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.rst, 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 { vendor | video | native | none } 26 If set to vendor, prefer vendor-specific driver 27 (e.g. thinkpad_acpi, sony_acpi, etc.) instead 28 of the ACPI video.ko driver. 29 If set to video, use the ACPI video.ko driver. 30 If set to native, use the device's native backlight mode. 31 If set to none, disable the ACPI backlight interface. 32 33 acpi_force_32bit_fadt_addr 34 force FADT to use 32 bit addresses rather than the 35 64 bit X_* addresses. Some firmware have broken 64 36 bit addresses for force ACPI ignore these and use 37 the older legacy 32 bit addresses. 38 39 acpica_no_return_repair [HW, ACPI] 40 Disable AML predefined validation mechanism 41 This mechanism can repair the evaluation result to make 42 the return objects more ACPI specification compliant. 43 This option is useful for developers to identify the 44 root cause of an AML interpreter issue when the issue 45 has something to do with the repair mechanism. 46 47 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG] 48 acpi.debug_level= [HW,ACPI,ACPI_DEBUG] 49 Format: <int> 50 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI 51 debug output. Bits in debug_layer correspond to a 52 _COMPONENT in an ACPI source file, e.g., 53 #define _COMPONENT ACPI_PCI_COMPONENT 54 Bits in debug_level correspond to a level in 55 ACPI_DEBUG_PRINT statements, e.g., 56 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ... 57 The debug_level mask defaults to "info". See 58 Documentation/firmware-guide/acpi/debug.rst for more information about 59 debug layers and levels. 60 61 Enable processor driver info messages: 62 acpi.debug_layer=0x20000000 63 Enable PCI/PCI interrupt routing info messages: 64 acpi.debug_layer=0x400000 65 Enable AML "Debug" output, i.e., stores to the Debug 66 object while interpreting AML: 67 acpi.debug_layer=0xffffffff acpi.debug_level=0x2 68 Enable all messages related to ACPI hardware: 69 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff 70 71 Some values produce so much output that the system is 72 unusable. The "log_buf_len" parameter may be useful 73 if you need to capture more output. 74 75 acpi_enforce_resources= [ACPI] 76 { strict | lax | no } 77 Check for resource conflicts between native drivers 78 and ACPI OperationRegions (SystemIO and SystemMemory 79 only). IO ports and memory declared in ACPI might be 80 used by the ACPI subsystem in arbitrary AML code and 81 can interfere with legacy drivers. 82 strict (default): access to resources claimed by ACPI 83 is denied; legacy drivers trying to access reserved 84 resources will fail to bind to device using them. 85 lax: access to resources claimed by ACPI is allowed; 86 legacy drivers trying to access reserved resources 87 will bind successfully but a warning message is logged. 88 no: ACPI OperationRegions are not marked as reserved, 89 no further checks are performed. 90 91 acpi_force_table_verification [HW,ACPI] 92 Enable table checksum verification during early stage. 93 By default, this is disabled due to x86 early mapping 94 size limitation. 95 96 acpi_irq_balance [HW,ACPI] 97 ACPI will balance active IRQs 98 default in APIC mode 99 100 acpi_irq_nobalance [HW,ACPI] 101 ACPI will not move active IRQs (default) 102 default in PIC mode 103 104 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA 105 Format: <irq>,<irq>... 106 107 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for 108 use by PCI 109 Format: <irq>,<irq>... 110 111 acpi_mask_gpe= [HW,ACPI] 112 Due to the existence of _Lxx/_Exx, some GPEs triggered 113 by unsupported hardware/firmware features can result in 114 GPE floodings that cannot be automatically disabled by 115 the GPE dispatcher. 116 This facility can be used to prevent such uncontrolled 117 GPE floodings. 118 Format: <byte> 119 120 acpi_no_auto_serialize [HW,ACPI] 121 Disable auto-serialization of AML methods 122 AML control methods that contain the opcodes to create 123 named objects will be marked as "Serialized" by the 124 auto-serialization feature. 125 This feature is enabled by default. 126 This option allows to turn off the feature. 127 128 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump 129 kernels. 130 131 acpi_no_static_ssdt [HW,ACPI] 132 Disable installation of static SSDTs at early boot time 133 By default, SSDTs contained in the RSDT/XSDT will be 134 installed automatically and they will appear under 135 /sys/firmware/acpi/tables. 136 This option turns off this feature. 137 Note that specifying this option does not affect 138 dynamic table installation which will install SSDT 139 tables to /sys/firmware/acpi/tables/dynamic. 140 141 acpi_no_watchdog [HW,ACPI,WDT] 142 Ignore the ACPI-based watchdog interface (WDAT) and let 143 a native driver control the watchdog device instead. 144 145 acpi_rsdp= [ACPI,EFI,KEXEC] 146 Pass the RSDP address to the kernel, mostly used 147 on machines running EFI runtime service to boot the 148 second kernel for kdump. 149 150 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS 151 Format: To spoof as Windows 98: ="Microsoft Windows" 152 153 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead 154 of 2 which is mandated by ACPI 6) as the supported ACPI 155 specification revision (when using this switch, it may 156 be necessary to carry out a cold reboot _twice_ in a 157 row to make it take effect on the platform firmware). 158 159 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings 160 acpi_osi="string1" # add string1 161 acpi_osi="!string2" # remove string2 162 acpi_osi=!* # remove all strings 163 acpi_osi=! # disable all built-in OS vendor 164 strings 165 acpi_osi=!! # enable all built-in OS vendor 166 strings 167 acpi_osi= # disable all strings 168 169 'acpi_osi=!' can be used in combination with single or 170 multiple 'acpi_osi="string1"' to support specific OS 171 vendor string(s). Note that such command can only 172 affect the default state of the OS vendor strings, thus 173 it cannot affect the default state of the feature group 174 strings and the current state of the OS vendor strings, 175 specifying it multiple times through kernel command line 176 is meaningless. This command is useful when one do not 177 care about the state of the feature group strings which 178 should be controlled by the OSPM. 179 Examples: 180 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent 181 to 'acpi_osi="Windows 2000" acpi_osi=!', they all 182 can make '_OSI("Windows 2000")' TRUE. 183 184 'acpi_osi=' cannot be used in combination with other 185 'acpi_osi=' command lines, the _OSI method will not 186 exist in the ACPI namespace. NOTE that such command can 187 only affect the _OSI support state, thus specifying it 188 multiple times through kernel command line is also 189 meaningless. 190 Examples: 191 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)' 192 FALSE. 193 194 'acpi_osi=!*' can be used in combination with single or 195 multiple 'acpi_osi="string1"' to support specific 196 string(s). Note that such command can affect the 197 current state of both the OS vendor strings and the 198 feature group strings, thus specifying it multiple times 199 through kernel command line is meaningful. But it may 200 still not able to affect the final state of a string if 201 there are quirks related to this string. This command 202 is useful when one want to control the state of the 203 feature group strings to debug BIOS issues related to 204 the OSPM features. 205 Examples: 206 1. 'acpi_osi="Module Device" acpi_osi=!*' can make 207 '_OSI("Module Device")' FALSE. 208 2. 'acpi_osi=!* acpi_osi="Module Device"' can make 209 '_OSI("Module Device")' TRUE. 210 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is 211 equivalent to 212 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"' 213 and 214 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!', 215 they all will make '_OSI("Windows 2000")' TRUE. 216 217 acpi_pm_good [X86] 218 Override the pmtimer bug detection: force the kernel 219 to assume that this machine's pmtimer latches its value 220 and always returns good values. 221 222 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode 223 Format: { level | edge | high | low } 224 225 acpi_skip_timer_override [HW,ACPI] 226 Recognize and ignore IRQ0/pin2 Interrupt Override. 227 For broken nForce2 BIOS resulting in XT-PIC timer. 228 229 acpi_sleep= [HW,ACPI] Sleep options 230 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig, 231 old_ordering, nonvs, sci_force_enable, nobl } 232 See Documentation/power/video.rst for information on 233 s3_bios and s3_mode. 234 s3_beep is for debugging; it makes the PC's speaker beep 235 as soon as the kernel's real-mode entry point is called. 236 s4_nohwsig prevents ACPI hardware signature from being 237 used during resume from hibernation. 238 old_ordering causes the ACPI 1.0 ordering of the _PTS 239 control method, with respect to putting devices into 240 low power states, to be enforced (the ACPI 2.0 ordering 241 of _PTS is used by default). 242 nonvs prevents the kernel from saving/restoring the 243 ACPI NVS memory during suspend/hibernation and resume. 244 sci_force_enable causes the kernel to set SCI_EN directly 245 on resume from S1/S3 (which is against the ACPI spec, 246 but some broken systems don't work without it). 247 nobl causes the internal blacklist of systems known to 248 behave incorrectly in some ways with respect to system 249 suspend and resume to be ignored (use wisely). 250 251 acpi_use_timer_override [HW,ACPI] 252 Use timer override. For some broken Nvidia NF5 boards 253 that require a timer override, but don't have HPET 254 255 add_efi_memmap [EFI; X86] Include EFI memory map in 256 kernel's map of available physical RAM. 257 258 agp= [AGP] 259 { off | try_unsupported } 260 off: disable AGP support 261 try_unsupported: try to drive unsupported chipsets 262 (may crash computer or cause data corruption) 263 264 ALSA [HW,ALSA] 265 See Documentation/sound/alsa-configuration.rst 266 267 alignment= [KNL,ARM] 268 Allow the default userspace alignment fault handler 269 behaviour to be specified. Bit 0 enables warnings, 270 bit 1 enables fixups, and bit 2 sends a segfault. 271 272 align_va_addr= [X86-64] 273 Align virtual addresses by clearing slice [14:12] when 274 allocating a VMA at process creation time. This option 275 gives you up to 3% performance improvement on AMD F15h 276 machines (where it is enabled by default) for a 277 CPU-intensive style benchmark, and it can vary highly in 278 a microbenchmark depending on workload and compiler. 279 280 32: only for 32-bit processes 281 64: only for 64-bit processes 282 on: enable for both 32- and 64-bit processes 283 off: disable for both 32- and 64-bit processes 284 285 alloc_snapshot [FTRACE] 286 Allocate the ftrace snapshot buffer on boot up when the 287 main buffer is allocated. This is handy if debugging 288 and you need to use tracing_snapshot() on boot up, and 289 do not want to use tracing_snapshot_alloc() as it needs 290 to be done where GFP_KERNEL allocations are allowed. 291 292 amd_iommu= [HW,X86-64] 293 Pass parameters to the AMD IOMMU driver in the system. 294 Possible values are: 295 fullflush - enable flushing of IO/TLB entries when 296 they are unmapped. Otherwise they are 297 flushed before they will be reused, which 298 is a lot of faster 299 off - do not initialize any AMD IOMMU found in 300 the system 301 force_isolation - Force device isolation for all 302 devices. The IOMMU driver is not 303 allowed anymore to lift isolation 304 requirements as needed. This option 305 does not override iommu=pt 306 307 amd_iommu_dump= [HW,X86-64] 308 Enable AMD IOMMU driver option to dump the ACPI table 309 for AMD IOMMU. With this option enabled, AMD IOMMU 310 driver will print ACPI tables for AMD IOMMU during 311 IOMMU initialization. 312 313 amd_iommu_intr= [HW,X86-64] 314 Specifies one of the following AMD IOMMU interrupt 315 remapping modes: 316 legacy - Use legacy interrupt remapping mode. 317 vapic - Use virtual APIC mode, which allows IOMMU 318 to inject interrupts directly into guest. 319 This mode requires kvm-amd.avic=1. 320 (Default when IOMMU HW support is present.) 321 322 amijoy.map= [HW,JOY] Amiga joystick support 323 Map of devices attached to JOY0DAT and JOY1DAT 324 Format: <a>,<b> 325 See also Documentation/input/joydev/joystick.rst 326 327 analog.map= [HW,JOY] Analog joystick and gamepad support 328 Specifies type or capabilities of an analog joystick 329 connected to one of 16 gameports 330 Format: <type1>,<type2>,..<type16> 331 332 apc= [HW,SPARC] 333 Power management functions (SPARCstation-4/5 + deriv.) 334 Format: noidle 335 Disable APC CPU standby support. SPARCstation-Fox does 336 not play well with APC CPU idle - disable it if you have 337 APC and your system crashes randomly. 338 339 apic= [APIC,X86] Advanced Programmable Interrupt Controller 340 Change the output verbosity while booting 341 Format: { quiet (default) | verbose | debug } 342 Change the amount of debugging information output 343 when initialising the APIC and IO-APIC components. 344 For X86-32, this can also be used to specify an APIC 345 driver name. 346 Format: apic=driver_name 347 Examples: apic=bigsmp 348 349 apic_extnmi= [APIC,X86] External NMI delivery setting 350 Format: { bsp (default) | all | none } 351 bsp: External NMI is delivered only to CPU 0 352 all: External NMIs are broadcast to all CPUs as a 353 backup of CPU 0 354 none: External NMI is masked for all CPUs. This is 355 useful so that a dump capture kernel won't be 356 shot down by NMI 357 358 autoconf= [IPV6] 359 See Documentation/networking/ipv6.rst. 360 361 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller 362 Limit apic dumping. The parameter defines the maximal 363 number of local apics being dumped. Also it is possible 364 to set it to "all" by meaning -- no limit here. 365 Format: { 1 (default) | 2 | ... | all }. 366 The parameter valid if only apic=debug or 367 apic=verbose is specified. 368 Example: apic=debug show_lapic=all 369 370 apm= [APM] Advanced Power Management 371 See header of arch/x86/kernel/apm_32.c. 372 373 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards 374 Format: <io>,<irq>,<nodeID> 375 376 ataflop= [HW,M68k] 377 378 atarimouse= [HW,MOUSE] Atari Mouse 379 380 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess, 381 EzKey and similar keyboards 382 383 atkbd.reset= [HW] Reset keyboard during initialization 384 385 atkbd.set= [HW] Select keyboard code set 386 Format: <int> (2 = AT (default), 3 = PS/2) 387 388 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar 389 keyboards 390 391 atkbd.softraw= [HW] Choose between synthetic and real raw mode 392 Format: <bool> (0 = real, 1 = synthetic (default)) 393 394 atkbd.softrepeat= [HW] 395 Use software keyboard repeat 396 397 audit= [KNL] Enable the audit sub-system 398 Format: { "0" | "1" | "off" | "on" } 399 0 | off - kernel audit is disabled and can not be 400 enabled until the next reboot 401 unset - kernel audit is initialized but disabled and 402 will be fully enabled by the userspace auditd. 403 1 | on - kernel audit is initialized and partially 404 enabled, storing at most audit_backlog_limit 405 messages in RAM until it is fully enabled by the 406 userspace auditd. 407 Default: unset 408 409 audit_backlog_limit= [KNL] Set the audit queue size limit. 410 Format: <int> (must be >=0) 411 Default: 64 412 413 bau= [X86_UV] Enable the BAU on SGI UV. The default 414 behavior is to disable the BAU (i.e. bau=0). 415 Format: { "0" | "1" } 416 0 - Disable the BAU. 417 1 - Enable the BAU. 418 unset - Disable the BAU. 419 420 baycom_epp= [HW,AX25] 421 Format: <io>,<mode> 422 423 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem 424 Format: <io>,<mode> 425 See header of drivers/net/hamradio/baycom_par.c. 426 427 baycom_ser_fdx= [HW,AX25] 428 BayCom Serial Port AX.25 Modem (Full Duplex Mode) 429 Format: <io>,<irq>,<mode>[,<baud>] 430 See header of drivers/net/hamradio/baycom_ser_fdx.c. 431 432 baycom_ser_hdx= [HW,AX25] 433 BayCom Serial Port AX.25 Modem (Half Duplex Mode) 434 Format: <io>,<irq>,<mode> 435 See header of drivers/net/hamradio/baycom_ser_hdx.c. 436 437 blkdevparts= Manual partition parsing of block device(s) for 438 embedded devices based on command line input. 439 See Documentation/block/cmdline-partition.rst 440 441 boot_delay= Milliseconds to delay each printk during boot. 442 Values larger than 10 seconds (10000) are changed to 443 no delay (0). 444 Format: integer 445 446 bootconfig [KNL] 447 Extended command line options can be added to an initrd 448 and this will cause the kernel to look for it. 449 450 See Documentation/admin-guide/bootconfig.rst 451 452 bert_disable [ACPI] 453 Disable BERT OS support on buggy BIOSes. 454 455 bgrt_disable [ACPI][X86] 456 Disable BGRT to avoid flickering OEM logo. 457 458 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards) 459 bttv.radio= Most important insmod options are available as 460 kernel args too. 461 bttv.pll= See Documentation/admin-guide/media/bttv.rst 462 bttv.tuner= 463 464 bulk_remove=off [PPC] This parameter disables the use of the pSeries 465 firmware feature for flushing multiple hpte entries 466 at a time. 467 468 c101= [NET] Moxa C101 synchronous serial card 469 470 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection. 471 Sometimes CPU hardware bugs make them report the cache 472 size incorrectly. The kernel will attempt work arounds 473 to fix known problems, but for some CPUs it is not 474 possible to determine what the correct size should be. 475 This option provides an override for these situations. 476 477 carrier_timeout= 478 [NET] Specifies amount of time (in seconds) that 479 the kernel should wait for a network carrier. By default 480 it waits 120 seconds. 481 482 ca_keys= [KEYS] This parameter identifies a specific key(s) on 483 the system trusted keyring to be used for certificate 484 trust validation. 485 format: { id:<keyid> | builtin } 486 487 cca= [MIPS] Override the kernel pages' cache coherency 488 algorithm. Accepted values range from 0 to 7 489 inclusive. See arch/mips/include/asm/pgtable-bits.h 490 for platform specific values (SB1, Loongson3 and 491 others). 492 493 ccw_timeout_log [S390] 494 See Documentation/s390/common_io.rst for details. 495 496 cgroup_disable= [KNL] Disable a particular controller 497 Format: {name of the controller(s) to disable} 498 The effects of cgroup_disable=foo are: 499 - foo isn't auto-mounted if you mount all cgroups in 500 a single hierarchy 501 - foo isn't visible as an individually mountable 502 subsystem 503 {Currently only "memory" controller deal with this and 504 cut the overhead, others just disable the usage. So 505 only cgroup_disable=memory is actually worthy} 506 507 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1 508 Format: { { controller | "all" | "named" } 509 [,{ controller | "all" | "named" }...] } 510 Like cgroup_disable, but only applies to cgroup v1; 511 the blacklisted controllers remain available in cgroup2. 512 "all" blacklists all controllers and "named" disables 513 named mounts. Specifying both "all" and "named" disables 514 all v1 hierarchies. 515 516 cgroup.memory= [KNL] Pass options to the cgroup memory controller. 517 Format: <string> 518 nosocket -- Disable socket memory accounting. 519 nokmem -- Disable kernel memory accounting. 520 521 checkreqprot [SELINUX] Set initial checkreqprot flag value. 522 Format: { "0" | "1" } 523 See security/selinux/Kconfig help text. 524 0 -- check protection applied by kernel (includes 525 any implied execute protection). 526 1 -- check protection requested by application. 527 Default value is set via a kernel config option. 528 Value can be changed at runtime via 529 /sys/fs/selinux/checkreqprot. 530 Setting checkreqprot to 1 is deprecated. 531 532 cio_ignore= [S390] 533 See Documentation/s390/common_io.rst for details. 534 clk_ignore_unused 535 [CLK] 536 Prevents the clock framework from automatically gating 537 clocks that have not been explicitly enabled by a Linux 538 device driver but are enabled in hardware at reset or 539 by the bootloader/firmware. Note that this does not 540 force such clocks to be always-on nor does it reserve 541 those clocks in any way. This parameter is useful for 542 debug and development, but should not be needed on a 543 platform with proper driver support. For more 544 information, see Documentation/driver-api/clk.rst. 545 546 clock= [BUGS=X86-32, HW] gettimeofday clocksource override. 547 [Deprecated] 548 Forces specified clocksource (if available) to be used 549 when calculating gettimeofday(). If specified 550 clocksource is not available, it defaults to PIT. 551 Format: { pit | tsc | cyclone | pmtmr } 552 553 clocksource= Override the default clocksource 554 Format: <string> 555 Override the default clocksource and use the clocksource 556 with the name specified. 557 Some clocksource names to choose from, depending on 558 the platform: 559 [all] jiffies (this is the base, fallback clocksource) 560 [ACPI] acpi_pm 561 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2, 562 pxa_timer,timer3,32k_counter,timer0_1 563 [X86-32] pit,hpet,tsc; 564 scx200_hrt on Geode; cyclone on IBM x440 565 [MIPS] MIPS 566 [PARISC] cr16 567 [S390] tod 568 [SH] SuperH 569 [SPARC64] tick 570 [X86-64] hpet,tsc 571 572 clocksource.arm_arch_timer.evtstrm= 573 [ARM,ARM64] 574 Format: <bool> 575 Enable/disable the eventstream feature of the ARM 576 architected timer so that code using WFE-based polling 577 loops can be debugged more effectively on production 578 systems. 579 580 clearcpuid=BITNUM[,BITNUM...] [X86] 581 Disable CPUID feature X for the kernel. See 582 arch/x86/include/asm/cpufeatures.h for the valid bit 583 numbers. Note the Linux specific bits are not necessarily 584 stable over kernel options, but the vendor specific 585 ones should be. 586 Also note that user programs calling CPUID directly 587 or using the feature without checking anything 588 will still see it. This just prevents it from 589 being used by the kernel or shown in /proc/cpuinfo. 590 Also note the kernel might malfunction if you disable 591 some critical bits. 592 593 cma=nn[MG]@[start[MG][-end[MG]]] 594 [KNL,CMA] 595 Sets the size of kernel global memory area for 596 contiguous memory allocations and optionally the 597 placement constraint by the physical address range of 598 memory allocations. A value of 0 disables CMA 599 altogether. For more information, see 600 kernel/dma/contiguous.c 601 602 cma_pernuma=nn[MG] 603 [ARM64,KNL] 604 Sets the size of kernel per-numa memory area for 605 contiguous memory allocations. A value of 0 disables 606 per-numa CMA altogether. And If this option is not 607 specificed, the default value is 0. 608 With per-numa CMA enabled, DMA users on node nid will 609 first try to allocate buffer from the pernuma area 610 which is located in node nid, if the allocation fails, 611 they will fallback to the global default memory area. 612 613 cmo_free_hint= [PPC] Format: { yes | no } 614 Specify whether pages are marked as being inactive 615 when they are freed. This is used in CMO environments 616 to determine OS memory pressure for page stealing by 617 a hypervisor. 618 Default: yes 619 620 coherent_pool=nn[KMG] [ARM,KNL] 621 Sets the size of memory pool for coherent, atomic dma 622 allocations, by default set to 256K. 623 624 com20020= [HW,NET] ARCnet - COM20020 chipset 625 Format: 626 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]] 627 628 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers) 629 Format: <io>[,<irq>] 630 631 com90xx= [HW,NET] 632 ARCnet - COM90xx chipset (memory-mapped buffers) 633 Format: <io>[,<irq>[,<memstart>]] 634 635 condev= [HW,S390] console device 636 conmode= 637 638 console= [KNL] Output console device and options. 639 640 tty<n> Use the virtual console device <n>. 641 642 ttyS<n>[,options] 643 ttyUSB0[,options] 644 Use the specified serial port. The options are of 645 the form "bbbbpnf", where "bbbb" is the baud rate, 646 "p" is parity ("n", "o", or "e"), "n" is number of 647 bits, and "f" is flow control ("r" for RTS or 648 omit it). Default is "9600n8". 649 650 See Documentation/admin-guide/serial-console.rst for more 651 information. See 652 Documentation/networking/netconsole.rst for an 653 alternative. 654 655 uart[8250],io,<addr>[,options] 656 uart[8250],mmio,<addr>[,options] 657 uart[8250],mmio16,<addr>[,options] 658 uart[8250],mmio32,<addr>[,options] 659 uart[8250],0x<addr>[,options] 660 Start an early, polled-mode console on the 8250/16550 661 UART at the specified I/O port or MMIO address, 662 switching to the matching ttyS device later. 663 MMIO inter-register address stride is either 8-bit 664 (mmio), 16-bit (mmio16), or 32-bit (mmio32). 665 If none of [io|mmio|mmio16|mmio32], <addr> is assumed 666 to be equivalent to 'mmio'. 'options' are specified in 667 the same format described for ttyS above; if unspecified, 668 the h/w is not re-initialized. 669 670 hvc<n> Use the hypervisor console device <n>. This is for 671 both Xen and PowerPC hypervisors. 672 673 If the device connected to the port is not a TTY but a braille 674 device, prepend "brl," before the device type, for instance 675 console=brl,ttyS0 676 For now, only VisioBraille is supported. 677 678 console_msg_format= 679 [KNL] Change console messages format 680 default 681 By default we print messages on consoles in 682 "[time stamp] text\n" format (time stamp may not be 683 printed, depending on CONFIG_PRINTK_TIME or 684 `printk_time' param). 685 syslog 686 Switch to syslog format: "<%u>[time stamp] text\n" 687 IOW, each message will have a facility and loglevel 688 prefix. The format is similar to one used by syslog() 689 syscall, or to executing "dmesg -S --raw" or to reading 690 from /proc/kmsg. 691 692 consoleblank= [KNL] The console blank (screen saver) timeout in 693 seconds. A value of 0 disables the blank timer. 694 Defaults to 0. 695 696 coredump_filter= 697 [KNL] Change the default value for 698 /proc/<pid>/coredump_filter. 699 See also Documentation/filesystems/proc.rst. 700 701 coresight_cpu_debug.enable 702 [ARM,ARM64] 703 Format: <bool> 704 Enable/disable the CPU sampling based debugging. 705 0: default value, disable debugging 706 1: enable debugging at boot time 707 708 cpuidle.off=1 [CPU_IDLE] 709 disable the cpuidle sub-system 710 711 cpuidle.governor= 712 [CPU_IDLE] Name of the cpuidle governor to use. 713 714 cpufreq.off=1 [CPU_FREQ] 715 disable the cpufreq sub-system 716 717 cpufreq.default_governor= 718 [CPU_FREQ] Name of the default cpufreq governor or 719 policy to use. This governor must be registered in the 720 kernel before the cpufreq driver probes. 721 722 cpu_init_udelay=N 723 [X86] Delay for N microsec between assert and de-assert 724 of APIC INIT to start processors. This delay occurs 725 on every CPU online, such as boot, and resume from suspend. 726 Default: 10000 727 728 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver 729 Format: 730 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] 731 732 crashkernel=size[KMG][@offset[KMG]] 733 [KNL] Using kexec, Linux can switch to a 'crash kernel' 734 upon panic. This parameter reserves the physical 735 memory region [offset, offset + size] for that kernel 736 image. If '@offset' is omitted, then a suitable offset 737 is selected automatically. 738 [KNL, X86-64] Select a region under 4G first, and 739 fall back to reserve region above 4G when '@offset' 740 hasn't been specified. 741 See Documentation/admin-guide/kdump/kdump.rst for further details. 742 743 crashkernel=range1:size1[,range2:size2,...][@offset] 744 [KNL] Same as above, but depends on the memory 745 in the running system. The syntax of range is 746 start-[end] where start and end are both 747 a memory unit (amount[KMG]). See also 748 Documentation/admin-guide/kdump/kdump.rst for an example. 749 750 crashkernel=size[KMG],high 751 [KNL, X86-64] range could be above 4G. Allow kernel 752 to allocate physical memory region from top, so could 753 be above 4G if system have more than 4G ram installed. 754 Otherwise memory region will be allocated below 4G, if 755 available. 756 It will be ignored if crashkernel=X is specified. 757 crashkernel=size[KMG],low 758 [KNL, X86-64] range under 4G. When crashkernel=X,high 759 is passed, kernel could allocate physical memory region 760 above 4G, that cause second kernel crash on system 761 that require some amount of low memory, e.g. swiotlb 762 requires at least 64M+32K low memory, also enough extra 763 low memory is needed to make sure DMA buffers for 32-bit 764 devices won't run out. Kernel would try to allocate at 765 at least 256M below 4G automatically. 766 This one let user to specify own low range under 4G 767 for second kernel instead. 768 0: to disable low allocation. 769 It will be ignored when crashkernel=X,high is not used 770 or memory reserved is below 4G. 771 772 cryptomgr.notests 773 [KNL] Disable crypto self-tests 774 775 cs89x0_dma= [HW,NET] 776 Format: <dma> 777 778 cs89x0_media= [HW,NET] 779 Format: { rj45 | aui | bnc } 780 781 dasd= [HW,NET] 782 See header of drivers/s390/block/dasd_devmap.c. 783 784 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port 785 (one device per port) 786 Format: <port#>,<type> 787 See also Documentation/input/devices/joystick-parport.rst 788 789 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot 790 time. See 791 Documentation/admin-guide/dynamic-debug-howto.rst for 792 details. Deprecated, see dyndbg. 793 794 debug [KNL] Enable kernel debugging (events log level). 795 796 debug_boot_weak_hash 797 [KNL] Enable printing [hashed] pointers early in the 798 boot sequence. If enabled, we use a weak hash instead 799 of siphash to hash pointers. Use this option if you are 800 seeing instances of '(___ptrval___)') and need to see a 801 value (hashed pointer) instead. Cryptographically 802 insecure, please do not use on production kernels. 803 804 debug_locks_verbose= 805 [KNL] verbose self-tests 806 Format=<0|1> 807 Print debugging info while doing the locking API 808 self-tests. 809 We default to 0 (no extra messages), setting it to 810 1 will print _a lot_ more information - normally 811 only useful to kernel developers. 812 813 debug_objects [KNL] Enable object debugging 814 815 no_debug_objects 816 [KNL] Disable object debugging 817 818 debug_guardpage_minorder= 819 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this 820 parameter allows control of the order of pages that will 821 be intentionally kept free (and hence protected) by the 822 buddy allocator. Bigger value increase the probability 823 of catching random memory corruption, but reduce the 824 amount of memory for normal system use. The maximum 825 possible value is MAX_ORDER/2. Setting this parameter 826 to 1 or 2 should be enough to identify most random 827 memory corruption problems caused by bugs in kernel or 828 driver code when a CPU writes to (or reads from) a 829 random memory location. Note that there exists a class 830 of memory corruptions problems caused by buggy H/W or 831 F/W or by drivers badly programing DMA (basically when 832 memory is written at bus level and the CPU MMU is 833 bypassed) which are not detectable by 834 CONFIG_DEBUG_PAGEALLOC, hence this option will not help 835 tracking down these problems. 836 837 debug_pagealloc= 838 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this parameter 839 enables the feature at boot time. By default, it is 840 disabled and the system will work mostly the same as a 841 kernel built without CONFIG_DEBUG_PAGEALLOC. 842 Note: to get most of debug_pagealloc error reports, it's 843 useful to also enable the page_owner functionality. 844 on: enable the feature 845 846 debugfs= [KNL] This parameter enables what is exposed to userspace 847 and debugfs internal clients. 848 Format: { on, no-mount, off } 849 on: All functions are enabled. 850 no-mount: 851 Filesystem is not registered but kernel clients can 852 access APIs and a crashkernel can be used to read 853 its content. There is nothing to mount. 854 off: Filesystem is not registered and clients 855 get a -EPERM as result when trying to register files 856 or directories within debugfs. 857 This is equivalent of the runtime functionality if 858 debugfs was not enabled in the kernel at all. 859 Default value is set in build-time with a kernel configuration. 860 861 debugpat [X86] Enable PAT debugging 862 863 decnet.addr= [HW,NET] 864 Format: <area>[,<node>] 865 See also Documentation/networking/decnet.rst. 866 867 default_hugepagesz= 868 [HW] The size of the default HugeTLB page. This is 869 the size represented by the legacy /proc/ hugepages 870 APIs. In addition, this is the default hugetlb size 871 used for shmget(), mmap() and mounting hugetlbfs 872 filesystems. If not specified, defaults to the 873 architecture's default huge page size. Huge page 874 sizes are architecture dependent. See also 875 Documentation/admin-guide/mm/hugetlbpage.rst. 876 Format: size[KMG] 877 878 deferred_probe_timeout= 879 [KNL] Debugging option to set a timeout in seconds for 880 deferred probe to give up waiting on dependencies to 881 probe. Only specific dependencies (subsystems or 882 drivers) that have opted in will be ignored. A timeout of 0 883 will timeout at the end of initcalls. This option will also 884 dump out devices still on the deferred probe list after 885 retrying. 886 887 dfltcc= [HW,S390] 888 Format: { on | off | def_only | inf_only | always } 889 on: s390 zlib hardware support for compression on 890 level 1 and decompression (default) 891 off: No s390 zlib hardware support 892 def_only: s390 zlib hardware support for deflate 893 only (compression on level 1) 894 inf_only: s390 zlib hardware support for inflate 895 only (decompression) 896 always: Same as 'on' but ignores the selected compression 897 level always using hardware support (used for debugging) 898 899 dhash_entries= [KNL] 900 Set number of hash buckets for dentry cache. 901 902 disable_1tb_segments [PPC] 903 Disables the use of 1TB hash page table segments. This 904 causes the kernel to fall back to 256MB segments which 905 can be useful when debugging issues that require an SLB 906 miss to occur. 907 908 stress_slb [PPC] 909 Limits the number of kernel SLB entries, and flushes 910 them frequently to increase the rate of SLB faults 911 on kernel addresses. 912 913 disable= [IPV6] 914 See Documentation/networking/ipv6.rst. 915 916 hardened_usercopy= 917 [KNL] Under CONFIG_HARDENED_USERCOPY, whether 918 hardening is enabled for this boot. Hardened 919 usercopy checking is used to protect the kernel 920 from reading or writing beyond known memory 921 allocation boundaries as a proactive defense 922 against bounds-checking flaws in the kernel's 923 copy_to_user()/copy_from_user() interface. 924 on Perform hardened usercopy checks (default). 925 off Disable hardened usercopy checks. 926 927 disable_radix [PPC] 928 Disable RADIX MMU mode on POWER9 929 930 radix_hcall_invalidate=on [PPC/PSERIES] 931 Disable RADIX GTSE feature and use hcall for TLB 932 invalidate. 933 934 disable_tlbie [PPC] 935 Disable TLBIE instruction. Currently does not work 936 with KVM, with HASH MMU, or with coherent accelerators. 937 938 disable_cpu_apicid= [X86,APIC,SMP] 939 Format: <int> 940 The number of initial APIC ID for the 941 corresponding CPU to be disabled at boot, 942 mostly used for the kdump 2nd kernel to 943 disable BSP to wake up multiple CPUs without 944 causing system reset or hang due to sending 945 INIT from AP to BSP. 946 947 perf_v4_pmi= [X86,INTEL] 948 Format: <bool> 949 Disable Intel PMU counter freezing feature. 950 The feature only exists starting from 951 Arch Perfmon v4 (Skylake and newer). 952 953 disable_ddw [PPC/PSERIES] 954 Disable Dynamic DMA Window support. Use this 955 to workaround buggy firmware. 956 957 disable_ipv6= [IPV6] 958 See Documentation/networking/ipv6.rst. 959 960 disable_mtrr_cleanup [X86] 961 The kernel tries to adjust MTRR layout from continuous 962 to discrete, to make X server driver able to add WB 963 entry later. This parameter disables that. 964 965 disable_mtrr_trim [X86, Intel and AMD only] 966 By default the kernel will trim any uncacheable 967 memory out of your available memory pool based on 968 MTRR settings. This parameter disables that behavior, 969 possibly causing your machine to run very slowly. 970 971 disable_timer_pin_1 [X86] 972 Disable PIN 1 of APIC timer 973 Can be useful to work around chipset bugs. 974 975 dis_ucode_ldr [X86] Disable the microcode loader. 976 977 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, 978 this option disables the debugging code at boot. 979 980 dma_debug_entries=<number> 981 This option allows to tune the number of preallocated 982 entries for DMA-API debugging code. One entry is 983 required per DMA-API allocation. Use this if the 984 DMA-API debugging code disables itself because the 985 architectural default is too low. 986 987 dma_debug_driver=<driver_name> 988 With this option the DMA-API debugging driver 989 filter feature can be enabled at boot time. Just 990 pass the driver to filter for as the parameter. 991 The filter can be disabled or changed to another 992 driver later using sysfs. 993 994 driver_async_probe= [KNL] 995 List of driver names to be probed asynchronously. 996 Format: <driver_name1>,<driver_name2>... 997 998 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>] 999 Broken monitors, graphic adapters, KVMs and EDIDless 1000 panels may send no or incorrect EDID data sets. 1001 This parameter allows to specify an EDID data sets 1002 in the /lib/firmware directory that are used instead. 1003 Generic built-in EDID data sets are used, if one of 1004 edid/1024x768.bin, edid/1280x1024.bin, 1005 edid/1680x1050.bin, or edid/1920x1080.bin is given 1006 and no file with the same name exists. Details and 1007 instructions how to build your own EDID data are 1008 available in Documentation/admin-guide/edid.rst. An EDID 1009 data set will only be used for a particular connector, 1010 if its name and a colon are prepended to the EDID 1011 name. Each connector may use a unique EDID data 1012 set by separating the files with a comma. An EDID 1013 data set with no connector name will be used for 1014 any connectors not explicitly specified. 1015 1016 dscc4.setup= [NET] 1017 1018 dt_cpu_ftrs= [PPC] 1019 Format: {"off" | "known"} 1020 Control how the dt_cpu_ftrs device-tree binding is 1021 used for CPU feature discovery and setup (if it 1022 exists). 1023 off: Do not use it, fall back to legacy cpu table. 1024 known: Do not pass through unknown features to guests 1025 or userspace, only those that the kernel is aware of. 1026 1027 dump_apple_properties [X86] 1028 Dump name and content of EFI device properties on 1029 x86 Macs. Useful for driver authors to determine 1030 what data is available or for reverse-engineering. 1031 1032 dyndbg[="val"] [KNL,DYNAMIC_DEBUG] 1033 <module>.dyndbg[="val"] 1034 Enable debug messages at boot time. See 1035 Documentation/admin-guide/dynamic-debug-howto.rst 1036 for details. 1037 1038 nopku [X86] Disable Memory Protection Keys CPU feature found 1039 in some Intel CPUs. 1040 1041 <module>.async_probe [KNL] 1042 Enable asynchronous probe on this module. 1043 1044 early_ioremap_debug [KNL] 1045 Enable debug messages in early_ioremap support. This 1046 is useful for tracking down temporary early mappings 1047 which are not unmapped. 1048 1049 earlycon= [KNL] Output early console device and options. 1050 1051 When used with no options, the early console is 1052 determined by stdout-path property in device tree's 1053 chosen node or the ACPI SPCR table if supported by 1054 the platform. 1055 1056 cdns,<addr>[,options] 1057 Start an early, polled-mode console on a Cadence 1058 (xuartps) serial port at the specified address. Only 1059 supported option is baud rate. If baud rate is not 1060 specified, the serial port must already be setup and 1061 configured. 1062 1063 uart[8250],io,<addr>[,options] 1064 uart[8250],mmio,<addr>[,options] 1065 uart[8250],mmio32,<addr>[,options] 1066 uart[8250],mmio32be,<addr>[,options] 1067 uart[8250],0x<addr>[,options] 1068 Start an early, polled-mode console on the 8250/16550 1069 UART at the specified I/O port or MMIO address. 1070 MMIO inter-register address stride is either 8-bit 1071 (mmio) or 32-bit (mmio32 or mmio32be). 1072 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed 1073 to be equivalent to 'mmio'. 'options' are specified 1074 in the same format described for "console=ttyS<n>"; if 1075 unspecified, the h/w is not initialized. 1076 1077 pl011,<addr> 1078 pl011,mmio32,<addr> 1079 Start an early, polled-mode console on a pl011 serial 1080 port at the specified address. The pl011 serial port 1081 must already be setup and configured. Options are not 1082 yet supported. If 'mmio32' is specified, then only 1083 the driver will use only 32-bit accessors to read/write 1084 the device registers. 1085 1086 meson,<addr> 1087 Start an early, polled-mode console on a meson serial 1088 port at the specified address. The serial port must 1089 already be setup and configured. Options are not yet 1090 supported. 1091 1092 msm_serial,<addr> 1093 Start an early, polled-mode console on an msm serial 1094 port at the specified address. The serial port 1095 must already be setup and configured. Options are not 1096 yet supported. 1097 1098 msm_serial_dm,<addr> 1099 Start an early, polled-mode console on an msm serial 1100 dm port at the specified address. The serial port 1101 must already be setup and configured. Options are not 1102 yet supported. 1103 1104 owl,<addr> 1105 Start an early, polled-mode console on a serial port 1106 of an Actions Semi SoC, such as S500 or S900, at the 1107 specified address. The serial port must already be 1108 setup and configured. Options are not yet supported. 1109 1110 rda,<addr> 1111 Start an early, polled-mode console on a serial port 1112 of an RDA Micro SoC, such as RDA8810PL, at the 1113 specified address. The serial port must already be 1114 setup and configured. Options are not yet supported. 1115 1116 sbi 1117 Use RISC-V SBI (Supervisor Binary Interface) for early 1118 console. 1119 1120 smh Use ARM semihosting calls for early console. 1121 1122 s3c2410,<addr> 1123 s3c2412,<addr> 1124 s3c2440,<addr> 1125 s3c6400,<addr> 1126 s5pv210,<addr> 1127 exynos4210,<addr> 1128 Use early console provided by serial driver available 1129 on Samsung SoCs, requires selecting proper type and 1130 a correct base address of the selected UART port. The 1131 serial port must already be setup and configured. 1132 Options are not yet supported. 1133 1134 lantiq,<addr> 1135 Start an early, polled-mode console on a lantiq serial 1136 (lqasc) port at the specified address. The serial port 1137 must already be setup and configured. Options are not 1138 yet supported. 1139 1140 lpuart,<addr> 1141 lpuart32,<addr> 1142 Use early console provided by Freescale LP UART driver 1143 found on Freescale Vybrid and QorIQ LS1021A processors. 1144 A valid base address must be provided, and the serial 1145 port must already be setup and configured. 1146 1147 ec_imx21,<addr> 1148 ec_imx6q,<addr> 1149 Start an early, polled-mode, output-only console on the 1150 Freescale i.MX UART at the specified address. The UART 1151 must already be setup and configured. 1152 1153 ar3700_uart,<addr> 1154 Start an early, polled-mode console on the 1155 Armada 3700 serial port at the specified 1156 address. The serial port must already be setup 1157 and configured. Options are not yet supported. 1158 1159 qcom_geni,<addr> 1160 Start an early, polled-mode console on a Qualcomm 1161 Generic Interface (GENI) based serial port at the 1162 specified address. The serial port must already be 1163 setup and configured. Options are not yet supported. 1164 1165 efifb,[options] 1166 Start an early, unaccelerated console on the EFI 1167 memory mapped framebuffer (if available). On cache 1168 coherent non-x86 systems that use system memory for 1169 the framebuffer, pass the 'ram' option so that it is 1170 mapped with the correct attributes. 1171 1172 linflex,<addr> 1173 Use early console provided by Freescale LINFlexD UART 1174 serial driver for NXP S32V234 SoCs. A valid base 1175 address must be provided, and the serial port must 1176 already be setup and configured. 1177 1178 earlyprintk= [X86,SH,ARM,M68k,S390] 1179 earlyprintk=vga 1180 earlyprintk=sclp 1181 earlyprintk=xen 1182 earlyprintk=serial[,ttySn[,baudrate]] 1183 earlyprintk=serial[,0x...[,baudrate]] 1184 earlyprintk=ttySn[,baudrate] 1185 earlyprintk=dbgp[debugController#] 1186 earlyprintk=pciserial[,force],bus:device.function[,baudrate] 1187 earlyprintk=xdbc[xhciController#] 1188 1189 earlyprintk is useful when the kernel crashes before 1190 the normal console is initialized. It is not enabled by 1191 default because it has some cosmetic problems. 1192 1193 Append ",keep" to not disable it when the real console 1194 takes over. 1195 1196 Only one of vga, efi, serial, or usb debug port can 1197 be used at a time. 1198 1199 Currently only ttyS0 and ttyS1 may be specified by 1200 name. Other I/O ports may be explicitly specified 1201 on some architectures (x86 and arm at least) by 1202 replacing ttySn with an I/O port address, like this: 1203 earlyprintk=serial,0x1008,115200 1204 You can find the port for a given device in 1205 /proc/tty/driver/serial: 1206 2: uart:ST16650V2 port:00001008 irq:18 ... 1207 1208 Interaction with the standard serial driver is not 1209 very good. 1210 1211 The VGA and EFI output is eventually overwritten by 1212 the real console. 1213 1214 The xen output can only be used by Xen PV guests. 1215 1216 The sclp output can only be used on s390. 1217 1218 The optional "force" to "pciserial" enables use of a 1219 PCI device even when its classcode is not of the 1220 UART class. 1221 1222 edac_report= [HW,EDAC] Control how to report EDAC event 1223 Format: {"on" | "off" | "force"} 1224 on: enable EDAC to report H/W event. May be overridden 1225 by other higher priority error reporting module. 1226 off: disable H/W event reporting through EDAC. 1227 force: enforce the use of EDAC to report H/W event. 1228 default: on. 1229 1230 ekgdboc= [X86,KGDB] Allow early kernel console debugging 1231 ekgdboc=kbd 1232 1233 This is designed to be used in conjunction with 1234 the boot argument: earlyprintk=vga 1235 1236 This parameter works in place of the kgdboc parameter 1237 but can only be used if the backing tty is available 1238 very early in the boot process. For early debugging 1239 via a serial port see kgdboc_earlycon instead. 1240 1241 edd= [EDD] 1242 Format: {"off" | "on" | "skip[mbr]"} 1243 1244 efi= [EFI] 1245 Format: { "debug", "disable_early_pci_dma", 1246 "nochunk", "noruntime", "nosoftreserve", 1247 "novamap", "no_disable_early_pci_dma" } 1248 debug: enable misc debug output. 1249 disable_early_pci_dma: disable the busmaster bit on all 1250 PCI bridges while in the EFI boot stub. 1251 nochunk: disable reading files in "chunks" in the EFI 1252 boot stub, as chunking can cause problems with some 1253 firmware implementations. 1254 noruntime : disable EFI runtime services support 1255 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose) 1256 attribute may cause the kernel to reserve the 1257 memory range for a memory mapping driver to 1258 claim. Specify efi=nosoftreserve to disable this 1259 reservation and treat the memory by its base type 1260 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM"). 1261 novamap: do not call SetVirtualAddressMap(). 1262 no_disable_early_pci_dma: Leave the busmaster bit set 1263 on all PCI bridges while in the EFI boot stub 1264 1265 efi_no_storage_paranoia [EFI; X86] 1266 Using this parameter you can use more than 50% of 1267 your efi variable storage. Use this parameter only if 1268 you are really sure that your UEFI does sane gc and 1269 fulfills the spec otherwise your board may brick. 1270 1271 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86] 1272 Add arbitrary attribute to specific memory range by 1273 updating original EFI memory map. 1274 Region of memory which aa attribute is added to is 1275 from ss to ss+nn. 1276 1277 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000 1278 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000) 1279 attribute is added to range 0x100000000-0x180000000 and 1280 0x10a0000000-0x1120000000. 1281 1282 If efi_fake_mem=8G@9G:0x40000 is specified, the 1283 EFI_MEMORY_SP(0x40000) attribute is added to 1284 range 0x240000000-0x43fffffff. 1285 1286 Using this parameter you can do debugging of EFI memmap 1287 related features. For example, you can do debugging of 1288 Address Range Mirroring feature even if your box 1289 doesn't support it, or mark specific memory as 1290 "soft reserved". 1291 1292 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT 1293 that is to be dynamically loaded by Linux. If there are 1294 multiple variables with the same name but with different 1295 vendor GUIDs, all of them will be loaded. See 1296 Documentation/admin-guide/acpi/ssdt-overlays.rst for details. 1297 1298 1299 eisa_irq_edge= [PARISC,HW] 1300 See header of drivers/parisc/eisa.c. 1301 1302 elanfreq= [X86-32] 1303 See comment before function elanfreq_setup() in 1304 arch/x86/kernel/cpu/cpufreq/elanfreq.c. 1305 1306 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390] 1307 Specifies physical address of start of kernel core 1308 image elf header and optionally the size. Generally 1309 kexec loader will pass this option to capture kernel. 1310 See Documentation/admin-guide/kdump/kdump.rst for details. 1311 1312 enable_mtrr_cleanup [X86] 1313 The kernel tries to adjust MTRR layout from continuous 1314 to discrete, to make X server driver able to add WB 1315 entry later. This parameter enables that. 1316 1317 enable_timer_pin_1 [X86] 1318 Enable PIN 1 of APIC timer 1319 Can be useful to work around chipset bugs 1320 (in particular on some ATI chipsets). 1321 The kernel tries to set a reasonable default. 1322 1323 enforcing [SELINUX] Set initial enforcing status. 1324 Format: {"0" | "1"} 1325 See security/selinux/Kconfig help text. 1326 0 -- permissive (log only, no denials). 1327 1 -- enforcing (deny and log). 1328 Default value is 0. 1329 Value can be changed at runtime via 1330 /sys/fs/selinux/enforce. 1331 1332 erst_disable [ACPI] 1333 Disable Error Record Serialization Table (ERST) 1334 support. 1335 1336 ether= [HW,NET] Ethernet cards parameters 1337 This option is obsoleted by the "netdev=" option, which 1338 has equivalent usage. See its documentation for details. 1339 1340 evm= [EVM] 1341 Format: { "fix" } 1342 Permit 'security.evm' to be updated regardless of 1343 current integrity status. 1344 1345 failslab= 1346 fail_usercopy= 1347 fail_page_alloc= 1348 fail_make_request=[KNL] 1349 General fault injection mechanism. 1350 Format: <interval>,<probability>,<space>,<times> 1351 See also Documentation/fault-injection/. 1352 1353 fb_tunnels= [NET] 1354 Format: { initns | none } 1355 See Documentation/admin-guide/sysctl/net.rst for 1356 fb_tunnels_only_for_init_ns 1357 1358 floppy= [HW] 1359 See Documentation/admin-guide/blockdev/floppy.rst. 1360 1361 force_pal_cache_flush 1362 [IA-64] Avoid check_sal_cache_flush which may hang on 1363 buggy SAL_CACHE_FLUSH implementations. Using this 1364 parameter will force ia64_sal_cache_flush to call 1365 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH. 1366 1367 forcepae [X86-32] 1368 Forcefully enable Physical Address Extension (PAE). 1369 Many Pentium M systems disable PAE but may have a 1370 functionally usable PAE implementation. 1371 Warning: use of this parameter will taint the kernel 1372 and may cause unknown problems. 1373 1374 ftrace=[tracer] 1375 [FTRACE] will set and start the specified tracer 1376 as early as possible in order to facilitate early 1377 boot debugging. 1378 1379 ftrace_dump_on_oops[=orig_cpu] 1380 [FTRACE] will dump the trace buffers on oops. 1381 If no parameter is passed, ftrace will dump 1382 buffers of all CPUs, but if you pass orig_cpu, it will 1383 dump only the buffer of the CPU that triggered the 1384 oops. 1385 1386 ftrace_filter=[function-list] 1387 [FTRACE] Limit the functions traced by the function 1388 tracer at boot up. function-list is a comma separated 1389 list of functions. This list can be changed at run 1390 time by the set_ftrace_filter file in the debugfs 1391 tracing directory. 1392 1393 ftrace_notrace=[function-list] 1394 [FTRACE] Do not trace the functions specified in 1395 function-list. This list can be changed at run time 1396 by the set_ftrace_notrace file in the debugfs 1397 tracing directory. 1398 1399 ftrace_graph_filter=[function-list] 1400 [FTRACE] Limit the top level callers functions traced 1401 by the function graph tracer at boot up. 1402 function-list is a comma separated list of functions 1403 that can be changed at run time by the 1404 set_graph_function file in the debugfs tracing directory. 1405 1406 ftrace_graph_notrace=[function-list] 1407 [FTRACE] Do not trace from the functions specified in 1408 function-list. This list is a comma separated list of 1409 functions that can be changed at run time by the 1410 set_graph_notrace file in the debugfs tracing directory. 1411 1412 ftrace_graph_max_depth=<uint> 1413 [FTRACE] Used with the function graph tracer. This is 1414 the max depth it will trace into a function. This value 1415 can be changed at run time by the max_graph_depth file 1416 in the tracefs tracing directory. default: 0 (no limit) 1417 1418 fw_devlink= [KNL] Create device links between consumer and supplier 1419 devices by scanning the firmware to infer the 1420 consumer/supplier relationships. This feature is 1421 especially useful when drivers are loaded as modules as 1422 it ensures proper ordering of tasks like device probing 1423 (suppliers first, then consumers), supplier boot state 1424 clean up (only after all consumers have probed), 1425 suspend/resume & runtime PM (consumers first, then 1426 suppliers). 1427 Format: { off | permissive | on | rpm } 1428 off -- Don't create device links from firmware info. 1429 permissive -- Create device links from firmware info 1430 but use it only for ordering boot state clean 1431 up (sync_state() calls). 1432 on -- Create device links from firmware info and use it 1433 to enforce probe and suspend/resume ordering. 1434 rpm -- Like "on", but also use to order runtime PM. 1435 1436 gamecon.map[2|3]= 1437 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 1438 support via parallel port (up to 5 devices per port) 1439 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 1440 See also Documentation/input/devices/joystick-parport.rst 1441 1442 gamma= [HW,DRM] 1443 1444 gart_fix_e820= [X86-64] disable the fix e820 for K8 GART 1445 Format: off | on 1446 default: on 1447 1448 gcov_persist= [GCOV] When non-zero (default), profiling data for 1449 kernel modules is saved and remains accessible via 1450 debugfs, even when the module is unloaded/reloaded. 1451 When zero, profiling data is discarded and associated 1452 debugfs files are removed at module unload time. 1453 1454 goldfish [X86] Enable the goldfish android emulator platform. 1455 Don't use this when you are not running on the 1456 android emulator 1457 1458 gpt [EFI] Forces disk with valid GPT signature but 1459 invalid Protective MBR to be treated as GPT. If the 1460 primary GPT is corrupted, it enables the backup/alternate 1461 GPT to be used instead. 1462 1463 grcan.enable0= [HW] Configuration of physical interface 0. Determines 1464 the "Enable 0" bit of the configuration register. 1465 Format: 0 | 1 1466 Default: 0 1467 grcan.enable1= [HW] Configuration of physical interface 1. Determines 1468 the "Enable 0" bit of the configuration register. 1469 Format: 0 | 1 1470 Default: 0 1471 grcan.select= [HW] Select which physical interface to use. 1472 Format: 0 | 1 1473 Default: 0 1474 grcan.txsize= [HW] Sets the size of the tx buffer. 1475 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. 1476 Default: 1024 1477 grcan.rxsize= [HW] Sets the size of the rx buffer. 1478 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. 1479 Default: 1024 1480 1481 gpio-mockup.gpio_mockup_ranges 1482 [HW] Sets the ranges of gpiochip of for this device. 1483 Format: <start1>,<end1>,<start2>,<end2>... 1484 1485 hardlockup_all_cpu_backtrace= 1486 [KNL] Should the hard-lockup detector generate 1487 backtraces on all cpus. 1488 Format: 0 | 1 1489 1490 hashdist= [KNL,NUMA] Large hashes allocated during boot 1491 are distributed across NUMA nodes. Defaults on 1492 for 64-bit NUMA, off otherwise. 1493 Format: 0 | 1 (for off | on) 1494 1495 hcl= [IA-64] SGI's Hardware Graph compatibility layer 1496 1497 hd= [EIDE] (E)IDE hard drive subsystem geometry 1498 Format: <cyl>,<head>,<sect> 1499 1500 hest_disable [ACPI] 1501 Disable Hardware Error Source Table (HEST) support; 1502 corresponding firmware-first mode error processing 1503 logic will be disabled. 1504 1505 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact 1506 size of <nn>. This works even on boxes that have no 1507 highmem otherwise. This also works to reduce highmem 1508 size on bigger boxes. 1509 1510 highres= [KNL] Enable/disable high resolution timer mode. 1511 Valid parameters: "on", "off" 1512 Default: "on" 1513 1514 hlt [BUGS=ARM,SH] 1515 1516 hpet= [X86-32,HPET] option to control HPET usage 1517 Format: { enable (default) | disable | force | 1518 verbose } 1519 disable: disable HPET and use PIT instead 1520 force: allow force enabled of undocumented chips (ICH4, 1521 VIA, nVidia) 1522 verbose: show contents of HPET registers during setup 1523 1524 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET 1525 registers. Default set by CONFIG_HPET_MMAP_DEFAULT. 1526 1527 hugetlb_cma= [HW] The size of a cma area used for allocation 1528 of gigantic hugepages. 1529 Format: nn[KMGTPE] 1530 1531 Reserve a cma area of given size and allocate gigantic 1532 hugepages using the cma allocator. If enabled, the 1533 boot-time allocation of gigantic hugepages is skipped. 1534 1535 hugepages= [HW] Number of HugeTLB pages to allocate at boot. 1536 If this follows hugepagesz (below), it specifies 1537 the number of pages of hugepagesz to be allocated. 1538 If this is the first HugeTLB parameter on the command 1539 line, it specifies the number of pages to allocate for 1540 the default huge page size. See also 1541 Documentation/admin-guide/mm/hugetlbpage.rst. 1542 Format: <integer> 1543 1544 hugepagesz= 1545 [HW] The size of the HugeTLB pages. This is used in 1546 conjunction with hugepages (above) to allocate huge 1547 pages of a specific size at boot. The pair 1548 hugepagesz=X hugepages=Y can be specified once for 1549 each supported huge page size. Huge page sizes are 1550 architecture dependent. See also 1551 Documentation/admin-guide/mm/hugetlbpage.rst. 1552 Format: size[KMG] 1553 1554 hung_task_panic= 1555 [KNL] Should the hung task detector generate panics. 1556 Format: 0 | 1 1557 1558 A value of 1 instructs the kernel to panic when a 1559 hung task is detected. The default value is controlled 1560 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time 1561 option. The value selected by this boot parameter can 1562 be changed later by the kernel.hung_task_panic sysctl. 1563 1564 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 1565 terminal devices. Valid values: 0..8 1566 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 1567 If specified, z/VM IUCV HVC accepts connections 1568 from listed z/VM user IDs only. 1569 1570 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations 1571 which allow the hypervisor to 'idle' the 1572 guest on lock contention. 1573 1574 keep_bootcon [KNL] 1575 Do not unregister boot console at start. This is only 1576 useful for debugging when something happens in the window 1577 between unregistering the boot console and initializing 1578 the real console. 1579 1580 i2c_bus= [HW] Override the default board specific I2C bus speed 1581 or register an additional I2C bus that is not 1582 registered from board initialization code. 1583 Format: 1584 <bus_id>,<clkrate> 1585 1586 i8042.debug [HW] Toggle i8042 debug mode 1587 i8042.unmask_kbd_data 1588 [HW] Enable printing of interrupt data from the KBD port 1589 (disabled by default, and as a pre-condition 1590 requires that i8042.debug=1 be enabled) 1591 i8042.direct [HW] Put keyboard port into non-translated mode 1592 i8042.dumbkbd [HW] Pretend that controller can only read data from 1593 keyboard and cannot control its state 1594 (Don't attempt to blink the leds) 1595 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 1596 i8042.nokbd [HW] Don't check/create keyboard port 1597 i8042.noloop [HW] Disable the AUX Loopback command while probing 1598 for the AUX port 1599 i8042.nomux [HW] Don't check presence of an active multiplexing 1600 controller 1601 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 1602 controllers 1603 i8042.notimeout [HW] Ignore timeout condition signalled by controller 1604 i8042.reset [HW] Reset the controller during init, cleanup and 1605 suspend-to-ram transitions, only during s2r 1606 transitions, or never reset 1607 Format: { 1 | Y | y | 0 | N | n } 1608 1, Y, y: always reset controller 1609 0, N, n: don't ever reset controller 1610 Default: only on s2r transitions on x86; most other 1611 architectures force reset to be always executed 1612 i8042.unlock [HW] Unlock (ignore) the keylock 1613 i8042.kbdreset [HW] Reset device connected to KBD port 1614 1615 i810= [HW,DRM] 1616 1617 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data 1618 indicates that the driver is running on unsupported 1619 hardware. 1620 i8k.force [HW] Activate i8k driver even if SMM BIOS signature 1621 does not match list of supported models. 1622 i8k.power_status 1623 [HW] Report power status in /proc/i8k 1624 (disabled by default) 1625 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN 1626 capability is set. 1627 1628 i915.invert_brightness= 1629 [DRM] Invert the sense of the variable that is used to 1630 set the brightness of the panel backlight. Normally a 1631 brightness value of 0 indicates backlight switched off, 1632 and the maximum of the brightness value sets the backlight 1633 to maximum brightness. If this parameter is set to 0 1634 (default) and the machine requires it, or this parameter 1635 is set to 1, a brightness value of 0 sets the backlight 1636 to maximum brightness, and the maximum of the brightness 1637 value switches the backlight off. 1638 -1 -- never invert brightness 1639 0 -- machine default 1640 1 -- force brightness inversion 1641 1642 icn= [HW,ISDN] 1643 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]] 1644 1645 ide-core.nodma= [HW] (E)IDE subsystem 1646 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc 1647 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr 1648 .cdrom .chs .ignore_cable are additional options 1649 See Documentation/ide/ide.rst. 1650 1651 ide-generic.probe-mask= [HW] (E)IDE subsystem 1652 Format: <int> 1653 Probe mask for legacy ISA IDE ports. Depending on 1654 platform up to 6 ports are supported, enabled by 1655 setting corresponding bits in the mask to 1. The 1656 default value is 0x0, which has a special meaning. 1657 On systems that have PCI, it triggers scanning the 1658 PCI bus for the first and the second port, which 1659 are then probed. On systems without PCI the value 1660 of 0x0 enables probing the two first ports as if it 1661 was 0x3. 1662 1663 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem 1664 Claim all unknown PCI IDE storage controllers. 1665 1666 idle= [X86] 1667 Format: idle=poll, idle=halt, idle=nomwait 1668 Poll forces a polling idle loop that can slightly 1669 improve the performance of waking up a idle CPU, but 1670 will use a lot of power and make the system run hot. 1671 Not recommended. 1672 idle=halt: Halt is forced to be used for CPU idle. 1673 In such case C2/C3 won't be used again. 1674 idle=nomwait: Disable mwait for CPU C-states 1675 1676 ieee754= [MIPS] Select IEEE Std 754 conformance mode 1677 Format: { strict | legacy | 2008 | relaxed } 1678 Default: strict 1679 1680 Choose which programs will be accepted for execution 1681 based on the IEEE 754 NaN encoding(s) supported by 1682 the FPU and the NaN encoding requested with the value 1683 of an ELF file header flag individually set by each 1684 binary. Hardware implementations are permitted to 1685 support either or both of the legacy and the 2008 NaN 1686 encoding mode. 1687 1688 Available settings are as follows: 1689 strict accept binaries that request a NaN encoding 1690 supported by the FPU 1691 legacy only accept legacy-NaN binaries, if supported 1692 by the FPU 1693 2008 only accept 2008-NaN binaries, if supported 1694 by the FPU 1695 relaxed accept any binaries regardless of whether 1696 supported by the FPU 1697 1698 The FPU emulator is always able to support both NaN 1699 encodings, so if no FPU hardware is present or it has 1700 been disabled with 'nofpu', then the settings of 1701 'legacy' and '2008' strap the emulator accordingly, 1702 'relaxed' straps the emulator for both legacy-NaN and 1703 2008-NaN, whereas 'strict' enables legacy-NaN only on 1704 legacy processors and both NaN encodings on MIPS32 or 1705 MIPS64 CPUs. 1706 1707 The setting for ABS.fmt/NEG.fmt instruction execution 1708 mode generally follows that for the NaN encoding, 1709 except where unsupported by hardware. 1710 1711 ignore_loglevel [KNL] 1712 Ignore loglevel setting - this will print /all/ 1713 kernel messages to the console. Useful for debugging. 1714 We also add it as printk module parameter, so users 1715 could change it dynamically, usually by 1716 /sys/module/printk/parameters/ignore_loglevel. 1717 1718 ignore_rlimit_data 1719 Ignore RLIMIT_DATA setting for data mappings, 1720 print warning at first misuse. Can be changed via 1721 /sys/module/kernel/parameters/ignore_rlimit_data. 1722 1723 ihash_entries= [KNL] 1724 Set number of hash buckets for inode cache. 1725 1726 ima_appraise= [IMA] appraise integrity measurements 1727 Format: { "off" | "enforce" | "fix" | "log" } 1728 default: "enforce" 1729 1730 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead. 1731 The builtin appraise policy appraises all files 1732 owned by uid=0. 1733 1734 ima_canonical_fmt [IMA] 1735 Use the canonical format for the binary runtime 1736 measurements, instead of host native format. 1737 1738 ima_hash= [IMA] 1739 Format: { md5 | sha1 | rmd160 | sha256 | sha384 1740 | sha512 | ... } 1741 default: "sha1" 1742 1743 The list of supported hash algorithms is defined 1744 in crypto/hash_info.h. 1745 1746 ima_policy= [IMA] 1747 The builtin policies to load during IMA setup. 1748 Format: "tcb | appraise_tcb | secure_boot | 1749 fail_securely" 1750 1751 The "tcb" policy measures all programs exec'd, files 1752 mmap'd for exec, and all files opened with the read 1753 mode bit set by either the effective uid (euid=0) or 1754 uid=0. 1755 1756 The "appraise_tcb" policy appraises the integrity of 1757 all files owned by root. 1758 1759 The "secure_boot" policy appraises the integrity 1760 of files (eg. kexec kernel image, kernel modules, 1761 firmware, policy, etc) based on file signatures. 1762 1763 The "fail_securely" policy forces file signature 1764 verification failure also on privileged mounted 1765 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE 1766 flag. 1767 1768 ima_tcb [IMA] Deprecated. Use ima_policy= instead. 1769 Load a policy which meets the needs of the Trusted 1770 Computing Base. This means IMA will measure all 1771 programs exec'd, files mmap'd for exec, and all files 1772 opened for read by uid=0. 1773 1774 ima_template= [IMA] 1775 Select one of defined IMA measurements template formats. 1776 Formats: { "ima" | "ima-ng" | "ima-sig" } 1777 Default: "ima-ng" 1778 1779 ima_template_fmt= 1780 [IMA] Define a custom template format. 1781 Format: { "field1|...|fieldN" } 1782 1783 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage 1784 Format: <min_file_size> 1785 Set the minimal file size for using asynchronous hash. 1786 If left unspecified, ahash usage is disabled. 1787 1788 ahash performance varies for different data sizes on 1789 different crypto accelerators. This option can be used 1790 to achieve the best performance for a particular HW. 1791 1792 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size 1793 Format: <bufsize> 1794 Set hashing buffer size. Default: 4k. 1795 1796 ahash performance varies for different chunk sizes on 1797 different crypto accelerators. This option can be used 1798 to achieve best performance for particular HW. 1799 1800 init= [KNL] 1801 Format: <full_path> 1802 Run specified binary instead of /sbin/init as init 1803 process. 1804 1805 initcall_debug [KNL] Trace initcalls as they are executed. Useful 1806 for working out where the kernel is dying during 1807 startup. 1808 1809 initcall_blacklist= [KNL] Do not execute a comma-separated list of 1810 initcall functions. Useful for debugging built-in 1811 modules and initcalls. 1812 1813 initrd= [BOOT] Specify the location of the initial ramdisk 1814 1815 initrdmem= [KNL] Specify a physical address and size from which to 1816 load the initrd. If an initrd is compiled in or 1817 specified in the bootparams, it takes priority over this 1818 setting. 1819 Format: ss[KMG],nn[KMG] 1820 Default is 0, 0 1821 1822 init_on_alloc= [MM] Fill newly allocated pages and heap objects with 1823 zeroes. 1824 Format: 0 | 1 1825 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON. 1826 1827 init_on_free= [MM] Fill freed pages and heap objects with zeroes. 1828 Format: 0 | 1 1829 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON. 1830 1831 init_pkru= [X86] Specify the default memory protection keys rights 1832 register contents for all processes. 0x55555554 by 1833 default (disallow access to all but pkey 0). Can 1834 override in debugfs after boot. 1835 1836 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 1837 Format: <irq> 1838 1839 int_pln_enable [X86] Enable power limit notification interrupt 1840 1841 integrity_audit=[IMA] 1842 Format: { "0" | "1" } 1843 0 -- basic integrity auditing messages. (Default) 1844 1 -- additional integrity auditing messages. 1845 1846 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 1847 on 1848 Enable intel iommu driver. 1849 off 1850 Disable intel iommu driver. 1851 igfx_off [Default Off] 1852 By default, gfx is mapped as normal device. If a gfx 1853 device has a dedicated DMAR unit, the DMAR unit is 1854 bypassed by not enabling DMAR with this option. In 1855 this case, gfx device will use physical address for 1856 DMA. 1857 forcedac [X86-64] 1858 With this option iommu will not optimize to look 1859 for io virtual address below 32-bit forcing dual 1860 address cycle on pci bus for cards supporting greater 1861 than 32-bit addressing. The default is to look 1862 for translation below 32-bit and if not available 1863 then look in the higher range. 1864 strict [Default Off] 1865 With this option on every unmap_single operation will 1866 result in a hardware IOTLB flush operation as opposed 1867 to batching them for performance. 1868 sp_off [Default Off] 1869 By default, super page will be supported if Intel IOMMU 1870 has the capability. With this option, super page will 1871 not be supported. 1872 sm_on [Default Off] 1873 By default, scalable mode will be disabled even if the 1874 hardware advertises that it has support for the scalable 1875 mode translation. With this option set, scalable mode 1876 will be used on hardware which claims to support it. 1877 tboot_noforce [Default Off] 1878 Do not force the Intel IOMMU enabled under tboot. 1879 By default, tboot will force Intel IOMMU on, which 1880 could harm performance of some high-throughput 1881 devices like 40GBit network cards, even if identity 1882 mapping is enabled. 1883 Note that using this option lowers the security 1884 provided by tboot because it makes the system 1885 vulnerable to DMA attacks. 1886 nobounce [Default off] 1887 Disable bounce buffer for untrusted devices such as 1888 the Thunderbolt devices. This will treat the untrusted 1889 devices as the trusted ones, hence might expose security 1890 risks of DMA attacks. 1891 1892 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 1893 0 disables intel_idle and fall back on acpi_idle. 1894 1 to 9 specify maximum depth of C-state. 1895 1896 intel_pstate= [X86] 1897 disable 1898 Do not enable intel_pstate as the default 1899 scaling driver for the supported processors 1900 passive 1901 Use intel_pstate as a scaling driver, but configure it 1902 to work with generic cpufreq governors (instead of 1903 enabling its internal governor). This mode cannot be 1904 used along with the hardware-managed P-states (HWP) 1905 feature. 1906 force 1907 Enable intel_pstate on systems that prohibit it by default 1908 in favor of acpi-cpufreq. Forcing the intel_pstate driver 1909 instead of acpi-cpufreq may disable platform features, such 1910 as thermal controls and power capping, that rely on ACPI 1911 P-States information being indicated to OSPM and therefore 1912 should be used with caution. This option does not work with 1913 processors that aren't supported by the intel_pstate driver 1914 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 1915 no_hwp 1916 Do not enable hardware P state control (HWP) 1917 if available. 1918 hwp_only 1919 Only load intel_pstate on systems which support 1920 hardware P state control (HWP) if available. 1921 support_acpi_ppc 1922 Enforce ACPI _PPC performance limits. If the Fixed ACPI 1923 Description Table, specifies preferred power management 1924 profile as "Enterprise Server" or "Performance Server", 1925 then this feature is turned on by default. 1926 per_cpu_perf_limits 1927 Allow per-logical-CPU P-State performance control limits using 1928 cpufreq sysfs interface 1929 1930 intremap= [X86-64, Intel-IOMMU] 1931 on enable Interrupt Remapping (default) 1932 off disable Interrupt Remapping 1933 nosid disable Source ID checking 1934 no_x2apic_optout 1935 BIOS x2APIC opt-out request will be ignored 1936 nopost disable Interrupt Posting 1937 1938 iomem= Disable strict checking of access to MMIO memory 1939 strict regions from userspace. 1940 relaxed 1941 1942 iommu= [X86] 1943 off 1944 force 1945 noforce 1946 biomerge 1947 panic 1948 nopanic 1949 merge 1950 nomerge 1951 soft 1952 pt [X86] 1953 nopt [X86] 1954 nobypass [PPC/POWERNV] 1955 Disable IOMMU bypass, using IOMMU for PCI devices. 1956 1957 iommu.strict= [ARM64] Configure TLB invalidation behaviour 1958 Format: { "0" | "1" } 1959 0 - Lazy mode. 1960 Request that DMA unmap operations use deferred 1961 invalidation of hardware TLBs, for increased 1962 throughput at the cost of reduced device isolation. 1963 Will fall back to strict mode if not supported by 1964 the relevant IOMMU driver. 1965 1 - Strict mode (default). 1966 DMA unmap operations invalidate IOMMU hardware TLBs 1967 synchronously. 1968 1969 iommu.passthrough= 1970 [ARM64, X86] Configure DMA to bypass the IOMMU by default. 1971 Format: { "0" | "1" } 1972 0 - Use IOMMU translation for DMA. 1973 1 - Bypass the IOMMU for DMA. 1974 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH. 1975 1976 io7= [HW] IO7 for Marvel-based Alpha systems 1977 See comment before marvel_specify_io7 in 1978 arch/alpha/kernel/core_marvel.c. 1979 1980 io_delay= [X86] I/O delay method 1981 0x80 1982 Standard port 0x80 based delay 1983 0xed 1984 Alternate port 0xed based delay (needed on some systems) 1985 udelay 1986 Simple two microseconds delay 1987 none 1988 No delay 1989 1990 ip= [IP_PNP] 1991 See Documentation/admin-guide/nfs/nfsroot.rst. 1992 1993 ipcmni_extend [KNL] Extend the maximum number of unique System V 1994 IPC identifiers from 32,768 to 16,777,216. 1995 1996 irqaffinity= [SMP] Set the default irq affinity mask 1997 The argument is a cpu list, as described above. 1998 1999 irqchip.gicv2_force_probe= 2000 [ARM, ARM64] 2001 Format: <bool> 2002 Force the kernel to look for the second 4kB page 2003 of a GICv2 controller even if the memory range 2004 exposed by the device tree is too small. 2005 2006 irqchip.gicv3_nolpi= 2007 [ARM, ARM64] 2008 Force the kernel to ignore the availability of 2009 LPIs (and by consequence ITSs). Intended for system 2010 that use the kernel as a bootloader, and thus want 2011 to let secondary kernels in charge of setting up 2012 LPIs. 2013 2014 irqchip.gicv3_pseudo_nmi= [ARM64] 2015 Enables support for pseudo-NMIs in the kernel. This 2016 requires the kernel to be built with 2017 CONFIG_ARM64_PSEUDO_NMI. 2018 2019 irqfixup [HW] 2020 When an interrupt is not handled search all handlers 2021 for it. Intended to get systems with badly broken 2022 firmware running. 2023 2024 irqpoll [HW] 2025 When an interrupt is not handled search all handlers 2026 for it. Also check all handlers each timer 2027 interrupt. Intended to get systems with badly broken 2028 firmware running. 2029 2030 isapnp= [ISAPNP] 2031 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 2032 2033 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance. 2034 [Deprecated - use cpusets instead] 2035 Format: [flag-list,]<cpu-list> 2036 2037 Specify one or more CPUs to isolate from disturbances 2038 specified in the flag list (default: domain): 2039 2040 nohz 2041 Disable the tick when a single task runs. 2042 2043 A residual 1Hz tick is offloaded to workqueues, which you 2044 need to affine to housekeeping through the global 2045 workqueue's affinity configured via the 2046 /sys/devices/virtual/workqueue/cpumask sysfs file, or 2047 by using the 'domain' flag described below. 2048 2049 NOTE: by default the global workqueue runs on all CPUs, 2050 so to protect individual CPUs the 'cpumask' file has to 2051 be configured manually after bootup. 2052 2053 domain 2054 Isolate from the general SMP balancing and scheduling 2055 algorithms. Note that performing domain isolation this way 2056 is irreversible: it's not possible to bring back a CPU to 2057 the domains once isolated through isolcpus. It's strongly 2058 advised to use cpusets instead to disable scheduler load 2059 balancing through the "cpuset.sched_load_balance" file. 2060 It offers a much more flexible interface where CPUs can 2061 move in and out of an isolated set anytime. 2062 2063 You can move a process onto or off an "isolated" CPU via 2064 the CPU affinity syscalls or cpuset. 2065 <cpu number> begins at 0 and the maximum value is 2066 "number of CPUs in system - 1". 2067 2068 managed_irq 2069 2070 Isolate from being targeted by managed interrupts 2071 which have an interrupt mask containing isolated 2072 CPUs. The affinity of managed interrupts is 2073 handled by the kernel and cannot be changed via 2074 the /proc/irq/* interfaces. 2075 2076 This isolation is best effort and only effective 2077 if the automatically assigned interrupt mask of a 2078 device queue contains isolated and housekeeping 2079 CPUs. If housekeeping CPUs are online then such 2080 interrupts are directed to the housekeeping CPU 2081 so that IO submitted on the housekeeping CPU 2082 cannot disturb the isolated CPU. 2083 2084 If a queue's affinity mask contains only isolated 2085 CPUs then this parameter has no effect on the 2086 interrupt routing decision, though interrupts are 2087 only delivered when tasks running on those 2088 isolated CPUs submit IO. IO submitted on 2089 housekeeping CPUs has no influence on those 2090 queues. 2091 2092 The format of <cpu-list> is described above. 2093 2094 iucv= [HW,NET] 2095 2096 ivrs_ioapic [HW,X86-64] 2097 Provide an override to the IOAPIC-ID<->DEVICE-ID 2098 mapping provided in the IVRS ACPI table. For 2099 example, to map IOAPIC-ID decimal 10 to 2100 PCI device 00:14.0 write the parameter as: 2101 ivrs_ioapic[10]=00:14.0 2102 2103 ivrs_hpet [HW,X86-64] 2104 Provide an override to the HPET-ID<->DEVICE-ID 2105 mapping provided in the IVRS ACPI table. For 2106 example, to map HPET-ID decimal 0 to 2107 PCI device 00:14.0 write the parameter as: 2108 ivrs_hpet[0]=00:14.0 2109 2110 ivrs_acpihid [HW,X86-64] 2111 Provide an override to the ACPI-HID:UID<->DEVICE-ID 2112 mapping provided in the IVRS ACPI table. For 2113 example, to map UART-HID:UID AMD0020:0 to 2114 PCI device 00:14.5 write the parameter as: 2115 ivrs_acpihid[00:14.5]=AMD0020:0 2116 2117 js= [HW,JOY] Analog joystick 2118 See Documentation/input/joydev/joystick.rst. 2119 2120 nokaslr [KNL] 2121 When CONFIG_RANDOMIZE_BASE is set, this disables 2122 kernel and module base offset ASLR (Address Space 2123 Layout Randomization). 2124 2125 kasan_multi_shot 2126 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print 2127 report on every invalid memory access. Without this 2128 parameter KASAN will print report only for the first 2129 invalid access. 2130 2131 keepinitrd [HW,ARM] 2132 2133 kernelcore= [KNL,X86,IA-64,PPC] 2134 Format: nn[KMGTPE] | nn% | "mirror" 2135 This parameter specifies the amount of memory usable by 2136 the kernel for non-movable allocations. The requested 2137 amount is spread evenly throughout all nodes in the 2138 system as ZONE_NORMAL. The remaining memory is used for 2139 movable memory in its own zone, ZONE_MOVABLE. In the 2140 event, a node is too small to have both ZONE_NORMAL and 2141 ZONE_MOVABLE, kernelcore memory will take priority and 2142 other nodes will have a larger ZONE_MOVABLE. 2143 2144 ZONE_MOVABLE is used for the allocation of pages that 2145 may be reclaimed or moved by the page migration 2146 subsystem. Note that allocations like PTEs-from-HighMem 2147 still use the HighMem zone if it exists, and the Normal 2148 zone if it does not. 2149 2150 It is possible to specify the exact amount of memory in 2151 the form of "nn[KMGTPE]", a percentage of total system 2152 memory in the form of "nn%", or "mirror". If "mirror" 2153 option is specified, mirrored (reliable) memory is used 2154 for non-movable allocations and remaining memory is used 2155 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror" 2156 are exclusive, so you cannot specify multiple forms. 2157 2158 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port. 2159 Format: <Controller#>[,poll interval] 2160 The controller # is the number of the ehci usb debug 2161 port as it is probed via PCI. The poll interval is 2162 optional and is the number seconds in between 2163 each poll cycle to the debug port in case you need 2164 the functionality for interrupting the kernel with 2165 gdb or control-c on the dbgp connection. When 2166 not using this parameter you use sysrq-g to break into 2167 the kernel debugger. 2168 2169 kgdboc= [KGDB,HW] kgdb over consoles. 2170 Requires a tty driver that supports console polling, 2171 or a supported polling keyboard driver (non-usb). 2172 Serial only format: <serial_device>[,baud] 2173 keyboard only format: kbd 2174 keyboard and serial format: kbd,<serial_device>[,baud] 2175 Optional Kernel mode setting: 2176 kms, kbd format: kms,kbd 2177 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 2178 2179 kgdboc_earlycon= [KGDB,HW] 2180 If the boot console provides the ability to read 2181 characters and can work in polling mode, you can use 2182 this parameter to tell kgdb to use it as a backend 2183 until the normal console is registered. Intended to 2184 be used together with the kgdboc parameter which 2185 specifies the normal console to transition to. 2186 2187 The name of the early console should be specified 2188 as the value of this parameter. Note that the name of 2189 the early console might be different than the tty 2190 name passed to kgdboc. It's OK to leave the value 2191 blank and the first boot console that implements 2192 read() will be picked. 2193 2194 kgdbwait [KGDB] Stop kernel execution and enter the 2195 kernel debugger at the earliest opportunity. 2196 2197 kmac= [MIPS] Korina ethernet MAC address. 2198 Configure the RouterBoard 532 series on-chip 2199 Ethernet adapter MAC address. 2200 2201 kmemleak= [KNL] Boot-time kmemleak enable/disable 2202 Valid arguments: on, off 2203 Default: on 2204 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 2205 the default is off. 2206 2207 kprobe_event=[probe-list] 2208 [FTRACE] Add kprobe events and enable at boot time. 2209 The probe-list is a semicolon delimited list of probe 2210 definitions. Each definition is same as kprobe_events 2211 interface, but the parameters are comma delimited. 2212 For example, to add a kprobe event on vfs_read with 2213 arg1 and arg2, add to the command line; 2214 2215 kprobe_event=p,vfs_read,$arg1,$arg2 2216 2217 See also Documentation/trace/kprobetrace.rst "Kernel 2218 Boot Parameter" section. 2219 2220 kpti= [ARM64] Control page table isolation of user 2221 and kernel address spaces. 2222 Default: enabled on cores which need mitigation. 2223 0: force disabled 2224 1: force enabled 2225 2226 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 2227 Default is 0 (don't ignore, but inject #GP) 2228 2229 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface. 2230 Default is false (don't support). 2231 2232 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit 2233 KVM MMU at runtime. 2234 Default is 0 (off) 2235 2236 kvm.nx_huge_pages= 2237 [KVM] Controls the software workaround for the 2238 X86_BUG_ITLB_MULTIHIT bug. 2239 force : Always deploy workaround. 2240 off : Never deploy workaround. 2241 auto : Deploy workaround based on the presence of 2242 X86_BUG_ITLB_MULTIHIT. 2243 2244 Default is 'auto'. 2245 2246 If the software workaround is enabled for the host, 2247 guests do need not to enable it for nested guests. 2248 2249 kvm.nx_huge_pages_recovery_ratio= 2250 [KVM] Controls how many 4KiB pages are periodically zapped 2251 back to huge pages. 0 disables the recovery, otherwise if 2252 the value is N KVM will zap 1/Nth of the 4KiB pages every 2253 minute. The default is 60. 2254 2255 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM. 2256 Default is 1 (enabled) 2257 2258 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU) 2259 for all guests. 2260 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode. 2261 2262 kvm-arm.vgic_v3_group0_trap= 2263 [KVM,ARM] Trap guest accesses to GICv3 group-0 2264 system registers 2265 2266 kvm-arm.vgic_v3_group1_trap= 2267 [KVM,ARM] Trap guest accesses to GICv3 group-1 2268 system registers 2269 2270 kvm-arm.vgic_v3_common_trap= 2271 [KVM,ARM] Trap guest accesses to GICv3 common 2272 system registers 2273 2274 kvm-arm.vgic_v4_enable= 2275 [KVM,ARM] Allow use of GICv4 for direct injection of 2276 LPIs. 2277 2278 kvm_cma_resv_ratio=n [PPC] 2279 Reserves given percentage from system memory area for 2280 contiguous memory allocation for KVM hash pagetable 2281 allocation. 2282 By default it reserves 5% of total system memory. 2283 Format: <integer> 2284 Default: 5 2285 2286 kvm-intel.ept= [KVM,Intel] Disable extended page tables 2287 (virtualized MMU) support on capable Intel chips. 2288 Default is 1 (enabled) 2289 2290 kvm-intel.emulate_invalid_guest_state= 2291 [KVM,Intel] Enable emulation of invalid guest states 2292 Default is 0 (disabled) 2293 2294 kvm-intel.flexpriority= 2295 [KVM,Intel] Disable FlexPriority feature (TPR shadow). 2296 Default is 1 (enabled) 2297 2298 kvm-intel.nested= 2299 [KVM,Intel] Enable VMX nesting (nVMX). 2300 Default is 0 (disabled) 2301 2302 kvm-intel.unrestricted_guest= 2303 [KVM,Intel] Disable unrestricted guest feature 2304 (virtualized real and unpaged mode) on capable 2305 Intel chips. Default is 1 (enabled) 2306 2307 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault 2308 CVE-2018-3620. 2309 2310 Valid arguments: never, cond, always 2311 2312 always: L1D cache flush on every VMENTER. 2313 cond: Flush L1D on VMENTER only when the code between 2314 VMEXIT and VMENTER can leak host memory. 2315 never: Disables the mitigation 2316 2317 Default is cond (do L1 cache flush in specific instances) 2318 2319 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification 2320 feature (tagged TLBs) on capable Intel chips. 2321 Default is 1 (enabled) 2322 2323 l1tf= [X86] Control mitigation of the L1TF vulnerability on 2324 affected CPUs 2325 2326 The kernel PTE inversion protection is unconditionally 2327 enabled and cannot be disabled. 2328 2329 full 2330 Provides all available mitigations for the 2331 L1TF vulnerability. Disables SMT and 2332 enables all mitigations in the 2333 hypervisors, i.e. unconditional L1D flush. 2334 2335 SMT control and L1D flush control via the 2336 sysfs interface is still possible after 2337 boot. Hypervisors will issue a warning 2338 when the first VM is started in a 2339 potentially insecure configuration, 2340 i.e. SMT enabled or L1D flush disabled. 2341 2342 full,force 2343 Same as 'full', but disables SMT and L1D 2344 flush runtime control. Implies the 2345 'nosmt=force' command line option. 2346 (i.e. sysfs control of SMT is disabled.) 2347 2348 flush 2349 Leaves SMT enabled and enables the default 2350 hypervisor mitigation, i.e. conditional 2351 L1D flush. 2352 2353 SMT control and L1D flush control via the 2354 sysfs interface is still possible after 2355 boot. Hypervisors will issue a warning 2356 when the first VM is started in a 2357 potentially insecure configuration, 2358 i.e. SMT enabled or L1D flush disabled. 2359 2360 flush,nosmt 2361 2362 Disables SMT and enables the default 2363 hypervisor mitigation. 2364 2365 SMT control and L1D flush control via the 2366 sysfs interface is still possible after 2367 boot. Hypervisors will issue a warning 2368 when the first VM is started in a 2369 potentially insecure configuration, 2370 i.e. SMT enabled or L1D flush disabled. 2371 2372 flush,nowarn 2373 Same as 'flush', but hypervisors will not 2374 warn when a VM is started in a potentially 2375 insecure configuration. 2376 2377 off 2378 Disables hypervisor mitigations and doesn't 2379 emit any warnings. 2380 It also drops the swap size and available 2381 RAM limit restriction on both hypervisor and 2382 bare metal. 2383 2384 Default is 'flush'. 2385 2386 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst 2387 2388 l2cr= [PPC] 2389 2390 l3cr= [PPC] 2391 2392 lapic [X86-32,APIC] Enable the local APIC even if BIOS 2393 disabled it. 2394 2395 lapic= [X86,APIC] Do not use TSC deadline 2396 value for LAPIC timer one-shot implementation. Default 2397 back to the programmable timer unit in the LAPIC. 2398 Format: notscdeadline 2399 2400 lapic_timer_c2_ok [X86,APIC] trust the local apic timer 2401 in C2 power state. 2402 2403 libata.dma= [LIBATA] DMA control 2404 libata.dma=0 Disable all PATA and SATA DMA 2405 libata.dma=1 PATA and SATA Disk DMA only 2406 libata.dma=2 ATAPI (CDROM) DMA only 2407 libata.dma=4 Compact Flash DMA only 2408 Combinations also work, so libata.dma=3 enables DMA 2409 for disks and CDROMs, but not CFs. 2410 2411 libata.ignore_hpa= [LIBATA] Ignore HPA limit 2412 libata.ignore_hpa=0 keep BIOS limits (default) 2413 libata.ignore_hpa=1 ignore limits, using full disk 2414 2415 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 2416 when set. 2417 Format: <int> 2418 2419 libata.force= [LIBATA] Force configurations. The format is comma 2420 separated list of "[ID:]VAL" where ID is 2421 PORT[.DEVICE]. PORT and DEVICE are decimal numbers 2422 matching port, link or device. Basically, it matches 2423 the ATA ID string printed on console by libata. If 2424 the whole ID part is omitted, the last PORT and DEVICE 2425 values are used. If ID hasn't been specified yet, the 2426 configuration applies to all ports, links and devices. 2427 2428 If only DEVICE is omitted, the parameter applies to 2429 the port and all links and devices behind it. DEVICE 2430 number of 0 either selects the first device or the 2431 first fan-out link behind PMP device. It does not 2432 select the host link. DEVICE number of 15 selects the 2433 host link and device attached to it. 2434 2435 The VAL specifies the configuration to force. As long 2436 as there's no ambiguity shortcut notation is allowed. 2437 For example, both 1.5 and 1.5G would work for 1.5Gbps. 2438 The following configurations can be forced. 2439 2440 * Cable type: 40c, 80c, short40c, unk, ign or sata. 2441 Any ID with matching PORT is used. 2442 2443 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 2444 2445 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 2446 udma[/][16,25,33,44,66,100,133] notation is also 2447 allowed. 2448 2449 * [no]ncq: Turn on or off NCQ. 2450 2451 * [no]ncqtrim: Turn off queued DSM TRIM. 2452 2453 * nohrst, nosrst, norst: suppress hard, soft 2454 and both resets. 2455 2456 * rstonce: only attempt one reset during 2457 hot-unplug link recovery 2458 2459 * dump_id: dump IDENTIFY data. 2460 2461 * atapi_dmadir: Enable ATAPI DMADIR bridge support 2462 2463 * disable: Disable this device. 2464 2465 If there are multiple matching configurations changing 2466 the same attribute, the last one is used. 2467 2468 memblock=debug [KNL] Enable memblock debug messages. 2469 2470 load_ramdisk= [RAM] [Deprecated] 2471 2472 lockd.nlm_grace_period=P [NFS] Assign grace period. 2473 Format: <integer> 2474 2475 lockd.nlm_tcpport=N [NFS] Assign TCP port. 2476 Format: <integer> 2477 2478 lockd.nlm_timeout=T [NFS] Assign timeout value. 2479 Format: <integer> 2480 2481 lockd.nlm_udpport=M [NFS] Assign UDP port. 2482 Format: <integer> 2483 2484 lockdown= [SECURITY] 2485 { integrity | confidentiality } 2486 Enable the kernel lockdown feature. If set to 2487 integrity, kernel features that allow userland to 2488 modify the running kernel are disabled. If set to 2489 confidentiality, kernel features that allow userland 2490 to extract confidential information from the kernel 2491 are also disabled. 2492 2493 locktorture.nreaders_stress= [KNL] 2494 Set the number of locking read-acquisition kthreads. 2495 Defaults to being automatically set based on the 2496 number of online CPUs. 2497 2498 locktorture.nwriters_stress= [KNL] 2499 Set the number of locking write-acquisition kthreads. 2500 2501 locktorture.onoff_holdoff= [KNL] 2502 Set time (s) after boot for CPU-hotplug testing. 2503 2504 locktorture.onoff_interval= [KNL] 2505 Set time (s) between CPU-hotplug operations, or 2506 zero to disable CPU-hotplug testing. 2507 2508 locktorture.shuffle_interval= [KNL] 2509 Set task-shuffle interval (jiffies). Shuffling 2510 tasks allows some CPUs to go into dyntick-idle 2511 mode during the locktorture test. 2512 2513 locktorture.shutdown_secs= [KNL] 2514 Set time (s) after boot system shutdown. This 2515 is useful for hands-off automated testing. 2516 2517 locktorture.stat_interval= [KNL] 2518 Time (s) between statistics printk()s. 2519 2520 locktorture.stutter= [KNL] 2521 Time (s) to stutter testing, for example, 2522 specifying five seconds causes the test to run for 2523 five seconds, wait for five seconds, and so on. 2524 This tests the locking primitive's ability to 2525 transition abruptly to and from idle. 2526 2527 locktorture.torture_type= [KNL] 2528 Specify the locking implementation to test. 2529 2530 locktorture.verbose= [KNL] 2531 Enable additional printk() statements. 2532 2533 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 2534 Format: <irq> 2535 2536 loglevel= All Kernel Messages with a loglevel smaller than the 2537 console loglevel will be printed to the console. It can 2538 also be changed with klogd or other programs. The 2539 loglevels are defined as follows: 2540 2541 0 (KERN_EMERG) system is unusable 2542 1 (KERN_ALERT) action must be taken immediately 2543 2 (KERN_CRIT) critical conditions 2544 3 (KERN_ERR) error conditions 2545 4 (KERN_WARNING) warning conditions 2546 5 (KERN_NOTICE) normal but significant condition 2547 6 (KERN_INFO) informational 2548 7 (KERN_DEBUG) debug-level messages 2549 2550 log_buf_len=n[KMG] Sets the size of the printk ring buffer, 2551 in bytes. n must be a power of two and greater 2552 than the minimal size. The minimal size is defined 2553 by LOG_BUF_SHIFT kernel config parameter. There is 2554 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter 2555 that allows to increase the default size depending on 2556 the number of CPUs. See init/Kconfig for more details. 2557 2558 logo.nologo [FB] Disables display of the built-in Linux logo. 2559 This may be used to provide more screen space for 2560 kernel log messages and is useful when debugging 2561 kernel boot problems. 2562 2563 lp=0 [LP] Specify parallel ports to use, e.g, 2564 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 2565 lp=reset first parallel port). 'lp=0' disables the 2566 lp=auto printer driver. 'lp=reset' (which can be 2567 specified in addition to the ports) causes 2568 attached printers to be reset. Using 2569 lp=port1,port2,... specifies the parallel ports 2570 to associate lp devices with, starting with 2571 lp0. A port specification may be 'none' to skip 2572 that lp device, or a parport name such as 2573 'parport0'. Specifying 'lp=auto' instead of a 2574 port specification list means that device IDs 2575 from each port should be examined, to see if 2576 an IEEE 1284-compliant printer is attached; if 2577 so, the driver will manage that printer. 2578 See also header of drivers/char/lp.c. 2579 2580 lpj=n [KNL] 2581 Sets loops_per_jiffy to given constant, thus avoiding 2582 time-consuming boot-time autodetection (up to 250 ms per 2583 CPU). 0 enables autodetection (default). To determine 2584 the correct value for your kernel, boot with normal 2585 autodetection and see what value is printed. Note that 2586 on SMP systems the preset will be applied to all CPUs, 2587 which is likely to cause problems if your CPUs need 2588 significantly divergent settings. An incorrect value 2589 will cause delays in the kernel to be wrong, leading to 2590 unpredictable I/O errors and other breakage. Although 2591 unlikely, in the extreme case this might damage your 2592 hardware. 2593 2594 ltpc= [NET] 2595 Format: <io>,<irq>,<dma> 2596 2597 lsm.debug [SECURITY] Enable LSM initialization debugging output. 2598 2599 lsm=lsm1,...,lsmN 2600 [SECURITY] Choose order of LSM initialization. This 2601 overrides CONFIG_LSM, and the "security=" parameter. 2602 2603 machvec= [IA-64] Force the use of a particular machine-vector 2604 (machvec) in a generic kernel. 2605 Example: machvec=hpzx1 2606 2607 machtype= [Loongson] Share the same kernel image file between 2608 different yeeloong laptops. 2609 Example: machtype=lemote-yeeloong-2f-7inch 2610 2611 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater 2612 than or equal to this physical address is ignored. 2613 2614 maxcpus= [SMP] Maximum number of processors that an SMP kernel 2615 will bring up during bootup. maxcpus=n : n >= 0 limits 2616 the kernel to bring up 'n' processors. Surely after 2617 bootup you can bring up the other plugged cpu by executing 2618 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 2619 only takes effect during system bootup. 2620 While n=0 is a special case, it is equivalent to "nosmp", 2621 which also disables the IO APIC. 2622 2623 max_loop= [LOOP] The number of loop block devices that get 2624 (loop.max_loop) unconditionally pre-created at init time. The default 2625 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 2626 of statically allocating a predefined number, loop 2627 devices can be requested on-demand with the 2628 /dev/loop-control interface. 2629 2630 mce [X86-32] Machine Check Exception 2631 2632 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.rst 2633 2634 md= [HW] RAID subsystems devices and level 2635 See Documentation/admin-guide/md.rst. 2636 2637 mdacon= [MDA] 2638 Format: <first>,<last> 2639 Specifies range of consoles to be captured by the MDA. 2640 2641 mds= [X86,INTEL] 2642 Control mitigation for the Micro-architectural Data 2643 Sampling (MDS) vulnerability. 2644 2645 Certain CPUs are vulnerable to an exploit against CPU 2646 internal buffers which can forward information to a 2647 disclosure gadget under certain conditions. 2648 2649 In vulnerable processors, the speculatively 2650 forwarded data can be used in a cache side channel 2651 attack, to access data to which the attacker does 2652 not have direct access. 2653 2654 This parameter controls the MDS mitigation. The 2655 options are: 2656 2657 full - Enable MDS mitigation on vulnerable CPUs 2658 full,nosmt - Enable MDS mitigation and disable 2659 SMT on vulnerable CPUs 2660 off - Unconditionally disable MDS mitigation 2661 2662 On TAA-affected machines, mds=off can be prevented by 2663 an active TAA mitigation as both vulnerabilities are 2664 mitigated with the same mechanism so in order to disable 2665 this mitigation, you need to specify tsx_async_abort=off 2666 too. 2667 2668 Not specifying this option is equivalent to 2669 mds=full. 2670 2671 For details see: Documentation/admin-guide/hw-vuln/mds.rst 2672 2673 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory 2674 Amount of memory to be used in cases as follows: 2675 2676 1 for test; 2677 2 when the kernel is not able to see the whole system memory; 2678 3 memory that lies after 'mem=' boundary is excluded from 2679 the hypervisor, then assigned to KVM guests. 2680 2681 [X86] Work as limiting max address. Use together 2682 with memmap= to avoid physical address space collisions. 2683 Without memmap= PCI devices could be placed at addresses 2684 belonging to unused RAM. 2685 2686 Note that this only takes effects during boot time since 2687 in above case 3, memory may need be hot added after boot 2688 if system memory of hypervisor is not sufficient. 2689 2690 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 2691 memory. 2692 2693 memchunk=nn[KMG] 2694 [KNL,SH] Allow user to override the default size for 2695 per-device physically contiguous DMA buffers. 2696 2697 memhp_default_state=online/offline 2698 [KNL] Set the initial state for the memory hotplug 2699 onlining policy. If not specified, the default value is 2700 set according to the 2701 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config 2702 option. 2703 See Documentation/admin-guide/mm/memory-hotplug.rst. 2704 2705 memmap=exactmap [KNL,X86] Enable setting of an exact 2706 E820 memory map, as specified by the user. 2707 Such memmap=exactmap lines can be constructed based on 2708 BIOS output or other requirements. See the memmap=nn@ss 2709 option description. 2710 2711 memmap=nn[KMG]@ss[KMG] 2712 [KNL] Force usage of a specific region of memory. 2713 Region of memory to be used is from ss to ss+nn. 2714 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], 2715 which limits max address to nn[KMG]. 2716 Multiple different regions can be specified, 2717 comma delimited. 2718 Example: 2719 memmap=100M@2G,100M#3G,1G!1024G 2720 2721 memmap=nn[KMG]#ss[KMG] 2722 [KNL,ACPI] Mark specific memory as ACPI data. 2723 Region of memory to be marked is from ss to ss+nn. 2724 2725 memmap=nn[KMG]$ss[KMG] 2726 [KNL,ACPI] Mark specific memory as reserved. 2727 Region of memory to be reserved is from ss to ss+nn. 2728 Example: Exclude memory from 0x18690000-0x1869ffff 2729 memmap=64K$0x18690000 2730 or 2731 memmap=0x10000$0x18690000 2732 Some bootloaders may need an escape character before '$', 2733 like Grub2, otherwise '$' and the following number 2734 will be eaten. 2735 2736 memmap=nn[KMG]!ss[KMG] 2737 [KNL,X86] Mark specific memory as protected. 2738 Region of memory to be used, from ss to ss+nn. 2739 The memory region may be marked as e820 type 12 (0xc) 2740 and is NVDIMM or ADR memory. 2741 2742 memmap=<size>%<offset>-<oldtype>+<newtype> 2743 [KNL,ACPI] Convert memory within the specified region 2744 from <oldtype> to <newtype>. If "-<oldtype>" is left 2745 out, the whole region will be marked as <newtype>, 2746 even if previously unavailable. If "+<newtype>" is left 2747 out, matching memory will be removed. Types are 2748 specified as e820 types, e.g., 1 = RAM, 2 = reserved, 2749 3 = ACPI, 12 = PRAM. 2750 2751 memory_corruption_check=0/1 [X86] 2752 Some BIOSes seem to corrupt the first 64k of 2753 memory when doing things like suspend/resume. 2754 Setting this option will scan the memory 2755 looking for corruption. Enabling this will 2756 both detect corruption and prevent the kernel 2757 from using the memory being corrupted. 2758 However, its intended as a diagnostic tool; if 2759 repeatable BIOS-originated corruption always 2760 affects the same memory, you can use memmap= 2761 to prevent the kernel from using that memory. 2762 2763 memory_corruption_check_size=size [X86] 2764 By default it checks for corruption in the low 2765 64k, making this memory unavailable for normal 2766 use. Use this parameter to scan for 2767 corruption in more or less memory. 2768 2769 memory_corruption_check_period=seconds [X86] 2770 By default it checks for corruption every 60 2771 seconds. Use this parameter to check at some 2772 other rate. 0 disables periodic checking. 2773 2774 memtest= [KNL,X86,ARM,PPC] Enable memtest 2775 Format: <integer> 2776 default : 0 <disable> 2777 Specifies the number of memtest passes to be 2778 performed. Each pass selects another test 2779 pattern from a given set of patterns. Memtest 2780 fills the memory with this pattern, validates 2781 memory contents and reserves bad memory 2782 regions that are detected. 2783 2784 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control 2785 Valid arguments: on, off 2786 Default (depends on kernel configuration option): 2787 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y) 2788 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n) 2789 mem_encrypt=on: Activate SME 2790 mem_encrypt=off: Do not activate SME 2791 2792 Refer to Documentation/virt/kvm/amd-memory-encryption.rst 2793 for details on when memory encryption can be activated. 2794 2795 mem_sleep_default= [SUSPEND] Default system suspend mode: 2796 s2idle - Suspend-To-Idle 2797 shallow - Power-On Suspend or equivalent (if supported) 2798 deep - Suspend-To-RAM or equivalent (if supported) 2799 See Documentation/admin-guide/pm/sleep-states.rst. 2800 2801 meye.*= [HW] Set MotionEye Camera parameters 2802 See Documentation/admin-guide/media/meye.rst. 2803 2804 mfgpt_irq= [IA-32] Specify the IRQ to use for the 2805 Multi-Function General Purpose Timers on AMD Geode 2806 platforms. 2807 2808 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 2809 the BIOS has incorrectly applied a workaround. TinyBIOS 2810 version 0.98 is known to be affected, 0.99 fixes the 2811 problem by letting the user disable the workaround. 2812 2813 mga= [HW,DRM] 2814 2815 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this 2816 physical address is ignored. 2817 2818 mini2440= [ARM,HW,KNL] 2819 Format:[0..2][b][c][t] 2820 Default: "0tb" 2821 MINI2440 configuration specification: 2822 0 - The attached screen is the 3.5" TFT 2823 1 - The attached screen is the 7" TFT 2824 2 - The VGA Shield is attached (1024x768) 2825 Leaving out the screen size parameter will not load 2826 the TFT driver, and the framebuffer will be left 2827 unconfigured. 2828 b - Enable backlight. The TFT backlight pin will be 2829 linked to the kernel VESA blanking code and a GPIO 2830 LED. This parameter is not necessary when using the 2831 VGA shield. 2832 c - Enable the s3c camera interface. 2833 t - Reserved for enabling touchscreen support. The 2834 touchscreen support is not enabled in the mainstream 2835 kernel as of 2.6.30, a preliminary port can be found 2836 in the "bleeding edge" mini2440 support kernel at 2837 https://repo.or.cz/w/linux-2.6/mini2440.git 2838 2839 mitigations= 2840 [X86,PPC,S390,ARM64] Control optional mitigations for 2841 CPU vulnerabilities. This is a set of curated, 2842 arch-independent options, each of which is an 2843 aggregation of existing arch-specific options. 2844 2845 off 2846 Disable all optional CPU mitigations. This 2847 improves system performance, but it may also 2848 expose users to several CPU vulnerabilities. 2849 Equivalent to: nopti [X86,PPC] 2850 kpti=0 [ARM64] 2851 nospectre_v1 [X86,PPC] 2852 nobp=0 [S390] 2853 nospectre_v2 [X86,PPC,S390,ARM64] 2854 spectre_v2_user=off [X86] 2855 spec_store_bypass_disable=off [X86,PPC] 2856 ssbd=force-off [ARM64] 2857 l1tf=off [X86] 2858 mds=off [X86] 2859 tsx_async_abort=off [X86] 2860 kvm.nx_huge_pages=off [X86] 2861 2862 Exceptions: 2863 This does not have any effect on 2864 kvm.nx_huge_pages when 2865 kvm.nx_huge_pages=force. 2866 2867 auto (default) 2868 Mitigate all CPU vulnerabilities, but leave SMT 2869 enabled, even if it's vulnerable. This is for 2870 users who don't want to be surprised by SMT 2871 getting disabled across kernel upgrades, or who 2872 have other ways of avoiding SMT-based attacks. 2873 Equivalent to: (default behavior) 2874 2875 auto,nosmt 2876 Mitigate all CPU vulnerabilities, disabling SMT 2877 if needed. This is for users who always want to 2878 be fully mitigated, even if it means losing SMT. 2879 Equivalent to: l1tf=flush,nosmt [X86] 2880 mds=full,nosmt [X86] 2881 tsx_async_abort=full,nosmt [X86] 2882 2883 mminit_loglevel= 2884 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this 2885 parameter allows control of the logging verbosity for 2886 the additional memory initialisation checks. A value 2887 of 0 disables mminit logging and a level of 4 will 2888 log everything. Information is printed at KERN_DEBUG 2889 so loglevel=8 may also need to be specified. 2890 2891 module.sig_enforce 2892 [KNL] When CONFIG_MODULE_SIG is set, this means that 2893 modules without (valid) signatures will fail to load. 2894 Note that if CONFIG_MODULE_SIG_FORCE is set, that 2895 is always true, so this option does nothing. 2896 2897 module_blacklist= [KNL] Do not load a comma-separated list of 2898 modules. Useful for debugging problem modules. 2899 2900 mousedev.tap_time= 2901 [MOUSE] Maximum time between finger touching and 2902 leaving touchpad surface for touch to be considered 2903 a tap and be reported as a left button click (for 2904 touchpads working in absolute mode only). 2905 Format: <msecs> 2906 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 2907 reporting absolute coordinates, such as tablets 2908 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 2909 reporting absolute coordinates, such as tablets 2910 2911 movablecore= [KNL,X86,IA-64,PPC] 2912 Format: nn[KMGTPE] | nn% 2913 This parameter is the complement to kernelcore=, it 2914 specifies the amount of memory used for migratable 2915 allocations. If both kernelcore and movablecore is 2916 specified, then kernelcore will be at *least* the 2917 specified value but may be more. If movablecore on its 2918 own is specified, the administrator must be careful 2919 that the amount of memory usable for all allocations 2920 is not too small. 2921 2922 movable_node [KNL] Boot-time switch to make hotplugable memory 2923 NUMA nodes to be movable. This means that the memory 2924 of such nodes will be usable only for movable 2925 allocations which rules out almost all kernel 2926 allocations. Use with caution! 2927 2928 MTD_Partition= [MTD] 2929 Format: <name>,<region-number>,<size>,<offset> 2930 2931 MTD_Region= [MTD] Format: 2932 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 2933 2934 mtdparts= [MTD] 2935 See drivers/mtd/parsers/cmdlinepart.c 2936 2937 multitce=off [PPC] This parameter disables the use of the pSeries 2938 firmware feature for updating multiple TCE entries 2939 at a time. 2940 2941 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 2942 2943 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 2944 2945 boundary - index of last SLC block on Flex-OneNAND. 2946 The remaining blocks are configured as MLC blocks. 2947 lock - Configure if Flex-OneNAND boundary should be locked. 2948 Once locked, the boundary cannot be changed. 2949 1 indicates lock status, 0 indicates unlock status. 2950 2951 mtdset= [ARM] 2952 ARM/S3C2412 JIVE boot control 2953 2954 See arch/arm/mach-s3c2412/mach-jive.c 2955 2956 mtouchusb.raw_coordinates= 2957 [HW] Make the MicroTouch USB driver use raw coordinates 2958 ('y', default) or cooked coordinates ('n') 2959 2960 mtrr_chunk_size=nn[KMG] [X86] 2961 used for mtrr cleanup. It is largest continuous chunk 2962 that could hold holes aka. UC entries. 2963 2964 mtrr_gran_size=nn[KMG] [X86] 2965 Used for mtrr cleanup. It is granularity of mtrr block. 2966 Default is 1. 2967 Large value could prevent small alignment from 2968 using up MTRRs. 2969 2970 mtrr_spare_reg_nr=n [X86] 2971 Format: <integer> 2972 Range: 0,7 : spare reg number 2973 Default : 1 2974 Used for mtrr cleanup. It is spare mtrr entries number. 2975 Set to 2 or more if your graphical card needs more. 2976 2977 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 2978 2979 netdev= [NET] Network devices parameters 2980 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 2981 Note that mem_start is often overloaded to mean 2982 something different and driver-specific. 2983 This usage is only documented in each driver source 2984 file if at all. 2985 2986 nf_conntrack.acct= 2987 [NETFILTER] Enable connection tracking flow accounting 2988 0 to disable accounting 2989 1 to enable accounting 2990 Default value is 0. 2991 2992 nfsaddrs= [NFS] Deprecated. Use ip= instead. 2993 See Documentation/admin-guide/nfs/nfsroot.rst. 2994 2995 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 2996 See Documentation/admin-guide/nfs/nfsroot.rst. 2997 2998 nfsrootdebug [NFS] enable nfsroot debugging messages. 2999 See Documentation/admin-guide/nfs/nfsroot.rst. 3000 3001 nfs.callback_nr_threads= 3002 [NFSv4] set the total number of threads that the 3003 NFS client will assign to service NFSv4 callback 3004 requests. 3005 3006 nfs.callback_tcpport= 3007 [NFS] set the TCP port on which the NFSv4 callback 3008 channel should listen. 3009 3010 nfs.cache_getent= 3011 [NFS] sets the pathname to the program which is used 3012 to update the NFS client cache entries. 3013 3014 nfs.cache_getent_timeout= 3015 [NFS] sets the timeout after which an attempt to 3016 update a cache entry is deemed to have failed. 3017 3018 nfs.idmap_cache_timeout= 3019 [NFS] set the maximum lifetime for idmapper cache 3020 entries. 3021 3022 nfs.enable_ino64= 3023 [NFS] enable 64-bit inode numbers. 3024 If zero, the NFS client will fake up a 32-bit inode 3025 number for the readdir() and stat() syscalls instead 3026 of returning the full 64-bit number. 3027 The default is to return 64-bit inode numbers. 3028 3029 nfs.max_session_cb_slots= 3030 [NFSv4.1] Sets the maximum number of session 3031 slots the client will assign to the callback 3032 channel. This determines the maximum number of 3033 callbacks the client will process in parallel for 3034 a particular server. 3035 3036 nfs.max_session_slots= 3037 [NFSv4.1] Sets the maximum number of session slots 3038 the client will attempt to negotiate with the server. 3039 This limits the number of simultaneous RPC requests 3040 that the client can send to the NFSv4.1 server. 3041 Note that there is little point in setting this 3042 value higher than the max_tcp_slot_table_limit. 3043 3044 nfs.nfs4_disable_idmapping= 3045 [NFSv4] When set to the default of '1', this option 3046 ensures that both the RPC level authentication 3047 scheme and the NFS level operations agree to use 3048 numeric uids/gids if the mount is using the 3049 'sec=sys' security flavour. In effect it is 3050 disabling idmapping, which can make migration from 3051 legacy NFSv2/v3 systems to NFSv4 easier. 3052 Servers that do not support this mode of operation 3053 will be autodetected by the client, and it will fall 3054 back to using the idmapper. 3055 To turn off this behaviour, set the value to '0'. 3056 nfs.nfs4_unique_id= 3057 [NFS4] Specify an additional fixed unique ident- 3058 ification string that NFSv4 clients can insert into 3059 their nfs_client_id4 string. This is typically a 3060 UUID that is generated at system install time. 3061 3062 nfs.send_implementation_id = 3063 [NFSv4.1] Send client implementation identification 3064 information in exchange_id requests. 3065 If zero, no implementation identification information 3066 will be sent. 3067 The default is to send the implementation identification 3068 information. 3069 3070 nfs.recover_lost_locks = 3071 [NFSv4] Attempt to recover locks that were lost due 3072 to a lease timeout on the server. Please note that 3073 doing this risks data corruption, since there are 3074 no guarantees that the file will remain unchanged 3075 after the locks are lost. 3076 If you want to enable the kernel legacy behaviour of 3077 attempting to recover these locks, then set this 3078 parameter to '1'. 3079 The default parameter value of '0' causes the kernel 3080 not to attempt recovery of lost locks. 3081 3082 nfs4.layoutstats_timer = 3083 [NFSv4.2] Change the rate at which the kernel sends 3084 layoutstats to the pNFS metadata server. 3085 3086 Setting this to value to 0 causes the kernel to use 3087 whatever value is the default set by the layout 3088 driver. A non-zero value sets the minimum interval 3089 in seconds between layoutstats transmissions. 3090 3091 nfsd.nfs4_disable_idmapping= 3092 [NFSv4] When set to the default of '1', the NFSv4 3093 server will return only numeric uids and gids to 3094 clients using auth_sys, and will accept numeric uids 3095 and gids from such clients. This is intended to ease 3096 migration from NFSv2/v3. 3097 3098 nmi_backtrace.backtrace_idle [KNL] 3099 Dump stacks even of idle CPUs in response to an 3100 NMI stack-backtrace request. 3101 3102 nmi_debug= [KNL,SH] Specify one or more actions to take 3103 when a NMI is triggered. 3104 Format: [state][,regs][,debounce][,die] 3105 3106 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 3107 Format: [panic,][nopanic,][num] 3108 Valid num: 0 or 1 3109 0 - turn hardlockup detector in nmi_watchdog off 3110 1 - turn hardlockup detector in nmi_watchdog on 3111 When panic is specified, panic when an NMI watchdog 3112 timeout occurs (or 'nopanic' to not panic on an NMI 3113 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set) 3114 To disable both hard and soft lockup detectors, 3115 please see 'nowatchdog'. 3116 This is useful when you use a panic=... timeout and 3117 need the box quickly up again. 3118 3119 These settings can be accessed at runtime via 3120 the nmi_watchdog and hardlockup_panic sysctls. 3121 3122 netpoll.carrier_timeout= 3123 [NET] Specifies amount of time (in seconds) that 3124 netpoll should wait for a carrier. By default netpoll 3125 waits 4 seconds. 3126 3127 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 3128 emulation library even if a 387 maths coprocessor 3129 is present. 3130 3131 no5lvl [X86-64] Disable 5-level paging mode. Forces 3132 kernel to use 4-level paging instead. 3133 3134 nofsgsbase [X86] Disables FSGSBASE instructions. 3135 3136 no_console_suspend 3137 [HW] Never suspend the console 3138 Disable suspending of consoles during suspend and 3139 hibernate operations. Once disabled, debugging 3140 messages can reach various consoles while the rest 3141 of the system is being put to sleep (ie, while 3142 debugging driver suspend/resume hooks). This may 3143 not work reliably with all consoles, but is known 3144 to work with serial and VGA consoles. 3145 To facilitate more flexible debugging, we also add 3146 console_suspend, a printk module parameter to control 3147 it. Users could use console_suspend (usually 3148 /sys/module/printk/parameters/console_suspend) to 3149 turn on/off it dynamically. 3150 3151 novmcoredd [KNL,KDUMP] 3152 Disable device dump. Device dump allows drivers to 3153 append dump data to vmcore so you can collect driver 3154 specified debug info. Drivers can append the data 3155 without any limit and this data is stored in memory, 3156 so this may cause significant memory stress. Disabling 3157 device dump can help save memory but the driver debug 3158 data will be no longer available. This parameter 3159 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP 3160 is set. 3161 3162 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien 3163 caches in the slab allocator. Saves per-node memory, 3164 but will impact performance. 3165 3166 noalign [KNL,ARM] 3167 3168 noaltinstr [S390] Disables alternative instructions patching 3169 (CPU alternatives feature). 3170 3171 noapic [SMP,APIC] Tells the kernel to not make use of any 3172 IOAPICs that may be present in the system. 3173 3174 noautogroup Disable scheduler automatic task group creation. 3175 3176 nobats [PPC] Do not use BATs for mapping kernel lowmem 3177 on "Classic" PPC cores. 3178 3179 nocache [ARM] 3180 3181 noclflush [BUGS=X86] Don't use the CLFLUSH instruction 3182 3183 nodelayacct [KNL] Disable per-task delay accounting 3184 3185 nodsp [SH] Disable hardware DSP at boot time. 3186 3187 noefi Disable EFI runtime services support. 3188 3189 noexec [IA-64] 3190 3191 noexec [X86] 3192 On X86-32 available only on PAE configured kernels. 3193 noexec=on: enable non-executable mappings (default) 3194 noexec=off: disable non-executable mappings 3195 3196 nosmap [X86,PPC] 3197 Disable SMAP (Supervisor Mode Access Prevention) 3198 even if it is supported by processor. 3199 3200 nosmep [X86,PPC] 3201 Disable SMEP (Supervisor Mode Execution Prevention) 3202 even if it is supported by processor. 3203 3204 noexec32 [X86-64] 3205 This affects only 32-bit executables. 3206 noexec32=on: enable non-executable mappings (default) 3207 read doesn't imply executable mappings 3208 noexec32=off: disable non-executable mappings 3209 read implies executable mappings 3210 3211 nofpu [MIPS,SH] Disable hardware FPU at boot time. 3212 3213 nofxsr [BUGS=X86-32] Disables x86 floating point extended 3214 register save and restore. The kernel will only save 3215 legacy floating-point registers on task switch. 3216 3217 nohugeiomap [KNL,X86,PPC,ARM64] Disable kernel huge I/O mappings. 3218 3219 nosmt [KNL,S390] Disable symmetric multithreading (SMT). 3220 Equivalent to smt=1. 3221 3222 [KNL,X86] Disable symmetric multithreading (SMT). 3223 nosmt=force: Force disable SMT, cannot be undone 3224 via the sysfs control file. 3225 3226 nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1 3227 (bounds check bypass). With this option data leaks are 3228 possible in the system. 3229 3230 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for 3231 the Spectre variant 2 (indirect branch prediction) 3232 vulnerability. System may allow data leaks with this 3233 option. 3234 3235 nospec_store_bypass_disable 3236 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability 3237 3238 noxsave [BUGS=X86] Disables x86 extended register state save 3239 and restore using xsave. The kernel will fallback to 3240 enabling legacy floating-point and sse state. 3241 3242 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 3243 register states. The kernel will fall back to use 3244 xsave to save the states. By using this parameter, 3245 performance of saving the states is degraded because 3246 xsave doesn't support modified optimization while 3247 xsaveopt supports it on xsaveopt enabled systems. 3248 3249 noxsaves [X86] Disables xsaves and xrstors used in saving and 3250 restoring x86 extended register state in compacted 3251 form of xsave area. The kernel will fall back to use 3252 xsaveopt and xrstor to save and restore the states 3253 in standard form of xsave area. By using this 3254 parameter, xsave area per process might occupy more 3255 memory on xsaves enabled systems. 3256 3257 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or 3258 wfi(ARM) instruction doesn't work correctly and not to 3259 use it. This is also useful when using JTAG debugger. 3260 3261 no_file_caps Tells the kernel not to honor file capabilities. The 3262 only way then for a file to be executed with privilege 3263 is to be setuid root or executed by root. 3264 3265 nohalt [IA-64] Tells the kernel not to use the power saving 3266 function PAL_HALT_LIGHT when idle. This increases 3267 power-consumption. On the positive side, it reduces 3268 interrupt wake-up latency, which may improve performance 3269 in certain environments such as networked servers or 3270 real-time systems. 3271 3272 nohibernate [HIBERNATION] Disable hibernation and resume. 3273 3274 nohz= [KNL] Boottime enable/disable dynamic ticks 3275 Valid arguments: on, off 3276 Default: on 3277 3278 nohz_full= [KNL,BOOT,SMP,ISOL] 3279 The argument is a cpu list, as described above. 3280 In kernels built with CONFIG_NO_HZ_FULL=y, set 3281 the specified list of CPUs whose tick will be stopped 3282 whenever possible. The boot CPU will be forced outside 3283 the range to maintain the timekeeping. Any CPUs 3284 in this list will have their RCU callbacks offloaded, 3285 just as if they had also been called out in the 3286 rcu_nocbs= boot parameter. 3287 3288 noiotrap [SH] Disables trapped I/O port accesses. 3289 3290 noirqdebug [X86-32] Disables the code which attempts to detect and 3291 disable unhandled interrupt sources. 3292 3293 no_timer_check [X86,APIC] Disables the code which tests for 3294 broken timer IRQ sources. 3295 3296 noisapnp [ISAPNP] Disables ISA PnP code. 3297 3298 noinitrd [RAM] Tells the kernel not to load any configured 3299 initial RAM disk. 3300 3301 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt 3302 remapping. 3303 [Deprecated - use intremap=off] 3304 3305 nointroute [IA-64] 3306 3307 noinvpcid [X86] Disable the INVPCID cpu feature. 3308 3309 nojitter [IA-64] Disables jitter checking for ITC timers. 3310 3311 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver 3312 3313 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page 3314 fault handling. 3315 3316 no-vmw-sched-clock 3317 [X86,PV_OPS] Disable paravirtualized VMware scheduler 3318 clock and use the default one. 3319 3320 no-steal-acc [X86,PV_OPS,ARM64] Disable paravirtualized steal time 3321 accounting. steal time is computed, but won't 3322 influence scheduler behaviour 3323 3324 nolapic [X86-32,APIC] Do not enable or use the local APIC. 3325 3326 nolapic_timer [X86-32,APIC] Do not use the local APIC timer. 3327 3328 noltlbs [PPC] Do not use large page/tlb entries for kernel 3329 lowmem mapping on PPC40x and PPC8xx 3330 3331 nomca [IA-64] Disable machine check abort handling 3332 3333 nomce [X86-32] Disable Machine Check Exception 3334 3335 nomfgpt [X86-32] Disable Multi-Function General Purpose 3336 Timer usage (for AMD Geode machines). 3337 3338 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 3339 shutdown the other cpus. Instead use the REBOOT_VECTOR 3340 irq. 3341 3342 nomodule Disable module load 3343 3344 nopat [X86] Disable PAT (page attribute table extension of 3345 pagetables) support. 3346 3347 nopcid [X86-64] Disable the PCID cpu feature. 3348 3349 norandmaps Don't use address space randomization. Equivalent to 3350 echo 0 > /proc/sys/kernel/randomize_va_space 3351 3352 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 3353 with UP alternatives 3354 3355 nordrand [X86] Disable kernel use of the RDRAND and 3356 RDSEED instructions even if they are supported 3357 by the processor. RDRAND and RDSEED are still 3358 available to user space applications. 3359 3360 noresume [SWSUSP] Disables resume and restores original swap 3361 space. 3362 3363 no-scroll [VGA] Disables scrollback. 3364 This is required for the Braillex ib80-piezo Braille 3365 reader made by F.H. Papenmeier (Germany). 3366 3367 nosbagart [IA-64] 3368 3369 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support. 3370 3371 nosmp [SMP] Tells an SMP kernel to act as a UP kernel, 3372 and disable the IO APIC. legacy for "maxcpus=0". 3373 3374 nosoftlockup [KNL] Disable the soft-lockup detector. 3375 3376 nosync [HW,M68K] Disables sync negotiation for all devices. 3377 3378 nowatchdog [KNL] Disable both lockup detectors, i.e. 3379 soft-lockup and NMI watchdog (hard-lockup). 3380 3381 nowb [ARM] 3382 3383 nox2apic [X86-64,APIC] Do not enable x2APIC mode. 3384 3385 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when 3386 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off. 3387 Some features depend on CPU0. Known dependencies are: 3388 1. Resume from suspend/hibernate depends on CPU0. 3389 Suspend/hibernate will fail if CPU0 is offline and you 3390 need to online CPU0 before suspend/hibernate. 3391 2. PIC interrupts also depend on CPU0. CPU0 can't be 3392 removed if a PIC interrupt is detected. 3393 It's said poweroff/reboot may depend on CPU0 on some 3394 machines although I haven't seen such issues so far 3395 after CPU0 is offline on a few tested machines. 3396 If the dependencies are under your control, you can 3397 turn on cpu0_hotplug. 3398 3399 nps_mtm_hs_ctr= [KNL,ARC] 3400 This parameter sets the maximum duration, in 3401 cycles, each HW thread of the CTOP can run 3402 without interruptions, before HW switches it. 3403 The actual maximum duration is 16 times this 3404 parameter's value. 3405 Format: integer between 1 and 255 3406 Default: 255 3407 3408 nptcg= [IA-64] Override max number of concurrent global TLB 3409 purges which is reported from either PAL_VM_SUMMARY or 3410 SAL PALO. 3411 3412 nr_cpus= [SMP] Maximum number of processors that an SMP kernel 3413 could support. nr_cpus=n : n >= 1 limits the kernel to 3414 support 'n' processors. It could be larger than the 3415 number of already plugged CPU during bootup, later in 3416 runtime you can physically add extra cpu until it reaches 3417 n. So during boot up some boot time memory for per-cpu 3418 variables need be pre-allocated for later physical cpu 3419 hot plugging. 3420 3421 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 3422 3423 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing. 3424 Allowed values are enable and disable 3425 3426 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 3427 'node', 'default' can be specified 3428 This can be set from sysctl after boot. 3429 See Documentation/admin-guide/sysctl/vm.rst for details. 3430 3431 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver. 3432 See Documentation/core-api/debugging-via-ohci1394.rst for more 3433 info. 3434 3435 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 3436 Rather than timing out after 20 ms if an EC 3437 command is not properly ACKed, override the length 3438 of the timeout. We have interrupts disabled while 3439 waiting for the ACK, so if this is set too high 3440 interrupts *may* be lost! 3441 3442 omap_mux= [OMAP] Override bootloader pin multiplexing. 3443 Format: <mux_mode0.mode_name=value>... 3444 For example, to override I2C bus2: 3445 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 3446 3447 oprofile.timer= [HW] 3448 Use timer interrupt instead of performance counters 3449 3450 oprofile.cpu_type= Force an oprofile cpu type 3451 This might be useful if you have an older oprofile 3452 userland or if you want common events. 3453 Format: { arch_perfmon } 3454 arch_perfmon: [X86] Force use of architectural 3455 perfmon on Intel CPUs instead of the 3456 CPU specific event set. 3457 timer: [X86] Force use of architectural NMI 3458 timer mode (see also oprofile.timer 3459 for generic hr timer mode) 3460 3461 oops=panic Always panic on oopses. Default is to just kill the 3462 process, but there is a small probability of 3463 deadlocking the machine. 3464 This will also cause panics on machine check exceptions. 3465 Useful together with panic=30 to trigger a reboot. 3466 3467 page_alloc.shuffle= 3468 [KNL] Boolean flag to control whether the page allocator 3469 should randomize its free lists. The randomization may 3470 be automatically enabled if the kernel detects it is 3471 running on a platform with a direct-mapped memory-side 3472 cache, and this parameter can be used to 3473 override/disable that behavior. The state of the flag 3474 can be read from sysfs at: 3475 /sys/module/page_alloc/parameters/shuffle. 3476 3477 page_owner= [KNL] Boot-time page_owner enabling option. 3478 Storage of the information about who allocated 3479 each page is disabled in default. With this switch, 3480 we can turn it on. 3481 on: enable the feature 3482 3483 page_poison= [KNL] Boot-time parameter changing the state of 3484 poisoning on the buddy allocator, available with 3485 CONFIG_PAGE_POISONING=y. 3486 off: turn off poisoning (default) 3487 on: turn on poisoning 3488 3489 panic= [KNL] Kernel behaviour on panic: delay <timeout> 3490 timeout > 0: seconds before rebooting 3491 timeout = 0: wait forever 3492 timeout < 0: reboot immediately 3493 Format: <timeout> 3494 3495 panic_print= Bitmask for printing system info when panic happens. 3496 User can chose combination of the following bits: 3497 bit 0: print all tasks info 3498 bit 1: print system memory info 3499 bit 2: print timer info 3500 bit 3: print locks info if CONFIG_LOCKDEP is on 3501 bit 4: print ftrace buffer 3502 bit 5: print all printk messages in buffer 3503 3504 panic_on_taint= Bitmask for conditionally calling panic() in add_taint() 3505 Format: <hex>[,nousertaint] 3506 Hexadecimal bitmask representing the set of TAINT flags 3507 that will cause the kernel to panic when add_taint() is 3508 called with any of the flags in this set. 3509 The optional switch "nousertaint" can be utilized to 3510 prevent userspace forced crashes by writing to sysctl 3511 /proc/sys/kernel/tainted any flagset matching with the 3512 bitmask set on panic_on_taint. 3513 See Documentation/admin-guide/tainted-kernels.rst for 3514 extra details on the taint flags that users can pick 3515 to compose the bitmask to assign to panic_on_taint. 3516 3517 panic_on_warn panic() instead of WARN(). Useful to cause kdump 3518 on a WARN(). 3519 3520 crash_kexec_post_notifiers 3521 Run kdump after running panic-notifiers and dumping 3522 kmsg. This only for the users who doubt kdump always 3523 succeeds in any situation. 3524 Note that this also increases risks of kdump failure, 3525 because some panic notifiers can make the crashed 3526 kernel more unstable. 3527 3528 parkbd.port= [HW] Parallel port number the keyboard adapter is 3529 connected to, default is 0. 3530 Format: <parport#> 3531 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 3532 0 for XT, 1 for AT (default is AT). 3533 Format: <mode> 3534 3535 parport= [HW,PPT] Specify parallel ports. 0 disables. 3536 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 3537 Use 'auto' to force the driver to use any 3538 IRQ/DMA settings detected (the default is to 3539 ignore detected IRQ/DMA settings because of 3540 possible conflicts). You can specify the base 3541 address, IRQ, and DMA settings; IRQ and DMA 3542 should be numbers, or 'auto' (for using detected 3543 settings on that particular port), or 'nofifo' 3544 (to avoid using a FIFO even if it is detected). 3545 Parallel ports are assigned in the order they 3546 are specified on the command line, starting 3547 with parport0. 3548 3549 parport_init_mode= [HW,PPT] 3550 Configure VIA parallel port to operate in 3551 a specific mode. This is necessary on Pegasos 3552 computer where firmware has no options for setting 3553 up parallel port mode and sets it to spp. 3554 Currently this function knows 686a and 8231 chips. 3555 Format: [spp|ps2|epp|ecp|ecpepp] 3556 3557 pause_on_oops= 3558 Halt all CPUs after the first oops has been printed for 3559 the specified number of seconds. This is to be used if 3560 your oopses keep scrolling off the screen. 3561 3562 pcbit= [HW,ISDN] 3563 3564 pcd. [PARIDE] 3565 See header of drivers/block/paride/pcd.c. 3566 See also Documentation/admin-guide/blockdev/paride.rst. 3567 3568 pci=option[,option...] [PCI] various PCI subsystem options. 3569 3570 Some options herein operate on a specific device 3571 or a set of devices (<pci_dev>). These are 3572 specified in one of the following formats: 3573 3574 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* 3575 pci:<vendor>:<device>[:<subvendor>:<subdevice>] 3576 3577 Note: the first format specifies a PCI 3578 bus/device/function address which may change 3579 if new hardware is inserted, if motherboard 3580 firmware changes, or due to changes caused 3581 by other kernel parameters. If the 3582 domain is left unspecified, it is 3583 taken to be zero. Optionally, a path 3584 to a device through multiple device/function 3585 addresses can be specified after the base 3586 address (this is more robust against 3587 renumbering issues). The second format 3588 selects devices using IDs from the 3589 configuration space which may match multiple 3590 devices in the system. 3591 3592 earlydump dump PCI config space before the kernel 3593 changes anything 3594 off [X86] don't probe for the PCI bus 3595 bios [X86-32] force use of PCI BIOS, don't access 3596 the hardware directly. Use this if your machine 3597 has a non-standard PCI host bridge. 3598 nobios [X86-32] disallow use of PCI BIOS, only direct 3599 hardware access methods are allowed. Use this 3600 if you experience crashes upon bootup and you 3601 suspect they are caused by the BIOS. 3602 conf1 [X86] Force use of PCI Configuration Access 3603 Mechanism 1 (config address in IO port 0xCF8, 3604 data in IO port 0xCFC, both 32-bit). 3605 conf2 [X86] Force use of PCI Configuration Access 3606 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 3607 the function, IO port 0xCFA, also 8-bit, sets 3608 bus number. The config space is then accessed 3609 through ports 0xC000-0xCFFF). 3610 See http://wiki.osdev.org/PCI for more info 3611 on the configuration access mechanisms. 3612 noaer [PCIE] If the PCIEAER kernel config parameter is 3613 enabled, this kernel boot option can be used to 3614 disable the use of PCIE advanced error reporting. 3615 nodomains [PCI] Disable support for multiple PCI 3616 root domains (aka PCI segments, in ACPI-speak). 3617 nommconf [X86] Disable use of MMCONFIG for PCI 3618 Configuration 3619 check_enable_amd_mmconf [X86] check for and enable 3620 properly configured MMIO access to PCI 3621 config space on AMD family 10h CPU 3622 nomsi [MSI] If the PCI_MSI kernel config parameter is 3623 enabled, this kernel boot option can be used to 3624 disable the use of MSI interrupts system-wide. 3625 noioapicquirk [APIC] Disable all boot interrupt quirks. 3626 Safety option to keep boot IRQs enabled. This 3627 should never be necessary. 3628 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 3629 primary IO-APIC for bridges that cannot disable 3630 boot IRQs. This fixes a source of spurious IRQs 3631 when the system masks IRQs. 3632 noioapicreroute [APIC] Disable workaround that uses the 3633 boot IRQ equivalent of an IRQ that connects to 3634 a chipset where boot IRQs cannot be disabled. 3635 The opposite of ioapicreroute. 3636 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 3637 routing table. These calls are known to be buggy 3638 on several machines and they hang the machine 3639 when used, but on other computers it's the only 3640 way to get the interrupt routing table. Try 3641 this option if the kernel is unable to allocate 3642 IRQs or discover secondary PCI buses on your 3643 motherboard. 3644 rom [X86] Assign address space to expansion ROMs. 3645 Use with caution as certain devices share 3646 address decoders between ROMs and other 3647 resources. 3648 norom [X86] Do not assign address space to 3649 expansion ROMs that do not already have 3650 BIOS assigned address ranges. 3651 nobar [X86] Do not assign address space to the 3652 BARs that weren't assigned by the BIOS. 3653 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 3654 assigned automatically to PCI devices. You can 3655 make the kernel exclude IRQs of your ISA cards 3656 this way. 3657 pirqaddr=0xAAAAA [X86] Specify the physical address 3658 of the PIRQ table (normally generated 3659 by the BIOS) if it is outside the 3660 F0000h-100000h range. 3661 lastbus=N [X86] Scan all buses thru bus #N. Can be 3662 useful if the kernel is unable to find your 3663 secondary buses and you want to tell it 3664 explicitly which ones they are. 3665 assign-busses [X86] Always assign all PCI bus 3666 numbers ourselves, overriding 3667 whatever the firmware may have done. 3668 usepirqmask [X86] Honor the possible IRQ mask stored 3669 in the BIOS $PIR table. This is needed on 3670 some systems with broken BIOSes, notably 3671 some HP Pavilion N5400 and Omnibook XE3 3672 notebooks. This will have no effect if ACPI 3673 IRQ routing is enabled. 3674 noacpi [X86] Do not use ACPI for IRQ routing 3675 or for PCI scanning. 3676 use_crs [X86] Use PCI host bridge window information 3677 from ACPI. On BIOSes from 2008 or later, this 3678 is enabled by default. If you need to use this, 3679 please report a bug. 3680 nocrs [X86] Ignore PCI host bridge windows from ACPI. 3681 If you need to use this, please report a bug. 3682 routeirq Do IRQ routing for all PCI devices. 3683 This is normally done in pci_enable_device(), 3684 so this option is a temporary workaround 3685 for broken drivers that don't call it. 3686 skip_isa_align [X86] do not align io start addr, so can 3687 handle more pci cards 3688 noearly [X86] Don't do any early type 1 scanning. 3689 This might help on some broken boards which 3690 machine check when some devices' config space 3691 is read. But various workarounds are disabled 3692 and some IOMMU drivers will not work. 3693 bfsort Sort PCI devices into breadth-first order. 3694 This sorting is done to get a device 3695 order compatible with older (<= 2.4) kernels. 3696 nobfsort Don't sort PCI devices into breadth-first order. 3697 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 3698 tuning and use the BIOS-configured MPS defaults. 3699 pcie_bus_safe Set every device's MPS to the largest value 3700 supported by all devices below the root complex. 3701 pcie_bus_perf Set device MPS to the largest allowable MPS 3702 based on its parent bus. Also set MRRS (Max 3703 Read Request Size) to the largest supported 3704 value (no larger than the MPS that the device 3705 or bus can support) for best performance. 3706 pcie_bus_peer2peer Set every device's MPS to 128B, which 3707 every device is guaranteed to support. This 3708 configuration allows peer-to-peer DMA between 3709 any pair of devices, possibly at the cost of 3710 reduced performance. This also guarantees 3711 that hot-added devices will work. 3712 cbiosize=nn[KMG] The fixed amount of bus space which is 3713 reserved for the CardBus bridge's IO window. 3714 The default value is 256 bytes. 3715 cbmemsize=nn[KMG] The fixed amount of bus space which is 3716 reserved for the CardBus bridge's memory 3717 window. The default value is 64 megabytes. 3718 resource_alignment= 3719 Format: 3720 [<order of align>@]<pci_dev>[; ...] 3721 Specifies alignment and device to reassign 3722 aligned memory resources. How to 3723 specify the device is described above. 3724 If <order of align> is not specified, 3725 PAGE_SIZE is used as alignment. 3726 A PCI-PCI bridge can be specified if resource 3727 windows need to be expanded. 3728 To specify the alignment for several 3729 instances of a device, the PCI vendor, 3730 device, subvendor, and subdevice may be 3731 specified, e.g., 12@pci:8086:9c22:103c:198f 3732 for 4096-byte alignment. 3733 ecrc= Enable/disable PCIe ECRC (transaction layer 3734 end-to-end CRC checking). 3735 bios: Use BIOS/firmware settings. This is the 3736 the default. 3737 off: Turn ECRC off 3738 on: Turn ECRC on. 3739 hpiosize=nn[KMG] The fixed amount of bus space which is 3740 reserved for hotplug bridge's IO window. 3741 Default size is 256 bytes. 3742 hpmmiosize=nn[KMG] The fixed amount of bus space which is 3743 reserved for hotplug bridge's MMIO window. 3744 Default size is 2 megabytes. 3745 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is 3746 reserved for hotplug bridge's MMIO_PREF window. 3747 Default size is 2 megabytes. 3748 hpmemsize=nn[KMG] The fixed amount of bus space which is 3749 reserved for hotplug bridge's MMIO and 3750 MMIO_PREF window. 3751 Default size is 2 megabytes. 3752 hpbussize=nn The minimum amount of additional bus numbers 3753 reserved for buses below a hotplug bridge. 3754 Default is 1. 3755 realloc= Enable/disable reallocating PCI bridge resources 3756 if allocations done by BIOS are too small to 3757 accommodate resources required by all child 3758 devices. 3759 off: Turn realloc off 3760 on: Turn realloc on 3761 realloc same as realloc=on 3762 noari do not use PCIe ARI. 3763 noats [PCIE, Intel-IOMMU, AMD-IOMMU] 3764 do not use PCIe ATS (and IOMMU device IOTLB). 3765 pcie_scan_all Scan all possible PCIe devices. Otherwise we 3766 only look for one device below a PCIe downstream 3767 port. 3768 big_root_window Try to add a big 64bit memory window to the PCIe 3769 root complex on AMD CPUs. Some GFX hardware 3770 can resize a BAR to allow access to all VRAM. 3771 Adding the window is slightly risky (it may 3772 conflict with unreported devices), so this 3773 taints the kernel. 3774 disable_acs_redir=<pci_dev>[; ...] 3775 Specify one or more PCI devices (in the format 3776 specified above) separated by semicolons. 3777 Each device specified will have the PCI ACS 3778 redirect capabilities forced off which will 3779 allow P2P traffic between devices through 3780 bridges without forcing it upstream. Note: 3781 this removes isolation between devices and 3782 may put more devices in an IOMMU group. 3783 force_floating [S390] Force usage of floating interrupts. 3784 nomio [S390] Do not use MIO instructions. 3785 norid [S390] ignore the RID field and force use of 3786 one PCI domain per PCI function 3787 3788 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power 3789 Management. 3790 off Disable ASPM. 3791 force Enable ASPM even on devices that claim not to support it. 3792 WARNING: Forcing ASPM on may cause system lockups. 3793 3794 pcie_ports= [PCIE] PCIe port services handling: 3795 native Use native PCIe services (PME, AER, DPC, PCIe hotplug) 3796 even if the platform doesn't give the OS permission to 3797 use them. This may cause conflicts if the platform 3798 also tries to use these services. 3799 dpc-native Use native PCIe service for DPC only. May 3800 cause conflicts if firmware uses AER or DPC. 3801 compat Disable native PCIe services (PME, AER, DPC, PCIe 3802 hotplug). 3803 3804 pcie_port_pm= [PCIE] PCIe port power management handling: 3805 off Disable power management of all PCIe ports 3806 force Forcibly enable power management of all PCIe ports 3807 3808 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 3809 nomsi Do not use MSI for native PCIe PME signaling (this makes 3810 all PCIe root ports use INTx for all services). 3811 3812 pcmv= [HW,PCMCIA] BadgePAD 4 3813 3814 pd_ignore_unused 3815 [PM] 3816 Keep all power-domains already enabled by bootloader on, 3817 even if no driver has claimed them. This is useful 3818 for debug and development, but should not be 3819 needed on a platform with proper driver support. 3820 3821 pd. [PARIDE] 3822 See Documentation/admin-guide/blockdev/paride.rst. 3823 3824 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 3825 boot time. 3826 Format: { 0 | 1 } 3827 See arch/parisc/kernel/pdc_chassis.c 3828 3829 percpu_alloc= Select which percpu first chunk allocator to use. 3830 Currently supported values are "embed" and "page". 3831 Archs may support subset or none of the selections. 3832 See comments in mm/percpu.c for details on each 3833 allocator. This parameter is primarily for debugging 3834 and performance comparison. 3835 3836 pf. [PARIDE] 3837 See Documentation/admin-guide/blockdev/paride.rst. 3838 3839 pg. [PARIDE] 3840 See Documentation/admin-guide/blockdev/paride.rst. 3841 3842 pirq= [SMP,APIC] Manual mp-table setup 3843 See Documentation/x86/i386/IO-APIC.rst. 3844 3845 plip= [PPT,NET] Parallel port network link 3846 Format: { parport<nr> | timid | 0 } 3847 See also Documentation/admin-guide/parport.rst. 3848 3849 pmtmr= [X86] Manual setup of pmtmr I/O Port. 3850 Override pmtimer IOPort with a hex value. 3851 e.g. pmtmr=0x508 3852 3853 pm_debug_messages [SUSPEND,KNL] 3854 Enable suspend/resume debug messages during boot up. 3855 3856 pnp.debug=1 [PNP] 3857 Enable PNP debug messages (depends on the 3858 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 3859 via /sys/module/pnp/parameters/debug. We always show 3860 current resource usage; turning this on also shows 3861 possible settings and some assignment information. 3862 3863 pnpacpi= [ACPI] 3864 { off } 3865 3866 pnpbios= [ISAPNP] 3867 { on | off | curr | res | no-curr | no-res } 3868 3869 pnp_reserve_irq= 3870 [ISAPNP] Exclude IRQs for the autoconfiguration 3871 3872 pnp_reserve_dma= 3873 [ISAPNP] Exclude DMAs for the autoconfiguration 3874 3875 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 3876 Ranges are in pairs (I/O port base and size). 3877 3878 pnp_reserve_mem= 3879 [ISAPNP] Exclude memory regions for the 3880 autoconfiguration. 3881 Ranges are in pairs (memory base and size). 3882 3883 ports= [IP_VS_FTP] IPVS ftp helper module 3884 Default is 21. 3885 Up to 8 (IP_VS_APP_MAX_PORTS) ports 3886 may be specified. 3887 Format: <port>,<port>.... 3888 3889 powersave=off [PPC] This option disables power saving features. 3890 It specifically disables cpuidle and sets the 3891 platform machine description specific power_save 3892 function to NULL. On Idle the CPU just reduces 3893 execution priority. 3894 3895 ppc_strict_facility_enable 3896 [PPC] This option catches any kernel floating point, 3897 Altivec, VSX and SPE outside of regions specifically 3898 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 3899 There is some performance impact when enabling this. 3900 3901 ppc_tm= [PPC] 3902 Format: {"off"} 3903 Disable Hardware Transactional Memory 3904 3905 print-fatal-signals= 3906 [KNL] debug: print fatal signals 3907 3908 If enabled, warn about various signal handling 3909 related application anomalies: too many signals, 3910 too many POSIX.1 timers, fatal signals causing a 3911 coredump - etc. 3912 3913 If you hit the warning due to signal overflow, 3914 you might want to try "ulimit -i unlimited". 3915 3916 default: off. 3917 3918 printk.always_kmsg_dump= 3919 Trigger kmsg_dump for cases other than kernel oops or 3920 panics 3921 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3922 default: disabled 3923 3924 printk.devkmsg={on,off,ratelimit} 3925 Control writing to /dev/kmsg. 3926 on - unlimited logging to /dev/kmsg from userspace 3927 off - logging to /dev/kmsg disabled 3928 ratelimit - ratelimit the logging 3929 Default: ratelimit 3930 3931 printk.time= Show timing data prefixed to each printk message line 3932 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3933 3934 processor.max_cstate= [HW,ACPI] 3935 Limit processor to maximum C-state 3936 max_cstate=9 overrides any DMI blacklist limit. 3937 3938 processor.nocst [HW,ACPI] 3939 Ignore the _CST method to determine C-states, 3940 instead using the legacy FADT method 3941 3942 profile= [KNL] Enable kernel profiling via /proc/profile 3943 Format: [<profiletype>,]<number> 3944 Param: <profiletype>: "schedule", "sleep", or "kvm" 3945 [defaults to kernel profiling] 3946 Param: "schedule" - profile schedule points. 3947 Param: "sleep" - profile D-state sleeping (millisecs). 3948 Requires CONFIG_SCHEDSTATS 3949 Param: "kvm" - profile VM exits. 3950 Param: <number> - step/bucket size as a power of 2 for 3951 statistical time based profiling. 3952 3953 prompt_ramdisk= [RAM] [Deprecated] 3954 3955 prot_virt= [S390] enable hosting protected virtual machines 3956 isolated from the hypervisor (if hardware supports 3957 that). 3958 Format: <bool> 3959 3960 psi= [KNL] Enable or disable pressure stall information 3961 tracking. 3962 Format: <bool> 3963 3964 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 3965 probe for; one of (bare|imps|exps|lifebook|any). 3966 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 3967 per second. 3968 psmouse.resetafter= [HW,MOUSE] 3969 Try to reset the device after so many bad packets 3970 (0 = never). 3971 psmouse.resolution= 3972 [HW,MOUSE] Set desired mouse resolution, in dpi. 3973 psmouse.smartscroll= 3974 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 3975 0 = disabled, 1 = enabled (default). 3976 3977 pstore.backend= Specify the name of the pstore backend to use 3978 3979 pt. [PARIDE] 3980 See Documentation/admin-guide/blockdev/paride.rst. 3981 3982 pti= [X86-64] Control Page Table Isolation of user and 3983 kernel address spaces. Disabling this feature 3984 removes hardening, but improves performance of 3985 system calls and interrupts. 3986 3987 on - unconditionally enable 3988 off - unconditionally disable 3989 auto - kernel detects whether your CPU model is 3990 vulnerable to issues that PTI mitigates 3991 3992 Not specifying this option is equivalent to pti=auto. 3993 3994 nopti [X86-64] 3995 Equivalent to pti=off 3996 3997 pty.legacy_count= 3998 [KNL] Number of legacy pty's. Overwrites compiled-in 3999 default number. 4000 4001 quiet [KNL] Disable most log messages 4002 4003 r128= [HW,DRM] 4004 4005 raid= [HW,RAID] 4006 See Documentation/admin-guide/md.rst. 4007 4008 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 4009 See Documentation/admin-guide/blockdev/ramdisk.rst. 4010 4011 ramdisk_start= [RAM] RAM disk image start address 4012 4013 random.trust_cpu={on,off} 4014 [KNL] Enable or disable trusting the use of the 4015 CPU's random number generator (if available) to 4016 fully seed the kernel's CRNG. Default is controlled 4017 by CONFIG_RANDOM_TRUST_CPU. 4018 4019 ras=option[,option,...] [KNL] RAS-specific options 4020 4021 cec_disable [X86] 4022 Disable the Correctable Errors Collector, 4023 see CONFIG_RAS_CEC help text. 4024 4025 rcu_nocbs= [KNL] 4026 The argument is a cpu list, as described above, 4027 except that the string "all" can be used to 4028 specify every CPU on the system. 4029 4030 In kernels built with CONFIG_RCU_NOCB_CPU=y, set 4031 the specified list of CPUs to be no-callback CPUs. 4032 Invocation of these CPUs' RCU callbacks will be 4033 offloaded to "rcuox/N" kthreads created for that 4034 purpose, where "x" is "p" for RCU-preempt, and 4035 "s" for RCU-sched, and "N" is the CPU number. 4036 This reduces OS jitter on the offloaded CPUs, 4037 which can be useful for HPC and real-time 4038 workloads. It can also improve energy efficiency 4039 for asymmetric multiprocessors. 4040 4041 rcu_nocb_poll [KNL] 4042 Rather than requiring that offloaded CPUs 4043 (specified by rcu_nocbs= above) explicitly 4044 awaken the corresponding "rcuoN" kthreads, 4045 make these kthreads poll for callbacks. 4046 This improves the real-time response for the 4047 offloaded CPUs by relieving them of the need to 4048 wake up the corresponding kthread, but degrades 4049 energy efficiency by requiring that the kthreads 4050 periodically wake up to do the polling. 4051 4052 rcutree.blimit= [KNL] 4053 Set maximum number of finished RCU callbacks to 4054 process in one batch. 4055 4056 rcutree.dump_tree= [KNL] 4057 Dump the structure of the rcu_node combining tree 4058 out at early boot. This is used for diagnostic 4059 purposes, to verify correct tree setup. 4060 4061 rcutree.gp_cleanup_delay= [KNL] 4062 Set the number of jiffies to delay each step of 4063 RCU grace-period cleanup. 4064 4065 rcutree.gp_init_delay= [KNL] 4066 Set the number of jiffies to delay each step of 4067 RCU grace-period initialization. 4068 4069 rcutree.gp_preinit_delay= [KNL] 4070 Set the number of jiffies to delay each step of 4071 RCU grace-period pre-initialization, that is, 4072 the propagation of recent CPU-hotplug changes up 4073 the rcu_node combining tree. 4074 4075 rcutree.use_softirq= [KNL] 4076 If set to zero, move all RCU_SOFTIRQ processing to 4077 per-CPU rcuc kthreads. Defaults to a non-zero 4078 value, meaning that RCU_SOFTIRQ is used by default. 4079 Specify rcutree.use_softirq=0 to use rcuc kthreads. 4080 4081 rcutree.rcu_fanout_exact= [KNL] 4082 Disable autobalancing of the rcu_node combining 4083 tree. This is used by rcutorture, and might 4084 possibly be useful for architectures having high 4085 cache-to-cache transfer latencies. 4086 4087 rcutree.rcu_fanout_leaf= [KNL] 4088 Change the number of CPUs assigned to each 4089 leaf rcu_node structure. Useful for very 4090 large systems, which will choose the value 64, 4091 and for NUMA systems with large remote-access 4092 latencies, which will choose a value aligned 4093 with the appropriate hardware boundaries. 4094 4095 rcutree.rcu_min_cached_objs= [KNL] 4096 Minimum number of objects which are cached and 4097 maintained per one CPU. Object size is equal 4098 to PAGE_SIZE. The cache allows to reduce the 4099 pressure to page allocator, also it makes the 4100 whole algorithm to behave better in low memory 4101 condition. 4102 4103 rcutree.jiffies_till_first_fqs= [KNL] 4104 Set delay from grace-period initialization to 4105 first attempt to force quiescent states. 4106 Units are jiffies, minimum value is zero, 4107 and maximum value is HZ. 4108 4109 rcutree.jiffies_till_next_fqs= [KNL] 4110 Set delay between subsequent attempts to force 4111 quiescent states. Units are jiffies, minimum 4112 value is one, and maximum value is HZ. 4113 4114 rcutree.jiffies_till_sched_qs= [KNL] 4115 Set required age in jiffies for a 4116 given grace period before RCU starts 4117 soliciting quiescent-state help from 4118 rcu_note_context_switch() and cond_resched(). 4119 If not specified, the kernel will calculate 4120 a value based on the most recent settings 4121 of rcutree.jiffies_till_first_fqs 4122 and rcutree.jiffies_till_next_fqs. 4123 This calculated value may be viewed in 4124 rcutree.jiffies_to_sched_qs. Any attempt to set 4125 rcutree.jiffies_to_sched_qs will be cheerfully 4126 overwritten. 4127 4128 rcutree.kthread_prio= [KNL,BOOT] 4129 Set the SCHED_FIFO priority of the RCU per-CPU 4130 kthreads (rcuc/N). This value is also used for 4131 the priority of the RCU boost threads (rcub/N) 4132 and for the RCU grace-period kthreads (rcu_bh, 4133 rcu_preempt, and rcu_sched). If RCU_BOOST is 4134 set, valid values are 1-99 and the default is 1 4135 (the least-favored priority). Otherwise, when 4136 RCU_BOOST is not set, valid values are 0-99 and 4137 the default is zero (non-realtime operation). 4138 4139 rcutree.rcu_nocb_gp_stride= [KNL] 4140 Set the number of NOCB callback kthreads in 4141 each group, which defaults to the square root 4142 of the number of CPUs. Larger numbers reduce 4143 the wakeup overhead on the global grace-period 4144 kthread, but increases that same overhead on 4145 each group's NOCB grace-period kthread. 4146 4147 rcutree.qhimark= [KNL] 4148 Set threshold of queued RCU callbacks beyond which 4149 batch limiting is disabled. 4150 4151 rcutree.qlowmark= [KNL] 4152 Set threshold of queued RCU callbacks below which 4153 batch limiting is re-enabled. 4154 4155 rcutree.qovld= [KNL] 4156 Set threshold of queued RCU callbacks beyond which 4157 RCU's force-quiescent-state scan will aggressively 4158 enlist help from cond_resched() and sched IPIs to 4159 help CPUs more quickly reach quiescent states. 4160 Set to less than zero to make this be set based 4161 on rcutree.qhimark at boot time and to zero to 4162 disable more aggressive help enlistment. 4163 4164 rcutree.rcu_idle_gp_delay= [KNL] 4165 Set wakeup interval for idle CPUs that have 4166 RCU callbacks (RCU_FAST_NO_HZ=y). 4167 4168 rcutree.rcu_idle_lazy_gp_delay= [KNL] 4169 Set wakeup interval for idle CPUs that have 4170 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y). 4171 Lazy RCU callbacks are those which RCU can 4172 prove do nothing more than free memory. 4173 4174 rcutree.rcu_kick_kthreads= [KNL] 4175 Cause the grace-period kthread to get an extra 4176 wake_up() if it sleeps three times longer than 4177 it should at force-quiescent-state time. 4178 This wake_up() will be accompanied by a 4179 WARN_ONCE() splat and an ftrace_dump(). 4180 4181 rcutree.rcu_unlock_delay= [KNL] 4182 In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels, 4183 this specifies an rcu_read_unlock()-time delay 4184 in microseconds. This defaults to zero. 4185 Larger delays increase the probability of 4186 catching RCU pointer leaks, that is, buggy use 4187 of RCU-protected pointers after the relevant 4188 rcu_read_unlock() has completed. 4189 4190 rcutree.sysrq_rcu= [KNL] 4191 Commandeer a sysrq key to dump out Tree RCU's 4192 rcu_node tree with an eye towards determining 4193 why a new grace period has not yet started. 4194 4195 rcuscale.gp_async= [KNL] 4196 Measure performance of asynchronous 4197 grace-period primitives such as call_rcu(). 4198 4199 rcuscale.gp_async_max= [KNL] 4200 Specify the maximum number of outstanding 4201 callbacks per writer thread. When a writer 4202 thread exceeds this limit, it invokes the 4203 corresponding flavor of rcu_barrier() to allow 4204 previously posted callbacks to drain. 4205 4206 rcuscale.gp_exp= [KNL] 4207 Measure performance of expedited synchronous 4208 grace-period primitives. 4209 4210 rcuscale.holdoff= [KNL] 4211 Set test-start holdoff period. The purpose of 4212 this parameter is to delay the start of the 4213 test until boot completes in order to avoid 4214 interference. 4215 4216 rcuscale.kfree_rcu_test= [KNL] 4217 Set to measure performance of kfree_rcu() flooding. 4218 4219 rcuscale.kfree_nthreads= [KNL] 4220 The number of threads running loops of kfree_rcu(). 4221 4222 rcuscale.kfree_alloc_num= [KNL] 4223 Number of allocations and frees done in an iteration. 4224 4225 rcuscale.kfree_loops= [KNL] 4226 Number of loops doing rcuscale.kfree_alloc_num number 4227 of allocations and frees. 4228 4229 rcuscale.nreaders= [KNL] 4230 Set number of RCU readers. The value -1 selects 4231 N, where N is the number of CPUs. A value 4232 "n" less than -1 selects N-n+1, where N is again 4233 the number of CPUs. For example, -2 selects N 4234 (the number of CPUs), -3 selects N+1, and so on. 4235 A value of "n" less than or equal to -N selects 4236 a single reader. 4237 4238 rcuscale.nwriters= [KNL] 4239 Set number of RCU writers. The values operate 4240 the same as for rcuscale.nreaders. 4241 N, where N is the number of CPUs 4242 4243 rcuscale.perf_type= [KNL] 4244 Specify the RCU implementation to test. 4245 4246 rcuscale.shutdown= [KNL] 4247 Shut the system down after performance tests 4248 complete. This is useful for hands-off automated 4249 testing. 4250 4251 rcuscale.verbose= [KNL] 4252 Enable additional printk() statements. 4253 4254 rcuscale.writer_holdoff= [KNL] 4255 Write-side holdoff between grace periods, 4256 in microseconds. The default of zero says 4257 no holdoff. 4258 4259 rcutorture.fqs_duration= [KNL] 4260 Set duration of force_quiescent_state bursts 4261 in microseconds. 4262 4263 rcutorture.fqs_holdoff= [KNL] 4264 Set holdoff time within force_quiescent_state bursts 4265 in microseconds. 4266 4267 rcutorture.fqs_stutter= [KNL] 4268 Set wait time between force_quiescent_state bursts 4269 in seconds. 4270 4271 rcutorture.fwd_progress= [KNL] 4272 Enable RCU grace-period forward-progress testing 4273 for the types of RCU supporting this notion. 4274 4275 rcutorture.fwd_progress_div= [KNL] 4276 Specify the fraction of a CPU-stall-warning 4277 period to do tight-loop forward-progress testing. 4278 4279 rcutorture.fwd_progress_holdoff= [KNL] 4280 Number of seconds to wait between successive 4281 forward-progress tests. 4282 4283 rcutorture.fwd_progress_need_resched= [KNL] 4284 Enclose cond_resched() calls within checks for 4285 need_resched() during tight-loop forward-progress 4286 testing. 4287 4288 rcutorture.gp_cond= [KNL] 4289 Use conditional/asynchronous update-side 4290 primitives, if available. 4291 4292 rcutorture.gp_exp= [KNL] 4293 Use expedited update-side primitives, if available. 4294 4295 rcutorture.gp_normal= [KNL] 4296 Use normal (non-expedited) asynchronous 4297 update-side primitives, if available. 4298 4299 rcutorture.gp_sync= [KNL] 4300 Use normal (non-expedited) synchronous 4301 update-side primitives, if available. If all 4302 of rcutorture.gp_cond=, rcutorture.gp_exp=, 4303 rcutorture.gp_normal=, and rcutorture.gp_sync= 4304 are zero, rcutorture acts as if is interpreted 4305 they are all non-zero. 4306 4307 rcutorture.irqreader= [KNL] 4308 Run RCU readers from irq handlers, or, more 4309 accurately, from a timer handler. Not all RCU 4310 flavors take kindly to this sort of thing. 4311 4312 rcutorture.leakpointer= [KNL] 4313 Leak an RCU-protected pointer out of the reader. 4314 This can of course result in splats, and is 4315 intended to test the ability of things like 4316 CONFIG_RCU_STRICT_GRACE_PERIOD=y to detect 4317 such leaks. 4318 4319 rcutorture.n_barrier_cbs= [KNL] 4320 Set callbacks/threads for rcu_barrier() testing. 4321 4322 rcutorture.nfakewriters= [KNL] 4323 Set number of concurrent RCU writers. These just 4324 stress RCU, they don't participate in the actual 4325 test, hence the "fake". 4326 4327 rcutorture.nreaders= [KNL] 4328 Set number of RCU readers. The value -1 selects 4329 N-1, where N is the number of CPUs. A value 4330 "n" less than -1 selects N-n-2, where N is again 4331 the number of CPUs. For example, -2 selects N 4332 (the number of CPUs), -3 selects N+1, and so on. 4333 4334 rcutorture.object_debug= [KNL] 4335 Enable debug-object double-call_rcu() testing. 4336 4337 rcutorture.onoff_holdoff= [KNL] 4338 Set time (s) after boot for CPU-hotplug testing. 4339 4340 rcutorture.onoff_interval= [KNL] 4341 Set time (jiffies) between CPU-hotplug operations, 4342 or zero to disable CPU-hotplug testing. 4343 4344 rcutorture.read_exit= [KNL] 4345 Set the number of read-then-exit kthreads used 4346 to test the interaction of RCU updaters and 4347 task-exit processing. 4348 4349 rcutorture.read_exit_burst= [KNL] 4350 The number of times in a given read-then-exit 4351 episode that a set of read-then-exit kthreads 4352 is spawned. 4353 4354 rcutorture.read_exit_delay= [KNL] 4355 The delay, in seconds, between successive 4356 read-then-exit testing episodes. 4357 4358 rcutorture.shuffle_interval= [KNL] 4359 Set task-shuffle interval (s). Shuffling tasks 4360 allows some CPUs to go into dyntick-idle mode 4361 during the rcutorture test. 4362 4363 rcutorture.shutdown_secs= [KNL] 4364 Set time (s) after boot system shutdown. This 4365 is useful for hands-off automated testing. 4366 4367 rcutorture.stall_cpu= [KNL] 4368 Duration of CPU stall (s) to test RCU CPU stall 4369 warnings, zero to disable. 4370 4371 rcutorture.stall_cpu_block= [KNL] 4372 Sleep while stalling if set. This will result 4373 in warnings from preemptible RCU in addition 4374 to any other stall-related activity. 4375 4376 rcutorture.stall_cpu_holdoff= [KNL] 4377 Time to wait (s) after boot before inducing stall. 4378 4379 rcutorture.stall_cpu_irqsoff= [KNL] 4380 Disable interrupts while stalling if set. 4381 4382 rcutorture.stall_gp_kthread= [KNL] 4383 Duration (s) of forced sleep within RCU 4384 grace-period kthread to test RCU CPU stall 4385 warnings, zero to disable. If both stall_cpu 4386 and stall_gp_kthread are specified, the 4387 kthread is starved first, then the CPU. 4388 4389 rcutorture.stat_interval= [KNL] 4390 Time (s) between statistics printk()s. 4391 4392 rcutorture.stutter= [KNL] 4393 Time (s) to stutter testing, for example, specifying 4394 five seconds causes the test to run for five seconds, 4395 wait for five seconds, and so on. This tests RCU's 4396 ability to transition abruptly to and from idle. 4397 4398 rcutorture.test_boost= [KNL] 4399 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 4400 "Maybe" means test if the RCU implementation 4401 under test support RCU priority boosting. 4402 4403 rcutorture.test_boost_duration= [KNL] 4404 Duration (s) of each individual boost test. 4405 4406 rcutorture.test_boost_interval= [KNL] 4407 Interval (s) between each boost test. 4408 4409 rcutorture.test_no_idle_hz= [KNL] 4410 Test RCU's dyntick-idle handling. See also the 4411 rcutorture.shuffle_interval parameter. 4412 4413 rcutorture.torture_type= [KNL] 4414 Specify the RCU implementation to test. 4415 4416 rcutorture.verbose= [KNL] 4417 Enable additional printk() statements. 4418 4419 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL] 4420 Dump ftrace buffer after reporting RCU CPU 4421 stall warning. 4422 4423 rcupdate.rcu_cpu_stall_suppress= [KNL] 4424 Suppress RCU CPU stall warning messages. 4425 4426 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL] 4427 Suppress RCU CPU stall warning messages and 4428 rcutorture writer stall warnings that occur 4429 during early boot, that is, during the time 4430 before the init task is spawned. 4431 4432 rcupdate.rcu_cpu_stall_timeout= [KNL] 4433 Set timeout for RCU CPU stall warning messages. 4434 4435 rcupdate.rcu_expedited= [KNL] 4436 Use expedited grace-period primitives, for 4437 example, synchronize_rcu_expedited() instead 4438 of synchronize_rcu(). This reduces latency, 4439 but can increase CPU utilization, degrade 4440 real-time latency, and degrade energy efficiency. 4441 No effect on CONFIG_TINY_RCU kernels. 4442 4443 rcupdate.rcu_normal= [KNL] 4444 Use only normal grace-period primitives, 4445 for example, synchronize_rcu() instead of 4446 synchronize_rcu_expedited(). This improves 4447 real-time latency, CPU utilization, and 4448 energy efficiency, but can expose users to 4449 increased grace-period latency. This parameter 4450 overrides rcupdate.rcu_expedited. No effect on 4451 CONFIG_TINY_RCU kernels. 4452 4453 rcupdate.rcu_normal_after_boot= [KNL] 4454 Once boot has completed (that is, after 4455 rcu_end_inkernel_boot() has been invoked), use 4456 only normal grace-period primitives. No effect 4457 on CONFIG_TINY_RCU kernels. 4458 4459 rcupdate.rcu_task_ipi_delay= [KNL] 4460 Set time in jiffies during which RCU tasks will 4461 avoid sending IPIs, starting with the beginning 4462 of a given grace period. Setting a large 4463 number avoids disturbing real-time workloads, 4464 but lengthens grace periods. 4465 4466 rcupdate.rcu_task_stall_timeout= [KNL] 4467 Set timeout in jiffies for RCU task stall warning 4468 messages. Disable with a value less than or equal 4469 to zero. 4470 4471 rcupdate.rcu_self_test= [KNL] 4472 Run the RCU early boot self tests 4473 4474 rdinit= [KNL] 4475 Format: <full_path> 4476 Run specified binary instead of /init from the ramdisk, 4477 used for early userspace startup. See initrd. 4478 4479 rdrand= [X86] 4480 force - Override the decision by the kernel to hide the 4481 advertisement of RDRAND support (this affects 4482 certain AMD processors because of buggy BIOS 4483 support, specifically around the suspend/resume 4484 path). 4485 4486 rdt= [HW,X86,RDT] 4487 Turn on/off individual RDT features. List is: 4488 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, 4489 mba. 4490 E.g. to turn on cmt and turn off mba use: 4491 rdt=cmt,!mba 4492 4493 reboot= [KNL] 4494 Format (x86 or x86_64): 4495 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \ 4496 [[,]s[mp]#### \ 4497 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 4498 [[,]f[orce] 4499 Where reboot_mode is one of warm (soft) or cold (hard) or gpio 4500 (prefix with 'panic_' to set mode for panic 4501 reboot only), 4502 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 4503 reboot_force is either force or not specified, 4504 reboot_cpu is s[mp]#### with #### being the processor 4505 to be used for rebooting. 4506 4507 refscale.holdoff= [KNL] 4508 Set test-start holdoff period. The purpose of 4509 this parameter is to delay the start of the 4510 test until boot completes in order to avoid 4511 interference. 4512 4513 refscale.loops= [KNL] 4514 Set the number of loops over the synchronization 4515 primitive under test. Increasing this number 4516 reduces noise due to loop start/end overhead, 4517 but the default has already reduced the per-pass 4518 noise to a handful of picoseconds on ca. 2020 4519 x86 laptops. 4520 4521 refscale.nreaders= [KNL] 4522 Set number of readers. The default value of -1 4523 selects N, where N is roughly 75% of the number 4524 of CPUs. A value of zero is an interesting choice. 4525 4526 refscale.nruns= [KNL] 4527 Set number of runs, each of which is dumped onto 4528 the console log. 4529 4530 refscale.readdelay= [KNL] 4531 Set the read-side critical-section duration, 4532 measured in microseconds. 4533 4534 refscale.scale_type= [KNL] 4535 Specify the read-protection implementation to test. 4536 4537 refscale.shutdown= [KNL] 4538 Shut down the system at the end of the performance 4539 test. This defaults to 1 (shut it down) when 4540 refscale is built into the kernel and to 0 (leave 4541 it running) when refscale is built as a module. 4542 4543 refscale.verbose= [KNL] 4544 Enable additional printk() statements. 4545 4546 relax_domain_level= 4547 [KNL, SMP] Set scheduler's default relax_domain_level. 4548 See Documentation/admin-guide/cgroup-v1/cpusets.rst. 4549 4550 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory 4551 Format: <base1>,<size1>[,<base2>,<size2>,...] 4552 Reserve I/O ports or memory so the kernel won't use 4553 them. If <base> is less than 0x10000, the region 4554 is assumed to be I/O ports; otherwise it is memory. 4555 4556 reservetop= [X86-32] 4557 Format: nn[KMG] 4558 Reserves a hole at the top of the kernel virtual 4559 address space. 4560 4561 reservelow= [X86] 4562 Format: nn[K] 4563 Set the amount of memory to reserve for BIOS at 4564 the bottom of the address space. 4565 4566 reset_devices [KNL] Force drivers to reset the underlying device 4567 during initialization. 4568 4569 resume= [SWSUSP] 4570 Specify the partition device for software suspend 4571 Format: 4572 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 4573 4574 resume_offset= [SWSUSP] 4575 Specify the offset from the beginning of the partition 4576 given by "resume=" at which the swap header is located, 4577 in <PAGE_SIZE> units (needed only for swap files). 4578 See Documentation/power/swsusp-and-swap-files.rst 4579 4580 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 4581 read the resume files 4582 4583 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 4584 Useful for devices that are detected asynchronously 4585 (e.g. USB and MMC devices). 4586 4587 hibernate= [HIBERNATION] 4588 noresume Don't check if there's a hibernation image 4589 present during boot. 4590 nocompress Don't compress/decompress hibernation images. 4591 no Disable hibernation and resume. 4592 protect_image Turn on image protection during restoration 4593 (that will set all pages holding image data 4594 during restoration read-only). 4595 4596 retain_initrd [RAM] Keep initrd memory after extraction 4597 4598 rfkill.default_state= 4599 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 4600 etc. communication is blocked by default. 4601 1 Unblocked. 4602 4603 rfkill.master_switch_mode= 4604 0 The "airplane mode" button does nothing. 4605 1 The "airplane mode" button toggles between everything 4606 blocked and the previous configuration. 4607 2 The "airplane mode" button toggles between everything 4608 blocked and everything unblocked. 4609 4610 rhash_entries= [KNL,NET] 4611 Set number of hash buckets for route cache 4612 4613 ring3mwait=disable 4614 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 4615 CPUs. 4616 4617 ro [KNL] Mount root device read-only on boot 4618 4619 rodata= [KNL] 4620 on Mark read-only kernel memory as read-only (default). 4621 off Leave read-only kernel memory writable for debugging. 4622 4623 rockchip.usb_uart 4624 Enable the uart passthrough on the designated usb port 4625 on Rockchip SoCs. When active, the signals of the 4626 debug-uart get routed to the D+ and D- pins of the usb 4627 port and the regular usb controller gets disabled. 4628 4629 root= [KNL] Root filesystem 4630 See name_to_dev_t comment in init/do_mounts.c. 4631 4632 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 4633 mount the root filesystem 4634 4635 rootflags= [KNL] Set root filesystem mount option string 4636 4637 rootfstype= [KNL] Set root filesystem type 4638 4639 rootwait [KNL] Wait (indefinitely) for root device to show up. 4640 Useful for devices that are detected asynchronously 4641 (e.g. USB and MMC devices). 4642 4643 rproc_mem=nn[KMG][@address] 4644 [KNL,ARM,CMA] Remoteproc physical memory block. 4645 Memory area to be used by remote processor image, 4646 managed by CMA. 4647 4648 rw [KNL] Mount root device read-write on boot 4649 4650 S [KNL] Run init in single mode 4651 4652 s390_iommu= [HW,S390] 4653 Set s390 IOTLB flushing mode 4654 strict 4655 With strict flushing every unmap operation will result in 4656 an IOTLB flush. Default is lazy flushing before reuse, 4657 which is faster. 4658 4659 sa1100ir [NET] 4660 See drivers/net/irda/sa1100_ir.c. 4661 4662 sbni= [NET] Granch SBNI12 leased line adapter 4663 4664 sched_debug [KNL] Enables verbose scheduler debug messages. 4665 4666 schedstats= [KNL,X86] Enable or disable scheduled statistics. 4667 Allowed values are enable and disable. This feature 4668 incurs a small amount of overhead in the scheduler 4669 but is useful for debugging and performance tuning. 4670 4671 sched_thermal_decay_shift= 4672 [KNL, SMP] Set a decay shift for scheduler thermal 4673 pressure signal. Thermal pressure signal follows the 4674 default decay period of other scheduler pelt 4675 signals(usually 32 ms but configurable). Setting 4676 sched_thermal_decay_shift will left shift the decay 4677 period for the thermal pressure signal by the shift 4678 value. 4679 i.e. with the default pelt decay period of 32 ms 4680 sched_thermal_decay_shift thermal pressure decay pr 4681 1 64 ms 4682 2 128 ms 4683 and so on. 4684 Format: integer between 0 and 10 4685 Default is 0. 4686 4687 scftorture.holdoff= [KNL] 4688 Number of seconds to hold off before starting 4689 test. Defaults to zero for module insertion and 4690 to 10 seconds for built-in smp_call_function() 4691 tests. 4692 4693 scftorture.longwait= [KNL] 4694 Request ridiculously long waits randomly selected 4695 up to the chosen limit in seconds. Zero (the 4696 default) disables this feature. Please note 4697 that requesting even small non-zero numbers of 4698 seconds can result in RCU CPU stall warnings, 4699 softlockup complaints, and so on. 4700 4701 scftorture.nthreads= [KNL] 4702 Number of kthreads to spawn to invoke the 4703 smp_call_function() family of functions. 4704 The default of -1 specifies a number of kthreads 4705 equal to the number of CPUs. 4706 4707 scftorture.onoff_holdoff= [KNL] 4708 Number seconds to wait after the start of the 4709 test before initiating CPU-hotplug operations. 4710 4711 scftorture.onoff_interval= [KNL] 4712 Number seconds to wait between successive 4713 CPU-hotplug operations. Specifying zero (which 4714 is the default) disables CPU-hotplug operations. 4715 4716 scftorture.shutdown_secs= [KNL] 4717 The number of seconds following the start of the 4718 test after which to shut down the system. The 4719 default of zero avoids shutting down the system. 4720 Non-zero values are useful for automated tests. 4721 4722 scftorture.stat_interval= [KNL] 4723 The number of seconds between outputting the 4724 current test statistics to the console. A value 4725 of zero disables statistics output. 4726 4727 scftorture.stutter_cpus= [KNL] 4728 The number of jiffies to wait between each change 4729 to the set of CPUs under test. 4730 4731 scftorture.use_cpus_read_lock= [KNL] 4732 Use use_cpus_read_lock() instead of the default 4733 preempt_disable() to disable CPU hotplug 4734 while invoking one of the smp_call_function*() 4735 functions. 4736 4737 scftorture.verbose= [KNL] 4738 Enable additional printk() statements. 4739 4740 scftorture.weight_single= [KNL] 4741 The probability weighting to use for the 4742 smp_call_function_single() function with a zero 4743 "wait" parameter. A value of -1 selects the 4744 default if all other weights are -1. However, 4745 if at least one weight has some other value, a 4746 value of -1 will instead select a weight of zero. 4747 4748 scftorture.weight_single_wait= [KNL] 4749 The probability weighting to use for the 4750 smp_call_function_single() function with a 4751 non-zero "wait" parameter. See weight_single. 4752 4753 scftorture.weight_many= [KNL] 4754 The probability weighting to use for the 4755 smp_call_function_many() function with a zero 4756 "wait" parameter. See weight_single. 4757 Note well that setting a high probability for 4758 this weighting can place serious IPI load 4759 on the system. 4760 4761 scftorture.weight_many_wait= [KNL] 4762 The probability weighting to use for the 4763 smp_call_function_many() function with a 4764 non-zero "wait" parameter. See weight_single 4765 and weight_many. 4766 4767 scftorture.weight_all= [KNL] 4768 The probability weighting to use for the 4769 smp_call_function_all() function with a zero 4770 "wait" parameter. See weight_single and 4771 weight_many. 4772 4773 scftorture.weight_all_wait= [KNL] 4774 The probability weighting to use for the 4775 smp_call_function_all() function with a 4776 non-zero "wait" parameter. See weight_single 4777 and weight_many. 4778 4779 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate 4780 xtime_lock contention on larger systems, and/or RCU lock 4781 contention on all systems with CONFIG_MAXSMP set. 4782 Format: { "0" | "1" } 4783 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 4784 1 -- enable. 4785 Note: increases power consumption, thus should only be 4786 enabled if running jitter sensitive (HPC/RT) workloads. 4787 4788 security= [SECURITY] Choose a legacy "major" security module to 4789 enable at boot. This has been deprecated by the 4790 "lsm=" parameter. 4791 4792 selinux= [SELINUX] Disable or enable SELinux at boot time. 4793 Format: { "0" | "1" } 4794 See security/selinux/Kconfig help text. 4795 0 -- disable. 4796 1 -- enable. 4797 Default value is 1. 4798 4799 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 4800 Format: { "0" | "1" } 4801 See security/apparmor/Kconfig help text 4802 0 -- disable. 4803 1 -- enable. 4804 Default value is set via kernel config option. 4805 4806 serialnumber [BUGS=X86-32] 4807 4808 shapers= [NET] 4809 Maximal number of shapers. 4810 4811 simeth= [IA-64] 4812 simscsi= 4813 4814 slram= [HW,MTD] 4815 4816 slab_nomerge [MM] 4817 Disable merging of slabs with similar size. May be 4818 necessary if there is some reason to distinguish 4819 allocs to different slabs, especially in hardened 4820 environments where the risk of heap overflows and 4821 layout control by attackers can usually be 4822 frustrated by disabling merging. This will reduce 4823 most of the exposure of a heap attack to a single 4824 cache (risks via metadata attacks are mostly 4825 unchanged). Debug options disable merging on their 4826 own. 4827 For more information see Documentation/vm/slub.rst. 4828 4829 slab_max_order= [MM, SLAB] 4830 Determines the maximum allowed order for slabs. 4831 A high setting may cause OOMs due to memory 4832 fragmentation. Defaults to 1 for systems with 4833 more than 32MB of RAM, 0 otherwise. 4834 4835 slub_debug[=options[,slabs][;[options[,slabs]]...] [MM, SLUB] 4836 Enabling slub_debug allows one to determine the 4837 culprit if slab objects become corrupted. Enabling 4838 slub_debug can create guard zones around objects and 4839 may poison objects when not in use. Also tracks the 4840 last alloc / free. For more information see 4841 Documentation/vm/slub.rst. 4842 4843 slub_memcg_sysfs= [MM, SLUB] 4844 Determines whether to enable sysfs directories for 4845 memory cgroup sub-caches. 1 to enable, 0 to disable. 4846 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON. 4847 Enabling this can lead to a very high number of debug 4848 directories and files being created under 4849 /sys/kernel/slub. 4850 4851 slub_max_order= [MM, SLUB] 4852 Determines the maximum allowed order for slabs. 4853 A high setting may cause OOMs due to memory 4854 fragmentation. For more information see 4855 Documentation/vm/slub.rst. 4856 4857 slub_min_objects= [MM, SLUB] 4858 The minimum number of objects per slab. SLUB will 4859 increase the slab order up to slub_max_order to 4860 generate a sufficiently large slab able to contain 4861 the number of objects indicated. The higher the number 4862 of objects the smaller the overhead of tracking slabs 4863 and the less frequently locks need to be acquired. 4864 For more information see Documentation/vm/slub.rst. 4865 4866 slub_min_order= [MM, SLUB] 4867 Determines the minimum page order for slabs. Must be 4868 lower than slub_max_order. 4869 For more information see Documentation/vm/slub.rst. 4870 4871 slub_nomerge [MM, SLUB] 4872 Same with slab_nomerge. This is supported for legacy. 4873 See slab_nomerge for more information. 4874 4875 smart2= [HW] 4876 Format: <io1>[,<io2>[,...,<io8>]] 4877 4878 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 4879 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 4880 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 4881 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 4882 smsc-ircc2.ircc_irq= [HW] IRQ line 4883 smsc-ircc2.ircc_dma= [HW] DMA channel 4884 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 4885 0: Toshiba Satellite 1800 (GP data pin select) 4886 1: Fast pin select (default) 4887 2: ATC IRMode 4888 4889 smt [KNL,S390] Set the maximum number of threads (logical 4890 CPUs) to use per physical CPU on systems capable of 4891 symmetric multithreading (SMT). Will be capped to the 4892 actual hardware limit. 4893 Format: <integer> 4894 Default: -1 (no limit) 4895 4896 softlockup_panic= 4897 [KNL] Should the soft-lockup detector generate panics. 4898 Format: 0 | 1 4899 4900 A value of 1 instructs the soft-lockup detector 4901 to panic the machine when a soft-lockup occurs. It is 4902 also controlled by the kernel.softlockup_panic sysctl 4903 and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the 4904 respective build-time switch to that functionality. 4905 4906 softlockup_all_cpu_backtrace= 4907 [KNL] Should the soft-lockup detector generate 4908 backtraces on all cpus. 4909 Format: 0 | 1 4910 4911 sonypi.*= [HW] Sony Programmable I/O Control Device driver 4912 See Documentation/admin-guide/laptops/sonypi.rst 4913 4914 spectre_v2= [X86] Control mitigation of Spectre variant 2 4915 (indirect branch speculation) vulnerability. 4916 The default operation protects the kernel from 4917 user space attacks. 4918 4919 on - unconditionally enable, implies 4920 spectre_v2_user=on 4921 off - unconditionally disable, implies 4922 spectre_v2_user=off 4923 auto - kernel detects whether your CPU model is 4924 vulnerable 4925 4926 Selecting 'on' will, and 'auto' may, choose a 4927 mitigation method at run time according to the 4928 CPU, the available microcode, the setting of the 4929 CONFIG_RETPOLINE configuration option, and the 4930 compiler with which the kernel was built. 4931 4932 Selecting 'on' will also enable the mitigation 4933 against user space to user space task attacks. 4934 4935 Selecting 'off' will disable both the kernel and 4936 the user space protections. 4937 4938 Specific mitigations can also be selected manually: 4939 4940 retpoline - replace indirect branches 4941 retpoline,generic - google's original retpoline 4942 retpoline,amd - AMD-specific minimal thunk 4943 4944 Not specifying this option is equivalent to 4945 spectre_v2=auto. 4946 4947 spectre_v2_user= 4948 [X86] Control mitigation of Spectre variant 2 4949 (indirect branch speculation) vulnerability between 4950 user space tasks 4951 4952 on - Unconditionally enable mitigations. Is 4953 enforced by spectre_v2=on 4954 4955 off - Unconditionally disable mitigations. Is 4956 enforced by spectre_v2=off 4957 4958 prctl - Indirect branch speculation is enabled, 4959 but mitigation can be enabled via prctl 4960 per thread. The mitigation control state 4961 is inherited on fork. 4962 4963 prctl,ibpb 4964 - Like "prctl" above, but only STIBP is 4965 controlled per thread. IBPB is issued 4966 always when switching between different user 4967 space processes. 4968 4969 seccomp 4970 - Same as "prctl" above, but all seccomp 4971 threads will enable the mitigation unless 4972 they explicitly opt out. 4973 4974 seccomp,ibpb 4975 - Like "seccomp" above, but only STIBP is 4976 controlled per thread. IBPB is issued 4977 always when switching between different 4978 user space processes. 4979 4980 auto - Kernel selects the mitigation depending on 4981 the available CPU features and vulnerability. 4982 4983 Default mitigation: 4984 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl" 4985 4986 Not specifying this option is equivalent to 4987 spectre_v2_user=auto. 4988 4989 spec_store_bypass_disable= 4990 [HW] Control Speculative Store Bypass (SSB) Disable mitigation 4991 (Speculative Store Bypass vulnerability) 4992 4993 Certain CPUs are vulnerable to an exploit against a 4994 a common industry wide performance optimization known 4995 as "Speculative Store Bypass" in which recent stores 4996 to the same memory location may not be observed by 4997 later loads during speculative execution. The idea 4998 is that such stores are unlikely and that they can 4999 be detected prior to instruction retirement at the 5000 end of a particular speculation execution window. 5001 5002 In vulnerable processors, the speculatively forwarded 5003 store can be used in a cache side channel attack, for 5004 example to read memory to which the attacker does not 5005 directly have access (e.g. inside sandboxed code). 5006 5007 This parameter controls whether the Speculative Store 5008 Bypass optimization is used. 5009 5010 On x86 the options are: 5011 5012 on - Unconditionally disable Speculative Store Bypass 5013 off - Unconditionally enable Speculative Store Bypass 5014 auto - Kernel detects whether the CPU model contains an 5015 implementation of Speculative Store Bypass and 5016 picks the most appropriate mitigation. If the 5017 CPU is not vulnerable, "off" is selected. If the 5018 CPU is vulnerable the default mitigation is 5019 architecture and Kconfig dependent. See below. 5020 prctl - Control Speculative Store Bypass per thread 5021 via prctl. Speculative Store Bypass is enabled 5022 for a process by default. The state of the control 5023 is inherited on fork. 5024 seccomp - Same as "prctl" above, but all seccomp threads 5025 will disable SSB unless they explicitly opt out. 5026 5027 Default mitigations: 5028 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl" 5029 5030 On powerpc the options are: 5031 5032 on,auto - On Power8 and Power9 insert a store-forwarding 5033 barrier on kernel entry and exit. On Power7 5034 perform a software flush on kernel entry and 5035 exit. 5036 off - No action. 5037 5038 Not specifying this option is equivalent to 5039 spec_store_bypass_disable=auto. 5040 5041 spia_io_base= [HW,MTD] 5042 spia_fio_base= 5043 spia_pedr= 5044 spia_peddr= 5045 5046 split_lock_detect= 5047 [X86] Enable split lock detection 5048 5049 When enabled (and if hardware support is present), atomic 5050 instructions that access data across cache line 5051 boundaries will result in an alignment check exception. 5052 5053 off - not enabled 5054 5055 warn - the kernel will emit rate limited warnings 5056 about applications triggering the #AC 5057 exception. This mode is the default on CPUs 5058 that supports split lock detection. 5059 5060 fatal - the kernel will send SIGBUS to applications 5061 that trigger the #AC exception. 5062 5063 If an #AC exception is hit in the kernel or in 5064 firmware (i.e. not while executing in user mode) 5065 the kernel will oops in either "warn" or "fatal" 5066 mode. 5067 5068 srbds= [X86,INTEL] 5069 Control the Special Register Buffer Data Sampling 5070 (SRBDS) mitigation. 5071 5072 Certain CPUs are vulnerable to an MDS-like 5073 exploit which can leak bits from the random 5074 number generator. 5075 5076 By default, this issue is mitigated by 5077 microcode. However, the microcode fix can cause 5078 the RDRAND and RDSEED instructions to become 5079 much slower. Among other effects, this will 5080 result in reduced throughput from /dev/urandom. 5081 5082 The microcode mitigation can be disabled with 5083 the following option: 5084 5085 off: Disable mitigation and remove 5086 performance impact to RDRAND and RDSEED 5087 5088 srcutree.counter_wrap_check [KNL] 5089 Specifies how frequently to check for 5090 grace-period sequence counter wrap for the 5091 srcu_data structure's ->srcu_gp_seq_needed field. 5092 The greater the number of bits set in this kernel 5093 parameter, the less frequently counter wrap will 5094 be checked for. Note that the bottom two bits 5095 are ignored. 5096 5097 srcutree.exp_holdoff [KNL] 5098 Specifies how many nanoseconds must elapse 5099 since the end of the last SRCU grace period for 5100 a given srcu_struct until the next normal SRCU 5101 grace period will be considered for automatic 5102 expediting. Set to zero to disable automatic 5103 expediting. 5104 5105 ssbd= [ARM64,HW] 5106 Speculative Store Bypass Disable control 5107 5108 On CPUs that are vulnerable to the Speculative 5109 Store Bypass vulnerability and offer a 5110 firmware based mitigation, this parameter 5111 indicates how the mitigation should be used: 5112 5113 force-on: Unconditionally enable mitigation for 5114 for both kernel and userspace 5115 force-off: Unconditionally disable mitigation for 5116 for both kernel and userspace 5117 kernel: Always enable mitigation in the 5118 kernel, and offer a prctl interface 5119 to allow userspace to register its 5120 interest in being mitigated too. 5121 5122 stack_guard_gap= [MM] 5123 override the default stack gap protection. The value 5124 is in page units and it defines how many pages prior 5125 to (for stacks growing down) resp. after (for stacks 5126 growing up) the main stack are reserved for no other 5127 mapping. Default value is 256 pages. 5128 5129 stacktrace [FTRACE] 5130 Enabled the stack tracer on boot up. 5131 5132 stacktrace_filter=[function-list] 5133 [FTRACE] Limit the functions that the stack tracer 5134 will trace at boot up. function-list is a comma separated 5135 list of functions. This list can be changed at run 5136 time by the stack_trace_filter file in the debugfs 5137 tracing directory. Note, this enables stack tracing 5138 and the stacktrace above is not needed. 5139 5140 sti= [PARISC,HW] 5141 Format: <num> 5142 Set the STI (builtin display/keyboard on the HP-PARISC 5143 machines) console (graphic card) which should be used 5144 as the initial boot-console. 5145 See also comment in drivers/video/console/sticore.c. 5146 5147 sti_font= [HW] 5148 See comment in drivers/video/console/sticore.c. 5149 5150 stifb= [HW] 5151 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 5152 5153 sunrpc.min_resvport= 5154 sunrpc.max_resvport= 5155 [NFS,SUNRPC] 5156 SunRPC servers often require that client requests 5157 originate from a privileged port (i.e. a port in the 5158 range 0 < portnr < 1024). 5159 An administrator who wishes to reserve some of these 5160 ports for other uses may adjust the range that the 5161 kernel's sunrpc client considers to be privileged 5162 using these two parameters to set the minimum and 5163 maximum port values. 5164 5165 sunrpc.svc_rpc_per_connection_limit= 5166 [NFS,SUNRPC] 5167 Limit the number of requests that the server will 5168 process in parallel from a single connection. 5169 The default value is 0 (no limit). 5170 5171 sunrpc.pool_mode= 5172 [NFS] 5173 Control how the NFS server code allocates CPUs to 5174 service thread pools. Depending on how many NICs 5175 you have and where their interrupts are bound, this 5176 option will affect which CPUs will do NFS serving. 5177 Note: this parameter cannot be changed while the 5178 NFS server is running. 5179 5180 auto the server chooses an appropriate mode 5181 automatically using heuristics 5182 global a single global pool contains all CPUs 5183 percpu one pool for each CPU 5184 pernode one pool for each NUMA node (equivalent 5185 to global on non-NUMA machines) 5186 5187 sunrpc.tcp_slot_table_entries= 5188 sunrpc.udp_slot_table_entries= 5189 [NFS,SUNRPC] 5190 Sets the upper limit on the number of simultaneous 5191 RPC calls that can be sent from the client to a 5192 server. Increasing these values may allow you to 5193 improve throughput, but will also increase the 5194 amount of memory reserved for use by the client. 5195 5196 suspend.pm_test_delay= 5197 [SUSPEND] 5198 Sets the number of seconds to remain in a suspend test 5199 mode before resuming the system (see 5200 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 5201 is set. Default value is 5. 5202 5203 svm= [PPC] 5204 Format: { on | off | y | n | 1 | 0 } 5205 This parameter controls use of the Protected 5206 Execution Facility on pSeries. 5207 5208 swapaccount=[0|1] 5209 [KNL] Enable accounting of swap in memory resource 5210 controller if no parameter or 1 is given or disable 5211 it if 0 is given (See Documentation/admin-guide/cgroup-v1/memory.rst) 5212 5213 swiotlb= [ARM,IA-64,PPC,MIPS,X86] 5214 Format: { <int> | force | noforce } 5215 <int> -- Number of I/O TLB slabs 5216 force -- force using of bounce buffers even if they 5217 wouldn't be automatically used by the kernel 5218 noforce -- Never use bounce buffers (for debugging) 5219 5220 switches= [HW,M68k] 5221 5222 sysctl.*= [KNL] 5223 Set a sysctl parameter, right before loading the init 5224 process, as if the value was written to the respective 5225 /proc/sys/... file. Both '.' and '/' are recognized as 5226 separators. Unrecognized parameters and invalid values 5227 are reported in the kernel log. Sysctls registered 5228 later by a loaded module cannot be set this way. 5229 Example: sysctl.vm.swappiness=40 5230 5231 sysfs.deprecated=0|1 [KNL] 5232 Enable/disable old style sysfs layout for old udev 5233 on older distributions. When this option is enabled 5234 very new udev will not work anymore. When this option 5235 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled) 5236 in older udev will not work anymore. 5237 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in 5238 the kernel configuration. 5239 5240 sysrq_always_enabled 5241 [KNL] 5242 Ignore sysrq setting - this boot parameter will 5243 neutralize any effect of /proc/sys/kernel/sysrq. 5244 Useful for debugging. 5245 5246 tcpmhash_entries= [KNL,NET] 5247 Set the number of tcp_metrics_hash slots. 5248 Default value is 8192 or 16384 depending on total 5249 ram pages. This is used to specify the TCP metrics 5250 cache size. See Documentation/networking/ip-sysctl.rst 5251 "tcp_no_metrics_save" section for more details. 5252 5253 tdfx= [HW,DRM] 5254 5255 test_suspend= [SUSPEND][,N] 5256 Specify "mem" (for Suspend-to-RAM) or "standby" (for 5257 standby suspend) or "freeze" (for suspend type freeze) 5258 as the system sleep state during system startup with 5259 the optional capability to repeat N number of times. 5260 The system is woken from this state using a 5261 wakeup-capable RTC alarm. 5262 5263 thash_entries= [KNL,NET] 5264 Set number of hash buckets for TCP connection 5265 5266 thermal.act= [HW,ACPI] 5267 -1: disable all active trip points in all thermal zones 5268 <degrees C>: override all lowest active trip points 5269 5270 thermal.crt= [HW,ACPI] 5271 -1: disable all critical trip points in all thermal zones 5272 <degrees C>: override all critical trip points 5273 5274 thermal.nocrt= [HW,ACPI] 5275 Set to disable actions on ACPI thermal zone 5276 critical and hot trip points. 5277 5278 thermal.off= [HW,ACPI] 5279 1: disable ACPI thermal control 5280 5281 thermal.psv= [HW,ACPI] 5282 -1: disable all passive trip points 5283 <degrees C>: override all passive trip points to this 5284 value 5285 5286 thermal.tzp= [HW,ACPI] 5287 Specify global default ACPI thermal zone polling rate 5288 <deci-seconds>: poll all this frequency 5289 0: no polling (default) 5290 5291 threadirqs [KNL] 5292 Force threading of all interrupt handlers except those 5293 marked explicitly IRQF_NO_THREAD. 5294 5295 topology= [S390] 5296 Format: {off | on} 5297 Specify if the kernel should make use of the cpu 5298 topology information if the hardware supports this. 5299 The scheduler will make use of this information and 5300 e.g. base its process migration decisions on it. 5301 Default is on. 5302 5303 topology_updates= [KNL, PPC, NUMA] 5304 Format: {off} 5305 Specify if the kernel should ignore (off) 5306 topology updates sent by the hypervisor to this 5307 LPAR. 5308 5309 torture.disable_onoff_at_boot= [KNL] 5310 Prevent the CPU-hotplug component of torturing 5311 until after init has spawned. 5312 5313 torture.ftrace_dump_at_shutdown= [KNL] 5314 Dump the ftrace buffer at torture-test shutdown, 5315 even if there were no errors. This can be a 5316 very costly operation when many torture tests 5317 are running concurrently, especially on systems 5318 with rotating-rust storage. 5319 5320 tp720= [HW,PS2] 5321 5322 tpm_suspend_pcr=[HW,TPM] 5323 Format: integer pcr id 5324 Specify that at suspend time, the tpm driver 5325 should extend the specified pcr with zeros, 5326 as a workaround for some chips which fail to 5327 flush the last written pcr on TPM_SaveState. 5328 This will guarantee that all the other pcrs 5329 are saved. 5330 5331 trace_buf_size=nn[KMG] 5332 [FTRACE] will set tracing buffer size on each cpu. 5333 5334 trace_event=[event-list] 5335 [FTRACE] Set and start specified trace events in order 5336 to facilitate early boot debugging. The event-list is a 5337 comma separated list of trace events to enable. See 5338 also Documentation/trace/events.rst 5339 5340 trace_options=[option-list] 5341 [FTRACE] Enable or disable tracer options at boot. 5342 The option-list is a comma delimited list of options 5343 that can be enabled or disabled just as if you were 5344 to echo the option name into 5345 5346 /sys/kernel/debug/tracing/trace_options 5347 5348 For example, to enable stacktrace option (to dump the 5349 stack trace of each event), add to the command line: 5350 5351 trace_options=stacktrace 5352 5353 See also Documentation/trace/ftrace.rst "trace options" 5354 section. 5355 5356 tp_printk[FTRACE] 5357 Have the tracepoints sent to printk as well as the 5358 tracing ring buffer. This is useful for early boot up 5359 where the system hangs or reboots and does not give the 5360 option for reading the tracing buffer or performing a 5361 ftrace_dump_on_oops. 5362 5363 To turn off having tracepoints sent to printk, 5364 echo 0 > /proc/sys/kernel/tracepoint_printk 5365 Note, echoing 1 into this file without the 5366 tracepoint_printk kernel cmdline option has no effect. 5367 5368 ** CAUTION ** 5369 5370 Having tracepoints sent to printk() and activating high 5371 frequency tracepoints such as irq or sched, can cause 5372 the system to live lock. 5373 5374 traceoff_on_warning 5375 [FTRACE] enable this option to disable tracing when a 5376 warning is hit. This turns off "tracing_on". Tracing can 5377 be enabled again by echoing '1' into the "tracing_on" 5378 file located in /sys/kernel/debug/tracing/ 5379 5380 This option is useful, as it disables the trace before 5381 the WARNING dump is called, which prevents the trace to 5382 be filled with content caused by the warning output. 5383 5384 This option can also be set at run time via the sysctl 5385 option: kernel/traceoff_on_warning 5386 5387 transparent_hugepage= 5388 [KNL] 5389 Format: [always|madvise|never] 5390 Can be used to control the default behavior of the system 5391 with respect to transparent hugepages. 5392 See Documentation/admin-guide/mm/transhuge.rst 5393 for more details. 5394 5395 tsc= Disable clocksource stability checks for TSC. 5396 Format: <string> 5397 [x86] reliable: mark tsc clocksource as reliable, this 5398 disables clocksource verification at runtime, as well 5399 as the stability checks done at bootup. Used to enable 5400 high-resolution timer mode on older hardware, and in 5401 virtualized environment. 5402 [x86] noirqtime: Do not use TSC to do irq accounting. 5403 Used to run time disable IRQ_TIME_ACCOUNTING on any 5404 platforms where RDTSC is slow and this accounting 5405 can add overhead. 5406 [x86] unstable: mark the TSC clocksource as unstable, this 5407 marks the TSC unconditionally unstable at bootup and 5408 avoids any further wobbles once the TSC watchdog notices. 5409 [x86] nowatchdog: disable clocksource watchdog. Used 5410 in situations with strict latency requirements (where 5411 interruptions from clocksource watchdog are not 5412 acceptable). 5413 5414 tsc_early_khz= [X86] Skip early TSC calibration and use the given 5415 value instead. Useful when the early TSC frequency discovery 5416 procedure is not reliable, such as on overclocked systems 5417 with CPUID.16h support and partial CPUID.15h support. 5418 Format: <unsigned int> 5419 5420 tsx= [X86] Control Transactional Synchronization 5421 Extensions (TSX) feature in Intel processors that 5422 support TSX control. 5423 5424 This parameter controls the TSX feature. The options are: 5425 5426 on - Enable TSX on the system. Although there are 5427 mitigations for all known security vulnerabilities, 5428 TSX has been known to be an accelerator for 5429 several previous speculation-related CVEs, and 5430 so there may be unknown security risks associated 5431 with leaving it enabled. 5432 5433 off - Disable TSX on the system. (Note that this 5434 option takes effect only on newer CPUs which are 5435 not vulnerable to MDS, i.e., have 5436 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get 5437 the new IA32_TSX_CTRL MSR through a microcode 5438 update. This new MSR allows for the reliable 5439 deactivation of the TSX functionality.) 5440 5441 auto - Disable TSX if X86_BUG_TAA is present, 5442 otherwise enable TSX on the system. 5443 5444 Not specifying this option is equivalent to tsx=off. 5445 5446 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 5447 for more details. 5448 5449 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async 5450 Abort (TAA) vulnerability. 5451 5452 Similar to Micro-architectural Data Sampling (MDS) 5453 certain CPUs that support Transactional 5454 Synchronization Extensions (TSX) are vulnerable to an 5455 exploit against CPU internal buffers which can forward 5456 information to a disclosure gadget under certain 5457 conditions. 5458 5459 In vulnerable processors, the speculatively forwarded 5460 data can be used in a cache side channel attack, to 5461 access data to which the attacker does not have direct 5462 access. 5463 5464 This parameter controls the TAA mitigation. The 5465 options are: 5466 5467 full - Enable TAA mitigation on vulnerable CPUs 5468 if TSX is enabled. 5469 5470 full,nosmt - Enable TAA mitigation and disable SMT on 5471 vulnerable CPUs. If TSX is disabled, SMT 5472 is not disabled because CPU is not 5473 vulnerable to cross-thread TAA attacks. 5474 off - Unconditionally disable TAA mitigation 5475 5476 On MDS-affected machines, tsx_async_abort=off can be 5477 prevented by an active MDS mitigation as both vulnerabilities 5478 are mitigated with the same mechanism so in order to disable 5479 this mitigation, you need to specify mds=off too. 5480 5481 Not specifying this option is equivalent to 5482 tsx_async_abort=full. On CPUs which are MDS affected 5483 and deploy MDS mitigation, TAA mitigation is not 5484 required and doesn't provide any additional 5485 mitigation. 5486 5487 For details see: 5488 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 5489 5490 turbografx.map[2|3]= [HW,JOY] 5491 TurboGraFX parallel port interface 5492 Format: 5493 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 5494 See also Documentation/input/devices/joystick-parport.rst 5495 5496 udbg-immortal [PPC] When debugging early kernel crashes that 5497 happen after console_init() and before a proper 5498 console driver takes over, this boot options might 5499 help "seeing" what's going on. 5500 5501 uhash_entries= [KNL,NET] 5502 Set number of hash buckets for UDP/UDP-Lite connections 5503 5504 uhci-hcd.ignore_oc= 5505 [USB] Ignore overcurrent events (default N). 5506 Some badly-designed motherboards generate lots of 5507 bogus events, for ports that aren't wired to 5508 anything. Set this parameter to avoid log spamming. 5509 Note that genuine overcurrent events won't be 5510 reported either. 5511 5512 unknown_nmi_panic 5513 [X86] Cause panic on unknown NMI. 5514 5515 usbcore.authorized_default= 5516 [USB] Default USB device authorization: 5517 (default -1 = authorized except for wireless USB, 5518 0 = not authorized, 1 = authorized, 2 = authorized 5519 if device connected to internal port) 5520 5521 usbcore.autosuspend= 5522 [USB] The autosuspend time delay (in seconds) used 5523 for newly-detected USB devices (default 2). This 5524 is the time required before an idle device will be 5525 autosuspended. Devices for which the delay is set 5526 to a negative value won't be autosuspended at all. 5527 5528 usbcore.usbfs_snoop= 5529 [USB] Set to log all usbfs traffic (default 0 = off). 5530 5531 usbcore.usbfs_snoop_max= 5532 [USB] Maximum number of bytes to snoop in each URB 5533 (default = 65536). 5534 5535 usbcore.blinkenlights= 5536 [USB] Set to cycle leds on hubs (default 0 = off). 5537 5538 usbcore.old_scheme_first= 5539 [USB] Start with the old device initialization 5540 scheme (default 0 = off). 5541 5542 usbcore.usbfs_memory_mb= 5543 [USB] Memory limit (in MB) for buffers allocated by 5544 usbfs (default = 16, 0 = max = 2047). 5545 5546 usbcore.use_both_schemes= 5547 [USB] Try the other device initialization scheme 5548 if the first one fails (default 1 = enabled). 5549 5550 usbcore.initial_descriptor_timeout= 5551 [USB] Specifies timeout for the initial 64-byte 5552 USB_REQ_GET_DESCRIPTOR request in milliseconds 5553 (default 5000 = 5.0 seconds). 5554 5555 usbcore.nousb [USB] Disable the USB subsystem 5556 5557 usbcore.quirks= 5558 [USB] A list of quirk entries to augment the built-in 5559 usb core quirk list. List entries are separated by 5560 commas. Each entry has the form 5561 VendorID:ProductID:Flags. The IDs are 4-digit hex 5562 numbers and Flags is a set of letters. Each letter 5563 will change the built-in quirk; setting it if it is 5564 clear and clearing it if it is set. The letters have 5565 the following meanings: 5566 a = USB_QUIRK_STRING_FETCH_255 (string 5567 descriptors must not be fetched using 5568 a 255-byte read); 5569 b = USB_QUIRK_RESET_RESUME (device can't resume 5570 correctly so reset it instead); 5571 c = USB_QUIRK_NO_SET_INTF (device can't handle 5572 Set-Interface requests); 5573 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't 5574 handle its Configuration or Interface 5575 strings); 5576 e = USB_QUIRK_RESET (device can't be reset 5577 (e.g morph devices), don't use reset); 5578 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has 5579 more interface descriptions than the 5580 bNumInterfaces count, and can't handle 5581 talking to these interfaces); 5582 g = USB_QUIRK_DELAY_INIT (device needs a pause 5583 during initialization, after we read 5584 the device descriptor); 5585 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For 5586 high speed and super speed interrupt 5587 endpoints, the USB 2.0 and USB 3.0 spec 5588 require the interval in microframes (1 5589 microframe = 125 microseconds) to be 5590 calculated as interval = 2 ^ 5591 (bInterval-1). 5592 Devices with this quirk report their 5593 bInterval as the result of this 5594 calculation instead of the exponent 5595 variable used in the calculation); 5596 i = USB_QUIRK_DEVICE_QUALIFIER (device can't 5597 handle device_qualifier descriptor 5598 requests); 5599 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device 5600 generates spurious wakeup, ignore 5601 remote wakeup capability); 5602 k = USB_QUIRK_NO_LPM (device can't handle Link 5603 Power Management); 5604 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL 5605 (Device reports its bInterval as linear 5606 frames instead of the USB 2.0 5607 calculation); 5608 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs 5609 to be disconnected before suspend to 5610 prevent spurious wakeup); 5611 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a 5612 pause after every control message); 5613 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra 5614 delay after resetting its port); 5615 Example: quirks=0781:5580:bk,0a5c:5834:gij 5616 5617 usbhid.mousepoll= 5618 [USBHID] The interval which mice are to be polled at. 5619 5620 usbhid.jspoll= 5621 [USBHID] The interval which joysticks are to be polled at. 5622 5623 usbhid.kbpoll= 5624 [USBHID] The interval which keyboards are to be polled at. 5625 5626 usb-storage.delay_use= 5627 [UMS] The delay in seconds before a new device is 5628 scanned for Logical Units (default 1). 5629 5630 usb-storage.quirks= 5631 [UMS] A list of quirks entries to supplement or 5632 override the built-in unusual_devs list. List 5633 entries are separated by commas. Each entry has 5634 the form VID:PID:Flags where VID and PID are Vendor 5635 and Product ID values (4-digit hex numbers) and 5636 Flags is a set of characters, each corresponding 5637 to a common usb-storage quirk flag as follows: 5638 a = SANE_SENSE (collect more than 18 bytes 5639 of sense data, not on uas); 5640 b = BAD_SENSE (don't collect more than 18 5641 bytes of sense data, not on uas); 5642 c = FIX_CAPACITY (decrease the reported 5643 device capacity by one sector); 5644 d = NO_READ_DISC_INFO (don't use 5645 READ_DISC_INFO command, not on uas); 5646 e = NO_READ_CAPACITY_16 (don't use 5647 READ_CAPACITY_16 command); 5648 f = NO_REPORT_OPCODES (don't use report opcodes 5649 command, uas only); 5650 g = MAX_SECTORS_240 (don't transfer more than 5651 240 sectors at a time, uas only); 5652 h = CAPACITY_HEURISTICS (decrease the 5653 reported device capacity by one 5654 sector if the number is odd); 5655 i = IGNORE_DEVICE (don't bind to this 5656 device); 5657 j = NO_REPORT_LUNS (don't use report luns 5658 command, uas only); 5659 l = NOT_LOCKABLE (don't try to lock and 5660 unlock ejectable media, not on uas); 5661 m = MAX_SECTORS_64 (don't transfer more 5662 than 64 sectors = 32 KB at a time, 5663 not on uas); 5664 n = INITIAL_READ10 (force a retry of the 5665 initial READ(10) command, not on uas); 5666 o = CAPACITY_OK (accept the capacity 5667 reported by the device, not on uas); 5668 p = WRITE_CACHE (the device cache is ON 5669 by default, not on uas); 5670 r = IGNORE_RESIDUE (the device reports 5671 bogus residue values, not on uas); 5672 s = SINGLE_LUN (the device has only one 5673 Logical Unit); 5674 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 5675 commands, uas only); 5676 u = IGNORE_UAS (don't bind to the uas driver); 5677 w = NO_WP_DETECT (don't test whether the 5678 medium is write-protected). 5679 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 5680 even if the device claims no cache, 5681 not on uas) 5682 Example: quirks=0419:aaf5:rl,0421:0433:rc 5683 5684 user_debug= [KNL,ARM] 5685 Format: <int> 5686 See arch/arm/Kconfig.debug help text. 5687 1 - undefined instruction events 5688 2 - system calls 5689 4 - invalid data aborts 5690 8 - SIGSEGV faults 5691 16 - SIGBUS faults 5692 Example: user_debug=31 5693 5694 userpte= 5695 [X86] Flags controlling user PTE allocations. 5696 5697 nohigh = do not allocate PTE pages in 5698 HIGHMEM regardless of setting 5699 of CONFIG_HIGHPTE. 5700 5701 vdso= [X86,SH] 5702 On X86_32, this is an alias for vdso32=. Otherwise: 5703 5704 vdso=1: enable VDSO (the default) 5705 vdso=0: disable VDSO mapping 5706 5707 vdso32= [X86] Control the 32-bit vDSO 5708 vdso32=1: enable 32-bit VDSO 5709 vdso32=0 or vdso32=2: disable 32-bit VDSO 5710 5711 See the help text for CONFIG_COMPAT_VDSO for more 5712 details. If CONFIG_COMPAT_VDSO is set, the default is 5713 vdso32=0; otherwise, the default is vdso32=1. 5714 5715 For compatibility with older kernels, vdso32=2 is an 5716 alias for vdso32=0. 5717 5718 Try vdso32=0 if you encounter an error that says: 5719 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 5720 5721 vector= [IA-64,SMP] 5722 vector=percpu: enable percpu vector domain 5723 5724 video= [FB] Frame buffer configuration 5725 See Documentation/fb/modedb.rst. 5726 5727 video.brightness_switch_enabled= [0,1] 5728 If set to 1, on receiving an ACPI notify event 5729 generated by hotkey, video driver will adjust brightness 5730 level and then send out the event to user space through 5731 the allocated input device; If set to 0, video driver 5732 will only send out the event without touching backlight 5733 brightness level. 5734 default: 1 5735 5736 virtio_mmio.device= 5737 [VMMIO] Memory mapped virtio (platform) device. 5738 5739 <size>@<baseaddr>:<irq>[:<id>] 5740 where: 5741 <size> := size (can use standard suffixes 5742 like K, M and G) 5743 <baseaddr> := physical base address 5744 <irq> := interrupt number (as passed to 5745 request_irq()) 5746 <id> := (optional) platform device id 5747 example: 5748 virtio_mmio.device=1K@0x100b0000:48:7 5749 5750 Can be used multiple times for multiple devices. 5751 5752 vga= [BOOT,X86-32] Select a particular video mode 5753 See Documentation/x86/boot.rst and 5754 Documentation/admin-guide/svga.rst. 5755 Use vga=ask for menu. 5756 This is actually a boot loader parameter; the value is 5757 passed to the kernel using a special protocol. 5758 5759 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. 5760 May slow down system boot speed, especially when 5761 enabled on systems with a large amount of memory. 5762 All options are enabled by default, and this 5763 interface is meant to allow for selectively 5764 enabling or disabling specific virtual memory 5765 debugging features. 5766 5767 Available options are: 5768 P Enable page structure init time poisoning 5769 - Disable all of the above options 5770 5771 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact 5772 size of <nn>. This can be used to increase the 5773 minimum size (128MB on x86). It can also be used to 5774 decrease the size and leave more room for directly 5775 mapped kernel RAM. 5776 5777 vmcp_cma=nn[MG] [KNL,S390] 5778 Sets the memory size reserved for contiguous memory 5779 allocations for the vmcp device driver. 5780 5781 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 5782 Format: <command> 5783 5784 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 5785 Format: <command> 5786 5787 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 5788 Format: <command> 5789 5790 vsyscall= [X86-64] 5791 Controls the behavior of vsyscalls (i.e. calls to 5792 fixed addresses of 0xffffffffff600x00 from legacy 5793 code). Most statically-linked binaries and older 5794 versions of glibc use these calls. Because these 5795 functions are at fixed addresses, they make nice 5796 targets for exploits that can control RIP. 5797 5798 emulate [default] Vsyscalls turn into traps and are 5799 emulated reasonably safely. The vsyscall 5800 page is readable. 5801 5802 xonly Vsyscalls turn into traps and are 5803 emulated reasonably safely. The vsyscall 5804 page is not readable. 5805 5806 none Vsyscalls don't work at all. This makes 5807 them quite hard to use for exploits but 5808 might break your system. 5809 5810 vt.color= [VT] Default text color. 5811 Format: 0xYX, X = foreground, Y = background. 5812 Default: 0x07 = light gray on black. 5813 5814 vt.cur_default= [VT] Default cursor shape. 5815 Format: 0xCCBBAA, where AA, BB, and CC are the same as 5816 the parameters of the <Esc>[?A;B;Cc escape sequence; 5817 see VGA-softcursor.txt. Default: 2 = underline. 5818 5819 vt.default_blu= [VT] 5820 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 5821 Change the default blue palette of the console. 5822 This is a 16-member array composed of values 5823 ranging from 0-255. 5824 5825 vt.default_grn= [VT] 5826 Format: <green0>,<green1>,<green2>,...,<green15> 5827 Change the default green palette of the console. 5828 This is a 16-member array composed of values 5829 ranging from 0-255. 5830 5831 vt.default_red= [VT] 5832 Format: <red0>,<red1>,<red2>,...,<red15> 5833 Change the default red palette of the console. 5834 This is a 16-member array composed of values 5835 ranging from 0-255. 5836 5837 vt.default_utf8= 5838 [VT] 5839 Format=<0|1> 5840 Set system-wide default UTF-8 mode for all tty's. 5841 Default is 1, i.e. UTF-8 mode is enabled for all 5842 newly opened terminals. 5843 5844 vt.global_cursor_default= 5845 [VT] 5846 Format=<-1|0|1> 5847 Set system-wide default for whether a cursor 5848 is shown on new VTs. Default is -1, 5849 i.e. cursors will be created by default unless 5850 overridden by individual drivers. 0 will hide 5851 cursors, 1 will display them. 5852 5853 vt.italic= [VT] Default color for italic text; 0-15. 5854 Default: 2 = green. 5855 5856 vt.underline= [VT] Default color for underlined text; 0-15. 5857 Default: 3 = cyan. 5858 5859 watchdog timers [HW,WDT] For information on watchdog timers, 5860 see Documentation/watchdog/watchdog-parameters.rst 5861 or other driver-specific files in the 5862 Documentation/watchdog/ directory. 5863 5864 watchdog_thresh= 5865 [KNL] 5866 Set the hard lockup detector stall duration 5867 threshold in seconds. The soft lockup detector 5868 threshold is set to twice the value. A value of 0 5869 disables both lockup detectors. Default is 10 5870 seconds. 5871 5872 workqueue.watchdog_thresh= 5873 If CONFIG_WQ_WATCHDOG is configured, workqueue can 5874 warn stall conditions and dump internal state to 5875 help debugging. 0 disables workqueue stall 5876 detection; otherwise, it's the stall threshold 5877 duration in seconds. The default value is 30 and 5878 it can be updated at runtime by writing to the 5879 corresponding sysfs file. 5880 5881 workqueue.disable_numa 5882 By default, all work items queued to unbound 5883 workqueues are affine to the NUMA nodes they're 5884 issued on, which results in better behavior in 5885 general. If NUMA affinity needs to be disabled for 5886 whatever reason, this option can be used. Note 5887 that this also can be controlled per-workqueue for 5888 workqueues visible under /sys/bus/workqueue/. 5889 5890 workqueue.power_efficient 5891 Per-cpu workqueues are generally preferred because 5892 they show better performance thanks to cache 5893 locality; unfortunately, per-cpu workqueues tend to 5894 be more power hungry than unbound workqueues. 5895 5896 Enabling this makes the per-cpu workqueues which 5897 were observed to contribute significantly to power 5898 consumption unbound, leading to measurably lower 5899 power usage at the cost of small performance 5900 overhead. 5901 5902 The default value of this parameter is determined by 5903 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 5904 5905 workqueue.debug_force_rr_cpu 5906 Workqueue used to implicitly guarantee that work 5907 items queued without explicit CPU specified are put 5908 on the local CPU. This guarantee is no longer true 5909 and while local CPU is still preferred work items 5910 may be put on foreign CPUs. This debug option 5911 forces round-robin CPU selection to flush out 5912 usages which depend on the now broken guarantee. 5913 When enabled, memory and cache locality will be 5914 impacted. 5915 5916 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of 5917 default x2apic cluster mode on platforms 5918 supporting x2apic. 5919 5920 x86_intel_mid_timer= [X86-32,APBT] 5921 Choose timer option for x86 Intel MID platform. 5922 Two valid options are apbt timer only and lapic timer 5923 plus one apbt timer for broadcast timer. 5924 x86_intel_mid_timer=apbt_only | lapic_and_apbt 5925 5926 xen_512gb_limit [KNL,X86-64,XEN] 5927 Restricts the kernel running paravirtualized under Xen 5928 to use only up to 512 GB of RAM. The reason to do so is 5929 crash analysis tools and Xen tools for doing domain 5930 save/restore/migration must be enabled to handle larger 5931 domains. 5932 5933 xen_emul_unplug= [HW,X86,XEN] 5934 Unplug Xen emulated devices 5935 Format: [unplug0,][unplug1] 5936 ide-disks -- unplug primary master IDE devices 5937 aux-ide-disks -- unplug non-primary-master IDE devices 5938 nics -- unplug network devices 5939 all -- unplug all emulated devices (NICs and IDE disks) 5940 unnecessary -- unplugging emulated devices is 5941 unnecessary even if the host did not respond to 5942 the unplug protocol 5943 never -- do not unplug even if version check succeeds 5944 5945 xen_legacy_crash [X86,XEN] 5946 Crash from Xen panic notifier, without executing late 5947 panic() code such as dumping handler. 5948 5949 xen_nopvspin [X86,XEN] 5950 Disables the qspinlock slowpath using Xen PV optimizations. 5951 This parameter is obsoleted by "nopvspin" parameter, which 5952 has equivalent effect for XEN platform. 5953 5954 xen_nopv [X86] 5955 Disables the PV optimizations forcing the HVM guest to 5956 run as generic HVM guest with no PV drivers. 5957 This option is obsoleted by the "nopv" option, which 5958 has equivalent effect for XEN platform. 5959 5960 xen_scrub_pages= [XEN] 5961 Boolean option to control scrubbing pages before giving them back 5962 to Xen, for use by other domains. Can be also changed at runtime 5963 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. 5964 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. 5965 5966 xen_timer_slop= [X86-64,XEN] 5967 Set the timer slop (in nanoseconds) for the virtual Xen 5968 timers (default is 100000). This adjusts the minimum 5969 delta of virtualized Xen timers, where lower values 5970 improve timer resolution at the expense of processing 5971 more timer interrupts. 5972 5973 xen.event_eoi_delay= [XEN] 5974 How long to delay EOI handling in case of event 5975 storms (jiffies). Default is 10. 5976 5977 xen.event_loop_timeout= [XEN] 5978 After which time (jiffies) the event handling loop 5979 should start to delay EOI handling. Default is 2. 5980 5981 xen.fifo_events= [XEN] 5982 Boolean parameter to disable using fifo event handling 5983 even if available. Normally fifo event handling is 5984 preferred over the 2-level event handling, as it is 5985 fairer and the number of possible event channels is 5986 much higher. Default is on (use fifo events). 5987 5988 nopv= [X86,XEN,KVM,HYPER_V,VMWARE] 5989 Disables the PV optimizations forcing the guest to run 5990 as generic guest with no PV drivers. Currently support 5991 XEN HVM, KVM, HYPER_V and VMWARE guest. 5992 5993 nopvspin [X86,XEN,KVM] 5994 Disables the qspinlock slow path using PV optimizations 5995 which allow the hypervisor to 'idle' the guest on lock 5996 contention. 5997 5998 xirc2ps_cs= [NET,PCMCIA] 5999 Format: 6000 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 6001 6002 xive= [PPC] 6003 By default on POWER9 and above, the kernel will 6004 natively use the XIVE interrupt controller. This option 6005 allows the fallback firmware mode to be used: 6006 6007 off Fallback to firmware control of XIVE interrupt 6008 controller on both pseries and powernv 6009 platforms. Only useful on POWER9 and above. 6010 6011 xhci-hcd.quirks [USB,KNL] 6012 A hex value specifying bitmask with supplemental xhci 6013 host controller quirks. Meaning of each bit can be 6014 consulted in header drivers/usb/host/xhci.h. 6015 6016 xmon [PPC] 6017 Format: { early | on | rw | ro | off } 6018 Controls if xmon debugger is enabled. Default is off. 6019 Passing only "xmon" is equivalent to "xmon=early". 6020 early Call xmon as early as possible on boot; xmon 6021 debugger is called from setup_arch(). 6022 on xmon debugger hooks will be installed so xmon 6023 is only called on a kernel crash. Default mode, 6024 i.e. either "ro" or "rw" mode, is controlled 6025 with CONFIG_XMON_DEFAULT_RO_MODE. 6026 rw xmon debugger hooks will be installed so xmon 6027 is called only on a kernel crash, mode is write, 6028 meaning SPR registers, memory and, other data 6029 can be written using xmon commands. 6030 ro same as "rw" option above but SPR registers, 6031 memory, and other data can't be written using 6032 xmon commands. 6033 off xmon is disabled. 6034