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.txt. 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/media/v4l-drivers/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 [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 [ARM,X86,KNL] 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 include/linux/dma-contiguous.h 601 602 cmo_free_hint= [PPC] Format: { yes | no } 603 Specify whether pages are marked as being inactive 604 when they are freed. This is used in CMO environments 605 to determine OS memory pressure for page stealing by 606 a hypervisor. 607 Default: yes 608 609 coherent_pool=nn[KMG] [ARM,KNL] 610 Sets the size of memory pool for coherent, atomic dma 611 allocations, by default set to 256K. 612 613 com20020= [HW,NET] ARCnet - COM20020 chipset 614 Format: 615 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]] 616 617 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers) 618 Format: <io>[,<irq>] 619 620 com90xx= [HW,NET] 621 ARCnet - COM90xx chipset (memory-mapped buffers) 622 Format: <io>[,<irq>[,<memstart>]] 623 624 condev= [HW,S390] console device 625 conmode= 626 627 console= [KNL] Output console device and options. 628 629 tty<n> Use the virtual console device <n>. 630 631 ttyS<n>[,options] 632 ttyUSB0[,options] 633 Use the specified serial port. The options are of 634 the form "bbbbpnf", where "bbbb" is the baud rate, 635 "p" is parity ("n", "o", or "e"), "n" is number of 636 bits, and "f" is flow control ("r" for RTS or 637 omit it). Default is "9600n8". 638 639 See Documentation/admin-guide/serial-console.rst for more 640 information. See 641 Documentation/networking/netconsole.txt for an 642 alternative. 643 644 uart[8250],io,<addr>[,options] 645 uart[8250],mmio,<addr>[,options] 646 uart[8250],mmio16,<addr>[,options] 647 uart[8250],mmio32,<addr>[,options] 648 uart[8250],0x<addr>[,options] 649 Start an early, polled-mode console on the 8250/16550 650 UART at the specified I/O port or MMIO address, 651 switching to the matching ttyS device later. 652 MMIO inter-register address stride is either 8-bit 653 (mmio), 16-bit (mmio16), or 32-bit (mmio32). 654 If none of [io|mmio|mmio16|mmio32], <addr> is assumed 655 to be equivalent to 'mmio'. 'options' are specified in 656 the same format described for ttyS above; if unspecified, 657 the h/w is not re-initialized. 658 659 hvc<n> Use the hypervisor console device <n>. This is for 660 both Xen and PowerPC hypervisors. 661 662 If the device connected to the port is not a TTY but a braille 663 device, prepend "brl," before the device type, for instance 664 console=brl,ttyS0 665 For now, only VisioBraille is supported. 666 667 console_msg_format= 668 [KNL] Change console messages format 669 default 670 By default we print messages on consoles in 671 "[time stamp] text\n" format (time stamp may not be 672 printed, depending on CONFIG_PRINTK_TIME or 673 `printk_time' param). 674 syslog 675 Switch to syslog format: "<%u>[time stamp] text\n" 676 IOW, each message will have a facility and loglevel 677 prefix. The format is similar to one used by syslog() 678 syscall, or to executing "dmesg -S --raw" or to reading 679 from /proc/kmsg. 680 681 consoleblank= [KNL] The console blank (screen saver) timeout in 682 seconds. A value of 0 disables the blank timer. 683 Defaults to 0. 684 685 coredump_filter= 686 [KNL] Change the default value for 687 /proc/<pid>/coredump_filter. 688 See also Documentation/filesystems/proc.rst. 689 690 coresight_cpu_debug.enable 691 [ARM,ARM64] 692 Format: <bool> 693 Enable/disable the CPU sampling based debugging. 694 0: default value, disable debugging 695 1: enable debugging at boot time 696 697 cpuidle.off=1 [CPU_IDLE] 698 disable the cpuidle sub-system 699 700 cpuidle.governor= 701 [CPU_IDLE] Name of the cpuidle governor to use. 702 703 cpufreq.off=1 [CPU_FREQ] 704 disable the cpufreq sub-system 705 706 cpu_init_udelay=N 707 [X86] Delay for N microsec between assert and de-assert 708 of APIC INIT to start processors. This delay occurs 709 on every CPU online, such as boot, and resume from suspend. 710 Default: 10000 711 712 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver 713 Format: 714 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] 715 716 crashkernel=size[KMG][@offset[KMG]] 717 [KNL] Using kexec, Linux can switch to a 'crash kernel' 718 upon panic. This parameter reserves the physical 719 memory region [offset, offset + size] for that kernel 720 image. If '@offset' is omitted, then a suitable offset 721 is selected automatically. 722 [KNL, x86_64] select a region under 4G first, and 723 fall back to reserve region above 4G when '@offset' 724 hasn't been specified. 725 See Documentation/admin-guide/kdump/kdump.rst for further details. 726 727 crashkernel=range1:size1[,range2:size2,...][@offset] 728 [KNL] Same as above, but depends on the memory 729 in the running system. The syntax of range is 730 start-[end] where start and end are both 731 a memory unit (amount[KMG]). See also 732 Documentation/admin-guide/kdump/kdump.rst for an example. 733 734 crashkernel=size[KMG],high 735 [KNL, x86_64] range could be above 4G. Allow kernel 736 to allocate physical memory region from top, so could 737 be above 4G if system have more than 4G ram installed. 738 Otherwise memory region will be allocated below 4G, if 739 available. 740 It will be ignored if crashkernel=X is specified. 741 crashkernel=size[KMG],low 742 [KNL, x86_64] range under 4G. When crashkernel=X,high 743 is passed, kernel could allocate physical memory region 744 above 4G, that cause second kernel crash on system 745 that require some amount of low memory, e.g. swiotlb 746 requires at least 64M+32K low memory, also enough extra 747 low memory is needed to make sure DMA buffers for 32-bit 748 devices won't run out. Kernel would try to allocate at 749 at least 256M below 4G automatically. 750 This one let user to specify own low range under 4G 751 for second kernel instead. 752 0: to disable low allocation. 753 It will be ignored when crashkernel=X,high is not used 754 or memory reserved is below 4G. 755 756 cryptomgr.notests 757 [KNL] Disable crypto self-tests 758 759 cs89x0_dma= [HW,NET] 760 Format: <dma> 761 762 cs89x0_media= [HW,NET] 763 Format: { rj45 | aui | bnc } 764 765 dasd= [HW,NET] 766 See header of drivers/s390/block/dasd_devmap.c. 767 768 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port 769 (one device per port) 770 Format: <port#>,<type> 771 See also Documentation/input/devices/joystick-parport.rst 772 773 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot 774 time. See 775 Documentation/admin-guide/dynamic-debug-howto.rst for 776 details. Deprecated, see dyndbg. 777 778 debug [KNL] Enable kernel debugging (events log level). 779 780 debug_boot_weak_hash 781 [KNL] Enable printing [hashed] pointers early in the 782 boot sequence. If enabled, we use a weak hash instead 783 of siphash to hash pointers. Use this option if you are 784 seeing instances of '(___ptrval___)') and need to see a 785 value (hashed pointer) instead. Cryptographically 786 insecure, please do not use on production kernels. 787 788 debug_locks_verbose= 789 [KNL] verbose self-tests 790 Format=<0|1> 791 Print debugging info while doing the locking API 792 self-tests. 793 We default to 0 (no extra messages), setting it to 794 1 will print _a lot_ more information - normally 795 only useful to kernel developers. 796 797 debug_objects [KNL] Enable object debugging 798 799 no_debug_objects 800 [KNL] Disable object debugging 801 802 debug_guardpage_minorder= 803 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this 804 parameter allows control of the order of pages that will 805 be intentionally kept free (and hence protected) by the 806 buddy allocator. Bigger value increase the probability 807 of catching random memory corruption, but reduce the 808 amount of memory for normal system use. The maximum 809 possible value is MAX_ORDER/2. Setting this parameter 810 to 1 or 2 should be enough to identify most random 811 memory corruption problems caused by bugs in kernel or 812 driver code when a CPU writes to (or reads from) a 813 random memory location. Note that there exists a class 814 of memory corruptions problems caused by buggy H/W or 815 F/W or by drivers badly programing DMA (basically when 816 memory is written at bus level and the CPU MMU is 817 bypassed) which are not detectable by 818 CONFIG_DEBUG_PAGEALLOC, hence this option will not help 819 tracking down these problems. 820 821 debug_pagealloc= 822 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this parameter 823 enables the feature at boot time. By default, it is 824 disabled and the system will work mostly the same as a 825 kernel built without CONFIG_DEBUG_PAGEALLOC. 826 Note: to get most of debug_pagealloc error reports, it's 827 useful to also enable the page_owner functionality. 828 on: enable the feature 829 830 debugpat [X86] Enable PAT debugging 831 832 decnet.addr= [HW,NET] 833 Format: <area>[,<node>] 834 See also Documentation/networking/decnet.txt. 835 836 default_hugepagesz= 837 [same as hugepagesz=] The size of the default 838 HugeTLB page size. This is the size represented by 839 the legacy /proc/ hugepages APIs, used for SHM, and 840 default size when mounting hugetlbfs filesystems. 841 Defaults to the default architecture's huge page size 842 if not specified. 843 844 deferred_probe_timeout= 845 [KNL] Debugging option to set a timeout in seconds for 846 deferred probe to give up waiting on dependencies to 847 probe. Only specific dependencies (subsystems or 848 drivers) that have opted in will be ignored. A timeout of 0 849 will timeout at the end of initcalls. This option will also 850 dump out devices still on the deferred probe list after 851 retrying. 852 853 dfltcc= [HW,S390] 854 Format: { on | off | def_only | inf_only | always } 855 on: s390 zlib hardware support for compression on 856 level 1 and decompression (default) 857 off: No s390 zlib hardware support 858 def_only: s390 zlib hardware support for deflate 859 only (compression on level 1) 860 inf_only: s390 zlib hardware support for inflate 861 only (decompression) 862 always: Same as 'on' but ignores the selected compression 863 level always using hardware support (used for debugging) 864 865 dhash_entries= [KNL] 866 Set number of hash buckets for dentry cache. 867 868 disable_1tb_segments [PPC] 869 Disables the use of 1TB hash page table segments. This 870 causes the kernel to fall back to 256MB segments which 871 can be useful when debugging issues that require an SLB 872 miss to occur. 873 874 disable= [IPV6] 875 See Documentation/networking/ipv6.txt. 876 877 hardened_usercopy= 878 [KNL] Under CONFIG_HARDENED_USERCOPY, whether 879 hardening is enabled for this boot. Hardened 880 usercopy checking is used to protect the kernel 881 from reading or writing beyond known memory 882 allocation boundaries as a proactive defense 883 against bounds-checking flaws in the kernel's 884 copy_to_user()/copy_from_user() interface. 885 on Perform hardened usercopy checks (default). 886 off Disable hardened usercopy checks. 887 888 disable_radix [PPC] 889 Disable RADIX MMU mode on POWER9 890 891 disable_tlbie [PPC] 892 Disable TLBIE instruction. Currently does not work 893 with KVM, with HASH MMU, or with coherent accelerators. 894 895 disable_cpu_apicid= [X86,APIC,SMP] 896 Format: <int> 897 The number of initial APIC ID for the 898 corresponding CPU to be disabled at boot, 899 mostly used for the kdump 2nd kernel to 900 disable BSP to wake up multiple CPUs without 901 causing system reset or hang due to sending 902 INIT from AP to BSP. 903 904 perf_v4_pmi= [X86,INTEL] 905 Format: <bool> 906 Disable Intel PMU counter freezing feature. 907 The feature only exists starting from 908 Arch Perfmon v4 (Skylake and newer). 909 910 disable_ddw [PPC/PSERIES] 911 Disable Dynamic DMA Window support. Use this if 912 to workaround buggy firmware. 913 914 disable_ipv6= [IPV6] 915 See Documentation/networking/ipv6.txt. 916 917 disable_mtrr_cleanup [X86] 918 The kernel tries to adjust MTRR layout from continuous 919 to discrete, to make X server driver able to add WB 920 entry later. This parameter disables that. 921 922 disable_mtrr_trim [X86, Intel and AMD only] 923 By default the kernel will trim any uncacheable 924 memory out of your available memory pool based on 925 MTRR settings. This parameter disables that behavior, 926 possibly causing your machine to run very slowly. 927 928 disable_timer_pin_1 [X86] 929 Disable PIN 1 of APIC timer 930 Can be useful to work around chipset bugs. 931 932 dis_ucode_ldr [X86] Disable the microcode loader. 933 934 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, 935 this option disables the debugging code at boot. 936 937 dma_debug_entries=<number> 938 This option allows to tune the number of preallocated 939 entries for DMA-API debugging code. One entry is 940 required per DMA-API allocation. Use this if the 941 DMA-API debugging code disables itself because the 942 architectural default is too low. 943 944 dma_debug_driver=<driver_name> 945 With this option the DMA-API debugging driver 946 filter feature can be enabled at boot time. Just 947 pass the driver to filter for as the parameter. 948 The filter can be disabled or changed to another 949 driver later using sysfs. 950 951 driver_async_probe= [KNL] 952 List of driver names to be probed asynchronously. 953 Format: <driver_name1>,<driver_name2>... 954 955 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>] 956 Broken monitors, graphic adapters, KVMs and EDIDless 957 panels may send no or incorrect EDID data sets. 958 This parameter allows to specify an EDID data sets 959 in the /lib/firmware directory that are used instead. 960 Generic built-in EDID data sets are used, if one of 961 edid/1024x768.bin, edid/1280x1024.bin, 962 edid/1680x1050.bin, or edid/1920x1080.bin is given 963 and no file with the same name exists. Details and 964 instructions how to build your own EDID data are 965 available in Documentation/admin-guide/edid.rst. An EDID 966 data set will only be used for a particular connector, 967 if its name and a colon are prepended to the EDID 968 name. Each connector may use a unique EDID data 969 set by separating the files with a comma. An EDID 970 data set with no connector name will be used for 971 any connectors not explicitly specified. 972 973 dscc4.setup= [NET] 974 975 dt_cpu_ftrs= [PPC] 976 Format: {"off" | "known"} 977 Control how the dt_cpu_ftrs device-tree binding is 978 used for CPU feature discovery and setup (if it 979 exists). 980 off: Do not use it, fall back to legacy cpu table. 981 known: Do not pass through unknown features to guests 982 or userspace, only those that the kernel is aware of. 983 984 dump_apple_properties [X86] 985 Dump name and content of EFI device properties on 986 x86 Macs. Useful for driver authors to determine 987 what data is available or for reverse-engineering. 988 989 dyndbg[="val"] [KNL,DYNAMIC_DEBUG] 990 module.dyndbg[="val"] 991 Enable debug messages at boot time. See 992 Documentation/admin-guide/dynamic-debug-howto.rst 993 for details. 994 995 nopku [X86] Disable Memory Protection Keys CPU feature found 996 in some Intel CPUs. 997 998 module.async_probe [KNL] 999 Enable asynchronous probe on this module. 1000 1001 early_ioremap_debug [KNL] 1002 Enable debug messages in early_ioremap support. This 1003 is useful for tracking down temporary early mappings 1004 which are not unmapped. 1005 1006 earlycon= [KNL] Output early console device and options. 1007 1008 When used with no options, the early console is 1009 determined by stdout-path property in device tree's 1010 chosen node or the ACPI SPCR table if supported by 1011 the platform. 1012 1013 cdns,<addr>[,options] 1014 Start an early, polled-mode console on a Cadence 1015 (xuartps) serial port at the specified address. Only 1016 supported option is baud rate. If baud rate is not 1017 specified, the serial port must already be setup and 1018 configured. 1019 1020 uart[8250],io,<addr>[,options] 1021 uart[8250],mmio,<addr>[,options] 1022 uart[8250],mmio32,<addr>[,options] 1023 uart[8250],mmio32be,<addr>[,options] 1024 uart[8250],0x<addr>[,options] 1025 Start an early, polled-mode console on the 8250/16550 1026 UART at the specified I/O port or MMIO address. 1027 MMIO inter-register address stride is either 8-bit 1028 (mmio) or 32-bit (mmio32 or mmio32be). 1029 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed 1030 to be equivalent to 'mmio'. 'options' are specified 1031 in the same format described for "console=ttyS<n>"; if 1032 unspecified, the h/w is not initialized. 1033 1034 pl011,<addr> 1035 pl011,mmio32,<addr> 1036 Start an early, polled-mode console on a pl011 serial 1037 port at the specified address. The pl011 serial port 1038 must already be setup and configured. Options are not 1039 yet supported. If 'mmio32' is specified, then only 1040 the driver will use only 32-bit accessors to read/write 1041 the device registers. 1042 1043 meson,<addr> 1044 Start an early, polled-mode console on a meson serial 1045 port at the specified address. The serial port must 1046 already be setup and configured. Options are not yet 1047 supported. 1048 1049 msm_serial,<addr> 1050 Start an early, polled-mode console on an msm serial 1051 port at the specified address. The serial port 1052 must already be setup and configured. Options are not 1053 yet supported. 1054 1055 msm_serial_dm,<addr> 1056 Start an early, polled-mode console on an msm serial 1057 dm port at the specified address. The serial port 1058 must already be setup and configured. Options are not 1059 yet supported. 1060 1061 owl,<addr> 1062 Start an early, polled-mode console on a serial port 1063 of an Actions Semi SoC, such as S500 or S900, at the 1064 specified address. The serial port must already be 1065 setup and configured. Options are not yet supported. 1066 1067 rda,<addr> 1068 Start an early, polled-mode console on a serial port 1069 of an RDA Micro SoC, such as RDA8810PL, at the 1070 specified address. The serial port must already be 1071 setup and configured. Options are not yet supported. 1072 1073 sbi 1074 Use RISC-V SBI (Supervisor Binary Interface) for early 1075 console. 1076 1077 smh Use ARM semihosting calls for early console. 1078 1079 s3c2410,<addr> 1080 s3c2412,<addr> 1081 s3c2440,<addr> 1082 s3c6400,<addr> 1083 s5pv210,<addr> 1084 exynos4210,<addr> 1085 Use early console provided by serial driver available 1086 on Samsung SoCs, requires selecting proper type and 1087 a correct base address of the selected UART port. The 1088 serial port must already be setup and configured. 1089 Options are not yet supported. 1090 1091 lantiq,<addr> 1092 Start an early, polled-mode console on a lantiq serial 1093 (lqasc) port at the specified address. The serial port 1094 must already be setup and configured. Options are not 1095 yet supported. 1096 1097 lpuart,<addr> 1098 lpuart32,<addr> 1099 Use early console provided by Freescale LP UART driver 1100 found on Freescale Vybrid and QorIQ LS1021A processors. 1101 A valid base address must be provided, and the serial 1102 port must already be setup and configured. 1103 1104 ec_imx21,<addr> 1105 ec_imx6q,<addr> 1106 Start an early, polled-mode, output-only console on the 1107 Freescale i.MX UART at the specified address. The UART 1108 must already be setup and configured. 1109 1110 ar3700_uart,<addr> 1111 Start an early, polled-mode console on the 1112 Armada 3700 serial port at the specified 1113 address. The serial port must already be setup 1114 and configured. Options are not yet supported. 1115 1116 qcom_geni,<addr> 1117 Start an early, polled-mode console on a Qualcomm 1118 Generic Interface (GENI) based serial port at the 1119 specified address. The serial port must already be 1120 setup and configured. Options are not yet supported. 1121 1122 efifb,[options] 1123 Start an early, unaccelerated console on the EFI 1124 memory mapped framebuffer (if available). On cache 1125 coherent non-x86 systems that use system memory for 1126 the framebuffer, pass the 'ram' option so that it is 1127 mapped with the correct attributes. 1128 1129 linflex,<addr> 1130 Use early console provided by Freescale LINFlexD UART 1131 serial driver for NXP S32V234 SoCs. A valid base 1132 address must be provided, and the serial port must 1133 already be setup and configured. 1134 1135 earlyprintk= [X86,SH,ARM,M68k,S390] 1136 earlyprintk=vga 1137 earlyprintk=sclp 1138 earlyprintk=xen 1139 earlyprintk=serial[,ttySn[,baudrate]] 1140 earlyprintk=serial[,0x...[,baudrate]] 1141 earlyprintk=ttySn[,baudrate] 1142 earlyprintk=dbgp[debugController#] 1143 earlyprintk=pciserial[,force],bus:device.function[,baudrate] 1144 earlyprintk=xdbc[xhciController#] 1145 1146 earlyprintk is useful when the kernel crashes before 1147 the normal console is initialized. It is not enabled by 1148 default because it has some cosmetic problems. 1149 1150 Append ",keep" to not disable it when the real console 1151 takes over. 1152 1153 Only one of vga, efi, serial, or usb debug port can 1154 be used at a time. 1155 1156 Currently only ttyS0 and ttyS1 may be specified by 1157 name. Other I/O ports may be explicitly specified 1158 on some architectures (x86 and arm at least) by 1159 replacing ttySn with an I/O port address, like this: 1160 earlyprintk=serial,0x1008,115200 1161 You can find the port for a given device in 1162 /proc/tty/driver/serial: 1163 2: uart:ST16650V2 port:00001008 irq:18 ... 1164 1165 Interaction with the standard serial driver is not 1166 very good. 1167 1168 The VGA and EFI output is eventually overwritten by 1169 the real console. 1170 1171 The xen output can only be used by Xen PV guests. 1172 1173 The sclp output can only be used on s390. 1174 1175 The optional "force" to "pciserial" enables use of a 1176 PCI device even when its classcode is not of the 1177 UART class. 1178 1179 edac_report= [HW,EDAC] Control how to report EDAC event 1180 Format: {"on" | "off" | "force"} 1181 on: enable EDAC to report H/W event. May be overridden 1182 by other higher priority error reporting module. 1183 off: disable H/W event reporting through EDAC. 1184 force: enforce the use of EDAC to report H/W event. 1185 default: on. 1186 1187 ekgdboc= [X86,KGDB] Allow early kernel console debugging 1188 ekgdboc=kbd 1189 1190 This is designed to be used in conjunction with 1191 the boot argument: earlyprintk=vga 1192 1193 edd= [EDD] 1194 Format: {"off" | "on" | "skip[mbr]"} 1195 1196 efi= [EFI] 1197 Format: { "old_map", "nochunk", "noruntime", "debug", 1198 "nosoftreserve", "disable_early_pci_dma", 1199 "no_disable_early_pci_dma" } 1200 old_map [X86-64]: switch to the old ioremap-based EFI 1201 runtime services mapping. [Needs CONFIG_X86_UV=y] 1202 nochunk: disable reading files in "chunks" in the EFI 1203 boot stub, as chunking can cause problems with some 1204 firmware implementations. 1205 noruntime : disable EFI runtime services support 1206 debug: enable misc debug output 1207 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose) 1208 attribute may cause the kernel to reserve the 1209 memory range for a memory mapping driver to 1210 claim. Specify efi=nosoftreserve to disable this 1211 reservation and treat the memory by its base type 1212 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM"). 1213 disable_early_pci_dma: Disable the busmaster bit on all 1214 PCI bridges while in the EFI boot stub 1215 no_disable_early_pci_dma: Leave the busmaster bit set 1216 on all PCI bridges while in the EFI boot stub 1217 1218 efi_no_storage_paranoia [EFI; X86] 1219 Using this parameter you can use more than 50% of 1220 your efi variable storage. Use this parameter only if 1221 you are really sure that your UEFI does sane gc and 1222 fulfills the spec otherwise your board may brick. 1223 1224 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86] 1225 Add arbitrary attribute to specific memory range by 1226 updating original EFI memory map. 1227 Region of memory which aa attribute is added to is 1228 from ss to ss+nn. 1229 1230 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000 1231 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000) 1232 attribute is added to range 0x100000000-0x180000000 and 1233 0x10a0000000-0x1120000000. 1234 1235 If efi_fake_mem=8G@9G:0x40000 is specified, the 1236 EFI_MEMORY_SP(0x40000) attribute is added to 1237 range 0x240000000-0x43fffffff. 1238 1239 Using this parameter you can do debugging of EFI memmap 1240 related features. For example, you can do debugging of 1241 Address Range Mirroring feature even if your box 1242 doesn't support it, or mark specific memory as 1243 "soft reserved". 1244 1245 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT 1246 that is to be dynamically loaded by Linux. If there are 1247 multiple variables with the same name but with different 1248 vendor GUIDs, all of them will be loaded. See 1249 Documentation/admin-guide/acpi/ssdt-overlays.rst for details. 1250 1251 1252 eisa_irq_edge= [PARISC,HW] 1253 See header of drivers/parisc/eisa.c. 1254 1255 elanfreq= [X86-32] 1256 See comment before function elanfreq_setup() in 1257 arch/x86/kernel/cpu/cpufreq/elanfreq.c. 1258 1259 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390] 1260 Specifies physical address of start of kernel core 1261 image elf header and optionally the size. Generally 1262 kexec loader will pass this option to capture kernel. 1263 See Documentation/admin-guide/kdump/kdump.rst for details. 1264 1265 enable_mtrr_cleanup [X86] 1266 The kernel tries to adjust MTRR layout from continuous 1267 to discrete, to make X server driver able to add WB 1268 entry later. This parameter enables that. 1269 1270 enable_timer_pin_1 [X86] 1271 Enable PIN 1 of APIC timer 1272 Can be useful to work around chipset bugs 1273 (in particular on some ATI chipsets). 1274 The kernel tries to set a reasonable default. 1275 1276 enforcing [SELINUX] Set initial enforcing status. 1277 Format: {"0" | "1"} 1278 See security/selinux/Kconfig help text. 1279 0 -- permissive (log only, no denials). 1280 1 -- enforcing (deny and log). 1281 Default value is 0. 1282 Value can be changed at runtime via 1283 /sys/fs/selinux/enforce. 1284 1285 erst_disable [ACPI] 1286 Disable Error Record Serialization Table (ERST) 1287 support. 1288 1289 ether= [HW,NET] Ethernet cards parameters 1290 This option is obsoleted by the "netdev=" option, which 1291 has equivalent usage. See its documentation for details. 1292 1293 evm= [EVM] 1294 Format: { "fix" } 1295 Permit 'security.evm' to be updated regardless of 1296 current integrity status. 1297 1298 failslab= 1299 fail_page_alloc= 1300 fail_make_request=[KNL] 1301 General fault injection mechanism. 1302 Format: <interval>,<probability>,<space>,<times> 1303 See also Documentation/fault-injection/. 1304 1305 floppy= [HW] 1306 See Documentation/admin-guide/blockdev/floppy.rst. 1307 1308 force_pal_cache_flush 1309 [IA-64] Avoid check_sal_cache_flush which may hang on 1310 buggy SAL_CACHE_FLUSH implementations. Using this 1311 parameter will force ia64_sal_cache_flush to call 1312 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH. 1313 1314 forcepae [X86-32] 1315 Forcefully enable Physical Address Extension (PAE). 1316 Many Pentium M systems disable PAE but may have a 1317 functionally usable PAE implementation. 1318 Warning: use of this parameter will taint the kernel 1319 and may cause unknown problems. 1320 1321 ftrace=[tracer] 1322 [FTRACE] will set and start the specified tracer 1323 as early as possible in order to facilitate early 1324 boot debugging. 1325 1326 ftrace_dump_on_oops[=orig_cpu] 1327 [FTRACE] will dump the trace buffers on oops. 1328 If no parameter is passed, ftrace will dump 1329 buffers of all CPUs, but if you pass orig_cpu, it will 1330 dump only the buffer of the CPU that triggered the 1331 oops. 1332 1333 ftrace_filter=[function-list] 1334 [FTRACE] Limit the functions traced by the function 1335 tracer at boot up. function-list is a comma separated 1336 list of functions. This list can be changed at run 1337 time by the set_ftrace_filter file in the debugfs 1338 tracing directory. 1339 1340 ftrace_notrace=[function-list] 1341 [FTRACE] Do not trace the functions specified in 1342 function-list. This list can be changed at run time 1343 by the set_ftrace_notrace file in the debugfs 1344 tracing directory. 1345 1346 ftrace_graph_filter=[function-list] 1347 [FTRACE] Limit the top level callers functions traced 1348 by the function graph tracer at boot up. 1349 function-list is a comma separated list of functions 1350 that can be changed at run time by the 1351 set_graph_function file in the debugfs tracing directory. 1352 1353 ftrace_graph_notrace=[function-list] 1354 [FTRACE] Do not trace from the functions specified in 1355 function-list. This list is a comma separated list of 1356 functions that can be changed at run time by the 1357 set_graph_notrace file in the debugfs tracing directory. 1358 1359 ftrace_graph_max_depth=<uint> 1360 [FTRACE] Used with the function graph tracer. This is 1361 the max depth it will trace into a function. This value 1362 can be changed at run time by the max_graph_depth file 1363 in the tracefs tracing directory. default: 0 (no limit) 1364 1365 fw_devlink= [KNL] Create device links between consumer and supplier 1366 devices by scanning the firmware to infer the 1367 consumer/supplier relationships. This feature is 1368 especially useful when drivers are loaded as modules as 1369 it ensures proper ordering of tasks like device probing 1370 (suppliers first, then consumers), supplier boot state 1371 clean up (only after all consumers have probed), 1372 suspend/resume & runtime PM (consumers first, then 1373 suppliers). 1374 Format: { off | permissive | on | rpm } 1375 off -- Don't create device links from firmware info. 1376 permissive -- Create device links from firmware info 1377 but use it only for ordering boot state clean 1378 up (sync_state() calls). 1379 on -- Create device links from firmware info and use it 1380 to enforce probe and suspend/resume ordering. 1381 rpm -- Like "on", but also use to order runtime PM. 1382 1383 gamecon.map[2|3]= 1384 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 1385 support via parallel port (up to 5 devices per port) 1386 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 1387 See also Documentation/input/devices/joystick-parport.rst 1388 1389 gamma= [HW,DRM] 1390 1391 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART 1392 Format: off | on 1393 default: on 1394 1395 gcov_persist= [GCOV] When non-zero (default), profiling data for 1396 kernel modules is saved and remains accessible via 1397 debugfs, even when the module is unloaded/reloaded. 1398 When zero, profiling data is discarded and associated 1399 debugfs files are removed at module unload time. 1400 1401 goldfish [X86] Enable the goldfish android emulator platform. 1402 Don't use this when you are not running on the 1403 android emulator 1404 1405 gpt [EFI] Forces disk with valid GPT signature but 1406 invalid Protective MBR to be treated as GPT. If the 1407 primary GPT is corrupted, it enables the backup/alternate 1408 GPT to be used instead. 1409 1410 grcan.enable0= [HW] Configuration of physical interface 0. Determines 1411 the "Enable 0" bit of the configuration register. 1412 Format: 0 | 1 1413 Default: 0 1414 grcan.enable1= [HW] Configuration of physical interface 1. Determines 1415 the "Enable 0" bit of the configuration register. 1416 Format: 0 | 1 1417 Default: 0 1418 grcan.select= [HW] Select which physical interface to use. 1419 Format: 0 | 1 1420 Default: 0 1421 grcan.txsize= [HW] Sets the size of the tx buffer. 1422 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. 1423 Default: 1024 1424 grcan.rxsize= [HW] Sets the size of the rx buffer. 1425 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. 1426 Default: 1024 1427 1428 gpio-mockup.gpio_mockup_ranges 1429 [HW] Sets the ranges of gpiochip of for this device. 1430 Format: <start1>,<end1>,<start2>,<end2>... 1431 1432 hardlockup_all_cpu_backtrace= 1433 [KNL] Should the hard-lockup detector generate 1434 backtraces on all cpus. 1435 Format: <integer> 1436 1437 hashdist= [KNL,NUMA] Large hashes allocated during boot 1438 are distributed across NUMA nodes. Defaults on 1439 for 64-bit NUMA, off otherwise. 1440 Format: 0 | 1 (for off | on) 1441 1442 hcl= [IA-64] SGI's Hardware Graph compatibility layer 1443 1444 hd= [EIDE] (E)IDE hard drive subsystem geometry 1445 Format: <cyl>,<head>,<sect> 1446 1447 hest_disable [ACPI] 1448 Disable Hardware Error Source Table (HEST) support; 1449 corresponding firmware-first mode error processing 1450 logic will be disabled. 1451 1452 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact 1453 size of <nn>. This works even on boxes that have no 1454 highmem otherwise. This also works to reduce highmem 1455 size on bigger boxes. 1456 1457 highres= [KNL] Enable/disable high resolution timer mode. 1458 Valid parameters: "on", "off" 1459 Default: "on" 1460 1461 hlt [BUGS=ARM,SH] 1462 1463 hpet= [X86-32,HPET] option to control HPET usage 1464 Format: { enable (default) | disable | force | 1465 verbose } 1466 disable: disable HPET and use PIT instead 1467 force: allow force enabled of undocumented chips (ICH4, 1468 VIA, nVidia) 1469 verbose: show contents of HPET registers during setup 1470 1471 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET 1472 registers. Default set by CONFIG_HPET_MMAP_DEFAULT. 1473 1474 hugetlb_cma= [HW] The size of a cma area used for allocation 1475 of gigantic hugepages. 1476 Format: nn[KMGTPE] 1477 1478 Reserve a cma area of given size and allocate gigantic 1479 hugepages using the cma allocator. If enabled, the 1480 boot-time allocation of gigantic hugepages is skipped. 1481 1482 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot. 1483 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages. 1484 On x86-64 and powerpc, this option can be specified 1485 multiple times interleaved with hugepages= to reserve 1486 huge pages of different sizes. Valid pages sizes on 1487 x86-64 are 2M (when the CPU supports "pse") and 1G 1488 (when the CPU supports the "pdpe1gb" cpuinfo flag). 1489 1490 hung_task_panic= 1491 [KNL] Should the hung task detector generate panics. 1492 Format: <integer> 1493 1494 A nonzero value instructs the kernel to panic when a 1495 hung task is detected. The default value is controlled 1496 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time 1497 option. The value selected by this boot parameter can 1498 be changed later by the kernel.hung_task_panic sysctl. 1499 1500 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 1501 terminal devices. Valid values: 0..8 1502 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 1503 If specified, z/VM IUCV HVC accepts connections 1504 from listed z/VM user IDs only. 1505 1506 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations 1507 which allow the hypervisor to 'idle' the 1508 guest on lock contention. 1509 1510 keep_bootcon [KNL] 1511 Do not unregister boot console at start. This is only 1512 useful for debugging when something happens in the window 1513 between unregistering the boot console and initializing 1514 the real console. 1515 1516 i2c_bus= [HW] Override the default board specific I2C bus speed 1517 or register an additional I2C bus that is not 1518 registered from board initialization code. 1519 Format: 1520 <bus_id>,<clkrate> 1521 1522 i8042.debug [HW] Toggle i8042 debug mode 1523 i8042.unmask_kbd_data 1524 [HW] Enable printing of interrupt data from the KBD port 1525 (disabled by default, and as a pre-condition 1526 requires that i8042.debug=1 be enabled) 1527 i8042.direct [HW] Put keyboard port into non-translated mode 1528 i8042.dumbkbd [HW] Pretend that controller can only read data from 1529 keyboard and cannot control its state 1530 (Don't attempt to blink the leds) 1531 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 1532 i8042.nokbd [HW] Don't check/create keyboard port 1533 i8042.noloop [HW] Disable the AUX Loopback command while probing 1534 for the AUX port 1535 i8042.nomux [HW] Don't check presence of an active multiplexing 1536 controller 1537 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 1538 controllers 1539 i8042.notimeout [HW] Ignore timeout condition signalled by controller 1540 i8042.reset [HW] Reset the controller during init, cleanup and 1541 suspend-to-ram transitions, only during s2r 1542 transitions, or never reset 1543 Format: { 1 | Y | y | 0 | N | n } 1544 1, Y, y: always reset controller 1545 0, N, n: don't ever reset controller 1546 Default: only on s2r transitions on x86; most other 1547 architectures force reset to be always executed 1548 i8042.unlock [HW] Unlock (ignore) the keylock 1549 i8042.kbdreset [HW] Reset device connected to KBD port 1550 1551 i810= [HW,DRM] 1552 1553 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data 1554 indicates that the driver is running on unsupported 1555 hardware. 1556 i8k.force [HW] Activate i8k driver even if SMM BIOS signature 1557 does not match list of supported models. 1558 i8k.power_status 1559 [HW] Report power status in /proc/i8k 1560 (disabled by default) 1561 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN 1562 capability is set. 1563 1564 i915.invert_brightness= 1565 [DRM] Invert the sense of the variable that is used to 1566 set the brightness of the panel backlight. Normally a 1567 brightness value of 0 indicates backlight switched off, 1568 and the maximum of the brightness value sets the backlight 1569 to maximum brightness. If this parameter is set to 0 1570 (default) and the machine requires it, or this parameter 1571 is set to 1, a brightness value of 0 sets the backlight 1572 to maximum brightness, and the maximum of the brightness 1573 value switches the backlight off. 1574 -1 -- never invert brightness 1575 0 -- machine default 1576 1 -- force brightness inversion 1577 1578 icn= [HW,ISDN] 1579 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]] 1580 1581 ide-core.nodma= [HW] (E)IDE subsystem 1582 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc 1583 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr 1584 .cdrom .chs .ignore_cable are additional options 1585 See Documentation/ide/ide.rst. 1586 1587 ide-generic.probe-mask= [HW] (E)IDE subsystem 1588 Format: <int> 1589 Probe mask for legacy ISA IDE ports. Depending on 1590 platform up to 6 ports are supported, enabled by 1591 setting corresponding bits in the mask to 1. The 1592 default value is 0x0, which has a special meaning. 1593 On systems that have PCI, it triggers scanning the 1594 PCI bus for the first and the second port, which 1595 are then probed. On systems without PCI the value 1596 of 0x0 enables probing the two first ports as if it 1597 was 0x3. 1598 1599 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem 1600 Claim all unknown PCI IDE storage controllers. 1601 1602 idle= [X86] 1603 Format: idle=poll, idle=halt, idle=nomwait 1604 Poll forces a polling idle loop that can slightly 1605 improve the performance of waking up a idle CPU, but 1606 will use a lot of power and make the system run hot. 1607 Not recommended. 1608 idle=halt: Halt is forced to be used for CPU idle. 1609 In such case C2/C3 won't be used again. 1610 idle=nomwait: Disable mwait for CPU C-states 1611 1612 ieee754= [MIPS] Select IEEE Std 754 conformance mode 1613 Format: { strict | legacy | 2008 | relaxed } 1614 Default: strict 1615 1616 Choose which programs will be accepted for execution 1617 based on the IEEE 754 NaN encoding(s) supported by 1618 the FPU and the NaN encoding requested with the value 1619 of an ELF file header flag individually set by each 1620 binary. Hardware implementations are permitted to 1621 support either or both of the legacy and the 2008 NaN 1622 encoding mode. 1623 1624 Available settings are as follows: 1625 strict accept binaries that request a NaN encoding 1626 supported by the FPU 1627 legacy only accept legacy-NaN binaries, if supported 1628 by the FPU 1629 2008 only accept 2008-NaN binaries, if supported 1630 by the FPU 1631 relaxed accept any binaries regardless of whether 1632 supported by the FPU 1633 1634 The FPU emulator is always able to support both NaN 1635 encodings, so if no FPU hardware is present or it has 1636 been disabled with 'nofpu', then the settings of 1637 'legacy' and '2008' strap the emulator accordingly, 1638 'relaxed' straps the emulator for both legacy-NaN and 1639 2008-NaN, whereas 'strict' enables legacy-NaN only on 1640 legacy processors and both NaN encodings on MIPS32 or 1641 MIPS64 CPUs. 1642 1643 The setting for ABS.fmt/NEG.fmt instruction execution 1644 mode generally follows that for the NaN encoding, 1645 except where unsupported by hardware. 1646 1647 ignore_loglevel [KNL] 1648 Ignore loglevel setting - this will print /all/ 1649 kernel messages to the console. Useful for debugging. 1650 We also add it as printk module parameter, so users 1651 could change it dynamically, usually by 1652 /sys/module/printk/parameters/ignore_loglevel. 1653 1654 ignore_rlimit_data 1655 Ignore RLIMIT_DATA setting for data mappings, 1656 print warning at first misuse. Can be changed via 1657 /sys/module/kernel/parameters/ignore_rlimit_data. 1658 1659 ihash_entries= [KNL] 1660 Set number of hash buckets for inode cache. 1661 1662 ima_appraise= [IMA] appraise integrity measurements 1663 Format: { "off" | "enforce" | "fix" | "log" } 1664 default: "enforce" 1665 1666 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead. 1667 The builtin appraise policy appraises all files 1668 owned by uid=0. 1669 1670 ima_canonical_fmt [IMA] 1671 Use the canonical format for the binary runtime 1672 measurements, instead of host native format. 1673 1674 ima_hash= [IMA] 1675 Format: { md5 | sha1 | rmd160 | sha256 | sha384 1676 | sha512 | ... } 1677 default: "sha1" 1678 1679 The list of supported hash algorithms is defined 1680 in crypto/hash_info.h. 1681 1682 ima_policy= [IMA] 1683 The builtin policies to load during IMA setup. 1684 Format: "tcb | appraise_tcb | secure_boot | 1685 fail_securely" 1686 1687 The "tcb" policy measures all programs exec'd, files 1688 mmap'd for exec, and all files opened with the read 1689 mode bit set by either the effective uid (euid=0) or 1690 uid=0. 1691 1692 The "appraise_tcb" policy appraises the integrity of 1693 all files owned by root. 1694 1695 The "secure_boot" policy appraises the integrity 1696 of files (eg. kexec kernel image, kernel modules, 1697 firmware, policy, etc) based on file signatures. 1698 1699 The "fail_securely" policy forces file signature 1700 verification failure also on privileged mounted 1701 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE 1702 flag. 1703 1704 ima_tcb [IMA] Deprecated. Use ima_policy= instead. 1705 Load a policy which meets the needs of the Trusted 1706 Computing Base. This means IMA will measure all 1707 programs exec'd, files mmap'd for exec, and all files 1708 opened for read by uid=0. 1709 1710 ima_template= [IMA] 1711 Select one of defined IMA measurements template formats. 1712 Formats: { "ima" | "ima-ng" | "ima-sig" } 1713 Default: "ima-ng" 1714 1715 ima_template_fmt= 1716 [IMA] Define a custom template format. 1717 Format: { "field1|...|fieldN" } 1718 1719 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage 1720 Format: <min_file_size> 1721 Set the minimal file size for using asynchronous hash. 1722 If left unspecified, ahash usage is disabled. 1723 1724 ahash performance varies for different data sizes on 1725 different crypto accelerators. This option can be used 1726 to achieve the best performance for a particular HW. 1727 1728 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size 1729 Format: <bufsize> 1730 Set hashing buffer size. Default: 4k. 1731 1732 ahash performance varies for different chunk sizes on 1733 different crypto accelerators. This option can be used 1734 to achieve best performance for particular HW. 1735 1736 init= [KNL] 1737 Format: <full_path> 1738 Run specified binary instead of /sbin/init as init 1739 process. 1740 1741 initcall_debug [KNL] Trace initcalls as they are executed. Useful 1742 for working out where the kernel is dying during 1743 startup. 1744 1745 initcall_blacklist= [KNL] Do not execute a comma-separated list of 1746 initcall functions. Useful for debugging built-in 1747 modules and initcalls. 1748 1749 initrd= [BOOT] Specify the location of the initial ramdisk 1750 1751 initrdmem= [KNL] Specify a physical address and size from which to 1752 load the initrd. If an initrd is compiled in or 1753 specified in the bootparams, it takes priority over this 1754 setting. 1755 Format: ss[KMG],nn[KMG] 1756 Default is 0, 0 1757 1758 init_on_alloc= [MM] Fill newly allocated pages and heap objects with 1759 zeroes. 1760 Format: 0 | 1 1761 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON. 1762 1763 init_on_free= [MM] Fill freed pages and heap objects with zeroes. 1764 Format: 0 | 1 1765 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON. 1766 1767 init_pkru= [x86] Specify the default memory protection keys rights 1768 register contents for all processes. 0x55555554 by 1769 default (disallow access to all but pkey 0). Can 1770 override in debugfs after boot. 1771 1772 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 1773 Format: <irq> 1774 1775 int_pln_enable [x86] Enable power limit notification interrupt 1776 1777 integrity_audit=[IMA] 1778 Format: { "0" | "1" } 1779 0 -- basic integrity auditing messages. (Default) 1780 1 -- additional integrity auditing messages. 1781 1782 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 1783 on 1784 Enable intel iommu driver. 1785 off 1786 Disable intel iommu driver. 1787 igfx_off [Default Off] 1788 By default, gfx is mapped as normal device. If a gfx 1789 device has a dedicated DMAR unit, the DMAR unit is 1790 bypassed by not enabling DMAR with this option. In 1791 this case, gfx device will use physical address for 1792 DMA. 1793 forcedac [x86_64] 1794 With this option iommu will not optimize to look 1795 for io virtual address below 32-bit forcing dual 1796 address cycle on pci bus for cards supporting greater 1797 than 32-bit addressing. The default is to look 1798 for translation below 32-bit and if not available 1799 then look in the higher range. 1800 strict [Default Off] 1801 With this option on every unmap_single operation will 1802 result in a hardware IOTLB flush operation as opposed 1803 to batching them for performance. 1804 sp_off [Default Off] 1805 By default, super page will be supported if Intel IOMMU 1806 has the capability. With this option, super page will 1807 not be supported. 1808 sm_on [Default Off] 1809 By default, scalable mode will be disabled even if the 1810 hardware advertises that it has support for the scalable 1811 mode translation. With this option set, scalable mode 1812 will be used on hardware which claims to support it. 1813 tboot_noforce [Default Off] 1814 Do not force the Intel IOMMU enabled under tboot. 1815 By default, tboot will force Intel IOMMU on, which 1816 could harm performance of some high-throughput 1817 devices like 40GBit network cards, even if identity 1818 mapping is enabled. 1819 Note that using this option lowers the security 1820 provided by tboot because it makes the system 1821 vulnerable to DMA attacks. 1822 nobounce [Default off] 1823 Disable bounce buffer for untrusted devices such as 1824 the Thunderbolt devices. This will treat the untrusted 1825 devices as the trusted ones, hence might expose security 1826 risks of DMA attacks. 1827 1828 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 1829 0 disables intel_idle and fall back on acpi_idle. 1830 1 to 9 specify maximum depth of C-state. 1831 1832 intel_pstate= [X86] 1833 disable 1834 Do not enable intel_pstate as the default 1835 scaling driver for the supported processors 1836 passive 1837 Use intel_pstate as a scaling driver, but configure it 1838 to work with generic cpufreq governors (instead of 1839 enabling its internal governor). This mode cannot be 1840 used along with the hardware-managed P-states (HWP) 1841 feature. 1842 force 1843 Enable intel_pstate on systems that prohibit it by default 1844 in favor of acpi-cpufreq. Forcing the intel_pstate driver 1845 instead of acpi-cpufreq may disable platform features, such 1846 as thermal controls and power capping, that rely on ACPI 1847 P-States information being indicated to OSPM and therefore 1848 should be used with caution. This option does not work with 1849 processors that aren't supported by the intel_pstate driver 1850 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 1851 no_hwp 1852 Do not enable hardware P state control (HWP) 1853 if available. 1854 hwp_only 1855 Only load intel_pstate on systems which support 1856 hardware P state control (HWP) if available. 1857 support_acpi_ppc 1858 Enforce ACPI _PPC performance limits. If the Fixed ACPI 1859 Description Table, specifies preferred power management 1860 profile as "Enterprise Server" or "Performance Server", 1861 then this feature is turned on by default. 1862 per_cpu_perf_limits 1863 Allow per-logical-CPU P-State performance control limits using 1864 cpufreq sysfs interface 1865 1866 intremap= [X86-64, Intel-IOMMU] 1867 on enable Interrupt Remapping (default) 1868 off disable Interrupt Remapping 1869 nosid disable Source ID checking 1870 no_x2apic_optout 1871 BIOS x2APIC opt-out request will be ignored 1872 nopost disable Interrupt Posting 1873 1874 iomem= Disable strict checking of access to MMIO memory 1875 strict regions from userspace. 1876 relaxed 1877 1878 iommu= [x86] 1879 off 1880 force 1881 noforce 1882 biomerge 1883 panic 1884 nopanic 1885 merge 1886 nomerge 1887 soft 1888 pt [x86] 1889 nopt [x86] 1890 nobypass [PPC/POWERNV] 1891 Disable IOMMU bypass, using IOMMU for PCI devices. 1892 1893 iommu.strict= [ARM64] Configure TLB invalidation behaviour 1894 Format: { "0" | "1" } 1895 0 - Lazy mode. 1896 Request that DMA unmap operations use deferred 1897 invalidation of hardware TLBs, for increased 1898 throughput at the cost of reduced device isolation. 1899 Will fall back to strict mode if not supported by 1900 the relevant IOMMU driver. 1901 1 - Strict mode (default). 1902 DMA unmap operations invalidate IOMMU hardware TLBs 1903 synchronously. 1904 1905 iommu.passthrough= 1906 [ARM64, X86] Configure DMA to bypass the IOMMU by default. 1907 Format: { "0" | "1" } 1908 0 - Use IOMMU translation for DMA. 1909 1 - Bypass the IOMMU for DMA. 1910 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH. 1911 1912 io7= [HW] IO7 for Marvel based alpha systems 1913 See comment before marvel_specify_io7 in 1914 arch/alpha/kernel/core_marvel.c. 1915 1916 io_delay= [X86] I/O delay method 1917 0x80 1918 Standard port 0x80 based delay 1919 0xed 1920 Alternate port 0xed based delay (needed on some systems) 1921 udelay 1922 Simple two microseconds delay 1923 none 1924 No delay 1925 1926 ip= [IP_PNP] 1927 See Documentation/admin-guide/nfs/nfsroot.rst. 1928 1929 ipcmni_extend [KNL] Extend the maximum number of unique System V 1930 IPC identifiers from 32,768 to 16,777,216. 1931 1932 irqaffinity= [SMP] Set the default irq affinity mask 1933 The argument is a cpu list, as described above. 1934 1935 irqchip.gicv2_force_probe= 1936 [ARM, ARM64] 1937 Format: <bool> 1938 Force the kernel to look for the second 4kB page 1939 of a GICv2 controller even if the memory range 1940 exposed by the device tree is too small. 1941 1942 irqchip.gicv3_nolpi= 1943 [ARM, ARM64] 1944 Force the kernel to ignore the availability of 1945 LPIs (and by consequence ITSs). Intended for system 1946 that use the kernel as a bootloader, and thus want 1947 to let secondary kernels in charge of setting up 1948 LPIs. 1949 1950 irqchip.gicv3_pseudo_nmi= [ARM64] 1951 Enables support for pseudo-NMIs in the kernel. This 1952 requires the kernel to be built with 1953 CONFIG_ARM64_PSEUDO_NMI. 1954 1955 irqfixup [HW] 1956 When an interrupt is not handled search all handlers 1957 for it. Intended to get systems with badly broken 1958 firmware running. 1959 1960 irqpoll [HW] 1961 When an interrupt is not handled search all handlers 1962 for it. Also check all handlers each timer 1963 interrupt. Intended to get systems with badly broken 1964 firmware running. 1965 1966 isapnp= [ISAPNP] 1967 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 1968 1969 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance. 1970 [Deprecated - use cpusets instead] 1971 Format: [flag-list,]<cpu-list> 1972 1973 Specify one or more CPUs to isolate from disturbances 1974 specified in the flag list (default: domain): 1975 1976 nohz 1977 Disable the tick when a single task runs. 1978 1979 A residual 1Hz tick is offloaded to workqueues, which you 1980 need to affine to housekeeping through the global 1981 workqueue's affinity configured via the 1982 /sys/devices/virtual/workqueue/cpumask sysfs file, or 1983 by using the 'domain' flag described below. 1984 1985 NOTE: by default the global workqueue runs on all CPUs, 1986 so to protect individual CPUs the 'cpumask' file has to 1987 be configured manually after bootup. 1988 1989 domain 1990 Isolate from the general SMP balancing and scheduling 1991 algorithms. Note that performing domain isolation this way 1992 is irreversible: it's not possible to bring back a CPU to 1993 the domains once isolated through isolcpus. It's strongly 1994 advised to use cpusets instead to disable scheduler load 1995 balancing through the "cpuset.sched_load_balance" file. 1996 It offers a much more flexible interface where CPUs can 1997 move in and out of an isolated set anytime. 1998 1999 You can move a process onto or off an "isolated" CPU via 2000 the CPU affinity syscalls or cpuset. 2001 <cpu number> begins at 0 and the maximum value is 2002 "number of CPUs in system - 1". 2003 2004 managed_irq 2005 2006 Isolate from being targeted by managed interrupts 2007 which have an interrupt mask containing isolated 2008 CPUs. The affinity of managed interrupts is 2009 handled by the kernel and cannot be changed via 2010 the /proc/irq/* interfaces. 2011 2012 This isolation is best effort and only effective 2013 if the automatically assigned interrupt mask of a 2014 device queue contains isolated and housekeeping 2015 CPUs. If housekeeping CPUs are online then such 2016 interrupts are directed to the housekeeping CPU 2017 so that IO submitted on the housekeeping CPU 2018 cannot disturb the isolated CPU. 2019 2020 If a queue's affinity mask contains only isolated 2021 CPUs then this parameter has no effect on the 2022 interrupt routing decision, though interrupts are 2023 only delivered when tasks running on those 2024 isolated CPUs submit IO. IO submitted on 2025 housekeeping CPUs has no influence on those 2026 queues. 2027 2028 The format of <cpu-list> is described above. 2029 2030 iucv= [HW,NET] 2031 2032 ivrs_ioapic [HW,X86_64] 2033 Provide an override to the IOAPIC-ID<->DEVICE-ID 2034 mapping provided in the IVRS ACPI table. For 2035 example, to map IOAPIC-ID decimal 10 to 2036 PCI device 00:14.0 write the parameter as: 2037 ivrs_ioapic[10]=00:14.0 2038 2039 ivrs_hpet [HW,X86_64] 2040 Provide an override to the HPET-ID<->DEVICE-ID 2041 mapping provided in the IVRS ACPI table. For 2042 example, to map HPET-ID decimal 0 to 2043 PCI device 00:14.0 write the parameter as: 2044 ivrs_hpet[0]=00:14.0 2045 2046 ivrs_acpihid [HW,X86_64] 2047 Provide an override to the ACPI-HID:UID<->DEVICE-ID 2048 mapping provided in the IVRS ACPI table. For 2049 example, to map UART-HID:UID AMD0020:0 to 2050 PCI device 00:14.5 write the parameter as: 2051 ivrs_acpihid[00:14.5]=AMD0020:0 2052 2053 js= [HW,JOY] Analog joystick 2054 See Documentation/input/joydev/joystick.rst. 2055 2056 nokaslr [KNL] 2057 When CONFIG_RANDOMIZE_BASE is set, this disables 2058 kernel and module base offset ASLR (Address Space 2059 Layout Randomization). 2060 2061 kasan_multi_shot 2062 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print 2063 report on every invalid memory access. Without this 2064 parameter KASAN will print report only for the first 2065 invalid access. 2066 2067 keepinitrd [HW,ARM] 2068 2069 kernelcore= [KNL,X86,IA-64,PPC] 2070 Format: nn[KMGTPE] | nn% | "mirror" 2071 This parameter specifies the amount of memory usable by 2072 the kernel for non-movable allocations. The requested 2073 amount is spread evenly throughout all nodes in the 2074 system as ZONE_NORMAL. The remaining memory is used for 2075 movable memory in its own zone, ZONE_MOVABLE. In the 2076 event, a node is too small to have both ZONE_NORMAL and 2077 ZONE_MOVABLE, kernelcore memory will take priority and 2078 other nodes will have a larger ZONE_MOVABLE. 2079 2080 ZONE_MOVABLE is used for the allocation of pages that 2081 may be reclaimed or moved by the page migration 2082 subsystem. Note that allocations like PTEs-from-HighMem 2083 still use the HighMem zone if it exists, and the Normal 2084 zone if it does not. 2085 2086 It is possible to specify the exact amount of memory in 2087 the form of "nn[KMGTPE]", a percentage of total system 2088 memory in the form of "nn%", or "mirror". If "mirror" 2089 option is specified, mirrored (reliable) memory is used 2090 for non-movable allocations and remaining memory is used 2091 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror" 2092 are exclusive, so you cannot specify multiple forms. 2093 2094 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port. 2095 Format: <Controller#>[,poll interval] 2096 The controller # is the number of the ehci usb debug 2097 port as it is probed via PCI. The poll interval is 2098 optional and is the number seconds in between 2099 each poll cycle to the debug port in case you need 2100 the functionality for interrupting the kernel with 2101 gdb or control-c on the dbgp connection. When 2102 not using this parameter you use sysrq-g to break into 2103 the kernel debugger. 2104 2105 kgdboc= [KGDB,HW] kgdb over consoles. 2106 Requires a tty driver that supports console polling, 2107 or a supported polling keyboard driver (non-usb). 2108 Serial only format: <serial_device>[,baud] 2109 keyboard only format: kbd 2110 keyboard and serial format: kbd,<serial_device>[,baud] 2111 Optional Kernel mode setting: 2112 kms, kbd format: kms,kbd 2113 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 2114 2115 kgdbwait [KGDB] Stop kernel execution and enter the 2116 kernel debugger at the earliest opportunity. 2117 2118 kmac= [MIPS] korina ethernet MAC address. 2119 Configure the RouterBoard 532 series on-chip 2120 Ethernet adapter MAC address. 2121 2122 kmemleak= [KNL] Boot-time kmemleak enable/disable 2123 Valid arguments: on, off 2124 Default: on 2125 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 2126 the default is off. 2127 2128 kprobe_event=[probe-list] 2129 [FTRACE] Add kprobe events and enable at boot time. 2130 The probe-list is a semicolon delimited list of probe 2131 definitions. Each definition is same as kprobe_events 2132 interface, but the parameters are comma delimited. 2133 For example, to add a kprobe event on vfs_read with 2134 arg1 and arg2, add to the command line; 2135 2136 kprobe_event=p,vfs_read,$arg1,$arg2 2137 2138 See also Documentation/trace/kprobetrace.rst "Kernel 2139 Boot Parameter" section. 2140 2141 kpti= [ARM64] Control page table isolation of user 2142 and kernel address spaces. 2143 Default: enabled on cores which need mitigation. 2144 0: force disabled 2145 1: force enabled 2146 2147 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 2148 Default is 0 (don't ignore, but inject #GP) 2149 2150 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface. 2151 Default is false (don't support). 2152 2153 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit 2154 KVM MMU at runtime. 2155 Default is 0 (off) 2156 2157 kvm.nx_huge_pages= 2158 [KVM] Controls the software workaround for the 2159 X86_BUG_ITLB_MULTIHIT bug. 2160 force : Always deploy workaround. 2161 off : Never deploy workaround. 2162 auto : Deploy workaround based on the presence of 2163 X86_BUG_ITLB_MULTIHIT. 2164 2165 Default is 'auto'. 2166 2167 If the software workaround is enabled for the host, 2168 guests do need not to enable it for nested guests. 2169 2170 kvm.nx_huge_pages_recovery_ratio= 2171 [KVM] Controls how many 4KiB pages are periodically zapped 2172 back to huge pages. 0 disables the recovery, otherwise if 2173 the value is N KVM will zap 1/Nth of the 4KiB pages every 2174 minute. The default is 60. 2175 2176 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM. 2177 Default is 1 (enabled) 2178 2179 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU) 2180 for all guests. 2181 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode. 2182 2183 kvm-arm.vgic_v3_group0_trap= 2184 [KVM,ARM] Trap guest accesses to GICv3 group-0 2185 system registers 2186 2187 kvm-arm.vgic_v3_group1_trap= 2188 [KVM,ARM] Trap guest accesses to GICv3 group-1 2189 system registers 2190 2191 kvm-arm.vgic_v3_common_trap= 2192 [KVM,ARM] Trap guest accesses to GICv3 common 2193 system registers 2194 2195 kvm-arm.vgic_v4_enable= 2196 [KVM,ARM] Allow use of GICv4 for direct injection of 2197 LPIs. 2198 2199 kvm-intel.ept= [KVM,Intel] Disable extended page tables 2200 (virtualized MMU) support on capable Intel chips. 2201 Default is 1 (enabled) 2202 2203 kvm-intel.emulate_invalid_guest_state= 2204 [KVM,Intel] Enable emulation of invalid guest states 2205 Default is 0 (disabled) 2206 2207 kvm-intel.flexpriority= 2208 [KVM,Intel] Disable FlexPriority feature (TPR shadow). 2209 Default is 1 (enabled) 2210 2211 kvm-intel.nested= 2212 [KVM,Intel] Enable VMX nesting (nVMX). 2213 Default is 0 (disabled) 2214 2215 kvm-intel.unrestricted_guest= 2216 [KVM,Intel] Disable unrestricted guest feature 2217 (virtualized real and unpaged mode) on capable 2218 Intel chips. Default is 1 (enabled) 2219 2220 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault 2221 CVE-2018-3620. 2222 2223 Valid arguments: never, cond, always 2224 2225 always: L1D cache flush on every VMENTER. 2226 cond: Flush L1D on VMENTER only when the code between 2227 VMEXIT and VMENTER can leak host memory. 2228 never: Disables the mitigation 2229 2230 Default is cond (do L1 cache flush in specific instances) 2231 2232 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification 2233 feature (tagged TLBs) on capable Intel chips. 2234 Default is 1 (enabled) 2235 2236 l1tf= [X86] Control mitigation of the L1TF vulnerability on 2237 affected CPUs 2238 2239 The kernel PTE inversion protection is unconditionally 2240 enabled and cannot be disabled. 2241 2242 full 2243 Provides all available mitigations for the 2244 L1TF vulnerability. Disables SMT and 2245 enables all mitigations in the 2246 hypervisors, i.e. unconditional L1D flush. 2247 2248 SMT control and L1D flush control via the 2249 sysfs interface is still possible after 2250 boot. Hypervisors will issue a warning 2251 when the first VM is started in a 2252 potentially insecure configuration, 2253 i.e. SMT enabled or L1D flush disabled. 2254 2255 full,force 2256 Same as 'full', but disables SMT and L1D 2257 flush runtime control. Implies the 2258 'nosmt=force' command line option. 2259 (i.e. sysfs control of SMT is disabled.) 2260 2261 flush 2262 Leaves SMT enabled and enables the default 2263 hypervisor mitigation, i.e. conditional 2264 L1D flush. 2265 2266 SMT control and L1D flush control via the 2267 sysfs interface is still possible after 2268 boot. Hypervisors will issue a warning 2269 when the first VM is started in a 2270 potentially insecure configuration, 2271 i.e. SMT enabled or L1D flush disabled. 2272 2273 flush,nosmt 2274 2275 Disables SMT and enables the default 2276 hypervisor mitigation. 2277 2278 SMT control and L1D flush control via the 2279 sysfs interface is still possible after 2280 boot. Hypervisors will issue a warning 2281 when the first VM is started in a 2282 potentially insecure configuration, 2283 i.e. SMT enabled or L1D flush disabled. 2284 2285 flush,nowarn 2286 Same as 'flush', but hypervisors will not 2287 warn when a VM is started in a potentially 2288 insecure configuration. 2289 2290 off 2291 Disables hypervisor mitigations and doesn't 2292 emit any warnings. 2293 It also drops the swap size and available 2294 RAM limit restriction on both hypervisor and 2295 bare metal. 2296 2297 Default is 'flush'. 2298 2299 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst 2300 2301 l2cr= [PPC] 2302 2303 l3cr= [PPC] 2304 2305 lapic [X86-32,APIC] Enable the local APIC even if BIOS 2306 disabled it. 2307 2308 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline 2309 value for LAPIC timer one-shot implementation. Default 2310 back to the programmable timer unit in the LAPIC. 2311 2312 lapic_timer_c2_ok [X86,APIC] trust the local apic timer 2313 in C2 power state. 2314 2315 libata.dma= [LIBATA] DMA control 2316 libata.dma=0 Disable all PATA and SATA DMA 2317 libata.dma=1 PATA and SATA Disk DMA only 2318 libata.dma=2 ATAPI (CDROM) DMA only 2319 libata.dma=4 Compact Flash DMA only 2320 Combinations also work, so libata.dma=3 enables DMA 2321 for disks and CDROMs, but not CFs. 2322 2323 libata.ignore_hpa= [LIBATA] Ignore HPA limit 2324 libata.ignore_hpa=0 keep BIOS limits (default) 2325 libata.ignore_hpa=1 ignore limits, using full disk 2326 2327 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 2328 when set. 2329 Format: <int> 2330 2331 libata.force= [LIBATA] Force configurations. The format is comma 2332 separated list of "[ID:]VAL" where ID is 2333 PORT[.DEVICE]. PORT and DEVICE are decimal numbers 2334 matching port, link or device. Basically, it matches 2335 the ATA ID string printed on console by libata. If 2336 the whole ID part is omitted, the last PORT and DEVICE 2337 values are used. If ID hasn't been specified yet, the 2338 configuration applies to all ports, links and devices. 2339 2340 If only DEVICE is omitted, the parameter applies to 2341 the port and all links and devices behind it. DEVICE 2342 number of 0 either selects the first device or the 2343 first fan-out link behind PMP device. It does not 2344 select the host link. DEVICE number of 15 selects the 2345 host link and device attached to it. 2346 2347 The VAL specifies the configuration to force. As long 2348 as there's no ambiguity shortcut notation is allowed. 2349 For example, both 1.5 and 1.5G would work for 1.5Gbps. 2350 The following configurations can be forced. 2351 2352 * Cable type: 40c, 80c, short40c, unk, ign or sata. 2353 Any ID with matching PORT is used. 2354 2355 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 2356 2357 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 2358 udma[/][16,25,33,44,66,100,133] notation is also 2359 allowed. 2360 2361 * [no]ncq: Turn on or off NCQ. 2362 2363 * [no]ncqtrim: Turn off queued DSM TRIM. 2364 2365 * nohrst, nosrst, norst: suppress hard, soft 2366 and both resets. 2367 2368 * rstonce: only attempt one reset during 2369 hot-unplug link recovery 2370 2371 * dump_id: dump IDENTIFY data. 2372 2373 * atapi_dmadir: Enable ATAPI DMADIR bridge support 2374 2375 * disable: Disable this device. 2376 2377 If there are multiple matching configurations changing 2378 the same attribute, the last one is used. 2379 2380 memblock=debug [KNL] Enable memblock debug messages. 2381 2382 load_ramdisk= [RAM] List of ramdisks to load from floppy 2383 See Documentation/admin-guide/blockdev/ramdisk.rst. 2384 2385 lockd.nlm_grace_period=P [NFS] Assign grace period. 2386 Format: <integer> 2387 2388 lockd.nlm_tcpport=N [NFS] Assign TCP port. 2389 Format: <integer> 2390 2391 lockd.nlm_timeout=T [NFS] Assign timeout value. 2392 Format: <integer> 2393 2394 lockd.nlm_udpport=M [NFS] Assign UDP port. 2395 Format: <integer> 2396 2397 lockdown= [SECURITY] 2398 { integrity | confidentiality } 2399 Enable the kernel lockdown feature. If set to 2400 integrity, kernel features that allow userland to 2401 modify the running kernel are disabled. If set to 2402 confidentiality, kernel features that allow userland 2403 to extract confidential information from the kernel 2404 are also disabled. 2405 2406 locktorture.nreaders_stress= [KNL] 2407 Set the number of locking read-acquisition kthreads. 2408 Defaults to being automatically set based on the 2409 number of online CPUs. 2410 2411 locktorture.nwriters_stress= [KNL] 2412 Set the number of locking write-acquisition kthreads. 2413 2414 locktorture.onoff_holdoff= [KNL] 2415 Set time (s) after boot for CPU-hotplug testing. 2416 2417 locktorture.onoff_interval= [KNL] 2418 Set time (s) between CPU-hotplug operations, or 2419 zero to disable CPU-hotplug testing. 2420 2421 locktorture.shuffle_interval= [KNL] 2422 Set task-shuffle interval (jiffies). Shuffling 2423 tasks allows some CPUs to go into dyntick-idle 2424 mode during the locktorture test. 2425 2426 locktorture.shutdown_secs= [KNL] 2427 Set time (s) after boot system shutdown. This 2428 is useful for hands-off automated testing. 2429 2430 locktorture.stat_interval= [KNL] 2431 Time (s) between statistics printk()s. 2432 2433 locktorture.stutter= [KNL] 2434 Time (s) to stutter testing, for example, 2435 specifying five seconds causes the test to run for 2436 five seconds, wait for five seconds, and so on. 2437 This tests the locking primitive's ability to 2438 transition abruptly to and from idle. 2439 2440 locktorture.torture_type= [KNL] 2441 Specify the locking implementation to test. 2442 2443 locktorture.verbose= [KNL] 2444 Enable additional printk() statements. 2445 2446 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 2447 Format: <irq> 2448 2449 loglevel= All Kernel Messages with a loglevel smaller than the 2450 console loglevel will be printed to the console. It can 2451 also be changed with klogd or other programs. The 2452 loglevels are defined as follows: 2453 2454 0 (KERN_EMERG) system is unusable 2455 1 (KERN_ALERT) action must be taken immediately 2456 2 (KERN_CRIT) critical conditions 2457 3 (KERN_ERR) error conditions 2458 4 (KERN_WARNING) warning conditions 2459 5 (KERN_NOTICE) normal but significant condition 2460 6 (KERN_INFO) informational 2461 7 (KERN_DEBUG) debug-level messages 2462 2463 log_buf_len=n[KMG] Sets the size of the printk ring buffer, 2464 in bytes. n must be a power of two and greater 2465 than the minimal size. The minimal size is defined 2466 by LOG_BUF_SHIFT kernel config parameter. There is 2467 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter 2468 that allows to increase the default size depending on 2469 the number of CPUs. See init/Kconfig for more details. 2470 2471 logo.nologo [FB] Disables display of the built-in Linux logo. 2472 This may be used to provide more screen space for 2473 kernel log messages and is useful when debugging 2474 kernel boot problems. 2475 2476 lp=0 [LP] Specify parallel ports to use, e.g, 2477 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 2478 lp=reset first parallel port). 'lp=0' disables the 2479 lp=auto printer driver. 'lp=reset' (which can be 2480 specified in addition to the ports) causes 2481 attached printers to be reset. Using 2482 lp=port1,port2,... specifies the parallel ports 2483 to associate lp devices with, starting with 2484 lp0. A port specification may be 'none' to skip 2485 that lp device, or a parport name such as 2486 'parport0'. Specifying 'lp=auto' instead of a 2487 port specification list means that device IDs 2488 from each port should be examined, to see if 2489 an IEEE 1284-compliant printer is attached; if 2490 so, the driver will manage that printer. 2491 See also header of drivers/char/lp.c. 2492 2493 lpj=n [KNL] 2494 Sets loops_per_jiffy to given constant, thus avoiding 2495 time-consuming boot-time autodetection (up to 250 ms per 2496 CPU). 0 enables autodetection (default). To determine 2497 the correct value for your kernel, boot with normal 2498 autodetection and see what value is printed. Note that 2499 on SMP systems the preset will be applied to all CPUs, 2500 which is likely to cause problems if your CPUs need 2501 significantly divergent settings. An incorrect value 2502 will cause delays in the kernel to be wrong, leading to 2503 unpredictable I/O errors and other breakage. Although 2504 unlikely, in the extreme case this might damage your 2505 hardware. 2506 2507 ltpc= [NET] 2508 Format: <io>,<irq>,<dma> 2509 2510 lsm.debug [SECURITY] Enable LSM initialization debugging output. 2511 2512 lsm=lsm1,...,lsmN 2513 [SECURITY] Choose order of LSM initialization. This 2514 overrides CONFIG_LSM, and the "security=" parameter. 2515 2516 machvec= [IA-64] Force the use of a particular machine-vector 2517 (machvec) in a generic kernel. 2518 Example: machvec=hpzx1 2519 2520 machtype= [Loongson] Share the same kernel image file between different 2521 yeeloong laptop. 2522 Example: machtype=lemote-yeeloong-2f-7inch 2523 2524 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater 2525 than or equal to this physical address is ignored. 2526 2527 maxcpus= [SMP] Maximum number of processors that an SMP kernel 2528 will bring up during bootup. maxcpus=n : n >= 0 limits 2529 the kernel to bring up 'n' processors. Surely after 2530 bootup you can bring up the other plugged cpu by executing 2531 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 2532 only takes effect during system bootup. 2533 While n=0 is a special case, it is equivalent to "nosmp", 2534 which also disables the IO APIC. 2535 2536 max_loop= [LOOP] The number of loop block devices that get 2537 (loop.max_loop) unconditionally pre-created at init time. The default 2538 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 2539 of statically allocating a predefined number, loop 2540 devices can be requested on-demand with the 2541 /dev/loop-control interface. 2542 2543 mce [X86-32] Machine Check Exception 2544 2545 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.rst 2546 2547 md= [HW] RAID subsystems devices and level 2548 See Documentation/admin-guide/md.rst. 2549 2550 mdacon= [MDA] 2551 Format: <first>,<last> 2552 Specifies range of consoles to be captured by the MDA. 2553 2554 mds= [X86,INTEL] 2555 Control mitigation for the Micro-architectural Data 2556 Sampling (MDS) vulnerability. 2557 2558 Certain CPUs are vulnerable to an exploit against CPU 2559 internal buffers which can forward information to a 2560 disclosure gadget under certain conditions. 2561 2562 In vulnerable processors, the speculatively 2563 forwarded data can be used in a cache side channel 2564 attack, to access data to which the attacker does 2565 not have direct access. 2566 2567 This parameter controls the MDS mitigation. The 2568 options are: 2569 2570 full - Enable MDS mitigation on vulnerable CPUs 2571 full,nosmt - Enable MDS mitigation and disable 2572 SMT on vulnerable CPUs 2573 off - Unconditionally disable MDS mitigation 2574 2575 On TAA-affected machines, mds=off can be prevented by 2576 an active TAA mitigation as both vulnerabilities are 2577 mitigated with the same mechanism so in order to disable 2578 this mitigation, you need to specify tsx_async_abort=off 2579 too. 2580 2581 Not specifying this option is equivalent to 2582 mds=full. 2583 2584 For details see: Documentation/admin-guide/hw-vuln/mds.rst 2585 2586 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory 2587 Amount of memory to be used in cases as follows: 2588 2589 1 for test; 2590 2 when the kernel is not able to see the whole system memory; 2591 3 memory that lies after 'mem=' boundary is excluded from 2592 the hypervisor, then assigned to KVM guests. 2593 2594 [X86] Work as limiting max address. Use together 2595 with memmap= to avoid physical address space collisions. 2596 Without memmap= PCI devices could be placed at addresses 2597 belonging to unused RAM. 2598 2599 Note that this only takes effects during boot time since 2600 in above case 3, memory may need be hot added after boot 2601 if system memory of hypervisor is not sufficient. 2602 2603 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 2604 memory. 2605 2606 memchunk=nn[KMG] 2607 [KNL,SH] Allow user to override the default size for 2608 per-device physically contiguous DMA buffers. 2609 2610 memhp_default_state=online/offline 2611 [KNL] Set the initial state for the memory hotplug 2612 onlining policy. If not specified, the default value is 2613 set according to the 2614 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config 2615 option. 2616 See Documentation/admin-guide/mm/memory-hotplug.rst. 2617 2618 memmap=exactmap [KNL,X86] Enable setting of an exact 2619 E820 memory map, as specified by the user. 2620 Such memmap=exactmap lines can be constructed based on 2621 BIOS output or other requirements. See the memmap=nn@ss 2622 option description. 2623 2624 memmap=nn[KMG]@ss[KMG] 2625 [KNL] Force usage of a specific region of memory. 2626 Region of memory to be used is from ss to ss+nn. 2627 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], 2628 which limits max address to nn[KMG]. 2629 Multiple different regions can be specified, 2630 comma delimited. 2631 Example: 2632 memmap=100M@2G,100M#3G,1G!1024G 2633 2634 memmap=nn[KMG]#ss[KMG] 2635 [KNL,ACPI] Mark specific memory as ACPI data. 2636 Region of memory to be marked is from ss to ss+nn. 2637 2638 memmap=nn[KMG]$ss[KMG] 2639 [KNL,ACPI] Mark specific memory as reserved. 2640 Region of memory to be reserved is from ss to ss+nn. 2641 Example: Exclude memory from 0x18690000-0x1869ffff 2642 memmap=64K$0x18690000 2643 or 2644 memmap=0x10000$0x18690000 2645 Some bootloaders may need an escape character before '$', 2646 like Grub2, otherwise '$' and the following number 2647 will be eaten. 2648 2649 memmap=nn[KMG]!ss[KMG] 2650 [KNL,X86] Mark specific memory as protected. 2651 Region of memory to be used, from ss to ss+nn. 2652 The memory region may be marked as e820 type 12 (0xc) 2653 and is NVDIMM or ADR memory. 2654 2655 memmap=<size>%<offset>-<oldtype>+<newtype> 2656 [KNL,ACPI] Convert memory within the specified region 2657 from <oldtype> to <newtype>. If "-<oldtype>" is left 2658 out, the whole region will be marked as <newtype>, 2659 even if previously unavailable. If "+<newtype>" is left 2660 out, matching memory will be removed. Types are 2661 specified as e820 types, e.g., 1 = RAM, 2 = reserved, 2662 3 = ACPI, 12 = PRAM. 2663 2664 memory_corruption_check=0/1 [X86] 2665 Some BIOSes seem to corrupt the first 64k of 2666 memory when doing things like suspend/resume. 2667 Setting this option will scan the memory 2668 looking for corruption. Enabling this will 2669 both detect corruption and prevent the kernel 2670 from using the memory being corrupted. 2671 However, its intended as a diagnostic tool; if 2672 repeatable BIOS-originated corruption always 2673 affects the same memory, you can use memmap= 2674 to prevent the kernel from using that memory. 2675 2676 memory_corruption_check_size=size [X86] 2677 By default it checks for corruption in the low 2678 64k, making this memory unavailable for normal 2679 use. Use this parameter to scan for 2680 corruption in more or less memory. 2681 2682 memory_corruption_check_period=seconds [X86] 2683 By default it checks for corruption every 60 2684 seconds. Use this parameter to check at some 2685 other rate. 0 disables periodic checking. 2686 2687 memtest= [KNL,X86,ARM,PPC] Enable memtest 2688 Format: <integer> 2689 default : 0 <disable> 2690 Specifies the number of memtest passes to be 2691 performed. Each pass selects another test 2692 pattern from a given set of patterns. Memtest 2693 fills the memory with this pattern, validates 2694 memory contents and reserves bad memory 2695 regions that are detected. 2696 2697 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control 2698 Valid arguments: on, off 2699 Default (depends on kernel configuration option): 2700 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y) 2701 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n) 2702 mem_encrypt=on: Activate SME 2703 mem_encrypt=off: Do not activate SME 2704 2705 Refer to Documentation/virt/kvm/amd-memory-encryption.rst 2706 for details on when memory encryption can be activated. 2707 2708 mem_sleep_default= [SUSPEND] Default system suspend mode: 2709 s2idle - Suspend-To-Idle 2710 shallow - Power-On Suspend or equivalent (if supported) 2711 deep - Suspend-To-RAM or equivalent (if supported) 2712 See Documentation/admin-guide/pm/sleep-states.rst. 2713 2714 meye.*= [HW] Set MotionEye Camera parameters 2715 See Documentation/media/v4l-drivers/meye.rst. 2716 2717 mfgpt_irq= [IA-32] Specify the IRQ to use for the 2718 Multi-Function General Purpose Timers on AMD Geode 2719 platforms. 2720 2721 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 2722 the BIOS has incorrectly applied a workaround. TinyBIOS 2723 version 0.98 is known to be affected, 0.99 fixes the 2724 problem by letting the user disable the workaround. 2725 2726 mga= [HW,DRM] 2727 2728 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this 2729 physical address is ignored. 2730 2731 mini2440= [ARM,HW,KNL] 2732 Format:[0..2][b][c][t] 2733 Default: "0tb" 2734 MINI2440 configuration specification: 2735 0 - The attached screen is the 3.5" TFT 2736 1 - The attached screen is the 7" TFT 2737 2 - The VGA Shield is attached (1024x768) 2738 Leaving out the screen size parameter will not load 2739 the TFT driver, and the framebuffer will be left 2740 unconfigured. 2741 b - Enable backlight. The TFT backlight pin will be 2742 linked to the kernel VESA blanking code and a GPIO 2743 LED. This parameter is not necessary when using the 2744 VGA shield. 2745 c - Enable the s3c camera interface. 2746 t - Reserved for enabling touchscreen support. The 2747 touchscreen support is not enabled in the mainstream 2748 kernel as of 2.6.30, a preliminary port can be found 2749 in the "bleeding edge" mini2440 support kernel at 2750 http://repo.or.cz/w/linux-2.6/mini2440.git 2751 2752 mitigations= 2753 [X86,PPC,S390,ARM64] Control optional mitigations for 2754 CPU vulnerabilities. This is a set of curated, 2755 arch-independent options, each of which is an 2756 aggregation of existing arch-specific options. 2757 2758 off 2759 Disable all optional CPU mitigations. This 2760 improves system performance, but it may also 2761 expose users to several CPU vulnerabilities. 2762 Equivalent to: nopti [X86,PPC] 2763 kpti=0 [ARM64] 2764 nospectre_v1 [X86,PPC] 2765 nobp=0 [S390] 2766 nospectre_v2 [X86,PPC,S390,ARM64] 2767 spectre_v2_user=off [X86] 2768 spec_store_bypass_disable=off [X86,PPC] 2769 ssbd=force-off [ARM64] 2770 l1tf=off [X86] 2771 mds=off [X86] 2772 tsx_async_abort=off [X86] 2773 kvm.nx_huge_pages=off [X86] 2774 2775 Exceptions: 2776 This does not have any effect on 2777 kvm.nx_huge_pages when 2778 kvm.nx_huge_pages=force. 2779 2780 auto (default) 2781 Mitigate all CPU vulnerabilities, but leave SMT 2782 enabled, even if it's vulnerable. This is for 2783 users who don't want to be surprised by SMT 2784 getting disabled across kernel upgrades, or who 2785 have other ways of avoiding SMT-based attacks. 2786 Equivalent to: (default behavior) 2787 2788 auto,nosmt 2789 Mitigate all CPU vulnerabilities, disabling SMT 2790 if needed. This is for users who always want to 2791 be fully mitigated, even if it means losing SMT. 2792 Equivalent to: l1tf=flush,nosmt [X86] 2793 mds=full,nosmt [X86] 2794 tsx_async_abort=full,nosmt [X86] 2795 2796 mminit_loglevel= 2797 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this 2798 parameter allows control of the logging verbosity for 2799 the additional memory initialisation checks. A value 2800 of 0 disables mminit logging and a level of 4 will 2801 log everything. Information is printed at KERN_DEBUG 2802 so loglevel=8 may also need to be specified. 2803 2804 module.sig_enforce 2805 [KNL] When CONFIG_MODULE_SIG is set, this means that 2806 modules without (valid) signatures will fail to load. 2807 Note that if CONFIG_MODULE_SIG_FORCE is set, that 2808 is always true, so this option does nothing. 2809 2810 module_blacklist= [KNL] Do not load a comma-separated list of 2811 modules. Useful for debugging problem modules. 2812 2813 mousedev.tap_time= 2814 [MOUSE] Maximum time between finger touching and 2815 leaving touchpad surface for touch to be considered 2816 a tap and be reported as a left button click (for 2817 touchpads working in absolute mode only). 2818 Format: <msecs> 2819 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 2820 reporting absolute coordinates, such as tablets 2821 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 2822 reporting absolute coordinates, such as tablets 2823 2824 movablecore= [KNL,X86,IA-64,PPC] 2825 Format: nn[KMGTPE] | nn% 2826 This parameter is the complement to kernelcore=, it 2827 specifies the amount of memory used for migratable 2828 allocations. If both kernelcore and movablecore is 2829 specified, then kernelcore will be at *least* the 2830 specified value but may be more. If movablecore on its 2831 own is specified, the administrator must be careful 2832 that the amount of memory usable for all allocations 2833 is not too small. 2834 2835 movable_node [KNL] Boot-time switch to make hotplugable memory 2836 NUMA nodes to be movable. This means that the memory 2837 of such nodes will be usable only for movable 2838 allocations which rules out almost all kernel 2839 allocations. Use with caution! 2840 2841 MTD_Partition= [MTD] 2842 Format: <name>,<region-number>,<size>,<offset> 2843 2844 MTD_Region= [MTD] Format: 2845 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 2846 2847 mtdparts= [MTD] 2848 See drivers/mtd/parsers/cmdlinepart.c 2849 2850 multitce=off [PPC] This parameter disables the use of the pSeries 2851 firmware feature for updating multiple TCE entries 2852 at a time. 2853 2854 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 2855 2856 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 2857 2858 boundary - index of last SLC block on Flex-OneNAND. 2859 The remaining blocks are configured as MLC blocks. 2860 lock - Configure if Flex-OneNAND boundary should be locked. 2861 Once locked, the boundary cannot be changed. 2862 1 indicates lock status, 0 indicates unlock status. 2863 2864 mtdset= [ARM] 2865 ARM/S3C2412 JIVE boot control 2866 2867 See arch/arm/mach-s3c2412/mach-jive.c 2868 2869 mtouchusb.raw_coordinates= 2870 [HW] Make the MicroTouch USB driver use raw coordinates 2871 ('y', default) or cooked coordinates ('n') 2872 2873 mtrr_chunk_size=nn[KMG] [X86] 2874 used for mtrr cleanup. It is largest continuous chunk 2875 that could hold holes aka. UC entries. 2876 2877 mtrr_gran_size=nn[KMG] [X86] 2878 Used for mtrr cleanup. It is granularity of mtrr block. 2879 Default is 1. 2880 Large value could prevent small alignment from 2881 using up MTRRs. 2882 2883 mtrr_spare_reg_nr=n [X86] 2884 Format: <integer> 2885 Range: 0,7 : spare reg number 2886 Default : 1 2887 Used for mtrr cleanup. It is spare mtrr entries number. 2888 Set to 2 or more if your graphical card needs more. 2889 2890 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 2891 2892 netdev= [NET] Network devices parameters 2893 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 2894 Note that mem_start is often overloaded to mean 2895 something different and driver-specific. 2896 This usage is only documented in each driver source 2897 file if at all. 2898 2899 nf_conntrack.acct= 2900 [NETFILTER] Enable connection tracking flow accounting 2901 0 to disable accounting 2902 1 to enable accounting 2903 Default value is 0. 2904 2905 nfsaddrs= [NFS] Deprecated. Use ip= instead. 2906 See Documentation/admin-guide/nfs/nfsroot.rst. 2907 2908 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 2909 See Documentation/admin-guide/nfs/nfsroot.rst. 2910 2911 nfsrootdebug [NFS] enable nfsroot debugging messages. 2912 See Documentation/admin-guide/nfs/nfsroot.rst. 2913 2914 nfs.callback_nr_threads= 2915 [NFSv4] set the total number of threads that the 2916 NFS client will assign to service NFSv4 callback 2917 requests. 2918 2919 nfs.callback_tcpport= 2920 [NFS] set the TCP port on which the NFSv4 callback 2921 channel should listen. 2922 2923 nfs.cache_getent= 2924 [NFS] sets the pathname to the program which is used 2925 to update the NFS client cache entries. 2926 2927 nfs.cache_getent_timeout= 2928 [NFS] sets the timeout after which an attempt to 2929 update a cache entry is deemed to have failed. 2930 2931 nfs.idmap_cache_timeout= 2932 [NFS] set the maximum lifetime for idmapper cache 2933 entries. 2934 2935 nfs.enable_ino64= 2936 [NFS] enable 64-bit inode numbers. 2937 If zero, the NFS client will fake up a 32-bit inode 2938 number for the readdir() and stat() syscalls instead 2939 of returning the full 64-bit number. 2940 The default is to return 64-bit inode numbers. 2941 2942 nfs.max_session_cb_slots= 2943 [NFSv4.1] Sets the maximum number of session 2944 slots the client will assign to the callback 2945 channel. This determines the maximum number of 2946 callbacks the client will process in parallel for 2947 a particular server. 2948 2949 nfs.max_session_slots= 2950 [NFSv4.1] Sets the maximum number of session slots 2951 the client will attempt to negotiate with the server. 2952 This limits the number of simultaneous RPC requests 2953 that the client can send to the NFSv4.1 server. 2954 Note that there is little point in setting this 2955 value higher than the max_tcp_slot_table_limit. 2956 2957 nfs.nfs4_disable_idmapping= 2958 [NFSv4] When set to the default of '1', this option 2959 ensures that both the RPC level authentication 2960 scheme and the NFS level operations agree to use 2961 numeric uids/gids if the mount is using the 2962 'sec=sys' security flavour. In effect it is 2963 disabling idmapping, which can make migration from 2964 legacy NFSv2/v3 systems to NFSv4 easier. 2965 Servers that do not support this mode of operation 2966 will be autodetected by the client, and it will fall 2967 back to using the idmapper. 2968 To turn off this behaviour, set the value to '0'. 2969 nfs.nfs4_unique_id= 2970 [NFS4] Specify an additional fixed unique ident- 2971 ification string that NFSv4 clients can insert into 2972 their nfs_client_id4 string. This is typically a 2973 UUID that is generated at system install time. 2974 2975 nfs.send_implementation_id = 2976 [NFSv4.1] Send client implementation identification 2977 information in exchange_id requests. 2978 If zero, no implementation identification information 2979 will be sent. 2980 The default is to send the implementation identification 2981 information. 2982 2983 nfs.recover_lost_locks = 2984 [NFSv4] Attempt to recover locks that were lost due 2985 to a lease timeout on the server. Please note that 2986 doing this risks data corruption, since there are 2987 no guarantees that the file will remain unchanged 2988 after the locks are lost. 2989 If you want to enable the kernel legacy behaviour of 2990 attempting to recover these locks, then set this 2991 parameter to '1'. 2992 The default parameter value of '0' causes the kernel 2993 not to attempt recovery of lost locks. 2994 2995 nfs4.layoutstats_timer = 2996 [NFSv4.2] Change the rate at which the kernel sends 2997 layoutstats to the pNFS metadata server. 2998 2999 Setting this to value to 0 causes the kernel to use 3000 whatever value is the default set by the layout 3001 driver. A non-zero value sets the minimum interval 3002 in seconds between layoutstats transmissions. 3003 3004 nfsd.nfs4_disable_idmapping= 3005 [NFSv4] When set to the default of '1', the NFSv4 3006 server will return only numeric uids and gids to 3007 clients using auth_sys, and will accept numeric uids 3008 and gids from such clients. This is intended to ease 3009 migration from NFSv2/v3. 3010 3011 nmi_debug= [KNL,SH] Specify one or more actions to take 3012 when a NMI is triggered. 3013 Format: [state][,regs][,debounce][,die] 3014 3015 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 3016 Format: [panic,][nopanic,][num] 3017 Valid num: 0 or 1 3018 0 - turn hardlockup detector in nmi_watchdog off 3019 1 - turn hardlockup detector in nmi_watchdog on 3020 When panic is specified, panic when an NMI watchdog 3021 timeout occurs (or 'nopanic' to not panic on an NMI 3022 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set) 3023 To disable both hard and soft lockup detectors, 3024 please see 'nowatchdog'. 3025 This is useful when you use a panic=... timeout and 3026 need the box quickly up again. 3027 3028 These settings can be accessed at runtime via 3029 the nmi_watchdog and hardlockup_panic sysctls. 3030 3031 netpoll.carrier_timeout= 3032 [NET] Specifies amount of time (in seconds) that 3033 netpoll should wait for a carrier. By default netpoll 3034 waits 4 seconds. 3035 3036 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 3037 emulation library even if a 387 maths coprocessor 3038 is present. 3039 3040 no5lvl [X86-64] Disable 5-level paging mode. Forces 3041 kernel to use 4-level paging instead. 3042 3043 no_console_suspend 3044 [HW] Never suspend the console 3045 Disable suspending of consoles during suspend and 3046 hibernate operations. Once disabled, debugging 3047 messages can reach various consoles while the rest 3048 of the system is being put to sleep (ie, while 3049 debugging driver suspend/resume hooks). This may 3050 not work reliably with all consoles, but is known 3051 to work with serial and VGA consoles. 3052 To facilitate more flexible debugging, we also add 3053 console_suspend, a printk module parameter to control 3054 it. Users could use console_suspend (usually 3055 /sys/module/printk/parameters/console_suspend) to 3056 turn on/off it dynamically. 3057 3058 novmcoredd [KNL,KDUMP] 3059 Disable device dump. Device dump allows drivers to 3060 append dump data to vmcore so you can collect driver 3061 specified debug info. Drivers can append the data 3062 without any limit and this data is stored in memory, 3063 so this may cause significant memory stress. Disabling 3064 device dump can help save memory but the driver debug 3065 data will be no longer available. This parameter 3066 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP 3067 is set. 3068 3069 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien 3070 caches in the slab allocator. Saves per-node memory, 3071 but will impact performance. 3072 3073 noalign [KNL,ARM] 3074 3075 noaltinstr [S390] Disables alternative instructions patching 3076 (CPU alternatives feature). 3077 3078 noapic [SMP,APIC] Tells the kernel to not make use of any 3079 IOAPICs that may be present in the system. 3080 3081 noautogroup Disable scheduler automatic task group creation. 3082 3083 nobats [PPC] Do not use BATs for mapping kernel lowmem 3084 on "Classic" PPC cores. 3085 3086 nocache [ARM] 3087 3088 noclflush [BUGS=X86] Don't use the CLFLUSH instruction 3089 3090 nodelayacct [KNL] Disable per-task delay accounting 3091 3092 nodsp [SH] Disable hardware DSP at boot time. 3093 3094 noefi Disable EFI runtime services support. 3095 3096 noexec [IA-64] 3097 3098 noexec [X86] 3099 On X86-32 available only on PAE configured kernels. 3100 noexec=on: enable non-executable mappings (default) 3101 noexec=off: disable non-executable mappings 3102 3103 nosmap [X86,PPC] 3104 Disable SMAP (Supervisor Mode Access Prevention) 3105 even if it is supported by processor. 3106 3107 nosmep [X86,PPC] 3108 Disable SMEP (Supervisor Mode Execution Prevention) 3109 even if it is supported by processor. 3110 3111 noexec32 [X86-64] 3112 This affects only 32-bit executables. 3113 noexec32=on: enable non-executable mappings (default) 3114 read doesn't imply executable mappings 3115 noexec32=off: disable non-executable mappings 3116 read implies executable mappings 3117 3118 nofpu [MIPS,SH] Disable hardware FPU at boot time. 3119 3120 nofxsr [BUGS=X86-32] Disables x86 floating point extended 3121 register save and restore. The kernel will only save 3122 legacy floating-point registers on task switch. 3123 3124 nohugeiomap [KNL,x86,PPC] Disable kernel huge I/O mappings. 3125 3126 nosmt [KNL,S390] Disable symmetric multithreading (SMT). 3127 Equivalent to smt=1. 3128 3129 [KNL,x86] Disable symmetric multithreading (SMT). 3130 nosmt=force: Force disable SMT, cannot be undone 3131 via the sysfs control file. 3132 3133 nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1 3134 (bounds check bypass). With this option data leaks are 3135 possible in the system. 3136 3137 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for 3138 the Spectre variant 2 (indirect branch prediction) 3139 vulnerability. System may allow data leaks with this 3140 option. 3141 3142 nospec_store_bypass_disable 3143 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability 3144 3145 noxsave [BUGS=X86] Disables x86 extended register state save 3146 and restore using xsave. The kernel will fallback to 3147 enabling legacy floating-point and sse state. 3148 3149 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 3150 register states. The kernel will fall back to use 3151 xsave to save the states. By using this parameter, 3152 performance of saving the states is degraded because 3153 xsave doesn't support modified optimization while 3154 xsaveopt supports it on xsaveopt enabled systems. 3155 3156 noxsaves [X86] Disables xsaves and xrstors used in saving and 3157 restoring x86 extended register state in compacted 3158 form of xsave area. The kernel will fall back to use 3159 xsaveopt and xrstor to save and restore the states 3160 in standard form of xsave area. By using this 3161 parameter, xsave area per process might occupy more 3162 memory on xsaves enabled systems. 3163 3164 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or 3165 wfi(ARM) instruction doesn't work correctly and not to 3166 use it. This is also useful when using JTAG debugger. 3167 3168 no_file_caps Tells the kernel not to honor file capabilities. The 3169 only way then for a file to be executed with privilege 3170 is to be setuid root or executed by root. 3171 3172 nohalt [IA-64] Tells the kernel not to use the power saving 3173 function PAL_HALT_LIGHT when idle. This increases 3174 power-consumption. On the positive side, it reduces 3175 interrupt wake-up latency, which may improve performance 3176 in certain environments such as networked servers or 3177 real-time systems. 3178 3179 nohibernate [HIBERNATION] Disable hibernation and resume. 3180 3181 nohz= [KNL] Boottime enable/disable dynamic ticks 3182 Valid arguments: on, off 3183 Default: on 3184 3185 nohz_full= [KNL,BOOT,SMP,ISOL] 3186 The argument is a cpu list, as described above. 3187 In kernels built with CONFIG_NO_HZ_FULL=y, set 3188 the specified list of CPUs whose tick will be stopped 3189 whenever possible. The boot CPU will be forced outside 3190 the range to maintain the timekeeping. Any CPUs 3191 in this list will have their RCU callbacks offloaded, 3192 just as if they had also been called out in the 3193 rcu_nocbs= boot parameter. 3194 3195 noiotrap [SH] Disables trapped I/O port accesses. 3196 3197 noirqdebug [X86-32] Disables the code which attempts to detect and 3198 disable unhandled interrupt sources. 3199 3200 no_timer_check [X86,APIC] Disables the code which tests for 3201 broken timer IRQ sources. 3202 3203 noisapnp [ISAPNP] Disables ISA PnP code. 3204 3205 noinitrd [RAM] Tells the kernel not to load any configured 3206 initial RAM disk. 3207 3208 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt 3209 remapping. 3210 [Deprecated - use intremap=off] 3211 3212 nointroute [IA-64] 3213 3214 noinvpcid [X86] Disable the INVPCID cpu feature. 3215 3216 nojitter [IA-64] Disables jitter checking for ITC timers. 3217 3218 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver 3219 3220 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page 3221 fault handling. 3222 3223 no-vmw-sched-clock 3224 [X86,PV_OPS] Disable paravirtualized VMware scheduler 3225 clock and use the default one. 3226 3227 no-steal-acc [X86,PV_OPS,ARM64] Disable paravirtualized steal time 3228 accounting. steal time is computed, but won't 3229 influence scheduler behaviour 3230 3231 nolapic [X86-32,APIC] Do not enable or use the local APIC. 3232 3233 nolapic_timer [X86-32,APIC] Do not use the local APIC timer. 3234 3235 noltlbs [PPC] Do not use large page/tlb entries for kernel 3236 lowmem mapping on PPC40x and PPC8xx 3237 3238 nomca [IA-64] Disable machine check abort handling 3239 3240 nomce [X86-32] Disable Machine Check Exception 3241 3242 nomfgpt [X86-32] Disable Multi-Function General Purpose 3243 Timer usage (for AMD Geode machines). 3244 3245 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 3246 shutdown the other cpus. Instead use the REBOOT_VECTOR 3247 irq. 3248 3249 nomodule Disable module load 3250 3251 nopat [X86] Disable PAT (page attribute table extension of 3252 pagetables) support. 3253 3254 nopcid [X86-64] Disable the PCID cpu feature. 3255 3256 norandmaps Don't use address space randomization. Equivalent to 3257 echo 0 > /proc/sys/kernel/randomize_va_space 3258 3259 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 3260 with UP alternatives 3261 3262 nordrand [X86] Disable kernel use of the RDRAND and 3263 RDSEED instructions even if they are supported 3264 by the processor. RDRAND and RDSEED are still 3265 available to user space applications. 3266 3267 noresume [SWSUSP] Disables resume and restores original swap 3268 space. 3269 3270 no-scroll [VGA] Disables scrollback. 3271 This is required for the Braillex ib80-piezo Braille 3272 reader made by F.H. Papenmeier (Germany). 3273 3274 nosbagart [IA-64] 3275 3276 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support. 3277 3278 nosmp [SMP] Tells an SMP kernel to act as a UP kernel, 3279 and disable the IO APIC. legacy for "maxcpus=0". 3280 3281 nosoftlockup [KNL] Disable the soft-lockup detector. 3282 3283 nosync [HW,M68K] Disables sync negotiation for all devices. 3284 3285 nowatchdog [KNL] Disable both lockup detectors, i.e. 3286 soft-lockup and NMI watchdog (hard-lockup). 3287 3288 nowb [ARM] 3289 3290 nox2apic [X86-64,APIC] Do not enable x2APIC mode. 3291 3292 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when 3293 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off. 3294 Some features depend on CPU0. Known dependencies are: 3295 1. Resume from suspend/hibernate depends on CPU0. 3296 Suspend/hibernate will fail if CPU0 is offline and you 3297 need to online CPU0 before suspend/hibernate. 3298 2. PIC interrupts also depend on CPU0. CPU0 can't be 3299 removed if a PIC interrupt is detected. 3300 It's said poweroff/reboot may depend on CPU0 on some 3301 machines although I haven't seen such issues so far 3302 after CPU0 is offline on a few tested machines. 3303 If the dependencies are under your control, you can 3304 turn on cpu0_hotplug. 3305 3306 nps_mtm_hs_ctr= [KNL,ARC] 3307 This parameter sets the maximum duration, in 3308 cycles, each HW thread of the CTOP can run 3309 without interruptions, before HW switches it. 3310 The actual maximum duration is 16 times this 3311 parameter's value. 3312 Format: integer between 1 and 255 3313 Default: 255 3314 3315 nptcg= [IA-64] Override max number of concurrent global TLB 3316 purges which is reported from either PAL_VM_SUMMARY or 3317 SAL PALO. 3318 3319 nr_cpus= [SMP] Maximum number of processors that an SMP kernel 3320 could support. nr_cpus=n : n >= 1 limits the kernel to 3321 support 'n' processors. It could be larger than the 3322 number of already plugged CPU during bootup, later in 3323 runtime you can physically add extra cpu until it reaches 3324 n. So during boot up some boot time memory for per-cpu 3325 variables need be pre-allocated for later physical cpu 3326 hot plugging. 3327 3328 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 3329 3330 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing. 3331 Allowed values are enable and disable 3332 3333 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 3334 'node', 'default' can be specified 3335 This can be set from sysctl after boot. 3336 See Documentation/admin-guide/sysctl/vm.rst for details. 3337 3338 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver. 3339 See Documentation/core-api/debugging-via-ohci1394.rst for more 3340 info. 3341 3342 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 3343 Rather than timing out after 20 ms if an EC 3344 command is not properly ACKed, override the length 3345 of the timeout. We have interrupts disabled while 3346 waiting for the ACK, so if this is set too high 3347 interrupts *may* be lost! 3348 3349 omap_mux= [OMAP] Override bootloader pin multiplexing. 3350 Format: <mux_mode0.mode_name=value>... 3351 For example, to override I2C bus2: 3352 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 3353 3354 oprofile.timer= [HW] 3355 Use timer interrupt instead of performance counters 3356 3357 oprofile.cpu_type= Force an oprofile cpu type 3358 This might be useful if you have an older oprofile 3359 userland or if you want common events. 3360 Format: { arch_perfmon } 3361 arch_perfmon: [X86] Force use of architectural 3362 perfmon on Intel CPUs instead of the 3363 CPU specific event set. 3364 timer: [X86] Force use of architectural NMI 3365 timer mode (see also oprofile.timer 3366 for generic hr timer mode) 3367 3368 oops=panic Always panic on oopses. Default is to just kill the 3369 process, but there is a small probability of 3370 deadlocking the machine. 3371 This will also cause panics on machine check exceptions. 3372 Useful together with panic=30 to trigger a reboot. 3373 3374 page_alloc.shuffle= 3375 [KNL] Boolean flag to control whether the page allocator 3376 should randomize its free lists. The randomization may 3377 be automatically enabled if the kernel detects it is 3378 running on a platform with a direct-mapped memory-side 3379 cache, and this parameter can be used to 3380 override/disable that behavior. The state of the flag 3381 can be read from sysfs at: 3382 /sys/module/page_alloc/parameters/shuffle. 3383 3384 page_owner= [KNL] Boot-time page_owner enabling option. 3385 Storage of the information about who allocated 3386 each page is disabled in default. With this switch, 3387 we can turn it on. 3388 on: enable the feature 3389 3390 page_poison= [KNL] Boot-time parameter changing the state of 3391 poisoning on the buddy allocator, available with 3392 CONFIG_PAGE_POISONING=y. 3393 off: turn off poisoning (default) 3394 on: turn on poisoning 3395 3396 panic= [KNL] Kernel behaviour on panic: delay <timeout> 3397 timeout > 0: seconds before rebooting 3398 timeout = 0: wait forever 3399 timeout < 0: reboot immediately 3400 Format: <timeout> 3401 3402 panic_print= Bitmask for printing system info when panic happens. 3403 User can chose combination of the following bits: 3404 bit 0: print all tasks info 3405 bit 1: print system memory info 3406 bit 2: print timer info 3407 bit 3: print locks info if CONFIG_LOCKDEP is on 3408 bit 4: print ftrace buffer 3409 bit 5: print all printk messages in buffer 3410 3411 panic_on_warn panic() instead of WARN(). Useful to cause kdump 3412 on a WARN(). 3413 3414 crash_kexec_post_notifiers 3415 Run kdump after running panic-notifiers and dumping 3416 kmsg. This only for the users who doubt kdump always 3417 succeeds in any situation. 3418 Note that this also increases risks of kdump failure, 3419 because some panic notifiers can make the crashed 3420 kernel more unstable. 3421 3422 parkbd.port= [HW] Parallel port number the keyboard adapter is 3423 connected to, default is 0. 3424 Format: <parport#> 3425 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 3426 0 for XT, 1 for AT (default is AT). 3427 Format: <mode> 3428 3429 parport= [HW,PPT] Specify parallel ports. 0 disables. 3430 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 3431 Use 'auto' to force the driver to use any 3432 IRQ/DMA settings detected (the default is to 3433 ignore detected IRQ/DMA settings because of 3434 possible conflicts). You can specify the base 3435 address, IRQ, and DMA settings; IRQ and DMA 3436 should be numbers, or 'auto' (for using detected 3437 settings on that particular port), or 'nofifo' 3438 (to avoid using a FIFO even if it is detected). 3439 Parallel ports are assigned in the order they 3440 are specified on the command line, starting 3441 with parport0. 3442 3443 parport_init_mode= [HW,PPT] 3444 Configure VIA parallel port to operate in 3445 a specific mode. This is necessary on Pegasos 3446 computer where firmware has no options for setting 3447 up parallel port mode and sets it to spp. 3448 Currently this function knows 686a and 8231 chips. 3449 Format: [spp|ps2|epp|ecp|ecpepp] 3450 3451 pause_on_oops= 3452 Halt all CPUs after the first oops has been printed for 3453 the specified number of seconds. This is to be used if 3454 your oopses keep scrolling off the screen. 3455 3456 pcbit= [HW,ISDN] 3457 3458 pcd. [PARIDE] 3459 See header of drivers/block/paride/pcd.c. 3460 See also Documentation/admin-guide/blockdev/paride.rst. 3461 3462 pci=option[,option...] [PCI] various PCI subsystem options. 3463 3464 Some options herein operate on a specific device 3465 or a set of devices (<pci_dev>). These are 3466 specified in one of the following formats: 3467 3468 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* 3469 pci:<vendor>:<device>[:<subvendor>:<subdevice>] 3470 3471 Note: the first format specifies a PCI 3472 bus/device/function address which may change 3473 if new hardware is inserted, if motherboard 3474 firmware changes, or due to changes caused 3475 by other kernel parameters. If the 3476 domain is left unspecified, it is 3477 taken to be zero. Optionally, a path 3478 to a device through multiple device/function 3479 addresses can be specified after the base 3480 address (this is more robust against 3481 renumbering issues). The second format 3482 selects devices using IDs from the 3483 configuration space which may match multiple 3484 devices in the system. 3485 3486 earlydump dump PCI config space before the kernel 3487 changes anything 3488 off [X86] don't probe for the PCI bus 3489 bios [X86-32] force use of PCI BIOS, don't access 3490 the hardware directly. Use this if your machine 3491 has a non-standard PCI host bridge. 3492 nobios [X86-32] disallow use of PCI BIOS, only direct 3493 hardware access methods are allowed. Use this 3494 if you experience crashes upon bootup and you 3495 suspect they are caused by the BIOS. 3496 conf1 [X86] Force use of PCI Configuration Access 3497 Mechanism 1 (config address in IO port 0xCF8, 3498 data in IO port 0xCFC, both 32-bit). 3499 conf2 [X86] Force use of PCI Configuration Access 3500 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 3501 the function, IO port 0xCFA, also 8-bit, sets 3502 bus number. The config space is then accessed 3503 through ports 0xC000-0xCFFF). 3504 See http://wiki.osdev.org/PCI for more info 3505 on the configuration access mechanisms. 3506 noaer [PCIE] If the PCIEAER kernel config parameter is 3507 enabled, this kernel boot option can be used to 3508 disable the use of PCIE advanced error reporting. 3509 nodomains [PCI] Disable support for multiple PCI 3510 root domains (aka PCI segments, in ACPI-speak). 3511 nommconf [X86] Disable use of MMCONFIG for PCI 3512 Configuration 3513 check_enable_amd_mmconf [X86] check for and enable 3514 properly configured MMIO access to PCI 3515 config space on AMD family 10h CPU 3516 nomsi [MSI] If the PCI_MSI kernel config parameter is 3517 enabled, this kernel boot option can be used to 3518 disable the use of MSI interrupts system-wide. 3519 noioapicquirk [APIC] Disable all boot interrupt quirks. 3520 Safety option to keep boot IRQs enabled. This 3521 should never be necessary. 3522 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 3523 primary IO-APIC for bridges that cannot disable 3524 boot IRQs. This fixes a source of spurious IRQs 3525 when the system masks IRQs. 3526 noioapicreroute [APIC] Disable workaround that uses the 3527 boot IRQ equivalent of an IRQ that connects to 3528 a chipset where boot IRQs cannot be disabled. 3529 The opposite of ioapicreroute. 3530 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 3531 routing table. These calls are known to be buggy 3532 on several machines and they hang the machine 3533 when used, but on other computers it's the only 3534 way to get the interrupt routing table. Try 3535 this option if the kernel is unable to allocate 3536 IRQs or discover secondary PCI buses on your 3537 motherboard. 3538 rom [X86] Assign address space to expansion ROMs. 3539 Use with caution as certain devices share 3540 address decoders between ROMs and other 3541 resources. 3542 norom [X86] Do not assign address space to 3543 expansion ROMs that do not already have 3544 BIOS assigned address ranges. 3545 nobar [X86] Do not assign address space to the 3546 BARs that weren't assigned by the BIOS. 3547 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 3548 assigned automatically to PCI devices. You can 3549 make the kernel exclude IRQs of your ISA cards 3550 this way. 3551 pirqaddr=0xAAAAA [X86] Specify the physical address 3552 of the PIRQ table (normally generated 3553 by the BIOS) if it is outside the 3554 F0000h-100000h range. 3555 lastbus=N [X86] Scan all buses thru bus #N. Can be 3556 useful if the kernel is unable to find your 3557 secondary buses and you want to tell it 3558 explicitly which ones they are. 3559 assign-busses [X86] Always assign all PCI bus 3560 numbers ourselves, overriding 3561 whatever the firmware may have done. 3562 usepirqmask [X86] Honor the possible IRQ mask stored 3563 in the BIOS $PIR table. This is needed on 3564 some systems with broken BIOSes, notably 3565 some HP Pavilion N5400 and Omnibook XE3 3566 notebooks. This will have no effect if ACPI 3567 IRQ routing is enabled. 3568 noacpi [X86] Do not use ACPI for IRQ routing 3569 or for PCI scanning. 3570 use_crs [X86] Use PCI host bridge window information 3571 from ACPI. On BIOSes from 2008 or later, this 3572 is enabled by default. If you need to use this, 3573 please report a bug. 3574 nocrs [X86] Ignore PCI host bridge windows from ACPI. 3575 If you need to use this, please report a bug. 3576 routeirq Do IRQ routing for all PCI devices. 3577 This is normally done in pci_enable_device(), 3578 so this option is a temporary workaround 3579 for broken drivers that don't call it. 3580 skip_isa_align [X86] do not align io start addr, so can 3581 handle more pci cards 3582 noearly [X86] Don't do any early type 1 scanning. 3583 This might help on some broken boards which 3584 machine check when some devices' config space 3585 is read. But various workarounds are disabled 3586 and some IOMMU drivers will not work. 3587 bfsort Sort PCI devices into breadth-first order. 3588 This sorting is done to get a device 3589 order compatible with older (<= 2.4) kernels. 3590 nobfsort Don't sort PCI devices into breadth-first order. 3591 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 3592 tuning and use the BIOS-configured MPS defaults. 3593 pcie_bus_safe Set every device's MPS to the largest value 3594 supported by all devices below the root complex. 3595 pcie_bus_perf Set device MPS to the largest allowable MPS 3596 based on its parent bus. Also set MRRS (Max 3597 Read Request Size) to the largest supported 3598 value (no larger than the MPS that the device 3599 or bus can support) for best performance. 3600 pcie_bus_peer2peer Set every device's MPS to 128B, which 3601 every device is guaranteed to support. This 3602 configuration allows peer-to-peer DMA between 3603 any pair of devices, possibly at the cost of 3604 reduced performance. This also guarantees 3605 that hot-added devices will work. 3606 cbiosize=nn[KMG] The fixed amount of bus space which is 3607 reserved for the CardBus bridge's IO window. 3608 The default value is 256 bytes. 3609 cbmemsize=nn[KMG] The fixed amount of bus space which is 3610 reserved for the CardBus bridge's memory 3611 window. The default value is 64 megabytes. 3612 resource_alignment= 3613 Format: 3614 [<order of align>@]<pci_dev>[; ...] 3615 Specifies alignment and device to reassign 3616 aligned memory resources. How to 3617 specify the device is described above. 3618 If <order of align> is not specified, 3619 PAGE_SIZE is used as alignment. 3620 A PCI-PCI bridge can be specified if resource 3621 windows need to be expanded. 3622 To specify the alignment for several 3623 instances of a device, the PCI vendor, 3624 device, subvendor, and subdevice may be 3625 specified, e.g., 12@pci:8086:9c22:103c:198f 3626 for 4096-byte alignment. 3627 ecrc= Enable/disable PCIe ECRC (transaction layer 3628 end-to-end CRC checking). 3629 bios: Use BIOS/firmware settings. This is the 3630 the default. 3631 off: Turn ECRC off 3632 on: Turn ECRC on. 3633 hpiosize=nn[KMG] The fixed amount of bus space which is 3634 reserved for hotplug bridge's IO window. 3635 Default size is 256 bytes. 3636 hpmmiosize=nn[KMG] The fixed amount of bus space which is 3637 reserved for hotplug bridge's MMIO window. 3638 Default size is 2 megabytes. 3639 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is 3640 reserved for hotplug bridge's MMIO_PREF window. 3641 Default size is 2 megabytes. 3642 hpmemsize=nn[KMG] The fixed amount of bus space which is 3643 reserved for hotplug bridge's MMIO and 3644 MMIO_PREF window. 3645 Default size is 2 megabytes. 3646 hpbussize=nn The minimum amount of additional bus numbers 3647 reserved for buses below a hotplug bridge. 3648 Default is 1. 3649 realloc= Enable/disable reallocating PCI bridge resources 3650 if allocations done by BIOS are too small to 3651 accommodate resources required by all child 3652 devices. 3653 off: Turn realloc off 3654 on: Turn realloc on 3655 realloc same as realloc=on 3656 noari do not use PCIe ARI. 3657 noats [PCIE, Intel-IOMMU, AMD-IOMMU] 3658 do not use PCIe ATS (and IOMMU device IOTLB). 3659 pcie_scan_all Scan all possible PCIe devices. Otherwise we 3660 only look for one device below a PCIe downstream 3661 port. 3662 big_root_window Try to add a big 64bit memory window to the PCIe 3663 root complex on AMD CPUs. Some GFX hardware 3664 can resize a BAR to allow access to all VRAM. 3665 Adding the window is slightly risky (it may 3666 conflict with unreported devices), so this 3667 taints the kernel. 3668 disable_acs_redir=<pci_dev>[; ...] 3669 Specify one or more PCI devices (in the format 3670 specified above) separated by semicolons. 3671 Each device specified will have the PCI ACS 3672 redirect capabilities forced off which will 3673 allow P2P traffic between devices through 3674 bridges without forcing it upstream. Note: 3675 this removes isolation between devices and 3676 may put more devices in an IOMMU group. 3677 force_floating [S390] Force usage of floating interrupts. 3678 nomio [S390] Do not use MIO instructions. 3679 3680 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power 3681 Management. 3682 off Disable ASPM. 3683 force Enable ASPM even on devices that claim not to support it. 3684 WARNING: Forcing ASPM on may cause system lockups. 3685 3686 pcie_ports= [PCIE] PCIe port services handling: 3687 native Use native PCIe services (PME, AER, DPC, PCIe hotplug) 3688 even if the platform doesn't give the OS permission to 3689 use them. This may cause conflicts if the platform 3690 also tries to use these services. 3691 dpc-native Use native PCIe service for DPC only. May 3692 cause conflicts if firmware uses AER or DPC. 3693 compat Disable native PCIe services (PME, AER, DPC, PCIe 3694 hotplug). 3695 3696 pcie_port_pm= [PCIE] PCIe port power management handling: 3697 off Disable power management of all PCIe ports 3698 force Forcibly enable power management of all PCIe ports 3699 3700 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 3701 nomsi Do not use MSI for native PCIe PME signaling (this makes 3702 all PCIe root ports use INTx for all services). 3703 3704 pcmv= [HW,PCMCIA] BadgePAD 4 3705 3706 pd_ignore_unused 3707 [PM] 3708 Keep all power-domains already enabled by bootloader on, 3709 even if no driver has claimed them. This is useful 3710 for debug and development, but should not be 3711 needed on a platform with proper driver support. 3712 3713 pd. [PARIDE] 3714 See Documentation/admin-guide/blockdev/paride.rst. 3715 3716 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 3717 boot time. 3718 Format: { 0 | 1 } 3719 See arch/parisc/kernel/pdc_chassis.c 3720 3721 percpu_alloc= Select which percpu first chunk allocator to use. 3722 Currently supported values are "embed" and "page". 3723 Archs may support subset or none of the selections. 3724 See comments in mm/percpu.c for details on each 3725 allocator. This parameter is primarily for debugging 3726 and performance comparison. 3727 3728 pf. [PARIDE] 3729 See Documentation/admin-guide/blockdev/paride.rst. 3730 3731 pg. [PARIDE] 3732 See Documentation/admin-guide/blockdev/paride.rst. 3733 3734 pirq= [SMP,APIC] Manual mp-table setup 3735 See Documentation/x86/i386/IO-APIC.rst. 3736 3737 plip= [PPT,NET] Parallel port network link 3738 Format: { parport<nr> | timid | 0 } 3739 See also Documentation/admin-guide/parport.rst. 3740 3741 pmtmr= [X86] Manual setup of pmtmr I/O Port. 3742 Override pmtimer IOPort with a hex value. 3743 e.g. pmtmr=0x508 3744 3745 pm_debug_messages [SUSPEND,KNL] 3746 Enable suspend/resume debug messages during boot up. 3747 3748 pnp.debug=1 [PNP] 3749 Enable PNP debug messages (depends on the 3750 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 3751 via /sys/module/pnp/parameters/debug. We always show 3752 current resource usage; turning this on also shows 3753 possible settings and some assignment information. 3754 3755 pnpacpi= [ACPI] 3756 { off } 3757 3758 pnpbios= [ISAPNP] 3759 { on | off | curr | res | no-curr | no-res } 3760 3761 pnp_reserve_irq= 3762 [ISAPNP] Exclude IRQs for the autoconfiguration 3763 3764 pnp_reserve_dma= 3765 [ISAPNP] Exclude DMAs for the autoconfiguration 3766 3767 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 3768 Ranges are in pairs (I/O port base and size). 3769 3770 pnp_reserve_mem= 3771 [ISAPNP] Exclude memory regions for the 3772 autoconfiguration. 3773 Ranges are in pairs (memory base and size). 3774 3775 ports= [IP_VS_FTP] IPVS ftp helper module 3776 Default is 21. 3777 Up to 8 (IP_VS_APP_MAX_PORTS) ports 3778 may be specified. 3779 Format: <port>,<port>.... 3780 3781 powersave=off [PPC] This option disables power saving features. 3782 It specifically disables cpuidle and sets the 3783 platform machine description specific power_save 3784 function to NULL. On Idle the CPU just reduces 3785 execution priority. 3786 3787 ppc_strict_facility_enable 3788 [PPC] This option catches any kernel floating point, 3789 Altivec, VSX and SPE outside of regions specifically 3790 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 3791 There is some performance impact when enabling this. 3792 3793 ppc_tm= [PPC] 3794 Format: {"off"} 3795 Disable Hardware Transactional Memory 3796 3797 print-fatal-signals= 3798 [KNL] debug: print fatal signals 3799 3800 If enabled, warn about various signal handling 3801 related application anomalies: too many signals, 3802 too many POSIX.1 timers, fatal signals causing a 3803 coredump - etc. 3804 3805 If you hit the warning due to signal overflow, 3806 you might want to try "ulimit -i unlimited". 3807 3808 default: off. 3809 3810 printk.always_kmsg_dump= 3811 Trigger kmsg_dump for cases other than kernel oops or 3812 panics 3813 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3814 default: disabled 3815 3816 printk.devkmsg={on,off,ratelimit} 3817 Control writing to /dev/kmsg. 3818 on - unlimited logging to /dev/kmsg from userspace 3819 off - logging to /dev/kmsg disabled 3820 ratelimit - ratelimit the logging 3821 Default: ratelimit 3822 3823 printk.time= Show timing data prefixed to each printk message line 3824 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3825 3826 processor.max_cstate= [HW,ACPI] 3827 Limit processor to maximum C-state 3828 max_cstate=9 overrides any DMI blacklist limit. 3829 3830 processor.nocst [HW,ACPI] 3831 Ignore the _CST method to determine C-states, 3832 instead using the legacy FADT method 3833 3834 profile= [KNL] Enable kernel profiling via /proc/profile 3835 Format: [<profiletype>,]<number> 3836 Param: <profiletype>: "schedule", "sleep", or "kvm" 3837 [defaults to kernel profiling] 3838 Param: "schedule" - profile schedule points. 3839 Param: "sleep" - profile D-state sleeping (millisecs). 3840 Requires CONFIG_SCHEDSTATS 3841 Param: "kvm" - profile VM exits. 3842 Param: <number> - step/bucket size as a power of 2 for 3843 statistical time based profiling. 3844 3845 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk 3846 before loading. 3847 See Documentation/admin-guide/blockdev/ramdisk.rst. 3848 3849 prot_virt= [S390] enable hosting protected virtual machines 3850 isolated from the hypervisor (if hardware supports 3851 that). 3852 Format: <bool> 3853 3854 psi= [KNL] Enable or disable pressure stall information 3855 tracking. 3856 Format: <bool> 3857 3858 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 3859 probe for; one of (bare|imps|exps|lifebook|any). 3860 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 3861 per second. 3862 psmouse.resetafter= [HW,MOUSE] 3863 Try to reset the device after so many bad packets 3864 (0 = never). 3865 psmouse.resolution= 3866 [HW,MOUSE] Set desired mouse resolution, in dpi. 3867 psmouse.smartscroll= 3868 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 3869 0 = disabled, 1 = enabled (default). 3870 3871 pstore.backend= Specify the name of the pstore backend to use 3872 3873 pt. [PARIDE] 3874 See Documentation/admin-guide/blockdev/paride.rst. 3875 3876 pti= [X86_64] Control Page Table Isolation of user and 3877 kernel address spaces. Disabling this feature 3878 removes hardening, but improves performance of 3879 system calls and interrupts. 3880 3881 on - unconditionally enable 3882 off - unconditionally disable 3883 auto - kernel detects whether your CPU model is 3884 vulnerable to issues that PTI mitigates 3885 3886 Not specifying this option is equivalent to pti=auto. 3887 3888 nopti [X86_64] 3889 Equivalent to pti=off 3890 3891 pty.legacy_count= 3892 [KNL] Number of legacy pty's. Overwrites compiled-in 3893 default number. 3894 3895 quiet [KNL] Disable most log messages 3896 3897 r128= [HW,DRM] 3898 3899 raid= [HW,RAID] 3900 See Documentation/admin-guide/md.rst. 3901 3902 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 3903 See Documentation/admin-guide/blockdev/ramdisk.rst. 3904 3905 random.trust_cpu={on,off} 3906 [KNL] Enable or disable trusting the use of the 3907 CPU's random number generator (if available) to 3908 fully seed the kernel's CRNG. Default is controlled 3909 by CONFIG_RANDOM_TRUST_CPU. 3910 3911 ras=option[,option,...] [KNL] RAS-specific options 3912 3913 cec_disable [X86] 3914 Disable the Correctable Errors Collector, 3915 see CONFIG_RAS_CEC help text. 3916 3917 rcu_nocbs= [KNL] 3918 The argument is a cpu list, as described above, 3919 except that the string "all" can be used to 3920 specify every CPU on the system. 3921 3922 In kernels built with CONFIG_RCU_NOCB_CPU=y, set 3923 the specified list of CPUs to be no-callback CPUs. 3924 Invocation of these CPUs' RCU callbacks will be 3925 offloaded to "rcuox/N" kthreads created for that 3926 purpose, where "x" is "p" for RCU-preempt, and 3927 "s" for RCU-sched, and "N" is the CPU number. 3928 This reduces OS jitter on the offloaded CPUs, 3929 which can be useful for HPC and real-time 3930 workloads. It can also improve energy efficiency 3931 for asymmetric multiprocessors. 3932 3933 rcu_nocb_poll [KNL] 3934 Rather than requiring that offloaded CPUs 3935 (specified by rcu_nocbs= above) explicitly 3936 awaken the corresponding "rcuoN" kthreads, 3937 make these kthreads poll for callbacks. 3938 This improves the real-time response for the 3939 offloaded CPUs by relieving them of the need to 3940 wake up the corresponding kthread, but degrades 3941 energy efficiency by requiring that the kthreads 3942 periodically wake up to do the polling. 3943 3944 rcutree.blimit= [KNL] 3945 Set maximum number of finished RCU callbacks to 3946 process in one batch. 3947 3948 rcutree.dump_tree= [KNL] 3949 Dump the structure of the rcu_node combining tree 3950 out at early boot. This is used for diagnostic 3951 purposes, to verify correct tree setup. 3952 3953 rcutree.gp_cleanup_delay= [KNL] 3954 Set the number of jiffies to delay each step of 3955 RCU grace-period cleanup. 3956 3957 rcutree.gp_init_delay= [KNL] 3958 Set the number of jiffies to delay each step of 3959 RCU grace-period initialization. 3960 3961 rcutree.gp_preinit_delay= [KNL] 3962 Set the number of jiffies to delay each step of 3963 RCU grace-period pre-initialization, that is, 3964 the propagation of recent CPU-hotplug changes up 3965 the rcu_node combining tree. 3966 3967 rcutree.use_softirq= [KNL] 3968 If set to zero, move all RCU_SOFTIRQ processing to 3969 per-CPU rcuc kthreads. Defaults to a non-zero 3970 value, meaning that RCU_SOFTIRQ is used by default. 3971 Specify rcutree.use_softirq=0 to use rcuc kthreads. 3972 3973 rcutree.rcu_fanout_exact= [KNL] 3974 Disable autobalancing of the rcu_node combining 3975 tree. This is used by rcutorture, and might 3976 possibly be useful for architectures having high 3977 cache-to-cache transfer latencies. 3978 3979 rcutree.rcu_fanout_leaf= [KNL] 3980 Change the number of CPUs assigned to each 3981 leaf rcu_node structure. Useful for very 3982 large systems, which will choose the value 64, 3983 and for NUMA systems with large remote-access 3984 latencies, which will choose a value aligned 3985 with the appropriate hardware boundaries. 3986 3987 rcutree.jiffies_till_first_fqs= [KNL] 3988 Set delay from grace-period initialization to 3989 first attempt to force quiescent states. 3990 Units are jiffies, minimum value is zero, 3991 and maximum value is HZ. 3992 3993 rcutree.jiffies_till_next_fqs= [KNL] 3994 Set delay between subsequent attempts to force 3995 quiescent states. Units are jiffies, minimum 3996 value is one, and maximum value is HZ. 3997 3998 rcutree.jiffies_till_sched_qs= [KNL] 3999 Set required age in jiffies for a 4000 given grace period before RCU starts 4001 soliciting quiescent-state help from 4002 rcu_note_context_switch() and cond_resched(). 4003 If not specified, the kernel will calculate 4004 a value based on the most recent settings 4005 of rcutree.jiffies_till_first_fqs 4006 and rcutree.jiffies_till_next_fqs. 4007 This calculated value may be viewed in 4008 rcutree.jiffies_to_sched_qs. Any attempt to set 4009 rcutree.jiffies_to_sched_qs will be cheerfully 4010 overwritten. 4011 4012 rcutree.kthread_prio= [KNL,BOOT] 4013 Set the SCHED_FIFO priority of the RCU per-CPU 4014 kthreads (rcuc/N). This value is also used for 4015 the priority of the RCU boost threads (rcub/N) 4016 and for the RCU grace-period kthreads (rcu_bh, 4017 rcu_preempt, and rcu_sched). If RCU_BOOST is 4018 set, valid values are 1-99 and the default is 1 4019 (the least-favored priority). Otherwise, when 4020 RCU_BOOST is not set, valid values are 0-99 and 4021 the default is zero (non-realtime operation). 4022 4023 rcutree.rcu_nocb_gp_stride= [KNL] 4024 Set the number of NOCB callback kthreads in 4025 each group, which defaults to the square root 4026 of the number of CPUs. Larger numbers reduce 4027 the wakeup overhead on the global grace-period 4028 kthread, but increases that same overhead on 4029 each group's NOCB grace-period kthread. 4030 4031 rcutree.qhimark= [KNL] 4032 Set threshold of queued RCU callbacks beyond which 4033 batch limiting is disabled. 4034 4035 rcutree.qlowmark= [KNL] 4036 Set threshold of queued RCU callbacks below which 4037 batch limiting is re-enabled. 4038 4039 rcutree.qovld= [KNL] 4040 Set threshold of queued RCU callbacks beyond which 4041 RCU's force-quiescent-state scan will aggressively 4042 enlist help from cond_resched() and sched IPIs to 4043 help CPUs more quickly reach quiescent states. 4044 Set to less than zero to make this be set based 4045 on rcutree.qhimark at boot time and to zero to 4046 disable more aggressive help enlistment. 4047 4048 rcutree.rcu_idle_gp_delay= [KNL] 4049 Set wakeup interval for idle CPUs that have 4050 RCU callbacks (RCU_FAST_NO_HZ=y). 4051 4052 rcutree.rcu_idle_lazy_gp_delay= [KNL] 4053 Set wakeup interval for idle CPUs that have 4054 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y). 4055 Lazy RCU callbacks are those which RCU can 4056 prove do nothing more than free memory. 4057 4058 rcutree.rcu_kick_kthreads= [KNL] 4059 Cause the grace-period kthread to get an extra 4060 wake_up() if it sleeps three times longer than 4061 it should at force-quiescent-state time. 4062 This wake_up() will be accompanied by a 4063 WARN_ONCE() splat and an ftrace_dump(). 4064 4065 rcutree.sysrq_rcu= [KNL] 4066 Commandeer a sysrq key to dump out Tree RCU's 4067 rcu_node tree with an eye towards determining 4068 why a new grace period has not yet started. 4069 4070 rcuperf.gp_async= [KNL] 4071 Measure performance of asynchronous 4072 grace-period primitives such as call_rcu(). 4073 4074 rcuperf.gp_async_max= [KNL] 4075 Specify the maximum number of outstanding 4076 callbacks per writer thread. When a writer 4077 thread exceeds this limit, it invokes the 4078 corresponding flavor of rcu_barrier() to allow 4079 previously posted callbacks to drain. 4080 4081 rcuperf.gp_exp= [KNL] 4082 Measure performance of expedited synchronous 4083 grace-period primitives. 4084 4085 rcuperf.holdoff= [KNL] 4086 Set test-start holdoff period. The purpose of 4087 this parameter is to delay the start of the 4088 test until boot completes in order to avoid 4089 interference. 4090 4091 rcuperf.kfree_rcu_test= [KNL] 4092 Set to measure performance of kfree_rcu() flooding. 4093 4094 rcuperf.kfree_nthreads= [KNL] 4095 The number of threads running loops of kfree_rcu(). 4096 4097 rcuperf.kfree_alloc_num= [KNL] 4098 Number of allocations and frees done in an iteration. 4099 4100 rcuperf.kfree_loops= [KNL] 4101 Number of loops doing rcuperf.kfree_alloc_num number 4102 of allocations and frees. 4103 4104 rcuperf.nreaders= [KNL] 4105 Set number of RCU readers. The value -1 selects 4106 N, where N is the number of CPUs. A value 4107 "n" less than -1 selects N-n+1, where N is again 4108 the number of CPUs. For example, -2 selects N 4109 (the number of CPUs), -3 selects N+1, and so on. 4110 A value of "n" less than or equal to -N selects 4111 a single reader. 4112 4113 rcuperf.nwriters= [KNL] 4114 Set number of RCU writers. The values operate 4115 the same as for rcuperf.nreaders. 4116 N, where N is the number of CPUs 4117 4118 rcuperf.perf_type= [KNL] 4119 Specify the RCU implementation to test. 4120 4121 rcuperf.shutdown= [KNL] 4122 Shut the system down after performance tests 4123 complete. This is useful for hands-off automated 4124 testing. 4125 4126 rcuperf.verbose= [KNL] 4127 Enable additional printk() statements. 4128 4129 rcuperf.writer_holdoff= [KNL] 4130 Write-side holdoff between grace periods, 4131 in microseconds. The default of zero says 4132 no holdoff. 4133 4134 rcutorture.fqs_duration= [KNL] 4135 Set duration of force_quiescent_state bursts 4136 in microseconds. 4137 4138 rcutorture.fqs_holdoff= [KNL] 4139 Set holdoff time within force_quiescent_state bursts 4140 in microseconds. 4141 4142 rcutorture.fqs_stutter= [KNL] 4143 Set wait time between force_quiescent_state bursts 4144 in seconds. 4145 4146 rcutorture.fwd_progress= [KNL] 4147 Enable RCU grace-period forward-progress testing 4148 for the types of RCU supporting this notion. 4149 4150 rcutorture.fwd_progress_div= [KNL] 4151 Specify the fraction of a CPU-stall-warning 4152 period to do tight-loop forward-progress testing. 4153 4154 rcutorture.fwd_progress_holdoff= [KNL] 4155 Number of seconds to wait between successive 4156 forward-progress tests. 4157 4158 rcutorture.fwd_progress_need_resched= [KNL] 4159 Enclose cond_resched() calls within checks for 4160 need_resched() during tight-loop forward-progress 4161 testing. 4162 4163 rcutorture.gp_cond= [KNL] 4164 Use conditional/asynchronous update-side 4165 primitives, if available. 4166 4167 rcutorture.gp_exp= [KNL] 4168 Use expedited update-side primitives, if available. 4169 4170 rcutorture.gp_normal= [KNL] 4171 Use normal (non-expedited) asynchronous 4172 update-side primitives, if available. 4173 4174 rcutorture.gp_sync= [KNL] 4175 Use normal (non-expedited) synchronous 4176 update-side primitives, if available. If all 4177 of rcutorture.gp_cond=, rcutorture.gp_exp=, 4178 rcutorture.gp_normal=, and rcutorture.gp_sync= 4179 are zero, rcutorture acts as if is interpreted 4180 they are all non-zero. 4181 4182 rcutorture.n_barrier_cbs= [KNL] 4183 Set callbacks/threads for rcu_barrier() testing. 4184 4185 rcutorture.nfakewriters= [KNL] 4186 Set number of concurrent RCU writers. These just 4187 stress RCU, they don't participate in the actual 4188 test, hence the "fake". 4189 4190 rcutorture.nreaders= [KNL] 4191 Set number of RCU readers. The value -1 selects 4192 N-1, where N is the number of CPUs. A value 4193 "n" less than -1 selects N-n-2, where N is again 4194 the number of CPUs. For example, -2 selects N 4195 (the number of CPUs), -3 selects N+1, and so on. 4196 4197 rcutorture.object_debug= [KNL] 4198 Enable debug-object double-call_rcu() testing. 4199 4200 rcutorture.onoff_holdoff= [KNL] 4201 Set time (s) after boot for CPU-hotplug testing. 4202 4203 rcutorture.onoff_interval= [KNL] 4204 Set time (jiffies) between CPU-hotplug operations, 4205 or zero to disable CPU-hotplug testing. 4206 4207 rcutorture.shuffle_interval= [KNL] 4208 Set task-shuffle interval (s). Shuffling tasks 4209 allows some CPUs to go into dyntick-idle mode 4210 during the rcutorture test. 4211 4212 rcutorture.shutdown_secs= [KNL] 4213 Set time (s) after boot system shutdown. This 4214 is useful for hands-off automated testing. 4215 4216 rcutorture.stall_cpu= [KNL] 4217 Duration of CPU stall (s) to test RCU CPU stall 4218 warnings, zero to disable. 4219 4220 rcutorture.stall_cpu_block= [KNL] 4221 Sleep while stalling if set. This will result 4222 in warnings from preemptible RCU in addition 4223 to any other stall-related activity. 4224 4225 rcutorture.stall_cpu_holdoff= [KNL] 4226 Time to wait (s) after boot before inducing stall. 4227 4228 rcutorture.stall_cpu_irqsoff= [KNL] 4229 Disable interrupts while stalling if set. 4230 4231 rcutorture.stall_gp_kthread= [KNL] 4232 Duration (s) of forced sleep within RCU 4233 grace-period kthread to test RCU CPU stall 4234 warnings, zero to disable. If both stall_cpu 4235 and stall_gp_kthread are specified, the 4236 kthread is starved first, then the CPU. 4237 4238 rcutorture.stat_interval= [KNL] 4239 Time (s) between statistics printk()s. 4240 4241 rcutorture.stutter= [KNL] 4242 Time (s) to stutter testing, for example, specifying 4243 five seconds causes the test to run for five seconds, 4244 wait for five seconds, and so on. This tests RCU's 4245 ability to transition abruptly to and from idle. 4246 4247 rcutorture.test_boost= [KNL] 4248 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 4249 "Maybe" means test if the RCU implementation 4250 under test support RCU priority boosting. 4251 4252 rcutorture.test_boost_duration= [KNL] 4253 Duration (s) of each individual boost test. 4254 4255 rcutorture.test_boost_interval= [KNL] 4256 Interval (s) between each boost test. 4257 4258 rcutorture.test_no_idle_hz= [KNL] 4259 Test RCU's dyntick-idle handling. See also the 4260 rcutorture.shuffle_interval parameter. 4261 4262 rcutorture.torture_type= [KNL] 4263 Specify the RCU implementation to test. 4264 4265 rcutorture.verbose= [KNL] 4266 Enable additional printk() statements. 4267 4268 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL] 4269 Dump ftrace buffer after reporting RCU CPU 4270 stall warning. 4271 4272 rcupdate.rcu_cpu_stall_suppress= [KNL] 4273 Suppress RCU CPU stall warning messages. 4274 4275 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL] 4276 Suppress RCU CPU stall warning messages and 4277 rcutorture writer stall warnings that occur 4278 during early boot, that is, during the time 4279 before the init task is spawned. 4280 4281 rcupdate.rcu_cpu_stall_timeout= [KNL] 4282 Set timeout for RCU CPU stall warning messages. 4283 4284 rcupdate.rcu_expedited= [KNL] 4285 Use expedited grace-period primitives, for 4286 example, synchronize_rcu_expedited() instead 4287 of synchronize_rcu(). This reduces latency, 4288 but can increase CPU utilization, degrade 4289 real-time latency, and degrade energy efficiency. 4290 No effect on CONFIG_TINY_RCU kernels. 4291 4292 rcupdate.rcu_normal= [KNL] 4293 Use only normal grace-period primitives, 4294 for example, synchronize_rcu() instead of 4295 synchronize_rcu_expedited(). This improves 4296 real-time latency, CPU utilization, and 4297 energy efficiency, but can expose users to 4298 increased grace-period latency. This parameter 4299 overrides rcupdate.rcu_expedited. No effect on 4300 CONFIG_TINY_RCU kernels. 4301 4302 rcupdate.rcu_normal_after_boot= [KNL] 4303 Once boot has completed (that is, after 4304 rcu_end_inkernel_boot() has been invoked), use 4305 only normal grace-period primitives. No effect 4306 on CONFIG_TINY_RCU kernels. 4307 4308 rcupdate.rcu_task_ipi_delay= [KNL] 4309 Set time in jiffies during which RCU tasks will 4310 avoid sending IPIs, starting with the beginning 4311 of a given grace period. Setting a large 4312 number avoids disturbing real-time workloads, 4313 but lengthens grace periods. 4314 4315 rcupdate.rcu_task_stall_timeout= [KNL] 4316 Set timeout in jiffies for RCU task stall warning 4317 messages. Disable with a value less than or equal 4318 to zero. 4319 4320 rcupdate.rcu_self_test= [KNL] 4321 Run the RCU early boot self tests 4322 4323 rdinit= [KNL] 4324 Format: <full_path> 4325 Run specified binary instead of /init from the ramdisk, 4326 used for early userspace startup. See initrd. 4327 4328 rdrand= [X86] 4329 force - Override the decision by the kernel to hide the 4330 advertisement of RDRAND support (this affects 4331 certain AMD processors because of buggy BIOS 4332 support, specifically around the suspend/resume 4333 path). 4334 4335 rdt= [HW,X86,RDT] 4336 Turn on/off individual RDT features. List is: 4337 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, 4338 mba. 4339 E.g. to turn on cmt and turn off mba use: 4340 rdt=cmt,!mba 4341 4342 reboot= [KNL] 4343 Format (x86 or x86_64): 4344 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \ 4345 [[,]s[mp]#### \ 4346 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 4347 [[,]f[orce] 4348 Where reboot_mode is one of warm (soft) or cold (hard) or gpio 4349 (prefix with 'panic_' to set mode for panic 4350 reboot only), 4351 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 4352 reboot_force is either force or not specified, 4353 reboot_cpu is s[mp]#### with #### being the processor 4354 to be used for rebooting. 4355 4356 relax_domain_level= 4357 [KNL, SMP] Set scheduler's default relax_domain_level. 4358 See Documentation/admin-guide/cgroup-v1/cpusets.rst. 4359 4360 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory 4361 Format: <base1>,<size1>[,<base2>,<size2>,...] 4362 Reserve I/O ports or memory so the kernel won't use 4363 them. If <base> is less than 0x10000, the region 4364 is assumed to be I/O ports; otherwise it is memory. 4365 4366 reservetop= [X86-32] 4367 Format: nn[KMG] 4368 Reserves a hole at the top of the kernel virtual 4369 address space. 4370 4371 reservelow= [X86] 4372 Format: nn[K] 4373 Set the amount of memory to reserve for BIOS at 4374 the bottom of the address space. 4375 4376 reset_devices [KNL] Force drivers to reset the underlying device 4377 during initialization. 4378 4379 resume= [SWSUSP] 4380 Specify the partition device for software suspend 4381 Format: 4382 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 4383 4384 resume_offset= [SWSUSP] 4385 Specify the offset from the beginning of the partition 4386 given by "resume=" at which the swap header is located, 4387 in <PAGE_SIZE> units (needed only for swap files). 4388 See Documentation/power/swsusp-and-swap-files.rst 4389 4390 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 4391 read the resume files 4392 4393 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 4394 Useful for devices that are detected asynchronously 4395 (e.g. USB and MMC devices). 4396 4397 hibernate= [HIBERNATION] 4398 noresume Don't check if there's a hibernation image 4399 present during boot. 4400 nocompress Don't compress/decompress hibernation images. 4401 no Disable hibernation and resume. 4402 protect_image Turn on image protection during restoration 4403 (that will set all pages holding image data 4404 during restoration read-only). 4405 4406 retain_initrd [RAM] Keep initrd memory after extraction 4407 4408 rfkill.default_state= 4409 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 4410 etc. communication is blocked by default. 4411 1 Unblocked. 4412 4413 rfkill.master_switch_mode= 4414 0 The "airplane mode" button does nothing. 4415 1 The "airplane mode" button toggles between everything 4416 blocked and the previous configuration. 4417 2 The "airplane mode" button toggles between everything 4418 blocked and everything unblocked. 4419 4420 rhash_entries= [KNL,NET] 4421 Set number of hash buckets for route cache 4422 4423 ring3mwait=disable 4424 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 4425 CPUs. 4426 4427 ro [KNL] Mount root device read-only on boot 4428 4429 rodata= [KNL] 4430 on Mark read-only kernel memory as read-only (default). 4431 off Leave read-only kernel memory writable for debugging. 4432 4433 rockchip.usb_uart 4434 Enable the uart passthrough on the designated usb port 4435 on Rockchip SoCs. When active, the signals of the 4436 debug-uart get routed to the D+ and D- pins of the usb 4437 port and the regular usb controller gets disabled. 4438 4439 root= [KNL] Root filesystem 4440 See name_to_dev_t comment in init/do_mounts.c. 4441 4442 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 4443 mount the root filesystem 4444 4445 rootflags= [KNL] Set root filesystem mount option string 4446 4447 rootfstype= [KNL] Set root filesystem type 4448 4449 rootwait [KNL] Wait (indefinitely) for root device to show up. 4450 Useful for devices that are detected asynchronously 4451 (e.g. USB and MMC devices). 4452 4453 rproc_mem=nn[KMG][@address] 4454 [KNL,ARM,CMA] Remoteproc physical memory block. 4455 Memory area to be used by remote processor image, 4456 managed by CMA. 4457 4458 rw [KNL] Mount root device read-write on boot 4459 4460 S [KNL] Run init in single mode 4461 4462 s390_iommu= [HW,S390] 4463 Set s390 IOTLB flushing mode 4464 strict 4465 With strict flushing every unmap operation will result in 4466 an IOTLB flush. Default is lazy flushing before reuse, 4467 which is faster. 4468 4469 sa1100ir [NET] 4470 See drivers/net/irda/sa1100_ir.c. 4471 4472 sbni= [NET] Granch SBNI12 leased line adapter 4473 4474 sched_debug [KNL] Enables verbose scheduler debug messages. 4475 4476 schedstats= [KNL,X86] Enable or disable scheduled statistics. 4477 Allowed values are enable and disable. This feature 4478 incurs a small amount of overhead in the scheduler 4479 but is useful for debugging and performance tuning. 4480 4481 sched_thermal_decay_shift= 4482 [KNL, SMP] Set a decay shift for scheduler thermal 4483 pressure signal. Thermal pressure signal follows the 4484 default decay period of other scheduler pelt 4485 signals(usually 32 ms but configurable). Setting 4486 sched_thermal_decay_shift will left shift the decay 4487 period for the thermal pressure signal by the shift 4488 value. 4489 i.e. with the default pelt decay period of 32 ms 4490 sched_thermal_decay_shift thermal pressure decay pr 4491 1 64 ms 4492 2 128 ms 4493 and so on. 4494 Format: integer between 0 and 10 4495 Default is 0. 4496 4497 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate 4498 xtime_lock contention on larger systems, and/or RCU lock 4499 contention on all systems with CONFIG_MAXSMP set. 4500 Format: { "0" | "1" } 4501 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 4502 1 -- enable. 4503 Note: increases power consumption, thus should only be 4504 enabled if running jitter sensitive (HPC/RT) workloads. 4505 4506 security= [SECURITY] Choose a legacy "major" security module to 4507 enable at boot. This has been deprecated by the 4508 "lsm=" parameter. 4509 4510 selinux= [SELINUX] Disable or enable SELinux at boot time. 4511 Format: { "0" | "1" } 4512 See security/selinux/Kconfig help text. 4513 0 -- disable. 4514 1 -- enable. 4515 Default value is 1. 4516 4517 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 4518 Format: { "0" | "1" } 4519 See security/apparmor/Kconfig help text 4520 0 -- disable. 4521 1 -- enable. 4522 Default value is set via kernel config option. 4523 4524 serialnumber [BUGS=X86-32] 4525 4526 shapers= [NET] 4527 Maximal number of shapers. 4528 4529 simeth= [IA-64] 4530 simscsi= 4531 4532 slram= [HW,MTD] 4533 4534 slab_nomerge [MM] 4535 Disable merging of slabs with similar size. May be 4536 necessary if there is some reason to distinguish 4537 allocs to different slabs, especially in hardened 4538 environments where the risk of heap overflows and 4539 layout control by attackers can usually be 4540 frustrated by disabling merging. This will reduce 4541 most of the exposure of a heap attack to a single 4542 cache (risks via metadata attacks are mostly 4543 unchanged). Debug options disable merging on their 4544 own. 4545 For more information see Documentation/vm/slub.rst. 4546 4547 slab_max_order= [MM, SLAB] 4548 Determines the maximum allowed order for slabs. 4549 A high setting may cause OOMs due to memory 4550 fragmentation. Defaults to 1 for systems with 4551 more than 32MB of RAM, 0 otherwise. 4552 4553 slub_debug[=options[,slabs]] [MM, SLUB] 4554 Enabling slub_debug allows one to determine the 4555 culprit if slab objects become corrupted. Enabling 4556 slub_debug can create guard zones around objects and 4557 may poison objects when not in use. Also tracks the 4558 last alloc / free. For more information see 4559 Documentation/vm/slub.rst. 4560 4561 slub_memcg_sysfs= [MM, SLUB] 4562 Determines whether to enable sysfs directories for 4563 memory cgroup sub-caches. 1 to enable, 0 to disable. 4564 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON. 4565 Enabling this can lead to a very high number of debug 4566 directories and files being created under 4567 /sys/kernel/slub. 4568 4569 slub_max_order= [MM, SLUB] 4570 Determines the maximum allowed order for slabs. 4571 A high setting may cause OOMs due to memory 4572 fragmentation. For more information see 4573 Documentation/vm/slub.rst. 4574 4575 slub_min_objects= [MM, SLUB] 4576 The minimum number of objects per slab. SLUB will 4577 increase the slab order up to slub_max_order to 4578 generate a sufficiently large slab able to contain 4579 the number of objects indicated. The higher the number 4580 of objects the smaller the overhead of tracking slabs 4581 and the less frequently locks need to be acquired. 4582 For more information see Documentation/vm/slub.rst. 4583 4584 slub_min_order= [MM, SLUB] 4585 Determines the minimum page order for slabs. Must be 4586 lower than slub_max_order. 4587 For more information see Documentation/vm/slub.rst. 4588 4589 slub_nomerge [MM, SLUB] 4590 Same with slab_nomerge. This is supported for legacy. 4591 See slab_nomerge for more information. 4592 4593 smart2= [HW] 4594 Format: <io1>[,<io2>[,...,<io8>]] 4595 4596 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 4597 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 4598 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 4599 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 4600 smsc-ircc2.ircc_irq= [HW] IRQ line 4601 smsc-ircc2.ircc_dma= [HW] DMA channel 4602 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 4603 0: Toshiba Satellite 1800 (GP data pin select) 4604 1: Fast pin select (default) 4605 2: ATC IRMode 4606 4607 smt [KNL,S390] Set the maximum number of threads (logical 4608 CPUs) to use per physical CPU on systems capable of 4609 symmetric multithreading (SMT). Will be capped to the 4610 actual hardware limit. 4611 Format: <integer> 4612 Default: -1 (no limit) 4613 4614 softlockup_panic= 4615 [KNL] Should the soft-lockup detector generate panics. 4616 Format: <integer> 4617 4618 A nonzero value instructs the soft-lockup detector 4619 to panic the machine when a soft-lockup occurs. It is 4620 also controlled by the kernel.softlockup_panic sysctl 4621 and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the 4622 respective build-time switch to that functionality. 4623 4624 softlockup_all_cpu_backtrace= 4625 [KNL] Should the soft-lockup detector generate 4626 backtraces on all cpus. 4627 Format: <integer> 4628 4629 sonypi.*= [HW] Sony Programmable I/O Control Device driver 4630 See Documentation/admin-guide/laptops/sonypi.rst 4631 4632 spectre_v2= [X86] Control mitigation of Spectre variant 2 4633 (indirect branch speculation) vulnerability. 4634 The default operation protects the kernel from 4635 user space attacks. 4636 4637 on - unconditionally enable, implies 4638 spectre_v2_user=on 4639 off - unconditionally disable, implies 4640 spectre_v2_user=off 4641 auto - kernel detects whether your CPU model is 4642 vulnerable 4643 4644 Selecting 'on' will, and 'auto' may, choose a 4645 mitigation method at run time according to the 4646 CPU, the available microcode, the setting of the 4647 CONFIG_RETPOLINE configuration option, and the 4648 compiler with which the kernel was built. 4649 4650 Selecting 'on' will also enable the mitigation 4651 against user space to user space task attacks. 4652 4653 Selecting 'off' will disable both the kernel and 4654 the user space protections. 4655 4656 Specific mitigations can also be selected manually: 4657 4658 retpoline - replace indirect branches 4659 retpoline,generic - google's original retpoline 4660 retpoline,amd - AMD-specific minimal thunk 4661 4662 Not specifying this option is equivalent to 4663 spectre_v2=auto. 4664 4665 spectre_v2_user= 4666 [X86] Control mitigation of Spectre variant 2 4667 (indirect branch speculation) vulnerability between 4668 user space tasks 4669 4670 on - Unconditionally enable mitigations. Is 4671 enforced by spectre_v2=on 4672 4673 off - Unconditionally disable mitigations. Is 4674 enforced by spectre_v2=off 4675 4676 prctl - Indirect branch speculation is enabled, 4677 but mitigation can be enabled via prctl 4678 per thread. The mitigation control state 4679 is inherited on fork. 4680 4681 prctl,ibpb 4682 - Like "prctl" above, but only STIBP is 4683 controlled per thread. IBPB is issued 4684 always when switching between different user 4685 space processes. 4686 4687 seccomp 4688 - Same as "prctl" above, but all seccomp 4689 threads will enable the mitigation unless 4690 they explicitly opt out. 4691 4692 seccomp,ibpb 4693 - Like "seccomp" above, but only STIBP is 4694 controlled per thread. IBPB is issued 4695 always when switching between different 4696 user space processes. 4697 4698 auto - Kernel selects the mitigation depending on 4699 the available CPU features and vulnerability. 4700 4701 Default mitigation: 4702 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl" 4703 4704 Not specifying this option is equivalent to 4705 spectre_v2_user=auto. 4706 4707 spec_store_bypass_disable= 4708 [HW] Control Speculative Store Bypass (SSB) Disable mitigation 4709 (Speculative Store Bypass vulnerability) 4710 4711 Certain CPUs are vulnerable to an exploit against a 4712 a common industry wide performance optimization known 4713 as "Speculative Store Bypass" in which recent stores 4714 to the same memory location may not be observed by 4715 later loads during speculative execution. The idea 4716 is that such stores are unlikely and that they can 4717 be detected prior to instruction retirement at the 4718 end of a particular speculation execution window. 4719 4720 In vulnerable processors, the speculatively forwarded 4721 store can be used in a cache side channel attack, for 4722 example to read memory to which the attacker does not 4723 directly have access (e.g. inside sandboxed code). 4724 4725 This parameter controls whether the Speculative Store 4726 Bypass optimization is used. 4727 4728 On x86 the options are: 4729 4730 on - Unconditionally disable Speculative Store Bypass 4731 off - Unconditionally enable Speculative Store Bypass 4732 auto - Kernel detects whether the CPU model contains an 4733 implementation of Speculative Store Bypass and 4734 picks the most appropriate mitigation. If the 4735 CPU is not vulnerable, "off" is selected. If the 4736 CPU is vulnerable the default mitigation is 4737 architecture and Kconfig dependent. See below. 4738 prctl - Control Speculative Store Bypass per thread 4739 via prctl. Speculative Store Bypass is enabled 4740 for a process by default. The state of the control 4741 is inherited on fork. 4742 seccomp - Same as "prctl" above, but all seccomp threads 4743 will disable SSB unless they explicitly opt out. 4744 4745 Default mitigations: 4746 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl" 4747 4748 On powerpc the options are: 4749 4750 on,auto - On Power8 and Power9 insert a store-forwarding 4751 barrier on kernel entry and exit. On Power7 4752 perform a software flush on kernel entry and 4753 exit. 4754 off - No action. 4755 4756 Not specifying this option is equivalent to 4757 spec_store_bypass_disable=auto. 4758 4759 spia_io_base= [HW,MTD] 4760 spia_fio_base= 4761 spia_pedr= 4762 spia_peddr= 4763 4764 split_lock_detect= 4765 [X86] Enable split lock detection 4766 4767 When enabled (and if hardware support is present), atomic 4768 instructions that access data across cache line 4769 boundaries will result in an alignment check exception. 4770 4771 off - not enabled 4772 4773 warn - the kernel will emit rate limited warnings 4774 about applications triggering the #AC 4775 exception. This mode is the default on CPUs 4776 that supports split lock detection. 4777 4778 fatal - the kernel will send SIGBUS to applications 4779 that trigger the #AC exception. 4780 4781 If an #AC exception is hit in the kernel or in 4782 firmware (i.e. not while executing in user mode) 4783 the kernel will oops in either "warn" or "fatal" 4784 mode. 4785 4786 srcutree.counter_wrap_check [KNL] 4787 Specifies how frequently to check for 4788 grace-period sequence counter wrap for the 4789 srcu_data structure's ->srcu_gp_seq_needed field. 4790 The greater the number of bits set in this kernel 4791 parameter, the less frequently counter wrap will 4792 be checked for. Note that the bottom two bits 4793 are ignored. 4794 4795 srcutree.exp_holdoff [KNL] 4796 Specifies how many nanoseconds must elapse 4797 since the end of the last SRCU grace period for 4798 a given srcu_struct until the next normal SRCU 4799 grace period will be considered for automatic 4800 expediting. Set to zero to disable automatic 4801 expediting. 4802 4803 ssbd= [ARM64,HW] 4804 Speculative Store Bypass Disable control 4805 4806 On CPUs that are vulnerable to the Speculative 4807 Store Bypass vulnerability and offer a 4808 firmware based mitigation, this parameter 4809 indicates how the mitigation should be used: 4810 4811 force-on: Unconditionally enable mitigation for 4812 for both kernel and userspace 4813 force-off: Unconditionally disable mitigation for 4814 for both kernel and userspace 4815 kernel: Always enable mitigation in the 4816 kernel, and offer a prctl interface 4817 to allow userspace to register its 4818 interest in being mitigated too. 4819 4820 stack_guard_gap= [MM] 4821 override the default stack gap protection. The value 4822 is in page units and it defines how many pages prior 4823 to (for stacks growing down) resp. after (for stacks 4824 growing up) the main stack are reserved for no other 4825 mapping. Default value is 256 pages. 4826 4827 stacktrace [FTRACE] 4828 Enabled the stack tracer on boot up. 4829 4830 stacktrace_filter=[function-list] 4831 [FTRACE] Limit the functions that the stack tracer 4832 will trace at boot up. function-list is a comma separated 4833 list of functions. This list can be changed at run 4834 time by the stack_trace_filter file in the debugfs 4835 tracing directory. Note, this enables stack tracing 4836 and the stacktrace above is not needed. 4837 4838 sti= [PARISC,HW] 4839 Format: <num> 4840 Set the STI (builtin display/keyboard on the HP-PARISC 4841 machines) console (graphic card) which should be used 4842 as the initial boot-console. 4843 See also comment in drivers/video/console/sticore.c. 4844 4845 sti_font= [HW] 4846 See comment in drivers/video/console/sticore.c. 4847 4848 stifb= [HW] 4849 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 4850 4851 sunrpc.min_resvport= 4852 sunrpc.max_resvport= 4853 [NFS,SUNRPC] 4854 SunRPC servers often require that client requests 4855 originate from a privileged port (i.e. a port in the 4856 range 0 < portnr < 1024). 4857 An administrator who wishes to reserve some of these 4858 ports for other uses may adjust the range that the 4859 kernel's sunrpc client considers to be privileged 4860 using these two parameters to set the minimum and 4861 maximum port values. 4862 4863 sunrpc.svc_rpc_per_connection_limit= 4864 [NFS,SUNRPC] 4865 Limit the number of requests that the server will 4866 process in parallel from a single connection. 4867 The default value is 0 (no limit). 4868 4869 sunrpc.pool_mode= 4870 [NFS] 4871 Control how the NFS server code allocates CPUs to 4872 service thread pools. Depending on how many NICs 4873 you have and where their interrupts are bound, this 4874 option will affect which CPUs will do NFS serving. 4875 Note: this parameter cannot be changed while the 4876 NFS server is running. 4877 4878 auto the server chooses an appropriate mode 4879 automatically using heuristics 4880 global a single global pool contains all CPUs 4881 percpu one pool for each CPU 4882 pernode one pool for each NUMA node (equivalent 4883 to global on non-NUMA machines) 4884 4885 sunrpc.tcp_slot_table_entries= 4886 sunrpc.udp_slot_table_entries= 4887 [NFS,SUNRPC] 4888 Sets the upper limit on the number of simultaneous 4889 RPC calls that can be sent from the client to a 4890 server. Increasing these values may allow you to 4891 improve throughput, but will also increase the 4892 amount of memory reserved for use by the client. 4893 4894 suspend.pm_test_delay= 4895 [SUSPEND] 4896 Sets the number of seconds to remain in a suspend test 4897 mode before resuming the system (see 4898 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 4899 is set. Default value is 5. 4900 4901 svm= [PPC] 4902 Format: { on | off | y | n | 1 | 0 } 4903 This parameter controls use of the Protected 4904 Execution Facility on pSeries. 4905 4906 swapaccount=[0|1] 4907 [KNL] Enable accounting of swap in memory resource 4908 controller if no parameter or 1 is given or disable 4909 it if 0 is given (See Documentation/admin-guide/cgroup-v1/memory.rst) 4910 4911 swiotlb= [ARM,IA-64,PPC,MIPS,X86] 4912 Format: { <int> | force | noforce } 4913 <int> -- Number of I/O TLB slabs 4914 force -- force using of bounce buffers even if they 4915 wouldn't be automatically used by the kernel 4916 noforce -- Never use bounce buffers (for debugging) 4917 4918 switches= [HW,M68k] 4919 4920 sysfs.deprecated=0|1 [KNL] 4921 Enable/disable old style sysfs layout for old udev 4922 on older distributions. When this option is enabled 4923 very new udev will not work anymore. When this option 4924 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled) 4925 in older udev will not work anymore. 4926 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in 4927 the kernel configuration. 4928 4929 sysrq_always_enabled 4930 [KNL] 4931 Ignore sysrq setting - this boot parameter will 4932 neutralize any effect of /proc/sys/kernel/sysrq. 4933 Useful for debugging. 4934 4935 tcpmhash_entries= [KNL,NET] 4936 Set the number of tcp_metrics_hash slots. 4937 Default value is 8192 or 16384 depending on total 4938 ram pages. This is used to specify the TCP metrics 4939 cache size. See Documentation/networking/ip-sysctl.txt 4940 "tcp_no_metrics_save" section for more details. 4941 4942 tdfx= [HW,DRM] 4943 4944 test_suspend= [SUSPEND][,N] 4945 Specify "mem" (for Suspend-to-RAM) or "standby" (for 4946 standby suspend) or "freeze" (for suspend type freeze) 4947 as the system sleep state during system startup with 4948 the optional capability to repeat N number of times. 4949 The system is woken from this state using a 4950 wakeup-capable RTC alarm. 4951 4952 thash_entries= [KNL,NET] 4953 Set number of hash buckets for TCP connection 4954 4955 thermal.act= [HW,ACPI] 4956 -1: disable all active trip points in all thermal zones 4957 <degrees C>: override all lowest active trip points 4958 4959 thermal.crt= [HW,ACPI] 4960 -1: disable all critical trip points in all thermal zones 4961 <degrees C>: override all critical trip points 4962 4963 thermal.nocrt= [HW,ACPI] 4964 Set to disable actions on ACPI thermal zone 4965 critical and hot trip points. 4966 4967 thermal.off= [HW,ACPI] 4968 1: disable ACPI thermal control 4969 4970 thermal.psv= [HW,ACPI] 4971 -1: disable all passive trip points 4972 <degrees C>: override all passive trip points to this 4973 value 4974 4975 thermal.tzp= [HW,ACPI] 4976 Specify global default ACPI thermal zone polling rate 4977 <deci-seconds>: poll all this frequency 4978 0: no polling (default) 4979 4980 threadirqs [KNL] 4981 Force threading of all interrupt handlers except those 4982 marked explicitly IRQF_NO_THREAD. 4983 4984 topology= [S390] 4985 Format: {off | on} 4986 Specify if the kernel should make use of the cpu 4987 topology information if the hardware supports this. 4988 The scheduler will make use of this information and 4989 e.g. base its process migration decisions on it. 4990 Default is on. 4991 4992 topology_updates= [KNL, PPC, NUMA] 4993 Format: {off} 4994 Specify if the kernel should ignore (off) 4995 topology updates sent by the hypervisor to this 4996 LPAR. 4997 4998 torture.disable_onoff_at_boot= [KNL] 4999 Prevent the CPU-hotplug component of torturing 5000 until after init has spawned. 5001 5002 tp720= [HW,PS2] 5003 5004 tpm_suspend_pcr=[HW,TPM] 5005 Format: integer pcr id 5006 Specify that at suspend time, the tpm driver 5007 should extend the specified pcr with zeros, 5008 as a workaround for some chips which fail to 5009 flush the last written pcr on TPM_SaveState. 5010 This will guarantee that all the other pcrs 5011 are saved. 5012 5013 trace_buf_size=nn[KMG] 5014 [FTRACE] will set tracing buffer size on each cpu. 5015 5016 trace_event=[event-list] 5017 [FTRACE] Set and start specified trace events in order 5018 to facilitate early boot debugging. The event-list is a 5019 comma separated list of trace events to enable. See 5020 also Documentation/trace/events.rst 5021 5022 trace_options=[option-list] 5023 [FTRACE] Enable or disable tracer options at boot. 5024 The option-list is a comma delimited list of options 5025 that can be enabled or disabled just as if you were 5026 to echo the option name into 5027 5028 /sys/kernel/debug/tracing/trace_options 5029 5030 For example, to enable stacktrace option (to dump the 5031 stack trace of each event), add to the command line: 5032 5033 trace_options=stacktrace 5034 5035 See also Documentation/trace/ftrace.rst "trace options" 5036 section. 5037 5038 tp_printk[FTRACE] 5039 Have the tracepoints sent to printk as well as the 5040 tracing ring buffer. This is useful for early boot up 5041 where the system hangs or reboots and does not give the 5042 option for reading the tracing buffer or performing a 5043 ftrace_dump_on_oops. 5044 5045 To turn off having tracepoints sent to printk, 5046 echo 0 > /proc/sys/kernel/tracepoint_printk 5047 Note, echoing 1 into this file without the 5048 tracepoint_printk kernel cmdline option has no effect. 5049 5050 ** CAUTION ** 5051 5052 Having tracepoints sent to printk() and activating high 5053 frequency tracepoints such as irq or sched, can cause 5054 the system to live lock. 5055 5056 traceoff_on_warning 5057 [FTRACE] enable this option to disable tracing when a 5058 warning is hit. This turns off "tracing_on". Tracing can 5059 be enabled again by echoing '1' into the "tracing_on" 5060 file located in /sys/kernel/debug/tracing/ 5061 5062 This option is useful, as it disables the trace before 5063 the WARNING dump is called, which prevents the trace to 5064 be filled with content caused by the warning output. 5065 5066 This option can also be set at run time via the sysctl 5067 option: kernel/traceoff_on_warning 5068 5069 transparent_hugepage= 5070 [KNL] 5071 Format: [always|madvise|never] 5072 Can be used to control the default behavior of the system 5073 with respect to transparent hugepages. 5074 See Documentation/admin-guide/mm/transhuge.rst 5075 for more details. 5076 5077 tsc= Disable clocksource stability checks for TSC. 5078 Format: <string> 5079 [x86] reliable: mark tsc clocksource as reliable, this 5080 disables clocksource verification at runtime, as well 5081 as the stability checks done at bootup. Used to enable 5082 high-resolution timer mode on older hardware, and in 5083 virtualized environment. 5084 [x86] noirqtime: Do not use TSC to do irq accounting. 5085 Used to run time disable IRQ_TIME_ACCOUNTING on any 5086 platforms where RDTSC is slow and this accounting 5087 can add overhead. 5088 [x86] unstable: mark the TSC clocksource as unstable, this 5089 marks the TSC unconditionally unstable at bootup and 5090 avoids any further wobbles once the TSC watchdog notices. 5091 [x86] nowatchdog: disable clocksource watchdog. Used 5092 in situations with strict latency requirements (where 5093 interruptions from clocksource watchdog are not 5094 acceptable). 5095 5096 tsx= [X86] Control Transactional Synchronization 5097 Extensions (TSX) feature in Intel processors that 5098 support TSX control. 5099 5100 This parameter controls the TSX feature. The options are: 5101 5102 on - Enable TSX on the system. Although there are 5103 mitigations for all known security vulnerabilities, 5104 TSX has been known to be an accelerator for 5105 several previous speculation-related CVEs, and 5106 so there may be unknown security risks associated 5107 with leaving it enabled. 5108 5109 off - Disable TSX on the system. (Note that this 5110 option takes effect only on newer CPUs which are 5111 not vulnerable to MDS, i.e., have 5112 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get 5113 the new IA32_TSX_CTRL MSR through a microcode 5114 update. This new MSR allows for the reliable 5115 deactivation of the TSX functionality.) 5116 5117 auto - Disable TSX if X86_BUG_TAA is present, 5118 otherwise enable TSX on the system. 5119 5120 Not specifying this option is equivalent to tsx=off. 5121 5122 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 5123 for more details. 5124 5125 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async 5126 Abort (TAA) vulnerability. 5127 5128 Similar to Micro-architectural Data Sampling (MDS) 5129 certain CPUs that support Transactional 5130 Synchronization Extensions (TSX) are vulnerable to an 5131 exploit against CPU internal buffers which can forward 5132 information to a disclosure gadget under certain 5133 conditions. 5134 5135 In vulnerable processors, the speculatively forwarded 5136 data can be used in a cache side channel attack, to 5137 access data to which the attacker does not have direct 5138 access. 5139 5140 This parameter controls the TAA mitigation. The 5141 options are: 5142 5143 full - Enable TAA mitigation on vulnerable CPUs 5144 if TSX is enabled. 5145 5146 full,nosmt - Enable TAA mitigation and disable SMT on 5147 vulnerable CPUs. If TSX is disabled, SMT 5148 is not disabled because CPU is not 5149 vulnerable to cross-thread TAA attacks. 5150 off - Unconditionally disable TAA mitigation 5151 5152 On MDS-affected machines, tsx_async_abort=off can be 5153 prevented by an active MDS mitigation as both vulnerabilities 5154 are mitigated with the same mechanism so in order to disable 5155 this mitigation, you need to specify mds=off too. 5156 5157 Not specifying this option is equivalent to 5158 tsx_async_abort=full. On CPUs which are MDS affected 5159 and deploy MDS mitigation, TAA mitigation is not 5160 required and doesn't provide any additional 5161 mitigation. 5162 5163 For details see: 5164 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 5165 5166 turbografx.map[2|3]= [HW,JOY] 5167 TurboGraFX parallel port interface 5168 Format: 5169 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 5170 See also Documentation/input/devices/joystick-parport.rst 5171 5172 udbg-immortal [PPC] When debugging early kernel crashes that 5173 happen after console_init() and before a proper 5174 console driver takes over, this boot options might 5175 help "seeing" what's going on. 5176 5177 uhash_entries= [KNL,NET] 5178 Set number of hash buckets for UDP/UDP-Lite connections 5179 5180 uhci-hcd.ignore_oc= 5181 [USB] Ignore overcurrent events (default N). 5182 Some badly-designed motherboards generate lots of 5183 bogus events, for ports that aren't wired to 5184 anything. Set this parameter to avoid log spamming. 5185 Note that genuine overcurrent events won't be 5186 reported either. 5187 5188 unknown_nmi_panic 5189 [X86] Cause panic on unknown NMI. 5190 5191 usbcore.authorized_default= 5192 [USB] Default USB device authorization: 5193 (default -1 = authorized except for wireless USB, 5194 0 = not authorized, 1 = authorized, 2 = authorized 5195 if device connected to internal port) 5196 5197 usbcore.autosuspend= 5198 [USB] The autosuspend time delay (in seconds) used 5199 for newly-detected USB devices (default 2). This 5200 is the time required before an idle device will be 5201 autosuspended. Devices for which the delay is set 5202 to a negative value won't be autosuspended at all. 5203 5204 usbcore.usbfs_snoop= 5205 [USB] Set to log all usbfs traffic (default 0 = off). 5206 5207 usbcore.usbfs_snoop_max= 5208 [USB] Maximum number of bytes to snoop in each URB 5209 (default = 65536). 5210 5211 usbcore.blinkenlights= 5212 [USB] Set to cycle leds on hubs (default 0 = off). 5213 5214 usbcore.old_scheme_first= 5215 [USB] Start with the old device initialization 5216 scheme (default 0 = off). 5217 5218 usbcore.usbfs_memory_mb= 5219 [USB] Memory limit (in MB) for buffers allocated by 5220 usbfs (default = 16, 0 = max = 2047). 5221 5222 usbcore.use_both_schemes= 5223 [USB] Try the other device initialization scheme 5224 if the first one fails (default 1 = enabled). 5225 5226 usbcore.initial_descriptor_timeout= 5227 [USB] Specifies timeout for the initial 64-byte 5228 USB_REQ_GET_DESCRIPTOR request in milliseconds 5229 (default 5000 = 5.0 seconds). 5230 5231 usbcore.nousb [USB] Disable the USB subsystem 5232 5233 usbcore.quirks= 5234 [USB] A list of quirk entries to augment the built-in 5235 usb core quirk list. List entries are separated by 5236 commas. Each entry has the form 5237 VendorID:ProductID:Flags. The IDs are 4-digit hex 5238 numbers and Flags is a set of letters. Each letter 5239 will change the built-in quirk; setting it if it is 5240 clear and clearing it if it is set. The letters have 5241 the following meanings: 5242 a = USB_QUIRK_STRING_FETCH_255 (string 5243 descriptors must not be fetched using 5244 a 255-byte read); 5245 b = USB_QUIRK_RESET_RESUME (device can't resume 5246 correctly so reset it instead); 5247 c = USB_QUIRK_NO_SET_INTF (device can't handle 5248 Set-Interface requests); 5249 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't 5250 handle its Configuration or Interface 5251 strings); 5252 e = USB_QUIRK_RESET (device can't be reset 5253 (e.g morph devices), don't use reset); 5254 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has 5255 more interface descriptions than the 5256 bNumInterfaces count, and can't handle 5257 talking to these interfaces); 5258 g = USB_QUIRK_DELAY_INIT (device needs a pause 5259 during initialization, after we read 5260 the device descriptor); 5261 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For 5262 high speed and super speed interrupt 5263 endpoints, the USB 2.0 and USB 3.0 spec 5264 require the interval in microframes (1 5265 microframe = 125 microseconds) to be 5266 calculated as interval = 2 ^ 5267 (bInterval-1). 5268 Devices with this quirk report their 5269 bInterval as the result of this 5270 calculation instead of the exponent 5271 variable used in the calculation); 5272 i = USB_QUIRK_DEVICE_QUALIFIER (device can't 5273 handle device_qualifier descriptor 5274 requests); 5275 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device 5276 generates spurious wakeup, ignore 5277 remote wakeup capability); 5278 k = USB_QUIRK_NO_LPM (device can't handle Link 5279 Power Management); 5280 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL 5281 (Device reports its bInterval as linear 5282 frames instead of the USB 2.0 5283 calculation); 5284 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs 5285 to be disconnected before suspend to 5286 prevent spurious wakeup); 5287 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a 5288 pause after every control message); 5289 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra 5290 delay after resetting its port); 5291 Example: quirks=0781:5580:bk,0a5c:5834:gij 5292 5293 usbhid.mousepoll= 5294 [USBHID] The interval which mice are to be polled at. 5295 5296 usbhid.jspoll= 5297 [USBHID] The interval which joysticks are to be polled at. 5298 5299 usbhid.kbpoll= 5300 [USBHID] The interval which keyboards are to be polled at. 5301 5302 usb-storage.delay_use= 5303 [UMS] The delay in seconds before a new device is 5304 scanned for Logical Units (default 1). 5305 5306 usb-storage.quirks= 5307 [UMS] A list of quirks entries to supplement or 5308 override the built-in unusual_devs list. List 5309 entries are separated by commas. Each entry has 5310 the form VID:PID:Flags where VID and PID are Vendor 5311 and Product ID values (4-digit hex numbers) and 5312 Flags is a set of characters, each corresponding 5313 to a common usb-storage quirk flag as follows: 5314 a = SANE_SENSE (collect more than 18 bytes 5315 of sense data, not on uas); 5316 b = BAD_SENSE (don't collect more than 18 5317 bytes of sense data, not on uas); 5318 c = FIX_CAPACITY (decrease the reported 5319 device capacity by one sector); 5320 d = NO_READ_DISC_INFO (don't use 5321 READ_DISC_INFO command, not on uas); 5322 e = NO_READ_CAPACITY_16 (don't use 5323 READ_CAPACITY_16 command); 5324 f = NO_REPORT_OPCODES (don't use report opcodes 5325 command, uas only); 5326 g = MAX_SECTORS_240 (don't transfer more than 5327 240 sectors at a time, uas only); 5328 h = CAPACITY_HEURISTICS (decrease the 5329 reported device capacity by one 5330 sector if the number is odd); 5331 i = IGNORE_DEVICE (don't bind to this 5332 device); 5333 j = NO_REPORT_LUNS (don't use report luns 5334 command, uas only); 5335 l = NOT_LOCKABLE (don't try to lock and 5336 unlock ejectable media, not on uas); 5337 m = MAX_SECTORS_64 (don't transfer more 5338 than 64 sectors = 32 KB at a time, 5339 not on uas); 5340 n = INITIAL_READ10 (force a retry of the 5341 initial READ(10) command, not on uas); 5342 o = CAPACITY_OK (accept the capacity 5343 reported by the device, not on uas); 5344 p = WRITE_CACHE (the device cache is ON 5345 by default, not on uas); 5346 r = IGNORE_RESIDUE (the device reports 5347 bogus residue values, not on uas); 5348 s = SINGLE_LUN (the device has only one 5349 Logical Unit); 5350 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 5351 commands, uas only); 5352 u = IGNORE_UAS (don't bind to the uas driver); 5353 w = NO_WP_DETECT (don't test whether the 5354 medium is write-protected). 5355 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 5356 even if the device claims no cache, 5357 not on uas) 5358 Example: quirks=0419:aaf5:rl,0421:0433:rc 5359 5360 user_debug= [KNL,ARM] 5361 Format: <int> 5362 See arch/arm/Kconfig.debug help text. 5363 1 - undefined instruction events 5364 2 - system calls 5365 4 - invalid data aborts 5366 8 - SIGSEGV faults 5367 16 - SIGBUS faults 5368 Example: user_debug=31 5369 5370 userpte= 5371 [X86] Flags controlling user PTE allocations. 5372 5373 nohigh = do not allocate PTE pages in 5374 HIGHMEM regardless of setting 5375 of CONFIG_HIGHPTE. 5376 5377 vdso= [X86,SH] 5378 On X86_32, this is an alias for vdso32=. Otherwise: 5379 5380 vdso=1: enable VDSO (the default) 5381 vdso=0: disable VDSO mapping 5382 5383 vdso32= [X86] Control the 32-bit vDSO 5384 vdso32=1: enable 32-bit VDSO 5385 vdso32=0 or vdso32=2: disable 32-bit VDSO 5386 5387 See the help text for CONFIG_COMPAT_VDSO for more 5388 details. If CONFIG_COMPAT_VDSO is set, the default is 5389 vdso32=0; otherwise, the default is vdso32=1. 5390 5391 For compatibility with older kernels, vdso32=2 is an 5392 alias for vdso32=0. 5393 5394 Try vdso32=0 if you encounter an error that says: 5395 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 5396 5397 vector= [IA-64,SMP] 5398 vector=percpu: enable percpu vector domain 5399 5400 video= [FB] Frame buffer configuration 5401 See Documentation/fb/modedb.rst. 5402 5403 video.brightness_switch_enabled= [0,1] 5404 If set to 1, on receiving an ACPI notify event 5405 generated by hotkey, video driver will adjust brightness 5406 level and then send out the event to user space through 5407 the allocated input device; If set to 0, video driver 5408 will only send out the event without touching backlight 5409 brightness level. 5410 default: 1 5411 5412 virtio_mmio.device= 5413 [VMMIO] Memory mapped virtio (platform) device. 5414 5415 <size>@<baseaddr>:<irq>[:<id>] 5416 where: 5417 <size> := size (can use standard suffixes 5418 like K, M and G) 5419 <baseaddr> := physical base address 5420 <irq> := interrupt number (as passed to 5421 request_irq()) 5422 <id> := (optional) platform device id 5423 example: 5424 virtio_mmio.device=1K@0x100b0000:48:7 5425 5426 Can be used multiple times for multiple devices. 5427 5428 vga= [BOOT,X86-32] Select a particular video mode 5429 See Documentation/x86/boot.rst and 5430 Documentation/admin-guide/svga.rst. 5431 Use vga=ask for menu. 5432 This is actually a boot loader parameter; the value is 5433 passed to the kernel using a special protocol. 5434 5435 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. 5436 May slow down system boot speed, especially when 5437 enabled on systems with a large amount of memory. 5438 All options are enabled by default, and this 5439 interface is meant to allow for selectively 5440 enabling or disabling specific virtual memory 5441 debugging features. 5442 5443 Available options are: 5444 P Enable page structure init time poisoning 5445 - Disable all of the above options 5446 5447 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact 5448 size of <nn>. This can be used to increase the 5449 minimum size (128MB on x86). It can also be used to 5450 decrease the size and leave more room for directly 5451 mapped kernel RAM. 5452 5453 vmcp_cma=nn[MG] [KNL,S390] 5454 Sets the memory size reserved for contiguous memory 5455 allocations for the vmcp device driver. 5456 5457 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 5458 Format: <command> 5459 5460 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 5461 Format: <command> 5462 5463 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 5464 Format: <command> 5465 5466 vsyscall= [X86-64] 5467 Controls the behavior of vsyscalls (i.e. calls to 5468 fixed addresses of 0xffffffffff600x00 from legacy 5469 code). Most statically-linked binaries and older 5470 versions of glibc use these calls. Because these 5471 functions are at fixed addresses, they make nice 5472 targets for exploits that can control RIP. 5473 5474 emulate [default] Vsyscalls turn into traps and are 5475 emulated reasonably safely. The vsyscall 5476 page is readable. 5477 5478 xonly Vsyscalls turn into traps and are 5479 emulated reasonably safely. The vsyscall 5480 page is not readable. 5481 5482 none Vsyscalls don't work at all. This makes 5483 them quite hard to use for exploits but 5484 might break your system. 5485 5486 vt.color= [VT] Default text color. 5487 Format: 0xYX, X = foreground, Y = background. 5488 Default: 0x07 = light gray on black. 5489 5490 vt.cur_default= [VT] Default cursor shape. 5491 Format: 0xCCBBAA, where AA, BB, and CC are the same as 5492 the parameters of the <Esc>[?A;B;Cc escape sequence; 5493 see VGA-softcursor.txt. Default: 2 = underline. 5494 5495 vt.default_blu= [VT] 5496 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 5497 Change the default blue palette of the console. 5498 This is a 16-member array composed of values 5499 ranging from 0-255. 5500 5501 vt.default_grn= [VT] 5502 Format: <green0>,<green1>,<green2>,...,<green15> 5503 Change the default green palette of the console. 5504 This is a 16-member array composed of values 5505 ranging from 0-255. 5506 5507 vt.default_red= [VT] 5508 Format: <red0>,<red1>,<red2>,...,<red15> 5509 Change the default red palette of the console. 5510 This is a 16-member array composed of values 5511 ranging from 0-255. 5512 5513 vt.default_utf8= 5514 [VT] 5515 Format=<0|1> 5516 Set system-wide default UTF-8 mode for all tty's. 5517 Default is 1, i.e. UTF-8 mode is enabled for all 5518 newly opened terminals. 5519 5520 vt.global_cursor_default= 5521 [VT] 5522 Format=<-1|0|1> 5523 Set system-wide default for whether a cursor 5524 is shown on new VTs. Default is -1, 5525 i.e. cursors will be created by default unless 5526 overridden by individual drivers. 0 will hide 5527 cursors, 1 will display them. 5528 5529 vt.italic= [VT] Default color for italic text; 0-15. 5530 Default: 2 = green. 5531 5532 vt.underline= [VT] Default color for underlined text; 0-15. 5533 Default: 3 = cyan. 5534 5535 watchdog timers [HW,WDT] For information on watchdog timers, 5536 see Documentation/watchdog/watchdog-parameters.rst 5537 or other driver-specific files in the 5538 Documentation/watchdog/ directory. 5539 5540 watchdog_thresh= 5541 [KNL] 5542 Set the hard lockup detector stall duration 5543 threshold in seconds. The soft lockup detector 5544 threshold is set to twice the value. A value of 0 5545 disables both lockup detectors. Default is 10 5546 seconds. 5547 5548 workqueue.watchdog_thresh= 5549 If CONFIG_WQ_WATCHDOG is configured, workqueue can 5550 warn stall conditions and dump internal state to 5551 help debugging. 0 disables workqueue stall 5552 detection; otherwise, it's the stall threshold 5553 duration in seconds. The default value is 30 and 5554 it can be updated at runtime by writing to the 5555 corresponding sysfs file. 5556 5557 workqueue.disable_numa 5558 By default, all work items queued to unbound 5559 workqueues are affine to the NUMA nodes they're 5560 issued on, which results in better behavior in 5561 general. If NUMA affinity needs to be disabled for 5562 whatever reason, this option can be used. Note 5563 that this also can be controlled per-workqueue for 5564 workqueues visible under /sys/bus/workqueue/. 5565 5566 workqueue.power_efficient 5567 Per-cpu workqueues are generally preferred because 5568 they show better performance thanks to cache 5569 locality; unfortunately, per-cpu workqueues tend to 5570 be more power hungry than unbound workqueues. 5571 5572 Enabling this makes the per-cpu workqueues which 5573 were observed to contribute significantly to power 5574 consumption unbound, leading to measurably lower 5575 power usage at the cost of small performance 5576 overhead. 5577 5578 The default value of this parameter is determined by 5579 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 5580 5581 workqueue.debug_force_rr_cpu 5582 Workqueue used to implicitly guarantee that work 5583 items queued without explicit CPU specified are put 5584 on the local CPU. This guarantee is no longer true 5585 and while local CPU is still preferred work items 5586 may be put on foreign CPUs. This debug option 5587 forces round-robin CPU selection to flush out 5588 usages which depend on the now broken guarantee. 5589 When enabled, memory and cache locality will be 5590 impacted. 5591 5592 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of 5593 default x2apic cluster mode on platforms 5594 supporting x2apic. 5595 5596 x86_intel_mid_timer= [X86-32,APBT] 5597 Choose timer option for x86 Intel MID platform. 5598 Two valid options are apbt timer only and lapic timer 5599 plus one apbt timer for broadcast timer. 5600 x86_intel_mid_timer=apbt_only | lapic_and_apbt 5601 5602 xen_512gb_limit [KNL,X86-64,XEN] 5603 Restricts the kernel running paravirtualized under Xen 5604 to use only up to 512 GB of RAM. The reason to do so is 5605 crash analysis tools and Xen tools for doing domain 5606 save/restore/migration must be enabled to handle larger 5607 domains. 5608 5609 xen_emul_unplug= [HW,X86,XEN] 5610 Unplug Xen emulated devices 5611 Format: [unplug0,][unplug1] 5612 ide-disks -- unplug primary master IDE devices 5613 aux-ide-disks -- unplug non-primary-master IDE devices 5614 nics -- unplug network devices 5615 all -- unplug all emulated devices (NICs and IDE disks) 5616 unnecessary -- unplugging emulated devices is 5617 unnecessary even if the host did not respond to 5618 the unplug protocol 5619 never -- do not unplug even if version check succeeds 5620 5621 xen_legacy_crash [X86,XEN] 5622 Crash from Xen panic notifier, without executing late 5623 panic() code such as dumping handler. 5624 5625 xen_nopvspin [X86,XEN] 5626 Disables the ticketlock slowpath using Xen PV 5627 optimizations. 5628 5629 xen_nopv [X86] 5630 Disables the PV optimizations forcing the HVM guest to 5631 run as generic HVM guest with no PV drivers. 5632 This option is obsoleted by the "nopv" option, which 5633 has equivalent effect for XEN platform. 5634 5635 xen_scrub_pages= [XEN] 5636 Boolean option to control scrubbing pages before giving them back 5637 to Xen, for use by other domains. Can be also changed at runtime 5638 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. 5639 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. 5640 5641 xen_timer_slop= [X86-64,XEN] 5642 Set the timer slop (in nanoseconds) for the virtual Xen 5643 timers (default is 100000). This adjusts the minimum 5644 delta of virtualized Xen timers, where lower values 5645 improve timer resolution at the expense of processing 5646 more timer interrupts. 5647 5648 nopv= [X86,XEN,KVM,HYPER_V,VMWARE] 5649 Disables the PV optimizations forcing the guest to run 5650 as generic guest with no PV drivers. Currently support 5651 XEN HVM, KVM, HYPER_V and VMWARE guest. 5652 5653 xirc2ps_cs= [NET,PCMCIA] 5654 Format: 5655 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 5656 5657 xive= [PPC] 5658 By default on POWER9 and above, the kernel will 5659 natively use the XIVE interrupt controller. This option 5660 allows the fallback firmware mode to be used: 5661 5662 off Fallback to firmware control of XIVE interrupt 5663 controller on both pseries and powernv 5664 platforms. Only useful on POWER9 and above. 5665 5666 xhci-hcd.quirks [USB,KNL] 5667 A hex value specifying bitmask with supplemental xhci 5668 host controller quirks. Meaning of each bit can be 5669 consulted in header drivers/usb/host/xhci.h. 5670 5671 xmon [PPC] 5672 Format: { early | on | rw | ro | off } 5673 Controls if xmon debugger is enabled. Default is off. 5674 Passing only "xmon" is equivalent to "xmon=early". 5675 early Call xmon as early as possible on boot; xmon 5676 debugger is called from setup_arch(). 5677 on xmon debugger hooks will be installed so xmon 5678 is only called on a kernel crash. Default mode, 5679 i.e. either "ro" or "rw" mode, is controlled 5680 with CONFIG_XMON_DEFAULT_RO_MODE. 5681 rw xmon debugger hooks will be installed so xmon 5682 is called only on a kernel crash, mode is write, 5683 meaning SPR registers, memory and, other data 5684 can be written using xmon commands. 5685 ro same as "rw" option above but SPR registers, 5686 memory, and other data can't be written using 5687 xmon commands. 5688 off xmon is disabled. 5689