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, X86, MIPS, XTENSA] 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 no_entry_flush [PPC] 2862 no_uaccess_flush [PPC] 2863 2864 Exceptions: 2865 This does not have any effect on 2866 kvm.nx_huge_pages when 2867 kvm.nx_huge_pages=force. 2868 2869 auto (default) 2870 Mitigate all CPU vulnerabilities, but leave SMT 2871 enabled, even if it's vulnerable. This is for 2872 users who don't want to be surprised by SMT 2873 getting disabled across kernel upgrades, or who 2874 have other ways of avoiding SMT-based attacks. 2875 Equivalent to: (default behavior) 2876 2877 auto,nosmt 2878 Mitigate all CPU vulnerabilities, disabling SMT 2879 if needed. This is for users who always want to 2880 be fully mitigated, even if it means losing SMT. 2881 Equivalent to: l1tf=flush,nosmt [X86] 2882 mds=full,nosmt [X86] 2883 tsx_async_abort=full,nosmt [X86] 2884 2885 mminit_loglevel= 2886 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this 2887 parameter allows control of the logging verbosity for 2888 the additional memory initialisation checks. A value 2889 of 0 disables mminit logging and a level of 4 will 2890 log everything. Information is printed at KERN_DEBUG 2891 so loglevel=8 may also need to be specified. 2892 2893 module.sig_enforce 2894 [KNL] When CONFIG_MODULE_SIG is set, this means that 2895 modules without (valid) signatures will fail to load. 2896 Note that if CONFIG_MODULE_SIG_FORCE is set, that 2897 is always true, so this option does nothing. 2898 2899 module_blacklist= [KNL] Do not load a comma-separated list of 2900 modules. Useful for debugging problem modules. 2901 2902 mousedev.tap_time= 2903 [MOUSE] Maximum time between finger touching and 2904 leaving touchpad surface for touch to be considered 2905 a tap and be reported as a left button click (for 2906 touchpads working in absolute mode only). 2907 Format: <msecs> 2908 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 2909 reporting absolute coordinates, such as tablets 2910 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 2911 reporting absolute coordinates, such as tablets 2912 2913 movablecore= [KNL,X86,IA-64,PPC] 2914 Format: nn[KMGTPE] | nn% 2915 This parameter is the complement to kernelcore=, it 2916 specifies the amount of memory used for migratable 2917 allocations. If both kernelcore and movablecore is 2918 specified, then kernelcore will be at *least* the 2919 specified value but may be more. If movablecore on its 2920 own is specified, the administrator must be careful 2921 that the amount of memory usable for all allocations 2922 is not too small. 2923 2924 movable_node [KNL] Boot-time switch to make hotplugable memory 2925 NUMA nodes to be movable. This means that the memory 2926 of such nodes will be usable only for movable 2927 allocations which rules out almost all kernel 2928 allocations. Use with caution! 2929 2930 MTD_Partition= [MTD] 2931 Format: <name>,<region-number>,<size>,<offset> 2932 2933 MTD_Region= [MTD] Format: 2934 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 2935 2936 mtdparts= [MTD] 2937 See drivers/mtd/parsers/cmdlinepart.c 2938 2939 multitce=off [PPC] This parameter disables the use of the pSeries 2940 firmware feature for updating multiple TCE entries 2941 at a time. 2942 2943 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 2944 2945 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 2946 2947 boundary - index of last SLC block on Flex-OneNAND. 2948 The remaining blocks are configured as MLC blocks. 2949 lock - Configure if Flex-OneNAND boundary should be locked. 2950 Once locked, the boundary cannot be changed. 2951 1 indicates lock status, 0 indicates unlock status. 2952 2953 mtdset= [ARM] 2954 ARM/S3C2412 JIVE boot control 2955 2956 See arch/arm/mach-s3c2412/mach-jive.c 2957 2958 mtouchusb.raw_coordinates= 2959 [HW] Make the MicroTouch USB driver use raw coordinates 2960 ('y', default) or cooked coordinates ('n') 2961 2962 mtrr_chunk_size=nn[KMG] [X86] 2963 used for mtrr cleanup. It is largest continuous chunk 2964 that could hold holes aka. UC entries. 2965 2966 mtrr_gran_size=nn[KMG] [X86] 2967 Used for mtrr cleanup. It is granularity of mtrr block. 2968 Default is 1. 2969 Large value could prevent small alignment from 2970 using up MTRRs. 2971 2972 mtrr_spare_reg_nr=n [X86] 2973 Format: <integer> 2974 Range: 0,7 : spare reg number 2975 Default : 1 2976 Used for mtrr cleanup. It is spare mtrr entries number. 2977 Set to 2 or more if your graphical card needs more. 2978 2979 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 2980 2981 netdev= [NET] Network devices parameters 2982 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 2983 Note that mem_start is often overloaded to mean 2984 something different and driver-specific. 2985 This usage is only documented in each driver source 2986 file if at all. 2987 2988 nf_conntrack.acct= 2989 [NETFILTER] Enable connection tracking flow accounting 2990 0 to disable accounting 2991 1 to enable accounting 2992 Default value is 0. 2993 2994 nfsaddrs= [NFS] Deprecated. Use ip= instead. 2995 See Documentation/admin-guide/nfs/nfsroot.rst. 2996 2997 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 2998 See Documentation/admin-guide/nfs/nfsroot.rst. 2999 3000 nfsrootdebug [NFS] enable nfsroot debugging messages. 3001 See Documentation/admin-guide/nfs/nfsroot.rst. 3002 3003 nfs.callback_nr_threads= 3004 [NFSv4] set the total number of threads that the 3005 NFS client will assign to service NFSv4 callback 3006 requests. 3007 3008 nfs.callback_tcpport= 3009 [NFS] set the TCP port on which the NFSv4 callback 3010 channel should listen. 3011 3012 nfs.cache_getent= 3013 [NFS] sets the pathname to the program which is used 3014 to update the NFS client cache entries. 3015 3016 nfs.cache_getent_timeout= 3017 [NFS] sets the timeout after which an attempt to 3018 update a cache entry is deemed to have failed. 3019 3020 nfs.idmap_cache_timeout= 3021 [NFS] set the maximum lifetime for idmapper cache 3022 entries. 3023 3024 nfs.enable_ino64= 3025 [NFS] enable 64-bit inode numbers. 3026 If zero, the NFS client will fake up a 32-bit inode 3027 number for the readdir() and stat() syscalls instead 3028 of returning the full 64-bit number. 3029 The default is to return 64-bit inode numbers. 3030 3031 nfs.max_session_cb_slots= 3032 [NFSv4.1] Sets the maximum number of session 3033 slots the client will assign to the callback 3034 channel. This determines the maximum number of 3035 callbacks the client will process in parallel for 3036 a particular server. 3037 3038 nfs.max_session_slots= 3039 [NFSv4.1] Sets the maximum number of session slots 3040 the client will attempt to negotiate with the server. 3041 This limits the number of simultaneous RPC requests 3042 that the client can send to the NFSv4.1 server. 3043 Note that there is little point in setting this 3044 value higher than the max_tcp_slot_table_limit. 3045 3046 nfs.nfs4_disable_idmapping= 3047 [NFSv4] When set to the default of '1', this option 3048 ensures that both the RPC level authentication 3049 scheme and the NFS level operations agree to use 3050 numeric uids/gids if the mount is using the 3051 'sec=sys' security flavour. In effect it is 3052 disabling idmapping, which can make migration from 3053 legacy NFSv2/v3 systems to NFSv4 easier. 3054 Servers that do not support this mode of operation 3055 will be autodetected by the client, and it will fall 3056 back to using the idmapper. 3057 To turn off this behaviour, set the value to '0'. 3058 nfs.nfs4_unique_id= 3059 [NFS4] Specify an additional fixed unique ident- 3060 ification string that NFSv4 clients can insert into 3061 their nfs_client_id4 string. This is typically a 3062 UUID that is generated at system install time. 3063 3064 nfs.send_implementation_id = 3065 [NFSv4.1] Send client implementation identification 3066 information in exchange_id requests. 3067 If zero, no implementation identification information 3068 will be sent. 3069 The default is to send the implementation identification 3070 information. 3071 3072 nfs.recover_lost_locks = 3073 [NFSv4] Attempt to recover locks that were lost due 3074 to a lease timeout on the server. Please note that 3075 doing this risks data corruption, since there are 3076 no guarantees that the file will remain unchanged 3077 after the locks are lost. 3078 If you want to enable the kernel legacy behaviour of 3079 attempting to recover these locks, then set this 3080 parameter to '1'. 3081 The default parameter value of '0' causes the kernel 3082 not to attempt recovery of lost locks. 3083 3084 nfs4.layoutstats_timer = 3085 [NFSv4.2] Change the rate at which the kernel sends 3086 layoutstats to the pNFS metadata server. 3087 3088 Setting this to value to 0 causes the kernel to use 3089 whatever value is the default set by the layout 3090 driver. A non-zero value sets the minimum interval 3091 in seconds between layoutstats transmissions. 3092 3093 nfsd.nfs4_disable_idmapping= 3094 [NFSv4] When set to the default of '1', the NFSv4 3095 server will return only numeric uids and gids to 3096 clients using auth_sys, and will accept numeric uids 3097 and gids from such clients. This is intended to ease 3098 migration from NFSv2/v3. 3099 3100 nmi_backtrace.backtrace_idle [KNL] 3101 Dump stacks even of idle CPUs in response to an 3102 NMI stack-backtrace request. 3103 3104 nmi_debug= [KNL,SH] Specify one or more actions to take 3105 when a NMI is triggered. 3106 Format: [state][,regs][,debounce][,die] 3107 3108 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 3109 Format: [panic,][nopanic,][num] 3110 Valid num: 0 or 1 3111 0 - turn hardlockup detector in nmi_watchdog off 3112 1 - turn hardlockup detector in nmi_watchdog on 3113 When panic is specified, panic when an NMI watchdog 3114 timeout occurs (or 'nopanic' to not panic on an NMI 3115 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set) 3116 To disable both hard and soft lockup detectors, 3117 please see 'nowatchdog'. 3118 This is useful when you use a panic=... timeout and 3119 need the box quickly up again. 3120 3121 These settings can be accessed at runtime via 3122 the nmi_watchdog and hardlockup_panic sysctls. 3123 3124 netpoll.carrier_timeout= 3125 [NET] Specifies amount of time (in seconds) that 3126 netpoll should wait for a carrier. By default netpoll 3127 waits 4 seconds. 3128 3129 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 3130 emulation library even if a 387 maths coprocessor 3131 is present. 3132 3133 no5lvl [X86-64] Disable 5-level paging mode. Forces 3134 kernel to use 4-level paging instead. 3135 3136 nofsgsbase [X86] Disables FSGSBASE instructions. 3137 3138 no_console_suspend 3139 [HW] Never suspend the console 3140 Disable suspending of consoles during suspend and 3141 hibernate operations. Once disabled, debugging 3142 messages can reach various consoles while the rest 3143 of the system is being put to sleep (ie, while 3144 debugging driver suspend/resume hooks). This may 3145 not work reliably with all consoles, but is known 3146 to work with serial and VGA consoles. 3147 To facilitate more flexible debugging, we also add 3148 console_suspend, a printk module parameter to control 3149 it. Users could use console_suspend (usually 3150 /sys/module/printk/parameters/console_suspend) to 3151 turn on/off it dynamically. 3152 3153 novmcoredd [KNL,KDUMP] 3154 Disable device dump. Device dump allows drivers to 3155 append dump data to vmcore so you can collect driver 3156 specified debug info. Drivers can append the data 3157 without any limit and this data is stored in memory, 3158 so this may cause significant memory stress. Disabling 3159 device dump can help save memory but the driver debug 3160 data will be no longer available. This parameter 3161 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP 3162 is set. 3163 3164 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien 3165 caches in the slab allocator. Saves per-node memory, 3166 but will impact performance. 3167 3168 noalign [KNL,ARM] 3169 3170 noaltinstr [S390] Disables alternative instructions patching 3171 (CPU alternatives feature). 3172 3173 noapic [SMP,APIC] Tells the kernel to not make use of any 3174 IOAPICs that may be present in the system. 3175 3176 noautogroup Disable scheduler automatic task group creation. 3177 3178 nobats [PPC] Do not use BATs for mapping kernel lowmem 3179 on "Classic" PPC cores. 3180 3181 nocache [ARM] 3182 3183 noclflush [BUGS=X86] Don't use the CLFLUSH instruction 3184 3185 nodelayacct [KNL] Disable per-task delay accounting 3186 3187 nodsp [SH] Disable hardware DSP at boot time. 3188 3189 noefi Disable EFI runtime services support. 3190 3191 no_entry_flush [PPC] Don't flush the L1-D cache when entering the kernel. 3192 3193 noexec [IA-64] 3194 3195 noexec [X86] 3196 On X86-32 available only on PAE configured kernels. 3197 noexec=on: enable non-executable mappings (default) 3198 noexec=off: disable non-executable mappings 3199 3200 nosmap [X86,PPC] 3201 Disable SMAP (Supervisor Mode Access Prevention) 3202 even if it is supported by processor. 3203 3204 nosmep [X86,PPC] 3205 Disable SMEP (Supervisor Mode Execution Prevention) 3206 even if it is supported by processor. 3207 3208 noexec32 [X86-64] 3209 This affects only 32-bit executables. 3210 noexec32=on: enable non-executable mappings (default) 3211 read doesn't imply executable mappings 3212 noexec32=off: disable non-executable mappings 3213 read implies executable mappings 3214 3215 nofpu [MIPS,SH] Disable hardware FPU at boot time. 3216 3217 nofxsr [BUGS=X86-32] Disables x86 floating point extended 3218 register save and restore. The kernel will only save 3219 legacy floating-point registers on task switch. 3220 3221 nohugeiomap [KNL,X86,PPC,ARM64] Disable kernel huge I/O mappings. 3222 3223 nosmt [KNL,S390] Disable symmetric multithreading (SMT). 3224 Equivalent to smt=1. 3225 3226 [KNL,X86] Disable symmetric multithreading (SMT). 3227 nosmt=force: Force disable SMT, cannot be undone 3228 via the sysfs control file. 3229 3230 nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1 3231 (bounds check bypass). With this option data leaks are 3232 possible in the system. 3233 3234 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for 3235 the Spectre variant 2 (indirect branch prediction) 3236 vulnerability. System may allow data leaks with this 3237 option. 3238 3239 nospec_store_bypass_disable 3240 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability 3241 3242 no_uaccess_flush 3243 [PPC] Don't flush the L1-D cache after accessing user data. 3244 3245 noxsave [BUGS=X86] Disables x86 extended register state save 3246 and restore using xsave. The kernel will fallback to 3247 enabling legacy floating-point and sse state. 3248 3249 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 3250 register states. The kernel will fall back to use 3251 xsave to save the states. By using this parameter, 3252 performance of saving the states is degraded because 3253 xsave doesn't support modified optimization while 3254 xsaveopt supports it on xsaveopt enabled systems. 3255 3256 noxsaves [X86] Disables xsaves and xrstors used in saving and 3257 restoring x86 extended register state in compacted 3258 form of xsave area. The kernel will fall back to use 3259 xsaveopt and xrstor to save and restore the states 3260 in standard form of xsave area. By using this 3261 parameter, xsave area per process might occupy more 3262 memory on xsaves enabled systems. 3263 3264 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or 3265 wfi(ARM) instruction doesn't work correctly and not to 3266 use it. This is also useful when using JTAG debugger. 3267 3268 no_file_caps Tells the kernel not to honor file capabilities. The 3269 only way then for a file to be executed with privilege 3270 is to be setuid root or executed by root. 3271 3272 nohalt [IA-64] Tells the kernel not to use the power saving 3273 function PAL_HALT_LIGHT when idle. This increases 3274 power-consumption. On the positive side, it reduces 3275 interrupt wake-up latency, which may improve performance 3276 in certain environments such as networked servers or 3277 real-time systems. 3278 3279 nohibernate [HIBERNATION] Disable hibernation and resume. 3280 3281 nohz= [KNL] Boottime enable/disable dynamic ticks 3282 Valid arguments: on, off 3283 Default: on 3284 3285 nohz_full= [KNL,BOOT,SMP,ISOL] 3286 The argument is a cpu list, as described above. 3287 In kernels built with CONFIG_NO_HZ_FULL=y, set 3288 the specified list of CPUs whose tick will be stopped 3289 whenever possible. The boot CPU will be forced outside 3290 the range to maintain the timekeeping. Any CPUs 3291 in this list will have their RCU callbacks offloaded, 3292 just as if they had also been called out in the 3293 rcu_nocbs= boot parameter. 3294 3295 noiotrap [SH] Disables trapped I/O port accesses. 3296 3297 noirqdebug [X86-32] Disables the code which attempts to detect and 3298 disable unhandled interrupt sources. 3299 3300 no_timer_check [X86,APIC] Disables the code which tests for 3301 broken timer IRQ sources. 3302 3303 noisapnp [ISAPNP] Disables ISA PnP code. 3304 3305 noinitrd [RAM] Tells the kernel not to load any configured 3306 initial RAM disk. 3307 3308 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt 3309 remapping. 3310 [Deprecated - use intremap=off] 3311 3312 nointroute [IA-64] 3313 3314 noinvpcid [X86] Disable the INVPCID cpu feature. 3315 3316 nojitter [IA-64] Disables jitter checking for ITC timers. 3317 3318 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver 3319 3320 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page 3321 fault handling. 3322 3323 no-vmw-sched-clock 3324 [X86,PV_OPS] Disable paravirtualized VMware scheduler 3325 clock and use the default one. 3326 3327 no-steal-acc [X86,PV_OPS,ARM64] Disable paravirtualized steal time 3328 accounting. steal time is computed, but won't 3329 influence scheduler behaviour 3330 3331 nolapic [X86-32,APIC] Do not enable or use the local APIC. 3332 3333 nolapic_timer [X86-32,APIC] Do not use the local APIC timer. 3334 3335 noltlbs [PPC] Do not use large page/tlb entries for kernel 3336 lowmem mapping on PPC40x and PPC8xx 3337 3338 nomca [IA-64] Disable machine check abort handling 3339 3340 nomce [X86-32] Disable Machine Check Exception 3341 3342 nomfgpt [X86-32] Disable Multi-Function General Purpose 3343 Timer usage (for AMD Geode machines). 3344 3345 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 3346 shutdown the other cpus. Instead use the REBOOT_VECTOR 3347 irq. 3348 3349 nomodule Disable module load 3350 3351 nopat [X86] Disable PAT (page attribute table extension of 3352 pagetables) support. 3353 3354 nopcid [X86-64] Disable the PCID cpu feature. 3355 3356 norandmaps Don't use address space randomization. Equivalent to 3357 echo 0 > /proc/sys/kernel/randomize_va_space 3358 3359 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 3360 with UP alternatives 3361 3362 nordrand [X86] Disable kernel use of the RDRAND and 3363 RDSEED instructions even if they are supported 3364 by the processor. RDRAND and RDSEED are still 3365 available to user space applications. 3366 3367 noresume [SWSUSP] Disables resume and restores original swap 3368 space. 3369 3370 no-scroll [VGA] Disables scrollback. 3371 This is required for the Braillex ib80-piezo Braille 3372 reader made by F.H. Papenmeier (Germany). 3373 3374 nosbagart [IA-64] 3375 3376 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support. 3377 3378 nosgx [X86-64,SGX] Disables Intel SGX kernel support. 3379 3380 nosmp [SMP] Tells an SMP kernel to act as a UP kernel, 3381 and disable the IO APIC. legacy for "maxcpus=0". 3382 3383 nosoftlockup [KNL] Disable the soft-lockup detector. 3384 3385 nosync [HW,M68K] Disables sync negotiation for all devices. 3386 3387 nowatchdog [KNL] Disable both lockup detectors, i.e. 3388 soft-lockup and NMI watchdog (hard-lockup). 3389 3390 nowb [ARM] 3391 3392 nox2apic [X86-64,APIC] Do not enable x2APIC mode. 3393 3394 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when 3395 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off. 3396 Some features depend on CPU0. Known dependencies are: 3397 1. Resume from suspend/hibernate depends on CPU0. 3398 Suspend/hibernate will fail if CPU0 is offline and you 3399 need to online CPU0 before suspend/hibernate. 3400 2. PIC interrupts also depend on CPU0. CPU0 can't be 3401 removed if a PIC interrupt is detected. 3402 It's said poweroff/reboot may depend on CPU0 on some 3403 machines although I haven't seen such issues so far 3404 after CPU0 is offline on a few tested machines. 3405 If the dependencies are under your control, you can 3406 turn on cpu0_hotplug. 3407 3408 nps_mtm_hs_ctr= [KNL,ARC] 3409 This parameter sets the maximum duration, in 3410 cycles, each HW thread of the CTOP can run 3411 without interruptions, before HW switches it. 3412 The actual maximum duration is 16 times this 3413 parameter's value. 3414 Format: integer between 1 and 255 3415 Default: 255 3416 3417 nptcg= [IA-64] Override max number of concurrent global TLB 3418 purges which is reported from either PAL_VM_SUMMARY or 3419 SAL PALO. 3420 3421 nr_cpus= [SMP] Maximum number of processors that an SMP kernel 3422 could support. nr_cpus=n : n >= 1 limits the kernel to 3423 support 'n' processors. It could be larger than the 3424 number of already plugged CPU during bootup, later in 3425 runtime you can physically add extra cpu until it reaches 3426 n. So during boot up some boot time memory for per-cpu 3427 variables need be pre-allocated for later physical cpu 3428 hot plugging. 3429 3430 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 3431 3432 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing. 3433 Allowed values are enable and disable 3434 3435 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 3436 'node', 'default' can be specified 3437 This can be set from sysctl after boot. 3438 See Documentation/admin-guide/sysctl/vm.rst for details. 3439 3440 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver. 3441 See Documentation/core-api/debugging-via-ohci1394.rst for more 3442 info. 3443 3444 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 3445 Rather than timing out after 20 ms if an EC 3446 command is not properly ACKed, override the length 3447 of the timeout. We have interrupts disabled while 3448 waiting for the ACK, so if this is set too high 3449 interrupts *may* be lost! 3450 3451 omap_mux= [OMAP] Override bootloader pin multiplexing. 3452 Format: <mux_mode0.mode_name=value>... 3453 For example, to override I2C bus2: 3454 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 3455 3456 oprofile.timer= [HW] 3457 Use timer interrupt instead of performance counters 3458 3459 oprofile.cpu_type= Force an oprofile cpu type 3460 This might be useful if you have an older oprofile 3461 userland or if you want common events. 3462 Format: { arch_perfmon } 3463 arch_perfmon: [X86] Force use of architectural 3464 perfmon on Intel CPUs instead of the 3465 CPU specific event set. 3466 timer: [X86] Force use of architectural NMI 3467 timer mode (see also oprofile.timer 3468 for generic hr timer mode) 3469 3470 oops=panic Always panic on oopses. Default is to just kill the 3471 process, but there is a small probability of 3472 deadlocking the machine. 3473 This will also cause panics on machine check exceptions. 3474 Useful together with panic=30 to trigger a reboot. 3475 3476 page_alloc.shuffle= 3477 [KNL] Boolean flag to control whether the page allocator 3478 should randomize its free lists. The randomization may 3479 be automatically enabled if the kernel detects it is 3480 running on a platform with a direct-mapped memory-side 3481 cache, and this parameter can be used to 3482 override/disable that behavior. The state of the flag 3483 can be read from sysfs at: 3484 /sys/module/page_alloc/parameters/shuffle. 3485 3486 page_owner= [KNL] Boot-time page_owner enabling option. 3487 Storage of the information about who allocated 3488 each page is disabled in default. With this switch, 3489 we can turn it on. 3490 on: enable the feature 3491 3492 page_poison= [KNL] Boot-time parameter changing the state of 3493 poisoning on the buddy allocator, available with 3494 CONFIG_PAGE_POISONING=y. 3495 off: turn off poisoning (default) 3496 on: turn on poisoning 3497 3498 panic= [KNL] Kernel behaviour on panic: delay <timeout> 3499 timeout > 0: seconds before rebooting 3500 timeout = 0: wait forever 3501 timeout < 0: reboot immediately 3502 Format: <timeout> 3503 3504 panic_print= Bitmask for printing system info when panic happens. 3505 User can chose combination of the following bits: 3506 bit 0: print all tasks info 3507 bit 1: print system memory info 3508 bit 2: print timer info 3509 bit 3: print locks info if CONFIG_LOCKDEP is on 3510 bit 4: print ftrace buffer 3511 bit 5: print all printk messages in buffer 3512 3513 panic_on_taint= Bitmask for conditionally calling panic() in add_taint() 3514 Format: <hex>[,nousertaint] 3515 Hexadecimal bitmask representing the set of TAINT flags 3516 that will cause the kernel to panic when add_taint() is 3517 called with any of the flags in this set. 3518 The optional switch "nousertaint" can be utilized to 3519 prevent userspace forced crashes by writing to sysctl 3520 /proc/sys/kernel/tainted any flagset matching with the 3521 bitmask set on panic_on_taint. 3522 See Documentation/admin-guide/tainted-kernels.rst for 3523 extra details on the taint flags that users can pick 3524 to compose the bitmask to assign to panic_on_taint. 3525 3526 panic_on_warn panic() instead of WARN(). Useful to cause kdump 3527 on a WARN(). 3528 3529 crash_kexec_post_notifiers 3530 Run kdump after running panic-notifiers and dumping 3531 kmsg. This only for the users who doubt kdump always 3532 succeeds in any situation. 3533 Note that this also increases risks of kdump failure, 3534 because some panic notifiers can make the crashed 3535 kernel more unstable. 3536 3537 parkbd.port= [HW] Parallel port number the keyboard adapter is 3538 connected to, default is 0. 3539 Format: <parport#> 3540 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 3541 0 for XT, 1 for AT (default is AT). 3542 Format: <mode> 3543 3544 parport= [HW,PPT] Specify parallel ports. 0 disables. 3545 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 3546 Use 'auto' to force the driver to use any 3547 IRQ/DMA settings detected (the default is to 3548 ignore detected IRQ/DMA settings because of 3549 possible conflicts). You can specify the base 3550 address, IRQ, and DMA settings; IRQ and DMA 3551 should be numbers, or 'auto' (for using detected 3552 settings on that particular port), or 'nofifo' 3553 (to avoid using a FIFO even if it is detected). 3554 Parallel ports are assigned in the order they 3555 are specified on the command line, starting 3556 with parport0. 3557 3558 parport_init_mode= [HW,PPT] 3559 Configure VIA parallel port to operate in 3560 a specific mode. This is necessary on Pegasos 3561 computer where firmware has no options for setting 3562 up parallel port mode and sets it to spp. 3563 Currently this function knows 686a and 8231 chips. 3564 Format: [spp|ps2|epp|ecp|ecpepp] 3565 3566 pause_on_oops= 3567 Halt all CPUs after the first oops has been printed for 3568 the specified number of seconds. This is to be used if 3569 your oopses keep scrolling off the screen. 3570 3571 pcbit= [HW,ISDN] 3572 3573 pcd. [PARIDE] 3574 See header of drivers/block/paride/pcd.c. 3575 See also Documentation/admin-guide/blockdev/paride.rst. 3576 3577 pci=option[,option...] [PCI] various PCI subsystem options. 3578 3579 Some options herein operate on a specific device 3580 or a set of devices (<pci_dev>). These are 3581 specified in one of the following formats: 3582 3583 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* 3584 pci:<vendor>:<device>[:<subvendor>:<subdevice>] 3585 3586 Note: the first format specifies a PCI 3587 bus/device/function address which may change 3588 if new hardware is inserted, if motherboard 3589 firmware changes, or due to changes caused 3590 by other kernel parameters. If the 3591 domain is left unspecified, it is 3592 taken to be zero. Optionally, a path 3593 to a device through multiple device/function 3594 addresses can be specified after the base 3595 address (this is more robust against 3596 renumbering issues). The second format 3597 selects devices using IDs from the 3598 configuration space which may match multiple 3599 devices in the system. 3600 3601 earlydump dump PCI config space before the kernel 3602 changes anything 3603 off [X86] don't probe for the PCI bus 3604 bios [X86-32] force use of PCI BIOS, don't access 3605 the hardware directly. Use this if your machine 3606 has a non-standard PCI host bridge. 3607 nobios [X86-32] disallow use of PCI BIOS, only direct 3608 hardware access methods are allowed. Use this 3609 if you experience crashes upon bootup and you 3610 suspect they are caused by the BIOS. 3611 conf1 [X86] Force use of PCI Configuration Access 3612 Mechanism 1 (config address in IO port 0xCF8, 3613 data in IO port 0xCFC, both 32-bit). 3614 conf2 [X86] Force use of PCI Configuration Access 3615 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 3616 the function, IO port 0xCFA, also 8-bit, sets 3617 bus number. The config space is then accessed 3618 through ports 0xC000-0xCFFF). 3619 See http://wiki.osdev.org/PCI for more info 3620 on the configuration access mechanisms. 3621 noaer [PCIE] If the PCIEAER kernel config parameter is 3622 enabled, this kernel boot option can be used to 3623 disable the use of PCIE advanced error reporting. 3624 nodomains [PCI] Disable support for multiple PCI 3625 root domains (aka PCI segments, in ACPI-speak). 3626 nommconf [X86] Disable use of MMCONFIG for PCI 3627 Configuration 3628 check_enable_amd_mmconf [X86] check for and enable 3629 properly configured MMIO access to PCI 3630 config space on AMD family 10h CPU 3631 nomsi [MSI] If the PCI_MSI kernel config parameter is 3632 enabled, this kernel boot option can be used to 3633 disable the use of MSI interrupts system-wide. 3634 noioapicquirk [APIC] Disable all boot interrupt quirks. 3635 Safety option to keep boot IRQs enabled. This 3636 should never be necessary. 3637 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 3638 primary IO-APIC for bridges that cannot disable 3639 boot IRQs. This fixes a source of spurious IRQs 3640 when the system masks IRQs. 3641 noioapicreroute [APIC] Disable workaround that uses the 3642 boot IRQ equivalent of an IRQ that connects to 3643 a chipset where boot IRQs cannot be disabled. 3644 The opposite of ioapicreroute. 3645 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 3646 routing table. These calls are known to be buggy 3647 on several machines and they hang the machine 3648 when used, but on other computers it's the only 3649 way to get the interrupt routing table. Try 3650 this option if the kernel is unable to allocate 3651 IRQs or discover secondary PCI buses on your 3652 motherboard. 3653 rom [X86] Assign address space to expansion ROMs. 3654 Use with caution as certain devices share 3655 address decoders between ROMs and other 3656 resources. 3657 norom [X86] Do not assign address space to 3658 expansion ROMs that do not already have 3659 BIOS assigned address ranges. 3660 nobar [X86] Do not assign address space to the 3661 BARs that weren't assigned by the BIOS. 3662 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 3663 assigned automatically to PCI devices. You can 3664 make the kernel exclude IRQs of your ISA cards 3665 this way. 3666 pirqaddr=0xAAAAA [X86] Specify the physical address 3667 of the PIRQ table (normally generated 3668 by the BIOS) if it is outside the 3669 F0000h-100000h range. 3670 lastbus=N [X86] Scan all buses thru bus #N. Can be 3671 useful if the kernel is unable to find your 3672 secondary buses and you want to tell it 3673 explicitly which ones they are. 3674 assign-busses [X86] Always assign all PCI bus 3675 numbers ourselves, overriding 3676 whatever the firmware may have done. 3677 usepirqmask [X86] Honor the possible IRQ mask stored 3678 in the BIOS $PIR table. This is needed on 3679 some systems with broken BIOSes, notably 3680 some HP Pavilion N5400 and Omnibook XE3 3681 notebooks. This will have no effect if ACPI 3682 IRQ routing is enabled. 3683 noacpi [X86] Do not use ACPI for IRQ routing 3684 or for PCI scanning. 3685 use_crs [X86] Use PCI host bridge window information 3686 from ACPI. On BIOSes from 2008 or later, this 3687 is enabled by default. If you need to use this, 3688 please report a bug. 3689 nocrs [X86] Ignore PCI host bridge windows from ACPI. 3690 If you need to use this, please report a bug. 3691 routeirq Do IRQ routing for all PCI devices. 3692 This is normally done in pci_enable_device(), 3693 so this option is a temporary workaround 3694 for broken drivers that don't call it. 3695 skip_isa_align [X86] do not align io start addr, so can 3696 handle more pci cards 3697 noearly [X86] Don't do any early type 1 scanning. 3698 This might help on some broken boards which 3699 machine check when some devices' config space 3700 is read. But various workarounds are disabled 3701 and some IOMMU drivers will not work. 3702 bfsort Sort PCI devices into breadth-first order. 3703 This sorting is done to get a device 3704 order compatible with older (<= 2.4) kernels. 3705 nobfsort Don't sort PCI devices into breadth-first order. 3706 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 3707 tuning and use the BIOS-configured MPS defaults. 3708 pcie_bus_safe Set every device's MPS to the largest value 3709 supported by all devices below the root complex. 3710 pcie_bus_perf Set device MPS to the largest allowable MPS 3711 based on its parent bus. Also set MRRS (Max 3712 Read Request Size) to the largest supported 3713 value (no larger than the MPS that the device 3714 or bus can support) for best performance. 3715 pcie_bus_peer2peer Set every device's MPS to 128B, which 3716 every device is guaranteed to support. This 3717 configuration allows peer-to-peer DMA between 3718 any pair of devices, possibly at the cost of 3719 reduced performance. This also guarantees 3720 that hot-added devices will work. 3721 cbiosize=nn[KMG] The fixed amount of bus space which is 3722 reserved for the CardBus bridge's IO window. 3723 The default value is 256 bytes. 3724 cbmemsize=nn[KMG] The fixed amount of bus space which is 3725 reserved for the CardBus bridge's memory 3726 window. The default value is 64 megabytes. 3727 resource_alignment= 3728 Format: 3729 [<order of align>@]<pci_dev>[; ...] 3730 Specifies alignment and device to reassign 3731 aligned memory resources. How to 3732 specify the device is described above. 3733 If <order of align> is not specified, 3734 PAGE_SIZE is used as alignment. 3735 A PCI-PCI bridge can be specified if resource 3736 windows need to be expanded. 3737 To specify the alignment for several 3738 instances of a device, the PCI vendor, 3739 device, subvendor, and subdevice may be 3740 specified, e.g., 12@pci:8086:9c22:103c:198f 3741 for 4096-byte alignment. 3742 ecrc= Enable/disable PCIe ECRC (transaction layer 3743 end-to-end CRC checking). 3744 bios: Use BIOS/firmware settings. This is the 3745 the default. 3746 off: Turn ECRC off 3747 on: Turn ECRC on. 3748 hpiosize=nn[KMG] The fixed amount of bus space which is 3749 reserved for hotplug bridge's IO window. 3750 Default size is 256 bytes. 3751 hpmmiosize=nn[KMG] The fixed amount of bus space which is 3752 reserved for hotplug bridge's MMIO window. 3753 Default size is 2 megabytes. 3754 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is 3755 reserved for hotplug bridge's MMIO_PREF window. 3756 Default size is 2 megabytes. 3757 hpmemsize=nn[KMG] The fixed amount of bus space which is 3758 reserved for hotplug bridge's MMIO and 3759 MMIO_PREF window. 3760 Default size is 2 megabytes. 3761 hpbussize=nn The minimum amount of additional bus numbers 3762 reserved for buses below a hotplug bridge. 3763 Default is 1. 3764 realloc= Enable/disable reallocating PCI bridge resources 3765 if allocations done by BIOS are too small to 3766 accommodate resources required by all child 3767 devices. 3768 off: Turn realloc off 3769 on: Turn realloc on 3770 realloc same as realloc=on 3771 noari do not use PCIe ARI. 3772 noats [PCIE, Intel-IOMMU, AMD-IOMMU] 3773 do not use PCIe ATS (and IOMMU device IOTLB). 3774 pcie_scan_all Scan all possible PCIe devices. Otherwise we 3775 only look for one device below a PCIe downstream 3776 port. 3777 big_root_window Try to add a big 64bit memory window to the PCIe 3778 root complex on AMD CPUs. Some GFX hardware 3779 can resize a BAR to allow access to all VRAM. 3780 Adding the window is slightly risky (it may 3781 conflict with unreported devices), so this 3782 taints the kernel. 3783 disable_acs_redir=<pci_dev>[; ...] 3784 Specify one or more PCI devices (in the format 3785 specified above) separated by semicolons. 3786 Each device specified will have the PCI ACS 3787 redirect capabilities forced off which will 3788 allow P2P traffic between devices through 3789 bridges without forcing it upstream. Note: 3790 this removes isolation between devices and 3791 may put more devices in an IOMMU group. 3792 force_floating [S390] Force usage of floating interrupts. 3793 nomio [S390] Do not use MIO instructions. 3794 norid [S390] ignore the RID field and force use of 3795 one PCI domain per PCI function 3796 3797 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power 3798 Management. 3799 off Disable ASPM. 3800 force Enable ASPM even on devices that claim not to support it. 3801 WARNING: Forcing ASPM on may cause system lockups. 3802 3803 pcie_ports= [PCIE] PCIe port services handling: 3804 native Use native PCIe services (PME, AER, DPC, PCIe hotplug) 3805 even if the platform doesn't give the OS permission to 3806 use them. This may cause conflicts if the platform 3807 also tries to use these services. 3808 dpc-native Use native PCIe service for DPC only. May 3809 cause conflicts if firmware uses AER or DPC. 3810 compat Disable native PCIe services (PME, AER, DPC, PCIe 3811 hotplug). 3812 3813 pcie_port_pm= [PCIE] PCIe port power management handling: 3814 off Disable power management of all PCIe ports 3815 force Forcibly enable power management of all PCIe ports 3816 3817 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 3818 nomsi Do not use MSI for native PCIe PME signaling (this makes 3819 all PCIe root ports use INTx for all services). 3820 3821 pcmv= [HW,PCMCIA] BadgePAD 4 3822 3823 pd_ignore_unused 3824 [PM] 3825 Keep all power-domains already enabled by bootloader on, 3826 even if no driver has claimed them. This is useful 3827 for debug and development, but should not be 3828 needed on a platform with proper driver support. 3829 3830 pd. [PARIDE] 3831 See Documentation/admin-guide/blockdev/paride.rst. 3832 3833 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 3834 boot time. 3835 Format: { 0 | 1 } 3836 See arch/parisc/kernel/pdc_chassis.c 3837 3838 percpu_alloc= Select which percpu first chunk allocator to use. 3839 Currently supported values are "embed" and "page". 3840 Archs may support subset or none of the selections. 3841 See comments in mm/percpu.c for details on each 3842 allocator. This parameter is primarily for debugging 3843 and performance comparison. 3844 3845 pf. [PARIDE] 3846 See Documentation/admin-guide/blockdev/paride.rst. 3847 3848 pg. [PARIDE] 3849 See Documentation/admin-guide/blockdev/paride.rst. 3850 3851 pirq= [SMP,APIC] Manual mp-table setup 3852 See Documentation/x86/i386/IO-APIC.rst. 3853 3854 plip= [PPT,NET] Parallel port network link 3855 Format: { parport<nr> | timid | 0 } 3856 See also Documentation/admin-guide/parport.rst. 3857 3858 pmtmr= [X86] Manual setup of pmtmr I/O Port. 3859 Override pmtimer IOPort with a hex value. 3860 e.g. pmtmr=0x508 3861 3862 pm_debug_messages [SUSPEND,KNL] 3863 Enable suspend/resume debug messages during boot up. 3864 3865 pnp.debug=1 [PNP] 3866 Enable PNP debug messages (depends on the 3867 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 3868 via /sys/module/pnp/parameters/debug. We always show 3869 current resource usage; turning this on also shows 3870 possible settings and some assignment information. 3871 3872 pnpacpi= [ACPI] 3873 { off } 3874 3875 pnpbios= [ISAPNP] 3876 { on | off | curr | res | no-curr | no-res } 3877 3878 pnp_reserve_irq= 3879 [ISAPNP] Exclude IRQs for the autoconfiguration 3880 3881 pnp_reserve_dma= 3882 [ISAPNP] Exclude DMAs for the autoconfiguration 3883 3884 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 3885 Ranges are in pairs (I/O port base and size). 3886 3887 pnp_reserve_mem= 3888 [ISAPNP] Exclude memory regions for the 3889 autoconfiguration. 3890 Ranges are in pairs (memory base and size). 3891 3892 ports= [IP_VS_FTP] IPVS ftp helper module 3893 Default is 21. 3894 Up to 8 (IP_VS_APP_MAX_PORTS) ports 3895 may be specified. 3896 Format: <port>,<port>.... 3897 3898 powersave=off [PPC] This option disables power saving features. 3899 It specifically disables cpuidle and sets the 3900 platform machine description specific power_save 3901 function to NULL. On Idle the CPU just reduces 3902 execution priority. 3903 3904 ppc_strict_facility_enable 3905 [PPC] This option catches any kernel floating point, 3906 Altivec, VSX and SPE outside of regions specifically 3907 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 3908 There is some performance impact when enabling this. 3909 3910 ppc_tm= [PPC] 3911 Format: {"off"} 3912 Disable Hardware Transactional Memory 3913 3914 print-fatal-signals= 3915 [KNL] debug: print fatal signals 3916 3917 If enabled, warn about various signal handling 3918 related application anomalies: too many signals, 3919 too many POSIX.1 timers, fatal signals causing a 3920 coredump - etc. 3921 3922 If you hit the warning due to signal overflow, 3923 you might want to try "ulimit -i unlimited". 3924 3925 default: off. 3926 3927 printk.always_kmsg_dump= 3928 Trigger kmsg_dump for cases other than kernel oops or 3929 panics 3930 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3931 default: disabled 3932 3933 printk.devkmsg={on,off,ratelimit} 3934 Control writing to /dev/kmsg. 3935 on - unlimited logging to /dev/kmsg from userspace 3936 off - logging to /dev/kmsg disabled 3937 ratelimit - ratelimit the logging 3938 Default: ratelimit 3939 3940 printk.time= Show timing data prefixed to each printk message line 3941 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3942 3943 processor.max_cstate= [HW,ACPI] 3944 Limit processor to maximum C-state 3945 max_cstate=9 overrides any DMI blacklist limit. 3946 3947 processor.nocst [HW,ACPI] 3948 Ignore the _CST method to determine C-states, 3949 instead using the legacy FADT method 3950 3951 profile= [KNL] Enable kernel profiling via /proc/profile 3952 Format: [<profiletype>,]<number> 3953 Param: <profiletype>: "schedule", "sleep", or "kvm" 3954 [defaults to kernel profiling] 3955 Param: "schedule" - profile schedule points. 3956 Param: "sleep" - profile D-state sleeping (millisecs). 3957 Requires CONFIG_SCHEDSTATS 3958 Param: "kvm" - profile VM exits. 3959 Param: <number> - step/bucket size as a power of 2 for 3960 statistical time based profiling. 3961 3962 prompt_ramdisk= [RAM] [Deprecated] 3963 3964 prot_virt= [S390] enable hosting protected virtual machines 3965 isolated from the hypervisor (if hardware supports 3966 that). 3967 Format: <bool> 3968 3969 psi= [KNL] Enable or disable pressure stall information 3970 tracking. 3971 Format: <bool> 3972 3973 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 3974 probe for; one of (bare|imps|exps|lifebook|any). 3975 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 3976 per second. 3977 psmouse.resetafter= [HW,MOUSE] 3978 Try to reset the device after so many bad packets 3979 (0 = never). 3980 psmouse.resolution= 3981 [HW,MOUSE] Set desired mouse resolution, in dpi. 3982 psmouse.smartscroll= 3983 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 3984 0 = disabled, 1 = enabled (default). 3985 3986 pstore.backend= Specify the name of the pstore backend to use 3987 3988 pt. [PARIDE] 3989 See Documentation/admin-guide/blockdev/paride.rst. 3990 3991 pti= [X86-64] Control Page Table Isolation of user and 3992 kernel address spaces. Disabling this feature 3993 removes hardening, but improves performance of 3994 system calls and interrupts. 3995 3996 on - unconditionally enable 3997 off - unconditionally disable 3998 auto - kernel detects whether your CPU model is 3999 vulnerable to issues that PTI mitigates 4000 4001 Not specifying this option is equivalent to pti=auto. 4002 4003 nopti [X86-64] 4004 Equivalent to pti=off 4005 4006 pty.legacy_count= 4007 [KNL] Number of legacy pty's. Overwrites compiled-in 4008 default number. 4009 4010 quiet [KNL] Disable most log messages 4011 4012 r128= [HW,DRM] 4013 4014 raid= [HW,RAID] 4015 See Documentation/admin-guide/md.rst. 4016 4017 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 4018 See Documentation/admin-guide/blockdev/ramdisk.rst. 4019 4020 ramdisk_start= [RAM] RAM disk image start address 4021 4022 random.trust_cpu={on,off} 4023 [KNL] Enable or disable trusting the use of the 4024 CPU's random number generator (if available) to 4025 fully seed the kernel's CRNG. Default is controlled 4026 by CONFIG_RANDOM_TRUST_CPU. 4027 4028 ras=option[,option,...] [KNL] RAS-specific options 4029 4030 cec_disable [X86] 4031 Disable the Correctable Errors Collector, 4032 see CONFIG_RAS_CEC help text. 4033 4034 rcu_nocbs= [KNL] 4035 The argument is a cpu list, as described above, 4036 except that the string "all" can be used to 4037 specify every CPU on the system. 4038 4039 In kernels built with CONFIG_RCU_NOCB_CPU=y, set 4040 the specified list of CPUs to be no-callback CPUs. 4041 Invocation of these CPUs' RCU callbacks will be 4042 offloaded to "rcuox/N" kthreads created for that 4043 purpose, where "x" is "p" for RCU-preempt, and 4044 "s" for RCU-sched, and "N" is the CPU number. 4045 This reduces OS jitter on the offloaded CPUs, 4046 which can be useful for HPC and real-time 4047 workloads. It can also improve energy efficiency 4048 for asymmetric multiprocessors. 4049 4050 rcu_nocb_poll [KNL] 4051 Rather than requiring that offloaded CPUs 4052 (specified by rcu_nocbs= above) explicitly 4053 awaken the corresponding "rcuoN" kthreads, 4054 make these kthreads poll for callbacks. 4055 This improves the real-time response for the 4056 offloaded CPUs by relieving them of the need to 4057 wake up the corresponding kthread, but degrades 4058 energy efficiency by requiring that the kthreads 4059 periodically wake up to do the polling. 4060 4061 rcutree.blimit= [KNL] 4062 Set maximum number of finished RCU callbacks to 4063 process in one batch. 4064 4065 rcutree.dump_tree= [KNL] 4066 Dump the structure of the rcu_node combining tree 4067 out at early boot. This is used for diagnostic 4068 purposes, to verify correct tree setup. 4069 4070 rcutree.gp_cleanup_delay= [KNL] 4071 Set the number of jiffies to delay each step of 4072 RCU grace-period cleanup. 4073 4074 rcutree.gp_init_delay= [KNL] 4075 Set the number of jiffies to delay each step of 4076 RCU grace-period initialization. 4077 4078 rcutree.gp_preinit_delay= [KNL] 4079 Set the number of jiffies to delay each step of 4080 RCU grace-period pre-initialization, that is, 4081 the propagation of recent CPU-hotplug changes up 4082 the rcu_node combining tree. 4083 4084 rcutree.use_softirq= [KNL] 4085 If set to zero, move all RCU_SOFTIRQ processing to 4086 per-CPU rcuc kthreads. Defaults to a non-zero 4087 value, meaning that RCU_SOFTIRQ is used by default. 4088 Specify rcutree.use_softirq=0 to use rcuc kthreads. 4089 4090 rcutree.rcu_fanout_exact= [KNL] 4091 Disable autobalancing of the rcu_node combining 4092 tree. This is used by rcutorture, and might 4093 possibly be useful for architectures having high 4094 cache-to-cache transfer latencies. 4095 4096 rcutree.rcu_fanout_leaf= [KNL] 4097 Change the number of CPUs assigned to each 4098 leaf rcu_node structure. Useful for very 4099 large systems, which will choose the value 64, 4100 and for NUMA systems with large remote-access 4101 latencies, which will choose a value aligned 4102 with the appropriate hardware boundaries. 4103 4104 rcutree.rcu_min_cached_objs= [KNL] 4105 Minimum number of objects which are cached and 4106 maintained per one CPU. Object size is equal 4107 to PAGE_SIZE. The cache allows to reduce the 4108 pressure to page allocator, also it makes the 4109 whole algorithm to behave better in low memory 4110 condition. 4111 4112 rcutree.jiffies_till_first_fqs= [KNL] 4113 Set delay from grace-period initialization to 4114 first attempt to force quiescent states. 4115 Units are jiffies, minimum value is zero, 4116 and maximum value is HZ. 4117 4118 rcutree.jiffies_till_next_fqs= [KNL] 4119 Set delay between subsequent attempts to force 4120 quiescent states. Units are jiffies, minimum 4121 value is one, and maximum value is HZ. 4122 4123 rcutree.jiffies_till_sched_qs= [KNL] 4124 Set required age in jiffies for a 4125 given grace period before RCU starts 4126 soliciting quiescent-state help from 4127 rcu_note_context_switch() and cond_resched(). 4128 If not specified, the kernel will calculate 4129 a value based on the most recent settings 4130 of rcutree.jiffies_till_first_fqs 4131 and rcutree.jiffies_till_next_fqs. 4132 This calculated value may be viewed in 4133 rcutree.jiffies_to_sched_qs. Any attempt to set 4134 rcutree.jiffies_to_sched_qs will be cheerfully 4135 overwritten. 4136 4137 rcutree.kthread_prio= [KNL,BOOT] 4138 Set the SCHED_FIFO priority of the RCU per-CPU 4139 kthreads (rcuc/N). This value is also used for 4140 the priority of the RCU boost threads (rcub/N) 4141 and for the RCU grace-period kthreads (rcu_bh, 4142 rcu_preempt, and rcu_sched). If RCU_BOOST is 4143 set, valid values are 1-99 and the default is 1 4144 (the least-favored priority). Otherwise, when 4145 RCU_BOOST is not set, valid values are 0-99 and 4146 the default is zero (non-realtime operation). 4147 4148 rcutree.rcu_nocb_gp_stride= [KNL] 4149 Set the number of NOCB callback kthreads in 4150 each group, which defaults to the square root 4151 of the number of CPUs. Larger numbers reduce 4152 the wakeup overhead on the global grace-period 4153 kthread, but increases that same overhead on 4154 each group's NOCB grace-period kthread. 4155 4156 rcutree.qhimark= [KNL] 4157 Set threshold of queued RCU callbacks beyond which 4158 batch limiting is disabled. 4159 4160 rcutree.qlowmark= [KNL] 4161 Set threshold of queued RCU callbacks below which 4162 batch limiting is re-enabled. 4163 4164 rcutree.qovld= [KNL] 4165 Set threshold of queued RCU callbacks beyond which 4166 RCU's force-quiescent-state scan will aggressively 4167 enlist help from cond_resched() and sched IPIs to 4168 help CPUs more quickly reach quiescent states. 4169 Set to less than zero to make this be set based 4170 on rcutree.qhimark at boot time and to zero to 4171 disable more aggressive help enlistment. 4172 4173 rcutree.rcu_idle_gp_delay= [KNL] 4174 Set wakeup interval for idle CPUs that have 4175 RCU callbacks (RCU_FAST_NO_HZ=y). 4176 4177 rcutree.rcu_idle_lazy_gp_delay= [KNL] 4178 Set wakeup interval for idle CPUs that have 4179 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y). 4180 Lazy RCU callbacks are those which RCU can 4181 prove do nothing more than free memory. 4182 4183 rcutree.rcu_kick_kthreads= [KNL] 4184 Cause the grace-period kthread to get an extra 4185 wake_up() if it sleeps three times longer than 4186 it should at force-quiescent-state time. 4187 This wake_up() will be accompanied by a 4188 WARN_ONCE() splat and an ftrace_dump(). 4189 4190 rcutree.rcu_unlock_delay= [KNL] 4191 In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels, 4192 this specifies an rcu_read_unlock()-time delay 4193 in microseconds. This defaults to zero. 4194 Larger delays increase the probability of 4195 catching RCU pointer leaks, that is, buggy use 4196 of RCU-protected pointers after the relevant 4197 rcu_read_unlock() has completed. 4198 4199 rcutree.sysrq_rcu= [KNL] 4200 Commandeer a sysrq key to dump out Tree RCU's 4201 rcu_node tree with an eye towards determining 4202 why a new grace period has not yet started. 4203 4204 rcuscale.gp_async= [KNL] 4205 Measure performance of asynchronous 4206 grace-period primitives such as call_rcu(). 4207 4208 rcuscale.gp_async_max= [KNL] 4209 Specify the maximum number of outstanding 4210 callbacks per writer thread. When a writer 4211 thread exceeds this limit, it invokes the 4212 corresponding flavor of rcu_barrier() to allow 4213 previously posted callbacks to drain. 4214 4215 rcuscale.gp_exp= [KNL] 4216 Measure performance of expedited synchronous 4217 grace-period primitives. 4218 4219 rcuscale.holdoff= [KNL] 4220 Set test-start holdoff period. The purpose of 4221 this parameter is to delay the start of the 4222 test until boot completes in order to avoid 4223 interference. 4224 4225 rcuscale.kfree_rcu_test= [KNL] 4226 Set to measure performance of kfree_rcu() flooding. 4227 4228 rcuscale.kfree_nthreads= [KNL] 4229 The number of threads running loops of kfree_rcu(). 4230 4231 rcuscale.kfree_alloc_num= [KNL] 4232 Number of allocations and frees done in an iteration. 4233 4234 rcuscale.kfree_loops= [KNL] 4235 Number of loops doing rcuscale.kfree_alloc_num number 4236 of allocations and frees. 4237 4238 rcuscale.nreaders= [KNL] 4239 Set number of RCU readers. The value -1 selects 4240 N, where N is the number of CPUs. A value 4241 "n" less than -1 selects N-n+1, where N is again 4242 the number of CPUs. For example, -2 selects N 4243 (the number of CPUs), -3 selects N+1, and so on. 4244 A value of "n" less than or equal to -N selects 4245 a single reader. 4246 4247 rcuscale.nwriters= [KNL] 4248 Set number of RCU writers. The values operate 4249 the same as for rcuscale.nreaders. 4250 N, where N is the number of CPUs 4251 4252 rcuscale.perf_type= [KNL] 4253 Specify the RCU implementation to test. 4254 4255 rcuscale.shutdown= [KNL] 4256 Shut the system down after performance tests 4257 complete. This is useful for hands-off automated 4258 testing. 4259 4260 rcuscale.verbose= [KNL] 4261 Enable additional printk() statements. 4262 4263 rcuscale.writer_holdoff= [KNL] 4264 Write-side holdoff between grace periods, 4265 in microseconds. The default of zero says 4266 no holdoff. 4267 4268 rcutorture.fqs_duration= [KNL] 4269 Set duration of force_quiescent_state bursts 4270 in microseconds. 4271 4272 rcutorture.fqs_holdoff= [KNL] 4273 Set holdoff time within force_quiescent_state bursts 4274 in microseconds. 4275 4276 rcutorture.fqs_stutter= [KNL] 4277 Set wait time between force_quiescent_state bursts 4278 in seconds. 4279 4280 rcutorture.fwd_progress= [KNL] 4281 Enable RCU grace-period forward-progress testing 4282 for the types of RCU supporting this notion. 4283 4284 rcutorture.fwd_progress_div= [KNL] 4285 Specify the fraction of a CPU-stall-warning 4286 period to do tight-loop forward-progress testing. 4287 4288 rcutorture.fwd_progress_holdoff= [KNL] 4289 Number of seconds to wait between successive 4290 forward-progress tests. 4291 4292 rcutorture.fwd_progress_need_resched= [KNL] 4293 Enclose cond_resched() calls within checks for 4294 need_resched() during tight-loop forward-progress 4295 testing. 4296 4297 rcutorture.gp_cond= [KNL] 4298 Use conditional/asynchronous update-side 4299 primitives, if available. 4300 4301 rcutorture.gp_exp= [KNL] 4302 Use expedited update-side primitives, if available. 4303 4304 rcutorture.gp_normal= [KNL] 4305 Use normal (non-expedited) asynchronous 4306 update-side primitives, if available. 4307 4308 rcutorture.gp_sync= [KNL] 4309 Use normal (non-expedited) synchronous 4310 update-side primitives, if available. If all 4311 of rcutorture.gp_cond=, rcutorture.gp_exp=, 4312 rcutorture.gp_normal=, and rcutorture.gp_sync= 4313 are zero, rcutorture acts as if is interpreted 4314 they are all non-zero. 4315 4316 rcutorture.irqreader= [KNL] 4317 Run RCU readers from irq handlers, or, more 4318 accurately, from a timer handler. Not all RCU 4319 flavors take kindly to this sort of thing. 4320 4321 rcutorture.leakpointer= [KNL] 4322 Leak an RCU-protected pointer out of the reader. 4323 This can of course result in splats, and is 4324 intended to test the ability of things like 4325 CONFIG_RCU_STRICT_GRACE_PERIOD=y to detect 4326 such leaks. 4327 4328 rcutorture.n_barrier_cbs= [KNL] 4329 Set callbacks/threads for rcu_barrier() testing. 4330 4331 rcutorture.nfakewriters= [KNL] 4332 Set number of concurrent RCU writers. These just 4333 stress RCU, they don't participate in the actual 4334 test, hence the "fake". 4335 4336 rcutorture.nreaders= [KNL] 4337 Set number of RCU readers. The value -1 selects 4338 N-1, where N is the number of CPUs. A value 4339 "n" less than -1 selects N-n-2, where N is again 4340 the number of CPUs. For example, -2 selects N 4341 (the number of CPUs), -3 selects N+1, and so on. 4342 4343 rcutorture.object_debug= [KNL] 4344 Enable debug-object double-call_rcu() testing. 4345 4346 rcutorture.onoff_holdoff= [KNL] 4347 Set time (s) after boot for CPU-hotplug testing. 4348 4349 rcutorture.onoff_interval= [KNL] 4350 Set time (jiffies) between CPU-hotplug operations, 4351 or zero to disable CPU-hotplug testing. 4352 4353 rcutorture.read_exit= [KNL] 4354 Set the number of read-then-exit kthreads used 4355 to test the interaction of RCU updaters and 4356 task-exit processing. 4357 4358 rcutorture.read_exit_burst= [KNL] 4359 The number of times in a given read-then-exit 4360 episode that a set of read-then-exit kthreads 4361 is spawned. 4362 4363 rcutorture.read_exit_delay= [KNL] 4364 The delay, in seconds, between successive 4365 read-then-exit testing episodes. 4366 4367 rcutorture.shuffle_interval= [KNL] 4368 Set task-shuffle interval (s). Shuffling tasks 4369 allows some CPUs to go into dyntick-idle mode 4370 during the rcutorture test. 4371 4372 rcutorture.shutdown_secs= [KNL] 4373 Set time (s) after boot system shutdown. This 4374 is useful for hands-off automated testing. 4375 4376 rcutorture.stall_cpu= [KNL] 4377 Duration of CPU stall (s) to test RCU CPU stall 4378 warnings, zero to disable. 4379 4380 rcutorture.stall_cpu_block= [KNL] 4381 Sleep while stalling if set. This will result 4382 in warnings from preemptible RCU in addition 4383 to any other stall-related activity. 4384 4385 rcutorture.stall_cpu_holdoff= [KNL] 4386 Time to wait (s) after boot before inducing stall. 4387 4388 rcutorture.stall_cpu_irqsoff= [KNL] 4389 Disable interrupts while stalling if set. 4390 4391 rcutorture.stall_gp_kthread= [KNL] 4392 Duration (s) of forced sleep within RCU 4393 grace-period kthread to test RCU CPU stall 4394 warnings, zero to disable. If both stall_cpu 4395 and stall_gp_kthread are specified, the 4396 kthread is starved first, then the CPU. 4397 4398 rcutorture.stat_interval= [KNL] 4399 Time (s) between statistics printk()s. 4400 4401 rcutorture.stutter= [KNL] 4402 Time (s) to stutter testing, for example, specifying 4403 five seconds causes the test to run for five seconds, 4404 wait for five seconds, and so on. This tests RCU's 4405 ability to transition abruptly to and from idle. 4406 4407 rcutorture.test_boost= [KNL] 4408 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 4409 "Maybe" means test if the RCU implementation 4410 under test support RCU priority boosting. 4411 4412 rcutorture.test_boost_duration= [KNL] 4413 Duration (s) of each individual boost test. 4414 4415 rcutorture.test_boost_interval= [KNL] 4416 Interval (s) between each boost test. 4417 4418 rcutorture.test_no_idle_hz= [KNL] 4419 Test RCU's dyntick-idle handling. See also the 4420 rcutorture.shuffle_interval parameter. 4421 4422 rcutorture.torture_type= [KNL] 4423 Specify the RCU implementation to test. 4424 4425 rcutorture.verbose= [KNL] 4426 Enable additional printk() statements. 4427 4428 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL] 4429 Dump ftrace buffer after reporting RCU CPU 4430 stall warning. 4431 4432 rcupdate.rcu_cpu_stall_suppress= [KNL] 4433 Suppress RCU CPU stall warning messages. 4434 4435 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL] 4436 Suppress RCU CPU stall warning messages and 4437 rcutorture writer stall warnings that occur 4438 during early boot, that is, during the time 4439 before the init task is spawned. 4440 4441 rcupdate.rcu_cpu_stall_timeout= [KNL] 4442 Set timeout for RCU CPU stall warning messages. 4443 4444 rcupdate.rcu_expedited= [KNL] 4445 Use expedited grace-period primitives, for 4446 example, synchronize_rcu_expedited() instead 4447 of synchronize_rcu(). This reduces latency, 4448 but can increase CPU utilization, degrade 4449 real-time latency, and degrade energy efficiency. 4450 No effect on CONFIG_TINY_RCU kernels. 4451 4452 rcupdate.rcu_normal= [KNL] 4453 Use only normal grace-period primitives, 4454 for example, synchronize_rcu() instead of 4455 synchronize_rcu_expedited(). This improves 4456 real-time latency, CPU utilization, and 4457 energy efficiency, but can expose users to 4458 increased grace-period latency. This parameter 4459 overrides rcupdate.rcu_expedited. No effect on 4460 CONFIG_TINY_RCU kernels. 4461 4462 rcupdate.rcu_normal_after_boot= [KNL] 4463 Once boot has completed (that is, after 4464 rcu_end_inkernel_boot() has been invoked), use 4465 only normal grace-period primitives. No effect 4466 on CONFIG_TINY_RCU kernels. 4467 4468 rcupdate.rcu_task_ipi_delay= [KNL] 4469 Set time in jiffies during which RCU tasks will 4470 avoid sending IPIs, starting with the beginning 4471 of a given grace period. Setting a large 4472 number avoids disturbing real-time workloads, 4473 but lengthens grace periods. 4474 4475 rcupdate.rcu_task_stall_timeout= [KNL] 4476 Set timeout in jiffies for RCU task stall warning 4477 messages. Disable with a value less than or equal 4478 to zero. 4479 4480 rcupdate.rcu_self_test= [KNL] 4481 Run the RCU early boot self tests 4482 4483 rdinit= [KNL] 4484 Format: <full_path> 4485 Run specified binary instead of /init from the ramdisk, 4486 used for early userspace startup. See initrd. 4487 4488 rdrand= [X86] 4489 force - Override the decision by the kernel to hide the 4490 advertisement of RDRAND support (this affects 4491 certain AMD processors because of buggy BIOS 4492 support, specifically around the suspend/resume 4493 path). 4494 4495 rdt= [HW,X86,RDT] 4496 Turn on/off individual RDT features. List is: 4497 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, 4498 mba. 4499 E.g. to turn on cmt and turn off mba use: 4500 rdt=cmt,!mba 4501 4502 reboot= [KNL] 4503 Format (x86 or x86_64): 4504 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \ 4505 [[,]s[mp]#### \ 4506 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 4507 [[,]f[orce] 4508 Where reboot_mode is one of warm (soft) or cold (hard) or gpio 4509 (prefix with 'panic_' to set mode for panic 4510 reboot only), 4511 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 4512 reboot_force is either force or not specified, 4513 reboot_cpu is s[mp]#### with #### being the processor 4514 to be used for rebooting. 4515 4516 refscale.holdoff= [KNL] 4517 Set test-start holdoff period. The purpose of 4518 this parameter is to delay the start of the 4519 test until boot completes in order to avoid 4520 interference. 4521 4522 refscale.loops= [KNL] 4523 Set the number of loops over the synchronization 4524 primitive under test. Increasing this number 4525 reduces noise due to loop start/end overhead, 4526 but the default has already reduced the per-pass 4527 noise to a handful of picoseconds on ca. 2020 4528 x86 laptops. 4529 4530 refscale.nreaders= [KNL] 4531 Set number of readers. The default value of -1 4532 selects N, where N is roughly 75% of the number 4533 of CPUs. A value of zero is an interesting choice. 4534 4535 refscale.nruns= [KNL] 4536 Set number of runs, each of which is dumped onto 4537 the console log. 4538 4539 refscale.readdelay= [KNL] 4540 Set the read-side critical-section duration, 4541 measured in microseconds. 4542 4543 refscale.scale_type= [KNL] 4544 Specify the read-protection implementation to test. 4545 4546 refscale.shutdown= [KNL] 4547 Shut down the system at the end of the performance 4548 test. This defaults to 1 (shut it down) when 4549 refscale is built into the kernel and to 0 (leave 4550 it running) when refscale is built as a module. 4551 4552 refscale.verbose= [KNL] 4553 Enable additional printk() statements. 4554 4555 relax_domain_level= 4556 [KNL, SMP] Set scheduler's default relax_domain_level. 4557 See Documentation/admin-guide/cgroup-v1/cpusets.rst. 4558 4559 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory 4560 Format: <base1>,<size1>[,<base2>,<size2>,...] 4561 Reserve I/O ports or memory so the kernel won't use 4562 them. If <base> is less than 0x10000, the region 4563 is assumed to be I/O ports; otherwise it is memory. 4564 4565 reservetop= [X86-32] 4566 Format: nn[KMG] 4567 Reserves a hole at the top of the kernel virtual 4568 address space. 4569 4570 reservelow= [X86] 4571 Format: nn[K] 4572 Set the amount of memory to reserve for BIOS at 4573 the bottom of the address space. 4574 4575 reset_devices [KNL] Force drivers to reset the underlying device 4576 during initialization. 4577 4578 resume= [SWSUSP] 4579 Specify the partition device for software suspend 4580 Format: 4581 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 4582 4583 resume_offset= [SWSUSP] 4584 Specify the offset from the beginning of the partition 4585 given by "resume=" at which the swap header is located, 4586 in <PAGE_SIZE> units (needed only for swap files). 4587 See Documentation/power/swsusp-and-swap-files.rst 4588 4589 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 4590 read the resume files 4591 4592 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 4593 Useful for devices that are detected asynchronously 4594 (e.g. USB and MMC devices). 4595 4596 hibernate= [HIBERNATION] 4597 noresume Don't check if there's a hibernation image 4598 present during boot. 4599 nocompress Don't compress/decompress hibernation images. 4600 no Disable hibernation and resume. 4601 protect_image Turn on image protection during restoration 4602 (that will set all pages holding image data 4603 during restoration read-only). 4604 4605 retain_initrd [RAM] Keep initrd memory after extraction 4606 4607 rfkill.default_state= 4608 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 4609 etc. communication is blocked by default. 4610 1 Unblocked. 4611 4612 rfkill.master_switch_mode= 4613 0 The "airplane mode" button does nothing. 4614 1 The "airplane mode" button toggles between everything 4615 blocked and the previous configuration. 4616 2 The "airplane mode" button toggles between everything 4617 blocked and everything unblocked. 4618 4619 rhash_entries= [KNL,NET] 4620 Set number of hash buckets for route cache 4621 4622 ring3mwait=disable 4623 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 4624 CPUs. 4625 4626 ro [KNL] Mount root device read-only on boot 4627 4628 rodata= [KNL] 4629 on Mark read-only kernel memory as read-only (default). 4630 off Leave read-only kernel memory writable for debugging. 4631 4632 rockchip.usb_uart 4633 Enable the uart passthrough on the designated usb port 4634 on Rockchip SoCs. When active, the signals of the 4635 debug-uart get routed to the D+ and D- pins of the usb 4636 port and the regular usb controller gets disabled. 4637 4638 root= [KNL] Root filesystem 4639 See name_to_dev_t comment in init/do_mounts.c. 4640 4641 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 4642 mount the root filesystem 4643 4644 rootflags= [KNL] Set root filesystem mount option string 4645 4646 rootfstype= [KNL] Set root filesystem type 4647 4648 rootwait [KNL] Wait (indefinitely) for root device to show up. 4649 Useful for devices that are detected asynchronously 4650 (e.g. USB and MMC devices). 4651 4652 rproc_mem=nn[KMG][@address] 4653 [KNL,ARM,CMA] Remoteproc physical memory block. 4654 Memory area to be used by remote processor image, 4655 managed by CMA. 4656 4657 rw [KNL] Mount root device read-write on boot 4658 4659 S [KNL] Run init in single mode 4660 4661 s390_iommu= [HW,S390] 4662 Set s390 IOTLB flushing mode 4663 strict 4664 With strict flushing every unmap operation will result in 4665 an IOTLB flush. Default is lazy flushing before reuse, 4666 which is faster. 4667 4668 sa1100ir [NET] 4669 See drivers/net/irda/sa1100_ir.c. 4670 4671 sbni= [NET] Granch SBNI12 leased line adapter 4672 4673 sched_debug [KNL] Enables verbose scheduler debug messages. 4674 4675 schedstats= [KNL,X86] Enable or disable scheduled statistics. 4676 Allowed values are enable and disable. This feature 4677 incurs a small amount of overhead in the scheduler 4678 but is useful for debugging and performance tuning. 4679 4680 sched_thermal_decay_shift= 4681 [KNL, SMP] Set a decay shift for scheduler thermal 4682 pressure signal. Thermal pressure signal follows the 4683 default decay period of other scheduler pelt 4684 signals(usually 32 ms but configurable). Setting 4685 sched_thermal_decay_shift will left shift the decay 4686 period for the thermal pressure signal by the shift 4687 value. 4688 i.e. with the default pelt decay period of 32 ms 4689 sched_thermal_decay_shift thermal pressure decay pr 4690 1 64 ms 4691 2 128 ms 4692 and so on. 4693 Format: integer between 0 and 10 4694 Default is 0. 4695 4696 scftorture.holdoff= [KNL] 4697 Number of seconds to hold off before starting 4698 test. Defaults to zero for module insertion and 4699 to 10 seconds for built-in smp_call_function() 4700 tests. 4701 4702 scftorture.longwait= [KNL] 4703 Request ridiculously long waits randomly selected 4704 up to the chosen limit in seconds. Zero (the 4705 default) disables this feature. Please note 4706 that requesting even small non-zero numbers of 4707 seconds can result in RCU CPU stall warnings, 4708 softlockup complaints, and so on. 4709 4710 scftorture.nthreads= [KNL] 4711 Number of kthreads to spawn to invoke the 4712 smp_call_function() family of functions. 4713 The default of -1 specifies a number of kthreads 4714 equal to the number of CPUs. 4715 4716 scftorture.onoff_holdoff= [KNL] 4717 Number seconds to wait after the start of the 4718 test before initiating CPU-hotplug operations. 4719 4720 scftorture.onoff_interval= [KNL] 4721 Number seconds to wait between successive 4722 CPU-hotplug operations. Specifying zero (which 4723 is the default) disables CPU-hotplug operations. 4724 4725 scftorture.shutdown_secs= [KNL] 4726 The number of seconds following the start of the 4727 test after which to shut down the system. The 4728 default of zero avoids shutting down the system. 4729 Non-zero values are useful for automated tests. 4730 4731 scftorture.stat_interval= [KNL] 4732 The number of seconds between outputting the 4733 current test statistics to the console. A value 4734 of zero disables statistics output. 4735 4736 scftorture.stutter_cpus= [KNL] 4737 The number of jiffies to wait between each change 4738 to the set of CPUs under test. 4739 4740 scftorture.use_cpus_read_lock= [KNL] 4741 Use use_cpus_read_lock() instead of the default 4742 preempt_disable() to disable CPU hotplug 4743 while invoking one of the smp_call_function*() 4744 functions. 4745 4746 scftorture.verbose= [KNL] 4747 Enable additional printk() statements. 4748 4749 scftorture.weight_single= [KNL] 4750 The probability weighting to use for the 4751 smp_call_function_single() function with a zero 4752 "wait" parameter. A value of -1 selects the 4753 default if all other weights are -1. However, 4754 if at least one weight has some other value, a 4755 value of -1 will instead select a weight of zero. 4756 4757 scftorture.weight_single_wait= [KNL] 4758 The probability weighting to use for the 4759 smp_call_function_single() function with a 4760 non-zero "wait" parameter. See weight_single. 4761 4762 scftorture.weight_many= [KNL] 4763 The probability weighting to use for the 4764 smp_call_function_many() function with a zero 4765 "wait" parameter. See weight_single. 4766 Note well that setting a high probability for 4767 this weighting can place serious IPI load 4768 on the system. 4769 4770 scftorture.weight_many_wait= [KNL] 4771 The probability weighting to use for the 4772 smp_call_function_many() function with a 4773 non-zero "wait" parameter. See weight_single 4774 and weight_many. 4775 4776 scftorture.weight_all= [KNL] 4777 The probability weighting to use for the 4778 smp_call_function_all() function with a zero 4779 "wait" parameter. See weight_single and 4780 weight_many. 4781 4782 scftorture.weight_all_wait= [KNL] 4783 The probability weighting to use for the 4784 smp_call_function_all() function with a 4785 non-zero "wait" parameter. See weight_single 4786 and weight_many. 4787 4788 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate 4789 xtime_lock contention on larger systems, and/or RCU lock 4790 contention on all systems with CONFIG_MAXSMP set. 4791 Format: { "0" | "1" } 4792 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 4793 1 -- enable. 4794 Note: increases power consumption, thus should only be 4795 enabled if running jitter sensitive (HPC/RT) workloads. 4796 4797 security= [SECURITY] Choose a legacy "major" security module to 4798 enable at boot. This has been deprecated by the 4799 "lsm=" parameter. 4800 4801 selinux= [SELINUX] Disable or enable SELinux at boot time. 4802 Format: { "0" | "1" } 4803 See security/selinux/Kconfig help text. 4804 0 -- disable. 4805 1 -- enable. 4806 Default value is 1. 4807 4808 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 4809 Format: { "0" | "1" } 4810 See security/apparmor/Kconfig help text 4811 0 -- disable. 4812 1 -- enable. 4813 Default value is set via kernel config option. 4814 4815 serialnumber [BUGS=X86-32] 4816 4817 shapers= [NET] 4818 Maximal number of shapers. 4819 4820 simeth= [IA-64] 4821 simscsi= 4822 4823 slram= [HW,MTD] 4824 4825 slab_nomerge [MM] 4826 Disable merging of slabs with similar size. May be 4827 necessary if there is some reason to distinguish 4828 allocs to different slabs, especially in hardened 4829 environments where the risk of heap overflows and 4830 layout control by attackers can usually be 4831 frustrated by disabling merging. This will reduce 4832 most of the exposure of a heap attack to a single 4833 cache (risks via metadata attacks are mostly 4834 unchanged). Debug options disable merging on their 4835 own. 4836 For more information see Documentation/vm/slub.rst. 4837 4838 slab_max_order= [MM, SLAB] 4839 Determines the maximum allowed order for slabs. 4840 A high setting may cause OOMs due to memory 4841 fragmentation. Defaults to 1 for systems with 4842 more than 32MB of RAM, 0 otherwise. 4843 4844 slub_debug[=options[,slabs][;[options[,slabs]]...] [MM, SLUB] 4845 Enabling slub_debug allows one to determine the 4846 culprit if slab objects become corrupted. Enabling 4847 slub_debug can create guard zones around objects and 4848 may poison objects when not in use. Also tracks the 4849 last alloc / free. For more information see 4850 Documentation/vm/slub.rst. 4851 4852 slub_memcg_sysfs= [MM, SLUB] 4853 Determines whether to enable sysfs directories for 4854 memory cgroup sub-caches. 1 to enable, 0 to disable. 4855 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON. 4856 Enabling this can lead to a very high number of debug 4857 directories and files being created under 4858 /sys/kernel/slub. 4859 4860 slub_max_order= [MM, SLUB] 4861 Determines the maximum allowed order for slabs. 4862 A high setting may cause OOMs due to memory 4863 fragmentation. For more information see 4864 Documentation/vm/slub.rst. 4865 4866 slub_min_objects= [MM, SLUB] 4867 The minimum number of objects per slab. SLUB will 4868 increase the slab order up to slub_max_order to 4869 generate a sufficiently large slab able to contain 4870 the number of objects indicated. The higher the number 4871 of objects the smaller the overhead of tracking slabs 4872 and the less frequently locks need to be acquired. 4873 For more information see Documentation/vm/slub.rst. 4874 4875 slub_min_order= [MM, SLUB] 4876 Determines the minimum page order for slabs. Must be 4877 lower than slub_max_order. 4878 For more information see Documentation/vm/slub.rst. 4879 4880 slub_nomerge [MM, SLUB] 4881 Same with slab_nomerge. This is supported for legacy. 4882 See slab_nomerge for more information. 4883 4884 smart2= [HW] 4885 Format: <io1>[,<io2>[,...,<io8>]] 4886 4887 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 4888 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 4889 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 4890 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 4891 smsc-ircc2.ircc_irq= [HW] IRQ line 4892 smsc-ircc2.ircc_dma= [HW] DMA channel 4893 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 4894 0: Toshiba Satellite 1800 (GP data pin select) 4895 1: Fast pin select (default) 4896 2: ATC IRMode 4897 4898 smt [KNL,S390] Set the maximum number of threads (logical 4899 CPUs) to use per physical CPU on systems capable of 4900 symmetric multithreading (SMT). Will be capped to the 4901 actual hardware limit. 4902 Format: <integer> 4903 Default: -1 (no limit) 4904 4905 softlockup_panic= 4906 [KNL] Should the soft-lockup detector generate panics. 4907 Format: 0 | 1 4908 4909 A value of 1 instructs the soft-lockup detector 4910 to panic the machine when a soft-lockup occurs. It is 4911 also controlled by the kernel.softlockup_panic sysctl 4912 and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the 4913 respective build-time switch to that functionality. 4914 4915 softlockup_all_cpu_backtrace= 4916 [KNL] Should the soft-lockup detector generate 4917 backtraces on all cpus. 4918 Format: 0 | 1 4919 4920 sonypi.*= [HW] Sony Programmable I/O Control Device driver 4921 See Documentation/admin-guide/laptops/sonypi.rst 4922 4923 spectre_v2= [X86] Control mitigation of Spectre variant 2 4924 (indirect branch speculation) vulnerability. 4925 The default operation protects the kernel from 4926 user space attacks. 4927 4928 on - unconditionally enable, implies 4929 spectre_v2_user=on 4930 off - unconditionally disable, implies 4931 spectre_v2_user=off 4932 auto - kernel detects whether your CPU model is 4933 vulnerable 4934 4935 Selecting 'on' will, and 'auto' may, choose a 4936 mitigation method at run time according to the 4937 CPU, the available microcode, the setting of the 4938 CONFIG_RETPOLINE configuration option, and the 4939 compiler with which the kernel was built. 4940 4941 Selecting 'on' will also enable the mitigation 4942 against user space to user space task attacks. 4943 4944 Selecting 'off' will disable both the kernel and 4945 the user space protections. 4946 4947 Specific mitigations can also be selected manually: 4948 4949 retpoline - replace indirect branches 4950 retpoline,generic - google's original retpoline 4951 retpoline,amd - AMD-specific minimal thunk 4952 4953 Not specifying this option is equivalent to 4954 spectre_v2=auto. 4955 4956 spectre_v2_user= 4957 [X86] Control mitigation of Spectre variant 2 4958 (indirect branch speculation) vulnerability between 4959 user space tasks 4960 4961 on - Unconditionally enable mitigations. Is 4962 enforced by spectre_v2=on 4963 4964 off - Unconditionally disable mitigations. Is 4965 enforced by spectre_v2=off 4966 4967 prctl - Indirect branch speculation is enabled, 4968 but mitigation can be enabled via prctl 4969 per thread. The mitigation control state 4970 is inherited on fork. 4971 4972 prctl,ibpb 4973 - Like "prctl" above, but only STIBP is 4974 controlled per thread. IBPB is issued 4975 always when switching between different user 4976 space processes. 4977 4978 seccomp 4979 - Same as "prctl" above, but all seccomp 4980 threads will enable the mitigation unless 4981 they explicitly opt out. 4982 4983 seccomp,ibpb 4984 - Like "seccomp" above, but only STIBP is 4985 controlled per thread. IBPB is issued 4986 always when switching between different 4987 user space processes. 4988 4989 auto - Kernel selects the mitigation depending on 4990 the available CPU features and vulnerability. 4991 4992 Default mitigation: 4993 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl" 4994 4995 Not specifying this option is equivalent to 4996 spectre_v2_user=auto. 4997 4998 spec_store_bypass_disable= 4999 [HW] Control Speculative Store Bypass (SSB) Disable mitigation 5000 (Speculative Store Bypass vulnerability) 5001 5002 Certain CPUs are vulnerable to an exploit against a 5003 a common industry wide performance optimization known 5004 as "Speculative Store Bypass" in which recent stores 5005 to the same memory location may not be observed by 5006 later loads during speculative execution. The idea 5007 is that such stores are unlikely and that they can 5008 be detected prior to instruction retirement at the 5009 end of a particular speculation execution window. 5010 5011 In vulnerable processors, the speculatively forwarded 5012 store can be used in a cache side channel attack, for 5013 example to read memory to which the attacker does not 5014 directly have access (e.g. inside sandboxed code). 5015 5016 This parameter controls whether the Speculative Store 5017 Bypass optimization is used. 5018 5019 On x86 the options are: 5020 5021 on - Unconditionally disable Speculative Store Bypass 5022 off - Unconditionally enable Speculative Store Bypass 5023 auto - Kernel detects whether the CPU model contains an 5024 implementation of Speculative Store Bypass and 5025 picks the most appropriate mitigation. If the 5026 CPU is not vulnerable, "off" is selected. If the 5027 CPU is vulnerable the default mitigation is 5028 architecture and Kconfig dependent. See below. 5029 prctl - Control Speculative Store Bypass per thread 5030 via prctl. Speculative Store Bypass is enabled 5031 for a process by default. The state of the control 5032 is inherited on fork. 5033 seccomp - Same as "prctl" above, but all seccomp threads 5034 will disable SSB unless they explicitly opt out. 5035 5036 Default mitigations: 5037 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl" 5038 5039 On powerpc the options are: 5040 5041 on,auto - On Power8 and Power9 insert a store-forwarding 5042 barrier on kernel entry and exit. On Power7 5043 perform a software flush on kernel entry and 5044 exit. 5045 off - No action. 5046 5047 Not specifying this option is equivalent to 5048 spec_store_bypass_disable=auto. 5049 5050 spia_io_base= [HW,MTD] 5051 spia_fio_base= 5052 spia_pedr= 5053 spia_peddr= 5054 5055 split_lock_detect= 5056 [X86] Enable split lock detection 5057 5058 When enabled (and if hardware support is present), atomic 5059 instructions that access data across cache line 5060 boundaries will result in an alignment check exception. 5061 5062 off - not enabled 5063 5064 warn - the kernel will emit rate limited warnings 5065 about applications triggering the #AC 5066 exception. This mode is the default on CPUs 5067 that supports split lock detection. 5068 5069 fatal - the kernel will send SIGBUS to applications 5070 that trigger the #AC exception. 5071 5072 If an #AC exception is hit in the kernel or in 5073 firmware (i.e. not while executing in user mode) 5074 the kernel will oops in either "warn" or "fatal" 5075 mode. 5076 5077 srbds= [X86,INTEL] 5078 Control the Special Register Buffer Data Sampling 5079 (SRBDS) mitigation. 5080 5081 Certain CPUs are vulnerable to an MDS-like 5082 exploit which can leak bits from the random 5083 number generator. 5084 5085 By default, this issue is mitigated by 5086 microcode. However, the microcode fix can cause 5087 the RDRAND and RDSEED instructions to become 5088 much slower. Among other effects, this will 5089 result in reduced throughput from /dev/urandom. 5090 5091 The microcode mitigation can be disabled with 5092 the following option: 5093 5094 off: Disable mitigation and remove 5095 performance impact to RDRAND and RDSEED 5096 5097 srcutree.counter_wrap_check [KNL] 5098 Specifies how frequently to check for 5099 grace-period sequence counter wrap for the 5100 srcu_data structure's ->srcu_gp_seq_needed field. 5101 The greater the number of bits set in this kernel 5102 parameter, the less frequently counter wrap will 5103 be checked for. Note that the bottom two bits 5104 are ignored. 5105 5106 srcutree.exp_holdoff [KNL] 5107 Specifies how many nanoseconds must elapse 5108 since the end of the last SRCU grace period for 5109 a given srcu_struct until the next normal SRCU 5110 grace period will be considered for automatic 5111 expediting. Set to zero to disable automatic 5112 expediting. 5113 5114 ssbd= [ARM64,HW] 5115 Speculative Store Bypass Disable control 5116 5117 On CPUs that are vulnerable to the Speculative 5118 Store Bypass vulnerability and offer a 5119 firmware based mitigation, this parameter 5120 indicates how the mitigation should be used: 5121 5122 force-on: Unconditionally enable mitigation for 5123 for both kernel and userspace 5124 force-off: Unconditionally disable mitigation for 5125 for both kernel and userspace 5126 kernel: Always enable mitigation in the 5127 kernel, and offer a prctl interface 5128 to allow userspace to register its 5129 interest in being mitigated too. 5130 5131 stack_guard_gap= [MM] 5132 override the default stack gap protection. The value 5133 is in page units and it defines how many pages prior 5134 to (for stacks growing down) resp. after (for stacks 5135 growing up) the main stack are reserved for no other 5136 mapping. Default value is 256 pages. 5137 5138 stacktrace [FTRACE] 5139 Enabled the stack tracer on boot up. 5140 5141 stacktrace_filter=[function-list] 5142 [FTRACE] Limit the functions that the stack tracer 5143 will trace at boot up. function-list is a comma separated 5144 list of functions. This list can be changed at run 5145 time by the stack_trace_filter file in the debugfs 5146 tracing directory. Note, this enables stack tracing 5147 and the stacktrace above is not needed. 5148 5149 sti= [PARISC,HW] 5150 Format: <num> 5151 Set the STI (builtin display/keyboard on the HP-PARISC 5152 machines) console (graphic card) which should be used 5153 as the initial boot-console. 5154 See also comment in drivers/video/console/sticore.c. 5155 5156 sti_font= [HW] 5157 See comment in drivers/video/console/sticore.c. 5158 5159 stifb= [HW] 5160 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 5161 5162 sunrpc.min_resvport= 5163 sunrpc.max_resvport= 5164 [NFS,SUNRPC] 5165 SunRPC servers often require that client requests 5166 originate from a privileged port (i.e. a port in the 5167 range 0 < portnr < 1024). 5168 An administrator who wishes to reserve some of these 5169 ports for other uses may adjust the range that the 5170 kernel's sunrpc client considers to be privileged 5171 using these two parameters to set the minimum and 5172 maximum port values. 5173 5174 sunrpc.svc_rpc_per_connection_limit= 5175 [NFS,SUNRPC] 5176 Limit the number of requests that the server will 5177 process in parallel from a single connection. 5178 The default value is 0 (no limit). 5179 5180 sunrpc.pool_mode= 5181 [NFS] 5182 Control how the NFS server code allocates CPUs to 5183 service thread pools. Depending on how many NICs 5184 you have and where their interrupts are bound, this 5185 option will affect which CPUs will do NFS serving. 5186 Note: this parameter cannot be changed while the 5187 NFS server is running. 5188 5189 auto the server chooses an appropriate mode 5190 automatically using heuristics 5191 global a single global pool contains all CPUs 5192 percpu one pool for each CPU 5193 pernode one pool for each NUMA node (equivalent 5194 to global on non-NUMA machines) 5195 5196 sunrpc.tcp_slot_table_entries= 5197 sunrpc.udp_slot_table_entries= 5198 [NFS,SUNRPC] 5199 Sets the upper limit on the number of simultaneous 5200 RPC calls that can be sent from the client to a 5201 server. Increasing these values may allow you to 5202 improve throughput, but will also increase the 5203 amount of memory reserved for use by the client. 5204 5205 suspend.pm_test_delay= 5206 [SUSPEND] 5207 Sets the number of seconds to remain in a suspend test 5208 mode before resuming the system (see 5209 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 5210 is set. Default value is 5. 5211 5212 svm= [PPC] 5213 Format: { on | off | y | n | 1 | 0 } 5214 This parameter controls use of the Protected 5215 Execution Facility on pSeries. 5216 5217 swapaccount=[0|1] 5218 [KNL] Enable accounting of swap in memory resource 5219 controller if no parameter or 1 is given or disable 5220 it if 0 is given (See Documentation/admin-guide/cgroup-v1/memory.rst) 5221 5222 swiotlb= [ARM,IA-64,PPC,MIPS,X86] 5223 Format: { <int> | force | noforce } 5224 <int> -- Number of I/O TLB slabs 5225 force -- force using of bounce buffers even if they 5226 wouldn't be automatically used by the kernel 5227 noforce -- Never use bounce buffers (for debugging) 5228 5229 switches= [HW,M68k] 5230 5231 sysctl.*= [KNL] 5232 Set a sysctl parameter, right before loading the init 5233 process, as if the value was written to the respective 5234 /proc/sys/... file. Both '.' and '/' are recognized as 5235 separators. Unrecognized parameters and invalid values 5236 are reported in the kernel log. Sysctls registered 5237 later by a loaded module cannot be set this way. 5238 Example: sysctl.vm.swappiness=40 5239 5240 sysfs.deprecated=0|1 [KNL] 5241 Enable/disable old style sysfs layout for old udev 5242 on older distributions. When this option is enabled 5243 very new udev will not work anymore. When this option 5244 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled) 5245 in older udev will not work anymore. 5246 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in 5247 the kernel configuration. 5248 5249 sysrq_always_enabled 5250 [KNL] 5251 Ignore sysrq setting - this boot parameter will 5252 neutralize any effect of /proc/sys/kernel/sysrq. 5253 Useful for debugging. 5254 5255 tcpmhash_entries= [KNL,NET] 5256 Set the number of tcp_metrics_hash slots. 5257 Default value is 8192 or 16384 depending on total 5258 ram pages. This is used to specify the TCP metrics 5259 cache size. See Documentation/networking/ip-sysctl.rst 5260 "tcp_no_metrics_save" section for more details. 5261 5262 tdfx= [HW,DRM] 5263 5264 test_suspend= [SUSPEND][,N] 5265 Specify "mem" (for Suspend-to-RAM) or "standby" (for 5266 standby suspend) or "freeze" (for suspend type freeze) 5267 as the system sleep state during system startup with 5268 the optional capability to repeat N number of times. 5269 The system is woken from this state using a 5270 wakeup-capable RTC alarm. 5271 5272 thash_entries= [KNL,NET] 5273 Set number of hash buckets for TCP connection 5274 5275 thermal.act= [HW,ACPI] 5276 -1: disable all active trip points in all thermal zones 5277 <degrees C>: override all lowest active trip points 5278 5279 thermal.crt= [HW,ACPI] 5280 -1: disable all critical trip points in all thermal zones 5281 <degrees C>: override all critical trip points 5282 5283 thermal.nocrt= [HW,ACPI] 5284 Set to disable actions on ACPI thermal zone 5285 critical and hot trip points. 5286 5287 thermal.off= [HW,ACPI] 5288 1: disable ACPI thermal control 5289 5290 thermal.psv= [HW,ACPI] 5291 -1: disable all passive trip points 5292 <degrees C>: override all passive trip points to this 5293 value 5294 5295 thermal.tzp= [HW,ACPI] 5296 Specify global default ACPI thermal zone polling rate 5297 <deci-seconds>: poll all this frequency 5298 0: no polling (default) 5299 5300 threadirqs [KNL] 5301 Force threading of all interrupt handlers except those 5302 marked explicitly IRQF_NO_THREAD. 5303 5304 topology= [S390] 5305 Format: {off | on} 5306 Specify if the kernel should make use of the cpu 5307 topology information if the hardware supports this. 5308 The scheduler will make use of this information and 5309 e.g. base its process migration decisions on it. 5310 Default is on. 5311 5312 topology_updates= [KNL, PPC, NUMA] 5313 Format: {off} 5314 Specify if the kernel should ignore (off) 5315 topology updates sent by the hypervisor to this 5316 LPAR. 5317 5318 torture.disable_onoff_at_boot= [KNL] 5319 Prevent the CPU-hotplug component of torturing 5320 until after init has spawned. 5321 5322 torture.ftrace_dump_at_shutdown= [KNL] 5323 Dump the ftrace buffer at torture-test shutdown, 5324 even if there were no errors. This can be a 5325 very costly operation when many torture tests 5326 are running concurrently, especially on systems 5327 with rotating-rust storage. 5328 5329 tp720= [HW,PS2] 5330 5331 tpm_suspend_pcr=[HW,TPM] 5332 Format: integer pcr id 5333 Specify that at suspend time, the tpm driver 5334 should extend the specified pcr with zeros, 5335 as a workaround for some chips which fail to 5336 flush the last written pcr on TPM_SaveState. 5337 This will guarantee that all the other pcrs 5338 are saved. 5339 5340 trace_buf_size=nn[KMG] 5341 [FTRACE] will set tracing buffer size on each cpu. 5342 5343 trace_event=[event-list] 5344 [FTRACE] Set and start specified trace events in order 5345 to facilitate early boot debugging. The event-list is a 5346 comma separated list of trace events to enable. See 5347 also Documentation/trace/events.rst 5348 5349 trace_options=[option-list] 5350 [FTRACE] Enable or disable tracer options at boot. 5351 The option-list is a comma delimited list of options 5352 that can be enabled or disabled just as if you were 5353 to echo the option name into 5354 5355 /sys/kernel/debug/tracing/trace_options 5356 5357 For example, to enable stacktrace option (to dump the 5358 stack trace of each event), add to the command line: 5359 5360 trace_options=stacktrace 5361 5362 See also Documentation/trace/ftrace.rst "trace options" 5363 section. 5364 5365 tp_printk[FTRACE] 5366 Have the tracepoints sent to printk as well as the 5367 tracing ring buffer. This is useful for early boot up 5368 where the system hangs or reboots and does not give the 5369 option for reading the tracing buffer or performing a 5370 ftrace_dump_on_oops. 5371 5372 To turn off having tracepoints sent to printk, 5373 echo 0 > /proc/sys/kernel/tracepoint_printk 5374 Note, echoing 1 into this file without the 5375 tracepoint_printk kernel cmdline option has no effect. 5376 5377 ** CAUTION ** 5378 5379 Having tracepoints sent to printk() and activating high 5380 frequency tracepoints such as irq or sched, can cause 5381 the system to live lock. 5382 5383 traceoff_on_warning 5384 [FTRACE] enable this option to disable tracing when a 5385 warning is hit. This turns off "tracing_on". Tracing can 5386 be enabled again by echoing '1' into the "tracing_on" 5387 file located in /sys/kernel/debug/tracing/ 5388 5389 This option is useful, as it disables the trace before 5390 the WARNING dump is called, which prevents the trace to 5391 be filled with content caused by the warning output. 5392 5393 This option can also be set at run time via the sysctl 5394 option: kernel/traceoff_on_warning 5395 5396 transparent_hugepage= 5397 [KNL] 5398 Format: [always|madvise|never] 5399 Can be used to control the default behavior of the system 5400 with respect to transparent hugepages. 5401 See Documentation/admin-guide/mm/transhuge.rst 5402 for more details. 5403 5404 tsc= Disable clocksource stability checks for TSC. 5405 Format: <string> 5406 [x86] reliable: mark tsc clocksource as reliable, this 5407 disables clocksource verification at runtime, as well 5408 as the stability checks done at bootup. Used to enable 5409 high-resolution timer mode on older hardware, and in 5410 virtualized environment. 5411 [x86] noirqtime: Do not use TSC to do irq accounting. 5412 Used to run time disable IRQ_TIME_ACCOUNTING on any 5413 platforms where RDTSC is slow and this accounting 5414 can add overhead. 5415 [x86] unstable: mark the TSC clocksource as unstable, this 5416 marks the TSC unconditionally unstable at bootup and 5417 avoids any further wobbles once the TSC watchdog notices. 5418 [x86] nowatchdog: disable clocksource watchdog. Used 5419 in situations with strict latency requirements (where 5420 interruptions from clocksource watchdog are not 5421 acceptable). 5422 5423 tsc_early_khz= [X86] Skip early TSC calibration and use the given 5424 value instead. Useful when the early TSC frequency discovery 5425 procedure is not reliable, such as on overclocked systems 5426 with CPUID.16h support and partial CPUID.15h support. 5427 Format: <unsigned int> 5428 5429 tsx= [X86] Control Transactional Synchronization 5430 Extensions (TSX) feature in Intel processors that 5431 support TSX control. 5432 5433 This parameter controls the TSX feature. The options are: 5434 5435 on - Enable TSX on the system. Although there are 5436 mitigations for all known security vulnerabilities, 5437 TSX has been known to be an accelerator for 5438 several previous speculation-related CVEs, and 5439 so there may be unknown security risks associated 5440 with leaving it enabled. 5441 5442 off - Disable TSX on the system. (Note that this 5443 option takes effect only on newer CPUs which are 5444 not vulnerable to MDS, i.e., have 5445 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get 5446 the new IA32_TSX_CTRL MSR through a microcode 5447 update. This new MSR allows for the reliable 5448 deactivation of the TSX functionality.) 5449 5450 auto - Disable TSX if X86_BUG_TAA is present, 5451 otherwise enable TSX on the system. 5452 5453 Not specifying this option is equivalent to tsx=off. 5454 5455 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 5456 for more details. 5457 5458 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async 5459 Abort (TAA) vulnerability. 5460 5461 Similar to Micro-architectural Data Sampling (MDS) 5462 certain CPUs that support Transactional 5463 Synchronization Extensions (TSX) are vulnerable to an 5464 exploit against CPU internal buffers which can forward 5465 information to a disclosure gadget under certain 5466 conditions. 5467 5468 In vulnerable processors, the speculatively forwarded 5469 data can be used in a cache side channel attack, to 5470 access data to which the attacker does not have direct 5471 access. 5472 5473 This parameter controls the TAA mitigation. The 5474 options are: 5475 5476 full - Enable TAA mitigation on vulnerable CPUs 5477 if TSX is enabled. 5478 5479 full,nosmt - Enable TAA mitigation and disable SMT on 5480 vulnerable CPUs. If TSX is disabled, SMT 5481 is not disabled because CPU is not 5482 vulnerable to cross-thread TAA attacks. 5483 off - Unconditionally disable TAA mitigation 5484 5485 On MDS-affected machines, tsx_async_abort=off can be 5486 prevented by an active MDS mitigation as both vulnerabilities 5487 are mitigated with the same mechanism so in order to disable 5488 this mitigation, you need to specify mds=off too. 5489 5490 Not specifying this option is equivalent to 5491 tsx_async_abort=full. On CPUs which are MDS affected 5492 and deploy MDS mitigation, TAA mitigation is not 5493 required and doesn't provide any additional 5494 mitigation. 5495 5496 For details see: 5497 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 5498 5499 turbografx.map[2|3]= [HW,JOY] 5500 TurboGraFX parallel port interface 5501 Format: 5502 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 5503 See also Documentation/input/devices/joystick-parport.rst 5504 5505 udbg-immortal [PPC] When debugging early kernel crashes that 5506 happen after console_init() and before a proper 5507 console driver takes over, this boot options might 5508 help "seeing" what's going on. 5509 5510 uhash_entries= [KNL,NET] 5511 Set number of hash buckets for UDP/UDP-Lite connections 5512 5513 uhci-hcd.ignore_oc= 5514 [USB] Ignore overcurrent events (default N). 5515 Some badly-designed motherboards generate lots of 5516 bogus events, for ports that aren't wired to 5517 anything. Set this parameter to avoid log spamming. 5518 Note that genuine overcurrent events won't be 5519 reported either. 5520 5521 unknown_nmi_panic 5522 [X86] Cause panic on unknown NMI. 5523 5524 usbcore.authorized_default= 5525 [USB] Default USB device authorization: 5526 (default -1 = authorized except for wireless USB, 5527 0 = not authorized, 1 = authorized, 2 = authorized 5528 if device connected to internal port) 5529 5530 usbcore.autosuspend= 5531 [USB] The autosuspend time delay (in seconds) used 5532 for newly-detected USB devices (default 2). This 5533 is the time required before an idle device will be 5534 autosuspended. Devices for which the delay is set 5535 to a negative value won't be autosuspended at all. 5536 5537 usbcore.usbfs_snoop= 5538 [USB] Set to log all usbfs traffic (default 0 = off). 5539 5540 usbcore.usbfs_snoop_max= 5541 [USB] Maximum number of bytes to snoop in each URB 5542 (default = 65536). 5543 5544 usbcore.blinkenlights= 5545 [USB] Set to cycle leds on hubs (default 0 = off). 5546 5547 usbcore.old_scheme_first= 5548 [USB] Start with the old device initialization 5549 scheme (default 0 = off). 5550 5551 usbcore.usbfs_memory_mb= 5552 [USB] Memory limit (in MB) for buffers allocated by 5553 usbfs (default = 16, 0 = max = 2047). 5554 5555 usbcore.use_both_schemes= 5556 [USB] Try the other device initialization scheme 5557 if the first one fails (default 1 = enabled). 5558 5559 usbcore.initial_descriptor_timeout= 5560 [USB] Specifies timeout for the initial 64-byte 5561 USB_REQ_GET_DESCRIPTOR request in milliseconds 5562 (default 5000 = 5.0 seconds). 5563 5564 usbcore.nousb [USB] Disable the USB subsystem 5565 5566 usbcore.quirks= 5567 [USB] A list of quirk entries to augment the built-in 5568 usb core quirk list. List entries are separated by 5569 commas. Each entry has the form 5570 VendorID:ProductID:Flags. The IDs are 4-digit hex 5571 numbers and Flags is a set of letters. Each letter 5572 will change the built-in quirk; setting it if it is 5573 clear and clearing it if it is set. The letters have 5574 the following meanings: 5575 a = USB_QUIRK_STRING_FETCH_255 (string 5576 descriptors must not be fetched using 5577 a 255-byte read); 5578 b = USB_QUIRK_RESET_RESUME (device can't resume 5579 correctly so reset it instead); 5580 c = USB_QUIRK_NO_SET_INTF (device can't handle 5581 Set-Interface requests); 5582 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't 5583 handle its Configuration or Interface 5584 strings); 5585 e = USB_QUIRK_RESET (device can't be reset 5586 (e.g morph devices), don't use reset); 5587 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has 5588 more interface descriptions than the 5589 bNumInterfaces count, and can't handle 5590 talking to these interfaces); 5591 g = USB_QUIRK_DELAY_INIT (device needs a pause 5592 during initialization, after we read 5593 the device descriptor); 5594 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For 5595 high speed and super speed interrupt 5596 endpoints, the USB 2.0 and USB 3.0 spec 5597 require the interval in microframes (1 5598 microframe = 125 microseconds) to be 5599 calculated as interval = 2 ^ 5600 (bInterval-1). 5601 Devices with this quirk report their 5602 bInterval as the result of this 5603 calculation instead of the exponent 5604 variable used in the calculation); 5605 i = USB_QUIRK_DEVICE_QUALIFIER (device can't 5606 handle device_qualifier descriptor 5607 requests); 5608 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device 5609 generates spurious wakeup, ignore 5610 remote wakeup capability); 5611 k = USB_QUIRK_NO_LPM (device can't handle Link 5612 Power Management); 5613 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL 5614 (Device reports its bInterval as linear 5615 frames instead of the USB 2.0 5616 calculation); 5617 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs 5618 to be disconnected before suspend to 5619 prevent spurious wakeup); 5620 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a 5621 pause after every control message); 5622 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra 5623 delay after resetting its port); 5624 Example: quirks=0781:5580:bk,0a5c:5834:gij 5625 5626 usbhid.mousepoll= 5627 [USBHID] The interval which mice are to be polled at. 5628 5629 usbhid.jspoll= 5630 [USBHID] The interval which joysticks are to be polled at. 5631 5632 usbhid.kbpoll= 5633 [USBHID] The interval which keyboards are to be polled at. 5634 5635 usb-storage.delay_use= 5636 [UMS] The delay in seconds before a new device is 5637 scanned for Logical Units (default 1). 5638 5639 usb-storage.quirks= 5640 [UMS] A list of quirks entries to supplement or 5641 override the built-in unusual_devs list. List 5642 entries are separated by commas. Each entry has 5643 the form VID:PID:Flags where VID and PID are Vendor 5644 and Product ID values (4-digit hex numbers) and 5645 Flags is a set of characters, each corresponding 5646 to a common usb-storage quirk flag as follows: 5647 a = SANE_SENSE (collect more than 18 bytes 5648 of sense data, not on uas); 5649 b = BAD_SENSE (don't collect more than 18 5650 bytes of sense data, not on uas); 5651 c = FIX_CAPACITY (decrease the reported 5652 device capacity by one sector); 5653 d = NO_READ_DISC_INFO (don't use 5654 READ_DISC_INFO command, not on uas); 5655 e = NO_READ_CAPACITY_16 (don't use 5656 READ_CAPACITY_16 command); 5657 f = NO_REPORT_OPCODES (don't use report opcodes 5658 command, uas only); 5659 g = MAX_SECTORS_240 (don't transfer more than 5660 240 sectors at a time, uas only); 5661 h = CAPACITY_HEURISTICS (decrease the 5662 reported device capacity by one 5663 sector if the number is odd); 5664 i = IGNORE_DEVICE (don't bind to this 5665 device); 5666 j = NO_REPORT_LUNS (don't use report luns 5667 command, uas only); 5668 k = NO_SAME (do not use WRITE_SAME, uas only) 5669 l = NOT_LOCKABLE (don't try to lock and 5670 unlock ejectable media, not on uas); 5671 m = MAX_SECTORS_64 (don't transfer more 5672 than 64 sectors = 32 KB at a time, 5673 not on uas); 5674 n = INITIAL_READ10 (force a retry of the 5675 initial READ(10) command, not on uas); 5676 o = CAPACITY_OK (accept the capacity 5677 reported by the device, not on uas); 5678 p = WRITE_CACHE (the device cache is ON 5679 by default, not on uas); 5680 r = IGNORE_RESIDUE (the device reports 5681 bogus residue values, not on uas); 5682 s = SINGLE_LUN (the device has only one 5683 Logical Unit); 5684 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 5685 commands, uas only); 5686 u = IGNORE_UAS (don't bind to the uas driver); 5687 w = NO_WP_DETECT (don't test whether the 5688 medium is write-protected). 5689 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 5690 even if the device claims no cache, 5691 not on uas) 5692 Example: quirks=0419:aaf5:rl,0421:0433:rc 5693 5694 user_debug= [KNL,ARM] 5695 Format: <int> 5696 See arch/arm/Kconfig.debug help text. 5697 1 - undefined instruction events 5698 2 - system calls 5699 4 - invalid data aborts 5700 8 - SIGSEGV faults 5701 16 - SIGBUS faults 5702 Example: user_debug=31 5703 5704 userpte= 5705 [X86] Flags controlling user PTE allocations. 5706 5707 nohigh = do not allocate PTE pages in 5708 HIGHMEM regardless of setting 5709 of CONFIG_HIGHPTE. 5710 5711 vdso= [X86,SH] 5712 On X86_32, this is an alias for vdso32=. Otherwise: 5713 5714 vdso=1: enable VDSO (the default) 5715 vdso=0: disable VDSO mapping 5716 5717 vdso32= [X86] Control the 32-bit vDSO 5718 vdso32=1: enable 32-bit VDSO 5719 vdso32=0 or vdso32=2: disable 32-bit VDSO 5720 5721 See the help text for CONFIG_COMPAT_VDSO for more 5722 details. If CONFIG_COMPAT_VDSO is set, the default is 5723 vdso32=0; otherwise, the default is vdso32=1. 5724 5725 For compatibility with older kernels, vdso32=2 is an 5726 alias for vdso32=0. 5727 5728 Try vdso32=0 if you encounter an error that says: 5729 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 5730 5731 vector= [IA-64,SMP] 5732 vector=percpu: enable percpu vector domain 5733 5734 video= [FB] Frame buffer configuration 5735 See Documentation/fb/modedb.rst. 5736 5737 video.brightness_switch_enabled= [0,1] 5738 If set to 1, on receiving an ACPI notify event 5739 generated by hotkey, video driver will adjust brightness 5740 level and then send out the event to user space through 5741 the allocated input device; If set to 0, video driver 5742 will only send out the event without touching backlight 5743 brightness level. 5744 default: 1 5745 5746 virtio_mmio.device= 5747 [VMMIO] Memory mapped virtio (platform) device. 5748 5749 <size>@<baseaddr>:<irq>[:<id>] 5750 where: 5751 <size> := size (can use standard suffixes 5752 like K, M and G) 5753 <baseaddr> := physical base address 5754 <irq> := interrupt number (as passed to 5755 request_irq()) 5756 <id> := (optional) platform device id 5757 example: 5758 virtio_mmio.device=1K@0x100b0000:48:7 5759 5760 Can be used multiple times for multiple devices. 5761 5762 vga= [BOOT,X86-32] Select a particular video mode 5763 See Documentation/x86/boot.rst and 5764 Documentation/admin-guide/svga.rst. 5765 Use vga=ask for menu. 5766 This is actually a boot loader parameter; the value is 5767 passed to the kernel using a special protocol. 5768 5769 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. 5770 May slow down system boot speed, especially when 5771 enabled on systems with a large amount of memory. 5772 All options are enabled by default, and this 5773 interface is meant to allow for selectively 5774 enabling or disabling specific virtual memory 5775 debugging features. 5776 5777 Available options are: 5778 P Enable page structure init time poisoning 5779 - Disable all of the above options 5780 5781 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact 5782 size of <nn>. This can be used to increase the 5783 minimum size (128MB on x86). It can also be used to 5784 decrease the size and leave more room for directly 5785 mapped kernel RAM. 5786 5787 vmcp_cma=nn[MG] [KNL,S390] 5788 Sets the memory size reserved for contiguous memory 5789 allocations for the vmcp device driver. 5790 5791 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 5792 Format: <command> 5793 5794 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 5795 Format: <command> 5796 5797 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 5798 Format: <command> 5799 5800 vsyscall= [X86-64] 5801 Controls the behavior of vsyscalls (i.e. calls to 5802 fixed addresses of 0xffffffffff600x00 from legacy 5803 code). Most statically-linked binaries and older 5804 versions of glibc use these calls. Because these 5805 functions are at fixed addresses, they make nice 5806 targets for exploits that can control RIP. 5807 5808 emulate [default] Vsyscalls turn into traps and are 5809 emulated reasonably safely. The vsyscall 5810 page is readable. 5811 5812 xonly Vsyscalls turn into traps and are 5813 emulated reasonably safely. The vsyscall 5814 page is not readable. 5815 5816 none Vsyscalls don't work at all. This makes 5817 them quite hard to use for exploits but 5818 might break your system. 5819 5820 vt.color= [VT] Default text color. 5821 Format: 0xYX, X = foreground, Y = background. 5822 Default: 0x07 = light gray on black. 5823 5824 vt.cur_default= [VT] Default cursor shape. 5825 Format: 0xCCBBAA, where AA, BB, and CC are the same as 5826 the parameters of the <Esc>[?A;B;Cc escape sequence; 5827 see VGA-softcursor.txt. Default: 2 = underline. 5828 5829 vt.default_blu= [VT] 5830 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 5831 Change the default blue palette of the console. 5832 This is a 16-member array composed of values 5833 ranging from 0-255. 5834 5835 vt.default_grn= [VT] 5836 Format: <green0>,<green1>,<green2>,...,<green15> 5837 Change the default green palette of the console. 5838 This is a 16-member array composed of values 5839 ranging from 0-255. 5840 5841 vt.default_red= [VT] 5842 Format: <red0>,<red1>,<red2>,...,<red15> 5843 Change the default red palette of the console. 5844 This is a 16-member array composed of values 5845 ranging from 0-255. 5846 5847 vt.default_utf8= 5848 [VT] 5849 Format=<0|1> 5850 Set system-wide default UTF-8 mode for all tty's. 5851 Default is 1, i.e. UTF-8 mode is enabled for all 5852 newly opened terminals. 5853 5854 vt.global_cursor_default= 5855 [VT] 5856 Format=<-1|0|1> 5857 Set system-wide default for whether a cursor 5858 is shown on new VTs. Default is -1, 5859 i.e. cursors will be created by default unless 5860 overridden by individual drivers. 0 will hide 5861 cursors, 1 will display them. 5862 5863 vt.italic= [VT] Default color for italic text; 0-15. 5864 Default: 2 = green. 5865 5866 vt.underline= [VT] Default color for underlined text; 0-15. 5867 Default: 3 = cyan. 5868 5869 watchdog timers [HW,WDT] For information on watchdog timers, 5870 see Documentation/watchdog/watchdog-parameters.rst 5871 or other driver-specific files in the 5872 Documentation/watchdog/ directory. 5873 5874 watchdog_thresh= 5875 [KNL] 5876 Set the hard lockup detector stall duration 5877 threshold in seconds. The soft lockup detector 5878 threshold is set to twice the value. A value of 0 5879 disables both lockup detectors. Default is 10 5880 seconds. 5881 5882 workqueue.watchdog_thresh= 5883 If CONFIG_WQ_WATCHDOG is configured, workqueue can 5884 warn stall conditions and dump internal state to 5885 help debugging. 0 disables workqueue stall 5886 detection; otherwise, it's the stall threshold 5887 duration in seconds. The default value is 30 and 5888 it can be updated at runtime by writing to the 5889 corresponding sysfs file. 5890 5891 workqueue.disable_numa 5892 By default, all work items queued to unbound 5893 workqueues are affine to the NUMA nodes they're 5894 issued on, which results in better behavior in 5895 general. If NUMA affinity needs to be disabled for 5896 whatever reason, this option can be used. Note 5897 that this also can be controlled per-workqueue for 5898 workqueues visible under /sys/bus/workqueue/. 5899 5900 workqueue.power_efficient 5901 Per-cpu workqueues are generally preferred because 5902 they show better performance thanks to cache 5903 locality; unfortunately, per-cpu workqueues tend to 5904 be more power hungry than unbound workqueues. 5905 5906 Enabling this makes the per-cpu workqueues which 5907 were observed to contribute significantly to power 5908 consumption unbound, leading to measurably lower 5909 power usage at the cost of small performance 5910 overhead. 5911 5912 The default value of this parameter is determined by 5913 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 5914 5915 workqueue.debug_force_rr_cpu 5916 Workqueue used to implicitly guarantee that work 5917 items queued without explicit CPU specified are put 5918 on the local CPU. This guarantee is no longer true 5919 and while local CPU is still preferred work items 5920 may be put on foreign CPUs. This debug option 5921 forces round-robin CPU selection to flush out 5922 usages which depend on the now broken guarantee. 5923 When enabled, memory and cache locality will be 5924 impacted. 5925 5926 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of 5927 default x2apic cluster mode on platforms 5928 supporting x2apic. 5929 5930 x86_intel_mid_timer= [X86-32,APBT] 5931 Choose timer option for x86 Intel MID platform. 5932 Two valid options are apbt timer only and lapic timer 5933 plus one apbt timer for broadcast timer. 5934 x86_intel_mid_timer=apbt_only | lapic_and_apbt 5935 5936 xen_512gb_limit [KNL,X86-64,XEN] 5937 Restricts the kernel running paravirtualized under Xen 5938 to use only up to 512 GB of RAM. The reason to do so is 5939 crash analysis tools and Xen tools for doing domain 5940 save/restore/migration must be enabled to handle larger 5941 domains. 5942 5943 xen_emul_unplug= [HW,X86,XEN] 5944 Unplug Xen emulated devices 5945 Format: [unplug0,][unplug1] 5946 ide-disks -- unplug primary master IDE devices 5947 aux-ide-disks -- unplug non-primary-master IDE devices 5948 nics -- unplug network devices 5949 all -- unplug all emulated devices (NICs and IDE disks) 5950 unnecessary -- unplugging emulated devices is 5951 unnecessary even if the host did not respond to 5952 the unplug protocol 5953 never -- do not unplug even if version check succeeds 5954 5955 xen_legacy_crash [X86,XEN] 5956 Crash from Xen panic notifier, without executing late 5957 panic() code such as dumping handler. 5958 5959 xen_nopvspin [X86,XEN] 5960 Disables the qspinlock slowpath using Xen PV optimizations. 5961 This parameter is obsoleted by "nopvspin" parameter, which 5962 has equivalent effect for XEN platform. 5963 5964 xen_nopv [X86] 5965 Disables the PV optimizations forcing the HVM guest to 5966 run as generic HVM guest with no PV drivers. 5967 This option is obsoleted by the "nopv" option, which 5968 has equivalent effect for XEN platform. 5969 5970 xen_scrub_pages= [XEN] 5971 Boolean option to control scrubbing pages before giving them back 5972 to Xen, for use by other domains. Can be also changed at runtime 5973 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. 5974 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. 5975 5976 xen_timer_slop= [X86-64,XEN] 5977 Set the timer slop (in nanoseconds) for the virtual Xen 5978 timers (default is 100000). This adjusts the minimum 5979 delta of virtualized Xen timers, where lower values 5980 improve timer resolution at the expense of processing 5981 more timer interrupts. 5982 5983 xen.event_eoi_delay= [XEN] 5984 How long to delay EOI handling in case of event 5985 storms (jiffies). Default is 10. 5986 5987 xen.event_loop_timeout= [XEN] 5988 After which time (jiffies) the event handling loop 5989 should start to delay EOI handling. Default is 2. 5990 5991 xen.fifo_events= [XEN] 5992 Boolean parameter to disable using fifo event handling 5993 even if available. Normally fifo event handling is 5994 preferred over the 2-level event handling, as it is 5995 fairer and the number of possible event channels is 5996 much higher. Default is on (use fifo events). 5997 5998 nopv= [X86,XEN,KVM,HYPER_V,VMWARE] 5999 Disables the PV optimizations forcing the guest to run 6000 as generic guest with no PV drivers. Currently support 6001 XEN HVM, KVM, HYPER_V and VMWARE guest. 6002 6003 nopvspin [X86,XEN,KVM] 6004 Disables the qspinlock slow path using PV optimizations 6005 which allow the hypervisor to 'idle' the guest on lock 6006 contention. 6007 6008 xirc2ps_cs= [NET,PCMCIA] 6009 Format: 6010 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 6011 6012 xive= [PPC] 6013 By default on POWER9 and above, the kernel will 6014 natively use the XIVE interrupt controller. This option 6015 allows the fallback firmware mode to be used: 6016 6017 off Fallback to firmware control of XIVE interrupt 6018 controller on both pseries and powernv 6019 platforms. Only useful on POWER9 and above. 6020 6021 xhci-hcd.quirks [USB,KNL] 6022 A hex value specifying bitmask with supplemental xhci 6023 host controller quirks. Meaning of each bit can be 6024 consulted in header drivers/usb/host/xhci.h. 6025 6026 xmon [PPC] 6027 Format: { early | on | rw | ro | off } 6028 Controls if xmon debugger is enabled. Default is off. 6029 Passing only "xmon" is equivalent to "xmon=early". 6030 early Call xmon as early as possible on boot; xmon 6031 debugger is called from setup_arch(). 6032 on xmon debugger hooks will be installed so xmon 6033 is only called on a kernel crash. Default mode, 6034 i.e. either "ro" or "rw" mode, is controlled 6035 with CONFIG_XMON_DEFAULT_RO_MODE. 6036 rw xmon debugger hooks will be installed so xmon 6037 is called only on a kernel crash, mode is write, 6038 meaning SPR registers, memory and, other data 6039 can be written using xmon commands. 6040 ro same as "rw" option above but SPR registers, 6041 memory, and other data can't be written using 6042 xmon commands. 6043 off xmon is disabled. 6044