMA measurements template formats. 1619 Formats: { "ima" | "ima-ng" | "ima-sig" } 1620 Default: "ima-ng" 1621 1622 ima_template_fmt= 1623 [IMA] Define a custom template format. 1624 Format: { "field1|...|fieldN" } 1625 1626 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage 1627 Format: <min_file_size> 1628 Set the minimal file size for using asynchronous hash. 1629 If left unspecified, ahash usage is disabled. 1630 1631 ahash performance varies for different data sizes on 1632 different crypto accelerators. This option can be used 1633 to achieve the best performance for a particular HW. 1634 1635 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size 1636 Format: <bufsize> 1637 Set hashing buffer size. Default: 4k. 1638 1639 ahash performance varies for different chunk sizes on 1640 different crypto accelerators. This option can be used 1641 to achieve best performance for particular HW. 1642 1643 init= [KNL] 1644 Format: <full_path> 1645 Run specified binary instead of /sbin/init as init 1646 process. 1647 1648 initcall_debug [KNL] Trace initcalls as they are executed. Useful 1649 for working out where the kernel is dying during 1650 startup. 1651 1652 initcall_blacklist= [KNL] Do not execute a comma-separated list of 1653 initcall functions. Useful for debugging built-in 1654 modules and initcalls. 1655 1656 initrd= [BOOT] Specify the location of the initial ramdisk 1657 1658 init_pkru= [x86] Specify the default memory protection keys rights 1659 register contents for all processes. 0x55555554 by 1660 default (disallow access to all but pkey 0). Can 1661 override in debugfs after boot. 1662 1663 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 1664 Format: <irq> 1665 1666 int_pln_enable [x86] Enable power limit notification interrupt 1667 1668 integrity_audit=[IMA] 1669 Format: { "0" | "1" } 1670 0 -- basic integrity auditing messages. (Default) 1671 1 -- additional integrity auditing messages. 1672 1673 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 1674 on 1675 Enable intel iommu driver. 1676 off 1677 Disable intel iommu driver. 1678 igfx_off [Default Off] 1679 By default, gfx is mapped as normal device. If a gfx 1680 device has a dedicated DMAR unit, the DMAR unit is 1681 bypassed by not enabling DMAR with this option. In 1682 this case, gfx device will use physical address for 1683 DMA. 1684 forcedac [x86_64] 1685 With this option iommu will not optimize to look 1686 for io virtual address below 32-bit forcing dual 1687 address cycle on pci bus for cards supporting greater 1688 than 32-bit addressing. The default is to look 1689 for translation below 32-bit and if not available 1690 then look in the higher range. 1691 strict [Default Off] 1692 With this option on every unmap_single operation will 1693 result in a hardware IOTLB flush operation as opposed 1694 to batching them for performance. 1695 sp_off [Default Off] 1696 By default, super page will be supported if Intel IOMMU 1697 has the capability. With this option, super page will 1698 not be supported. 1699 sm_on [Default Off] 1700 By default, scalable mode will be disabled even if the 1701 hardware advertises that it has support for the scalable 1702 mode translation. With this option set, scalable mode 1703 will be used on hardware which claims to support it. 1704 tboot_noforce [Default Off] 1705 Do not force the Intel IOMMU enabled under tboot. 1706 By default, tboot will force Intel IOMMU on, which 1707 could harm performance of some high-throughput 1708 devices like 40GBit network cards, even if identity 1709 mapping is enabled. 1710 Note that using this option lowers the security 1711 provided by tboot because it makes the system 1712 vulnerable to DMA attacks. 1713 1714 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 1715 0 disables intel_idle and fall back on acpi_idle. 1716 1 to 9 specify maximum depth of C-state. 1717 1718 intel_pstate= [X86] 1719 disable 1720 Do not enable intel_pstate as the default 1721 scaling driver for the supported processors 1722 passive 1723 Use intel_pstate as a scaling driver, but configure it 1724 to work with generic cpufreq governors (instead of 1725 enabling its internal governor). This mode cannot be 1726 used along with the hardware-managed P-states (HWP) 1727 feature. 1728 force 1729 Enable intel_pstate on systems that prohibit it by default 1730 in favor of acpi-cpufreq. Forcing the intel_pstate driver 1731 instead of acpi-cpufreq may disable platform features, such 1732 as thermal controls and power capping, that rely on ACPI 1733 P-States information being indicated to OSPM and therefore 1734 should be used with caution. This option does not work with 1735 processors that aren't supported by the intel_pstate driver 1736 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 1737 no_hwp 1738 Do not enable hardware P state control (HWP) 1739 if available. 1740 hwp_only 1741 Only load intel_pstate on systems which support 1742 hardware P state control (HWP) if available. 1743 support_acpi_ppc 1744 Enforce ACPI _PPC performance limits. If the Fixed ACPI 1745 Description Table, specifies preferred power management 1746 profile as "Enterprise Server" or "Performance Server", 1747 then this feature is turned on by default. 1748 per_cpu_perf_limits 1749 Allow per-logical-CPU P-State performance control limits using 1750 cpufreq sysfs interface 1751 1752 intremap= [X86-64, Intel-IOMMU] 1753 on enable Interrupt Remapping (default) 1754 off disable Interrupt Remapping 1755 nosid disable Source ID checking 1756 no_x2apic_optout 1757 BIOS x2APIC opt-out request will be ignored 1758 nopost disable Interrupt Posting 1759 1760 iomem= Disable strict checking of access to MMIO memory 1761 strict regions from userspace. 1762 relaxed 1763 1764 iommu= [x86] 1765 off 1766 force 1767 noforce 1768 biomerge 1769 panic 1770 nopanic 1771 merge 1772 nomerge 1773 soft 1774 pt [x86] 1775 nopt [x86] 1776 nobypass [PPC/POWERNV] 1777 Disable IOMMU bypass, using IOMMU for PCI devices. 1778 1779 iommu.strict= [ARM64] Configure TLB invalidation behaviour 1780 Format: { "0" | "1" } 1781 0 - Lazy mode. 1782 Request that DMA unmap operations use deferred 1783 invalidation of hardware TLBs, for increased 1784 throughput at the cost of reduced device isolation. 1785 Will fall back to strict mode if not supported by 1786 the relevant IOMMU driver. 1787 1 - Strict mode (default). 1788 DMA unmap operations invalidate IOMMU hardware TLBs 1789 synchronously. 1790 1791 iommu.passthrough= 1792 [ARM64] Configure DMA to bypass the IOMMU by default. 1793 Format: { "0" | "1" } 1794 0 - Use IOMMU translation for DMA. 1795 1 - Bypass the IOMMU for DMA. 1796 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH. 1797 1798 io7= [HW] IO7 for Marvel based alpha systems 1799 See comment before marvel_specify_io7 in 1800 arch/alpha/kernel/core_marvel.c. 1801 1802 io_delay= [X86] I/O delay method 1803 0x80 1804 Standard port 0x80 based delay 1805 0xed 1806 Alternate port 0xed based delay (needed on some systems) 1807 udelay 1808 Simple two microseconds delay 1809 none 1810 No delay 1811 1812 ip= [IP_PNP] 1813 See Documentation/filesystems/nfs/nfsroot.txt. 1814 1815 irqaffinity= [SMP] Set the default irq affinity mask 1816 The argument is a cpu list, as described above. 1817 1818 irqchip.gicv2_force_probe= 1819 [ARM, ARM64] 1820 Format: <bool> 1821 Force the kernel to look for the second 4kB page 1822 of a GICv2 controller even if the memory range 1823 exposed by the device tree is too small. 1824 1825 irqchip.gicv3_nolpi= 1826 [ARM, ARM64] 1827 Force the kernel to ignore the availability of 1828 LPIs (and by consequence ITSs). Intended for system 1829 that use the kernel as a bootloader, and thus want 1830 to let secondary kernels in charge of setting up 1831 LPIs. 1832 1833 irqfixup [HW] 1834 When an interrupt is not handled search all handlers 1835 for it. Intended to get systems with badly broken 1836 firmware running. 1837 1838 irqpoll [HW] 1839 When an interrupt is not handled search all handlers 1840 for it. Also check all handlers each timer 1841 interrupt. Intended to get systems with badly broken 1842 firmware running. 1843 1844 isapnp= [ISAPNP] 1845 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 1846 1847 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance. 1848 [Deprecated - use cpusets instead] 1849 Format: [flag-list,]<cpu-list> 1850 1851 Specify one or more CPUs to isolate from disturbances 1852 specified in the flag list (default: domain): 1853 1854 nohz 1855 Disable the tick when a single task runs. 1856 1857 A residual 1Hz tick is offloaded to workqueues, which you 1858 need to affine to housekeeping through the global 1859 workqueue's affinity configured via the 1860 /sys/devices/virtual/workqueue/cpumask sysfs file, or 1861 by using the 'domain' flag described below. 1862 1863 NOTE: by default the global workqueue runs on all CPUs, 1864 so to protect individual CPUs the 'cpumask' file has to 1865 be configured manually after bootup. 1866 1867 domain 1868 Isolate from the general SMP balancing and scheduling 1869 algorithms. Note that performing domain isolation this way 1870 is irreversible: it's not possible to bring back a CPU to 1871 the domains once isolated through isolcpus. It's strongly 1872 advised to use cpusets instead to disable scheduler load 1873 balancing through the "cpuset.sched_load_balance" file. 1874 It offers a much more flexible interface where CPUs can 1875 move in and out of an isolated set anytime. 1876 1877 You can move a process onto or off an "isolated" CPU via 1878 the CPU affinity syscalls or cpuset. 1879 <cpu number> begins at 0 and the maximum value is 1880 "number of CPUs in system - 1". 1881 1882 The format of <cpu-list> is described above. 1883 1884 1885 1886 iucv= [HW,NET] 1887 1888 ivrs_ioapic [HW,X86_64] 1889 Provide an override to the IOAPIC-ID<->DEVICE-ID 1890 mapping provided in the IVRS ACPI table. For 1891 example, to map IOAPIC-ID decimal 10 to 1892 PCI device 00:14.0 write the parameter as: 1893 ivrs_ioapic[10]=00:14.0 1894 1895 ivrs_hpet [HW,X86_64] 1896 Provide an override to the HPET-ID<->DEVICE-ID 1897 mapping provided in the IVRS ACPI table. For 1898 example, to map HPET-ID decimal 0 to 1899 PCI device 00:14.0 write the parameter as: 1900 ivrs_hpet[0]=00:14.0 1901 1902 ivrs_acpihid [HW,X86_64] 1903 Provide an override to the ACPI-HID:UID<->DEVICE-ID 1904 mapping provided in the IVRS ACPI table. For 1905 example, to map UART-HID:UID AMD0020:0 to 1906 PCI device 00:14.5 write the parameter as: 1907 ivrs_acpihid[00:14.5]=AMD0020:0 1908 1909 js= [HW,JOY] Analog joystick 1910 See Documentation/input/joydev/joystick.rst. 1911 1912 nokaslr [KNL] 1913 When CONFIG_RANDOMIZE_BASE is set, this disables 1914 kernel and module base offset ASLR (Address Space 1915 Layout Randomization). 1916 1917 kasan_multi_shot 1918 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print 1919 report on every invalid memory access. Without this 1920 parameter KASAN will print report only for the first 1921 invalid access. 1922 1923 keepinitrd [HW,ARM] 1924 1925 kernelcore= [KNL,X86,IA-64,PPC] 1926 Format: nn[KMGTPE] | nn% | "mirror" 1927 This parameter specifies the amount of memory usable by 1928 the kernel for non-movable allocations. The requested 1929 amount is spread evenly throughout all nodes in the 1930 system as ZONE_NORMAL. The remaining memory is used for 1931 movable memory in its own zone, ZONE_MOVABLE. In the 1932 event, a node is too small to have both ZONE_NORMAL and 1933 ZONE_MOVABLE, kernelcore memory will take priority and 1934 other nodes will have a larger ZONE_MOVABLE. 1935 1936 ZONE_MOVABLE is used for the allocation of pages that 1937 may be reclaimed or moved by the page migration 1938 subsystem. Note that allocations like PTEs-from-HighMem 1939 still use the HighMem zone if it exists, and the Normal 1940 zone if it does not. 1941 1942 It is possible to specify the exact amount of memory in 1943 the form of "nn[KMGTPE]", a percentage of total system 1944 memory in the form of "nn%", or "mirror". If "mirror" 1945 option is specified, mirrored (reliable) memory is used 1946 for non-movable allocations and remaining memory is used 1947 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror" 1948 are exclusive, so you cannot specify multiple forms. 1949 1950 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port. 1951 Format: <Controller#>[,poll interval] 1952 The controller # is the number of the ehci usb debug 1953 port as it is probed via PCI. The poll interval is 1954 optional and is the number seconds in between 1955 each poll cycle to the debug port in case you need 1956 the functionality for interrupting the kernel with 1957 gdb or control-c on the dbgp connection. When 1958 not using this parameter you use sysrq-g to break into 1959 the kernel debugger. 1960 1961 kgdboc= [KGDB,HW] kgdb over consoles. 1962 Requires a tty driver that supports console polling, 1963 or a supported polling keyboard driver (non-usb). 1964 Serial only format: <serial_device>[,baud] 1965 keyboard only format: kbd 1966 keyboard and serial format: kbd,<serial_device>[,baud] 1967 Optional Kernel mode setting: 1968 kms, kbd format: kms,kbd 1969 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 1970 1971 kgdbwait [KGDB] Stop kernel execution and enter the 1972 kernel debugger at the earliest opportunity. 1973 1974 kmac= [MIPS] korina ethernet MAC address. 1975 Configure the RouterBoard 532 series on-chip 1976 Ethernet adapter MAC address. 1977 1978 kmemleak= [KNL] Boot-time kmemleak enable/disable 1979 Valid arguments: on, off 1980 Default: on 1981 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 1982 the default is off. 1983 1984 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 1985 Default is 0 (don't ignore, but inject #GP) 1986 1987 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface. 1988 Default is false (don't support). 1989 1990 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit 1991 KVM MMU at runtime. 1992 Default is 0 (off) 1993 1994 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM. 1995 Default is 1 (enabled) 1996 1997 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU) 1998 for all guests. 1999 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode. 2000 2001 kvm-arm.vgic_v3_group0_trap= 2002 [KVM,ARM] Trap guest accesses to GICv3 group-0 2003 system registers 2004 2005 kvm-arm.vgic_v3_group1_trap= 2006 [KVM,ARM] Trap guest accesses to GICv3 group-1 2007 system registers 2008 2009 kvm-arm.vgic_v3_common_trap= 2010 [KVM,ARM] Trap guest accesses to GICv3 common 2011 system registers 2012 2013 kvm-arm.vgic_v4_enable= 2014 [KVM,ARM] Allow use of GICv4 for direct injection of 2015 LPIs. 2016 2017 kvm-intel.ept= [KVM,Intel] Disable extended page tables 2018 (virtualized MMU) support on capable Intel chips. 2019 Default is 1 (enabled) 2020 2021 kvm-intel.emulate_invalid_guest_state= 2022 [KVM,Intel] Enable emulation of invalid guest states 2023 Default is 0 (disabled) 2024 2025 kvm-intel.flexpriority= 2026 [KVM,Intel] Disable FlexPriority feature (TPR shadow). 2027 Default is 1 (enabled) 2028 2029 kvm-intel.nested= 2030 [KVM,Intel] Enable VMX nesting (nVMX). 2031 Default is 0 (disabled) 2032 2033 kvm-intel.unrestricted_guest= 2034 [KVM,Intel] Disable unrestricted guest feature 2035 (virtualized real and unpaged mode) on capable 2036 Intel chips. Default is 1 (enabled) 2037 2038 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault 2039 CVE-2018-3620. 2040 2041 Valid arguments: never, cond, always 2042 2043 always: L1D cache flush on every VMENTER. 2044 cond: Flush L1D on VMENTER only when the code between 2045 VMEXIT and VMENTER can leak host memory. 2046 never: Disables the mitigation 2047 2048 Default is cond (do L1 cache flush in specific instances) 2049 2050 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification 2051 feature (tagged TLBs) on capable Intel chips. 2052 Default is 1 (enabled) 2053 2054 l1tf= [X86] Control mitigation of the L1TF vulnerability on 2055 affected CPUs 2056 2057 The kernel PTE inversion protection is unconditionally 2058 enabled and cannot be disabled. 2059 2060 full 2061 Provides all available mitigations for the 2062 L1TF vulnerability. Disables SMT and 2063 enables all mitigations in the 2064 hypervisors, i.e. unconditional L1D flush. 2065 2066 SMT control and L1D flush control via the 2067 sysfs interface is still possible after 2068 boot. Hypervisors will issue a warning 2069 when the first VM is started in a 2070 potentially insecure configuration, 2071 i.e. SMT enabled or L1D flush disabled. 2072 2073 full,force 2074 Same as 'full', but disables SMT and L1D 2075 flush runtime control. Implies the 2076 'nosmt=force' command line option. 2077 (i.e. sysfs control of SMT is disabled.) 2078 2079 flush 2080 Leaves SMT enabled and enables the default 2081 hypervisor mitigation, i.e. conditional 2082 L1D flush. 2083 2084 SMT control and L1D flush control via the 2085 sysfs interface is still possible after 2086 boot. Hypervisors will issue a warning 2087 when the first VM is started in a 2088 potentially insecure configuration, 2089 i.e. SMT enabled or L1D flush disabled. 2090 2091 flush,nosmt 2092 2093 Disables SMT and enables the default 2094 hypervisor mitigation. 2095 2096 SMT control and L1D flush control via the 2097 sysfs interface is still possible after 2098 boot. Hypervisors will issue a warning 2099 when the first VM is started in a 2100 potentially insecure configuration, 2101 i.e. SMT enabled or L1D flush disabled. 2102 2103 flush,nowarn 2104 Same as 'flush', but hypervisors will not 2105 warn when a VM is started in a potentially 2106 insecure configuration. 2107 2108 off 2109 Disables hypervisor mitigations and doesn't 2110 emit any warnings. 2111 It also drops the swap size and available 2112 RAM limit restriction on both hypervisor and 2113 bare metal. 2114 2115 Default is 'flush'. 2116 2117 For details see: Documentation/admin-guide/l1tf.rst 2118 2119 l2cr= [PPC] 2120 2121 l3cr= [PPC] 2122 2123 lapic [X86-32,APIC] Enable the local APIC even if BIOS 2124 disabled it. 2125 2126 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline 2127 value for LAPIC timer one-shot implementation. Default 2128 back to the programmable timer unit in the LAPIC. 2129 2130 lapic_timer_c2_ok [X86,APIC] trust the local apic timer 2131 in C2 power state. 2132 2133 libata.dma= [LIBATA] DMA control 2134 libata.dma=0 Disable all PATA and SATA DMA 2135 libata.dma=1 PATA and SATA Disk DMA only 2136 libata.dma=2 ATAPI (CDROM) DMA only 2137 libata.dma=4 Compact Flash DMA only 2138 Combinations also work, so libata.dma=3 enables DMA 2139 for disks and CDROMs, but not CFs. 2140 2141 libata.ignore_hpa= [LIBATA] Ignore HPA limit 2142 libata.ignore_hpa=0 keep BIOS limits (default) 2143 libata.ignore_hpa=1 ignore limits, using full disk 2144 2145 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 2146 when set. 2147 Format: <int> 2148 2149 libata.force= [LIBATA] Force configurations. The format is comma 2150 separated list of "[ID:]VAL" where ID is 2151 PORT[.DEVICE]. PORT and DEVICE are decimal numbers 2152 matching port, link or device. Basically, it matches 2153 the ATA ID string printed on console by libata. If 2154 the whole ID part is omitted, the last PORT and DEVICE 2155 values are used. If ID hasn't been specified yet, the 2156 configuration applies to all ports, links and devices. 2157 2158 If only DEVICE is omitted, the parameter applies to 2159 the port and all links and devices behind it. DEVICE 2160 number of 0 either selects the first device or the 2161 first fan-out link behind PMP device. It does not 2162 select the host link. DEVICE number of 15 selects the 2163 host link and device attached to it. 2164 2165 The VAL specifies the configuration to force. As long 2166 as there's no ambiguity shortcut notation is allowed. 2167 For example, both 1.5 and 1.5G would work for 1.5Gbps. 2168 The following configurations can be forced. 2169 2170 * Cable type: 40c, 80c, short40c, unk, ign or sata. 2171 Any ID with matching PORT is used. 2172 2173 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 2174 2175 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 2176 udma[/][16,25,33,44,66,100,133] notation is also 2177 allowed. 2178 2179 * [no]ncq: Turn on or off NCQ. 2180 2181 * [no]ncqtrim: Turn off queued DSM TRIM. 2182 2183 * nohrst, nosrst, norst: suppress hard, soft 2184 and both resets. 2185 2186 * rstonce: only attempt one reset during 2187 hot-unplug link recovery 2188 2189 * dump_id: dump IDENTIFY data. 2190 2191 * atapi_dmadir: Enable ATAPI DMADIR bridge support 2192 2193 * disable: Disable this device. 2194 2195 If there are multiple matching configurations changing 2196 the same attribute, the last one is used. 2197 2198 memblock=debug [KNL] Enable memblock debug messages. 2199 2200 load_ramdisk= [RAM] List of ramdisks to load from floppy 2201 See Documentation/blockdev/ramdisk.txt. 2202 2203 lockd.nlm_grace_period=P [NFS] Assign grace period. 2204 Format: <integer> 2205 2206 lockd.nlm_tcpport=N [NFS] Assign TCP port. 2207 Format: <integer> 2208 2209 lockd.nlm_timeout=T [NFS] Assign timeout value. 2210 Format: <integer> 2211 2212 lockd.nlm_udpport=M [NFS] Assign UDP port. 2213 Format: <integer> 2214 2215 locktorture.nreaders_stress= [KNL] 2216 Set the number of locking read-acquisition kthreads. 2217 Defaults to being automatically set based on the 2218 number of online CPUs. 2219 2220 locktorture.nwriters_stress= [KNL] 2221 Set the number of locking write-acquisition kthreads. 2222 2223 locktorture.onoff_holdoff= [KNL] 2224 Set time (s) after boot for CPU-hotplug testing. 2225 2226 locktorture.onoff_interval= [KNL] 2227 Set time (s) between CPU-hotplug operations, or 2228 zero to disable CPU-hotplug testing. 2229 2230 locktorture.shuffle_interval= [KNL] 2231 Set task-shuffle interval (jiffies). Shuffling 2232 tasks allows some CPUs to go into dyntick-idle 2233 mode during the locktorture test. 2234 2235 locktorture.shutdown_secs= [KNL] 2236 Set time (s) after boot system shutdown. This 2237 is useful for hands-off automated testing. 2238 2239 locktorture.stat_interval= [KNL] 2240 Time (s) between statistics printk()s. 2241 2242 locktorture.stutter= [KNL] 2243 Time (s) to stutter testing, for example, 2244 specifying five seconds causes the test to run for 2245 five seconds, wait for five seconds, and so on. 2246 This tests the locking primitive's ability to 2247 transition abruptly to and from idle. 2248 2249 locktorture.torture_type= [KNL] 2250 Specify the locking implementation to test. 2251 2252 locktorture.verbose= [KNL] 2253 Enable additional printk() statements. 2254 2255 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 2256 Format: <irq> 2257 2258 loglevel= All Kernel Messages with a loglevel smaller than the 2259 console loglevel will be printed to the console. It can 2260 also be changed with klogd or other programs. The 2261 loglevels are defined as follows: 2262 2263 0 (KERN_EMERG) system is unusable 2264 1 (KERN_ALERT) action must be taken immediately 2265 2 (KERN_CRIT) critical conditions 2266 3 (KERN_ERR) error conditions 2267 4 (KERN_WARNING) warning conditions 2268 5 (KERN_NOTICE) normal but significant condition 2269 6 (KERN_INFO) informational 2270 7 (KERN_DEBUG) debug-level messages 2271 2272 log_buf_len=n[KMG] Sets the size of the printk ring buffer, 2273 in bytes. n must be a power of two and greater 2274 than the minimal size. The minimal size is defined 2275 by LOG_BUF_SHIFT kernel config parameter. There is 2276 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter 2277 that allows to increase the default size depending on 2278 the number of CPUs. See init/Kconfig for more details. 2279 2280 logo.nologo [FB] Disables display of the built-in Linux logo. 2281 This may be used to provide more screen space for 2282 kernel log messages and is useful when debugging 2283 kernel boot problems. 2284 2285 lp=0 [LP] Specify parallel ports to use, e.g, 2286 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 2287 lp=reset first parallel port). 'lp=0' disables the 2288 lp=auto printer driver. 'lp=reset' (which can be 2289 specified in addition to the ports) causes 2290 attached printers to be reset. Using 2291 lp=port1,port2,... specifies the parallel ports 2292 to associate lp devices with, starting with 2293 lp0. A port specification may be 'none' to skip 2294 that lp device, or a parport name such as 2295 'parport0'. Specifying 'lp=auto' instead of a 2296 port specification list means that device IDs 2297 from each port should be examined, to see if 2298 an IEEE 1284-compliant printer is attached; if 2299 so, the driver will manage that printer. 2300 See also header of drivers/char/lp.c. 2301 2302 lpj=n [KNL] 2303 Sets loops_per_jiffy to given constant, thus avoiding 2304 time-consuming boot-time autodetection (up to 250 ms per 2305 CPU). 0 enables autodetection (default). To determine 2306 the correct value for your kernel, boot with normal 2307 autodetection and see what value is printed. Note that 2308 on SMP systems the preset will be applied to all CPUs, 2309 which is likely to cause problems if your CPUs need 2310 significantly divergent settings. An incorrect value 2311 will cause delays in the kernel to be wrong, leading to 2312 unpredictable I/O errors and other breakage. Although 2313 unlikely, in the extreme case this might damage your 2314 hardware. 2315 2316 ltpc= [NET] 2317 Format: <io>,<irq>,<dma> 2318 2319 lsm.debug [SECURITY] Enable LSM initialization debugging output. 2320 2321 machvec= [IA-64] Force the use of a particular machine-vector 2322 (machvec) in a generic kernel. 2323 Example: machvec=hpzx1_swiotlb 2324 2325 machtype= [Loongson] Share the same kernel image file between different 2326 yeeloong laptop. 2327 Example: machtype=lemote-yeeloong-2f-7inch 2328 2329 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater 2330 than or equal to this physical address is ignored. 2331 2332 maxcpus= [SMP] Maximum number of processors that an SMP kernel 2333 will bring up during bootup. maxcpus=n : n >= 0 limits 2334 the kernel to bring up 'n' processors. Surely after 2335 bootup you can bring up the other plugged cpu by executing 2336 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 2337 only takes effect during system bootup. 2338 While n=0 is a special case, it is equivalent to "nosmp", 2339 which also disables the IO APIC. 2340 2341 max_loop= [LOOP] The number of loop block devices that get 2342 (loop.max_loop) unconditionally pre-created at init time. The default 2343 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 2344 of statically allocating a predefined number, loop 2345 devices can be requested on-demand with the 2346 /dev/loop-control interface. 2347 2348 mce [X86-32] Machine Check Exception 2349 2350 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt 2351 2352 md= [HW] RAID subsystems devices and level 2353 See Documentation/admin-guide/md.rst. 2354 2355 mdacon= [MDA] 2356 Format: <first>,<last> 2357 Specifies range of consoles to be captured by the MDA. 2358 2359 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory 2360 Amount of memory to be used when the kernel is not able 2361 to see the whole system memory or for test. 2362 [X86] Work as limiting max address. Use together 2363 with memmap= to avoid physical address space collisions. 2364 Without memmap= PCI devices could be placed at addresses 2365 belonging to unused RAM. 2366 2367 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 2368 memory. 2369 2370 memchunk=nn[KMG] 2371 [KNL,SH] Allow user to override the default size for 2372 per-device physically contiguous DMA buffers. 2373 2374 memhp_default_state=online/offline 2375 [KNL] Set the initial state for the memory hotplug 2376 onlining policy. If not specified, the default value is 2377 set according to the 2378 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config 2379 option. 2380 See Documentation/memory-hotplug.txt. 2381 2382 memmap=exactmap [KNL,X86] Enable setting of an exact 2383 E820 memory map, as specified by the user. 2384 Such memmap=exactmap lines can be constructed based on 2385 BIOS output or other requirements. See the memmap=nn@ss 2386 option description. 2387 2388 memmap=nn[KMG]@ss[KMG] 2389 [KNL] Force usage of a specific region of memory. 2390 Region of memory to be used is from ss to ss+nn. 2391 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], 2392 which limits max address to nn[KMG]. 2393 Multiple different regions can be specified, 2394 comma delimited. 2395 Example: 2396 memmap=100M@2G,100M#3G,1G!1024G 2397 2398 memmap=nn[KMG]#ss[KMG] 2399 [KNL,ACPI] Mark specific memory as ACPI data. 2400 Region of memory to be marked is from ss to ss+nn. 2401 2402 memmap=nn[KMG]$ss[KMG] 2403 [KNL,ACPI] Mark specific memory as reserved. 2404 Region of memory to be reserved is from ss to ss+nn. 2405 Example: Exclude memory from 0x18690000-0x1869ffff 2406 memmap=64K$0x18690000 2407 or 2408 memmap=0x10000$0x18690000 2409 Some bootloaders may need an escape character before '$', 2410 like Grub2, otherwise '$' and the following number 2411 will be eaten. 2412 2413 memmap=nn[KMG]!ss[KMG] 2414 [KNL,X86] Mark specific memory as protected. 2415 Region of memory to be used, from ss to ss+nn. 2416 The memory region may be marked as e820 type 12 (0xc) 2417 and is NVDIMM or ADR memory. 2418 2419 memmap=<size>%<offset>-<oldtype>+<newtype> 2420 [KNL,ACPI] Convert memory within the specified region 2421 from <oldtype> to <newtype>. If "-<oldtype>" is left 2422 out, the whole region will be marked as <newtype>, 2423 even if previously unavailable. If "+<newtype>" is left 2424 out, matching memory will be removed. Types are 2425 specified as e820 types, e.g., 1 = RAM, 2 = reserved, 2426 3 = ACPI, 12 = PRAM. 2427 2428 memory_corruption_check=0/1 [X86] 2429 Some BIOSes seem to corrupt the first 64k of 2430 memory when doing things like suspend/resume. 2431 Setting this option will scan the memory 2432 looking for corruption. Enabling this will 2433 both detect corruption and prevent the kernel 2434 from using the memory being corrupted. 2435 However, its intended as a diagnostic tool; if 2436 repeatable BIOS-originated corruption always 2437 affects the same memory, you can use memmap= 2438 to prevent the kernel from using that memory. 2439 2440 memory_corruption_check_size=size [X86] 2441 By default it checks for corruption in the low 2442 64k, making this memory unavailable for normal 2443 use. Use this parameter to scan for 2444 corruption in more or less memory. 2445 2446 memory_corruption_check_period=seconds [X86] 2447 By default it checks for corruption every 60 2448 seconds. Use this parameter to check at some 2449 other rate. 0 disables periodic checking. 2450 2451 memtest= [KNL,X86,ARM,PPC] Enable memtest 2452 Format: <integer> 2453 default : 0 <disable> 2454 Specifies the number of memtest passes to be 2455 performed. Each pass selects another test 2456 pattern from a given set of patterns. Memtest 2457 fills the memory with this pattern, validates 2458 memory contents and reserves bad memory 2459 regions that are detected. 2460 2461 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control 2462 Valid arguments: on, off 2463 Default (depends on kernel configuration option): 2464 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y) 2465 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n) 2466 mem_encrypt=on: Activate SME 2467 mem_encrypt=off: Do not activate SME 2468 2469 Refer to Documentation/x86/amd-memory-encryption.txt 2470 for details on when memory encryption can be activated. 2471 2472 mem_sleep_default= [SUSPEND] Default system suspend mode: 2473 s2idle - Suspend-To-Idle 2474 shallow - Power-On Suspend or equivalent (if supported) 2475 deep - Suspend-To-RAM or equivalent (if supported) 2476 See Documentation/admin-guide/pm/sleep-states.rst. 2477 2478 meye.*= [HW] Set MotionEye Camera parameters 2479 See Documentation/media/v4l-drivers/meye.rst. 2480 2481 mfgpt_irq= [IA-32] Specify the IRQ to use for the 2482 Multi-Function General Purpose Timers on AMD Geode 2483 platforms. 2484 2485 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 2486 the BIOS has incorrectly applied a workaround. TinyBIOS 2487 version 0.98 is known to be affected, 0.99 fixes the 2488 problem by letting the user disable the workaround. 2489 2490 mga= [HW,DRM] 2491 2492 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this 2493 physical address is ignored. 2494 2495 mini2440= [ARM,HW,KNL] 2496 Format:[0..2][b][c][t] 2497 Default: "0tb" 2498 MINI2440 configuration specification: 2499 0 - The attached screen is the 3.5" TFT 2500 1 - The attached screen is the 7" TFT 2501 2 - The VGA Shield is attached (1024x768) 2502 Leaving out the screen size parameter will not load 2503 the TFT driver, and the framebuffer will be left 2504 unconfigured. 2505 b - Enable backlight. The TFT backlight pin will be 2506 linked to the kernel VESA blanking code and a GPIO 2507 LED. This parameter is not necessary when using the 2508 VGA shield. 2509 c - Enable the s3c camera interface. 2510 t - Reserved for enabling touchscreen support. The 2511 touchscreen support is not enabled in the mainstream 2512 kernel as of 2.6.30, a preliminary port can be found 2513 in the "bleeding edge" mini2440 support kernel at 2514 http://repo.or.cz/w/linux-2.6/mini2440.git 2515 2516 mminit_loglevel= 2517 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this 2518 parameter allows control of the logging verbosity for 2519 the additional memory initialisation checks. A value 2520 of 0 disables mminit logging and a level of 4 will 2521 log everything. Information is printed at KERN_DEBUG 2522 so loglevel=8 may also need to be specified. 2523 2524 module.sig_enforce 2525 [KNL] When CONFIG_MODULE_SIG is set, this means that 2526 modules without (valid) signatures will fail to load. 2527 Note that if CONFIG_MODULE_SIG_FORCE is set, that 2528 is always true, so this option does nothing. 2529 2530 module_blacklist= [KNL] Do not load a comma-separated list of 2531 modules. Useful for debugging problem modules. 2532 2533 mousedev.tap_time= 2534 [MOUSE] Maximum time between finger touching and 2535 leaving touchpad surface for touch to be considered 2536 a tap and be reported as a left button click (for 2537 touchpads working in absolute mode only). 2538 Format: <msecs> 2539 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 2540 reporting absolute coordinates, such as tablets 2541 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 2542 reporting absolute coordinates, such as tablets 2543 2544 movablecore= [KNL,X86,IA-64,PPC] 2545 Format: nn[KMGTPE] | nn% 2546 This parameter is the complement to kernelcore=, it 2547 specifies the amount of memory used for migratable 2548 allocations. If both kernelcore and movablecore is 2549 specified, then kernelcore will be at *least* the 2550 specified value but may be more. If movablecore on its 2551 own is specified, the administrator must be careful 2552 that the amount of memory usable for all allocations 2553 is not too small. 2554 2555 movable_node [KNL] Boot-time switch to make hotplugable memory 2556 NUMA nodes to be movable. This means that the memory 2557 of such nodes will be usable only for movable 2558 allocations which rules out almost all kernel 2559 allocations. Use with caution! 2560 2561 MTD_Partition= [MTD] 2562 Format: <name>,<region-number>,<size>,<offset> 2563 2564 MTD_Region= [MTD] Format: 2565 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 2566 2567 mtdparts= [MTD] 2568 See drivers/mtd/cmdlinepart.c. 2569 2570 multitce=off [PPC] This parameter disables the use of the pSeries 2571 firmware feature for updating multiple TCE entries 2572 at a time. 2573 2574 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 2575 2576 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 2577 2578 boundary - index of last SLC block on Flex-OneNAND. 2579 The remaining blocks are configured as MLC blocks. 2580 lock - Configure if Flex-OneNAND boundary should be locked. 2581 Once locked, the boundary cannot be changed. 2582 1 indicates lock status, 0 indicates unlock status. 2583 2584 mtdset= [ARM] 2585 ARM/S3C2412 JIVE boot control 2586 2587 See arch/arm/mach-s3c2412/mach-jive.c 2588 2589 mtouchusb.raw_coordinates= 2590 [HW] Make the MicroTouch USB driver use raw coordinates 2591 ('y', default) or cooked coordinates ('n') 2592 2593 mtrr_chunk_size=nn[KMG] [X86] 2594 used for mtrr cleanup. It is largest continuous chunk 2595 that could hold holes aka. UC entries. 2596 2597 mtrr_gran_size=nn[KMG] [X86] 2598 Used for mtrr cleanup. It is granularity of mtrr block. 2599 Default is 1. 2600 Large value could prevent small alignment from 2601 using up MTRRs. 2602 2603 mtrr_spare_reg_nr=n [X86] 2604 Format: <integer> 2605 Range: 0,7 : spare reg number 2606 Default : 1 2607 Used for mtrr cleanup. It is spare mtrr entries number. 2608 Set to 2 or more if your graphical card needs more. 2609 2610 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 2611 2612 netdev= [NET] Network devices parameters 2613 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 2614 Note that mem_start is often overloaded to mean 2615 something different and driver-specific. 2616 This usage is only documented in each driver source 2617 file if at all. 2618 2619 nf_conntrack.acct= 2620 [NETFILTER] Enable connection tracking flow accounting 2621 0 to disable accounting 2622 1 to enable accounting 2623 Default value is 0. 2624 2625 nfsaddrs= [NFS] Deprecated. Use ip= instead. 2626 See Documentation/filesystems/nfs/nfsroot.txt. 2627 2628 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 2629 See Documentation/filesystems/nfs/nfsroot.txt. 2630 2631 nfsrootdebug [NFS] enable nfsroot debugging messages. 2632 See Documentation/filesystems/nfs/nfsroot.txt. 2633 2634 nfs.callback_nr_threads= 2635 [NFSv4] set the total number of threads that the 2636 NFS client will assign to service NFSv4 callback 2637 requests. 2638 2639 nfs.callback_tcpport= 2640 [NFS] set the TCP port on which the NFSv4 callback 2641 channel should listen. 2642 2643 nfs.cache_getent= 2644 [NFS] sets the pathname to the program which is used 2645 to update the NFS client cache entries. 2646 2647 nfs.cache_getent_timeout= 2648 [NFS] sets the timeout after which an attempt to 2649 update a cache entry is deemed to have failed. 2650 2651 nfs.idmap_cache_timeout= 2652 [NFS] set the maximum lifetime for idmapper cache 2653 entries. 2654 2655 nfs.enable_ino64= 2656 [NFS] enable 64-bit inode numbers. 2657 If zero, the NFS client will fake up a 32-bit inode 2658 number for the readdir() and stat() syscalls instead 2659 of returning the full 64-bit number. 2660 The default is to return 64-bit inode numbers. 2661 2662 nfs.max_session_cb_slots= 2663 [NFSv4.1] Sets the maximum number of session 2664 slots the client will assign to the callback 2665 channel. This determines the maximum number of 2666 callbacks the client will process in parallel for 2667 a particular server. 2668 2669 nfs.max_session_slots= 2670 [NFSv4.1] Sets the maximum number of session slots 2671 the client will attempt to negotiate with the server. 2672 This limits the number of simultaneous RPC requests 2673 that the client can send to the NFSv4.1 server. 2674 Note that there is little point in setting this 2675 value higher than the max_tcp_slot_table_limit. 2676 2677 nfs.nfs4_disable_idmapping= 2678 [NFSv4] When set to the default of '1', this option 2679 ensures that both the RPC level authentication 2680 scheme and the NFS level operations agree to use 2681 numeric uids/gids if the mount is using the 2682 'sec=sys' security flavour. In effect it is 2683 disabling idmapping, which can make migration from 2684 legacy NFSv2/v3 systems to NFSv4 easier. 2685 Servers that do not support this mode of operation 2686 will be autodetected by the client, and it will fall 2687 back to using the idmapper. 2688 To turn off this behaviour, set the value to '0'. 2689 nfs.nfs4_unique_id= 2690 [NFS4] Specify an additional fixed unique ident- 2691 ification string that NFSv4 clients can insert into 2692 their nfs_client_id4 string. This is typically a 2693 UUID that is generated at system install time. 2694 2695 nfs.send_implementation_id = 2696 [NFSv4.1] Send client implementation identification 2697 information in exchange_id requests. 2698 If zero, no implementation identification information 2699 will be sent. 2700 The default is to send the implementation identification 2701 information. 2702 2703 nfs.recover_lost_locks = 2704 [NFSv4] Attempt to recover locks that were lost due 2705 to a lease timeout on the server. Please note that 2706 doing this risks data corruption, since there are 2707 no guarantees that the file will remain unchanged 2708 after the locks are lost. 2709 If you want to enable the kernel legacy behaviour of 2710 attempting to recover these locks, then set this 2711 parameter to '1'. 2712 The default parameter value of '0' causes the kernel 2713 not to attempt recovery of lost locks. 2714 2715 nfs4.layoutstats_timer = 2716 [NFSv4.2] Change the rate at which the kernel sends 2717 layoutstats to the pNFS metadata server. 2718 2719 Setting this to value to 0 causes the kernel to use 2720 whatever value is the default set by the layout 2721 driver. A non-zero value sets the minimum interval 2722 in seconds between layoutstats transmissions. 2723 2724 nfsd.nfs4_disable_idmapping= 2725 [NFSv4] When set to the default of '1', the NFSv4 2726 server will return only numeric uids and gids to 2727 clients using auth_sys, and will accept numeric uids 2728 and gids from such clients. This is intended to ease 2729 migration from NFSv2/v3. 2730 2731 nmi_debug= [KNL,SH] Specify one or more actions to take 2732 when a NMI is triggered. 2733 Format: [state][,regs][,debounce][,die] 2734 2735 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 2736 Format: [panic,][nopanic,][num] 2737 Valid num: 0 or 1 2738 0 - turn hardlockup detector in nmi_watchdog off 2739 1 - turn hardlockup detector in nmi_watchdog on 2740 When panic is specified, panic when an NMI watchdog 2741 timeout occurs (or 'nopanic' to override the opposite 2742 default). To disable both hard and soft lockup detectors, 2743 please see 'nowatchdog'. 2744 This is useful when you use a panic=... timeout and 2745 need the box quickly up again. 2746 2747 These settings can be accessed at runtime via 2748 the nmi_watchdog and hardlockup_panic sysctls. 2749 2750 netpoll.carrier_timeout= 2751 [NET] Specifies amount of time (in seconds) that 2752 netpoll should wait for a carrier. By default netpoll 2753 waits 4 seconds. 2754 2755 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 2756 emulation library even if a 387 maths coprocessor 2757 is present. 2758 2759 no5lvl [X86-64] Disable 5-level paging mode. Forces 2760 kernel to use 4-level paging instead. 2761 2762 no_console_suspend 2763 [HW] Never suspend the console 2764 Disable suspending of consoles during suspend and 2765 hibernate operations. Once disabled, debugging 2766 messages can reach various consoles while the rest 2767 of the system is being put to sleep (ie, while 2768 debugging driver suspend/resume hooks). This may 2769 not work reliably with all consoles, but is known 2770 to work with serial and VGA consoles. 2771 To facilitate more flexible debugging, we also add 2772 console_suspend, a printk module parameter to control 2773 it. Users could use console_suspend (usually 2774 /sys/module/printk/parameters/console_suspend) to 2775 turn on/off it dynamically. 2776 2777 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien 2778 caches in the slab allocator. Saves per-node memory, 2779 but will impact performance. 2780 2781 noalign [KNL,ARM] 2782 2783 noaltinstr [S390] Disables alternative instructions patching 2784 (CPU alternatives feature). 2785 2786 noapic [SMP,APIC] Tells the kernel to not make use of any 2787 IOAPICs that may be present in the system. 2788 2789 noautogroup Disable scheduler automatic task group creation. 2790 2791 nobats [PPC] Do not use BATs for mapping kernel lowmem 2792 on "Classic" PPC cores. 2793 2794 nocache [ARM] 2795 2796 noclflush [BUGS=X86] Don't use the CLFLUSH instruction 2797 2798 nodelayacct [KNL] Disable per-task delay accounting 2799 2800 nodsp [SH] Disable hardware DSP at boot time. 2801 2802 noefi Disable EFI runtime services support. 2803 2804 noexec [IA-64] 2805 2806 noexec [X86] 2807 On X86-32 available only on PAE configured kernels. 2808 noexec=on: enable non-executable mappings (default) 2809 noexec=off: disable non-executable mappings 2810 2811 nosmap [X86] 2812 Disable SMAP (Supervisor Mode Access Prevention) 2813 even if it is supported by processor. 2814 2815 nosmep [X86] 2816 Disable SMEP (Supervisor Mode Execution Prevention) 2817 even if it is supported by processor. 2818 2819 noexec32 [X86-64] 2820 This affects only 32-bit executables. 2821 noexec32=on: enable non-executable mappings (default) 2822 read doesn't imply executable mappings 2823 noexec32=off: disable non-executable mappings 2824 read implies executable mappings 2825 2826 nofpu [MIPS,SH] Disable hardware FPU at boot time. 2827 2828 nofxsr [BUGS=X86-32] Disables x86 floating point extended 2829 register save and restore. The kernel will only save 2830 legacy floating-point registers on task switch. 2831 2832 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings. 2833 2834 nosmt [KNL,S390] Disable symmetric multithreading (SMT). 2835 Equivalent to smt=1. 2836 2837 [KNL,x86] Disable symmetric multithreading (SMT). 2838 nosmt=force: Force disable SMT, cannot be undone 2839 via the sysfs control file. 2840 2841 nospectre_v1 [PPC] Disable mitigations for Spectre Variant 1 (bounds 2842 check bypass). With this option data leaks are possible 2843 in the system. 2844 2845 nospectre_v2 [X86,PPC_FSL_BOOK3E] Disable all mitigations for the Spectre variant 2 2846 (indirect branch prediction) vulnerability. System may 2847 allow data leaks with this option, which is equivalent 2848 to spectre_v2=off. 2849 2850 nospec_store_bypass_disable 2851 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability 2852 2853 noxsave [BUGS=X86] Disables x86 extended register state save 2854 and restore using xsave. The kernel will fallback to 2855 enabling legacy floating-point and sse state. 2856 2857 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 2858 register states. The kernel will fall back to use 2859 xsave to save the states. By using this parameter, 2860 performance of saving the states is degraded because 2861 xsave doesn't support modified optimization while 2862 xsaveopt supports it on xsaveopt enabled systems. 2863 2864 noxsaves [X86] Disables xsaves and xrstors used in saving and 2865 restoring x86 extended register state in compacted 2866 form of xsave area. The kernel will fall back to use 2867 xsaveopt and xrstor to save and restore the states 2868 in standard form of xsave area. By using this 2869 parameter, xsave area per process might occupy more 2870 memory on xsaves enabled systems. 2871 2872 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or 2873 wfi(ARM) instruction doesn't work correctly and not to 2874 use it. This is also useful when using JTAG debugger. 2875 2876 no_file_caps Tells the kernel not to honor file capabilities. The 2877 only way then for a file to be executed with privilege 2878 is to be setuid root or executed by root. 2879 2880 nohalt [IA-64] Tells the kernel not to use the power saving 2881 function PAL_HALT_LIGHT when idle. This increases 2882 power-consumption. On the positive side, it reduces 2883 interrupt wake-up latency, which may improve performance 2884 in certain environments such as networked servers or 2885 real-time systems. 2886 2887 nohibernate [HIBERNATION] Disable hibernation and resume. 2888 2889 nohz= [KNL] Boottime enable/disable dynamic ticks 2890 Valid arguments: on, off 2891 Default: on 2892 2893 nohz_full= [KNL,BOOT,SMP,ISOL] 2894 The argument is a cpu list, as described above. 2895 In kernels built with CONFIG_NO_HZ_FULL=y, set 2896 the specified list of CPUs whose tick will be stopped 2897 whenever possible. The boot CPU will be forced outside 2898 the range to maintain the timekeeping. Any CPUs 2899 in this list will have their RCU callbacks offloaded, 2900 just as if they had also been called out in the 2901 rcu_nocbs= boot parameter. 2902 2903 noiotrap [SH] Disables trapped I/O port accesses. 2904 2905 noirqdebug [X86-32] Disables the code which attempts to detect and 2906 disable unhandled interrupt sources. 2907 2908 no_timer_check [X86,APIC] Disables the code which tests for 2909 broken timer IRQ sources. 2910 2911 noisapnp [ISAPNP] Disables ISA PnP code. 2912 2913 noinitrd [RAM] Tells the kernel not to load any configured 2914 initial RAM disk. 2915 2916 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt 2917 remapping. 2918 [Deprecated - use intremap=off] 2919 2920 nointroute [IA-64] 2921 2922 noinvpcid [X86] Disable the INVPCID cpu feature. 2923 2924 nojitter [IA-64] Disables jitter checking for ITC timers. 2925 2926 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver 2927 2928 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page 2929 fault handling. 2930 2931 no-vmw-sched-clock 2932 [X86,PV_OPS] Disable paravirtualized VMware scheduler 2933 clock and use the default one. 2934 2935 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting. 2936 steal time is computed, but won't influence scheduler 2937 behaviour 2938 2939 nolapic [X86-32,APIC] Do not enable or use the local APIC. 2940 2941 nolapic_timer [X86-32,APIC] Do not use the local APIC timer. 2942 2943 noltlbs [PPC] Do not use large page/tlb entries for kernel 2944 lowmem mapping on PPC40x and PPC8xx 2945 2946 nomca [IA-64] Disable machine check abort handling 2947 2948 nomce [X86-32] Disable Machine Check Exception 2949 2950 nomfgpt [X86-32] Disable Multi-Function General Purpose 2951 Timer usage (for AMD Geode machines). 2952 2953 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 2954 shutdown the other cpus. Instead use the REBOOT_VECTOR 2955 irq. 2956 2957 nomodule Disable module load 2958 2959 nopat [X86] Disable PAT (page attribute table extension of 2960 pagetables) support. 2961 2962 nopcid [X86-64] Disable the PCID cpu feature. 2963 2964 norandmaps Don't use address space randomization. Equivalent to 2965 echo 0 > /proc/sys/kernel/randomize_va_space 2966 2967 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 2968 with UP alternatives 2969 2970 nordrand [X86] Disable kernel use of the RDRAND and 2971 RDSEED instructions even if they are supported 2972 by the processor. RDRAND and RDSEED are still 2973 available to user space applications. 2974 2975 noresume [SWSUSP] Disables resume and restores original swap 2976 space. 2977 2978 no-scroll [VGA] Disables scrollback. 2979 This is required for the Braillex ib80-piezo Braille 2980 reader made by F.H. Papenmeier (Germany). 2981 2982 nosbagart [IA-64] 2983 2984 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support. 2985 2986 nosmp [SMP] Tells an SMP kernel to act as a UP kernel, 2987 and disable the IO APIC. legacy for "maxcpus=0". 2988 2989 nosoftlockup [KNL] Disable the soft-lockup detector. 2990 2991 nosync [HW,M68K] Disables sync negotiation for all devices. 2992 2993 nowatchdog [KNL] Disable both lockup detectors, i.e. 2994 soft-lockup and NMI watchdog (hard-lockup). 2995 2996 nowb [ARM] 2997 2998 nox2apic [X86-64,APIC] Do not enable x2APIC mode. 2999 3000 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when 3001 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off. 3002 Some features depend on CPU0. Known dependencies are: 3003 1. Resume from suspend/hibernate depends on CPU0. 3004 Suspend/hibernate will fail if CPU0 is offline and you 3005 need to online CPU0 before suspend/hibernate. 3006 2. PIC interrupts also depend on CPU0. CPU0 can't be 3007 removed if a PIC interrupt is detected. 3008 It's said poweroff/reboot may depend on CPU0 on some 3009 machines although I haven't seen such issues so far 3010 after CPU0 is offline on a few tested machines. 3011 If the dependencies are under your control, you can 3012 turn on cpu0_hotplug. 3013 3014 nps_mtm_hs_ctr= [KNL,ARC] 3015 This parameter sets the maximum duration, in 3016 cycles, each HW thread of the CTOP can run 3017 without interruptions, before HW switches it. 3018 The actual maximum duration is 16 times this 3019 parameter's value. 3020 Format: integer between 1 and 255 3021 Default: 255 3022 3023 nptcg= [IA-64] Override max number of concurrent global TLB 3024 purges which is reported from either PAL_VM_SUMMARY or 3025 SAL PALO. 3026 3027 nr_cpus= [SMP] Maximum number of processors that an SMP kernel 3028 could support. nr_cpus=n : n >= 1 limits the kernel to 3029 support 'n' processors. It could be larger than the 3030 number of already plugged CPU during bootup, later in 3031 runtime you can physically add extra cpu until it reaches 3032 n. So during boot up some boot time memory for per-cpu 3033 variables need be pre-allocated for later physical cpu 3034 hot plugging. 3035 3036 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 3037 3038 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing. 3039 Allowed values are enable and disable 3040 3041 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 3042 'node', 'default' can be specified 3043 This can be set from sysctl after boot. 3044 See Documentation/sysctl/vm.txt for details. 3045 3046 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver. 3047 See Documentation/debugging-via-ohci1394.txt for more 3048 info. 3049 3050 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 3051 Rather than timing out after 20 ms if an EC 3052 command is not properly ACKed, override the length 3053 of the timeout. We have interrupts disabled while 3054 waiting for the ACK, so if this is set too high 3055 interrupts *may* be lost! 3056 3057 omap_mux= [OMAP] Override bootloader pin multiplexing. 3058 Format: <mux_mode0.mode_name=value>... 3059 For example, to override I2C bus2: 3060 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 3061 3062 oprofile.timer= [HW] 3063 Use timer interrupt instead of performance counters 3064 3065 oprofile.cpu_type= Force an oprofile cpu type 3066 This might be useful if you have an older oprofile 3067 userland or if you want common events. 3068 Format: { arch_perfmon } 3069 arch_perfmon: [X86] Force use of architectural 3070 perfmon on Intel CPUs instead of the 3071 CPU specific event set. 3072 timer: [X86] Force use of architectural NMI 3073 timer mode (see also oprofile.timer 3074 for generic hr timer mode) 3075 3076 oops=panic Always panic on oopses. Default is to just kill the 3077 process, but there is a small probability of 3078 deadlocking the machine. 3079 This will also cause panics on machine check exceptions. 3080 Useful together with panic=30 to trigger a reboot. 3081 3082 page_owner= [KNL] Boot-time page_owner enabling option. 3083 Storage of the information about who allocated 3084 each page is disabled in default. With this switch, 3085 we can turn it on. 3086 on: enable the feature 3087 3088 page_poison= [KNL] Boot-time parameter changing the state of 3089 poisoning on the buddy allocator, available with 3090 CONFIG_PAGE_POISONING=y. 3091 off: turn off poisoning (default) 3092 on: turn on poisoning 3093 3094 panic= [KNL] Kernel behaviour on panic: delay <timeout> 3095 timeout > 0: seconds before rebooting 3096 timeout = 0: wait forever 3097 timeout < 0: reboot immediately 3098 Format: <timeout> 3099 3100 panic_print= Bitmask for printing system info when panic happens. 3101 User can chose combination of the following bits: 3102 bit 0: print all tasks info 3103 bit 1: print system memory info 3104 bit 2: print timer info 3105 bit 3: print locks info if CONFIG_LOCKDEP is on 3106 bit 4: print ftrace buffer 3107 3108 panic_on_warn panic() instead of WARN(). Useful to cause kdump 3109 on a WARN(). 3110 3111 crash_kexec_post_notifiers 3112 Run kdump after running panic-notifiers and dumping 3113 kmsg. This only for the users who doubt kdump always 3114 succeeds in any situation. 3115 Note that this also increases risks of kdump failure, 3116 because some panic notifiers can make the crashed 3117 kernel more unstable. 3118 3119 parkbd.port= [HW] Parallel port number the keyboard adapter is 3120 connected to, default is 0. 3121 Format: <parport#> 3122 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 3123 0 for XT, 1 for AT (default is AT). 3124 Format: <mode> 3125 3126 parport= [HW,PPT] Specify parallel ports. 0 disables. 3127 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 3128 Use 'auto' to force the driver to use any 3129 IRQ/DMA settings detected (the default is to 3130 ignore detected IRQ/DMA settings because of 3131 possible conflicts). You can specify the base 3132 address, IRQ, and DMA settings; IRQ and DMA 3133 should be numbers, or 'auto' (for using detected 3134 settings on that particular port), or 'nofifo' 3135 (to avoid using a FIFO even if it is detected). 3136 Parallel ports are assigned in the order they 3137 are specified on the command line, starting 3138 with parport0. 3139 3140 parport_init_mode= [HW,PPT] 3141 Configure VIA parallel port to operate in 3142 a specific mode. This is necessary on Pegasos 3143 computer where firmware has no options for setting 3144 up parallel port mode and sets it to spp. 3145 Currently this function knows 686a and 8231 chips. 3146 Format: [spp|ps2|epp|ecp|ecpepp] 3147 3148 pause_on_oops= 3149 Halt all CPUs after the first oops has been printed for 3150 the specified number of seconds. This is to be used if 3151 your oopses keep scrolling off the screen. 3152 3153 pcbit= [HW,ISDN] 3154 3155 pcd. [PARIDE] 3156 See header of drivers/block/paride/pcd.c. 3157 See also Documentation/blockdev/paride.txt. 3158 3159 pci=option[,option...] [PCI] various PCI subsystem options. 3160 3161 Some options herein operate on a specific device 3162 or a set of devices (<pci_dev>). These are 3163 specified in one of the following formats: 3164 3165 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* 3166 pci:<vendor>:<device>[:<subvendor>:<subdevice>] 3167 3168 Note: the first format specifies a PCI 3169 bus/device/function address which may change 3170 if new hardware is inserted, if motherboard 3171 firmware changes, or due to changes caused 3172 by other kernel parameters. If the 3173 domain is left unspecified, it is 3174 taken to be zero. Optionally, a path 3175 to a device through multiple device/function 3176 addresses can be specified after the base 3177 address (this is more robust against 3178 renumbering issues). The second format 3179 selects devices using IDs from the 3180 configuration space which may match multiple 3181 devices in the system. 3182 3183 earlydump dump PCI config space before the kernel 3184 changes anything 3185 off [X86] don't probe for the PCI bus 3186 bios [X86-32] force use of PCI BIOS, don't access 3187 the hardware directly. Use this if your machine 3188 has a non-standard PCI host bridge. 3189 nobios [X86-32] disallow use of PCI BIOS, only direct 3190 hardware access methods are allowed. Use this 3191 if you experience crashes upon bootup and you 3192 suspect they are caused by the BIOS. 3193 conf1 [X86] Force use of PCI Configuration Access 3194 Mechanism 1 (config address in IO port 0xCF8, 3195 data in IO port 0xCFC, both 32-bit). 3196 conf2 [X86] Force use of PCI Configuration Access 3197 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 3198 the function, IO port 0xCFA, also 8-bit, sets 3199 bus number. The config space is then accessed 3200 through ports 0xC000-0xCFFF). 3201 See http://wiki.osdev.org/PCI for more info 3202 on the configuration access mechanisms. 3203 noaer [PCIE] If the PCIEAER kernel config parameter is 3204 enabled, this kernel boot option can be used to 3205 disable the use of PCIE advanced error reporting. 3206 nodomains [PCI] Disable support for multiple PCI 3207 root domains (aka PCI segments, in ACPI-speak). 3208 nommconf [X86] Disable use of MMCONFIG for PCI 3209 Configuration 3210 check_enable_amd_mmconf [X86] check for and enable 3211 properly configured MMIO access to PCI 3212 config space on AMD family 10h CPU 3213 nomsi [MSI] If the PCI_MSI kernel config parameter is 3214 enabled, this kernel boot option can be used to 3215 disable the use of MSI interrupts system-wide. 3216 noioapicquirk [APIC] Disable all boot interrupt quirks. 3217 Safety option to keep boot IRQs enabled. This 3218 should never be necessary. 3219 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 3220 primary IO-APIC for bridges that cannot disable 3221 boot IRQs. This fixes a source of spurious IRQs 3222 when the system masks IRQs. 3223 noioapicreroute [APIC] Disable workaround that uses the 3224 boot IRQ equivalent of an IRQ that connects to 3225 a chipset where boot IRQs cannot be disabled. 3226 The opposite of ioapicreroute. 3227 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 3228 routing table. These calls are known to be buggy 3229 on several machines and they hang the machine 3230 when used, but on other computers it's the only 3231 way to get the interrupt routing table. Try 3232 this option if the kernel is unable to allocate 3233 IRQs or discover secondary PCI buses on your 3234 motherboard. 3235 rom [X86] Assign address space to expansion ROMs. 3236 Use with caution as certain devices share 3237 address decoders between ROMs and other 3238 resources. 3239 norom [X86] Do not assign address space to 3240 expansion ROMs that do not already have 3241 BIOS assigned address ranges. 3242 nobar [X86] Do not assign address space to the 3243 BARs that weren't assigned by the BIOS. 3244 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 3245 assigned automatically to PCI devices. You can 3246 make the kernel exclude IRQs of your ISA cards 3247 this way. 3248 pirqaddr=0xAAAAA [X86] Specify the physical address 3249 of the PIRQ table (normally generated 3250 by the BIOS) if it is outside the 3251 F0000h-100000h range. 3252 lastbus=N [X86] Scan all buses thru bus #N. Can be 3253 useful if the kernel is unable to find your 3254 secondary buses and you want to tell it 3255 explicitly which ones they are. 3256 assign-busses [X86] Always assign all PCI bus 3257 numbers ourselves, overriding 3258 whatever the firmware may have done. 3259 usepirqmask [X86] Honor the possible IRQ mask stored 3260 in the BIOS $PIR table. This is needed on 3261 some systems with broken BIOSes, notably 3262 some HP Pavilion N5400 and Omnibook XE3 3263 notebooks. This will have no effect if ACPI 3264 IRQ routing is enabled. 3265 noacpi [X86] Do not use ACPI for IRQ routing 3266 or for PCI scanning. 3267 use_crs [X86] Use PCI host bridge window information 3268 from ACPI. On BIOSes from 2008 or later, this 3269 is enabled by default. If you need to use this, 3270 please report a bug. 3271 nocrs [X86] Ignore PCI host bridge windows from ACPI. 3272 If you need to use this, please report a bug. 3273 routeirq Do IRQ routing for all PCI devices. 3274 This is normally done in pci_enable_device(), 3275 so this option is a temporary workaround 3276 for broken drivers that don't call it. 3277 skip_isa_align [X86] do not align io start addr, so can 3278 handle more pci cards 3279 noearly [X86] Don't do any early type 1 scanning. 3280 This might help on some broken boards which 3281 machine check when some devices' config space 3282 is read. But various workarounds are disabled 3283 and some IOMMU drivers will not work. 3284 bfsort Sort PCI devices into breadth-first order. 3285 This sorting is done to get a device 3286 order compatible with older (<= 2.4) kernels. 3287 nobfsort Don't sort PCI devices into breadth-first order. 3288 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 3289 tuning and use the BIOS-configured MPS defaults. 3290 pcie_bus_safe Set every device's MPS to the largest value 3291 supported by all devices below the root complex. 3292 pcie_bus_perf Set device MPS to the largest allowable MPS 3293 based on its parent bus. Also set MRRS (Max 3294 Read Request Size) to the largest supported 3295 value (no larger than the MPS that the device 3296 or bus can support) for best performance. 3297 pcie_bus_peer2peer Set every device's MPS to 128B, which 3298 every device is guaranteed to support. This 3299 configuration allows peer-to-peer DMA between 3300 any pair of devices, possibly at the cost of 3301 reduced performance. This also guarantees 3302 that hot-added devices will work. 3303 cbiosize=nn[KMG] The fixed amount of bus space which is 3304 reserved for the CardBus bridge's IO window. 3305 The default value is 256 bytes. 3306 cbmemsize=nn[KMG] The fixed amount of bus space which is 3307 reserved for the CardBus bridge's memory 3308 window. The default value is 64 megabytes. 3309 resource_alignment= 3310 Format: 3311 [<order of align>@]<pci_dev>[; ...] 3312 Specifies alignment and device to reassign 3313 aligned memory resources. How to 3314 specify the device is described above. 3315 If <order of align> is not specified, 3316 PAGE_SIZE is used as alignment. 3317 PCI-PCI bridge can be specified, if resource 3318 windows need to be expanded. 3319 To specify the alignment for several 3320 instances of a device, the PCI vendor, 3321 device, subvendor, and subdevice may be 3322 specified, e.g., 4096@pci:8086:9c22:103c:198f 3323 ecrc= Enable/disable PCIe ECRC (transaction layer 3324 end-to-end CRC checking). 3325 bios: Use BIOS/firmware settings. This is the 3326 the default. 3327 off: Turn ECRC off 3328 on: Turn ECRC on. 3329 hpiosize=nn[KMG] The fixed amount of bus space which is 3330 reserved for hotplug bridge's IO window. 3331 Default size is 256 bytes. 3332 hpmemsize=nn[KMG] The fixed amount of bus space which is 3333 reserved for hotplug bridge's memory window. 3334 Default size is 2 megabytes. 3335 hpbussize=nn The minimum amount of additional bus numbers 3336 reserved for buses below a hotplug bridge. 3337 Default is 1. 3338 realloc= Enable/disable reallocating PCI bridge resources 3339 if allocations done by BIOS are too small to 3340 accommodate resources required by all child 3341 devices. 3342 off: Turn realloc off 3343 on: Turn realloc on 3344 realloc same as realloc=on 3345 noari do not use PCIe ARI. 3346 noats [PCIE, Intel-IOMMU, AMD-IOMMU] 3347 do not use PCIe ATS (and IOMMU device IOTLB). 3348 pcie_scan_all Scan all possible PCIe devices. Otherwise we 3349 only look for one device below a PCIe downstream 3350 port. 3351 big_root_window Try to add a big 64bit memory window to the PCIe 3352 root complex on AMD CPUs. Some GFX hardware 3353 can resize a BAR to allow access to all VRAM. 3354 Adding the window is slightly risky (it may 3355 conflict with unreported devices), so this 3356 taints the kernel. 3357 disable_acs_redir=<pci_dev>[; ...] 3358 Specify one or more PCI devices (in the format 3359 specified above) separated by semicolons. 3360 Each device specified will have the PCI ACS 3361 redirect capabilities forced off which will 3362 allow P2P traffic between devices through 3363 bridges without forcing it upstream. Note: 3364 this removes isolation between devices and 3365 may put more devices in an IOMMU group. 3366 3367 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power 3368 Management. 3369 off Disable ASPM. 3370 force Enable ASPM even on devices that claim not to support it. 3371 WARNING: Forcing ASPM on may cause system lockups. 3372 3373 pcie_ports= [PCIE] PCIe port services handling: 3374 native Use native PCIe services (PME, AER, DPC, PCIe hotplug) 3375 even if the platform doesn't give the OS permission to 3376 use them. This may cause conflicts if the platform 3377 also tries to use these services. 3378 compat Disable native PCIe services (PME, AER, DPC, PCIe 3379 hotplug). 3380 3381 pcie_port_pm= [PCIE] PCIe port power management handling: 3382 off Disable power management of all PCIe ports 3383 force Forcibly enable power management of all PCIe ports 3384 3385 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 3386 nomsi Do not use MSI for native PCIe PME signaling (this makes 3387 all PCIe root ports use INTx for all services). 3388 3389 pcmv= [HW,PCMCIA] BadgePAD 4 3390 3391 pd_ignore_unused 3392 [PM] 3393 Keep all power-domains already enabled by bootloader on, 3394 even if no driver has claimed them. This is useful 3395 for debug and development, but should not be 3396 needed on a platform with proper driver support. 3397 3398 pd. [PARIDE] 3399 See Documentation/blockdev/paride.txt. 3400 3401 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 3402 boot time. 3403 Format: { 0 | 1 } 3404 See arch/parisc/kernel/pdc_chassis.c 3405 3406 percpu_alloc= Select which percpu first chunk allocator to use. 3407 Currently supported values are "embed" and "page". 3408 Archs may support subset or none of the selections. 3409 See comments in mm/percpu.c for details on each 3410 allocator. This parameter is primarily for debugging 3411 and performance comparison. 3412 3413 pf. [PARIDE] 3414 See Documentation/blockdev/paride.txt. 3415 3416 pg. [PARIDE] 3417 See Documentation/blockdev/paride.txt. 3418 3419 pirq= [SMP,APIC] Manual mp-table setup 3420 See Documentation/x86/i386/IO-APIC.txt. 3421 3422 plip= [PPT,NET] Parallel port network link 3423 Format: { parport<nr> | timid | 0 } 3424 See also Documentation/admin-guide/parport.rst. 3425 3426 pmtmr= [X86] Manual setup of pmtmr I/O Port. 3427 Override pmtimer IOPort with a hex value. 3428 e.g. pmtmr=0x508 3429 3430 pnp.debug=1 [PNP] 3431 Enable PNP debug messages (depends on the 3432 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 3433 via /sys/module/pnp/parameters/debug. We always show 3434 current resource usage; turning this on also shows 3435 possible settings and some assignment information. 3436 3437 pnpacpi= [ACPI] 3438 { off } 3439 3440 pnpbios= [ISAPNP] 3441 { on | off | curr | res | no-curr | no-res } 3442 3443 pnp_reserve_irq= 3444 [ISAPNP] Exclude IRQs for the autoconfiguration 3445 3446 pnp_reserve_dma= 3447 [ISAPNP] Exclude DMAs for the autoconfiguration 3448 3449 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 3450 Ranges are in pairs (I/O port base and size). 3451 3452 pnp_reserve_mem= 3453 [ISAPNP] Exclude memory regions for the 3454 autoconfiguration. 3455 Ranges are in pairs (memory base and size). 3456 3457 ports= [IP_VS_FTP] IPVS ftp helper module 3458 Default is 21. 3459 Up to 8 (IP_VS_APP_MAX_PORTS) ports 3460 may be specified. 3461 Format: <port>,<port>.... 3462 3463 powersave=off [PPC] This option disables power saving features. 3464 It specifically disables cpuidle and sets the 3465 platform machine description specific power_save 3466 function to NULL. On Idle the CPU just reduces 3467 execution priority. 3468 3469 ppc_strict_facility_enable 3470 [PPC] This option catches any kernel floating point, 3471 Altivec, VSX and SPE outside of regions specifically 3472 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 3473 There is some performance impact when enabling this. 3474 3475 ppc_tm= [PPC] 3476 Format: {"off"} 3477 Disable Hardware Transactional Memory 3478 3479 print-fatal-signals= 3480 [KNL] debug: print fatal signals 3481 3482 If enabled, warn about various signal handling 3483 related application anomalies: too many signals, 3484 too many POSIX.1 timers, fatal signals causing a 3485 coredump - etc. 3486 3487 If you hit the warning due to signal overflow, 3488 you might want to try "ulimit -i unlimited". 3489 3490 default: off. 3491 3492 printk.always_kmsg_dump= 3493 Trigger kmsg_dump for cases other than kernel oops or 3494 panics 3495 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3496 default: disabled 3497 3498 printk.devkmsg={on,off,ratelimit} 3499 Control writing to /dev/kmsg. 3500 on - unlimited logging to /dev/kmsg from userspace 3501 off - logging to /dev/kmsg disabled 3502 ratelimit - ratelimit the logging 3503 Default: ratelimit 3504 3505 printk.time= Show timing data prefixed to each printk message line 3506 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3507 3508 processor.max_cstate= [HW,ACPI] 3509 Limit processor to maximum C-state 3510 max_cstate=9 overrides any DMI blacklist limit. 3511 3512 processor.nocst [HW,ACPI] 3513 Ignore the _CST method to determine C-states, 3514 instead using the legacy FADT method 3515 3516 profile= [KNL] Enable kernel profiling via /proc/profile 3517 Format: [<profiletype>,]<number> 3518 Param: <profiletype>: "schedule", "sleep", or "kvm" 3519 [defaults to kernel profiling] 3520 Param: "schedule" - profile schedule points. 3521 Param: "sleep" - profile D-state sleeping (millisecs). 3522 Requires CONFIG_SCHEDSTATS 3523 Param: "kvm" - profile VM exits. 3524 Param: <number> - step/bucket size as a power of 2 for 3525 statistical time based profiling. 3526 3527 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk 3528 before loading. 3529 See Documentation/blockdev/ramdisk.txt. 3530 3531 psi= [KNL] Enable or disable pressure stall information 3532 tracking. 3533 Format: <bool> 3534 3535 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 3536 probe for; one of (bare|imps|exps|lifebook|any). 3537 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 3538 per second. 3539 psmouse.resetafter= [HW,MOUSE] 3540 Try to reset the device after so many bad packets 3541 (0 = never). 3542 psmouse.resolution= 3543 [HW,MOUSE] Set desired mouse resolution, in dpi. 3544 psmouse.smartscroll= 3545 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 3546 0 = disabled, 1 = enabled (default). 3547 3548 pstore.backend= Specify the name of the pstore backend to use 3549 3550 pt. [PARIDE] 3551 See Documentation/blockdev/paride.txt. 3552 3553 pti= [X86_64] Control Page Table Isolation of user and 3554 kernel address spaces. Disabling this feature 3555 removes hardening, but improves performance of 3556 system calls and interrupts. 3557 3558 on - unconditionally enable 3559 off - unconditionally disable 3560 auto - kernel detects whether your CPU model is 3561 vulnerable to issues that PTI mitigates 3562 3563 Not specifying this option is equivalent to pti=auto. 3564 3565 nopti [X86_64] 3566 Equivalent to pti=off 3567 3568 pty.legacy_count= 3569 [KNL] Number of legacy pty's. Overwrites compiled-in 3570 default number. 3571 3572 quiet [KNL] Disable most log messages 3573 3574 r128= [HW,DRM] 3575 3576 raid= [HW,RAID] 3577 See Documentation/admin-guide/md.rst. 3578 3579 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 3580 See Documentation/blockdev/ramdisk.txt. 3581 3582 random.trust_cpu={on,off} 3583 [KNL] Enable or disable trusting the use of the 3584 CPU's random number generator (if available) to 3585 fully seed the kernel's CRNG. Default is controlled 3586 by CONFIG_RANDOM_TRUST_CPU. 3587 3588 ras=option[,option,...] [KNL] RAS-specific options 3589 3590 cec_disable [X86] 3591 Disable the Correctable Errors Collector, 3592 see CONFIG_RAS_CEC help text. 3593 3594 rcu_nocbs= [KNL] 3595 The argument is a cpu list, as described above. 3596 3597 In kernels built with CONFIG_RCU_NOCB_CPU=y, set 3598 the specified list of CPUs to be no-callback CPUs. 3599 Invocation of these CPUs' RCU callbacks will be 3600 offloaded to "rcuox/N" kthreads created for that 3601 purpose, where "x" is "p" for RCU-preempt, and 3602 "s" for RCU-sched, and "N" is the CPU number. 3603 This reduces OS jitter on the offloaded CPUs, 3604 which can be useful for HPC and real-time 3605 workloads. It can also improve energy efficiency 3606 for asymmetric multiprocessors. 3607 3608 rcu_nocb_poll [KNL] 3609 Rather than requiring that offloaded CPUs 3610 (specified by rcu_nocbs= above) explicitly 3611 awaken the corresponding "rcuoN" kthreads, 3612 make these kthreads poll for callbacks. 3613 This improves the real-time response for the 3614 offloaded CPUs by relieving them of the need to 3615 wake up the corresponding kthread, but degrades 3616 energy efficiency by requiring that the kthreads 3617 periodically wake up to do the polling. 3618 3619 rcutree.blimit= [KNL] 3620 Set maximum number of finished RCU callbacks to 3621 process in one batch. 3622 3623 rcutree.dump_tree= [KNL] 3624 Dump the structure of the rcu_node combining tree 3625 out at early boot. This is used for diagnostic 3626 purposes, to verify correct tree setup. 3627 3628 rcutree.gp_cleanup_delay= [KNL] 3629 Set the number of jiffies to delay each step of 3630 RCU grace-period cleanup. 3631 3632 rcutree.gp_init_delay= [KNL] 3633 Set the number of jiffies to delay each step of 3634 RCU grace-period initialization. 3635 3636 rcutree.gp_preinit_delay= [KNL] 3637 Set the number of jiffies to delay each step of 3638 RCU grace-period pre-initialization, that is, 3639 the propagation of recent CPU-hotplug changes up 3640 the rcu_node combining tree. 3641 3642 rcutree.rcu_fanout_exact= [KNL] 3643 Disable autobalancing of the rcu_node combining 3644 tree. This is used by rcutorture, and might 3645 possibly be useful for architectures having high 3646 cache-to-cache transfer latencies. 3647 3648 rcutree.rcu_fanout_leaf= [KNL] 3649 Change the number of CPUs assigned to each 3650 leaf rcu_node structure. Useful for very 3651 large systems, which will choose the value 64, 3652 and for NUMA systems with large remote-access 3653 latencies, which will choose a value aligned 3654 with the appropriate hardware boundaries. 3655 3656 rcutree.jiffies_till_sched_qs= [KNL] 3657 Set required age in jiffies for a 3658 given grace period before RCU starts 3659 soliciting quiescent-state help from 3660 rcu_note_context_switch(). If not specified, the 3661 kernel will calculate a value based on the most 3662 recent settings of rcutree.jiffies_till_first_fqs 3663 and rcutree.jiffies_till_next_fqs. 3664 This calculated value may be viewed in 3665 rcutree.jiffies_to_sched_qs. Any attempt to 3666 set rcutree.jiffies_to_sched_qs will be 3667 cheerfully overwritten. 3668 3669 rcutree.jiffies_till_first_fqs= [KNL] 3670 Set delay from grace-period initialization to 3671 first attempt to force quiescent states. 3672 Units are jiffies, minimum value is zero, 3673 and maximum value is HZ. 3674 3675 rcutree.jiffies_till_next_fqs= [KNL] 3676 Set delay between subsequent attempts to force 3677 quiescent states. Units are jiffies, minimum 3678 value is one, and maximum value is HZ. 3679 3680 rcutree.kthread_prio= [KNL,BOOT] 3681 Set the SCHED_FIFO priority of the RCU per-CPU 3682 kthreads (rcuc/N). This value is also used for 3683 the priority of the RCU boost threads (rcub/N) 3684 and for the RCU grace-period kthreads (rcu_bh, 3685 rcu_preempt, and rcu_sched). If RCU_BOOST is 3686 set, valid values are 1-99 and the default is 1 3687 (the least-favored priority). Otherwise, when 3688 RCU_BOOST is not set, valid values are 0-99 and 3689 the default is zero (non-realtime operation). 3690 3691 rcutree.rcu_nocb_leader_stride= [KNL] 3692 Set the number of NOCB kthread groups, which 3693 defaults to the square root of the number of 3694 CPUs. Larger numbers reduces the wakeup overhead 3695 on the per-CPU grace-period kthreads, but increases 3696 that same overhead on each group's leader. 3697 3698 rcutree.qhimark= [KNL] 3699 Set threshold of queued RCU callbacks beyond which 3700 batch limiting is disabled. 3701 3702 rcutree.qlowmark= [KNL] 3703 Set threshold of queued RCU callbacks below which 3704 batch limiting is re-enabled. 3705 3706 rcutree.rcu_idle_gp_delay= [KNL] 3707 Set wakeup interval for idle CPUs that have 3708 RCU callbacks (RCU_FAST_NO_HZ=y). 3709 3710 rcutree.rcu_idle_lazy_gp_delay= [KNL] 3711 Set wakeup interval for idle CPUs that have 3712 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y). 3713 Lazy RCU callbacks are those which RCU can 3714 prove do nothing more than free memory. 3715 3716 rcutree.rcu_kick_kthreads= [KNL] 3717 Cause the grace-period kthread to get an extra 3718 wake_up() if it sleeps three times longer than 3719 it should at force-quiescent-state time. 3720 This wake_up() will be accompanied by a 3721 WARN_ONCE() splat and an ftrace_dump(). 3722 3723 rcuperf.gp_async= [KNL] 3724 Measure performance of asynchronous 3725 grace-period primitives such as call_rcu(). 3726 3727 rcuperf.gp_async_max= [KNL] 3728 Specify the maximum number of outstanding 3729 callbacks per writer thread. When a writer 3730 thread exceeds this limit, it invokes the 3731 corresponding flavor of rcu_barrier() to allow 3732 previously posted callbacks to drain. 3733 3734 rcuperf.gp_exp= [KNL] 3735 Measure performance of expedited synchronous 3736 grace-period primitives. 3737 3738 rcuperf.holdoff= [KNL] 3739 Set test-start holdoff period. The purpose of 3740 this parameter is to delay the start of the 3741 test until boot completes in order to avoid 3742 interference. 3743 3744 rcuperf.nreaders= [KNL] 3745 Set number of RCU readers. The value -1 selects 3746 N, where N is the number of CPUs. A value 3747 "n" less than -1 selects N-n+1, where N is again 3748 the number of CPUs. For example, -2 selects N 3749 (the number of CPUs), -3 selects N+1, and so on. 3750 A value of "n" less than or equal to -N selects 3751 a single reader. 3752 3753 rcuperf.nwriters= [KNL] 3754 Set number of RCU writers. The values operate 3755 the same as for rcuperf.nreaders. 3756 N, where N is the number of CPUs 3757 3758 rcuperf.perf_type= [KNL] 3759 Specify the RCU implementation to test. 3760 3761 rcuperf.shutdown= [KNL] 3762 Shut the system down after performance tests 3763 complete. This is useful for hands-off automated 3764 testing. 3765 3766 rcuperf.verbose= [KNL] 3767 Enable additional printk() statements. 3768 3769 rcuperf.writer_holdoff= [KNL] 3770 Write-side holdoff between grace periods, 3771 in microseconds. The default of zero says 3772 no holdoff. 3773 3774 rcutorture.fqs_duration= [KNL] 3775 Set duration of force_quiescent_state bursts 3776 in microseconds. 3777 3778 rcutorture.fqs_holdoff= [KNL] 3779 Set holdoff time within force_quiescent_state bursts 3780 in microseconds. 3781 3782 rcutorture.fqs_stutter= [KNL] 3783 Set wait time between force_quiescent_state bursts 3784 in seconds. 3785 3786 rcutorture.fwd_progress= [KNL] 3787 Enable RCU grace-period forward-progress testing 3788 for the types of RCU supporting this notion. 3789 3790 rcutorture.fwd_progress_div= [KNL] 3791 Specify the fraction of a CPU-stall-warning 3792 period to do tight-loop forward-progress testing. 3793 3794 rcutorture.fwd_progress_holdoff= [KNL] 3795 Number of seconds to wait between successive 3796 forward-progress tests. 3797 3798 rcutorture.fwd_progress_need_resched= [KNL] 3799 Enclose cond_resched() calls within checks for 3800 need_resched() during tight-loop forward-progress 3801 testing. 3802 3803 rcutorture.gp_cond= [KNL] 3804 Use conditional/asynchronous update-side 3805 primitives, if available. 3806 3807 rcutorture.gp_exp= [KNL] 3808 Use expedited update-side primitives, if available. 3809 3810 rcutorture.gp_normal= [KNL] 3811 Use normal (non-expedited) asynchronous 3812 update-side primitives, if available. 3813 3814 rcutorture.gp_sync= [KNL] 3815 Use normal (non-expedited) synchronous 3816 update-side primitives, if available. If all 3817 of rcutorture.gp_cond=, rcutorture.gp_exp=, 3818 rcutorture.gp_normal=, and rcutorture.gp_sync= 3819 are zero, rcutorture acts as if is interpreted 3820 they are all non-zero. 3821 3822 rcutorture.n_barrier_cbs= [KNL] 3823 Set callbacks/threads for rcu_barrier() testing. 3824 3825 rcutorture.nfakewriters= [KNL] 3826 Set number of concurrent RCU writers. These just 3827 stress RCU, they don't participate in the actual 3828 test, hence the "fake". 3829 3830 rcutorture.nreaders= [KNL] 3831 Set number of RCU readers. The value -1 selects 3832 N-1, where N is the number of CPUs. A value 3833 "n" less than -1 selects N-n-2, where N is again 3834 the number of CPUs. For example, -2 selects N 3835 (the number of CPUs), -3 selects N+1, and so on. 3836 3837 rcutorture.object_debug= [KNL] 3838 Enable debug-object double-call_rcu() testing. 3839 3840 rcutorture.onoff_holdoff= [KNL] 3841 Set time (s) after boot for CPU-hotplug testing. 3842 3843 rcutorture.onoff_interval= [KNL] 3844 Set time (jiffies) between CPU-hotplug operations, 3845 or zero to disable CPU-hotplug testing. 3846 3847 rcutorture.shuffle_interval= [KNL] 3848 Set task-shuffle interval (s). Shuffling tasks 3849 allows some CPUs to go into dyntick-idle mode 3850 during the rcutorture test. 3851 3852 rcutorture.shutdown_secs= [KNL] 3853 Set time (s) after boot system shutdown. This 3854 is useful for hands-off automated testing. 3855 3856 rcutorture.stall_cpu= [KNL] 3857 Duration of CPU stall (s) to test RCU CPU stall 3858 warnings, zero to disable. 3859 3860 rcutorture.stall_cpu_holdoff= [KNL] 3861 Time to wait (s) after boot before inducing stall. 3862 3863 rcutorture.stall_cpu_irqsoff= [KNL] 3864 Disable interrupts while stalling if set. 3865 3866 rcutorture.stat_interval= [KNL] 3867 Time (s) between statistics printk()s. 3868 3869 rcutorture.stutter= [KNL] 3870 Time (s) to stutter testing, for example, specifying 3871 five seconds causes the test to run for five seconds, 3872 wait for five seconds, and so on. This tests RCU's 3873 ability to transition abruptly to and from idle. 3874 3875 rcutorture.test_boost= [KNL] 3876 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 3877 "Maybe" means test if the RCU implementation 3878 under test support RCU priority boosting. 3879 3880 rcutorture.test_boost_duration= [KNL] 3881 Duration (s) of each individual boost test. 3882 3883 rcutorture.test_boost_interval= [KNL] 3884 Interval (s) between each boost test. 3885 3886 rcutorture.test_no_idle_hz= [KNL] 3887 Test RCU's dyntick-idle handling. See also the 3888 rcutorture.shuffle_interval parameter. 3889 3890 rcutorture.torture_type= [KNL] 3891 Specify the RCU implementation to test. 3892 3893 rcutorture.verbose= [KNL] 3894 Enable additional printk() statements. 3895 3896 rcupdate.rcu_cpu_stall_suppress= [KNL] 3897 Suppress RCU CPU stall warning messages. 3898 3899 rcupdate.rcu_cpu_stall_timeout= [KNL] 3900 Set timeout for RCU CPU stall warning messages. 3901 3902 rcupdate.rcu_expedited= [KNL] 3903 Use expedited grace-period primitives, for 3904 example, synchronize_rcu_expedited() instead 3905 of synchronize_rcu(). This reduces latency, 3906 but can increase CPU utilization, degrade 3907 real-time latency, and degrade energy efficiency. 3908 No effect on CONFIG_TINY_RCU kernels. 3909 3910 rcupdate.rcu_normal= [KNL] 3911 Use only normal grace-period primitives, 3912 for example, synchronize_rcu() instead of 3913 synchronize_rcu_expedited(). This improves 3914 real-time latency, CPU utilization, and 3915 energy efficiency, but can expose users to 3916 increased grace-period latency. This parameter 3917 overrides rcupdate.rcu_expedited. No effect on 3918 CONFIG_TINY_RCU kernels. 3919 3920 rcupdate.rcu_normal_after_boot= [KNL] 3921 Once boot has completed (that is, after 3922 rcu_end_inkernel_boot() has been invoked), use 3923 only normal grace-period primitives. No effect 3924 on CONFIG_TINY_RCU kernels. 3925 3926 rcupdate.rcu_task_stall_timeout= [KNL] 3927 Set timeout in jiffies for RCU task stall warning 3928 messages. Disable with a value less than or equal 3929 to zero. 3930 3931 rcupdate.rcu_self_test= [KNL] 3932 Run the RCU early boot self tests 3933 3934 rdinit= [KNL] 3935 Format: <full_path> 3936 Run specified binary instead of /init from the ramdisk, 3937 used for early userspace startup. See initrd. 3938 3939 rdt= [HW,X86,RDT] 3940 Turn on/off individual RDT features. List is: 3941 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, 3942 mba. 3943 E.g. to turn on cmt and turn off mba use: 3944 rdt=cmt,!mba 3945 3946 reboot= [KNL] 3947 Format (x86 or x86_64): 3948 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \ 3949 [[,]s[mp]#### \ 3950 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 3951 [[,]f[orce] 3952 Where reboot_mode is one of warm (soft) or cold (hard) or gpio, 3953 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 3954 reboot_force is either force or not specified, 3955 reboot_cpu is s[mp]#### with #### being the processor 3956 to be used for rebooting. 3957 3958 relax_domain_level= 3959 [KNL, SMP] Set scheduler's default relax_domain_level. 3960 See Documentation/cgroup-v1/cpusets.txt. 3961 3962 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory 3963 Format: <base1>,<size1>[,<base2>,<size2>,...] 3964 Reserve I/O ports or memory so the kernel won't use 3965 them. If <base> is less than 0x10000, the region 3966 is assumed to be I/O ports; otherwise it is memory. 3967 3968 reservetop= [X86-32] 3969 Format: nn[KMG] 3970 Reserves a hole at the top of the kernel virtual 3971 address space. 3972 3973 reservelow= [X86] 3974 Format: nn[K] 3975 Set the amount of memory to reserve for BIOS at 3976 the bottom of the address space. 3977 3978 reset_devices [KNL] Force drivers to reset the underlying device 3979 during initialization. 3980 3981 resume= [SWSUSP] 3982 Specify the partition device for software suspend 3983 Format: 3984 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 3985 3986 resume_offset= [SWSUSP] 3987 Specify the offset from the beginning of the partition 3988 given by "resume=" at which the swap header is located, 3989 in <PAGE_SIZE> units (needed only for swap files). 3990 See Documentation/power/swsusp-and-swap-files.txt 3991 3992 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 3993 read the resume files 3994 3995 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 3996 Useful for devices that are detected asynchronously 3997 (e.g. USB and MMC devices). 3998 3999 hibernate= [HIBERNATION] 4000 noresume Don't check if there's a hibernation image 4001 present during boot. 4002 nocompress Don't compress/decompress hibernation images. 4003 no Disable hibernation and resume. 4004 protect_image Turn on image protection during restoration 4005 (that will set all pages holding image data 4006 during restoration read-only). 4007 4008 retain_initrd [RAM] Keep initrd memory after extraction 4009 4010 rfkill.default_state= 4011 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 4012 etc. communication is blocked by default. 4013 1 Unblocked. 4014 4015 rfkill.master_switch_mode= 4016 0 The "airplane mode" button does nothing. 4017 1 The "airplane mode" button toggles between everything 4018 blocked and the previous configuration. 4019 2 The "airplane mode" button toggles between everything 4020 blocked and everything unblocked. 4021 4022 rhash_entries= [KNL,NET] 4023 Set number of hash buckets for route cache 4024 4025 ring3mwait=disable 4026 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 4027 CPUs. 4028 4029 ro [KNL] Mount root device read-only on boot 4030 4031 rodata= [KNL] 4032 on Mark read-only kernel memory as read-only (default). 4033 off Leave read-only kernel memory writable for debugging. 4034 4035 rockchip.usb_uart 4036 Enable the uart passthrough on the designated usb port 4037 on Rockchip SoCs. When active, the signals of the 4038 debug-uart get routed to the D+ and D- pins of the usb 4039 port and the regular usb controller gets disabled. 4040 4041 root= [KNL] Root filesystem 4042 See name_to_dev_t comment in init/do_mounts.c. 4043 4044 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 4045 mount the root filesystem 4046 4047 rootflags= [KNL] Set root filesystem mount option string 4048 4049 rootfstype= [KNL] Set root filesystem type 4050 4051 rootwait [KNL] Wait (indefinitely) for root device to show up. 4052 Useful for devices that are detected asynchronously 4053 (e.g. USB and MMC devices). 4054 4055 rproc_mem=nn[KMG][@address] 4056 [KNL,ARM,CMA] Remoteproc physical memory block. 4057 Memory area to be used by remote processor image, 4058 managed by CMA. 4059 4060 rw [KNL] Mount root device read-write on boot 4061 4062 S [KNL] Run init in single mode 4063 4064 s390_iommu= [HW,S390] 4065 Set s390 IOTLB flushing mode 4066 strict 4067 With strict flushing every unmap operation will result in 4068 an IOTLB flush. Default is lazy flushing before reuse, 4069 which is faster. 4070 4071 sa1100ir [NET] 4072 See drivers/net/irda/sa1100_ir.c. 4073 4074 sbni= [NET] Granch SBNI12 leased line adapter 4075 4076 sched_debug [KNL] Enables verbose scheduler debug messages. 4077 4078 schedstats= [KNL,X86] Enable or disable scheduled statistics. 4079 Allowed values are enable and disable. This feature 4080 incurs a small amount of overhead in the scheduler 4081 but is useful for debugging and performance tuning. 4082 4083 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate 4084 xtime_lock contention on larger systems, and/or RCU lock 4085 contention on all systems with CONFIG_MAXSMP set. 4086 Format: { "0" | "1" } 4087 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 4088 1 -- enable. 4089 Note: increases power consumption, thus should only be 4090 enabled if running jitter sensitive (HPC/RT) workloads. 4091 4092 security= [SECURITY] Choose a security module to enable at boot. 4093 If this boot parameter is not specified, only the first 4094 security module asking for security registration will be 4095 loaded. An invalid security module name will be treated 4096 as if no module has been chosen. 4097 4098 selinux= [SELINUX] Disable or enable SELinux at boot time. 4099 Format: { "0" | "1" } 4100 See security/selinux/Kconfig help text. 4101 0 -- disable. 4102 1 -- enable. 4103 Default value is set via kernel config option. 4104 If enabled at boot time, /selinux/disable can be used 4105 later to disable prior to initial policy load. 4106 4107 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 4108 Format: { "0" | "1" } 4109 See security/apparmor/Kconfig help text 4110 0 -- disable. 4111 1 -- enable. 4112 Default value is set via kernel config option. 4113 4114 serialnumber [BUGS=X86-32] 4115 4116 shapers= [NET] 4117 Maximal number of shapers. 4118 4119 simeth= [IA-64] 4120 simscsi= 4121 4122 slram= [HW,MTD] 4123 4124 slab_nomerge [MM] 4125 Disable merging of slabs with similar size. May be 4126 necessary if there is some reason to distinguish 4127 allocs to different slabs, especially in hardened 4128 environments where the risk of heap overflows and 4129 layout control by attackers can usually be 4130 frustrated by disabling merging. This will reduce 4131 most of the exposure of a heap attack to a single 4132 cache (risks via metadata attacks are mostly 4133 unchanged). Debug options disable merging on their 4134 own. 4135 For more information see Documentation/vm/slub.rst. 4136 4137 slab_max_order= [MM, SLAB] 4138 Determines the maximum allowed order for slabs. 4139 A high setting may cause OOMs due to memory 4140 fragmentation. Defaults to 1 for systems with 4141 more than 32MB of RAM, 0 otherwise. 4142 4143 slub_debug[=options[,slabs]] [MM, SLUB] 4144 Enabling slub_debug allows one to determine the 4145 culprit if slab objects become corrupted. Enabling 4146 slub_debug can create guard zones around objects and 4147 may poison objects when not in use. Also tracks the 4148 last alloc / free. For more information see 4149 Documentation/vm/slub.rst. 4150 4151 slub_memcg_sysfs= [MM, SLUB] 4152 Determines whether to enable sysfs directories for 4153 memory cgroup sub-caches. 1 to enable, 0 to disable. 4154 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON. 4155 Enabling this can lead to a very high number of debug 4156 directories and files being created under 4157 /sys/kernel/slub. 4158 4159 slub_max_order= [MM, SLUB] 4160 Determines the maximum allowed order for slabs. 4161 A high setting may cause OOMs due to memory 4162 fragmentation. For more information see 4163 Documentation/vm/slub.rst. 4164 4165 slub_min_objects= [MM, SLUB] 4166 The minimum number of objects per slab. SLUB will 4167 increase the slab order up to slub_max_order to 4168 generate a sufficiently large slab able to contain 4169 the number of objects indicated. The higher the number 4170 of objects the smaller the overhead of tracking slabs 4171 and the less frequently locks need to be acquired. 4172 For more information see Documentation/vm/slub.rst. 4173 4174 slub_min_order= [MM, SLUB] 4175 Determines the minimum page order for slabs. Must be 4176 lower than slub_max_order. 4177 For more information see Documentation/vm/slub.rst. 4178 4179 slub_nomerge [MM, SLUB] 4180 Same with slab_nomerge. This is supported for legacy. 4181 See slab_nomerge for more information. 4182 4183 smart2= [HW] 4184 Format: <io1>[,<io2>[,...,<io8>]] 4185 4186 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 4187 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 4188 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 4189 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 4190 smsc-ircc2.ircc_irq= [HW] IRQ line 4191 smsc-ircc2.ircc_dma= [HW] DMA channel 4192 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 4193 0: Toshiba Satellite 1800 (GP data pin select) 4194 1: Fast pin select (default) 4195 2: ATC IRMode 4196 4197 smt [KNL,S390] Set the maximum number of threads (logical 4198 CPUs) to use per physical CPU on systems capable of 4199 symmetric multithreading (SMT). Will be capped to the 4200 actual hardware limit. 4201 Format: <integer> 4202 Default: -1 (no limit) 4203 4204 softlockup_panic= 4205 [KNL] Should the soft-lockup detector generate panics. 4206 Format: <integer> 4207 4208 A nonzero value instructs the soft-lockup detector 4209 to panic the machine when a soft-lockup occurs. This 4210 is also controlled by CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC 4211 which is the respective build-time switch to that 4212 functionality. 4213 4214 softlockup_all_cpu_backtrace= 4215 [KNL] Should the soft-lockup detector generate 4216 backtraces on all cpus. 4217 Format: <integer> 4218 4219 sonypi.*= [HW] Sony Programmable I/O Control Device driver 4220 See Documentation/laptops/sonypi.txt 4221 4222 spectre_v2= [X86] Control mitigation of Spectre variant 2 4223 (indirect branch speculation) vulnerability. 4224 The default operation protects the kernel from 4225 user space attacks. 4226 4227 on - unconditionally enable, implies 4228 spectre_v2_user=on 4229 off - unconditionally disable, implies 4230 spectre_v2_user=off 4231 auto - kernel detects whether your CPU model is 4232 vulnerable 4233 4234 Selecting 'on' will, and 'auto' may, choose a 4235 mitigation method at run time according to the 4236 CPU, the available microcode, the setting of the 4237 CONFIG_RETPOLINE configuration option, and the 4238 compiler with which the kernel was built. 4239 4240 Selecting 'on' will also enable the mitigation 4241 against user space to user space task attacks. 4242 4243 Selecting 'off' will disable both the kernel and 4244 the user space protections. 4245 4246 Specific mitigations can also be selected manually: 4247 4248 retpoline - replace indirect branches 4249 retpoline,generic - google's original retpoline 4250 retpoline,amd - AMD-specific minimal thunk 4251 4252 Not specifying this option is equivalent to 4253 spectre_v2=auto. 4254 4255 spectre_v2_user= 4256 [X86] Control mitigation of Spectre variant 2 4257 (indirect branch speculation) vulnerability between 4258 user space tasks 4259 4260 on - Unconditionally enable mitigations. Is 4261 enforced by spectre_v2=on 4262 4263 off - Unconditionally disable mitigations. Is 4264 enforced by spectre_v2=off 4265 4266 prctl - Indirect branch speculation is enabled, 4267 but mitigation can be enabled via prctl 4268 per thread. The mitigation control state 4269 is inherited on fork. 4270 4271 prctl,ibpb 4272 - Like "prctl" above, but only STIBP is 4273 controlled per thread. IBPB is issued 4274 always when switching between different user 4275 space processes. 4276 4277 seccomp 4278 - Same as "prctl" above, but all seccomp 4279 threads will enable the mitigation unless 4280 they explicitly opt out. 4281 4282 seccomp,ibpb 4283 - Like "seccomp" above, but only STIBP is 4284 controlled per thread. IBPB is issued 4285 always when switching between different 4286 user space processes. 4287 4288 auto - Kernel selects the mitigation depending on 4289 the available CPU features and vulnerability. 4290 4291 Default mitigation: 4292 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl" 4293 4294 Not specifying this option is equivalent to 4295 spectre_v2_user=auto. 4296 4297 spec_store_bypass_disable= 4298 [HW] Control Speculative Store Bypass (SSB) Disable mitigation 4299 (Speculative Store Bypass vulnerability) 4300 4301 Certain CPUs are vulnerable to an exploit against a 4302 a common industry wide performance optimization known 4303 as "Speculative Store Bypass" in which recent stores 4304 to the same memory location may not be observed by 4305 later loads during speculative execution. The idea 4306 is that such stores are unlikely and that they can 4307 be detected prior to instruction retirement at the 4308 end of a particular speculation execution window. 4309 4310 In vulnerable processors, the speculatively forwarded 4311 store can be used in a cache side channel attack, for 4312 example to read memory to which the attacker does not 4313 directly have access (e.g. inside sandboxed code). 4314 4315 This parameter controls whether the Speculative Store 4316 Bypass optimization is used. 4317 4318 On x86 the options are: 4319 4320 on - Unconditionally disable Speculative Store Bypass 4321 off - Unconditionally enable Speculative Store Bypass 4322 auto - Kernel detects whether the CPU model contains an 4323 implementation of Speculative Store Bypass and 4324 picks the most appropriate mitigation. If the 4325 CPU is not vulnerable, "off" is selected. If the 4326 CPU is vulnerable the default mitigation is 4327 architecture and Kconfig dependent. See below. 4328 prctl - Control Speculative Store Bypass per thread 4329 via prctl. Speculative Store Bypass is enabled 4330 for a process by default. The state of the control 4331 is inherited on fork. 4332 seccomp - Same as "prctl" above, but all seccomp threads 4333 will disable SSB unless they explicitly opt out. 4334 4335 Default mitigations: 4336 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl" 4337 4338 On powerpc the options are: 4339 4340 on,auto - On Power8 and Power9 insert a store-forwarding 4341 barrier on kernel entry and exit. On Power7 4342 perform a software flush on kernel entry and 4343 exit. 4344 off - No action. 4345 4346 Not specifying this option is equivalent to 4347 spec_store_bypass_disable=auto. 4348 4349 spia_io_base= [HW,MTD] 4350 spia_fio_base= 4351 spia_pedr= 4352 spia_peddr= 4353 4354 srcutree.counter_wrap_check [KNL] 4355 Specifies how frequently to check for 4356 grace-period sequence counter wrap for the 4357 srcu_data structure's ->srcu_gp_seq_needed field. 4358 The greater the number of bits set in this kernel 4359 parameter, the less frequently counter wrap will 4360 be checked for. Note that the bottom two bits 4361 are ignored. 4362 4363 srcutree.exp_holdoff [KNL] 4364 Specifies how many nanoseconds must elapse 4365 since the end of the last SRCU grace period for 4366 a given srcu_struct until the next normal SRCU 4367 grace period will be considered for automatic 4368 expediting. Set to zero to disable automatic 4369 expediting. 4370 4371 ssbd= [ARM64,HW] 4372 Speculative Store Bypass Disable control 4373 4374 On CPUs that are vulnerable to the Speculative 4375 Store Bypass vulnerability and offer a 4376 firmware based mitigation, this parameter 4377 indicates how the mitigation should be used: 4378 4379 force-on: Unconditionally enable mitigation for 4380 for both kernel and userspace 4381 force-off: Unconditionally disable mitigation for 4382 for both kernel and userspace 4383 kernel: Always enable mitigation in the 4384 kernel, and offer a prctl interface 4385 to allow userspace to register its 4386 interest in being mitigated too. 4387 4388 stack_guard_gap= [MM] 4389 override the default stack gap protection. The value 4390 is in page units and it defines how many pages prior 4391 to (for stacks growing down) resp. after (for stacks 4392 growing up) the main stack are reserved for no other 4393 mapping. Default value is 256 pages. 4394 4395 stacktrace [FTRACE] 4396 Enabled the stack tracer on boot up. 4397 4398 stacktrace_filter=[function-list] 4399 [FTRACE] Limit the functions that the stack tracer 4400 will trace at boot up. function-list is a comma separated 4401 list of functions. This list can be changed at run 4402 time by the stack_trace_filter file in the debugfs 4403 tracing directory. Note, this enables stack tracing 4404 and the stacktrace above is not needed. 4405 4406 sti= [PARISC,HW] 4407 Format: <num> 4408 Set the STI (builtin display/keyboard on the HP-PARISC 4409 machines) console (graphic card) which should be used 4410 as the initial boot-console. 4411 See also comment in drivers/video/console/sticore.c. 4412 4413 sti_font= [HW] 4414 See comment in drivers/video/console/sticore.c. 4415 4416 stifb= [HW] 4417 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 4418 4419 sunrpc.min_resvport= 4420 sunrpc.max_resvport= 4421 [NFS,SUNRPC] 4422 SunRPC servers often require that client requests 4423 originate from a privileged port (i.e. a port in the 4424 range 0 < portnr < 1024). 4425 An administrator who wishes to reserve some of these 4426 ports for other uses may adjust the range that the 4427 kernel's sunrpc client considers to be privileged 4428 using these two parameters to set the minimum and 4429 maximum port values. 4430 4431 sunrpc.svc_rpc_per_connection_limit= 4432 [NFS,SUNRPC] 4433 Limit the number of requests that the server will 4434 process in parallel from a single connection. 4435 The default value is 0 (no limit). 4436 4437 sunrpc.pool_mode= 4438 [NFS] 4439 Control how the NFS server code allocates CPUs to 4440 service thread pools. Depending on how many NICs 4441 you have and where their interrupts are bound, this 4442 option will affect which CPUs will do NFS serving. 4443 Note: this parameter cannot be changed while the 4444 NFS server is running. 4445 4446 auto the server chooses an appropriate mode 4447 automatically using heuristics 4448 global a single global pool contains all CPUs 4449 percpu one pool for each CPU 4450 pernode one pool for each NUMA node (equivalent 4451 to global on non-NUMA machines) 4452 4453 sunrpc.tcp_slot_table_entries= 4454 sunrpc.udp_slot_table_entries= 4455 [NFS,SUNRPC] 4456 Sets the upper limit on the number of simultaneous 4457 RPC calls that can be sent from the client to a 4458 server. Increasing these values may allow you to 4459 improve throughput, but will also increase the 4460 amount of memory reserved for use by the client. 4461 4462 suspend.pm_test_delay= 4463 [SUSPEND] 4464 Sets the number of seconds to remain in a suspend test 4465 mode before resuming the system (see 4466 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 4467 is set. Default value is 5. 4468 4469 swapaccount=[0|1] 4470 [KNL] Enable accounting of swap in memory resource 4471 controller if no parameter or 1 is given or disable 4472 it if 0 is given (See Documentation/cgroup-v1/memory.txt) 4473 4474 swiotlb= [ARM,IA-64,PPC,MIPS,X86] 4475 Format: { <int> | force | noforce } 4476 <int> -- Number of I/O TLB slabs 4477 force -- force using of bounce buffers even if they 4478 wouldn't be automatically used by the kernel 4479 noforce -- Never use bounce buffers (for debugging) 4480 4481 switches= [HW,M68k] 4482 4483 sysfs.deprecated=0|1 [KNL] 4484 Enable/disable old style sysfs layout for old udev 4485 on older distributions. When this option is enabled 4486 very new udev will not work anymore. When this option 4487 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled) 4488 in older udev will not work anymore. 4489 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in 4490 the kernel configuration. 4491 4492 sysrq_always_enabled 4493 [KNL] 4494 Ignore sysrq setting - this boot parameter will 4495 neutralize any effect of /proc/sys/kernel/sysrq. 4496 Useful for debugging. 4497 4498 tcpmhash_entries= [KNL,NET] 4499 Set the number of tcp_metrics_hash slots. 4500 Default value is 8192 or 16384 depending on total 4501 ram pages. This is used to specify the TCP metrics 4502 cache size. See Documentation/networking/ip-sysctl.txt 4503 "tcp_no_metrics_save" section for more details. 4504 4505 tdfx= [HW,DRM] 4506 4507 test_suspend= [SUSPEND][,N] 4508 Specify "mem" (for Suspend-to-RAM) or "standby" (for 4509 standby suspend) or "freeze" (for suspend type freeze) 4510 as the system sleep state during system startup with 4511 the optional capability to repeat N number of times. 4512 The system is woken from this state using a 4513 wakeup-capable RTC alarm. 4514 4515 thash_entries= [KNL,NET] 4516 Set number of hash buckets for TCP connection 4517 4518 thermal.act= [HW,ACPI] 4519 -1: disable all active trip points in all thermal zones 4520 <degrees C>: override all lowest active trip points 4521 4522 thermal.crt= [HW,ACPI] 4523 -1: disable all critical trip points in all thermal zones 4524 <degrees C>: override all critical trip points 4525 4526 thermal.nocrt= [HW,ACPI] 4527 Set to disable actions on ACPI thermal zone 4528 critical and hot trip points. 4529 4530 thermal.off= [HW,ACPI] 4531 1: disable ACPI thermal control 4532 4533 thermal.psv= [HW,ACPI] 4534 -1: disable all passive trip points 4535 <degrees C>: override all passive trip points to this 4536 value 4537 4538 thermal.tzp= [HW,ACPI] 4539 Specify global default ACPI thermal zone polling rate 4540 <deci-seconds>: poll all this frequency 4541 0: no polling (default) 4542 4543 threadirqs [KNL] 4544 Force threading of all interrupt handlers except those 4545 marked explicitly IRQF_NO_THREAD. 4546 4547 tmem [KNL,XEN] 4548 Enable the Transcendent memory driver if built-in. 4549 4550 tmem.cleancache=0|1 [KNL, XEN] 4551 Default is on (1). Disable the usage of the cleancache 4552 API to send anonymous pages to the hypervisor. 4553 4554 tmem.frontswap=0|1 [KNL, XEN] 4555 Default is on (1). Disable the usage of the frontswap 4556 API to send swap pages to the hypervisor. If disabled 4557 the selfballooning and selfshrinking are force disabled. 4558 4559 tmem.selfballooning=0|1 [KNL, XEN] 4560 Default is on (1). Disable the driving of swap pages 4561 to the hypervisor. 4562 4563 tmem.selfshrinking=0|1 [KNL, XEN] 4564 Default is on (1). Partial swapoff that immediately 4565 transfers pages from Xen hypervisor back to the 4566 kernel based on different criteria. 4567 4568 topology= [S390] 4569 Format: {off | on} 4570 Specify if the kernel should make use of the cpu 4571 topology information if the hardware supports this. 4572 The scheduler will make use of this information and 4573 e.g. base its process migration decisions on it. 4574 Default is on. 4575 4576 topology_updates= [KNL, PPC, NUMA] 4577 Format: {off} 4578 Specify if the kernel should ignore (off) 4579 topology updates sent by the hypervisor to this 4580 LPAR. 4581 4582 tp720= [HW,PS2] 4583 4584 tpm_suspend_pcr=[HW,TPM] 4585 Format: integer pcr id 4586 Specify that at suspend time, the tpm driver 4587 should extend the specified pcr with zeros, 4588 as a workaround for some chips which fail to 4589 flush the last written pcr on TPM_SaveState. 4590 This will guarantee that all the other pcrs 4591 are saved. 4592 4593 trace_buf_size=nn[KMG] 4594 [FTRACE] will set tracing buffer size on each cpu. 4595 4596 trace_event=[event-list] 4597 [FTRACE] Set and start specified trace events in order 4598 to facilitate early boot debugging. The event-list is a 4599 comma separated list of trace events to enable. See 4600 also Documentation/trace/events.rst 4601 4602 trace_options=[option-list] 4603 [FTRACE] Enable or disable tracer options at boot. 4604 The option-list is a comma delimited list of options 4605 that can be enabled or disabled just as if you were 4606 to echo the option name into 4607 4608 /sys/kernel/debug/tracing/trace_options 4609 4610 For example, to enable stacktrace option (to dump the 4611 stack trace of each event), add to the command line: 4612 4613 trace_options=stacktrace 4614 4615 See also Documentation/trace/ftrace.rst "trace options" 4616 section. 4617 4618 tp_printk[FTRACE] 4619 Have the tracepoints sent to printk as well as the 4620 tracing ring buffer. This is useful for early boot up 4621 where the system hangs or reboots and does not give the 4622 option for reading the tracing buffer or performing a 4623 ftrace_dump_on_oops. 4624 4625 To turn off having tracepoints sent to printk, 4626 echo 0 > /proc/sys/kernel/tracepoint_printk 4627 Note, echoing 1 into this file without the 4628 tracepoint_printk kernel cmdline option has no effect. 4629 4630 ** CAUTION ** 4631 4632 Having tracepoints sent to printk() and activating high 4633 frequency tracepoints such as irq or sched, can cause 4634 the system to live lock. 4635 4636 traceoff_on_warning 4637 [FTRACE] enable this option to disable tracing when a 4638 warning is hit. This turns off "tracing_on". Tracing can 4639 be enabled again by echoing '1' into the "tracing_on" 4640 file located in /sys/kernel/debug/tracing/ 4641 4642 This option is useful, as it disables the trace before 4643 the WARNING dump is called, which prevents the trace to 4644 be filled with content caused by the warning output. 4645 4646 This option can also be set at run time via the sysctl 4647 option: kernel/traceoff_on_warning 4648 4649 transparent_hugepage= 4650 [KNL] 4651 Format: [always|madvise|never] 4652 Can be used to control the default behavior of the system 4653 with respect to transparent hugepages. 4654 See Documentation/admin-guide/mm/transhuge.rst 4655 for more details. 4656 4657 tsc= Disable clocksource stability checks for TSC. 4658 Format: <string> 4659 [x86] reliable: mark tsc clocksource as reliable, this 4660 disables clocksource verification at runtime, as well 4661 as the stability checks done at bootup. Used to enable 4662 high-resolution timer mode on older hardware, and in 4663 virtualized environment. 4664 [x86] noirqtime: Do not use TSC to do irq accounting. 4665 Used to run time disable IRQ_TIME_ACCOUNTING on any 4666 platforms where RDTSC is slow and this accounting 4667 can add overhead. 4668 [x86] unstable: mark the TSC clocksource as unstable, this 4669 marks the TSC unconditionally unstable at bootup and 4670 avoids any further wobbles once the TSC watchdog notices. 4671 4672 turbografx.map[2|3]= [HW,JOY] 4673 TurboGraFX parallel port interface 4674 Format: 4675 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 4676 See also Documentation/input/devices/joystick-parport.rst 4677 4678 udbg-immortal [PPC] When debugging early kernel crashes that 4679 happen after console_init() and before a proper 4680 console driver takes over, this boot options might 4681 help "seeing" what's going on. 4682 4683 uhash_entries= [KNL,NET] 4684 Set number of hash buckets for UDP/UDP-Lite connections 4685 4686 uhci-hcd.ignore_oc= 4687 [USB] Ignore overcurrent events (default N). 4688 Some badly-designed motherboards generate lots of 4689 bogus events, for ports that aren't wired to 4690 anything. Set this parameter to avoid log spamming. 4691 Note that genuine overcurrent events won't be 4692 reported either. 4693 4694 unknown_nmi_panic 4695 [X86] Cause panic on unknown NMI. 4696 4697 usbcore.authorized_default= 4698 [USB] Default USB device authorization: 4699 (default -1 = authorized except for wireless USB, 4700 0 = not authorized, 1 = authorized) 4701 4702 usbcore.autosuspend= 4703 [USB] The autosuspend time delay (in seconds) used 4704 for newly-detected USB devices (default 2). This 4705 is the time required before an idle device will be 4706 autosuspended. Devices for which the delay is set 4707 to a negative value won't be autosuspended at all. 4708 4709 usbcore.usbfs_snoop= 4710 [USB] Set to log all usbfs traffic (default 0 = off). 4711 4712 usbcore.usbfs_snoop_max= 4713 [USB] Maximum number of bytes to snoop in each URB 4714 (default = 65536). 4715 4716 usbcore.blinkenlights= 4717 [USB] Set to cycle leds on hubs (default 0 = off). 4718 4719 usbcore.old_scheme_first= 4720 [USB] Start with the old device initialization 4721 scheme, applies only to low and full-speed devices 4722 (default 0 = off). 4723 4724 usbcore.usbfs_memory_mb= 4725 [USB] Memory limit (in MB) for buffers allocated by 4726 usbfs (default = 16, 0 = max = 2047). 4727 4728 usbcore.use_both_schemes= 4729 [USB] Try the other device initialization scheme 4730 if the first one fails (default 1 = enabled). 4731 4732 usbcore.initial_descriptor_timeout= 4733 [USB] Specifies timeout for the initial 64-byte 4734 USB_REQ_GET_DESCRIPTOR request in milliseconds 4735 (default 5000 = 5.0 seconds). 4736 4737 usbcore.nousb [USB] Disable the USB subsystem 4738 4739 usbcore.quirks= 4740 [USB] A list of quirk entries to augment the built-in 4741 usb core quirk list. List entries are separated by 4742 commas. Each entry has the form 4743 VendorID:ProductID:Flags. The IDs are 4-digit hex 4744 numbers and Flags is a set of letters. Each letter 4745 will change the built-in quirk; setting it if it is 4746 clear and clearing it if it is set. The letters have 4747 the following meanings: 4748 a = USB_QUIRK_STRING_FETCH_255 (string 4749 descriptors must not be fetched using 4750 a 255-byte read); 4751 b = USB_QUIRK_RESET_RESUME (device can't resume 4752 correctly so reset it instead); 4753 c = USB_QUIRK_NO_SET_INTF (device can't handle 4754 Set-Interface requests); 4755 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't 4756 handle its Configuration or Interface 4757 strings); 4758 e = USB_QUIRK_RESET (device can't be reset 4759 (e.g morph devices), don't use reset); 4760 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has 4761 more interface descriptions than the 4762 bNumInterfaces count, and can't handle 4763 talking to these interfaces); 4764 g = USB_QUIRK_DELAY_INIT (device needs a pause 4765 during initialization, after we read 4766 the device descriptor); 4767 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For 4768 high speed and super speed interrupt 4769 endpoints, the USB 2.0 and USB 3.0 spec 4770 require the interval in microframes (1 4771 microframe = 125 microseconds) to be 4772 calculated as interval = 2 ^ 4773 (bInterval-1). 4774 Devices with this quirk report their 4775 bInterval as the result of this 4776 calculation instead of the exponent 4777 variable used in the calculation); 4778 i = USB_QUIRK_DEVICE_QUALIFIER (device can't 4779 handle device_qualifier descriptor 4780 requests); 4781 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device 4782 generates spurious wakeup, ignore 4783 remote wakeup capability); 4784 k = USB_QUIRK_NO_LPM (device can't handle Link 4785 Power Management); 4786 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL 4787 (Device reports its bInterval as linear 4788 frames instead of the USB 2.0 4789 calculation); 4790 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs 4791 to be disconnected before suspend to 4792 prevent spurious wakeup); 4793 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a 4794 pause after every control message); 4795 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra 4796 delay after resetting its port); 4797 Example: quirks=0781:5580:bk,0a5c:5834:gij 4798 4799 usbhid.mousepoll= 4800 [USBHID] The interval which mice are to be polled at. 4801 4802 usbhid.jspoll= 4803 [USBHID] The interval which joysticks are to be polled at. 4804 4805 usbhid.kbpoll= 4806 [USBHID] The interval which keyboards are to be polled at. 4807 4808 usb-storage.delay_use= 4809 [UMS] The delay in seconds before a new device is 4810 scanned for Logical Units (default 1). 4811 4812 usb-storage.quirks= 4813 [UMS] A list of quirks entries to supplement or 4814 override the built-in unusual_devs list. List 4815 entries are separated by commas. Each entry has 4816 the form VID:PID:Flags where VID and PID are Vendor 4817 and Product ID values (4-digit hex numbers) and 4818 Flags is a set of characters, each corresponding 4819 to a common usb-storage quirk flag as follows: 4820 a = SANE_SENSE (collect more than 18 bytes 4821 of sense data); 4822 b = BAD_SENSE (don't collect more than 18 4823 bytes of sense data); 4824 c = FIX_CAPACITY (decrease the reported 4825 device capacity by one sector); 4826 d = NO_READ_DISC_INFO (don't use 4827 READ_DISC_INFO command); 4828 e = NO_READ_CAPACITY_16 (don't use 4829 READ_CAPACITY_16 command); 4830 f = NO_REPORT_OPCODES (don't use report opcodes 4831 command, uas only); 4832 g = MAX_SECTORS_240 (don't transfer more than 4833 240 sectors at a time, uas only); 4834 h = CAPACITY_HEURISTICS (decrease the 4835 reported device capacity by one 4836 sector if the number is odd); 4837 i = IGNORE_DEVICE (don't bind to this 4838 device); 4839 j = NO_REPORT_LUNS (don't use report luns 4840 command, uas only); 4841 l = NOT_LOCKABLE (don't try to lock and 4842 unlock ejectable media); 4843 m = MAX_SECTORS_64 (don't transfer more 4844 than 64 sectors = 32 KB at a time); 4845 n = INITIAL_READ10 (force a retry of the 4846 initial READ(10) command); 4847 o = CAPACITY_OK (accept the capacity 4848 reported by the device); 4849 p = WRITE_CACHE (the device cache is ON 4850 by default); 4851 r = IGNORE_RESIDUE (the device reports 4852 bogus residue values); 4853 s = SINGLE_LUN (the device has only one 4854 Logical Unit); 4855 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 4856 commands, uas only); 4857 u = IGNORE_UAS (don't bind to the uas driver); 4858 w = NO_WP_DETECT (don't test whether the 4859 medium is write-protected). 4860 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 4861 even if the device claims no cache) 4862 Example: quirks=0419:aaf5:rl,0421:0433:rc 4863 4864 user_debug= [KNL,ARM] 4865 Format: <int> 4866 See arch/arm/Kconfig.debug help text. 4867 1 - undefined instruction events 4868 2 - system calls 4869 4 - invalid data aborts 4870 8 - SIGSEGV faults 4871 16 - SIGBUS faults 4872 Example: user_debug=31 4873 4874 userpte= 4875 [X86] Flags controlling user PTE allocations. 4876 4877 nohigh = do not allocate PTE pages in 4878 HIGHMEM regardless of setting 4879 of CONFIG_HIGHPTE. 4880 4881 vdso= [X86,SH] 4882 On X86_32, this is an alias for vdso32=. Otherwise: 4883 4884 vdso=1: enable VDSO (the default) 4885 vdso=0: disable VDSO mapping 4886 4887 vdso32= [X86] Control the 32-bit vDSO 4888 vdso32=1: enable 32-bit VDSO 4889 vdso32=0 or vdso32=2: disable 32-bit VDSO 4890 4891 See the help text for CONFIG_COMPAT_VDSO for more 4892 details. If CONFIG_COMPAT_VDSO is set, the default is 4893 vdso32=0; otherwise, the default is vdso32=1. 4894 4895 For compatibility with older kernels, vdso32=2 is an 4896 alias for vdso32=0. 4897 4898 Try vdso32=0 if you encounter an error that says: 4899 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 4900 4901 vector= [IA-64,SMP] 4902 vector=percpu: enable percpu vector domain 4903 4904 video= [FB] Frame buffer configuration 4905 See Documentation/fb/modedb.txt. 4906 4907 video.brightness_switch_enabled= [0,1] 4908 If set to 1, on receiving an ACPI notify event 4909 generated by hotkey, video driver will adjust brightness 4910 level and then send out the event to user space through 4911 the allocated input device; If set to 0, video driver 4912 will only send out the event without touching backlight 4913 brightness level. 4914 default: 1 4915 4916 virtio_mmio.device= 4917 [VMMIO] Memory mapped virtio (platform) device. 4918 4919 <size>@<baseaddr>:<irq>[:<id>] 4920 where: 4921 <size> := size (can use standard suffixes 4922 like K, M and G) 4923 <baseaddr> := physical base address 4924 <irq> := interrupt number (as passed to 4925 request_irq()) 4926 <id> := (optional) platform device id 4927 example: 4928 virtio_mmio.device=1K@0x100b0000:48:7 4929 4930 Can be used multiple times for multiple devices. 4931 4932 vga= [BOOT,X86-32] Select a particular video mode 4933 See Documentation/x86/boot.txt and 4934 Documentation/svga.txt. 4935 Use vga=ask for menu. 4936 This is actually a boot loader parameter; the value is 4937 passed to the kernel using a special protocol. 4938 4939 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. 4940 May slow down system boot speed, especially when 4941 enabled on systems with a large amount of memory. 4942 All options are enabled by default, and this 4943 interface is meant to allow for selectively 4944 enabling or disabling specific virtual memory 4945 debugging features. 4946 4947 Available options are: 4948 P Enable page structure init time poisoning 4949 - Disable all of the above options 4950 4951 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact 4952 size of <nn>. This can be used to increase the 4953 minimum size (128MB on x86). It can also be used to 4954 decrease the size and leave more room for directly 4955 mapped kernel RAM. 4956 4957 vmcp_cma=nn[MG] [KNL,S390] 4958 Sets the memory size reserved for contiguous memory 4959 allocations for the vmcp device driver. 4960 4961 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 4962 Format: <command> 4963 4964 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 4965 Format: <command> 4966 4967 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 4968 Format: <command> 4969 4970 vsyscall= [X86-64] 4971 Controls the behavior of vsyscalls (i.e. calls to 4972 fixed addresses of 0xffffffffff600x00 from legacy 4973 code). Most statically-linked binaries and older 4974 versions of glibc use these calls. Because these 4975 functions are at fixed addresses, they make nice 4976 targets for exploits that can control RIP. 4977 4978 emulate [default] Vsyscalls turn into traps and are 4979 emulated reasonably safely. 4980 4981 native Vsyscalls are native syscall instructions. 4982 This is a little bit faster than trapping 4983 and makes a few dynamic recompilers work 4984 better than they would in emulation mode. 4985 It also makes exploits much easier to write. 4986 4987 none Vsyscalls don't work at all. This makes 4988 them quite hard to use for exploits but 4989 might break your system. 4990 4991 vt.color= [VT] Default text color. 4992 Format: 0xYX, X = foreground, Y = background. 4993 Default: 0x07 = light gray on black. 4994 4995 vt.cur_default= [VT] Default cursor shape. 4996 Format: 0xCCBBAA, where AA, BB, and CC are the same as 4997 the parameters of the <Esc>[?A;B;Cc escape sequence; 4998 see VGA-softcursor.txt. Default: 2 = underline. 4999 5000 vt.default_blu= [VT] 5001 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 5002 Change the default blue palette of the console. 5003 This is a 16-member array composed of values 5004 ranging from 0-255. 5005 5006 vt.default_grn= [VT] 5007 Format: <green0>,<green1>,<green2>,...,<green15> 5008 Change the default green palette of the console. 5009 This is a 16-member array composed of values 5010 ranging from 0-255. 5011 5012 vt.default_red= [VT] 5013 Format: <red0>,<red1>,<red2>,...,<red15> 5014 Change the default red palette of the console. 5015 This is a 16-member array composed of values 5016 ranging from 0-255. 5017 5018 vt.default_utf8= 5019 [VT] 5020 Format=<0|1> 5021 Set system-wide default UTF-8 mode for all tty's. 5022 Default is 1, i.e. UTF-8 mode is enabled for all 5023 newly opened terminals. 5024 5025 vt.global_cursor_default= 5026 [VT] 5027 Format=<-1|0|1> 5028 Set system-wide default for whether a cursor 5029 is shown on new VTs. Default is -1, 5030 i.e. cursors will be created by default unless 5031 overridden by individual drivers. 0 will hide 5032 cursors, 1 will display them. 5033 5034 vt.italic= [VT] Default color for italic text; 0-15. 5035 Default: 2 = green. 5036 5037 vt.underline= [VT] Default color for underlined text; 0-15. 5038 Default: 3 = cyan. 5039 5040 watchdog timers [HW,WDT] For information on watchdog timers, 5041 see Documentation/watchdog/watchdog-parameters.txt 5042 or other driver-specific files in the 5043 Documentation/watchdog/ directory. 5044 5045 workqueue.watchdog_thresh= 5046 If CONFIG_WQ_WATCHDOG is configured, workqueue can 5047 warn stall conditions and dump internal state to 5048 help debugging. 0 disables workqueue stall 5049 detection; otherwise, it's the stall threshold 5050 duration in seconds. The default value is 30 and 5051 it can be updated at runtime by writing to the 5052 corresponding sysfs file. 5053 5054 workqueue.disable_numa 5055 By default, all work items queued to unbound 5056 workqueues are affine to the NUMA nodes they're 5057 issued on, which results in better behavior in 5058 general. If NUMA affinity needs to be disabled for 5059 whatever reason, this option can be used. Note 5060 that this also can be controlled per-workqueue for 5061 workqueues visible under /sys/bus/workqueue/. 5062 5063 workqueue.power_efficient 5064 Per-cpu workqueues are generally preferred because 5065 they show better performance thanks to cache 5066 locality; unfortunately, per-cpu workqueues tend to 5067 be more power hungry than unbound workqueues. 5068 5069 Enabling this makes the per-cpu workqueues which 5070 were observed to contribute significantly to power 5071 consumption unbound, leading to measurably lower 5072 power usage at the cost of small performance 5073 overhead. 5074 5075 The default value of this parameter is determined by 5076 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 5077 5078 workqueue.debug_force_rr_cpu 5079 Workqueue used to implicitly guarantee that work 5080 items queued without explicit CPU specified are put 5081 on the local CPU. This guarantee is no longer true 5082 and while local CPU is still preferred work items 5083 may be put on foreign CPUs. This debug option 5084 forces round-robin CPU selection to flush out 5085 usages which depend on the now broken guarantee. 5086 When enabled, memory and cache locality will be 5087 impacted. 5088 5089 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of 5090 default x2apic cluster mode on platforms 5091 supporting x2apic. 5092 5093 x86_intel_mid_timer= [X86-32,APBT] 5094 Choose timer option for x86 Intel MID platform. 5095 Two valid options are apbt timer only and lapic timer 5096 plus one apbt timer for broadcast timer. 5097 x86_intel_mid_timer=apbt_only | lapic_and_apbt 5098 5099 xen_512gb_limit [KNL,X86-64,XEN] 5100 Restricts the kernel running paravirtualized under Xen 5101 to use only up to 512 GB of RAM. The reason to do so is 5102 crash analysis tools and Xen tools for doing domain 5103 save/restore/migration must be enabled to handle larger 5104 domains. 5105 5106 xen_emul_unplug= [HW,X86,XEN] 5107 Unplug Xen emulated devices 5108 Format: [unplug0,][unplug1] 5109 ide-disks -- unplug primary master IDE devices 5110 aux-ide-disks -- unplug non-primary-master IDE devices 5111 nics -- unplug network devices 5112 all -- unplug all emulated devices (NICs and IDE disks) 5113 unnecessary -- unplugging emulated devices is 5114 unnecessary even if the host did not respond to 5115 the unplug protocol 5116 never -- do not unplug even if version check succeeds 5117 5118 xen_nopvspin [X86,XEN] 5119 Disables the ticketlock slowpath using Xen PV 5120 optimizations. 5121 5122 xen_nopv [X86] 5123 Disables the PV optimizations forcing the HVM guest to 5124 run as generic HVM guest with no PV drivers. 5125 5126 xen_scrub_pages= [XEN] 5127 Boolean option to control scrubbing pages before giving them back 5128 to Xen, for use by other domains. Can be also changed at runtime 5129 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. 5130 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. 5131 5132 xirc2ps_cs= [NET,PCMCIA] 5133 Format: 5134 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 5135 5136 xhci-hcd.quirks [USB,KNL] 5137 A hex value specifying bitmask with supplemental xhci 5138 host controller quirks. Meaning of each bit can be 5139 consulted in header drivers/usb/host/xhci.h. 5140