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 1887 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 1888 0 disables intel_idle and fall back on acpi_idle. 1889 1 to 9 specify maximum depth of C-state. 1890 1891 intel_pstate= [X86] 1892 disable 1893 Do not enable intel_pstate as the default 1894 scaling driver for the supported processors 1895 passive 1896 Use intel_pstate as a scaling driver, but configure it 1897 to work with generic cpufreq governors (instead of 1898 enabling its internal governor). This mode cannot be 1899 used along with the hardware-managed P-states (HWP) 1900 feature. 1901 force 1902 Enable intel_pstate on systems that prohibit it by default 1903 in favor of acpi-cpufreq. Forcing the intel_pstate driver 1904 instead of acpi-cpufreq may disable platform features, such 1905 as thermal controls and power capping, that rely on ACPI 1906 P-States information being indicated to OSPM and therefore 1907 should be used with caution. This option does not work with 1908 processors that aren't supported by the intel_pstate driver 1909 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 1910 no_hwp 1911 Do not enable hardware P state control (HWP) 1912 if available. 1913 hwp_only 1914 Only load intel_pstate on systems which support 1915 hardware P state control (HWP) if available. 1916 support_acpi_ppc 1917 Enforce ACPI _PPC performance limits. If the Fixed ACPI 1918 Description Table, specifies preferred power management 1919 profile as "Enterprise Server" or "Performance Server", 1920 then this feature is turned on by default. 1921 per_cpu_perf_limits 1922 Allow per-logical-CPU P-State performance control limits using 1923 cpufreq sysfs interface 1924 1925 intremap= [X86-64, Intel-IOMMU] 1926 on enable Interrupt Remapping (default) 1927 off disable Interrupt Remapping 1928 nosid disable Source ID checking 1929 no_x2apic_optout 1930 BIOS x2APIC opt-out request will be ignored 1931 nopost disable Interrupt Posting 1932 1933 iomem= Disable strict checking of access to MMIO memory 1934 strict regions from userspace. 1935 relaxed 1936 1937 iommu= [X86] 1938 off 1939 force 1940 noforce 1941 biomerge 1942 panic 1943 nopanic 1944 merge 1945 nomerge 1946 soft 1947 pt [X86] 1948 nopt [X86] 1949 nobypass [PPC/POWERNV] 1950 Disable IOMMU bypass, using IOMMU for PCI devices. 1951 1952 iommu.strict= [ARM64] Configure TLB invalidation behaviour 1953 Format: { "0" | "1" } 1954 0 - Lazy mode. 1955 Request that DMA unmap operations use deferred 1956 invalidation of hardware TLBs, for increased 1957 throughput at the cost of reduced device isolation. 1958 Will fall back to strict mode if not supported by 1959 the relevant IOMMU driver. 1960 1 - Strict mode (default). 1961 DMA unmap operations invalidate IOMMU hardware TLBs 1962 synchronously. 1963 1964 iommu.passthrough= 1965 [ARM64, X86] Configure DMA to bypass the IOMMU by default. 1966 Format: { "0" | "1" } 1967 0 - Use IOMMU translation for DMA. 1968 1 - Bypass the IOMMU for DMA. 1969 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH. 1970 1971 io7= [HW] IO7 for Marvel-based Alpha systems 1972 See comment before marvel_specify_io7 in 1973 arch/alpha/kernel/core_marvel.c. 1974 1975 io_delay= [X86] I/O delay method 1976 0x80 1977 Standard port 0x80 based delay 1978 0xed 1979 Alternate port 0xed based delay (needed on some systems) 1980 udelay 1981 Simple two microseconds delay 1982 none 1983 No delay 1984 1985 ip= [IP_PNP] 1986 See Documentation/admin-guide/nfs/nfsroot.rst. 1987 1988 ipcmni_extend [KNL] Extend the maximum number of unique System V 1989 IPC identifiers from 32,768 to 16,777,216. 1990 1991 irqaffinity= [SMP] Set the default irq affinity mask 1992 The argument is a cpu list, as described above. 1993 1994 irqchip.gicv2_force_probe= 1995 [ARM, ARM64] 1996 Format: <bool> 1997 Force the kernel to look for the second 4kB page 1998 of a GICv2 controller even if the memory range 1999 exposed by the device tree is too small. 2000 2001 irqchip.gicv3_nolpi= 2002 [ARM, ARM64] 2003 Force the kernel to ignore the availability of 2004 LPIs (and by consequence ITSs). Intended for system 2005 that use the kernel as a bootloader, and thus want 2006 to let secondary kernels in charge of setting up 2007 LPIs. 2008 2009 irqchip.gicv3_pseudo_nmi= [ARM64] 2010 Enables support for pseudo-NMIs in the kernel. This 2011 requires the kernel to be built with 2012 CONFIG_ARM64_PSEUDO_NMI. 2013 2014 irqfixup [HW] 2015 When an interrupt is not handled search all handlers 2016 for it. Intended to get systems with badly broken 2017 firmware running. 2018 2019 irqpoll [HW] 2020 When an interrupt is not handled search all handlers 2021 for it. Also check all handlers each timer 2022 interrupt. Intended to get systems with badly broken 2023 firmware running. 2024 2025 isapnp= [ISAPNP] 2026 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 2027 2028 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance. 2029 [Deprecated - use cpusets instead] 2030 Format: [flag-list,]<cpu-list> 2031 2032 Specify one or more CPUs to isolate from disturbances 2033 specified in the flag list (default: domain): 2034 2035 nohz 2036 Disable the tick when a single task runs. 2037 2038 A residual 1Hz tick is offloaded to workqueues, which you 2039 need to affine to housekeeping through the global 2040 workqueue's affinity configured via the 2041 /sys/devices/virtual/workqueue/cpumask sysfs file, or 2042 by using the 'domain' flag described below. 2043 2044 NOTE: by default the global workqueue runs on all CPUs, 2045 so to protect individual CPUs the 'cpumask' file has to 2046 be configured manually after bootup. 2047 2048 domain 2049 Isolate from the general SMP balancing and scheduling 2050 algorithms. Note that performing domain isolation this way 2051 is irreversible: it's not possible to bring back a CPU to 2052 the domains once isolated through isolcpus. It's strongly 2053 advised to use cpusets instead to disable scheduler load 2054 balancing through the "cpuset.sched_load_balance" file. 2055 It offers a much more flexible interface where CPUs can 2056 move in and out of an isolated set anytime. 2057 2058 You can move a process onto or off an "isolated" CPU via 2059 the CPU affinity syscalls or cpuset. 2060 <cpu number> begins at 0 and the maximum value is 2061 "number of CPUs in system - 1". 2062 2063 managed_irq 2064 2065 Isolate from being targeted by managed interrupts 2066 which have an interrupt mask containing isolated 2067 CPUs. The affinity of managed interrupts is 2068 handled by the kernel and cannot be changed via 2069 the /proc/irq/* interfaces. 2070 2071 This isolation is best effort and only effective 2072 if the automatically assigned interrupt mask of a 2073 device queue contains isolated and housekeeping 2074 CPUs. If housekeeping CPUs are online then such 2075 interrupts are directed to the housekeeping CPU 2076 so that IO submitted on the housekeeping CPU 2077 cannot disturb the isolated CPU. 2078 2079 If a queue's affinity mask contains only isolated 2080 CPUs then this parameter has no effect on the 2081 interrupt routing decision, though interrupts are 2082 only delivered when tasks running on those 2083 isolated CPUs submit IO. IO submitted on 2084 housekeeping CPUs has no influence on those 2085 queues. 2086 2087 The format of <cpu-list> is described above. 2088 2089 iucv= [HW,NET] 2090 2091 ivrs_ioapic [HW,X86-64] 2092 Provide an override to the IOAPIC-ID<->DEVICE-ID 2093 mapping provided in the IVRS ACPI table. For 2094 example, to map IOAPIC-ID decimal 10 to 2095 PCI device 00:14.0 write the parameter as: 2096 ivrs_ioapic[10]=00:14.0 2097 2098 ivrs_hpet [HW,X86-64] 2099 Provide an override to the HPET-ID<->DEVICE-ID 2100 mapping provided in the IVRS ACPI table. For 2101 example, to map HPET-ID decimal 0 to 2102 PCI device 00:14.0 write the parameter as: 2103 ivrs_hpet[0]=00:14.0 2104 2105 ivrs_acpihid [HW,X86-64] 2106 Provide an override to the ACPI-HID:UID<->DEVICE-ID 2107 mapping provided in the IVRS ACPI table. For 2108 example, to map UART-HID:UID AMD0020:0 to 2109 PCI device 00:14.5 write the parameter as: 2110 ivrs_acpihid[00:14.5]=AMD0020:0 2111 2112 js= [HW,JOY] Analog joystick 2113 See Documentation/input/joydev/joystick.rst. 2114 2115 nokaslr [KNL] 2116 When CONFIG_RANDOMIZE_BASE is set, this disables 2117 kernel and module base offset ASLR (Address Space 2118 Layout Randomization). 2119 2120 kasan_multi_shot 2121 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print 2122 report on every invalid memory access. Without this 2123 parameter KASAN will print report only for the first 2124 invalid access. 2125 2126 keepinitrd [HW,ARM] 2127 2128 kernelcore= [KNL,X86,IA-64,PPC] 2129 Format: nn[KMGTPE] | nn% | "mirror" 2130 This parameter specifies the amount of memory usable by 2131 the kernel for non-movable allocations. The requested 2132 amount is spread evenly throughout all nodes in the 2133 system as ZONE_NORMAL. The remaining memory is used for 2134 movable memory in its own zone, ZONE_MOVABLE. In the 2135 event, a node is too small to have both ZONE_NORMAL and 2136 ZONE_MOVABLE, kernelcore memory will take priority and 2137 other nodes will have a larger ZONE_MOVABLE. 2138 2139 ZONE_MOVABLE is used for the allocation of pages that 2140 may be reclaimed or moved by the page migration 2141 subsystem. Note that allocations like PTEs-from-HighMem 2142 still use the HighMem zone if it exists, and the Normal 2143 zone if it does not. 2144 2145 It is possible to specify the exact amount of memory in 2146 the form of "nn[KMGTPE]", a percentage of total system 2147 memory in the form of "nn%", or "mirror". If "mirror" 2148 option is specified, mirrored (reliable) memory is used 2149 for non-movable allocations and remaining memory is used 2150 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror" 2151 are exclusive, so you cannot specify multiple forms. 2152 2153 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port. 2154 Format: <Controller#>[,poll interval] 2155 The controller # is the number of the ehci usb debug 2156 port as it is probed via PCI. The poll interval is 2157 optional and is the number seconds in between 2158 each poll cycle to the debug port in case you need 2159 the functionality for interrupting the kernel with 2160 gdb or control-c on the dbgp connection. When 2161 not using this parameter you use sysrq-g to break into 2162 the kernel debugger. 2163 2164 kgdboc= [KGDB,HW] kgdb over consoles. 2165 Requires a tty driver that supports console polling, 2166 or a supported polling keyboard driver (non-usb). 2167 Serial only format: <serial_device>[,baud] 2168 keyboard only format: kbd 2169 keyboard and serial format: kbd,<serial_device>[,baud] 2170 Optional Kernel mode setting: 2171 kms, kbd format: kms,kbd 2172 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 2173 2174 kgdboc_earlycon= [KGDB,HW] 2175 If the boot console provides the ability to read 2176 characters and can work in polling mode, you can use 2177 this parameter to tell kgdb to use it as a backend 2178 until the normal console is registered. Intended to 2179 be used together with the kgdboc parameter which 2180 specifies the normal console to transition to. 2181 2182 The name of the early console should be specified 2183 as the value of this parameter. Note that the name of 2184 the early console might be different than the tty 2185 name passed to kgdboc. It's OK to leave the value 2186 blank and the first boot console that implements 2187 read() will be picked. 2188 2189 kgdbwait [KGDB] Stop kernel execution and enter the 2190 kernel debugger at the earliest opportunity. 2191 2192 kmac= [MIPS] Korina ethernet MAC address. 2193 Configure the RouterBoard 532 series on-chip 2194 Ethernet adapter MAC address. 2195 2196 kmemleak= [KNL] Boot-time kmemleak enable/disable 2197 Valid arguments: on, off 2198 Default: on 2199 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 2200 the default is off. 2201 2202 kprobe_event=[probe-list] 2203 [FTRACE] Add kprobe events and enable at boot time. 2204 The probe-list is a semicolon delimited list of probe 2205 definitions. Each definition is same as kprobe_events 2206 interface, but the parameters are comma delimited. 2207 For example, to add a kprobe event on vfs_read with 2208 arg1 and arg2, add to the command line; 2209 2210 kprobe_event=p,vfs_read,$arg1,$arg2 2211 2212 See also Documentation/trace/kprobetrace.rst "Kernel 2213 Boot Parameter" section. 2214 2215 kpti= [ARM64] Control page table isolation of user 2216 and kernel address spaces. 2217 Default: enabled on cores which need mitigation. 2218 0: force disabled 2219 1: force enabled 2220 2221 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 2222 Default is 0 (don't ignore, but inject #GP) 2223 2224 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface. 2225 Default is false (don't support). 2226 2227 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit 2228 KVM MMU at runtime. 2229 Default is 0 (off) 2230 2231 kvm.nx_huge_pages= 2232 [KVM] Controls the software workaround for the 2233 X86_BUG_ITLB_MULTIHIT bug. 2234 force : Always deploy workaround. 2235 off : Never deploy workaround. 2236 auto : Deploy workaround based on the presence of 2237 X86_BUG_ITLB_MULTIHIT. 2238 2239 Default is 'auto'. 2240 2241 If the software workaround is enabled for the host, 2242 guests do need not to enable it for nested guests. 2243 2244 kvm.nx_huge_pages_recovery_ratio= 2245 [KVM] Controls how many 4KiB pages are periodically zapped 2246 back to huge pages. 0 disables the recovery, otherwise if 2247 the value is N KVM will zap 1/Nth of the 4KiB pages every 2248 minute. The default is 60. 2249 2250 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM. 2251 Default is 1 (enabled) 2252 2253 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU) 2254 for all guests. 2255 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode. 2256 2257 kvm-arm.mode= 2258 [KVM,ARM] Select one of KVM/arm64's modes of operation. 2259 2260 protected: nVHE-based mode with support for guests whose 2261 state is kept private from the host. 2262 Not valid if the kernel is running in EL2. 2263 2264 Defaults to VHE/nVHE based on hardware support and 2265 the value of CONFIG_ARM64_VHE. 2266 2267 kvm-arm.vgic_v3_group0_trap= 2268 [KVM,ARM] Trap guest accesses to GICv3 group-0 2269 system registers 2270 2271 kvm-arm.vgic_v3_group1_trap= 2272 [KVM,ARM] Trap guest accesses to GICv3 group-1 2273 system registers 2274 2275 kvm-arm.vgic_v3_common_trap= 2276 [KVM,ARM] Trap guest accesses to GICv3 common 2277 system registers 2278 2279 kvm-arm.vgic_v4_enable= 2280 [KVM,ARM] Allow use of GICv4 for direct injection of 2281 LPIs. 2282 2283 kvm_cma_resv_ratio=n [PPC] 2284 Reserves given percentage from system memory area for 2285 contiguous memory allocation for KVM hash pagetable 2286 allocation. 2287 By default it reserves 5% of total system memory. 2288 Format: <integer> 2289 Default: 5 2290 2291 kvm-intel.ept= [KVM,Intel] Disable extended page tables 2292 (virtualized MMU) support on capable Intel chips. 2293 Default is 1 (enabled) 2294 2295 kvm-intel.emulate_invalid_guest_state= 2296 [KVM,Intel] Enable emulation of invalid guest states 2297 Default is 0 (disabled) 2298 2299 kvm-intel.flexpriority= 2300 [KVM,Intel] Disable FlexPriority feature (TPR shadow). 2301 Default is 1 (enabled) 2302 2303 kvm-intel.nested= 2304 [KVM,Intel] Enable VMX nesting (nVMX). 2305 Default is 0 (disabled) 2306 2307 kvm-intel.unrestricted_guest= 2308 [KVM,Intel] Disable unrestricted guest feature 2309 (virtualized real and unpaged mode) on capable 2310 Intel chips. Default is 1 (enabled) 2311 2312 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault 2313 CVE-2018-3620. 2314 2315 Valid arguments: never, cond, always 2316 2317 always: L1D cache flush on every VMENTER. 2318 cond: Flush L1D on VMENTER only when the code between 2319 VMEXIT and VMENTER can leak host memory. 2320 never: Disables the mitigation 2321 2322 Default is cond (do L1 cache flush in specific instances) 2323 2324 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification 2325 feature (tagged TLBs) on capable Intel chips. 2326 Default is 1 (enabled) 2327 2328 l1tf= [X86] Control mitigation of the L1TF vulnerability on 2329 affected CPUs 2330 2331 The kernel PTE inversion protection is unconditionally 2332 enabled and cannot be disabled. 2333 2334 full 2335 Provides all available mitigations for the 2336 L1TF vulnerability. Disables SMT and 2337 enables all mitigations in the 2338 hypervisors, i.e. unconditional L1D flush. 2339 2340 SMT control and L1D flush control via the 2341 sysfs interface is still possible after 2342 boot. Hypervisors will issue a warning 2343 when the first VM is started in a 2344 potentially insecure configuration, 2345 i.e. SMT enabled or L1D flush disabled. 2346 2347 full,force 2348 Same as 'full', but disables SMT and L1D 2349 flush runtime control. Implies the 2350 'nosmt=force' command line option. 2351 (i.e. sysfs control of SMT is disabled.) 2352 2353 flush 2354 Leaves SMT enabled and enables the default 2355 hypervisor mitigation, i.e. conditional 2356 L1D flush. 2357 2358 SMT control and L1D flush control via the 2359 sysfs interface is still possible after 2360 boot. Hypervisors will issue a warning 2361 when the first VM is started in a 2362 potentially insecure configuration, 2363 i.e. SMT enabled or L1D flush disabled. 2364 2365 flush,nosmt 2366 2367 Disables SMT and enables the default 2368 hypervisor mitigation. 2369 2370 SMT control and L1D flush control via the 2371 sysfs interface is still possible after 2372 boot. Hypervisors will issue a warning 2373 when the first VM is started in a 2374 potentially insecure configuration, 2375 i.e. SMT enabled or L1D flush disabled. 2376 2377 flush,nowarn 2378 Same as 'flush', but hypervisors will not 2379 warn when a VM is started in a potentially 2380 insecure configuration. 2381 2382 off 2383 Disables hypervisor mitigations and doesn't 2384 emit any warnings. 2385 It also drops the swap size and available 2386 RAM limit restriction on both hypervisor and 2387 bare metal. 2388 2389 Default is 'flush'. 2390 2391 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst 2392 2393 l2cr= [PPC] 2394 2395 l3cr= [PPC] 2396 2397 lapic [X86-32,APIC] Enable the local APIC even if BIOS 2398 disabled it. 2399 2400 lapic= [X86,APIC] Do not use TSC deadline 2401 value for LAPIC timer one-shot implementation. Default 2402 back to the programmable timer unit in the LAPIC. 2403 Format: notscdeadline 2404 2405 lapic_timer_c2_ok [X86,APIC] trust the local apic timer 2406 in C2 power state. 2407 2408 libata.dma= [LIBATA] DMA control 2409 libata.dma=0 Disable all PATA and SATA DMA 2410 libata.dma=1 PATA and SATA Disk DMA only 2411 libata.dma=2 ATAPI (CDROM) DMA only 2412 libata.dma=4 Compact Flash DMA only 2413 Combinations also work, so libata.dma=3 enables DMA 2414 for disks and CDROMs, but not CFs. 2415 2416 libata.ignore_hpa= [LIBATA] Ignore HPA limit 2417 libata.ignore_hpa=0 keep BIOS limits (default) 2418 libata.ignore_hpa=1 ignore limits, using full disk 2419 2420 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 2421 when set. 2422 Format: <int> 2423 2424 libata.force= [LIBATA] Force configurations. The format is comma- 2425 separated list of "[ID:]VAL" where ID is 2426 PORT[.DEVICE]. PORT and DEVICE are decimal numbers 2427 matching port, link or device. Basically, it matches 2428 the ATA ID string printed on console by libata. If 2429 the whole ID part is omitted, the last PORT and DEVICE 2430 values are used. If ID hasn't been specified yet, the 2431 configuration applies to all ports, links and devices. 2432 2433 If only DEVICE is omitted, the parameter applies to 2434 the port and all links and devices behind it. DEVICE 2435 number of 0 either selects the first device or the 2436 first fan-out link behind PMP device. It does not 2437 select the host link. DEVICE number of 15 selects the 2438 host link and device attached to it. 2439 2440 The VAL specifies the configuration to force. As long 2441 as there's no ambiguity shortcut notation is allowed. 2442 For example, both 1.5 and 1.5G would work for 1.5Gbps. 2443 The following configurations can be forced. 2444 2445 * Cable type: 40c, 80c, short40c, unk, ign or sata. 2446 Any ID with matching PORT is used. 2447 2448 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 2449 2450 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 2451 udma[/][16,25,33,44,66,100,133] notation is also 2452 allowed. 2453 2454 * [no]ncq: Turn on or off NCQ. 2455 2456 * [no]ncqtrim: Turn off queued DSM TRIM. 2457 2458 * nohrst, nosrst, norst: suppress hard, soft 2459 and both resets. 2460 2461 * rstonce: only attempt one reset during 2462 hot-unplug link recovery 2463 2464 * dump_id: dump IDENTIFY data. 2465 2466 * atapi_dmadir: Enable ATAPI DMADIR bridge support 2467 2468 * disable: Disable this device. 2469 2470 If there are multiple matching configurations changing 2471 the same attribute, the last one is used. 2472 2473 memblock=debug [KNL] Enable memblock debug messages. 2474 2475 load_ramdisk= [RAM] [Deprecated] 2476 2477 lockd.nlm_grace_period=P [NFS] Assign grace period. 2478 Format: <integer> 2479 2480 lockd.nlm_tcpport=N [NFS] Assign TCP port. 2481 Format: <integer> 2482 2483 lockd.nlm_timeout=T [NFS] Assign timeout value. 2484 Format: <integer> 2485 2486 lockd.nlm_udpport=M [NFS] Assign UDP port. 2487 Format: <integer> 2488 2489 lockdown= [SECURITY] 2490 { integrity | confidentiality } 2491 Enable the kernel lockdown feature. If set to 2492 integrity, kernel features that allow userland to 2493 modify the running kernel are disabled. If set to 2494 confidentiality, kernel features that allow userland 2495 to extract confidential information from the kernel 2496 are also disabled. 2497 2498 locktorture.nreaders_stress= [KNL] 2499 Set the number of locking read-acquisition kthreads. 2500 Defaults to being automatically set based on the 2501 number of online CPUs. 2502 2503 locktorture.nwriters_stress= [KNL] 2504 Set the number of locking write-acquisition kthreads. 2505 2506 locktorture.onoff_holdoff= [KNL] 2507 Set time (s) after boot for CPU-hotplug testing. 2508 2509 locktorture.onoff_interval= [KNL] 2510 Set time (s) between CPU-hotplug operations, or 2511 zero to disable CPU-hotplug testing. 2512 2513 locktorture.shuffle_interval= [KNL] 2514 Set task-shuffle interval (jiffies). Shuffling 2515 tasks allows some CPUs to go into dyntick-idle 2516 mode during the locktorture test. 2517 2518 locktorture.shutdown_secs= [KNL] 2519 Set time (s) after boot system shutdown. This 2520 is useful for hands-off automated testing. 2521 2522 locktorture.stat_interval= [KNL] 2523 Time (s) between statistics printk()s. 2524 2525 locktorture.stutter= [KNL] 2526 Time (s) to stutter testing, for example, 2527 specifying five seconds causes the test to run for 2528 five seconds, wait for five seconds, and so on. 2529 This tests the locking primitive's ability to 2530 transition abruptly to and from idle. 2531 2532 locktorture.torture_type= [KNL] 2533 Specify the locking implementation to test. 2534 2535 locktorture.verbose= [KNL] 2536 Enable additional printk() statements. 2537 2538 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 2539 Format: <irq> 2540 2541 loglevel= All Kernel Messages with a loglevel smaller than the 2542 console loglevel will be printed to the console. It can 2543 also be changed with klogd or other programs. The 2544 loglevels are defined as follows: 2545 2546 0 (KERN_EMERG) system is unusable 2547 1 (KERN_ALERT) action must be taken immediately 2548 2 (KERN_CRIT) critical conditions 2549 3 (KERN_ERR) error conditions 2550 4 (KERN_WARNING) warning conditions 2551 5 (KERN_NOTICE) normal but significant condition 2552 6 (KERN_INFO) informational 2553 7 (KERN_DEBUG) debug-level messages 2554 2555 log_buf_len=n[KMG] Sets the size of the printk ring buffer, 2556 in bytes. n must be a power of two and greater 2557 than the minimal size. The minimal size is defined 2558 by LOG_BUF_SHIFT kernel config parameter. There is 2559 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter 2560 that allows to increase the default size depending on 2561 the number of CPUs. See init/Kconfig for more details. 2562 2563 logo.nologo [FB] Disables display of the built-in Linux logo. 2564 This may be used to provide more screen space for 2565 kernel log messages and is useful when debugging 2566 kernel boot problems. 2567 2568 lp=0 [LP] Specify parallel ports to use, e.g, 2569 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 2570 lp=reset first parallel port). 'lp=0' disables the 2571 lp=auto printer driver. 'lp=reset' (which can be 2572 specified in addition to the ports) causes 2573 attached printers to be reset. Using 2574 lp=port1,port2,... specifies the parallel ports 2575 to associate lp devices with, starting with 2576 lp0. A port specification may be 'none' to skip 2577 that lp device, or a parport name such as 2578 'parport0'. Specifying 'lp=auto' instead of a 2579 port specification list means that device IDs 2580 from each port should be examined, to see if 2581 an IEEE 1284-compliant printer is attached; if 2582 so, the driver will manage that printer. 2583 See also header of drivers/char/lp.c. 2584 2585 lpj=n [KNL] 2586 Sets loops_per_jiffy to given constant, thus avoiding 2587 time-consuming boot-time autodetection (up to 250 ms per 2588 CPU). 0 enables autodetection (default). To determine 2589 the correct value for your kernel, boot with normal 2590 autodetection and see what value is printed. Note that 2591 on SMP systems the preset will be applied to all CPUs, 2592 which is likely to cause problems if your CPUs need 2593 significantly divergent settings. An incorrect value 2594 will cause delays in the kernel to be wrong, leading to 2595 unpredictable I/O errors and other breakage. Although 2596 unlikely, in the extreme case this might damage your 2597 hardware. 2598 2599 ltpc= [NET] 2600 Format: <io>,<irq>,<dma> 2601 2602 lsm.debug [SECURITY] Enable LSM initialization debugging output. 2603 2604 lsm=lsm1,...,lsmN 2605 [SECURITY] Choose order of LSM initialization. This 2606 overrides CONFIG_LSM, and the "security=" parameter. 2607 2608 machvec= [IA-64] Force the use of a particular machine-vector 2609 (machvec) in a generic kernel. 2610 Example: machvec=hpzx1 2611 2612 machtype= [Loongson] Share the same kernel image file between 2613 different yeeloong laptops. 2614 Example: machtype=lemote-yeeloong-2f-7inch 2615 2616 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater 2617 than or equal to this physical address is ignored. 2618 2619 maxcpus= [SMP] Maximum number of processors that an SMP kernel 2620 will bring up during bootup. maxcpus=n : n >= 0 limits 2621 the kernel to bring up 'n' processors. Surely after 2622 bootup you can bring up the other plugged cpu by executing 2623 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 2624 only takes effect during system bootup. 2625 While n=0 is a special case, it is equivalent to "nosmp", 2626 which also disables the IO APIC. 2627 2628 max_loop= [LOOP] The number of loop block devices that get 2629 (loop.max_loop) unconditionally pre-created at init time. The default 2630 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 2631 of statically allocating a predefined number, loop 2632 devices can be requested on-demand with the 2633 /dev/loop-control interface. 2634 2635 mce [X86-32] Machine Check Exception 2636 2637 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.rst 2638 2639 md= [HW] RAID subsystems devices and level 2640 See Documentation/admin-guide/md.rst. 2641 2642 mdacon= [MDA] 2643 Format: <first>,<last> 2644 Specifies range of consoles to be captured by the MDA. 2645 2646 mds= [X86,INTEL] 2647 Control mitigation for the Micro-architectural Data 2648 Sampling (MDS) vulnerability. 2649 2650 Certain CPUs are vulnerable to an exploit against CPU 2651 internal buffers which can forward information to a 2652 disclosure gadget under certain conditions. 2653 2654 In vulnerable processors, the speculatively 2655 forwarded data can be used in a cache side channel 2656 attack, to access data to which the attacker does 2657 not have direct access. 2658 2659 This parameter controls the MDS mitigation. The 2660 options are: 2661 2662 full - Enable MDS mitigation on vulnerable CPUs 2663 full,nosmt - Enable MDS mitigation and disable 2664 SMT on vulnerable CPUs 2665 off - Unconditionally disable MDS mitigation 2666 2667 On TAA-affected machines, mds=off can be prevented by 2668 an active TAA mitigation as both vulnerabilities are 2669 mitigated with the same mechanism so in order to disable 2670 this mitigation, you need to specify tsx_async_abort=off 2671 too. 2672 2673 Not specifying this option is equivalent to 2674 mds=full. 2675 2676 For details see: Documentation/admin-guide/hw-vuln/mds.rst 2677 2678 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory 2679 Amount of memory to be used in cases as follows: 2680 2681 1 for test; 2682 2 when the kernel is not able to see the whole system memory; 2683 3 memory that lies after 'mem=' boundary is excluded from 2684 the hypervisor, then assigned to KVM guests. 2685 2686 [X86] Work as limiting max address. Use together 2687 with memmap= to avoid physical address space collisions. 2688 Without memmap= PCI devices could be placed at addresses 2689 belonging to unused RAM. 2690 2691 Note that this only takes effects during boot time since 2692 in above case 3, memory may need be hot added after boot 2693 if system memory of hypervisor is not sufficient. 2694 2695 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 2696 memory. 2697 2698 memchunk=nn[KMG] 2699 [KNL,SH] Allow user to override the default size for 2700 per-device physically contiguous DMA buffers. 2701 2702 memhp_default_state=online/offline 2703 [KNL] Set the initial state for the memory hotplug 2704 onlining policy. If not specified, the default value is 2705 set according to the 2706 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config 2707 option. 2708 See Documentation/admin-guide/mm/memory-hotplug.rst. 2709 2710 memmap=exactmap [KNL,X86] Enable setting of an exact 2711 E820 memory map, as specified by the user. 2712 Such memmap=exactmap lines can be constructed based on 2713 BIOS output or other requirements. See the memmap=nn@ss 2714 option description. 2715 2716 memmap=nn[KMG]@ss[KMG] 2717 [KNL, X86, MIPS, XTENSA] Force usage of a specific region of memory. 2718 Region of memory to be used is from ss to ss+nn. 2719 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], 2720 which limits max address to nn[KMG]. 2721 Multiple different regions can be specified, 2722 comma delimited. 2723 Example: 2724 memmap=100M@2G,100M#3G,1G!1024G 2725 2726 memmap=nn[KMG]#ss[KMG] 2727 [KNL,ACPI] Mark specific memory as ACPI data. 2728 Region of memory to be marked is from ss to ss+nn. 2729 2730 memmap=nn[KMG]$ss[KMG] 2731 [KNL,ACPI] Mark specific memory as reserved. 2732 Region of memory to be reserved is from ss to ss+nn. 2733 Example: Exclude memory from 0x18690000-0x1869ffff 2734 memmap=64K$0x18690000 2735 or 2736 memmap=0x10000$0x18690000 2737 Some bootloaders may need an escape character before '$', 2738 like Grub2, otherwise '$' and the following number 2739 will be eaten. 2740 2741 memmap=nn[KMG]!ss[KMG] 2742 [KNL,X86] Mark specific memory as protected. 2743 Region of memory to be used, from ss to ss+nn. 2744 The memory region may be marked as e820 type 12 (0xc) 2745 and is NVDIMM or ADR memory. 2746 2747 memmap=<size>%<offset>-<oldtype>+<newtype> 2748 [KNL,ACPI] Convert memory within the specified region 2749 from <oldtype> to <newtype>. If "-<oldtype>" is left 2750 out, the whole region will be marked as <newtype>, 2751 even if previously unavailable. If "+<newtype>" is left 2752 out, matching memory will be removed. Types are 2753 specified as e820 types, e.g., 1 = RAM, 2 = reserved, 2754 3 = ACPI, 12 = PRAM. 2755 2756 memory_corruption_check=0/1 [X86] 2757 Some BIOSes seem to corrupt the first 64k of 2758 memory when doing things like suspend/resume. 2759 Setting this option will scan the memory 2760 looking for corruption. Enabling this will 2761 both detect corruption and prevent the kernel 2762 from using the memory being corrupted. 2763 However, its intended as a diagnostic tool; if 2764 repeatable BIOS-originated corruption always 2765 affects the same memory, you can use memmap= 2766 to prevent the kernel from using that memory. 2767 2768 memory_corruption_check_size=size [X86] 2769 By default it checks for corruption in the low 2770 64k, making this memory unavailable for normal 2771 use. Use this parameter to scan for 2772 corruption in more or less memory. 2773 2774 memory_corruption_check_period=seconds [X86] 2775 By default it checks for corruption every 60 2776 seconds. Use this parameter to check at some 2777 other rate. 0 disables periodic checking. 2778 2779 memtest= [KNL,X86,ARM,PPC] Enable memtest 2780 Format: <integer> 2781 default : 0 <disable> 2782 Specifies the number of memtest passes to be 2783 performed. Each pass selects another test 2784 pattern from a given set of patterns. Memtest 2785 fills the memory with this pattern, validates 2786 memory contents and reserves bad memory 2787 regions that are detected. 2788 2789 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control 2790 Valid arguments: on, off 2791 Default (depends on kernel configuration option): 2792 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y) 2793 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n) 2794 mem_encrypt=on: Activate SME 2795 mem_encrypt=off: Do not activate SME 2796 2797 Refer to Documentation/virt/kvm/amd-memory-encryption.rst 2798 for details on when memory encryption can be activated. 2799 2800 mem_sleep_default= [SUSPEND] Default system suspend mode: 2801 s2idle - Suspend-To-Idle 2802 shallow - Power-On Suspend or equivalent (if supported) 2803 deep - Suspend-To-RAM or equivalent (if supported) 2804 See Documentation/admin-guide/pm/sleep-states.rst. 2805 2806 meye.*= [HW] Set MotionEye Camera parameters 2807 See Documentation/admin-guide/media/meye.rst. 2808 2809 mfgpt_irq= [IA-32] Specify the IRQ to use for the 2810 Multi-Function General Purpose Timers on AMD Geode 2811 platforms. 2812 2813 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 2814 the BIOS has incorrectly applied a workaround. TinyBIOS 2815 version 0.98 is known to be affected, 0.99 fixes the 2816 problem by letting the user disable the workaround. 2817 2818 mga= [HW,DRM] 2819 2820 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this 2821 physical address is ignored. 2822 2823 mini2440= [ARM,HW,KNL] 2824 Format:[0..2][b][c][t] 2825 Default: "0tb" 2826 MINI2440 configuration specification: 2827 0 - The attached screen is the 3.5" TFT 2828 1 - The attached screen is the 7" TFT 2829 2 - The VGA Shield is attached (1024x768) 2830 Leaving out the screen size parameter will not load 2831 the TFT driver, and the framebuffer will be left 2832 unconfigured. 2833 b - Enable backlight. The TFT backlight pin will be 2834 linked to the kernel VESA blanking code and a GPIO 2835 LED. This parameter is not necessary when using the 2836 VGA shield. 2837 c - Enable the s3c camera interface. 2838 t - Reserved for enabling touchscreen support. The 2839 touchscreen support is not enabled in the mainstream 2840 kernel as of 2.6.30, a preliminary port can be found 2841 in the "bleeding edge" mini2440 support kernel at 2842 https://repo.or.cz/w/linux-2.6/mini2440.git 2843 2844 mitigations= 2845 [X86,PPC,S390,ARM64] Control optional mitigations for 2846 CPU vulnerabilities. This is a set of curated, 2847 arch-independent options, each of which is an 2848 aggregation of existing arch-specific options. 2849 2850 off 2851 Disable all optional CPU mitigations. This 2852 improves system performance, but it may also 2853 expose users to several CPU vulnerabilities. 2854 Equivalent to: nopti [X86,PPC] 2855 kpti=0 [ARM64] 2856 nospectre_v1 [X86,PPC] 2857 nobp=0 [S390] 2858 nospectre_v2 [X86,PPC,S390,ARM64] 2859 spectre_v2_user=off [X86] 2860 spec_store_bypass_disable=off [X86,PPC] 2861 ssbd=force-off [ARM64] 2862 l1tf=off [X86] 2863 mds=off [X86] 2864 tsx_async_abort=off [X86] 2865 kvm.nx_huge_pages=off [X86] 2866 no_entry_flush [PPC] 2867 no_uaccess_flush [PPC] 2868 2869 Exceptions: 2870 This does not have any effect on 2871 kvm.nx_huge_pages when 2872 kvm.nx_huge_pages=force. 2873 2874 auto (default) 2875 Mitigate all CPU vulnerabilities, but leave SMT 2876 enabled, even if it's vulnerable. This is for 2877 users who don't want to be surprised by SMT 2878 getting disabled across kernel upgrades, or who 2879 have other ways of avoiding SMT-based attacks. 2880 Equivalent to: (default behavior) 2881 2882 auto,nosmt 2883 Mitigate all CPU vulnerabilities, disabling SMT 2884 if needed. This is for users who always want to 2885 be fully mitigated, even if it means losing SMT. 2886 Equivalent to: l1tf=flush,nosmt [X86] 2887 mds=full,nosmt [X86] 2888 tsx_async_abort=full,nosmt [X86] 2889 2890 mminit_loglevel= 2891 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this 2892 parameter allows control of the logging verbosity for 2893 the additional memory initialisation checks. A value 2894 of 0 disables mminit logging and a level of 4 will 2895 log everything. Information is printed at KERN_DEBUG 2896 so loglevel=8 may also need to be specified. 2897 2898 module.sig_enforce 2899 [KNL] When CONFIG_MODULE_SIG is set, this means that 2900 modules without (valid) signatures will fail to load. 2901 Note that if CONFIG_MODULE_SIG_FORCE is set, that 2902 is always true, so this option does nothing. 2903 2904 module_blacklist= [KNL] Do not load a comma-separated list of 2905 modules. Useful for debugging problem modules. 2906 2907 mousedev.tap_time= 2908 [MOUSE] Maximum time between finger touching and 2909 leaving touchpad surface for touch to be considered 2910 a tap and be reported as a left button click (for 2911 touchpads working in absolute mode only). 2912 Format: <msecs> 2913 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 2914 reporting absolute coordinates, such as tablets 2915 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 2916 reporting absolute coordinates, such as tablets 2917 2918 movablecore= [KNL,X86,IA-64,PPC] 2919 Format: nn[KMGTPE] | nn% 2920 This parameter is the complement to kernelcore=, it 2921 specifies the amount of memory used for migratable 2922 allocations. If both kernelcore and movablecore is 2923 specified, then kernelcore will be at *least* the 2924 specified value but may be more. If movablecore on its 2925 own is specified, the administrator must be careful 2926 that the amount of memory usable for all allocations 2927 is not too small. 2928 2929 movable_node [KNL] Boot-time switch to make hotplugable memory 2930 NUMA nodes to be movable. This means that the memory 2931 of such nodes will be usable only for movable 2932 allocations which rules out almost all kernel 2933 allocations. Use with caution! 2934 2935 MTD_Partition= [MTD] 2936 Format: <name>,<region-number>,<size>,<offset> 2937 2938 MTD_Region= [MTD] Format: 2939 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 2940 2941 mtdparts= [MTD] 2942 See drivers/mtd/parsers/cmdlinepart.c 2943 2944 multitce=off [PPC] This parameter disables the use of the pSeries 2945 firmware feature for updating multiple TCE entries 2946 at a time. 2947 2948 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 2949 2950 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 2951 2952 boundary - index of last SLC block on Flex-OneNAND. 2953 The remaining blocks are configured as MLC blocks. 2954 lock - Configure if Flex-OneNAND boundary should be locked. 2955 Once locked, the boundary cannot be changed. 2956 1 indicates lock status, 0 indicates unlock status. 2957 2958 mtdset= [ARM] 2959 ARM/S3C2412 JIVE boot control 2960 2961 See arch/arm/mach-s3c/mach-jive.c 2962 2963 mtouchusb.raw_coordinates= 2964 [HW] Make the MicroTouch USB driver use raw coordinates 2965 ('y', default) or cooked coordinates ('n') 2966 2967 mtrr_chunk_size=nn[KMG] [X86] 2968 used for mtrr cleanup. It is largest continuous chunk 2969 that could hold holes aka. UC entries. 2970 2971 mtrr_gran_size=nn[KMG] [X86] 2972 Used for mtrr cleanup. It is granularity of mtrr block. 2973 Default is 1. 2974 Large value could prevent small alignment from 2975 using up MTRRs. 2976 2977 mtrr_spare_reg_nr=n [X86] 2978 Format: <integer> 2979 Range: 0,7 : spare reg number 2980 Default : 1 2981 Used for mtrr cleanup. It is spare mtrr entries number. 2982 Set to 2 or more if your graphical card needs more. 2983 2984 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 2985 2986 netdev= [NET] Network devices parameters 2987 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 2988 Note that mem_start is often overloaded to mean 2989 something different and driver-specific. 2990 This usage is only documented in each driver source 2991 file if at all. 2992 2993 nf_conntrack.acct= 2994 [NETFILTER] Enable connection tracking flow accounting 2995 0 to disable accounting 2996 1 to enable accounting 2997 Default value is 0. 2998 2999 nfsaddrs= [NFS] Deprecated. Use ip= instead. 3000 See Documentation/admin-guide/nfs/nfsroot.rst. 3001 3002 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 3003 See Documentation/admin-guide/nfs/nfsroot.rst. 3004 3005 nfsrootdebug [NFS] enable nfsroot debugging messages. 3006 See Documentation/admin-guide/nfs/nfsroot.rst. 3007 3008 nfs.callback_nr_threads= 3009 [NFSv4] set the total number of threads that the 3010 NFS client will assign to service NFSv4 callback 3011 requests. 3012 3013 nfs.callback_tcpport= 3014 [NFS] set the TCP port on which the NFSv4 callback 3015 channel should listen. 3016 3017 nfs.cache_getent= 3018 [NFS] sets the pathname to the program which is used 3019 to update the NFS client cache entries. 3020 3021 nfs.cache_getent_timeout= 3022 [NFS] sets the timeout after which an attempt to 3023 update a cache entry is deemed to have failed. 3024 3025 nfs.idmap_cache_timeout= 3026 [NFS] set the maximum lifetime for idmapper cache 3027 entries. 3028 3029 nfs.enable_ino64= 3030 [NFS] enable 64-bit inode numbers. 3031 If zero, the NFS client will fake up a 32-bit inode 3032 number for the readdir() and stat() syscalls instead 3033 of returning the full 64-bit number. 3034 The default is to return 64-bit inode numbers. 3035 3036 nfs.max_session_cb_slots= 3037 [NFSv4.1] Sets the maximum number of session 3038 slots the client will assign to the callback 3039 channel. This determines the maximum number of 3040 callbacks the client will process in parallel for 3041 a particular server. 3042 3043 nfs.max_session_slots= 3044 [NFSv4.1] Sets the maximum number of session slots 3045 the client will attempt to negotiate with the server. 3046 This limits the number of simultaneous RPC requests 3047 that the client can send to the NFSv4.1 server. 3048 Note that there is little point in setting this 3049 value higher than the max_tcp_slot_table_limit. 3050 3051 nfs.nfs4_disable_idmapping= 3052 [NFSv4] When set to the default of '1', this option 3053 ensures that both the RPC level authentication 3054 scheme and the NFS level operations agree to use 3055 numeric uids/gids if the mount is using the 3056 'sec=sys' security flavour. In effect it is 3057 disabling idmapping, which can make migration from 3058 legacy NFSv2/v3 systems to NFSv4 easier. 3059 Servers that do not support this mode of operation 3060 will be autodetected by the client, and it will fall 3061 back to using the idmapper. 3062 To turn off this behaviour, set the value to '0'. 3063 nfs.nfs4_unique_id= 3064 [NFS4] Specify an additional fixed unique ident- 3065 ification string that NFSv4 clients can insert into 3066 their nfs_client_id4 string. This is typically a 3067 UUID that is generated at system install time. 3068 3069 nfs.send_implementation_id = 3070 [NFSv4.1] Send client implementation identification 3071 information in exchange_id requests. 3072 If zero, no implementation identification information 3073 will be sent. 3074 The default is to send the implementation identification 3075 information. 3076 3077 nfs.recover_lost_locks = 3078 [NFSv4] Attempt to recover locks that were lost due 3079 to a lease timeout on the server. Please note that 3080 doing this risks data corruption, since there are 3081 no guarantees that the file will remain unchanged 3082 after the locks are lost. 3083 If you want to enable the kernel legacy behaviour of 3084 attempting to recover these locks, then set this 3085 parameter to '1'. 3086 The default parameter value of '0' causes the kernel 3087 not to attempt recovery of lost locks. 3088 3089 nfs4.layoutstats_timer = 3090 [NFSv4.2] Change the rate at which the kernel sends 3091 layoutstats to the pNFS metadata server. 3092 3093 Setting this to value to 0 causes the kernel to use 3094 whatever value is the default set by the layout 3095 driver. A non-zero value sets the minimum interval 3096 in seconds between layoutstats transmissions. 3097 3098 nfsd.nfs4_disable_idmapping= 3099 [NFSv4] When set to the default of '1', the NFSv4 3100 server will return only numeric uids and gids to 3101 clients using auth_sys, and will accept numeric uids 3102 and gids from such clients. This is intended to ease 3103 migration from NFSv2/v3. 3104 3105 nmi_backtrace.backtrace_idle [KNL] 3106 Dump stacks even of idle CPUs in response to an 3107 NMI stack-backtrace request. 3108 3109 nmi_debug= [KNL,SH] Specify one or more actions to take 3110 when a NMI is triggered. 3111 Format: [state][,regs][,debounce][,die] 3112 3113 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 3114 Format: [panic,][nopanic,][num] 3115 Valid num: 0 or 1 3116 0 - turn hardlockup detector in nmi_watchdog off 3117 1 - turn hardlockup detector in nmi_watchdog on 3118 When panic is specified, panic when an NMI watchdog 3119 timeout occurs (or 'nopanic' to not panic on an NMI 3120 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set) 3121 To disable both hard and soft lockup detectors, 3122 please see 'nowatchdog'. 3123 This is useful when you use a panic=... timeout and 3124 need the box quickly up again. 3125 3126 These settings can be accessed at runtime via 3127 the nmi_watchdog and hardlockup_panic sysctls. 3128 3129 netpoll.carrier_timeout= 3130 [NET] Specifies amount of time (in seconds) that 3131 netpoll should wait for a carrier. By default netpoll 3132 waits 4 seconds. 3133 3134 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 3135 emulation library even if a 387 maths coprocessor 3136 is present. 3137 3138 no5lvl [X86-64] Disable 5-level paging mode. Forces 3139 kernel to use 4-level paging instead. 3140 3141 nofsgsbase [X86] Disables FSGSBASE instructions. 3142 3143 no_console_suspend 3144 [HW] Never suspend the console 3145 Disable suspending of consoles during suspend and 3146 hibernate operations. Once disabled, debugging 3147 messages can reach various consoles while the rest 3148 of the system is being put to sleep (ie, while 3149 debugging driver suspend/resume hooks). This may 3150 not work reliably with all consoles, but is known 3151 to work with serial and VGA consoles. 3152 To facilitate more flexible debugging, we also add 3153 console_suspend, a printk module parameter to control 3154 it. Users could use console_suspend (usually 3155 /sys/module/printk/parameters/console_suspend) to 3156 turn on/off it dynamically. 3157 3158 novmcoredd [KNL,KDUMP] 3159 Disable device dump. Device dump allows drivers to 3160 append dump data to vmcore so you can collect driver 3161 specified debug info. Drivers can append the data 3162 without any limit and this data is stored in memory, 3163 so this may cause significant memory stress. Disabling 3164 device dump can help save memory but the driver debug 3165 data will be no longer available. This parameter 3166 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP 3167 is set. 3168 3169 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien 3170 caches in the slab allocator. Saves per-node memory, 3171 but will impact performance. 3172 3173 noalign [KNL,ARM] 3174 3175 noaltinstr [S390] Disables alternative instructions patching 3176 (CPU alternatives feature). 3177 3178 noapic [SMP,APIC] Tells the kernel to not make use of any 3179 IOAPICs that may be present in the system. 3180 3181 noautogroup Disable scheduler automatic task group creation. 3182 3183 nobats [PPC] Do not use BATs for mapping kernel lowmem 3184 on "Classic" PPC cores. 3185 3186 nocache [ARM] 3187 3188 noclflush [BUGS=X86] Don't use the CLFLUSH instruction 3189 3190 nodelayacct [KNL] Disable per-task delay accounting 3191 3192 nodsp [SH] Disable hardware DSP at boot time. 3193 3194 noefi Disable EFI runtime services support. 3195 3196 no_entry_flush [PPC] Don't flush the L1-D cache when entering the kernel. 3197 3198 noexec [IA-64] 3199 3200 noexec [X86] 3201 On X86-32 available only on PAE configured kernels. 3202 noexec=on: enable non-executable mappings (default) 3203 noexec=off: disable non-executable mappings 3204 3205 nosmap [X86,PPC] 3206 Disable SMAP (Supervisor Mode Access Prevention) 3207 even if it is supported by processor. 3208 3209 nosmep [X86,PPC] 3210 Disable SMEP (Supervisor Mode Execution Prevention) 3211 even if it is supported by processor. 3212 3213 noexec32 [X86-64] 3214 This affects only 32-bit executables. 3215 noexec32=on: enable non-executable mappings (default) 3216 read doesn't imply executable mappings 3217 noexec32=off: disable non-executable mappings 3218 read implies executable mappings 3219 3220 nofpu [MIPS,SH] Disable hardware FPU at boot time. 3221 3222 nofxsr [BUGS=X86-32] Disables x86 floating point extended 3223 register save and restore. The kernel will only save 3224 legacy floating-point registers on task switch. 3225 3226 nohugeiomap [KNL,X86,PPC,ARM64] Disable kernel huge I/O mappings. 3227 3228 nosmt [KNL,S390] Disable symmetric multithreading (SMT). 3229 Equivalent to smt=1. 3230 3231 [KNL,X86] Disable symmetric multithreading (SMT). 3232 nosmt=force: Force disable SMT, cannot be undone 3233 via the sysfs control file. 3234 3235 nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1 3236 (bounds check bypass). With this option data leaks are 3237 possible in the system. 3238 3239 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for 3240 the Spectre variant 2 (indirect branch prediction) 3241 vulnerability. System may allow data leaks with this 3242 option. 3243 3244 nospec_store_bypass_disable 3245 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability 3246 3247 no_uaccess_flush 3248 [PPC] Don't flush the L1-D cache after accessing user data. 3249 3250 noxsave [BUGS=X86] Disables x86 extended register state save 3251 and restore using xsave. The kernel will fallback to 3252 enabling legacy floating-point and sse state. 3253 3254 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 3255 register states. The kernel will fall back to use 3256 xsave to save the states. By using this parameter, 3257 performance of saving the states is degraded because 3258 xsave doesn't support modified optimization while 3259 xsaveopt supports it on xsaveopt enabled systems. 3260 3261 noxsaves [X86] Disables xsaves and xrstors used in saving and 3262 restoring x86 extended register state in compacted 3263 form of xsave area. The kernel will fall back to use 3264 xsaveopt and xrstor to save and restore the states 3265 in standard form of xsave area. By using this 3266 parameter, xsave area per process might occupy more 3267 memory on xsaves enabled systems. 3268 3269 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or 3270 wfi(ARM) instruction doesn't work correctly and not to 3271 use it. This is also useful when using JTAG debugger. 3272 3273 no_file_caps Tells the kernel not to honor file capabilities. The 3274 only way then for a file to be executed with privilege 3275 is to be setuid root or executed by root. 3276 3277 nohalt [IA-64] Tells the kernel not to use the power saving 3278 function PAL_HALT_LIGHT when idle. This increases 3279 power-consumption. On the positive side, it reduces 3280 interrupt wake-up latency, which may improve performance 3281 in certain environments such as networked servers or 3282 real-time systems. 3283 3284 nohibernate [HIBERNATION] Disable hibernation and resume. 3285 3286 nohz= [KNL] Boottime enable/disable dynamic ticks 3287 Valid arguments: on, off 3288 Default: on 3289 3290 nohz_full= [KNL,BOOT,SMP,ISOL] 3291 The argument is a cpu list, as described above. 3292 In kernels built with CONFIG_NO_HZ_FULL=y, set 3293 the specified list of CPUs whose tick will be stopped 3294 whenever possible. The boot CPU will be forced outside 3295 the range to maintain the timekeeping. Any CPUs 3296 in this list will have their RCU callbacks offloaded, 3297 just as if they had also been called out in the 3298 rcu_nocbs= boot parameter. 3299 3300 noiotrap [SH] Disables trapped I/O port accesses. 3301 3302 noirqdebug [X86-32] Disables the code which attempts to detect and 3303 disable unhandled interrupt sources. 3304 3305 no_timer_check [X86,APIC] Disables the code which tests for 3306 broken timer IRQ sources. 3307 3308 noisapnp [ISAPNP] Disables ISA PnP code. 3309 3310 noinitrd [RAM] Tells the kernel not to load any configured 3311 initial RAM disk. 3312 3313 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt 3314 remapping. 3315 [Deprecated - use intremap=off] 3316 3317 nointroute [IA-64] 3318 3319 noinvpcid [X86] Disable the INVPCID cpu feature. 3320 3321 nojitter [IA-64] Disables jitter checking for ITC timers. 3322 3323 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver 3324 3325 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page 3326 fault handling. 3327 3328 no-vmw-sched-clock 3329 [X86,PV_OPS] Disable paravirtualized VMware scheduler 3330 clock and use the default one. 3331 3332 no-steal-acc [X86,PV_OPS,ARM64] Disable paravirtualized steal time 3333 accounting. steal time is computed, but won't 3334 influence scheduler behaviour 3335 3336 nolapic [X86-32,APIC] Do not enable or use the local APIC. 3337 3338 nolapic_timer [X86-32,APIC] Do not use the local APIC timer. 3339 3340 noltlbs [PPC] Do not use large page/tlb entries for kernel 3341 lowmem mapping on PPC40x and PPC8xx 3342 3343 nomca [IA-64] Disable machine check abort handling 3344 3345 nomce [X86-32] Disable Machine Check Exception 3346 3347 nomfgpt [X86-32] Disable Multi-Function General Purpose 3348 Timer usage (for AMD Geode machines). 3349 3350 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 3351 shutdown the other cpus. Instead use the REBOOT_VECTOR 3352 irq. 3353 3354 nomodule Disable module load 3355 3356 nopat [X86] Disable PAT (page attribute table extension of 3357 pagetables) support. 3358 3359 nopcid [X86-64] Disable the PCID cpu feature. 3360 3361 norandmaps Don't use address space randomization. Equivalent to 3362 echo 0 > /proc/sys/kernel/randomize_va_space 3363 3364 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 3365 with UP alternatives 3366 3367 nordrand [X86] Disable kernel use of the RDRAND and 3368 RDSEED instructions even if they are supported 3369 by the processor. RDRAND and RDSEED are still 3370 available to user space applications. 3371 3372 noresume [SWSUSP] Disables resume and restores original swap 3373 space. 3374 3375 no-scroll [VGA] Disables scrollback. 3376 This is required for the Braillex ib80-piezo Braille 3377 reader made by F.H. Papenmeier (Germany). 3378 3379 nosbagart [IA-64] 3380 3381 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support. 3382 3383 nosgx [X86-64,SGX] Disables Intel SGX kernel support. 3384 3385 nosmp [SMP] Tells an SMP kernel to act as a UP kernel, 3386 and disable the IO APIC. legacy for "maxcpus=0". 3387 3388 nosoftlockup [KNL] Disable the soft-lockup detector. 3389 3390 nosync [HW,M68K] Disables sync negotiation for all devices. 3391 3392 nowatchdog [KNL] Disable both lockup detectors, i.e. 3393 soft-lockup and NMI watchdog (hard-lockup). 3394 3395 nowb [ARM] 3396 3397 nox2apic [X86-64,APIC] Do not enable x2APIC mode. 3398 3399 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when 3400 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off. 3401 Some features depend on CPU0. Known dependencies are: 3402 1. Resume from suspend/hibernate depends on CPU0. 3403 Suspend/hibernate will fail if CPU0 is offline and you 3404 need to online CPU0 before suspend/hibernate. 3405 2. PIC interrupts also depend on CPU0. CPU0 can't be 3406 removed if a PIC interrupt is detected. 3407 It's said poweroff/reboot may depend on CPU0 on some 3408 machines although I haven't seen such issues so far 3409 after CPU0 is offline on a few tested machines. 3410 If the dependencies are under your control, you can 3411 turn on cpu0_hotplug. 3412 3413 nps_mtm_hs_ctr= [KNL,ARC] 3414 This parameter sets the maximum duration, in 3415 cycles, each HW thread of the CTOP can run 3416 without interruptions, before HW switches it. 3417 The actual maximum duration is 16 times this 3418 parameter's value. 3419 Format: integer between 1 and 255 3420 Default: 255 3421 3422 nptcg= [IA-64] Override max number of concurrent global TLB 3423 purges which is reported from either PAL_VM_SUMMARY or 3424 SAL PALO. 3425 3426 nr_cpus= [SMP] Maximum number of processors that an SMP kernel 3427 could support. nr_cpus=n : n >= 1 limits the kernel to 3428 support 'n' processors. It could be larger than the 3429 number of already plugged CPU during bootup, later in 3430 runtime you can physically add extra cpu until it reaches 3431 n. So during boot up some boot time memory for per-cpu 3432 variables need be pre-allocated for later physical cpu 3433 hot plugging. 3434 3435 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 3436 3437 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing. 3438 Allowed values are enable and disable 3439 3440 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 3441 'node', 'default' can be specified 3442 This can be set from sysctl after boot. 3443 See Documentation/admin-guide/sysctl/vm.rst for details. 3444 3445 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver. 3446 See Documentation/core-api/debugging-via-ohci1394.rst for more 3447 info. 3448 3449 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 3450 Rather than timing out after 20 ms if an EC 3451 command is not properly ACKed, override the length 3452 of the timeout. We have interrupts disabled while 3453 waiting for the ACK, so if this is set too high 3454 interrupts *may* be lost! 3455 3456 omap_mux= [OMAP] Override bootloader pin multiplexing. 3457 Format: <mux_mode0.mode_name=value>... 3458 For example, to override I2C bus2: 3459 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 3460 3461 oprofile.timer= [HW] 3462 Use timer interrupt instead of performance counters 3463 3464 oprofile.cpu_type= Force an oprofile cpu type 3465 This might be useful if you have an older oprofile 3466 userland or if you want common events. 3467 Format: { arch_perfmon } 3468 arch_perfmon: [X86] Force use of architectural 3469 perfmon on Intel CPUs instead of the 3470 CPU specific event set. 3471 timer: [X86] Force use of architectural NMI 3472 timer mode (see also oprofile.timer 3473 for generic hr timer mode) 3474 3475 oops=panic Always panic on oopses. Default is to just kill the 3476 process, but there is a small probability of 3477 deadlocking the machine. 3478 This will also cause panics on machine check exceptions. 3479 Useful together with panic=30 to trigger a reboot. 3480 3481 page_alloc.shuffle= 3482 [KNL] Boolean flag to control whether the page allocator 3483 should randomize its free lists. The randomization may 3484 be automatically enabled if the kernel detects it is 3485 running on a platform with a direct-mapped memory-side 3486 cache, and this parameter can be used to 3487 override/disable that behavior. The state of the flag 3488 can be read from sysfs at: 3489 /sys/module/page_alloc/parameters/shuffle. 3490 3491 page_owner= [KNL] Boot-time page_owner enabling option. 3492 Storage of the information about who allocated 3493 each page is disabled in default. With this switch, 3494 we can turn it on. 3495 on: enable the feature 3496 3497 page_poison= [KNL] Boot-time parameter changing the state of 3498 poisoning on the buddy allocator, available with 3499 CONFIG_PAGE_POISONING=y. 3500 off: turn off poisoning (default) 3501 on: turn on poisoning 3502 3503 panic= [KNL] Kernel behaviour on panic: delay <timeout> 3504 timeout > 0: seconds before rebooting 3505 timeout = 0: wait forever 3506 timeout < 0: reboot immediately 3507 Format: <timeout> 3508 3509 panic_print= Bitmask for printing system info when panic happens. 3510 User can chose combination of the following bits: 3511 bit 0: print all tasks info 3512 bit 1: print system memory info 3513 bit 2: print timer info 3514 bit 3: print locks info if CONFIG_LOCKDEP is on 3515 bit 4: print ftrace buffer 3516 bit 5: print all printk messages in buffer 3517 3518 panic_on_taint= Bitmask for conditionally calling panic() in add_taint() 3519 Format: <hex>[,nousertaint] 3520 Hexadecimal bitmask representing the set of TAINT flags 3521 that will cause the kernel to panic when add_taint() is 3522 called with any of the flags in this set. 3523 The optional switch "nousertaint" can be utilized to 3524 prevent userspace forced crashes by writing to sysctl 3525 /proc/sys/kernel/tainted any flagset matching with the 3526 bitmask set on panic_on_taint. 3527 See Documentation/admin-guide/tainted-kernels.rst for 3528 extra details on the taint flags that users can pick 3529 to compose the bitmask to assign to panic_on_taint. 3530 3531 panic_on_warn panic() instead of WARN(). Useful to cause kdump 3532 on a WARN(). 3533 3534 crash_kexec_post_notifiers 3535 Run kdump after running panic-notifiers and dumping 3536 kmsg. This only for the users who doubt kdump always 3537 succeeds in any situation. 3538 Note that this also increases risks of kdump failure, 3539 because some panic notifiers can make the crashed 3540 kernel more unstable. 3541 3542 parkbd.port= [HW] Parallel port number the keyboard adapter is 3543 connected to, default is 0. 3544 Format: <parport#> 3545 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 3546 0 for XT, 1 for AT (default is AT). 3547 Format: <mode> 3548 3549 parport= [HW,PPT] Specify parallel ports. 0 disables. 3550 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 3551 Use 'auto' to force the driver to use any 3552 IRQ/DMA settings detected (the default is to 3553 ignore detected IRQ/DMA settings because of 3554 possible conflicts). You can specify the base 3555 address, IRQ, and DMA settings; IRQ and DMA 3556 should be numbers, or 'auto' (for using detected 3557 settings on that particular port), or 'nofifo' 3558 (to avoid using a FIFO even if it is detected). 3559 Parallel ports are assigned in the order they 3560 are specified on the command line, starting 3561 with parport0. 3562 3563 parport_init_mode= [HW,PPT] 3564 Configure VIA parallel port to operate in 3565 a specific mode. This is necessary on Pegasos 3566 computer where firmware has no options for setting 3567 up parallel port mode and sets it to spp. 3568 Currently this function knows 686a and 8231 chips. 3569 Format: [spp|ps2|epp|ecp|ecpepp] 3570 3571 pause_on_oops= 3572 Halt all CPUs after the first oops has been printed for 3573 the specified number of seconds. This is to be used if 3574 your oopses keep scrolling off the screen. 3575 3576 pcbit= [HW,ISDN] 3577 3578 pcd. [PARIDE] 3579 See header of drivers/block/paride/pcd.c. 3580 See also Documentation/admin-guide/blockdev/paride.rst. 3581 3582 pci=option[,option...] [PCI] various PCI subsystem options. 3583 3584 Some options herein operate on a specific device 3585 or a set of devices (<pci_dev>). These are 3586 specified in one of the following formats: 3587 3588 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* 3589 pci:<vendor>:<device>[:<subvendor>:<subdevice>] 3590 3591 Note: the first format specifies a PCI 3592 bus/device/function address which may change 3593 if new hardware is inserted, if motherboard 3594 firmware changes, or due to changes caused 3595 by other kernel parameters. If the 3596 domain is left unspecified, it is 3597 taken to be zero. Optionally, a path 3598 to a device through multiple device/function 3599 addresses can be specified after the base 3600 address (this is more robust against 3601 renumbering issues). The second format 3602 selects devices using IDs from the 3603 configuration space which may match multiple 3604 devices in the system. 3605 3606 earlydump dump PCI config space before the kernel 3607 changes anything 3608 off [X86] don't probe for the PCI bus 3609 bios [X86-32] force use of PCI BIOS, don't access 3610 the hardware directly. Use this if your machine 3611 has a non-standard PCI host bridge. 3612 nobios [X86-32] disallow use of PCI BIOS, only direct 3613 hardware access methods are allowed. Use this 3614 if you experience crashes upon bootup and you 3615 suspect they are caused by the BIOS. 3616 conf1 [X86] Force use of PCI Configuration Access 3617 Mechanism 1 (config address in IO port 0xCF8, 3618 data in IO port 0xCFC, both 32-bit). 3619 conf2 [X86] Force use of PCI Configuration Access 3620 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 3621 the function, IO port 0xCFA, also 8-bit, sets 3622 bus number. The config space is then accessed 3623 through ports 0xC000-0xCFFF). 3624 See http://wiki.osdev.org/PCI for more info 3625 on the configuration access mechanisms. 3626 noaer [PCIE] If the PCIEAER kernel config parameter is 3627 enabled, this kernel boot option can be used to 3628 disable the use of PCIE advanced error reporting. 3629 nodomains [PCI] Disable support for multiple PCI 3630 root domains (aka PCI segments, in ACPI-speak). 3631 nommconf [X86] Disable use of MMCONFIG for PCI 3632 Configuration 3633 check_enable_amd_mmconf [X86] check for and enable 3634 properly configured MMIO access to PCI 3635 config space on AMD family 10h CPU 3636 nomsi [MSI] If the PCI_MSI kernel config parameter is 3637 enabled, this kernel boot option can be used to 3638 disable the use of MSI interrupts system-wide. 3639 noioapicquirk [APIC] Disable all boot interrupt quirks. 3640 Safety option to keep boot IRQs enabled. This 3641 should never be necessary. 3642 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 3643 primary IO-APIC for bridges that cannot disable 3644 boot IRQs. This fixes a source of spurious IRQs 3645 when the system masks IRQs. 3646 noioapicreroute [APIC] Disable workaround that uses the 3647 boot IRQ equivalent of an IRQ that connects to 3648 a chipset where boot IRQs cannot be disabled. 3649 The opposite of ioapicreroute. 3650 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 3651 routing table. These calls are known to be buggy 3652 on several machines and they hang the machine 3653 when used, but on other computers it's the only 3654 way to get the interrupt routing table. Try 3655 this option if the kernel is unable to allocate 3656 IRQs or discover secondary PCI buses on your 3657 motherboard. 3658 rom [X86] Assign address space to expansion ROMs. 3659 Use with caution as certain devices share 3660 address decoders between ROMs and other 3661 resources. 3662 norom [X86] Do not assign address space to 3663 expansion ROMs that do not already have 3664 BIOS assigned address ranges. 3665 nobar [X86] Do not assign address space to the 3666 BARs that weren't assigned by the BIOS. 3667 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 3668 assigned automatically to PCI devices. You can 3669 make the kernel exclude IRQs of your ISA cards 3670 this way. 3671 pirqaddr=0xAAAAA [X86] Specify the physical address 3672 of the PIRQ table (normally generated 3673 by the BIOS) if it is outside the 3674 F0000h-100000h range. 3675 lastbus=N [X86] Scan all buses thru bus #N. Can be 3676 useful if the kernel is unable to find your 3677 secondary buses and you want to tell it 3678 explicitly which ones they are. 3679 assign-busses [X86] Always assign all PCI bus 3680 numbers ourselves, overriding 3681 whatever the firmware may have done. 3682 usepirqmask [X86] Honor the possible IRQ mask stored 3683 in the BIOS $PIR table. This is needed on 3684 some systems with broken BIOSes, notably 3685 some HP Pavilion N5400 and Omnibook XE3 3686 notebooks. This will have no effect if ACPI 3687 IRQ routing is enabled. 3688 noacpi [X86] Do not use ACPI for IRQ routing 3689 or for PCI scanning. 3690 use_crs [X86] Use PCI host bridge window information 3691 from ACPI. On BIOSes from 2008 or later, this 3692 is enabled by default. If you need to use this, 3693 please report a bug. 3694 nocrs [X86] Ignore PCI host bridge windows from ACPI. 3695 If you need to use this, please report a bug. 3696 routeirq Do IRQ routing for all PCI devices. 3697 This is normally done in pci_enable_device(), 3698 so this option is a temporary workaround 3699 for broken drivers that don't call it. 3700 skip_isa_align [X86] do not align io start addr, so can 3701 handle more pci cards 3702 noearly [X86] Don't do any early type 1 scanning. 3703 This might help on some broken boards which 3704 machine check when some devices' config space 3705 is read. But various workarounds are disabled 3706 and some IOMMU drivers will not work. 3707 bfsort Sort PCI devices into breadth-first order. 3708 This sorting is done to get a device 3709 order compatible with older (<= 2.4) kernels. 3710 nobfsort Don't sort PCI devices into breadth-first order. 3711 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 3712 tuning and use the BIOS-configured MPS defaults. 3713 pcie_bus_safe Set every device's MPS to the largest value 3714 supported by all devices below the root complex. 3715 pcie_bus_perf Set device MPS to the largest allowable MPS 3716 based on its parent bus. Also set MRRS (Max 3717 Read Request Size) to the largest supported 3718 value (no larger than the MPS that the device 3719 or bus can support) for best performance. 3720 pcie_bus_peer2peer Set every device's MPS to 128B, which 3721 every device is guaranteed to support. This 3722 configuration allows peer-to-peer DMA between 3723 any pair of devices, possibly at the cost of 3724 reduced performance. This also guarantees 3725 that hot-added devices will work. 3726 cbiosize=nn[KMG] The fixed amount of bus space which is 3727 reserved for the CardBus bridge's IO window. 3728 The default value is 256 bytes. 3729 cbmemsize=nn[KMG] The fixed amount of bus space which is 3730 reserved for the CardBus bridge's memory 3731 window. The default value is 64 megabytes. 3732 resource_alignment= 3733 Format: 3734 [<order of align>@]<pci_dev>[; ...] 3735 Specifies alignment and device to reassign 3736 aligned memory resources. How to 3737 specify the device is described above. 3738 If <order of align> is not specified, 3739 PAGE_SIZE is used as alignment. 3740 A PCI-PCI bridge can be specified if resource 3741 windows need to be expanded. 3742 To specify the alignment for several 3743 instances of a device, the PCI vendor, 3744 device, subvendor, and subdevice may be 3745 specified, e.g., 12@pci:8086:9c22:103c:198f 3746 for 4096-byte alignment. 3747 ecrc= Enable/disable PCIe ECRC (transaction layer 3748 end-to-end CRC checking). 3749 bios: Use BIOS/firmware settings. This is the 3750 the default. 3751 off: Turn ECRC off 3752 on: Turn ECRC on. 3753 hpiosize=nn[KMG] The fixed amount of bus space which is 3754 reserved for hotplug bridge's IO window. 3755 Default size is 256 bytes. 3756 hpmmiosize=nn[KMG] The fixed amount of bus space which is 3757 reserved for hotplug bridge's MMIO window. 3758 Default size is 2 megabytes. 3759 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is 3760 reserved for hotplug bridge's MMIO_PREF window. 3761 Default size is 2 megabytes. 3762 hpmemsize=nn[KMG] The fixed amount of bus space which is 3763 reserved for hotplug bridge's MMIO and 3764 MMIO_PREF window. 3765 Default size is 2 megabytes. 3766 hpbussize=nn The minimum amount of additional bus numbers 3767 reserved for buses below a hotplug bridge. 3768 Default is 1. 3769 realloc= Enable/disable reallocating PCI bridge resources 3770 if allocations done by BIOS are too small to 3771 accommodate resources required by all child 3772 devices. 3773 off: Turn realloc off 3774 on: Turn realloc on 3775 realloc same as realloc=on 3776 noari do not use PCIe ARI. 3777 noats [PCIE, Intel-IOMMU, AMD-IOMMU] 3778 do not use PCIe ATS (and IOMMU device IOTLB). 3779 pcie_scan_all Scan all possible PCIe devices. Otherwise we 3780 only look for one device below a PCIe downstream 3781 port. 3782 big_root_window Try to add a big 64bit memory window to the PCIe 3783 root complex on AMD CPUs. Some GFX hardware 3784 can resize a BAR to allow access to all VRAM. 3785 Adding the window is slightly risky (it may 3786 conflict with unreported devices), so this 3787 taints the kernel. 3788 disable_acs_redir=<pci_dev>[; ...] 3789 Specify one or more PCI devices (in the format 3790 specified above) separated by semicolons. 3791 Each device specified will have the PCI ACS 3792 redirect capabilities forced off which will 3793 allow P2P traffic between devices through 3794 bridges without forcing it upstream. Note: 3795 this removes isolation between devices and 3796 may put more devices in an IOMMU group. 3797 force_floating [S390] Force usage of floating interrupts. 3798 nomio [S390] Do not use MIO instructions. 3799 norid [S390] ignore the RID field and force use of 3800 one PCI domain per PCI function 3801 3802 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power 3803 Management. 3804 off Disable ASPM. 3805 force Enable ASPM even on devices that claim not to support it. 3806 WARNING: Forcing ASPM on may cause system lockups. 3807 3808 pcie_ports= [PCIE] PCIe port services handling: 3809 native Use native PCIe services (PME, AER, DPC, PCIe hotplug) 3810 even if the platform doesn't give the OS permission to 3811 use them. This may cause conflicts if the platform 3812 also tries to use these services. 3813 dpc-native Use native PCIe service for DPC only. May 3814 cause conflicts if firmware uses AER or DPC. 3815 compat Disable native PCIe services (PME, AER, DPC, PCIe 3816 hotplug). 3817 3818 pcie_port_pm= [PCIE] PCIe port power management handling: 3819 off Disable power management of all PCIe ports 3820 force Forcibly enable power management of all PCIe ports 3821 3822 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 3823 nomsi Do not use MSI for native PCIe PME signaling (this makes 3824 all PCIe root ports use INTx for all services). 3825 3826 pcmv= [HW,PCMCIA] BadgePAD 4 3827 3828 pd_ignore_unused 3829 [PM] 3830 Keep all power-domains already enabled by bootloader on, 3831 even if no driver has claimed them. This is useful 3832 for debug and development, but should not be 3833 needed on a platform with proper driver support. 3834 3835 pd. [PARIDE] 3836 See Documentation/admin-guide/blockdev/paride.rst. 3837 3838 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 3839 boot time. 3840 Format: { 0 | 1 } 3841 See arch/parisc/kernel/pdc_chassis.c 3842 3843 percpu_alloc= Select which percpu first chunk allocator to use. 3844 Currently supported values are "embed" and "page". 3845 Archs may support subset or none of the selections. 3846 See comments in mm/percpu.c for details on each 3847 allocator. This parameter is primarily for debugging 3848 and performance comparison. 3849 3850 pf. [PARIDE] 3851 See Documentation/admin-guide/blockdev/paride.rst. 3852 3853 pg. [PARIDE] 3854 See Documentation/admin-guide/blockdev/paride.rst. 3855 3856 pirq= [SMP,APIC] Manual mp-table setup 3857 See Documentation/x86/i386/IO-APIC.rst. 3858 3859 plip= [PPT,NET] Parallel port network link 3860 Format: { parport<nr> | timid | 0 } 3861 See also Documentation/admin-guide/parport.rst. 3862 3863 pmtmr= [X86] Manual setup of pmtmr I/O Port. 3864 Override pmtimer IOPort with a hex value. 3865 e.g. pmtmr=0x508 3866 3867 pm_debug_messages [SUSPEND,KNL] 3868 Enable suspend/resume debug messages during boot up. 3869 3870 pnp.debug=1 [PNP] 3871 Enable PNP debug messages (depends on the 3872 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 3873 via /sys/module/pnp/parameters/debug. We always show 3874 current resource usage; turning this on also shows 3875 possible settings and some assignment information. 3876 3877 pnpacpi= [ACPI] 3878 { off } 3879 3880 pnpbios= [ISAPNP] 3881 { on | off | curr | res | no-curr | no-res } 3882 3883 pnp_reserve_irq= 3884 [ISAPNP] Exclude IRQs for the autoconfiguration 3885 3886 pnp_reserve_dma= 3887 [ISAPNP] Exclude DMAs for the autoconfiguration 3888 3889 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 3890 Ranges are in pairs (I/O port base and size). 3891 3892 pnp_reserve_mem= 3893 [ISAPNP] Exclude memory regions for the 3894 autoconfiguration. 3895 Ranges are in pairs (memory base and size). 3896 3897 ports= [IP_VS_FTP] IPVS ftp helper module 3898 Default is 21. 3899 Up to 8 (IP_VS_APP_MAX_PORTS) ports 3900 may be specified. 3901 Format: <port>,<port>.... 3902 3903 powersave=off [PPC] This option disables power saving features. 3904 It specifically disables cpuidle and sets the 3905 platform machine description specific power_save 3906 function to NULL. On Idle the CPU just reduces 3907 execution priority. 3908 3909 ppc_strict_facility_enable 3910 [PPC] This option catches any kernel floating point, 3911 Altivec, VSX and SPE outside of regions specifically 3912 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 3913 There is some performance impact when enabling this. 3914 3915 ppc_tm= [PPC] 3916 Format: {"off"} 3917 Disable Hardware Transactional Memory 3918 3919 print-fatal-signals= 3920 [KNL] debug: print fatal signals 3921 3922 If enabled, warn about various signal handling 3923 related application anomalies: too many signals, 3924 too many POSIX.1 timers, fatal signals causing a 3925 coredump - etc. 3926 3927 If you hit the warning due to signal overflow, 3928 you might want to try "ulimit -i unlimited". 3929 3930 default: off. 3931 3932 printk.always_kmsg_dump= 3933 Trigger kmsg_dump for cases other than kernel oops or 3934 panics 3935 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3936 default: disabled 3937 3938 printk.devkmsg={on,off,ratelimit} 3939 Control writing to /dev/kmsg. 3940 on - unlimited logging to /dev/kmsg from userspace 3941 off - logging to /dev/kmsg disabled 3942 ratelimit - ratelimit the logging 3943 Default: ratelimit 3944 3945 printk.time= Show timing data prefixed to each printk message line 3946 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3947 3948 processor.max_cstate= [HW,ACPI] 3949 Limit processor to maximum C-state 3950 max_cstate=9 overrides any DMI blacklist limit. 3951 3952 processor.nocst [HW,ACPI] 3953 Ignore the _CST method to determine C-states, 3954 instead using the legacy FADT method 3955 3956 profile= [KNL] Enable kernel profiling via /proc/profile 3957 Format: [<profiletype>,]<number> 3958 Param: <profiletype>: "schedule", "sleep", or "kvm" 3959 [defaults to kernel profiling] 3960 Param: "schedule" - profile schedule points. 3961 Param: "sleep" - profile D-state sleeping (millisecs). 3962 Requires CONFIG_SCHEDSTATS 3963 Param: "kvm" - profile VM exits. 3964 Param: <number> - step/bucket size as a power of 2 for 3965 statistical time based profiling. 3966 3967 prompt_ramdisk= [RAM] [Deprecated] 3968 3969 prot_virt= [S390] enable hosting protected virtual machines 3970 isolated from the hypervisor (if hardware supports 3971 that). 3972 Format: <bool> 3973 3974 psi= [KNL] Enable or disable pressure stall information 3975 tracking. 3976 Format: <bool> 3977 3978 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 3979 probe for; one of (bare|imps|exps|lifebook|any). 3980 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 3981 per second. 3982 psmouse.resetafter= [HW,MOUSE] 3983 Try to reset the device after so many bad packets 3984 (0 = never). 3985 psmouse.resolution= 3986 [HW,MOUSE] Set desired mouse resolution, in dpi. 3987 psmouse.smartscroll= 3988 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 3989 0 = disabled, 1 = enabled (default). 3990 3991 pstore.backend= Specify the name of the pstore backend to use 3992 3993 pt. [PARIDE] 3994 See Documentation/admin-guide/blockdev/paride.rst. 3995 3996 pti= [X86-64] Control Page Table Isolation of user and 3997 kernel address spaces. Disabling this feature 3998 removes hardening, but improves performance of 3999 system calls and interrupts. 4000 4001 on - unconditionally enable 4002 off - unconditionally disable 4003 auto - kernel detects whether your CPU model is 4004 vulnerable to issues that PTI mitigates 4005 4006 Not specifying this option is equivalent to pti=auto. 4007 4008 nopti [X86-64] 4009 Equivalent to pti=off 4010 4011 pty.legacy_count= 4012 [KNL] Number of legacy pty's. Overwrites compiled-in 4013 default number. 4014 4015 quiet [KNL] Disable most log messages 4016 4017 r128= [HW,DRM] 4018 4019 raid= [HW,RAID] 4020 See Documentation/admin-guide/md.rst. 4021 4022 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 4023 See Documentation/admin-guide/blockdev/ramdisk.rst. 4024 4025 ramdisk_start= [RAM] RAM disk image start address 4026 4027 random.trust_cpu={on,off} 4028 [KNL] Enable or disable trusting the use of the 4029 CPU's random number generator (if available) to 4030 fully seed the kernel's CRNG. Default is controlled 4031 by CONFIG_RANDOM_TRUST_CPU. 4032 4033 ras=option[,option,...] [KNL] RAS-specific options 4034 4035 cec_disable [X86] 4036 Disable the Correctable Errors Collector, 4037 see CONFIG_RAS_CEC help text. 4038 4039 rcu_nocbs= [KNL] 4040 The argument is a cpu list, as described above, 4041 except that the string "all" can be used to 4042 specify every CPU on the system. 4043 4044 In kernels built with CONFIG_RCU_NOCB_CPU=y, set 4045 the specified list of CPUs to be no-callback CPUs. 4046 Invocation of these CPUs' RCU callbacks will be 4047 offloaded to "rcuox/N" kthreads created for that 4048 purpose, where "x" is "p" for RCU-preempt, and 4049 "s" for RCU-sched, and "N" is the CPU number. 4050 This reduces OS jitter on the offloaded CPUs, 4051 which can be useful for HPC and real-time 4052 workloads. It can also improve energy efficiency 4053 for asymmetric multiprocessors. 4054 4055 rcu_nocb_poll [KNL] 4056 Rather than requiring that offloaded CPUs 4057 (specified by rcu_nocbs= above) explicitly 4058 awaken the corresponding "rcuoN" kthreads, 4059 make these kthreads poll for callbacks. 4060 This improves the real-time response for the 4061 offloaded CPUs by relieving them of the need to 4062 wake up the corresponding kthread, but degrades 4063 energy efficiency by requiring that the kthreads 4064 periodically wake up to do the polling. 4065 4066 rcutree.blimit= [KNL] 4067 Set maximum number of finished RCU callbacks to 4068 process in one batch. 4069 4070 rcutree.dump_tree= [KNL] 4071 Dump the structure of the rcu_node combining tree 4072 out at early boot. This is used for diagnostic 4073 purposes, to verify correct tree setup. 4074 4075 rcutree.gp_cleanup_delay= [KNL] 4076 Set the number of jiffies to delay each step of 4077 RCU grace-period cleanup. 4078 4079 rcutree.gp_init_delay= [KNL] 4080 Set the number of jiffies to delay each step of 4081 RCU grace-period initialization. 4082 4083 rcutree.gp_preinit_delay= [KNL] 4084 Set the number of jiffies to delay each step of 4085 RCU grace-period pre-initialization, that is, 4086 the propagation of recent CPU-hotplug changes up 4087 the rcu_node combining tree. 4088 4089 rcutree.use_softirq= [KNL] 4090 If set to zero, move all RCU_SOFTIRQ processing to 4091 per-CPU rcuc kthreads. Defaults to a non-zero 4092 value, meaning that RCU_SOFTIRQ is used by default. 4093 Specify rcutree.use_softirq=0 to use rcuc kthreads. 4094 4095 rcutree.rcu_fanout_exact= [KNL] 4096 Disable autobalancing of the rcu_node combining 4097 tree. This is used by rcutorture, and might 4098 possibly be useful for architectures having high 4099 cache-to-cache transfer latencies. 4100 4101 rcutree.rcu_fanout_leaf= [KNL] 4102 Change the number of CPUs assigned to each 4103 leaf rcu_node structure. Useful for very 4104 large systems, which will choose the value 64, 4105 and for NUMA systems with large remote-access 4106 latencies, which will choose a value aligned 4107 with the appropriate hardware boundaries. 4108 4109 rcutree.rcu_min_cached_objs= [KNL] 4110 Minimum number of objects which are cached and 4111 maintained per one CPU. Object size is equal 4112 to PAGE_SIZE. The cache allows to reduce the 4113 pressure to page allocator, also it makes the 4114 whole algorithm to behave better in low memory 4115 condition. 4116 4117 rcutree.jiffies_till_first_fqs= [KNL] 4118 Set delay from grace-period initialization to 4119 first attempt to force quiescent states. 4120 Units are jiffies, minimum value is zero, 4121 and maximum value is HZ. 4122 4123 rcutree.jiffies_till_next_fqs= [KNL] 4124 Set delay between subsequent attempts to force 4125 quiescent states. Units are jiffies, minimum 4126 value is one, and maximum value is HZ. 4127 4128 rcutree.jiffies_till_sched_qs= [KNL] 4129 Set required age in jiffies for a 4130 given grace period before RCU starts 4131 soliciting quiescent-state help from 4132 rcu_note_context_switch() and cond_resched(). 4133 If not specified, the kernel will calculate 4134 a value based on the most recent settings 4135 of rcutree.jiffies_till_first_fqs 4136 and rcutree.jiffies_till_next_fqs. 4137 This calculated value may be viewed in 4138 rcutree.jiffies_to_sched_qs. Any attempt to set 4139 rcutree.jiffies_to_sched_qs will be cheerfully 4140 overwritten. 4141 4142 rcutree.kthread_prio= [KNL,BOOT] 4143 Set the SCHED_FIFO priority of the RCU per-CPU 4144 kthreads (rcuc/N). This value is also used for 4145 the priority of the RCU boost threads (rcub/N) 4146 and for the RCU grace-period kthreads (rcu_bh, 4147 rcu_preempt, and rcu_sched). If RCU_BOOST is 4148 set, valid values are 1-99 and the default is 1 4149 (the least-favored priority). Otherwise, when 4150 RCU_BOOST is not set, valid values are 0-99 and 4151 the default is zero (non-realtime operation). 4152 4153 rcutree.rcu_nocb_gp_stride= [KNL] 4154 Set the number of NOCB callback kthreads in 4155 each group, which defaults to the square root 4156 of the number of CPUs. Larger numbers reduce 4157 the wakeup overhead on the global grace-period 4158 kthread, but increases that same overhead on 4159 each group's NOCB grace-period kthread. 4160 4161 rcutree.qhimark= [KNL] 4162 Set threshold of queued RCU callbacks beyond which 4163 batch limiting is disabled. 4164 4165 rcutree.qlowmark= [KNL] 4166 Set threshold of queued RCU callbacks below which 4167 batch limiting is re-enabled. 4168 4169 rcutree.qovld= [KNL] 4170 Set threshold of queued RCU callbacks beyond which 4171 RCU's force-quiescent-state scan will aggressively 4172 enlist help from cond_resched() and sched IPIs to 4173 help CPUs more quickly reach quiescent states. 4174 Set to less than zero to make this be set based 4175 on rcutree.qhimark at boot time and to zero to 4176 disable more aggressive help enlistment. 4177 4178 rcutree.rcu_idle_gp_delay= [KNL] 4179 Set wakeup interval for idle CPUs that have 4180 RCU callbacks (RCU_FAST_NO_HZ=y). 4181 4182 rcutree.rcu_idle_lazy_gp_delay= [KNL] 4183 Set wakeup interval for idle CPUs that have 4184 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y). 4185 Lazy RCU callbacks are those which RCU can 4186 prove do nothing more than free memory. 4187 4188 rcutree.rcu_kick_kthreads= [KNL] 4189 Cause the grace-period kthread to get an extra 4190 wake_up() if it sleeps three times longer than 4191 it should at force-quiescent-state time. 4192 This wake_up() will be accompanied by a 4193 WARN_ONCE() splat and an ftrace_dump(). 4194 4195 rcutree.rcu_unlock_delay= [KNL] 4196 In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels, 4197 this specifies an rcu_read_unlock()-time delay 4198 in microseconds. This defaults to zero. 4199 Larger delays increase the probability of 4200 catching RCU pointer leaks, that is, buggy use 4201 of RCU-protected pointers after the relevant 4202 rcu_read_unlock() has completed. 4203 4204 rcutree.sysrq_rcu= [KNL] 4205 Commandeer a sysrq key to dump out Tree RCU's 4206 rcu_node tree with an eye towards determining 4207 why a new grace period has not yet started. 4208 4209 rcuscale.gp_async= [KNL] 4210 Measure performance of asynchronous 4211 grace-period primitives such as call_rcu(). 4212 4213 rcuscale.gp_async_max= [KNL] 4214 Specify the maximum number of outstanding 4215 callbacks per writer thread. When a writer 4216 thread exceeds this limit, it invokes the 4217 corresponding flavor of rcu_barrier() to allow 4218 previously posted callbacks to drain. 4219 4220 rcuscale.gp_exp= [KNL] 4221 Measure performance of expedited synchronous 4222 grace-period primitives. 4223 4224 rcuscale.holdoff= [KNL] 4225 Set test-start holdoff period. The purpose of 4226 this parameter is to delay the start of the 4227 test until boot completes in order to avoid 4228 interference. 4229 4230 rcuscale.kfree_rcu_test= [KNL] 4231 Set to measure performance of kfree_rcu() flooding. 4232 4233 rcuscale.kfree_nthreads= [KNL] 4234 The number of threads running loops of kfree_rcu(). 4235 4236 rcuscale.kfree_alloc_num= [KNL] 4237 Number of allocations and frees done in an iteration. 4238 4239 rcuscale.kfree_loops= [KNL] 4240 Number of loops doing rcuscale.kfree_alloc_num number 4241 of allocations and frees. 4242 4243 rcuscale.nreaders= [KNL] 4244 Set number of RCU readers. The value -1 selects 4245 N, where N is the number of CPUs. A value 4246 "n" less than -1 selects N-n+1, where N is again 4247 the number of CPUs. For example, -2 selects N 4248 (the number of CPUs), -3 selects N+1, and so on. 4249 A value of "n" less than or equal to -N selects 4250 a single reader. 4251 4252 rcuscale.nwriters= [KNL] 4253 Set number of RCU writers. The values operate 4254 the same as for rcuscale.nreaders. 4255 N, where N is the number of CPUs 4256 4257 rcuscale.perf_type= [KNL] 4258 Specify the RCU implementation to test. 4259 4260 rcuscale.shutdown= [KNL] 4261 Shut the system down after performance tests 4262 complete. This is useful for hands-off automated 4263 testing. 4264 4265 rcuscale.verbose= [KNL] 4266 Enable additional printk() statements. 4267 4268 rcuscale.writer_holdoff= [KNL] 4269 Write-side holdoff between grace periods, 4270 in microseconds. The default of zero says 4271 no holdoff. 4272 4273 rcutorture.fqs_duration= [KNL] 4274 Set duration of force_quiescent_state bursts 4275 in microseconds. 4276 4277 rcutorture.fqs_holdoff= [KNL] 4278 Set holdoff time within force_quiescent_state bursts 4279 in microseconds. 4280 4281 rcutorture.fqs_stutter= [KNL] 4282 Set wait time between force_quiescent_state bursts 4283 in seconds. 4284 4285 rcutorture.fwd_progress= [KNL] 4286 Enable RCU grace-period forward-progress testing 4287 for the types of RCU supporting this notion. 4288 4289 rcutorture.fwd_progress_div= [KNL] 4290 Specify the fraction of a CPU-stall-warning 4291 period to do tight-loop forward-progress testing. 4292 4293 rcutorture.fwd_progress_holdoff= [KNL] 4294 Number of seconds to wait between successive 4295 forward-progress tests. 4296 4297 rcutorture.fwd_progress_need_resched= [KNL] 4298 Enclose cond_resched() calls within checks for 4299 need_resched() during tight-loop forward-progress 4300 testing. 4301 4302 rcutorture.gp_cond= [KNL] 4303 Use conditional/asynchronous update-side 4304 primitives, if available. 4305 4306 rcutorture.gp_exp= [KNL] 4307 Use expedited update-side primitives, if available. 4308 4309 rcutorture.gp_normal= [KNL] 4310 Use normal (non-expedited) asynchronous 4311 update-side primitives, if available. 4312 4313 rcutorture.gp_sync= [KNL] 4314 Use normal (non-expedited) synchronous 4315 update-side primitives, if available. If all 4316 of rcutorture.gp_cond=, rcutorture.gp_exp=, 4317 rcutorture.gp_normal=, and rcutorture.gp_sync= 4318 are zero, rcutorture acts as if is interpreted 4319 they are all non-zero. 4320 4321 rcutorture.irqreader= [KNL] 4322 Run RCU readers from irq handlers, or, more 4323 accurately, from a timer handler. Not all RCU 4324 flavors take kindly to this sort of thing. 4325 4326 rcutorture.leakpointer= [KNL] 4327 Leak an RCU-protected pointer out of the reader. 4328 This can of course result in splats, and is 4329 intended to test the ability of things like 4330 CONFIG_RCU_STRICT_GRACE_PERIOD=y to detect 4331 such leaks. 4332 4333 rcutorture.n_barrier_cbs= [KNL] 4334 Set callbacks/threads for rcu_barrier() testing. 4335 4336 rcutorture.nfakewriters= [KNL] 4337 Set number of concurrent RCU writers. These just 4338 stress RCU, they don't participate in the actual 4339 test, hence the "fake". 4340 4341 rcutorture.nreaders= [KNL] 4342 Set number of RCU readers. The value -1 selects 4343 N-1, where N is the number of CPUs. A value 4344 "n" less than -1 selects N-n-2, where N is again 4345 the number of CPUs. For example, -2 selects N 4346 (the number of CPUs), -3 selects N+1, and so on. 4347 4348 rcutorture.object_debug= [KNL] 4349 Enable debug-object double-call_rcu() testing. 4350 4351 rcutorture.onoff_holdoff= [KNL] 4352 Set time (s) after boot for CPU-hotplug testing. 4353 4354 rcutorture.onoff_interval= [KNL] 4355 Set time (jiffies) between CPU-hotplug operations, 4356 or zero to disable CPU-hotplug testing. 4357 4358 rcutorture.read_exit= [KNL] 4359 Set the number of read-then-exit kthreads used 4360 to test the interaction of RCU updaters and 4361 task-exit processing. 4362 4363 rcutorture.read_exit_burst= [KNL] 4364 The number of times in a given read-then-exit 4365 episode that a set of read-then-exit kthreads 4366 is spawned. 4367 4368 rcutorture.read_exit_delay= [KNL] 4369 The delay, in seconds, between successive 4370 read-then-exit testing episodes. 4371 4372 rcutorture.shuffle_interval= [KNL] 4373 Set task-shuffle interval (s). Shuffling tasks 4374 allows some CPUs to go into dyntick-idle mode 4375 during the rcutorture test. 4376 4377 rcutorture.shutdown_secs= [KNL] 4378 Set time (s) after boot system shutdown. This 4379 is useful for hands-off automated testing. 4380 4381 rcutorture.stall_cpu= [KNL] 4382 Duration of CPU stall (s) to test RCU CPU stall 4383 warnings, zero to disable. 4384 4385 rcutorture.stall_cpu_block= [KNL] 4386 Sleep while stalling if set. This will result 4387 in warnings from preemptible RCU in addition 4388 to any other stall-related activity. 4389 4390 rcutorture.stall_cpu_holdoff= [KNL] 4391 Time to wait (s) after boot before inducing stall. 4392 4393 rcutorture.stall_cpu_irqsoff= [KNL] 4394 Disable interrupts while stalling if set. 4395 4396 rcutorture.stall_gp_kthread= [KNL] 4397 Duration (s) of forced sleep within RCU 4398 grace-period kthread to test RCU CPU stall 4399 warnings, zero to disable. If both stall_cpu 4400 and stall_gp_kthread are specified, the 4401 kthread is starved first, then the CPU. 4402 4403 rcutorture.stat_interval= [KNL] 4404 Time (s) between statistics printk()s. 4405 4406 rcutorture.stutter= [KNL] 4407 Time (s) to stutter testing, for example, specifying 4408 five seconds causes the test to run for five seconds, 4409 wait for five seconds, and so on. This tests RCU's 4410 ability to transition abruptly to and from idle. 4411 4412 rcutorture.test_boost= [KNL] 4413 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 4414 "Maybe" means test if the RCU implementation 4415 under test support RCU priority boosting. 4416 4417 rcutorture.test_boost_duration= [KNL] 4418 Duration (s) of each individual boost test. 4419 4420 rcutorture.test_boost_interval= [KNL] 4421 Interval (s) between each boost test. 4422 4423 rcutorture.test_no_idle_hz= [KNL] 4424 Test RCU's dyntick-idle handling. See also the 4425 rcutorture.shuffle_interval parameter. 4426 4427 rcutorture.torture_type= [KNL] 4428 Specify the RCU implementation to test. 4429 4430 rcutorture.verbose= [KNL] 4431 Enable additional printk() statements. 4432 4433 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL] 4434 Dump ftrace buffer after reporting RCU CPU 4435 stall warning. 4436 4437 rcupdate.rcu_cpu_stall_suppress= [KNL] 4438 Suppress RCU CPU stall warning messages. 4439 4440 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL] 4441 Suppress RCU CPU stall warning messages and 4442 rcutorture writer stall warnings that occur 4443 during early boot, that is, during the time 4444 before the init task is spawned. 4445 4446 rcupdate.rcu_cpu_stall_timeout= [KNL] 4447 Set timeout for RCU CPU stall warning messages. 4448 4449 rcupdate.rcu_expedited= [KNL] 4450 Use expedited grace-period primitives, for 4451 example, synchronize_rcu_expedited() instead 4452 of synchronize_rcu(). This reduces latency, 4453 but can increase CPU utilization, degrade 4454 real-time latency, and degrade energy efficiency. 4455 No effect on CONFIG_TINY_RCU kernels. 4456 4457 rcupdate.rcu_normal= [KNL] 4458 Use only normal grace-period primitives, 4459 for example, synchronize_rcu() instead of 4460 synchronize_rcu_expedited(). This improves 4461 real-time latency, CPU utilization, and 4462 energy efficiency, but can expose users to 4463 increased grace-period latency. This parameter 4464 overrides rcupdate.rcu_expedited. No effect on 4465 CONFIG_TINY_RCU kernels. 4466 4467 rcupdate.rcu_normal_after_boot= [KNL] 4468 Once boot has completed (that is, after 4469 rcu_end_inkernel_boot() has been invoked), use 4470 only normal grace-period primitives. No effect 4471 on CONFIG_TINY_RCU kernels. 4472 4473 rcupdate.rcu_task_ipi_delay= [KNL] 4474 Set time in jiffies during which RCU tasks will 4475 avoid sending IPIs, starting with the beginning 4476 of a given grace period. Setting a large 4477 number avoids disturbing real-time workloads, 4478 but lengthens grace periods. 4479 4480 rcupdate.rcu_task_stall_timeout= [KNL] 4481 Set timeout in jiffies for RCU task stall warning 4482 messages. Disable with a value less than or equal 4483 to zero. 4484 4485 rcupdate.rcu_self_test= [KNL] 4486 Run the RCU early boot self tests 4487 4488 rdinit= [KNL] 4489 Format: <full_path> 4490 Run specified binary instead of /init from the ramdisk, 4491 used for early userspace startup. See initrd. 4492 4493 rdrand= [X86] 4494 force - Override the decision by the kernel to hide the 4495 advertisement of RDRAND support (this affects 4496 certain AMD processors because of buggy BIOS 4497 support, specifically around the suspend/resume 4498 path). 4499 4500 rdt= [HW,X86,RDT] 4501 Turn on/off individual RDT features. List is: 4502 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, 4503 mba. 4504 E.g. to turn on cmt and turn off mba use: 4505 rdt=cmt,!mba 4506 4507 reboot= [KNL] 4508 Format (x86 or x86_64): 4509 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \ 4510 [[,]s[mp]#### \ 4511 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 4512 [[,]f[orce] 4513 Where reboot_mode is one of warm (soft) or cold (hard) or gpio 4514 (prefix with 'panic_' to set mode for panic 4515 reboot only), 4516 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 4517 reboot_force is either force or not specified, 4518 reboot_cpu is s[mp]#### with #### being the processor 4519 to be used for rebooting. 4520 4521 refscale.holdoff= [KNL] 4522 Set test-start holdoff period. The purpose of 4523 this parameter is to delay the start of the 4524 test until boot completes in order to avoid 4525 interference. 4526 4527 refscale.loops= [KNL] 4528 Set the number of loops over the synchronization 4529 primitive under test. Increasing this number 4530 reduces noise due to loop start/end overhead, 4531 but the default has already reduced the per-pass 4532 noise to a handful of picoseconds on ca. 2020 4533 x86 laptops. 4534 4535 refscale.nreaders= [KNL] 4536 Set number of readers. The default value of -1 4537 selects N, where N is roughly 75% of the number 4538 of CPUs. A value of zero is an interesting choice. 4539 4540 refscale.nruns= [KNL] 4541 Set number of runs, each of which is dumped onto 4542 the console log. 4543 4544 refscale.readdelay= [KNL] 4545 Set the read-side critical-section duration, 4546 measured in microseconds. 4547 4548 refscale.scale_type= [KNL] 4549 Specify the read-protection implementation to test. 4550 4551 refscale.shutdown= [KNL] 4552 Shut down the system at the end of the performance 4553 test. This defaults to 1 (shut it down) when 4554 refscale is built into the kernel and to 0 (leave 4555 it running) when refscale is built as a module. 4556 4557 refscale.verbose= [KNL] 4558 Enable additional printk() statements. 4559 4560 relax_domain_level= 4561 [KNL, SMP] Set scheduler's default relax_domain_level. 4562 See Documentation/admin-guide/cgroup-v1/cpusets.rst. 4563 4564 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory 4565 Format: <base1>,<size1>[,<base2>,<size2>,...] 4566 Reserve I/O ports or memory so the kernel won't use 4567 them. If <base> is less than 0x10000, the region 4568 is assumed to be I/O ports; otherwise it is memory. 4569 4570 reservetop= [X86-32] 4571 Format: nn[KMG] 4572 Reserves a hole at the top of the kernel virtual 4573 address space. 4574 4575 reservelow= [X86] 4576 Format: nn[K] 4577 Set the amount of memory to reserve for BIOS at 4578 the bottom of the address space. 4579 4580 reset_devices [KNL] Force drivers to reset the underlying device 4581 during initialization. 4582 4583 resume= [SWSUSP] 4584 Specify the partition device for software suspend 4585 Format: 4586 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 4587 4588 resume_offset= [SWSUSP] 4589 Specify the offset from the beginning of the partition 4590 given by "resume=" at which the swap header is located, 4591 in <PAGE_SIZE> units (needed only for swap files). 4592 See Documentation/power/swsusp-and-swap-files.rst 4593 4594 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 4595 read the resume files 4596 4597 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 4598 Useful for devices that are detected asynchronously 4599 (e.g. USB and MMC devices). 4600 4601 hibernate= [HIBERNATION] 4602 noresume Don't check if there's a hibernation image 4603 present during boot. 4604 nocompress Don't compress/decompress hibernation images. 4605 no Disable hibernation and resume. 4606 protect_image Turn on image protection during restoration 4607 (that will set all pages holding image data 4608 during restoration read-only). 4609 4610 retain_initrd [RAM] Keep initrd memory after extraction 4611 4612 rfkill.default_state= 4613 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 4614 etc. communication is blocked by default. 4615 1 Unblocked. 4616 4617 rfkill.master_switch_mode= 4618 0 The "airplane mode" button does nothing. 4619 1 The "airplane mode" button toggles between everything 4620 blocked and the previous configuration. 4621 2 The "airplane mode" button toggles between everything 4622 blocked and everything unblocked. 4623 4624 rhash_entries= [KNL,NET] 4625 Set number of hash buckets for route cache 4626 4627 ring3mwait=disable 4628 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 4629 CPUs. 4630 4631 ro [KNL] Mount root device read-only on boot 4632 4633 rodata= [KNL] 4634 on Mark read-only kernel memory as read-only (default). 4635 off Leave read-only kernel memory writable for debugging. 4636 4637 rockchip.usb_uart 4638 Enable the uart passthrough on the designated usb port 4639 on Rockchip SoCs. When active, the signals of the 4640 debug-uart get routed to the D+ and D- pins of the usb 4641 port and the regular usb controller gets disabled. 4642 4643 root= [KNL] Root filesystem 4644 See name_to_dev_t comment in init/do_mounts.c. 4645 4646 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 4647 mount the root filesystem 4648 4649 rootflags= [KNL] Set root filesystem mount option string 4650 4651 rootfstype= [KNL] Set root filesystem type 4652 4653 rootwait [KNL] Wait (indefinitely) for root device to show up. 4654 Useful for devices that are detected asynchronously 4655 (e.g. USB and MMC devices). 4656 4657 rproc_mem=nn[KMG][@address] 4658 [KNL,ARM,CMA] Remoteproc physical memory block. 4659 Memory area to be used by remote processor image, 4660 managed by CMA. 4661 4662 rw [KNL] Mount root device read-write on boot 4663 4664 S [KNL] Run init in single mode 4665 4666 s390_iommu= [HW,S390] 4667 Set s390 IOTLB flushing mode 4668 strict 4669 With strict flushing every unmap operation will result in 4670 an IOTLB flush. Default is lazy flushing before reuse, 4671 which is faster. 4672 4673 sa1100ir [NET] 4674 See drivers/net/irda/sa1100_ir.c. 4675 4676 sbni= [NET] Granch SBNI12 leased line adapter 4677 4678 sched_debug [KNL] Enables verbose scheduler debug messages. 4679 4680 schedstats= [KNL,X86] Enable or disable scheduled statistics. 4681 Allowed values are enable and disable. This feature 4682 incurs a small amount of overhead in the scheduler 4683 but is useful for debugging and performance tuning. 4684 4685 sched_thermal_decay_shift= 4686 [KNL, SMP] Set a decay shift for scheduler thermal 4687 pressure signal. Thermal pressure signal follows the 4688 default decay period of other scheduler pelt 4689 signals(usually 32 ms but configurable). Setting 4690 sched_thermal_decay_shift will left shift the decay 4691 period for the thermal pressure signal by the shift 4692 value. 4693 i.e. with the default pelt decay period of 32 ms 4694 sched_thermal_decay_shift thermal pressure decay pr 4695 1 64 ms 4696 2 128 ms 4697 and so on. 4698 Format: integer between 0 and 10 4699 Default is 0. 4700 4701 scftorture.holdoff= [KNL] 4702 Number of seconds to hold off before starting 4703 test. Defaults to zero for module insertion and 4704 to 10 seconds for built-in smp_call_function() 4705 tests. 4706 4707 scftorture.longwait= [KNL] 4708 Request ridiculously long waits randomly selected 4709 up to the chosen limit in seconds. Zero (the 4710 default) disables this feature. Please note 4711 that requesting even small non-zero numbers of 4712 seconds can result in RCU CPU stall warnings, 4713 softlockup complaints, and so on. 4714 4715 scftorture.nthreads= [KNL] 4716 Number of kthreads to spawn to invoke the 4717 smp_call_function() family of functions. 4718 The default of -1 specifies a number of kthreads 4719 equal to the number of CPUs. 4720 4721 scftorture.onoff_holdoff= [KNL] 4722 Number seconds to wait after the start of the 4723 test before initiating CPU-hotplug operations. 4724 4725 scftorture.onoff_interval= [KNL] 4726 Number seconds to wait between successive 4727 CPU-hotplug operations. Specifying zero (which 4728 is the default) disables CPU-hotplug operations. 4729 4730 scftorture.shutdown_secs= [KNL] 4731 The number of seconds following the start of the 4732 test after which to shut down the system. The 4733 default of zero avoids shutting down the system. 4734 Non-zero values are useful for automated tests. 4735 4736 scftorture.stat_interval= [KNL] 4737 The number of seconds between outputting the 4738 current test statistics to the console. A value 4739 of zero disables statistics output. 4740 4741 scftorture.stutter_cpus= [KNL] 4742 The number of jiffies to wait between each change 4743 to the set of CPUs under test. 4744 4745 scftorture.use_cpus_read_lock= [KNL] 4746 Use use_cpus_read_lock() instead of the default 4747 preempt_disable() to disable CPU hotplug 4748 while invoking one of the smp_call_function*() 4749 functions. 4750 4751 scftorture.verbose= [KNL] 4752 Enable additional printk() statements. 4753 4754 scftorture.weight_single= [KNL] 4755 The probability weighting to use for the 4756 smp_call_function_single() function with a zero 4757 "wait" parameter. A value of -1 selects the 4758 default if all other weights are -1. However, 4759 if at least one weight has some other value, a 4760 value of -1 will instead select a weight of zero. 4761 4762 scftorture.weight_single_wait= [KNL] 4763 The probability weighting to use for the 4764 smp_call_function_single() function with a 4765 non-zero "wait" parameter. See weight_single. 4766 4767 scftorture.weight_many= [KNL] 4768 The probability weighting to use for the 4769 smp_call_function_many() function with a zero 4770 "wait" parameter. See weight_single. 4771 Note well that setting a high probability for 4772 this weighting can place serious IPI load 4773 on the system. 4774 4775 scftorture.weight_many_wait= [KNL] 4776 The probability weighting to use for the 4777 smp_call_function_many() function with a 4778 non-zero "wait" parameter. See weight_single 4779 and weight_many. 4780 4781 scftorture.weight_all= [KNL] 4782 The probability weighting to use for the 4783 smp_call_function_all() function with a zero 4784 "wait" parameter. See weight_single and 4785 weight_many. 4786 4787 scftorture.weight_all_wait= [KNL] 4788 The probability weighting to use for the 4789 smp_call_function_all() function with a 4790 non-zero "wait" parameter. See weight_single 4791 and weight_many. 4792 4793 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate 4794 xtime_lock contention on larger systems, and/or RCU lock 4795 contention on all systems with CONFIG_MAXSMP set. 4796 Format: { "0" | "1" } 4797 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 4798 1 -- enable. 4799 Note: increases power consumption, thus should only be 4800 enabled if running jitter sensitive (HPC/RT) workloads. 4801 4802 security= [SECURITY] Choose a legacy "major" security module to 4803 enable at boot. This has been deprecated by the 4804 "lsm=" parameter. 4805 4806 selinux= [SELINUX] Disable or enable SELinux at boot time. 4807 Format: { "0" | "1" } 4808 See security/selinux/Kconfig help text. 4809 0 -- disable. 4810 1 -- enable. 4811 Default value is 1. 4812 4813 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 4814 Format: { "0" | "1" } 4815 See security/apparmor/Kconfig help text 4816 0 -- disable. 4817 1 -- enable. 4818 Default value is set via kernel config option. 4819 4820 serialnumber [BUGS=X86-32] 4821 4822 shapers= [NET] 4823 Maximal number of shapers. 4824 4825 simeth= [IA-64] 4826 simscsi= 4827 4828 slram= [HW,MTD] 4829 4830 slab_nomerge [MM] 4831 Disable merging of slabs with similar size. May be 4832 necessary if there is some reason to distinguish 4833 allocs to different slabs, especially in hardened 4834 environments where the risk of heap overflows and 4835 layout control by attackers can usually be 4836 frustrated by disabling merging. This will reduce 4837 most of the exposure of a heap attack to a single 4838 cache (risks via metadata attacks are mostly 4839 unchanged). Debug options disable merging on their 4840 own. 4841 For more information see Documentation/vm/slub.rst. 4842 4843 slab_max_order= [MM, SLAB] 4844 Determines the maximum allowed order for slabs. 4845 A high setting may cause OOMs due to memory 4846 fragmentation. Defaults to 1 for systems with 4847 more than 32MB of RAM, 0 otherwise. 4848 4849 slub_debug[=options[,slabs][;[options[,slabs]]...] [MM, SLUB] 4850 Enabling slub_debug allows one to determine the 4851 culprit if slab objects become corrupted. Enabling 4852 slub_debug can create guard zones around objects and 4853 may poison objects when not in use. Also tracks the 4854 last alloc / free. For more information see 4855 Documentation/vm/slub.rst. 4856 4857 slub_memcg_sysfs= [MM, SLUB] 4858 Determines whether to enable sysfs directories for 4859 memory cgroup sub-caches. 1 to enable, 0 to disable. 4860 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON. 4861 Enabling this can lead to a very high number of debug 4862 directories and files being created under 4863 /sys/kernel/slub. 4864 4865 slub_max_order= [MM, SLUB] 4866 Determines the maximum allowed order for slabs. 4867 A high setting may cause OOMs due to memory 4868 fragmentation. For more information see 4869 Documentation/vm/slub.rst. 4870 4871 slub_min_objects= [MM, SLUB] 4872 The minimum number of objects per slab. SLUB will 4873 increase the slab order up to slub_max_order to 4874 generate a sufficiently large slab able to contain 4875 the number of objects indicated. The higher the number 4876 of objects the smaller the overhead of tracking slabs 4877 and the less frequently locks need to be acquired. 4878 For more information see Documentation/vm/slub.rst. 4879 4880 slub_min_order= [MM, SLUB] 4881 Determines the minimum page order for slabs. Must be 4882 lower than slub_max_order. 4883 For more information see Documentation/vm/slub.rst. 4884 4885 slub_nomerge [MM, SLUB] 4886 Same with slab_nomerge. This is supported for legacy. 4887 See slab_nomerge for more information. 4888 4889 smart2= [HW] 4890 Format: <io1>[,<io2>[,...,<io8>]] 4891 4892 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 4893 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 4894 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 4895 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 4896 smsc-ircc2.ircc_irq= [HW] IRQ line 4897 smsc-ircc2.ircc_dma= [HW] DMA channel 4898 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 4899 0: Toshiba Satellite 1800 (GP data pin select) 4900 1: Fast pin select (default) 4901 2: ATC IRMode 4902 4903 smt [KNL,S390] Set the maximum number of threads (logical 4904 CPUs) to use per physical CPU on systems capable of 4905 symmetric multithreading (SMT). Will be capped to the 4906 actual hardware limit. 4907 Format: <integer> 4908 Default: -1 (no limit) 4909 4910 softlockup_panic= 4911 [KNL] Should the soft-lockup detector generate panics. 4912 Format: 0 | 1 4913 4914 A value of 1 instructs the soft-lockup detector 4915 to panic the machine when a soft-lockup occurs. It is 4916 also controlled by the kernel.softlockup_panic sysctl 4917 and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the 4918 respective build-time switch to that functionality. 4919 4920 softlockup_all_cpu_backtrace= 4921 [KNL] Should the soft-lockup detector generate 4922 backtraces on all cpus. 4923 Format: 0 | 1 4924 4925 sonypi.*= [HW] Sony Programmable I/O Control Device driver 4926 See Documentation/admin-guide/laptops/sonypi.rst 4927 4928 spectre_v2= [X86] Control mitigation of Spectre variant 2 4929 (indirect branch speculation) vulnerability. 4930 The default operation protects the kernel from 4931 user space attacks. 4932 4933 on - unconditionally enable, implies 4934 spectre_v2_user=on 4935 off - unconditionally disable, implies 4936 spectre_v2_user=off 4937 auto - kernel detects whether your CPU model is 4938 vulnerable 4939 4940 Selecting 'on' will, and 'auto' may, choose a 4941 mitigation method at run time according to the 4942 CPU, the available microcode, the setting of the 4943 CONFIG_RETPOLINE configuration option, and the 4944 compiler with which the kernel was built. 4945 4946 Selecting 'on' will also enable the mitigation 4947 against user space to user space task attacks. 4948 4949 Selecting 'off' will disable both the kernel and 4950 the user space protections. 4951 4952 Specific mitigations can also be selected manually: 4953 4954 retpoline - replace indirect branches 4955 retpoline,generic - google's original retpoline 4956 retpoline,amd - AMD-specific minimal thunk 4957 4958 Not specifying this option is equivalent to 4959 spectre_v2=auto. 4960 4961 spectre_v2_user= 4962 [X86] Control mitigation of Spectre variant 2 4963 (indirect branch speculation) vulnerability between 4964 user space tasks 4965 4966 on - Unconditionally enable mitigations. Is 4967 enforced by spectre_v2=on 4968 4969 off - Unconditionally disable mitigations. Is 4970 enforced by spectre_v2=off 4971 4972 prctl - Indirect branch speculation is enabled, 4973 but mitigation can be enabled via prctl 4974 per thread. The mitigation control state 4975 is inherited on fork. 4976 4977 prctl,ibpb 4978 - Like "prctl" above, but only STIBP is 4979 controlled per thread. IBPB is issued 4980 always when switching between different user 4981 space processes. 4982 4983 seccomp 4984 - Same as "prctl" above, but all seccomp 4985 threads will enable the mitigation unless 4986 they explicitly opt out. 4987 4988 seccomp,ibpb 4989 - Like "seccomp" above, but only STIBP is 4990 controlled per thread. IBPB is issued 4991 always when switching between different 4992 user space processes. 4993 4994 auto - Kernel selects the mitigation depending on 4995 the available CPU features and vulnerability. 4996 4997 Default mitigation: 4998 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl" 4999 5000 Not specifying this option is equivalent to 5001 spectre_v2_user=auto. 5002 5003 spec_store_bypass_disable= 5004 [HW] Control Speculative Store Bypass (SSB) Disable mitigation 5005 (Speculative Store Bypass vulnerability) 5006 5007 Certain CPUs are vulnerable to an exploit against a 5008 a common industry wide performance optimization known 5009 as "Speculative Store Bypass" in which recent stores 5010 to the same memory location may not be observed by 5011 later loads during speculative execution. The idea 5012 is that such stores are unlikely and that they can 5013 be detected prior to instruction retirement at the 5014 end of a particular speculation execution window. 5015 5016 In vulnerable processors, the speculatively forwarded 5017 store can be used in a cache side channel attack, for 5018 example to read memory to which the attacker does not 5019 directly have access (e.g. inside sandboxed code). 5020 5021 This parameter controls whether the Speculative Store 5022 Bypass optimization is used. 5023 5024 On x86 the options are: 5025 5026 on - Unconditionally disable Speculative Store Bypass 5027 off - Unconditionally enable Speculative Store Bypass 5028 auto - Kernel detects whether the CPU model contains an 5029 implementation of Speculative Store Bypass and 5030 picks the most appropriate mitigation. If the 5031 CPU is not vulnerable, "off" is selected. If the 5032 CPU is vulnerable the default mitigation is 5033 architecture and Kconfig dependent. See below. 5034 prctl - Control Speculative Store Bypass per thread 5035 via prctl. Speculative Store Bypass is enabled 5036 for a process by default. The state of the control 5037 is inherited on fork. 5038 seccomp - Same as "prctl" above, but all seccomp threads 5039 will disable SSB unless they explicitly opt out. 5040 5041 Default mitigations: 5042 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl" 5043 5044 On powerpc the options are: 5045 5046 on,auto - On Power8 and Power9 insert a store-forwarding 5047 barrier on kernel entry and exit. On Power7 5048 perform a software flush on kernel entry and 5049 exit. 5050 off - No action. 5051 5052 Not specifying this option is equivalent to 5053 spec_store_bypass_disable=auto. 5054 5055 spia_io_base= [HW,MTD] 5056 spia_fio_base= 5057 spia_pedr= 5058 spia_peddr= 5059 5060 split_lock_detect= 5061 [X86] Enable split lock detection 5062 5063 When enabled (and if hardware support is present), atomic 5064 instructions that access data across cache line 5065 boundaries will result in an alignment check exception. 5066 5067 off - not enabled 5068 5069 warn - the kernel will emit rate limited warnings 5070 about applications triggering the #AC 5071 exception. This mode is the default on CPUs 5072 that supports split lock detection. 5073 5074 fatal - the kernel will send SIGBUS to applications 5075 that trigger the #AC exception. 5076 5077 If an #AC exception is hit in the kernel or in 5078 firmware (i.e. not while executing in user mode) 5079 the kernel will oops in either "warn" or "fatal" 5080 mode. 5081 5082 srbds= [X86,INTEL] 5083 Control the Special Register Buffer Data Sampling 5084 (SRBDS) mitigation. 5085 5086 Certain CPUs are vulnerable to an MDS-like 5087 exploit which can leak bits from the random 5088 number generator. 5089 5090 By default, this issue is mitigated by 5091 microcode. However, the microcode fix can cause 5092 the RDRAND and RDSEED instructions to become 5093 much slower. Among other effects, this will 5094 result in reduced throughput from /dev/urandom. 5095 5096 The microcode mitigation can be disabled with 5097 the following option: 5098 5099 off: Disable mitigation and remove 5100 performance impact to RDRAND and RDSEED 5101 5102 srcutree.counter_wrap_check [KNL] 5103 Specifies how frequently to check for 5104 grace-period sequence counter wrap for the 5105 srcu_data structure's ->srcu_gp_seq_needed field. 5106 The greater the number of bits set in this kernel 5107 parameter, the less frequently counter wrap will 5108 be checked for. Note that the bottom two bits 5109 are ignored. 5110 5111 srcutree.exp_holdoff [KNL] 5112 Specifies how many nanoseconds must elapse 5113 since the end of the last SRCU grace period for 5114 a given srcu_struct until the next normal SRCU 5115 grace period will be considered for automatic 5116 expediting. Set to zero to disable automatic 5117 expediting. 5118 5119 ssbd= [ARM64,HW] 5120 Speculative Store Bypass Disable control 5121 5122 On CPUs that are vulnerable to the Speculative 5123 Store Bypass vulnerability and offer a 5124 firmware based mitigation, this parameter 5125 indicates how the mitigation should be used: 5126 5127 force-on: Unconditionally enable mitigation for 5128 for both kernel and userspace 5129 force-off: Unconditionally disable mitigation for 5130 for both kernel and userspace 5131 kernel: Always enable mitigation in the 5132 kernel, and offer a prctl interface 5133 to allow userspace to register its 5134 interest in being mitigated too. 5135 5136 stack_guard_gap= [MM] 5137 override the default stack gap protection. The value 5138 is in page units and it defines how many pages prior 5139 to (for stacks growing down) resp. after (for stacks 5140 growing up) the main stack are reserved for no other 5141 mapping. Default value is 256 pages. 5142 5143 stacktrace [FTRACE] 5144 Enabled the stack tracer on boot up. 5145 5146 stacktrace_filter=[function-list] 5147 [FTRACE] Limit the functions that the stack tracer 5148 will trace at boot up. function-list is a comma-separated 5149 list of functions. This list can be changed at run 5150 time by the stack_trace_filter file in the debugfs 5151 tracing directory. Note, this enables stack tracing 5152 and the stacktrace above is not needed. 5153 5154 sti= [PARISC,HW] 5155 Format: <num> 5156 Set the STI (builtin display/keyboard on the HP-PARISC 5157 machines) console (graphic card) which should be used 5158 as the initial boot-console. 5159 See also comment in drivers/video/console/sticore.c. 5160 5161 sti_font= [HW] 5162 See comment in drivers/video/console/sticore.c. 5163 5164 stifb= [HW] 5165 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 5166 5167 sunrpc.min_resvport= 5168 sunrpc.max_resvport= 5169 [NFS,SUNRPC] 5170 SunRPC servers often require that client requests 5171 originate from a privileged port (i.e. a port in the 5172 range 0 < portnr < 1024). 5173 An administrator who wishes to reserve some of these 5174 ports for other uses may adjust the range that the 5175 kernel's sunrpc client considers to be privileged 5176 using these two parameters to set the minimum and 5177 maximum port values. 5178 5179 sunrpc.svc_rpc_per_connection_limit= 5180 [NFS,SUNRPC] 5181 Limit the number of requests that the server will 5182 process in parallel from a single connection. 5183 The default value is 0 (no limit). 5184 5185 sunrpc.pool_mode= 5186 [NFS] 5187 Control how the NFS server code allocates CPUs to 5188 service thread pools. Depending on how many NICs 5189 you have and where their interrupts are bound, this 5190 option will affect which CPUs will do NFS serving. 5191 Note: this parameter cannot be changed while the 5192 NFS server is running. 5193 5194 auto the server chooses an appropriate mode 5195 automatically using heuristics 5196 global a single global pool contains all CPUs 5197 percpu one pool for each CPU 5198 pernode one pool for each NUMA node (equivalent 5199 to global on non-NUMA machines) 5200 5201 sunrpc.tcp_slot_table_entries= 5202 sunrpc.udp_slot_table_entries= 5203 [NFS,SUNRPC] 5204 Sets the upper limit on the number of simultaneous 5205 RPC calls that can be sent from the client to a 5206 server. Increasing these values may allow you to 5207 improve throughput, but will also increase the 5208 amount of memory reserved for use by the client. 5209 5210 suspend.pm_test_delay= 5211 [SUSPEND] 5212 Sets the number of seconds to remain in a suspend test 5213 mode before resuming the system (see 5214 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 5215 is set. Default value is 5. 5216 5217 svm= [PPC] 5218 Format: { on | off | y | n | 1 | 0 } 5219 This parameter controls use of the Protected 5220 Execution Facility on pSeries. 5221 5222 swapaccount=[0|1] 5223 [KNL] Enable accounting of swap in memory resource 5224 controller if no parameter or 1 is given or disable 5225 it if 0 is given (See Documentation/admin-guide/cgroup-v1/memory.rst) 5226 5227 swiotlb= [ARM,IA-64,PPC,MIPS,X86] 5228 Format: { <int> | force | noforce } 5229 <int> -- Number of I/O TLB slabs 5230 force -- force using of bounce buffers even if they 5231 wouldn't be automatically used by the kernel 5232 noforce -- Never use bounce buffers (for debugging) 5233 5234 switches= [HW,M68k] 5235 5236 sysctl.*= [KNL] 5237 Set a sysctl parameter, right before loading the init 5238 process, as if the value was written to the respective 5239 /proc/sys/... file. Both '.' and '/' are recognized as 5240 separators. Unrecognized parameters and invalid values 5241 are reported in the kernel log. Sysctls registered 5242 later by a loaded module cannot be set this way. 5243 Example: sysctl.vm.swappiness=40 5244 5245 sysfs.deprecated=0|1 [KNL] 5246 Enable/disable old style sysfs layout for old udev 5247 on older distributions. When this option is enabled 5248 very new udev will not work anymore. When this option 5249 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled) 5250 in older udev will not work anymore. 5251 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in 5252 the kernel configuration. 5253 5254 sysrq_always_enabled 5255 [KNL] 5256 Ignore sysrq setting - this boot parameter will 5257 neutralize any effect of /proc/sys/kernel/sysrq. 5258 Useful for debugging. 5259 5260 tcpmhash_entries= [KNL,NET] 5261 Set the number of tcp_metrics_hash slots. 5262 Default value is 8192 or 16384 depending on total 5263 ram pages. This is used to specify the TCP metrics 5264 cache size. See Documentation/networking/ip-sysctl.rst 5265 "tcp_no_metrics_save" section for more details. 5266 5267 tdfx= [HW,DRM] 5268 5269 test_suspend= [SUSPEND][,N] 5270 Specify "mem" (for Suspend-to-RAM) or "standby" (for 5271 standby suspend) or "freeze" (for suspend type freeze) 5272 as the system sleep state during system startup with 5273 the optional capability to repeat N number of times. 5274 The system is woken from this state using a 5275 wakeup-capable RTC alarm. 5276 5277 thash_entries= [KNL,NET] 5278 Set number of hash buckets for TCP connection 5279 5280 thermal.act= [HW,ACPI] 5281 -1: disable all active trip points in all thermal zones 5282 <degrees C>: override all lowest active trip points 5283 5284 thermal.crt= [HW,ACPI] 5285 -1: disable all critical trip points in all thermal zones 5286 <degrees C>: override all critical trip points 5287 5288 thermal.nocrt= [HW,ACPI] 5289 Set to disable actions on ACPI thermal zone 5290 critical and hot trip points. 5291 5292 thermal.off= [HW,ACPI] 5293 1: disable ACPI thermal control 5294 5295 thermal.psv= [HW,ACPI] 5296 -1: disable all passive trip points 5297 <degrees C>: override all passive trip points to this 5298 value 5299 5300 thermal.tzp= [HW,ACPI] 5301 Specify global default ACPI thermal zone polling rate 5302 <deci-seconds>: poll all this frequency 5303 0: no polling (default) 5304 5305 threadirqs [KNL] 5306 Force threading of all interrupt handlers except those 5307 marked explicitly IRQF_NO_THREAD. 5308 5309 topology= [S390] 5310 Format: {off | on} 5311 Specify if the kernel should make use of the cpu 5312 topology information if the hardware supports this. 5313 The scheduler will make use of this information and 5314 e.g. base its process migration decisions on it. 5315 Default is on. 5316 5317 topology_updates= [KNL, PPC, NUMA] 5318 Format: {off} 5319 Specify if the kernel should ignore (off) 5320 topology updates sent by the hypervisor to this 5321 LPAR. 5322 5323 torture.disable_onoff_at_boot= [KNL] 5324 Prevent the CPU-hotplug component of torturing 5325 until after init has spawned. 5326 5327 torture.ftrace_dump_at_shutdown= [KNL] 5328 Dump the ftrace buffer at torture-test shutdown, 5329 even if there were no errors. This can be a 5330 very costly operation when many torture tests 5331 are running concurrently, especially on systems 5332 with rotating-rust storage. 5333 5334 tp720= [HW,PS2] 5335 5336 tpm_suspend_pcr=[HW,TPM] 5337 Format: integer pcr id 5338 Specify that at suspend time, the tpm driver 5339 should extend the specified pcr with zeros, 5340 as a workaround for some chips which fail to 5341 flush the last written pcr on TPM_SaveState. 5342 This will guarantee that all the other pcrs 5343 are saved. 5344 5345 trace_buf_size=nn[KMG] 5346 [FTRACE] will set tracing buffer size on each cpu. 5347 5348 trace_event=[event-list] 5349 [FTRACE] Set and start specified trace events in order 5350 to facilitate early boot debugging. The event-list is a 5351 comma-separated list of trace events to enable. See 5352 also Documentation/trace/events.rst 5353 5354 trace_options=[option-list] 5355 [FTRACE] Enable or disable tracer options at boot. 5356 The option-list is a comma delimited list of options 5357 that can be enabled or disabled just as if you were 5358 to echo the option name into 5359 5360 /sys/kernel/debug/tracing/trace_options 5361 5362 For example, to enable stacktrace option (to dump the 5363 stack trace of each event), add to the command line: 5364 5365 trace_options=stacktrace 5366 5367 See also Documentation/trace/ftrace.rst "trace options" 5368 section. 5369 5370 tp_printk[FTRACE] 5371 Have the tracepoints sent to printk as well as the 5372 tracing ring buffer. This is useful for early boot up 5373 where the system hangs or reboots and does not give the 5374 option for reading the tracing buffer or performing a 5375 ftrace_dump_on_oops. 5376 5377 To turn off having tracepoints sent to printk, 5378 echo 0 > /proc/sys/kernel/tracepoint_printk 5379 Note, echoing 1 into this file without the 5380 tracepoint_printk kernel cmdline option has no effect. 5381 5382 ** CAUTION ** 5383 5384 Having tracepoints sent to printk() and activating high 5385 frequency tracepoints such as irq or sched, can cause 5386 the system to live lock. 5387 5388 traceoff_on_warning 5389 [FTRACE] enable this option to disable tracing when a 5390 warning is hit. This turns off "tracing_on". Tracing can 5391 be enabled again by echoing '1' into the "tracing_on" 5392 file located in /sys/kernel/debug/tracing/ 5393 5394 This option is useful, as it disables the trace before 5395 the WARNING dump is called, which prevents the trace to 5396 be filled with content caused by the warning output. 5397 5398 This option can also be set at run time via the sysctl 5399 option: kernel/traceoff_on_warning 5400 5401 transparent_hugepage= 5402 [KNL] 5403 Format: [always|madvise|never] 5404 Can be used to control the default behavior of the system 5405 with respect to transparent hugepages. 5406 See Documentation/admin-guide/mm/transhuge.rst 5407 for more details. 5408 5409 tsc= Disable clocksource stability checks for TSC. 5410 Format: <string> 5411 [x86] reliable: mark tsc clocksource as reliable, this 5412 disables clocksource verification at runtime, as well 5413 as the stability checks done at bootup. Used to enable 5414 high-resolution timer mode on older hardware, and in 5415 virtualized environment. 5416 [x86] noirqtime: Do not use TSC to do irq accounting. 5417 Used to run time disable IRQ_TIME_ACCOUNTING on any 5418 platforms where RDTSC is slow and this accounting 5419 can add overhead. 5420 [x86] unstable: mark the TSC clocksource as unstable, this 5421 marks the TSC unconditionally unstable at bootup and 5422 avoids any further wobbles once the TSC watchdog notices. 5423 [x86] nowatchdog: disable clocksource watchdog. Used 5424 in situations with strict latency requirements (where 5425 interruptions from clocksource watchdog are not 5426 acceptable). 5427 5428 tsc_early_khz= [X86] Skip early TSC calibration and use the given 5429 value instead. Useful when the early TSC frequency discovery 5430 procedure is not reliable, such as on overclocked systems 5431 with CPUID.16h support and partial CPUID.15h support. 5432 Format: <unsigned int> 5433 5434 tsx= [X86] Control Transactional Synchronization 5435 Extensions (TSX) feature in Intel processors that 5436 support TSX control. 5437 5438 This parameter controls the TSX feature. The options are: 5439 5440 on - Enable TSX on the system. Although there are 5441 mitigations for all known security vulnerabilities, 5442 TSX has been known to be an accelerator for 5443 several previous speculation-related CVEs, and 5444 so there may be unknown security risks associated 5445 with leaving it enabled. 5446 5447 off - Disable TSX on the system. (Note that this 5448 option takes effect only on newer CPUs which are 5449 not vulnerable to MDS, i.e., have 5450 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get 5451 the new IA32_TSX_CTRL MSR through a microcode 5452 update. This new MSR allows for the reliable 5453 deactivation of the TSX functionality.) 5454 5455 auto - Disable TSX if X86_BUG_TAA is present, 5456 otherwise enable TSX on the system. 5457 5458 Not specifying this option is equivalent to tsx=off. 5459 5460 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 5461 for more details. 5462 5463 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async 5464 Abort (TAA) vulnerability. 5465 5466 Similar to Micro-architectural Data Sampling (MDS) 5467 certain CPUs that support Transactional 5468 Synchronization Extensions (TSX) are vulnerable to an 5469 exploit against CPU internal buffers which can forward 5470 information to a disclosure gadget under certain 5471 conditions. 5472 5473 In vulnerable processors, the speculatively forwarded 5474 data can be used in a cache side channel attack, to 5475 access data to which the attacker does not have direct 5476 access. 5477 5478 This parameter controls the TAA mitigation. The 5479 options are: 5480 5481 full - Enable TAA mitigation on vulnerable CPUs 5482 if TSX is enabled. 5483 5484 full,nosmt - Enable TAA mitigation and disable SMT on 5485 vulnerable CPUs. If TSX is disabled, SMT 5486 is not disabled because CPU is not 5487 vulnerable to cross-thread TAA attacks. 5488 off - Unconditionally disable TAA mitigation 5489 5490 On MDS-affected machines, tsx_async_abort=off can be 5491 prevented by an active MDS mitigation as both vulnerabilities 5492 are mitigated with the same mechanism so in order to disable 5493 this mitigation, you need to specify mds=off too. 5494 5495 Not specifying this option is equivalent to 5496 tsx_async_abort=full. On CPUs which are MDS affected 5497 and deploy MDS mitigation, TAA mitigation is not 5498 required and doesn't provide any additional 5499 mitigation. 5500 5501 For details see: 5502 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 5503 5504 turbografx.map[2|3]= [HW,JOY] 5505 TurboGraFX parallel port interface 5506 Format: 5507 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 5508 See also Documentation/input/devices/joystick-parport.rst 5509 5510 udbg-immortal [PPC] When debugging early kernel crashes that 5511 happen after console_init() and before a proper 5512 console driver takes over, this boot options might 5513 help "seeing" what's going on. 5514 5515 uhash_entries= [KNL,NET] 5516 Set number of hash buckets for UDP/UDP-Lite connections 5517 5518 uhci-hcd.ignore_oc= 5519 [USB] Ignore overcurrent events (default N). 5520 Some badly-designed motherboards generate lots of 5521 bogus events, for ports that aren't wired to 5522 anything. Set this parameter to avoid log spamming. 5523 Note that genuine overcurrent events won't be 5524 reported either. 5525 5526 unknown_nmi_panic 5527 [X86] Cause panic on unknown NMI. 5528 5529 usbcore.authorized_default= 5530 [USB] Default USB device authorization: 5531 (default -1 = authorized except for wireless USB, 5532 0 = not authorized, 1 = authorized, 2 = authorized 5533 if device connected to internal port) 5534 5535 usbcore.autosuspend= 5536 [USB] The autosuspend time delay (in seconds) used 5537 for newly-detected USB devices (default 2). This 5538 is the time required before an idle device will be 5539 autosuspended. Devices for which the delay is set 5540 to a negative value won't be autosuspended at all. 5541 5542 usbcore.usbfs_snoop= 5543 [USB] Set to log all usbfs traffic (default 0 = off). 5544 5545 usbcore.usbfs_snoop_max= 5546 [USB] Maximum number of bytes to snoop in each URB 5547 (default = 65536). 5548 5549 usbcore.blinkenlights= 5550 [USB] Set to cycle leds on hubs (default 0 = off). 5551 5552 usbcore.old_scheme_first= 5553 [USB] Start with the old device initialization 5554 scheme (default 0 = off). 5555 5556 usbcore.usbfs_memory_mb= 5557 [USB] Memory limit (in MB) for buffers allocated by 5558 usbfs (default = 16, 0 = max = 2047). 5559 5560 usbcore.use_both_schemes= 5561 [USB] Try the other device initialization scheme 5562 if the first one fails (default 1 = enabled). 5563 5564 usbcore.initial_descriptor_timeout= 5565 [USB] Specifies timeout for the initial 64-byte 5566 USB_REQ_GET_DESCRIPTOR request in milliseconds 5567 (default 5000 = 5.0 seconds). 5568 5569 usbcore.nousb [USB] Disable the USB subsystem 5570 5571 usbcore.quirks= 5572 [USB] A list of quirk entries to augment the built-in 5573 usb core quirk list. List entries are separated by 5574 commas. Each entry has the form 5575 VendorID:ProductID:Flags. The IDs are 4-digit hex 5576 numbers and Flags is a set of letters. Each letter 5577 will change the built-in quirk; setting it if it is 5578 clear and clearing it if it is set. The letters have 5579 the following meanings: 5580 a = USB_QUIRK_STRING_FETCH_255 (string 5581 descriptors must not be fetched using 5582 a 255-byte read); 5583 b = USB_QUIRK_RESET_RESUME (device can't resume 5584 correctly so reset it instead); 5585 c = USB_QUIRK_NO_SET_INTF (device can't handle 5586 Set-Interface requests); 5587 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't 5588 handle its Configuration or Interface 5589 strings); 5590 e = USB_QUIRK_RESET (device can't be reset 5591 (e.g morph devices), don't use reset); 5592 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has 5593 more interface descriptions than the 5594 bNumInterfaces count, and can't handle 5595 talking to these interfaces); 5596 g = USB_QUIRK_DELAY_INIT (device needs a pause 5597 during initialization, after we read 5598 the device descriptor); 5599 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For 5600 high speed and super speed interrupt 5601 endpoints, the USB 2.0 and USB 3.0 spec 5602 require the interval in microframes (1 5603 microframe = 125 microseconds) to be 5604 calculated as interval = 2 ^ 5605 (bInterval-1). 5606 Devices with this quirk report their 5607 bInterval as the result of this 5608 calculation instead of the exponent 5609 variable used in the calculation); 5610 i = USB_QUIRK_DEVICE_QUALIFIER (device can't 5611 handle device_qualifier descriptor 5612 requests); 5613 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device 5614 generates spurious wakeup, ignore 5615 remote wakeup capability); 5616 k = USB_QUIRK_NO_LPM (device can't handle Link 5617 Power Management); 5618 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL 5619 (Device reports its bInterval as linear 5620 frames instead of the USB 2.0 5621 calculation); 5622 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs 5623 to be disconnected before suspend to 5624 prevent spurious wakeup); 5625 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a 5626 pause after every control message); 5627 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra 5628 delay after resetting its port); 5629 Example: quirks=0781:5580:bk,0a5c:5834:gij 5630 5631 usbhid.mousepoll= 5632 [USBHID] The interval which mice are to be polled at. 5633 5634 usbhid.jspoll= 5635 [USBHID] The interval which joysticks are to be polled at. 5636 5637 usbhid.kbpoll= 5638 [USBHID] The interval which keyboards are to be polled at. 5639 5640 usb-storage.delay_use= 5641 [UMS] The delay in seconds before a new device is 5642 scanned for Logical Units (default 1). 5643 5644 usb-storage.quirks= 5645 [UMS] A list of quirks entries to supplement or 5646 override the built-in unusual_devs list. List 5647 entries are separated by commas. Each entry has 5648 the form VID:PID:Flags where VID and PID are Vendor 5649 and Product ID values (4-digit hex numbers) and 5650 Flags is a set of characters, each corresponding 5651 to a common usb-storage quirk flag as follows: 5652 a = SANE_SENSE (collect more than 18 bytes 5653 of sense data, not on uas); 5654 b = BAD_SENSE (don't collect more than 18 5655 bytes of sense data, not on uas); 5656 c = FIX_CAPACITY (decrease the reported 5657 device capacity by one sector); 5658 d = NO_READ_DISC_INFO (don't use 5659 READ_DISC_INFO command, not on uas); 5660 e = NO_READ_CAPACITY_16 (don't use 5661 READ_CAPACITY_16 command); 5662 f = NO_REPORT_OPCODES (don't use report opcodes 5663 command, uas only); 5664 g = MAX_SECTORS_240 (don't transfer more than 5665 240 sectors at a time, uas only); 5666 h = CAPACITY_HEURISTICS (decrease the 5667 reported device capacity by one 5668 sector if the number is odd); 5669 i = IGNORE_DEVICE (don't bind to this 5670 device); 5671 j = NO_REPORT_LUNS (don't use report luns 5672 command, uas only); 5673 k = NO_SAME (do not use WRITE_SAME, uas only) 5674 l = NOT_LOCKABLE (don't try to lock and 5675 unlock ejectable media, not on uas); 5676 m = MAX_SECTORS_64 (don't transfer more 5677 than 64 sectors = 32 KB at a time, 5678 not on uas); 5679 n = INITIAL_READ10 (force a retry of the 5680 initial READ(10) command, not on uas); 5681 o = CAPACITY_OK (accept the capacity 5682 reported by the device, not on uas); 5683 p = WRITE_CACHE (the device cache is ON 5684 by default, not on uas); 5685 r = IGNORE_RESIDUE (the device reports 5686 bogus residue values, not on uas); 5687 s = SINGLE_LUN (the device has only one 5688 Logical Unit); 5689 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 5690 commands, uas only); 5691 u = IGNORE_UAS (don't bind to the uas driver); 5692 w = NO_WP_DETECT (don't test whether the 5693 medium is write-protected). 5694 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 5695 even if the device claims no cache, 5696 not on uas) 5697 Example: quirks=0419:aaf5:rl,0421:0433:rc 5698 5699 user_debug= [KNL,ARM] 5700 Format: <int> 5701 See arch/arm/Kconfig.debug help text. 5702 1 - undefined instruction events 5703 2 - system calls 5704 4 - invalid data aborts 5705 8 - SIGSEGV faults 5706 16 - SIGBUS faults 5707 Example: user_debug=31 5708 5709 userpte= 5710 [X86] Flags controlling user PTE allocations. 5711 5712 nohigh = do not allocate PTE pages in 5713 HIGHMEM regardless of setting 5714 of CONFIG_HIGHPTE. 5715 5716 vdso= [X86,SH] 5717 On X86_32, this is an alias for vdso32=. Otherwise: 5718 5719 vdso=1: enable VDSO (the default) 5720 vdso=0: disable VDSO mapping 5721 5722 vdso32= [X86] Control the 32-bit vDSO 5723 vdso32=1: enable 32-bit VDSO 5724 vdso32=0 or vdso32=2: disable 32-bit VDSO 5725 5726 See the help text for CONFIG_COMPAT_VDSO for more 5727 details. If CONFIG_COMPAT_VDSO is set, the default is 5728 vdso32=0; otherwise, the default is vdso32=1. 5729 5730 For compatibility with older kernels, vdso32=2 is an 5731 alias for vdso32=0. 5732 5733 Try vdso32=0 if you encounter an error that says: 5734 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 5735 5736 vector= [IA-64,SMP] 5737 vector=percpu: enable percpu vector domain 5738 5739 video= [FB] Frame buffer configuration 5740 See Documentation/fb/modedb.rst. 5741 5742 video.brightness_switch_enabled= [0,1] 5743 If set to 1, on receiving an ACPI notify event 5744 generated by hotkey, video driver will adjust brightness 5745 level and then send out the event to user space through 5746 the allocated input device; If set to 0, video driver 5747 will only send out the event without touching backlight 5748 brightness level. 5749 default: 1 5750 5751 virtio_mmio.device= 5752 [VMMIO] Memory mapped virtio (platform) device. 5753 5754 <size>@<baseaddr>:<irq>[:<id>] 5755 where: 5756 <size> := size (can use standard suffixes 5757 like K, M and G) 5758 <baseaddr> := physical base address 5759 <irq> := interrupt number (as passed to 5760 request_irq()) 5761 <id> := (optional) platform device id 5762 example: 5763 virtio_mmio.device=1K@0x100b0000:48:7 5764 5765 Can be used multiple times for multiple devices. 5766 5767 vga= [BOOT,X86-32] Select a particular video mode 5768 See Documentation/x86/boot.rst and 5769 Documentation/admin-guide/svga.rst. 5770 Use vga=ask for menu. 5771 This is actually a boot loader parameter; the value is 5772 passed to the kernel using a special protocol. 5773 5774 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. 5775 May slow down system boot speed, especially when 5776 enabled on systems with a large amount of memory. 5777 All options are enabled by default, and this 5778 interface is meant to allow for selectively 5779 enabling or disabling specific virtual memory 5780 debugging features. 5781 5782 Available options are: 5783 P Enable page structure init time poisoning 5784 - Disable all of the above options 5785 5786 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact 5787 size of <nn>. This can be used to increase the 5788 minimum size (128MB on x86). It can also be used to 5789 decrease the size and leave more room for directly 5790 mapped kernel RAM. 5791 5792 vmcp_cma=nn[MG] [KNL,S390] 5793 Sets the memory size reserved for contiguous memory 5794 allocations for the vmcp device driver. 5795 5796 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 5797 Format: <command> 5798 5799 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 5800 Format: <command> 5801 5802 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 5803 Format: <command> 5804 5805 vsyscall= [X86-64] 5806 Controls the behavior of vsyscalls (i.e. calls to 5807 fixed addresses of 0xffffffffff600x00 from legacy 5808 code). Most statically-linked binaries and older 5809 versions of glibc use these calls. Because these 5810 functions are at fixed addresses, they make nice 5811 targets for exploits that can control RIP. 5812 5813 emulate [default] Vsyscalls turn into traps and are 5814 emulated reasonably safely. The vsyscall 5815 page is readable. 5816 5817 xonly Vsyscalls turn into traps and are 5818 emulated reasonably safely. The vsyscall 5819 page is not readable. 5820 5821 none Vsyscalls don't work at all. This makes 5822 them quite hard to use for exploits but 5823 might break your system. 5824 5825 vt.color= [VT] Default text color. 5826 Format: 0xYX, X = foreground, Y = background. 5827 Default: 0x07 = light gray on black. 5828 5829 vt.cur_default= [VT] Default cursor shape. 5830 Format: 0xCCBBAA, where AA, BB, and CC are the same as 5831 the parameters of the <Esc>[?A;B;Cc escape sequence; 5832 see VGA-softcursor.txt. Default: 2 = underline. 5833 5834 vt.default_blu= [VT] 5835 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 5836 Change the default blue palette of the console. 5837 This is a 16-member array composed of values 5838 ranging from 0-255. 5839 5840 vt.default_grn= [VT] 5841 Format: <green0>,<green1>,<green2>,...,<green15> 5842 Change the default green palette of the console. 5843 This is a 16-member array composed of values 5844 ranging from 0-255. 5845 5846 vt.default_red= [VT] 5847 Format: <red0>,<red1>,<red2>,...,<red15> 5848 Change the default red palette of the console. 5849 This is a 16-member array composed of values 5850 ranging from 0-255. 5851 5852 vt.default_utf8= 5853 [VT] 5854 Format=<0|1> 5855 Set system-wide default UTF-8 mode for all tty's. 5856 Default is 1, i.e. UTF-8 mode is enabled for all 5857 newly opened terminals. 5858 5859 vt.global_cursor_default= 5860 [VT] 5861 Format=<-1|0|1> 5862 Set system-wide default for whether a cursor 5863 is shown on new VTs. Default is -1, 5864 i.e. cursors will be created by default unless 5865 overridden by individual drivers. 0 will hide 5866 cursors, 1 will display them. 5867 5868 vt.italic= [VT] Default color for italic text; 0-15. 5869 Default: 2 = green. 5870 5871 vt.underline= [VT] Default color for underlined text; 0-15. 5872 Default: 3 = cyan. 5873 5874 watchdog timers [HW,WDT] For information on watchdog timers, 5875 see Documentation/watchdog/watchdog-parameters.rst 5876 or other driver-specific files in the 5877 Documentation/watchdog/ directory. 5878 5879 watchdog_thresh= 5880 [KNL] 5881 Set the hard lockup detector stall duration 5882 threshold in seconds. The soft lockup detector 5883 threshold is set to twice the value. A value of 0 5884 disables both lockup detectors. Default is 10 5885 seconds. 5886 5887 workqueue.watchdog_thresh= 5888 If CONFIG_WQ_WATCHDOG is configured, workqueue can 5889 warn stall conditions and dump internal state to 5890 help debugging. 0 disables workqueue stall 5891 detection; otherwise, it's the stall threshold 5892 duration in seconds. The default value is 30 and 5893 it can be updated at runtime by writing to the 5894 corresponding sysfs file. 5895 5896 workqueue.disable_numa 5897 By default, all work items queued to unbound 5898 workqueues are affine to the NUMA nodes they're 5899 issued on, which results in better behavior in 5900 general. If NUMA affinity needs to be disabled for 5901 whatever reason, this option can be used. Note 5902 that this also can be controlled per-workqueue for 5903 workqueues visible under /sys/bus/workqueue/. 5904 5905 workqueue.power_efficient 5906 Per-cpu workqueues are generally preferred because 5907 they show better performance thanks to cache 5908 locality; unfortunately, per-cpu workqueues tend to 5909 be more power hungry than unbound workqueues. 5910 5911 Enabling this makes the per-cpu workqueues which 5912 were observed to contribute significantly to power 5913 consumption unbound, leading to measurably lower 5914 power usage at the cost of small performance 5915 overhead. 5916 5917 The default value of this parameter is determined by 5918 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 5919 5920 workqueue.debug_force_rr_cpu 5921 Workqueue used to implicitly guarantee that work 5922 items queued without explicit CPU specified are put 5923 on the local CPU. This guarantee is no longer true 5924 and while local CPU is still preferred work items 5925 may be put on foreign CPUs. This debug option 5926 forces round-robin CPU selection to flush out 5927 usages which depend on the now broken guarantee. 5928 When enabled, memory and cache locality will be 5929 impacted. 5930 5931 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of 5932 default x2apic cluster mode on platforms 5933 supporting x2apic. 5934 5935 x86_intel_mid_timer= [X86-32,APBT] 5936 Choose timer option for x86 Intel MID platform. 5937 Two valid options are apbt timer only and lapic timer 5938 plus one apbt timer for broadcast timer. 5939 x86_intel_mid_timer=apbt_only | lapic_and_apbt 5940 5941 xen_512gb_limit [KNL,X86-64,XEN] 5942 Restricts the kernel running paravirtualized under Xen 5943 to use only up to 512 GB of RAM. The reason to do so is 5944 crash analysis tools and Xen tools for doing domain 5945 save/restore/migration must be enabled to handle larger 5946 domains. 5947 5948 xen_emul_unplug= [HW,X86,XEN] 5949 Unplug Xen emulated devices 5950 Format: [unplug0,][unplug1] 5951 ide-disks -- unplug primary master IDE devices 5952 aux-ide-disks -- unplug non-primary-master IDE devices 5953 nics -- unplug network devices 5954 all -- unplug all emulated devices (NICs and IDE disks) 5955 unnecessary -- unplugging emulated devices is 5956 unnecessary even if the host did not respond to 5957 the unplug protocol 5958 never -- do not unplug even if version check succeeds 5959 5960 xen_legacy_crash [X86,XEN] 5961 Crash from Xen panic notifier, without executing late 5962 panic() code such as dumping handler. 5963 5964 xen_nopvspin [X86,XEN] 5965 Disables the qspinlock slowpath using Xen PV optimizations. 5966 This parameter is obsoleted by "nopvspin" parameter, which 5967 has equivalent effect for XEN platform. 5968 5969 xen_nopv [X86] 5970 Disables the PV optimizations forcing the HVM guest to 5971 run as generic HVM guest with no PV drivers. 5972 This option is obsoleted by the "nopv" option, which 5973 has equivalent effect for XEN platform. 5974 5975 xen_no_vector_callback 5976 [KNL,X86,XEN] Disable the vector callback for Xen 5977 event channel interrupts. 5978 5979 xen_scrub_pages= [XEN] 5980 Boolean option to control scrubbing pages before giving them back 5981 to Xen, for use by other domains. Can be also changed at runtime 5982 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. 5983 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. 5984 5985 xen_timer_slop= [X86-64,XEN] 5986 Set the timer slop (in nanoseconds) for the virtual Xen 5987 timers (default is 100000). This adjusts the minimum 5988 delta of virtualized Xen timers, where lower values 5989 improve timer resolution at the expense of processing 5990 more timer interrupts. 5991 5992 xen.event_eoi_delay= [XEN] 5993 How long to delay EOI handling in case of event 5994 storms (jiffies). Default is 10. 5995 5996 xen.event_loop_timeout= [XEN] 5997 After which time (jiffies) the event handling loop 5998 should start to delay EOI handling. Default is 2. 5999 6000 xen.fifo_events= [XEN] 6001 Boolean parameter to disable using fifo event handling 6002 even if available. Normally fifo event handling is 6003 preferred over the 2-level event handling, as it is 6004 fairer and the number of possible event channels is 6005 much higher. Default is on (use fifo events). 6006 6007 nopv= [X86,XEN,KVM,HYPER_V,VMWARE] 6008 Disables the PV optimizations forcing the guest to run 6009 as generic guest with no PV drivers. Currently support 6010 XEN HVM, KVM, HYPER_V and VMWARE guest. 6011 6012 nopvspin [X86,XEN,KVM] 6013 Disables the qspinlock slow path using PV optimizations 6014 which allow the hypervisor to 'idle' the guest on lock 6015 contention. 6016 6017 xirc2ps_cs= [NET,PCMCIA] 6018 Format: 6019 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 6020 6021 xive= [PPC] 6022 By default on POWER9 and above, the kernel will 6023 natively use the XIVE interrupt controller. This option 6024 allows the fallback firmware mode to be used: 6025 6026 off Fallback to firmware control of XIVE interrupt 6027 controller on both pseries and powernv 6028 platforms. Only useful on POWER9 and above. 6029 6030 xhci-hcd.quirks [USB,KNL] 6031 A hex value specifying bitmask with supplemental xhci 6032 host controller quirks. Meaning of each bit can be 6033 consulted in header drivers/usb/host/xhci.h. 6034 6035 xmon [PPC] 6036 Format: { early | on | rw | ro | off } 6037 Controls if xmon debugger is enabled. Default is off. 6038 Passing only "xmon" is equivalent to "xmon=early". 6039 early Call xmon as early as possible on boot; xmon 6040 debugger is called from setup_arch(). 6041 on xmon debugger hooks will be installed so xmon 6042 is only called on a kernel crash. Default mode, 6043 i.e. either "ro" or "rw" mode, is controlled 6044 with CONFIG_XMON_DEFAULT_RO_MODE. 6045 rw xmon debugger hooks will be installed so xmon 6046 is called only on a kernel crash, mode is write, 6047 meaning SPR registers, memory and, other data 6048 can be written using xmon commands. 6049 ro same as "rw" option above but SPR registers, 6050 memory, and other data can't be written using 6051 xmon commands. 6052 off xmon is disabled. 6053