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 acpi_backlight=vendor 26 acpi_backlight=video 27 If set to vendor, prefer vendor specific driver 28 (e.g. thinkpad_acpi, sony_acpi, etc.) instead 29 of the ACPI video.ko driver. 30 31 acpi_force_32bit_fadt_addr 32 force FADT to use 32 bit addresses rather than the 33 64 bit X_* addresses. Some firmware have broken 64 34 bit addresses for force ACPI ignore these and use 35 the older legacy 32 bit addresses. 36 37 acpica_no_return_repair [HW, ACPI] 38 Disable AML predefined validation mechanism 39 This mechanism can repair the evaluation result to make 40 the return objects more ACPI specification compliant. 41 This option is useful for developers to identify the 42 root cause of an AML interpreter issue when the issue 43 has something to do with the repair mechanism. 44 45 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG] 46 acpi.debug_level= [HW,ACPI,ACPI_DEBUG] 47 Format: <int> 48 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI 49 debug output. Bits in debug_layer correspond to a 50 _COMPONENT in an ACPI source file, e.g., 51 #define _COMPONENT ACPI_PCI_COMPONENT 52 Bits in debug_level correspond to a level in 53 ACPI_DEBUG_PRINT statements, e.g., 54 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ... 55 The debug_level mask defaults to "info". See 56 Documentation/firmware-guide/acpi/debug.rst for more information about 57 debug layers and levels. 58 59 Enable processor driver info messages: 60 acpi.debug_layer=0x20000000 61 Enable PCI/PCI interrupt routing info messages: 62 acpi.debug_layer=0x400000 63 Enable AML "Debug" output, i.e., stores to the Debug 64 object while interpreting AML: 65 acpi.debug_layer=0xffffffff acpi.debug_level=0x2 66 Enable all messages related to ACPI hardware: 67 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff 68 69 Some values produce so much output that the system is 70 unusable. The "log_buf_len" parameter may be useful 71 if you need to capture more output. 72 73 acpi_enforce_resources= [ACPI] 74 { strict | lax | no } 75 Check for resource conflicts between native drivers 76 and ACPI OperationRegions (SystemIO and SystemMemory 77 only). IO ports and memory declared in ACPI might be 78 used by the ACPI subsystem in arbitrary AML code and 79 can interfere with legacy drivers. 80 strict (default): access to resources claimed by ACPI 81 is denied; legacy drivers trying to access reserved 82 resources will fail to bind to device using them. 83 lax: access to resources claimed by ACPI is allowed; 84 legacy drivers trying to access reserved resources 85 will bind successfully but a warning message is logged. 86 no: ACPI OperationRegions are not marked as reserved, 87 no further checks are performed. 88 89 acpi_force_table_verification [HW,ACPI] 90 Enable table checksum verification during early stage. 91 By default, this is disabled due to x86 early mapping 92 size limitation. 93 94 acpi_irq_balance [HW,ACPI] 95 ACPI will balance active IRQs 96 default in APIC mode 97 98 acpi_irq_nobalance [HW,ACPI] 99 ACPI will not move active IRQs (default) 100 default in PIC mode 101 102 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA 103 Format: <irq>,<irq>... 104 105 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for 106 use by PCI 107 Format: <irq>,<irq>... 108 109 acpi_mask_gpe= [HW,ACPI] 110 Due to the existence of _Lxx/_Exx, some GPEs triggered 111 by unsupported hardware/firmware features can result in 112 GPE floodings that cannot be automatically disabled by 113 the GPE dispatcher. 114 This facility can be used to prevent such uncontrolled 115 GPE floodings. 116 Format: <byte> 117 118 acpi_no_auto_serialize [HW,ACPI] 119 Disable auto-serialization of AML methods 120 AML control methods that contain the opcodes to create 121 named objects will be marked as "Serialized" by the 122 auto-serialization feature. 123 This feature is enabled by default. 124 This option allows to turn off the feature. 125 126 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump 127 kernels. 128 129 acpi_no_static_ssdt [HW,ACPI] 130 Disable installation of static SSDTs at early boot time 131 By default, SSDTs contained in the RSDT/XSDT will be 132 installed automatically and they will appear under 133 /sys/firmware/acpi/tables. 134 This option turns off this feature. 135 Note that specifying this option does not affect 136 dynamic table installation which will install SSDT 137 tables to /sys/firmware/acpi/tables/dynamic. 138 139 acpi_rsdp= [ACPI,EFI,KEXEC] 140 Pass the RSDP address to the kernel, mostly used 141 on machines running EFI runtime service to boot the 142 second kernel for kdump. 143 144 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS 145 Format: To spoof as Windows 98: ="Microsoft Windows" 146 147 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead 148 of 2 which is mandated by ACPI 6) as the supported ACPI 149 specification revision (when using this switch, it may 150 be necessary to carry out a cold reboot _twice_ in a 151 row to make it take effect on the platform firmware). 152 153 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings 154 acpi_osi="string1" # add string1 155 acpi_osi="!string2" # remove string2 156 acpi_osi=!* # remove all strings 157 acpi_osi=! # disable all built-in OS vendor 158 strings 159 acpi_osi=!! # enable all built-in OS vendor 160 strings 161 acpi_osi= # disable all strings 162 163 'acpi_osi=!' can be used in combination with single or 164 multiple 'acpi_osi="string1"' to support specific OS 165 vendor string(s). Note that such command can only 166 affect the default state of the OS vendor strings, thus 167 it cannot affect the default state of the feature group 168 strings and the current state of the OS vendor strings, 169 specifying it multiple times through kernel command line 170 is meaningless. This command is useful when one do not 171 care about the state of the feature group strings which 172 should be controlled by the OSPM. 173 Examples: 174 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent 175 to 'acpi_osi="Windows 2000" acpi_osi=!', they all 176 can make '_OSI("Windows 2000")' TRUE. 177 178 'acpi_osi=' cannot be used in combination with other 179 'acpi_osi=' command lines, the _OSI method will not 180 exist in the ACPI namespace. NOTE that such command can 181 only affect the _OSI support state, thus specifying it 182 multiple times through kernel command line is also 183 meaningless. 184 Examples: 185 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)' 186 FALSE. 187 188 'acpi_osi=!*' can be used in combination with single or 189 multiple 'acpi_osi="string1"' to support specific 190 string(s). Note that such command can affect the 191 current state of both the OS vendor strings and the 192 feature group strings, thus specifying it multiple times 193 through kernel command line is meaningful. But it may 194 still not able to affect the final state of a string if 195 there are quirks related to this string. This command 196 is useful when one want to control the state of the 197 feature group strings to debug BIOS issues related to 198 the OSPM features. 199 Examples: 200 1. 'acpi_osi="Module Device" acpi_osi=!*' can make 201 '_OSI("Module Device")' FALSE. 202 2. 'acpi_osi=!* acpi_osi="Module Device"' can make 203 '_OSI("Module Device")' TRUE. 204 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is 205 equivalent to 206 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"' 207 and 208 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!', 209 they all will make '_OSI("Windows 2000")' TRUE. 210 211 acpi_pm_good [X86] 212 Override the pmtimer bug detection: force the kernel 213 to assume that this machine's pmtimer latches its value 214 and always returns good values. 215 216 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode 217 Format: { level | edge | high | low } 218 219 acpi_skip_timer_override [HW,ACPI] 220 Recognize and ignore IRQ0/pin2 Interrupt Override. 221 For broken nForce2 BIOS resulting in XT-PIC timer. 222 223 acpi_sleep= [HW,ACPI] Sleep options 224 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig, 225 old_ordering, nonvs, sci_force_enable, nobl } 226 See Documentation/power/video.rst for information on 227 s3_bios and s3_mode. 228 s3_beep is for debugging; it makes the PC's speaker beep 229 as soon as the kernel's real-mode entry point is called. 230 s4_nohwsig prevents ACPI hardware signature from being 231 used during resume from hibernation. 232 old_ordering causes the ACPI 1.0 ordering of the _PTS 233 control method, with respect to putting devices into 234 low power states, to be enforced (the ACPI 2.0 ordering 235 of _PTS is used by default). 236 nonvs prevents the kernel from saving/restoring the 237 ACPI NVS memory during suspend/hibernation and resume. 238 sci_force_enable causes the kernel to set SCI_EN directly 239 on resume from S1/S3 (which is against the ACPI spec, 240 but some broken systems don't work without it). 241 nobl causes the internal blacklist of systems known to 242 behave incorrectly in some ways with respect to system 243 suspend and resume to be ignored (use wisely). 244 245 acpi_use_timer_override [HW,ACPI] 246 Use timer override. For some broken Nvidia NF5 boards 247 that require a timer override, but don't have HPET 248 249 add_efi_memmap [EFI; X86] Include EFI memory map in 250 kernel's map of available physical RAM. 251 252 agp= [AGP] 253 { off | try_unsupported } 254 off: disable AGP support 255 try_unsupported: try to drive unsupported chipsets 256 (may crash computer or cause data corruption) 257 258 ALSA [HW,ALSA] 259 See Documentation/sound/alsa-configuration.rst 260 261 alignment= [KNL,ARM] 262 Allow the default userspace alignment fault handler 263 behaviour to be specified. Bit 0 enables warnings, 264 bit 1 enables fixups, and bit 2 sends a segfault. 265 266 align_va_addr= [X86-64] 267 Align virtual addresses by clearing slice [14:12] when 268 allocating a VMA at process creation time. This option 269 gives you up to 3% performance improvement on AMD F15h 270 machines (where it is enabled by default) for a 271 CPU-intensive style benchmark, and it can vary highly in 272 a microbenchmark depending on workload and compiler. 273 274 32: only for 32-bit processes 275 64: only for 64-bit processes 276 on: enable for both 32- and 64-bit processes 277 off: disable for both 32- and 64-bit processes 278 279 alloc_snapshot [FTRACE] 280 Allocate the ftrace snapshot buffer on boot up when the 281 main buffer is allocated. This is handy if debugging 282 and you need to use tracing_snapshot() on boot up, and 283 do not want to use tracing_snapshot_alloc() as it needs 284 to be done where GFP_KERNEL allocations are allowed. 285 286 amd_iommu= [HW,X86-64] 287 Pass parameters to the AMD IOMMU driver in the system. 288 Possible values are: 289 fullflush - enable flushing of IO/TLB entries when 290 they are unmapped. Otherwise they are 291 flushed before they will be reused, which 292 is a lot of faster 293 off - do not initialize any AMD IOMMU found in 294 the system 295 force_isolation - Force device isolation for all 296 devices. The IOMMU driver is not 297 allowed anymore to lift isolation 298 requirements as needed. This option 299 does not override iommu=pt 300 301 amd_iommu_dump= [HW,X86-64] 302 Enable AMD IOMMU driver option to dump the ACPI table 303 for AMD IOMMU. With this option enabled, AMD IOMMU 304 driver will print ACPI tables for AMD IOMMU during 305 IOMMU initialization. 306 307 amd_iommu_intr= [HW,X86-64] 308 Specifies one of the following AMD IOMMU interrupt 309 remapping modes: 310 legacy - Use legacy interrupt remapping mode. 311 vapic - Use virtual APIC mode, which allows IOMMU 312 to inject interrupts directly into guest. 313 This mode requires kvm-amd.avic=1. 314 (Default when IOMMU HW support is present.) 315 316 amijoy.map= [HW,JOY] Amiga joystick support 317 Map of devices attached to JOY0DAT and JOY1DAT 318 Format: <a>,<b> 319 See also Documentation/input/joydev/joystick.rst 320 321 analog.map= [HW,JOY] Analog joystick and gamepad support 322 Specifies type or capabilities of an analog joystick 323 connected to one of 16 gameports 324 Format: <type1>,<type2>,..<type16> 325 326 apc= [HW,SPARC] 327 Power management functions (SPARCstation-4/5 + deriv.) 328 Format: noidle 329 Disable APC CPU standby support. SPARCstation-Fox does 330 not play well with APC CPU idle - disable it if you have 331 APC and your system crashes randomly. 332 333 apic= [APIC,X86] Advanced Programmable Interrupt Controller 334 Change the output verbosity while booting 335 Format: { quiet (default) | verbose | debug } 336 Change the amount of debugging information output 337 when initialising the APIC and IO-APIC components. 338 For X86-32, this can also be used to specify an APIC 339 driver name. 340 Format: apic=driver_name 341 Examples: apic=bigsmp 342 343 apic_extnmi= [APIC,X86] External NMI delivery setting 344 Format: { bsp (default) | all | none } 345 bsp: External NMI is delivered only to CPU 0 346 all: External NMIs are broadcast to all CPUs as a 347 backup of CPU 0 348 none: External NMI is masked for all CPUs. This is 349 useful so that a dump capture kernel won't be 350 shot down by NMI 351 352 autoconf= [IPV6] 353 See Documentation/networking/ipv6.txt. 354 355 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller 356 Limit apic dumping. The parameter defines the maximal 357 number of local apics being dumped. Also it is possible 358 to set it to "all" by meaning -- no limit here. 359 Format: { 1 (default) | 2 | ... | all }. 360 The parameter valid if only apic=debug or 361 apic=verbose is specified. 362 Example: apic=debug show_lapic=all 363 364 apm= [APM] Advanced Power Management 365 See header of arch/x86/kernel/apm_32.c. 366 367 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards 368 Format: <io>,<irq>,<nodeID> 369 370 ataflop= [HW,M68k] 371 372 atarimouse= [HW,MOUSE] Atari Mouse 373 374 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess, 375 EzKey and similar keyboards 376 377 atkbd.reset= [HW] Reset keyboard during initialization 378 379 atkbd.set= [HW] Select keyboard code set 380 Format: <int> (2 = AT (default), 3 = PS/2) 381 382 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar 383 keyboards 384 385 atkbd.softraw= [HW] Choose between synthetic and real raw mode 386 Format: <bool> (0 = real, 1 = synthetic (default)) 387 388 atkbd.softrepeat= [HW] 389 Use software keyboard repeat 390 391 audit= [KNL] Enable the audit sub-system 392 Format: { "0" | "1" | "off" | "on" } 393 0 | off - kernel audit is disabled and can not be 394 enabled until the next reboot 395 unset - kernel audit is initialized but disabled and 396 will be fully enabled by the userspace auditd. 397 1 | on - kernel audit is initialized and partially 398 enabled, storing at most audit_backlog_limit 399 messages in RAM until it is fully enabled by the 400 userspace auditd. 401 Default: unset 402 403 audit_backlog_limit= [KNL] Set the audit queue size limit. 404 Format: <int> (must be >=0) 405 Default: 64 406 407 bau= [X86_UV] Enable the BAU on SGI UV. The default 408 behavior is to disable the BAU (i.e. bau=0). 409 Format: { "0" | "1" } 410 0 - Disable the BAU. 411 1 - Enable the BAU. 412 unset - Disable the BAU. 413 414 baycom_epp= [HW,AX25] 415 Format: <io>,<mode> 416 417 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem 418 Format: <io>,<mode> 419 See header of drivers/net/hamradio/baycom_par.c. 420 421 baycom_ser_fdx= [HW,AX25] 422 BayCom Serial Port AX.25 Modem (Full Duplex Mode) 423 Format: <io>,<irq>,<mode>[,<baud>] 424 See header of drivers/net/hamradio/baycom_ser_fdx.c. 425 426 baycom_ser_hdx= [HW,AX25] 427 BayCom Serial Port AX.25 Modem (Half Duplex Mode) 428 Format: <io>,<irq>,<mode> 429 See header of drivers/net/hamradio/baycom_ser_hdx.c. 430 431 blkdevparts= Manual partition parsing of block device(s) for 432 embedded devices based on command line input. 433 See Documentation/block/cmdline-partition.rst 434 435 boot_delay= Milliseconds to delay each printk during boot. 436 Values larger than 10 seconds (10000) are changed to 437 no delay (0). 438 Format: integer 439 440 bert_disable [ACPI] 441 Disable BERT OS support on buggy BIOSes. 442 443 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards) 444 bttv.radio= Most important insmod options are available as 445 kernel args too. 446 bttv.pll= See Documentation/media/v4l-drivers/bttv.rst 447 bttv.tuner= 448 449 bulk_remove=off [PPC] This parameter disables the use of the pSeries 450 firmware feature for flushing multiple hpte entries 451 at a time. 452 453 c101= [NET] Moxa C101 synchronous serial card 454 455 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection. 456 Sometimes CPU hardware bugs make them report the cache 457 size incorrectly. The kernel will attempt work arounds 458 to fix known problems, but for some CPUs it is not 459 possible to determine what the correct size should be. 460 This option provides an override for these situations. 461 462 carrier_timeout= 463 [NET] Specifies amount of time (in seconds) that 464 the kernel should wait for a network carrier. By default 465 it waits 120 seconds. 466 467 ca_keys= [KEYS] This parameter identifies a specific key(s) on 468 the system trusted keyring to be used for certificate 469 trust validation. 470 format: { id:<keyid> | builtin } 471 472 cca= [MIPS] Override the kernel pages' cache coherency 473 algorithm. Accepted values range from 0 to 7 474 inclusive. See arch/mips/include/asm/pgtable-bits.h 475 for platform specific values (SB1, Loongson3 and 476 others). 477 478 ccw_timeout_log [S390] 479 See Documentation/s390/common_io.rst for details. 480 481 cgroup_disable= [KNL] Disable a particular controller 482 Format: {name of the controller(s) to disable} 483 The effects of cgroup_disable=foo are: 484 - foo isn't auto-mounted if you mount all cgroups in 485 a single hierarchy 486 - foo isn't visible as an individually mountable 487 subsystem 488 {Currently only "memory" controller deal with this and 489 cut the overhead, others just disable the usage. So 490 only cgroup_disable=memory is actually worthy} 491 492 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1 493 Format: { { controller | "all" | "named" } 494 [,{ controller | "all" | "named" }...] } 495 Like cgroup_disable, but only applies to cgroup v1; 496 the blacklisted controllers remain available in cgroup2. 497 "all" blacklists all controllers and "named" disables 498 named mounts. Specifying both "all" and "named" disables 499 all v1 hierarchies. 500 501 cgroup.memory= [KNL] Pass options to the cgroup memory controller. 502 Format: <string> 503 nosocket -- Disable socket memory accounting. 504 nokmem -- Disable kernel memory accounting. 505 506 checkreqprot [SELINUX] Set initial checkreqprot flag value. 507 Format: { "0" | "1" } 508 See security/selinux/Kconfig help text. 509 0 -- check protection applied by kernel (includes 510 any implied execute protection). 511 1 -- check protection requested by application. 512 Default value is set via a kernel config option. 513 Value can be changed at runtime via 514 /selinux/checkreqprot. 515 516 cio_ignore= [S390] 517 See Documentation/s390/common_io.rst for details. 518 clk_ignore_unused 519 [CLK] 520 Prevents the clock framework from automatically gating 521 clocks that have not been explicitly enabled by a Linux 522 device driver but are enabled in hardware at reset or 523 by the bootloader/firmware. Note that this does not 524 force such clocks to be always-on nor does it reserve 525 those clocks in any way. This parameter is useful for 526 debug and development, but should not be needed on a 527 platform with proper driver support. For more 528 information, see Documentation/driver-api/clk.rst. 529 530 clock= [BUGS=X86-32, HW] gettimeofday clocksource override. 531 [Deprecated] 532 Forces specified clocksource (if available) to be used 533 when calculating gettimeofday(). If specified 534 clocksource is not available, it defaults to PIT. 535 Format: { pit | tsc | cyclone | pmtmr } 536 537 clocksource= Override the default clocksource 538 Format: <string> 539 Override the default clocksource and use the clocksource 540 with the name specified. 541 Some clocksource names to choose from, depending on 542 the platform: 543 [all] jiffies (this is the base, fallback clocksource) 544 [ACPI] acpi_pm 545 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2, 546 pxa_timer,timer3,32k_counter,timer0_1 547 [X86-32] pit,hpet,tsc; 548 scx200_hrt on Geode; cyclone on IBM x440 549 [MIPS] MIPS 550 [PARISC] cr16 551 [S390] tod 552 [SH] SuperH 553 [SPARC64] tick 554 [X86-64] hpet,tsc 555 556 clocksource.arm_arch_timer.evtstrm= 557 [ARM,ARM64] 558 Format: <bool> 559 Enable/disable the eventstream feature of the ARM 560 architected timer so that code using WFE-based polling 561 loops can be debugged more effectively on production 562 systems. 563 564 clearcpuid=BITNUM [X86] 565 Disable CPUID feature X for the kernel. See 566 arch/x86/include/asm/cpufeatures.h for the valid bit 567 numbers. Note the Linux specific bits are not necessarily 568 stable over kernel options, but the vendor specific 569 ones should be. 570 Also note that user programs calling CPUID directly 571 or using the feature without checking anything 572 will still see it. This just prevents it from 573 being used by the kernel or shown in /proc/cpuinfo. 574 Also note the kernel might malfunction if you disable 575 some critical bits. 576 577 cma=nn[MG]@[start[MG][-end[MG]]] 578 [ARM,X86,KNL] 579 Sets the size of kernel global memory area for 580 contiguous memory allocations and optionally the 581 placement constraint by the physical address range of 582 memory allocations. A value of 0 disables CMA 583 altogether. For more information, see 584 include/linux/dma-contiguous.h 585 586 cmo_free_hint= [PPC] Format: { yes | no } 587 Specify whether pages are marked as being inactive 588 when they are freed. This is used in CMO environments 589 to determine OS memory pressure for page stealing by 590 a hypervisor. 591 Default: yes 592 593 coherent_pool=nn[KMG] [ARM,KNL] 594 Sets the size of memory pool for coherent, atomic dma 595 allocations, by default set to 256K. 596 597 com20020= [HW,NET] ARCnet - COM20020 chipset 598 Format: 599 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]] 600 601 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers) 602 Format: <io>[,<irq>] 603 604 com90xx= [HW,NET] 605 ARCnet - COM90xx chipset (memory-mapped buffers) 606 Format: <io>[,<irq>[,<memstart>]] 607 608 condev= [HW,S390] console device 609 conmode= 610 611 console= [KNL] Output console device and options. 612 613 tty<n> Use the virtual console device <n>. 614 615 ttyS<n>[,options] 616 ttyUSB0[,options] 617 Use the specified serial port. The options are of 618 the form "bbbbpnf", where "bbbb" is the baud rate, 619 "p" is parity ("n", "o", or "e"), "n" is number of 620 bits, and "f" is flow control ("r" for RTS or 621 omit it). Default is "9600n8". 622 623 See Documentation/admin-guide/serial-console.rst for more 624 information. See 625 Documentation/networking/netconsole.txt for an 626 alternative. 627 628 uart[8250],io,<addr>[,options] 629 uart[8250],mmio,<addr>[,options] 630 uart[8250],mmio16,<addr>[,options] 631 uart[8250],mmio32,<addr>[,options] 632 uart[8250],0x<addr>[,options] 633 Start an early, polled-mode console on the 8250/16550 634 UART at the specified I/O port or MMIO address, 635 switching to the matching ttyS device later. 636 MMIO inter-register address stride is either 8-bit 637 (mmio), 16-bit (mmio16), or 32-bit (mmio32). 638 If none of [io|mmio|mmio16|mmio32], <addr> is assumed 639 to be equivalent to 'mmio'. 'options' are specified in 640 the same format described for ttyS above; if unspecified, 641 the h/w is not re-initialized. 642 643 hvc<n> Use the hypervisor console device <n>. This is for 644 both Xen and PowerPC hypervisors. 645 646 If the device connected to the port is not a TTY but a braille 647 device, prepend "brl," before the device type, for instance 648 console=brl,ttyS0 649 For now, only VisioBraille is supported. 650 651 console_msg_format= 652 [KNL] Change console messages format 653 default 654 By default we print messages on consoles in 655 "[time stamp] text\n" format (time stamp may not be 656 printed, depending on CONFIG_PRINTK_TIME or 657 `printk_time' param). 658 syslog 659 Switch to syslog format: "<%u>[time stamp] text\n" 660 IOW, each message will have a facility and loglevel 661 prefix. The format is similar to one used by syslog() 662 syscall, or to executing "dmesg -S --raw" or to reading 663 from /proc/kmsg. 664 665 consoleblank= [KNL] The console blank (screen saver) timeout in 666 seconds. A value of 0 disables the blank timer. 667 Defaults to 0. 668 669 coredump_filter= 670 [KNL] Change the default value for 671 /proc/<pid>/coredump_filter. 672 See also Documentation/filesystems/proc.txt. 673 674 coresight_cpu_debug.enable 675 [ARM,ARM64] 676 Format: <bool> 677 Enable/disable the CPU sampling based debugging. 678 0: default value, disable debugging 679 1: enable debugging at boot time 680 681 cpuidle.off=1 [CPU_IDLE] 682 disable the cpuidle sub-system 683 684 cpuidle.governor= 685 [CPU_IDLE] Name of the cpuidle governor to use. 686 687 cpufreq.off=1 [CPU_FREQ] 688 disable the cpufreq sub-system 689 690 cpu_init_udelay=N 691 [X86] Delay for N microsec between assert and de-assert 692 of APIC INIT to start processors. This delay occurs 693 on every CPU online, such as boot, and resume from suspend. 694 Default: 10000 695 696 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver 697 Format: 698 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] 699 700 crashkernel=size[KMG][@offset[KMG]] 701 [KNL] Using kexec, Linux can switch to a 'crash kernel' 702 upon panic. This parameter reserves the physical 703 memory region [offset, offset + size] for that kernel 704 image. If '@offset' is omitted, then a suitable offset 705 is selected automatically. 706 [KNL, x86_64] select a region under 4G first, and 707 fall back to reserve region above 4G when '@offset' 708 hasn't been specified. 709 See Documentation/admin-guide/kdump/kdump.rst for further details. 710 711 crashkernel=range1:size1[,range2:size2,...][@offset] 712 [KNL] Same as above, but depends on the memory 713 in the running system. The syntax of range is 714 start-[end] where start and end are both 715 a memory unit (amount[KMG]). See also 716 Documentation/admin-guide/kdump/kdump.rst for an example. 717 718 crashkernel=size[KMG],high 719 [KNL, x86_64] range could be above 4G. Allow kernel 720 to allocate physical memory region from top, so could 721 be above 4G if system have more than 4G ram installed. 722 Otherwise memory region will be allocated below 4G, if 723 available. 724 It will be ignored if crashkernel=X is specified. 725 crashkernel=size[KMG],low 726 [KNL, x86_64] range under 4G. When crashkernel=X,high 727 is passed, kernel could allocate physical memory region 728 above 4G, that cause second kernel crash on system 729 that require some amount of low memory, e.g. swiotlb 730 requires at least 64M+32K low memory, also enough extra 731 low memory is needed to make sure DMA buffers for 32-bit 732 devices won't run out. Kernel would try to allocate at 733 at least 256M below 4G automatically. 734 This one let user to specify own low range under 4G 735 for second kernel instead. 736 0: to disable low allocation. 737 It will be ignored when crashkernel=X,high is not used 738 or memory reserved is below 4G. 739 740 cryptomgr.notests 741 [KNL] Disable crypto self-tests 742 743 cs89x0_dma= [HW,NET] 744 Format: <dma> 745 746 cs89x0_media= [HW,NET] 747 Format: { rj45 | aui | bnc } 748 749 dasd= [HW,NET] 750 See header of drivers/s390/block/dasd_devmap.c. 751 752 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port 753 (one device per port) 754 Format: <port#>,<type> 755 See also Documentation/input/devices/joystick-parport.rst 756 757 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot 758 time. See 759 Documentation/admin-guide/dynamic-debug-howto.rst for 760 details. Deprecated, see dyndbg. 761 762 debug [KNL] Enable kernel debugging (events log level). 763 764 debug_boot_weak_hash 765 [KNL] Enable printing [hashed] pointers early in the 766 boot sequence. If enabled, we use a weak hash instead 767 of siphash to hash pointers. Use this option if you are 768 seeing instances of '(___ptrval___)') and need to see a 769 value (hashed pointer) instead. Cryptographically 770 insecure, please do not use on production kernels. 771 772 debug_locks_verbose= 773 [KNL] verbose self-tests 774 Format=<0|1> 775 Print debugging info while doing the locking API 776 self-tests. 777 We default to 0 (no extra messages), setting it to 778 1 will print _a lot_ more information - normally 779 only useful to kernel developers. 780 781 debug_objects [KNL] Enable object debugging 782 783 no_debug_objects 784 [KNL] Disable object debugging 785 786 debug_guardpage_minorder= 787 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this 788 parameter allows control of the order of pages that will 789 be intentionally kept free (and hence protected) by the 790 buddy allocator. Bigger value increase the probability 791 of catching random memory corruption, but reduce the 792 amount of memory for normal system use. The maximum 793 possible value is MAX_ORDER/2. Setting this parameter 794 to 1 or 2 should be enough to identify most random 795 memory corruption problems caused by bugs in kernel or 796 driver code when a CPU writes to (or reads from) a 797 random memory location. Note that there exists a class 798 of memory corruptions problems caused by buggy H/W or 799 F/W or by drivers badly programing DMA (basically when 800 memory is written at bus level and the CPU MMU is 801 bypassed) which are not detectable by 802 CONFIG_DEBUG_PAGEALLOC, hence this option will not help 803 tracking down these problems. 804 805 debug_pagealloc= 806 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this parameter 807 enables the feature at boot time. By default, it is 808 disabled and the system will work mostly the same as a 809 kernel built without CONFIG_DEBUG_PAGEALLOC. 810 Note: to get most of debug_pagealloc error reports, it's 811 useful to also enable the page_owner functionality. 812 on: enable the feature 813 814 debugpat [X86] Enable PAT debugging 815 816 decnet.addr= [HW,NET] 817 Format: <area>[,<node>] 818 See also Documentation/networking/decnet.txt. 819 820 default_hugepagesz= 821 [same as hugepagesz=] The size of the default 822 HugeTLB page size. This is the size represented by 823 the legacy /proc/ hugepages APIs, used for SHM, and 824 default size when mounting hugetlbfs filesystems. 825 Defaults to the default architecture's huge page size 826 if not specified. 827 828 deferred_probe_timeout= 829 [KNL] Debugging option to set a timeout in seconds for 830 deferred probe to give up waiting on dependencies to 831 probe. Only specific dependencies (subsystems or 832 drivers) that have opted in will be ignored. A timeout of 0 833 will timeout at the end of initcalls. This option will also 834 dump out devices still on the deferred probe list after 835 retrying. 836 837 dhash_entries= [KNL] 838 Set number of hash buckets for dentry cache. 839 840 disable_1tb_segments [PPC] 841 Disables the use of 1TB hash page table segments. This 842 causes the kernel to fall back to 256MB segments which 843 can be useful when debugging issues that require an SLB 844 miss to occur. 845 846 disable= [IPV6] 847 See Documentation/networking/ipv6.txt. 848 849 hardened_usercopy= 850 [KNL] Under CONFIG_HARDENED_USERCOPY, whether 851 hardening is enabled for this boot. Hardened 852 usercopy checking is used to protect the kernel 853 from reading or writing beyond known memory 854 allocation boundaries as a proactive defense 855 against bounds-checking flaws in the kernel's 856 copy_to_user()/copy_from_user() interface. 857 on Perform hardened usercopy checks (default). 858 off Disable hardened usercopy checks. 859 860 disable_radix [PPC] 861 Disable RADIX MMU mode on POWER9 862 863 disable_tlbie [PPC] 864 Disable TLBIE instruction. Currently does not work 865 with KVM, with HASH MMU, or with coherent accelerators. 866 867 disable_cpu_apicid= [X86,APIC,SMP] 868 Format: <int> 869 The number of initial APIC ID for the 870 corresponding CPU to be disabled at boot, 871 mostly used for the kdump 2nd kernel to 872 disable BSP to wake up multiple CPUs without 873 causing system reset or hang due to sending 874 INIT from AP to BSP. 875 876 perf_v4_pmi= [X86,INTEL] 877 Format: <bool> 878 Disable Intel PMU counter freezing feature. 879 The feature only exists starting from 880 Arch Perfmon v4 (Skylake and newer). 881 882 disable_ddw [PPC/PSERIES] 883 Disable Dynamic DMA Window support. Use this if 884 to workaround buggy firmware. 885 886 disable_ipv6= [IPV6] 887 See Documentation/networking/ipv6.txt. 888 889 disable_mtrr_cleanup [X86] 890 The kernel tries to adjust MTRR layout from continuous 891 to discrete, to make X server driver able to add WB 892 entry later. This parameter disables that. 893 894 disable_mtrr_trim [X86, Intel and AMD only] 895 By default the kernel will trim any uncacheable 896 memory out of your available memory pool based on 897 MTRR settings. This parameter disables that behavior, 898 possibly causing your machine to run very slowly. 899 900 disable_timer_pin_1 [X86] 901 Disable PIN 1 of APIC timer 902 Can be useful to work around chipset bugs. 903 904 dis_ucode_ldr [X86] Disable the microcode loader. 905 906 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, 907 this option disables the debugging code at boot. 908 909 dma_debug_entries=<number> 910 This option allows to tune the number of preallocated 911 entries for DMA-API debugging code. One entry is 912 required per DMA-API allocation. Use this if the 913 DMA-API debugging code disables itself because the 914 architectural default is too low. 915 916 dma_debug_driver=<driver_name> 917 With this option the DMA-API debugging driver 918 filter feature can be enabled at boot time. Just 919 pass the driver to filter for as the parameter. 920 The filter can be disabled or changed to another 921 driver later using sysfs. 922 923 driver_async_probe= [KNL] 924 List of driver names to be probed asynchronously. 925 Format: <driver_name1>,<driver_name2>... 926 927 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>] 928 Broken monitors, graphic adapters, KVMs and EDIDless 929 panels may send no or incorrect EDID data sets. 930 This parameter allows to specify an EDID data sets 931 in the /lib/firmware directory that are used instead. 932 Generic built-in EDID data sets are used, if one of 933 edid/1024x768.bin, edid/1280x1024.bin, 934 edid/1680x1050.bin, or edid/1920x1080.bin is given 935 and no file with the same name exists. Details and 936 instructions how to build your own EDID data are 937 available in Documentation/driver-api/edid.rst. An EDID 938 data set will only be used for a particular connector, 939 if its name and a colon are prepended to the EDID 940 name. Each connector may use a unique EDID data 941 set by separating the files with a comma. An EDID 942 data set with no connector name will be used for 943 any connectors not explicitly specified. 944 945 dscc4.setup= [NET] 946 947 dt_cpu_ftrs= [PPC] 948 Format: {"off" | "known"} 949 Control how the dt_cpu_ftrs device-tree binding is 950 used for CPU feature discovery and setup (if it 951 exists). 952 off: Do not use it, fall back to legacy cpu table. 953 known: Do not pass through unknown features to guests 954 or userspace, only those that the kernel is aware of. 955 956 dump_apple_properties [X86] 957 Dump name and content of EFI device properties on 958 x86 Macs. Useful for driver authors to determine 959 what data is available or for reverse-engineering. 960 961 dyndbg[="val"] [KNL,DYNAMIC_DEBUG] 962 module.dyndbg[="val"] 963 Enable debug messages at boot time. See 964 Documentation/admin-guide/dynamic-debug-howto.rst 965 for details. 966 967 nompx [X86] Disables Intel Memory Protection Extensions. 968 See Documentation/x86/intel_mpx.rst for more 969 information about the feature. 970 971 nopku [X86] Disable Memory Protection Keys CPU feature found 972 in some Intel CPUs. 973 974 module.async_probe [KNL] 975 Enable asynchronous probe on this module. 976 977 early_ioremap_debug [KNL] 978 Enable debug messages in early_ioremap support. This 979 is useful for tracking down temporary early mappings 980 which are not unmapped. 981 982 earlycon= [KNL] Output early console device and options. 983 984 When used with no options, the early console is 985 determined by stdout-path property in device tree's 986 chosen node or the ACPI SPCR table if supported by 987 the platform. 988 989 cdns,<addr>[,options] 990 Start an early, polled-mode console on a Cadence 991 (xuartps) serial port at the specified address. Only 992 supported option is baud rate. If baud rate is not 993 specified, the serial port must already be setup and 994 configured. 995 996 uart[8250],io,<addr>[,options] 997 uart[8250],mmio,<addr>[,options] 998 uart[8250],mmio32,<addr>[,options] 999 uart[8250],mmio32be,<addr>[,options] 1000 uart[8250],0x<addr>[,options] 1001 Start an early, polled-mode console on the 8250/16550 1002 UART at the specified I/O port or MMIO address. 1003 MMIO inter-register address stride is either 8-bit 1004 (mmio) or 32-bit (mmio32 or mmio32be). 1005 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed 1006 to be equivalent to 'mmio'. 'options' are specified 1007 in the same format described for "console=ttyS<n>"; if 1008 unspecified, the h/w is not initialized. 1009 1010 pl011,<addr> 1011 pl011,mmio32,<addr> 1012 Start an early, polled-mode console on a pl011 serial 1013 port at the specified address. The pl011 serial port 1014 must already be setup and configured. Options are not 1015 yet supported. If 'mmio32' is specified, then only 1016 the driver will use only 32-bit accessors to read/write 1017 the device registers. 1018 1019 meson,<addr> 1020 Start an early, polled-mode console on a meson serial 1021 port at the specified address. The serial port must 1022 already be setup and configured. Options are not yet 1023 supported. 1024 1025 msm_serial,<addr> 1026 Start an early, polled-mode console on an msm serial 1027 port at the specified address. The serial port 1028 must already be setup and configured. Options are not 1029 yet supported. 1030 1031 msm_serial_dm,<addr> 1032 Start an early, polled-mode console on an msm serial 1033 dm port at the specified address. The serial port 1034 must already be setup and configured. Options are not 1035 yet supported. 1036 1037 owl,<addr> 1038 Start an early, polled-mode console on a serial port 1039 of an Actions Semi SoC, such as S500 or S900, at the 1040 specified address. The serial port must already be 1041 setup and configured. Options are not yet supported. 1042 1043 rda,<addr> 1044 Start an early, polled-mode console on a serial port 1045 of an RDA Micro SoC, such as RDA8810PL, at the 1046 specified address. The serial port must already be 1047 setup and configured. Options are not yet supported. 1048 1049 sbi 1050 Use RISC-V SBI (Supervisor Binary Interface) for early 1051 console. 1052 1053 smh Use ARM semihosting calls for early console. 1054 1055 s3c2410,<addr> 1056 s3c2412,<addr> 1057 s3c2440,<addr> 1058 s3c6400,<addr> 1059 s5pv210,<addr> 1060 exynos4210,<addr> 1061 Use early console provided by serial driver available 1062 on Samsung SoCs, requires selecting proper type and 1063 a correct base address of the selected UART port. The 1064 serial port must already be setup and configured. 1065 Options are not yet supported. 1066 1067 lantiq,<addr> 1068 Start an early, polled-mode console on a lantiq serial 1069 (lqasc) port at the specified address. The serial port 1070 must already be setup and configured. Options are not 1071 yet supported. 1072 1073 lpuart,<addr> 1074 lpuart32,<addr> 1075 Use early console provided by Freescale LP UART driver 1076 found on Freescale Vybrid and QorIQ LS1021A processors. 1077 A valid base address must be provided, and the serial 1078 port must already be setup and configured. 1079 1080 ar3700_uart,<addr> 1081 Start an early, polled-mode console on the 1082 Armada 3700 serial port at the specified 1083 address. The serial port must already be setup 1084 and configured. Options are not yet supported. 1085 1086 qcom_geni,<addr> 1087 Start an early, polled-mode console on a Qualcomm 1088 Generic Interface (GENI) based serial port at the 1089 specified address. The serial port must already be 1090 setup and configured. Options are not yet supported. 1091 1092 efifb,[options] 1093 Start an early, unaccelerated console on the EFI 1094 memory mapped framebuffer (if available). On cache 1095 coherent non-x86 systems that use system memory for 1096 the framebuffer, pass the 'ram' option so that it is 1097 mapped with the correct attributes. 1098 1099 linflex,<addr> 1100 Use early console provided by Freescale LINFlexD UART 1101 serial driver for NXP S32V234 SoCs. A valid base 1102 address must be provided, and the serial port must 1103 already be setup and configured. 1104 1105 earlyprintk= [X86,SH,ARM,M68k,S390] 1106 earlyprintk=vga 1107 earlyprintk=sclp 1108 earlyprintk=xen 1109 earlyprintk=serial[,ttySn[,baudrate]] 1110 earlyprintk=serial[,0x...[,baudrate]] 1111 earlyprintk=ttySn[,baudrate] 1112 earlyprintk=dbgp[debugController#] 1113 earlyprintk=pciserial[,force],bus:device.function[,baudrate] 1114 earlyprintk=xdbc[xhciController#] 1115 1116 earlyprintk is useful when the kernel crashes before 1117 the normal console is initialized. It is not enabled by 1118 default because it has some cosmetic problems. 1119 1120 Append ",keep" to not disable it when the real console 1121 takes over. 1122 1123 Only one of vga, efi, serial, or usb debug port can 1124 be used at a time. 1125 1126 Currently only ttyS0 and ttyS1 may be specified by 1127 name. Other I/O ports may be explicitly specified 1128 on some architectures (x86 and arm at least) by 1129 replacing ttySn with an I/O port address, like this: 1130 earlyprintk=serial,0x1008,115200 1131 You can find the port for a given device in 1132 /proc/tty/driver/serial: 1133 2: uart:ST16650V2 port:00001008 irq:18 ... 1134 1135 Interaction with the standard serial driver is not 1136 very good. 1137 1138 The VGA and EFI output is eventually overwritten by 1139 the real console. 1140 1141 The xen output can only be used by Xen PV guests. 1142 1143 The sclp output can only be used on s390. 1144 1145 The optional "force" to "pciserial" enables use of a 1146 PCI device even when its classcode is not of the 1147 UART class. 1148 1149 edac_report= [HW,EDAC] Control how to report EDAC event 1150 Format: {"on" | "off" | "force"} 1151 on: enable EDAC to report H/W event. May be overridden 1152 by other higher priority error reporting module. 1153 off: disable H/W event reporting through EDAC. 1154 force: enforce the use of EDAC to report H/W event. 1155 default: on. 1156 1157 ekgdboc= [X86,KGDB] Allow early kernel console debugging 1158 ekgdboc=kbd 1159 1160 This is designed to be used in conjunction with 1161 the boot argument: earlyprintk=vga 1162 1163 edd= [EDD] 1164 Format: {"off" | "on" | "skip[mbr]"} 1165 1166 efi= [EFI] 1167 Format: { "old_map", "nochunk", "noruntime", "debug", 1168 "nosoftreserve" } 1169 old_map [X86-64]: switch to the old ioremap-based EFI 1170 runtime services mapping. 32-bit still uses this one by 1171 default. 1172 nochunk: disable reading files in "chunks" in the EFI 1173 boot stub, as chunking can cause problems with some 1174 firmware implementations. 1175 noruntime : disable EFI runtime services support 1176 debug: enable misc debug output 1177 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose) 1178 attribute may cause the kernel to reserve the 1179 memory range for a memory mapping driver to 1180 claim. Specify efi=nosoftreserve to disable this 1181 reservation and treat the memory by its base type 1182 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM"). 1183 1184 efi_no_storage_paranoia [EFI; X86] 1185 Using this parameter you can use more than 50% of 1186 your efi variable storage. Use this parameter only if 1187 you are really sure that your UEFI does sane gc and 1188 fulfills the spec otherwise your board may brick. 1189 1190 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86] 1191 Add arbitrary attribute to specific memory range by 1192 updating original EFI memory map. 1193 Region of memory which aa attribute is added to is 1194 from ss to ss+nn. 1195 1196 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000 1197 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000) 1198 attribute is added to range 0x100000000-0x180000000 and 1199 0x10a0000000-0x1120000000. 1200 1201 If efi_fake_mem=8G@9G:0x40000 is specified, the 1202 EFI_MEMORY_SP(0x40000) attribute is added to 1203 range 0x240000000-0x43fffffff. 1204 1205 Using this parameter you can do debugging of EFI memmap 1206 related features. For example, you can do debugging of 1207 Address Range Mirroring feature even if your box 1208 doesn't support it, or mark specific memory as 1209 "soft reserved". 1210 1211 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT 1212 that is to be dynamically loaded by Linux. If there are 1213 multiple variables with the same name but with different 1214 vendor GUIDs, all of them will be loaded. See 1215 Documentation/admin-guide/acpi/ssdt-overlays.rst for details. 1216 1217 1218 eisa_irq_edge= [PARISC,HW] 1219 See header of drivers/parisc/eisa.c. 1220 1221 elanfreq= [X86-32] 1222 See comment before function elanfreq_setup() in 1223 arch/x86/kernel/cpu/cpufreq/elanfreq.c. 1224 1225 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390] 1226 Specifies physical address of start of kernel core 1227 image elf header and optionally the size. Generally 1228 kexec loader will pass this option to capture kernel. 1229 See Documentation/admin-guide/kdump/kdump.rst for details. 1230 1231 enable_mtrr_cleanup [X86] 1232 The kernel tries to adjust MTRR layout from continuous 1233 to discrete, to make X server driver able to add WB 1234 entry later. This parameter enables that. 1235 1236 enable_timer_pin_1 [X86] 1237 Enable PIN 1 of APIC timer 1238 Can be useful to work around chipset bugs 1239 (in particular on some ATI chipsets). 1240 The kernel tries to set a reasonable default. 1241 1242 enforcing [SELINUX] Set initial enforcing status. 1243 Format: {"0" | "1"} 1244 See security/selinux/Kconfig help text. 1245 0 -- permissive (log only, no denials). 1246 1 -- enforcing (deny and log). 1247 Default value is 0. 1248 Value can be changed at runtime via /selinux/enforce. 1249 1250 erst_disable [ACPI] 1251 Disable Error Record Serialization Table (ERST) 1252 support. 1253 1254 ether= [HW,NET] Ethernet cards parameters 1255 This option is obsoleted by the "netdev=" option, which 1256 has equivalent usage. See its documentation for details. 1257 1258 evm= [EVM] 1259 Format: { "fix" } 1260 Permit 'security.evm' to be updated regardless of 1261 current integrity status. 1262 1263 failslab= 1264 fail_page_alloc= 1265 fail_make_request=[KNL] 1266 General fault injection mechanism. 1267 Format: <interval>,<probability>,<space>,<times> 1268 See also Documentation/fault-injection/. 1269 1270 floppy= [HW] 1271 See Documentation/admin-guide/blockdev/floppy.rst. 1272 1273 force_pal_cache_flush 1274 [IA-64] Avoid check_sal_cache_flush which may hang on 1275 buggy SAL_CACHE_FLUSH implementations. Using this 1276 parameter will force ia64_sal_cache_flush to call 1277 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH. 1278 1279 forcepae [X86-32] 1280 Forcefully enable Physical Address Extension (PAE). 1281 Many Pentium M systems disable PAE but may have a 1282 functionally usable PAE implementation. 1283 Warning: use of this parameter will taint the kernel 1284 and may cause unknown problems. 1285 1286 ftrace=[tracer] 1287 [FTRACE] will set and start the specified tracer 1288 as early as possible in order to facilitate early 1289 boot debugging. 1290 1291 ftrace_dump_on_oops[=orig_cpu] 1292 [FTRACE] will dump the trace buffers on oops. 1293 If no parameter is passed, ftrace will dump 1294 buffers of all CPUs, but if you pass orig_cpu, it will 1295 dump only the buffer of the CPU that triggered the 1296 oops. 1297 1298 ftrace_filter=[function-list] 1299 [FTRACE] Limit the functions traced by the function 1300 tracer at boot up. function-list is a comma separated 1301 list of functions. This list can be changed at run 1302 time by the set_ftrace_filter file in the debugfs 1303 tracing directory. 1304 1305 ftrace_notrace=[function-list] 1306 [FTRACE] Do not trace the functions specified in 1307 function-list. This list can be changed at run time 1308 by the set_ftrace_notrace file in the debugfs 1309 tracing directory. 1310 1311 ftrace_graph_filter=[function-list] 1312 [FTRACE] Limit the top level callers functions traced 1313 by the function graph tracer at boot up. 1314 function-list is a comma separated list of functions 1315 that can be changed at run time by the 1316 set_graph_function file in the debugfs tracing directory. 1317 1318 ftrace_graph_notrace=[function-list] 1319 [FTRACE] Do not trace from the functions specified in 1320 function-list. This list is a comma separated list of 1321 functions that can be changed at run time by the 1322 set_graph_notrace file in the debugfs tracing directory. 1323 1324 ftrace_graph_max_depth=<uint> 1325 [FTRACE] Used with the function graph tracer. This is 1326 the max depth it will trace into a function. This value 1327 can be changed at run time by the max_graph_depth file 1328 in the tracefs tracing directory. default: 0 (no limit) 1329 1330 gamecon.map[2|3]= 1331 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 1332 support via parallel port (up to 5 devices per port) 1333 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 1334 See also Documentation/input/devices/joystick-parport.rst 1335 1336 gamma= [HW,DRM] 1337 1338 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART 1339 Format: off | on 1340 default: on 1341 1342 gcov_persist= [GCOV] When non-zero (default), profiling data for 1343 kernel modules is saved and remains accessible via 1344 debugfs, even when the module is unloaded/reloaded. 1345 When zero, profiling data is discarded and associated 1346 debugfs files are removed at module unload time. 1347 1348 goldfish [X86] Enable the goldfish android emulator platform. 1349 Don't use this when you are not running on the 1350 android emulator 1351 1352 gpt [EFI] Forces disk with valid GPT signature but 1353 invalid Protective MBR to be treated as GPT. If the 1354 primary GPT is corrupted, it enables the backup/alternate 1355 GPT to be used instead. 1356 1357 grcan.enable0= [HW] Configuration of physical interface 0. Determines 1358 the "Enable 0" bit of the configuration register. 1359 Format: 0 | 1 1360 Default: 0 1361 grcan.enable1= [HW] Configuration of physical interface 1. Determines 1362 the "Enable 0" bit of the configuration register. 1363 Format: 0 | 1 1364 Default: 0 1365 grcan.select= [HW] Select which physical interface to use. 1366 Format: 0 | 1 1367 Default: 0 1368 grcan.txsize= [HW] Sets the size of the tx buffer. 1369 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. 1370 Default: 1024 1371 grcan.rxsize= [HW] Sets the size of the rx buffer. 1372 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. 1373 Default: 1024 1374 1375 gpio-mockup.gpio_mockup_ranges 1376 [HW] Sets the ranges of gpiochip of for this device. 1377 Format: <start1>,<end1>,<start2>,<end2>... 1378 1379 hardlockup_all_cpu_backtrace= 1380 [KNL] Should the hard-lockup detector generate 1381 backtraces on all cpus. 1382 Format: <integer> 1383 1384 hashdist= [KNL,NUMA] Large hashes allocated during boot 1385 are distributed across NUMA nodes. Defaults on 1386 for 64-bit NUMA, off otherwise. 1387 Format: 0 | 1 (for off | on) 1388 1389 hcl= [IA-64] SGI's Hardware Graph compatibility layer 1390 1391 hd= [EIDE] (E)IDE hard drive subsystem geometry 1392 Format: <cyl>,<head>,<sect> 1393 1394 hest_disable [ACPI] 1395 Disable Hardware Error Source Table (HEST) support; 1396 corresponding firmware-first mode error processing 1397 logic will be disabled. 1398 1399 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact 1400 size of <nn>. This works even on boxes that have no 1401 highmem otherwise. This also works to reduce highmem 1402 size on bigger boxes. 1403 1404 highres= [KNL] Enable/disable high resolution timer mode. 1405 Valid parameters: "on", "off" 1406 Default: "on" 1407 1408 hlt [BUGS=ARM,SH] 1409 1410 hpet= [X86-32,HPET] option to control HPET usage 1411 Format: { enable (default) | disable | force | 1412 verbose } 1413 disable: disable HPET and use PIT instead 1414 force: allow force enabled of undocumented chips (ICH4, 1415 VIA, nVidia) 1416 verbose: show contents of HPET registers during setup 1417 1418 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET 1419 registers. Default set by CONFIG_HPET_MMAP_DEFAULT. 1420 1421 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot. 1422 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages. 1423 On x86-64 and powerpc, this option can be specified 1424 multiple times interleaved with hugepages= to reserve 1425 huge pages of different sizes. Valid pages sizes on 1426 x86-64 are 2M (when the CPU supports "pse") and 1G 1427 (when the CPU supports the "pdpe1gb" cpuinfo flag). 1428 1429 hung_task_panic= 1430 [KNL] Should the hung task detector generate panics. 1431 Format: <integer> 1432 1433 A nonzero value instructs the kernel to panic when a 1434 hung task is detected. The default value is controlled 1435 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time 1436 option. The value selected by this boot parameter can 1437 be changed later by the kernel.hung_task_panic sysctl. 1438 1439 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 1440 terminal devices. Valid values: 0..8 1441 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 1442 If specified, z/VM IUCV HVC accepts connections 1443 from listed z/VM user IDs only. 1444 1445 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations 1446 which allow the hypervisor to 'idle' the 1447 guest on lock contention. 1448 1449 keep_bootcon [KNL] 1450 Do not unregister boot console at start. This is only 1451 useful for debugging when something happens in the window 1452 between unregistering the boot console and initializing 1453 the real console. 1454 1455 i2c_bus= [HW] Override the default board specific I2C bus speed 1456 or register an additional I2C bus that is not 1457 registered from board initialization code. 1458 Format: 1459 <bus_id>,<clkrate> 1460 1461 i8042.debug [HW] Toggle i8042 debug mode 1462 i8042.unmask_kbd_data 1463 [HW] Enable printing of interrupt data from the KBD port 1464 (disabled by default, and as a pre-condition 1465 requires that i8042.debug=1 be enabled) 1466 i8042.direct [HW] Put keyboard port into non-translated mode 1467 i8042.dumbkbd [HW] Pretend that controller can only read data from 1468 keyboard and cannot control its state 1469 (Don't attempt to blink the leds) 1470 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 1471 i8042.nokbd [HW] Don't check/create keyboard port 1472 i8042.noloop [HW] Disable the AUX Loopback command while probing 1473 for the AUX port 1474 i8042.nomux [HW] Don't check presence of an active multiplexing 1475 controller 1476 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 1477 controllers 1478 i8042.notimeout [HW] Ignore timeout condition signalled by controller 1479 i8042.reset [HW] Reset the controller during init, cleanup and 1480 suspend-to-ram transitions, only during s2r 1481 transitions, or never reset 1482 Format: { 1 | Y | y | 0 | N | n } 1483 1, Y, y: always reset controller 1484 0, N, n: don't ever reset controller 1485 Default: only on s2r transitions on x86; most other 1486 architectures force reset to be always executed 1487 i8042.unlock [HW] Unlock (ignore) the keylock 1488 i8042.kbdreset [HW] Reset device connected to KBD port 1489 1490 i810= [HW,DRM] 1491 1492 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data 1493 indicates that the driver is running on unsupported 1494 hardware. 1495 i8k.force [HW] Activate i8k driver even if SMM BIOS signature 1496 does not match list of supported models. 1497 i8k.power_status 1498 [HW] Report power status in /proc/i8k 1499 (disabled by default) 1500 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN 1501 capability is set. 1502 1503 i915.invert_brightness= 1504 [DRM] Invert the sense of the variable that is used to 1505 set the brightness of the panel backlight. Normally a 1506 brightness value of 0 indicates backlight switched off, 1507 and the maximum of the brightness value sets the backlight 1508 to maximum brightness. If this parameter is set to 0 1509 (default) and the machine requires it, or this parameter 1510 is set to 1, a brightness value of 0 sets the backlight 1511 to maximum brightness, and the maximum of the brightness 1512 value switches the backlight off. 1513 -1 -- never invert brightness 1514 0 -- machine default 1515 1 -- force brightness inversion 1516 1517 icn= [HW,ISDN] 1518 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]] 1519 1520 ide-core.nodma= [HW] (E)IDE subsystem 1521 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc 1522 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr 1523 .cdrom .chs .ignore_cable are additional options 1524 See Documentation/ide/ide.rst. 1525 1526 ide-generic.probe-mask= [HW] (E)IDE subsystem 1527 Format: <int> 1528 Probe mask for legacy ISA IDE ports. Depending on 1529 platform up to 6 ports are supported, enabled by 1530 setting corresponding bits in the mask to 1. The 1531 default value is 0x0, which has a special meaning. 1532 On systems that have PCI, it triggers scanning the 1533 PCI bus for the first and the second port, which 1534 are then probed. On systems without PCI the value 1535 of 0x0 enables probing the two first ports as if it 1536 was 0x3. 1537 1538 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem 1539 Claim all unknown PCI IDE storage controllers. 1540 1541 idle= [X86] 1542 Format: idle=poll, idle=halt, idle=nomwait 1543 Poll forces a polling idle loop that can slightly 1544 improve the performance of waking up a idle CPU, but 1545 will use a lot of power and make the system run hot. 1546 Not recommended. 1547 idle=halt: Halt is forced to be used for CPU idle. 1548 In such case C2/C3 won't be used again. 1549 idle=nomwait: Disable mwait for CPU C-states 1550 1551 ieee754= [MIPS] Select IEEE Std 754 conformance mode 1552 Format: { strict | legacy | 2008 | relaxed } 1553 Default: strict 1554 1555 Choose which programs will be accepted for execution 1556 based on the IEEE 754 NaN encoding(s) supported by 1557 the FPU and the NaN encoding requested with the value 1558 of an ELF file header flag individually set by each 1559 binary. Hardware implementations are permitted to 1560 support either or both of the legacy and the 2008 NaN 1561 encoding mode. 1562 1563 Available settings are as follows: 1564 strict accept binaries that request a NaN encoding 1565 supported by the FPU 1566 legacy only accept legacy-NaN binaries, if supported 1567 by the FPU 1568 2008 only accept 2008-NaN binaries, if supported 1569 by the FPU 1570 relaxed accept any binaries regardless of whether 1571 supported by the FPU 1572 1573 The FPU emulator is always able to support both NaN 1574 encodings, so if no FPU hardware is present or it has 1575 been disabled with 'nofpu', then the settings of 1576 'legacy' and '2008' strap the emulator accordingly, 1577 'relaxed' straps the emulator for both legacy-NaN and 1578 2008-NaN, whereas 'strict' enables legacy-NaN only on 1579 legacy processors and both NaN encodings on MIPS32 or 1580 MIPS64 CPUs. 1581 1582 The setting for ABS.fmt/NEG.fmt instruction execution 1583 mode generally follows that for the NaN encoding, 1584 except where unsupported by hardware. 1585 1586 ignore_loglevel [KNL] 1587 Ignore loglevel setting - this will print /all/ 1588 kernel messages to the console. Useful for debugging. 1589 We also add it as printk module parameter, so users 1590 could change it dynamically, usually by 1591 /sys/module/printk/parameters/ignore_loglevel. 1592 1593 ignore_rlimit_data 1594 Ignore RLIMIT_DATA setting for data mappings, 1595 print warning at first misuse. Can be changed via 1596 /sys/module/kernel/parameters/ignore_rlimit_data. 1597 1598 ihash_entries= [KNL] 1599 Set number of hash buckets for inode cache. 1600 1601 ima_appraise= [IMA] appraise integrity measurements 1602 Format: { "off" | "enforce" | "fix" | "log" } 1603 default: "enforce" 1604 1605 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead. 1606 The builtin appraise policy appraises all files 1607 owned by uid=0. 1608 1609 ima_canonical_fmt [IMA] 1610 Use the canonical format for the binary runtime 1611 measurements, instead of host native format. 1612 1613 ima_hash= [IMA] 1614 Format: { md5 | sha1 | rmd160 | sha256 | sha384 1615 | sha512 | ... } 1616 default: "sha1" 1617 1618 The list of supported hash algorithms is defined 1619 in crypto/hash_info.h. 1620 1621 ima_policy= [IMA] 1622 The builtin policies to load during IMA setup. 1623 Format: "tcb | appraise_tcb | secure_boot | 1624 fail_securely" 1625 1626 The "tcb" policy measures all programs exec'd, files 1627 mmap'd for exec, and all files opened with the read 1628 mode bit set by either the effective uid (euid=0) or 1629 uid=0. 1630 1631 The "appraise_tcb" policy appraises the integrity of 1632 all files owned by root. 1633 1634 The "secure_boot" policy appraises the integrity 1635 of files (eg. kexec kernel image, kernel modules, 1636 firmware, policy, etc) based on file signatures. 1637 1638 The "fail_securely" policy forces file signature 1639 verification failure also on privileged mounted 1640 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE 1641 flag. 1642 1643 ima_tcb [IMA] Deprecated. Use ima_policy= instead. 1644 Load a policy which meets the needs of the Trusted 1645 Computing Base. This means IMA will measure all 1646 programs exec'd, files mmap'd for exec, and all files 1647 opened for read by uid=0. 1648 1649 ima_template= [IMA] 1650 Select one of defined IMA measurements template formats. 1651 Formats: { "ima" | "ima-ng" | "ima-sig" } 1652 Default: "ima-ng" 1653 1654 ima_template_fmt= 1655 [IMA] Define a custom template format. 1656 Format: { "field1|...|fieldN" } 1657 1658 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage 1659 Format: <min_file_size> 1660 Set the minimal file size for using asynchronous hash. 1661 If left unspecified, ahash usage is disabled. 1662 1663 ahash performance varies for different data sizes on 1664 different crypto accelerators. This option can be used 1665 to achieve the best performance for a particular HW. 1666 1667 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size 1668 Format: <bufsize> 1669 Set hashing buffer size. Default: 4k. 1670 1671 ahash performance varies for different chunk sizes on 1672 different crypto accelerators. This option can be used 1673 to achieve best performance for particular HW. 1674 1675 init= [KNL] 1676 Format: <full_path> 1677 Run specified binary instead of /sbin/init as init 1678 process. 1679 1680 initcall_debug [KNL] Trace initcalls as they are executed. Useful 1681 for working out where the kernel is dying during 1682 startup. 1683 1684 initcall_blacklist= [KNL] Do not execute a comma-separated list of 1685 initcall functions. Useful for debugging built-in 1686 modules and initcalls. 1687 1688 initrd= [BOOT] Specify the location of the initial ramdisk 1689 1690 init_on_alloc= [MM] Fill newly allocated pages and heap objects with 1691 zeroes. 1692 Format: 0 | 1 1693 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON. 1694 1695 init_on_free= [MM] Fill freed pages and heap objects with zeroes. 1696 Format: 0 | 1 1697 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON. 1698 1699 init_pkru= [x86] Specify the default memory protection keys rights 1700 register contents for all processes. 0x55555554 by 1701 default (disallow access to all but pkey 0). Can 1702 override in debugfs after boot. 1703 1704 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 1705 Format: <irq> 1706 1707 int_pln_enable [x86] Enable power limit notification interrupt 1708 1709 integrity_audit=[IMA] 1710 Format: { "0" | "1" } 1711 0 -- basic integrity auditing messages. (Default) 1712 1 -- additional integrity auditing messages. 1713 1714 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 1715 on 1716 Enable intel iommu driver. 1717 off 1718 Disable intel iommu driver. 1719 igfx_off [Default Off] 1720 By default, gfx is mapped as normal device. If a gfx 1721 device has a dedicated DMAR unit, the DMAR unit is 1722 bypassed by not enabling DMAR with this option. In 1723 this case, gfx device will use physical address for 1724 DMA. 1725 forcedac [x86_64] 1726 With this option iommu will not optimize to look 1727 for io virtual address below 32-bit forcing dual 1728 address cycle on pci bus for cards supporting greater 1729 than 32-bit addressing. The default is to look 1730 for translation below 32-bit and if not available 1731 then look in the higher range. 1732 strict [Default Off] 1733 With this option on every unmap_single operation will 1734 result in a hardware IOTLB flush operation as opposed 1735 to batching them for performance. 1736 sp_off [Default Off] 1737 By default, super page will be supported if Intel IOMMU 1738 has the capability. With this option, super page will 1739 not be supported. 1740 sm_on [Default Off] 1741 By default, scalable mode will be disabled even if the 1742 hardware advertises that it has support for the scalable 1743 mode translation. With this option set, scalable mode 1744 will be used on hardware which claims to support it. 1745 tboot_noforce [Default Off] 1746 Do not force the Intel IOMMU enabled under tboot. 1747 By default, tboot will force Intel IOMMU on, which 1748 could harm performance of some high-throughput 1749 devices like 40GBit network cards, even if identity 1750 mapping is enabled. 1751 Note that using this option lowers the security 1752 provided by tboot because it makes the system 1753 vulnerable to DMA attacks. 1754 nobounce [Default off] 1755 Disable bounce buffer for unstrusted devices such as 1756 the Thunderbolt devices. This will treat the untrusted 1757 devices as the trusted ones, hence might expose security 1758 risks of DMA attacks. 1759 1760 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 1761 0 disables intel_idle and fall back on acpi_idle. 1762 1 to 9 specify maximum depth of C-state. 1763 1764 intel_pstate= [X86] 1765 disable 1766 Do not enable intel_pstate as the default 1767 scaling driver for the supported processors 1768 passive 1769 Use intel_pstate as a scaling driver, but configure it 1770 to work with generic cpufreq governors (instead of 1771 enabling its internal governor). This mode cannot be 1772 used along with the hardware-managed P-states (HWP) 1773 feature. 1774 force 1775 Enable intel_pstate on systems that prohibit it by default 1776 in favor of acpi-cpufreq. Forcing the intel_pstate driver 1777 instead of acpi-cpufreq may disable platform features, such 1778 as thermal controls and power capping, that rely on ACPI 1779 P-States information being indicated to OSPM and therefore 1780 should be used with caution. This option does not work with 1781 processors that aren't supported by the intel_pstate driver 1782 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 1783 no_hwp 1784 Do not enable hardware P state control (HWP) 1785 if available. 1786 hwp_only 1787 Only load intel_pstate on systems which support 1788 hardware P state control (HWP) if available. 1789 support_acpi_ppc 1790 Enforce ACPI _PPC performance limits. If the Fixed ACPI 1791 Description Table, specifies preferred power management 1792 profile as "Enterprise Server" or "Performance Server", 1793 then this feature is turned on by default. 1794 per_cpu_perf_limits 1795 Allow per-logical-CPU P-State performance control limits using 1796 cpufreq sysfs interface 1797 1798 intremap= [X86-64, Intel-IOMMU] 1799 on enable Interrupt Remapping (default) 1800 off disable Interrupt Remapping 1801 nosid disable Source ID checking 1802 no_x2apic_optout 1803 BIOS x2APIC opt-out request will be ignored 1804 nopost disable Interrupt Posting 1805 1806 iomem= Disable strict checking of access to MMIO memory 1807 strict regions from userspace. 1808 relaxed 1809 1810 iommu= [x86] 1811 off 1812 force 1813 noforce 1814 biomerge 1815 panic 1816 nopanic 1817 merge 1818 nomerge 1819 soft 1820 pt [x86] 1821 nopt [x86] 1822 nobypass [PPC/POWERNV] 1823 Disable IOMMU bypass, using IOMMU for PCI devices. 1824 1825 iommu.strict= [ARM64] Configure TLB invalidation behaviour 1826 Format: { "0" | "1" } 1827 0 - Lazy mode. 1828 Request that DMA unmap operations use deferred 1829 invalidation of hardware TLBs, for increased 1830 throughput at the cost of reduced device isolation. 1831 Will fall back to strict mode if not supported by 1832 the relevant IOMMU driver. 1833 1 - Strict mode (default). 1834 DMA unmap operations invalidate IOMMU hardware TLBs 1835 synchronously. 1836 1837 iommu.passthrough= 1838 [ARM64, X86] Configure DMA to bypass the IOMMU by default. 1839 Format: { "0" | "1" } 1840 0 - Use IOMMU translation for DMA. 1841 1 - Bypass the IOMMU for DMA. 1842 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH. 1843 1844 io7= [HW] IO7 for Marvel based alpha systems 1845 See comment before marvel_specify_io7 in 1846 arch/alpha/kernel/core_marvel.c. 1847 1848 io_delay= [X86] I/O delay method 1849 0x80 1850 Standard port 0x80 based delay 1851 0xed 1852 Alternate port 0xed based delay (needed on some systems) 1853 udelay 1854 Simple two microseconds delay 1855 none 1856 No delay 1857 1858 ip= [IP_PNP] 1859 See Documentation/filesystems/nfs/nfsroot.txt. 1860 1861 ipcmni_extend [KNL] Extend the maximum number of unique System V 1862 IPC identifiers from 32,768 to 16,777,216. 1863 1864 irqaffinity= [SMP] Set the default irq affinity mask 1865 The argument is a cpu list, as described above. 1866 1867 irqchip.gicv2_force_probe= 1868 [ARM, ARM64] 1869 Format: <bool> 1870 Force the kernel to look for the second 4kB page 1871 of a GICv2 controller even if the memory range 1872 exposed by the device tree is too small. 1873 1874 irqchip.gicv3_nolpi= 1875 [ARM, ARM64] 1876 Force the kernel to ignore the availability of 1877 LPIs (and by consequence ITSs). Intended for system 1878 that use the kernel as a bootloader, and thus want 1879 to let secondary kernels in charge of setting up 1880 LPIs. 1881 1882 irqchip.gicv3_pseudo_nmi= [ARM64] 1883 Enables support for pseudo-NMIs in the kernel. This 1884 requires the kernel to be built with 1885 CONFIG_ARM64_PSEUDO_NMI. 1886 1887 irqfixup [HW] 1888 When an interrupt is not handled search all handlers 1889 for it. Intended to get systems with badly broken 1890 firmware running. 1891 1892 irqpoll [HW] 1893 When an interrupt is not handled search all handlers 1894 for it. Also check all handlers each timer 1895 interrupt. Intended to get systems with badly broken 1896 firmware running. 1897 1898 isapnp= [ISAPNP] 1899 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 1900 1901 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance. 1902 [Deprecated - use cpusets instead] 1903 Format: [flag-list,]<cpu-list> 1904 1905 Specify one or more CPUs to isolate from disturbances 1906 specified in the flag list (default: domain): 1907 1908 nohz 1909 Disable the tick when a single task runs. 1910 1911 A residual 1Hz tick is offloaded to workqueues, which you 1912 need to affine to housekeeping through the global 1913 workqueue's affinity configured via the 1914 /sys/devices/virtual/workqueue/cpumask sysfs file, or 1915 by using the 'domain' flag described below. 1916 1917 NOTE: by default the global workqueue runs on all CPUs, 1918 so to protect individual CPUs the 'cpumask' file has to 1919 be configured manually after bootup. 1920 1921 domain 1922 Isolate from the general SMP balancing and scheduling 1923 algorithms. Note that performing domain isolation this way 1924 is irreversible: it's not possible to bring back a CPU to 1925 the domains once isolated through isolcpus. It's strongly 1926 advised to use cpusets instead to disable scheduler load 1927 balancing through the "cpuset.sched_load_balance" file. 1928 It offers a much more flexible interface where CPUs can 1929 move in and out of an isolated set anytime. 1930 1931 You can move a process onto or off an "isolated" CPU via 1932 the CPU affinity syscalls or cpuset. 1933 <cpu number> begins at 0 and the maximum value is 1934 "number of CPUs in system - 1". 1935 1936 The format of <cpu-list> is described above. 1937 1938 1939 1940 iucv= [HW,NET] 1941 1942 ivrs_ioapic [HW,X86_64] 1943 Provide an override to the IOAPIC-ID<->DEVICE-ID 1944 mapping provided in the IVRS ACPI table. For 1945 example, to map IOAPIC-ID decimal 10 to 1946 PCI device 00:14.0 write the parameter as: 1947 ivrs_ioapic[10]=00:14.0 1948 1949 ivrs_hpet [HW,X86_64] 1950 Provide an override to the HPET-ID<->DEVICE-ID 1951 mapping provided in the IVRS ACPI table. For 1952 example, to map HPET-ID decimal 0 to 1953 PCI device 00:14.0 write the parameter as: 1954 ivrs_hpet[0]=00:14.0 1955 1956 ivrs_acpihid [HW,X86_64] 1957 Provide an override to the ACPI-HID:UID<->DEVICE-ID 1958 mapping provided in the IVRS ACPI table. For 1959 example, to map UART-HID:UID AMD0020:0 to 1960 PCI device 00:14.5 write the parameter as: 1961 ivrs_acpihid[00:14.5]=AMD0020:0 1962 1963 js= [HW,JOY] Analog joystick 1964 See Documentation/input/joydev/joystick.rst. 1965 1966 nokaslr [KNL] 1967 When CONFIG_RANDOMIZE_BASE is set, this disables 1968 kernel and module base offset ASLR (Address Space 1969 Layout Randomization). 1970 1971 kasan_multi_shot 1972 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print 1973 report on every invalid memory access. Without this 1974 parameter KASAN will print report only for the first 1975 invalid access. 1976 1977 keepinitrd [HW,ARM] 1978 1979 kernelcore= [KNL,X86,IA-64,PPC] 1980 Format: nn[KMGTPE] | nn% | "mirror" 1981 This parameter specifies the amount of memory usable by 1982 the kernel for non-movable allocations. The requested 1983 amount is spread evenly throughout all nodes in the 1984 system as ZONE_NORMAL. The remaining memory is used for 1985 movable memory in its own zone, ZONE_MOVABLE. In the 1986 event, a node is too small to have both ZONE_NORMAL and 1987 ZONE_MOVABLE, kernelcore memory will take priority and 1988 other nodes will have a larger ZONE_MOVABLE. 1989 1990 ZONE_MOVABLE is used for the allocation of pages that 1991 may be reclaimed or moved by the page migration 1992 subsystem. Note that allocations like PTEs-from-HighMem 1993 still use the HighMem zone if it exists, and the Normal 1994 zone if it does not. 1995 1996 It is possible to specify the exact amount of memory in 1997 the form of "nn[KMGTPE]", a percentage of total system 1998 memory in the form of "nn%", or "mirror". If "mirror" 1999 option is specified, mirrored (reliable) memory is used 2000 for non-movable allocations and remaining memory is used 2001 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror" 2002 are exclusive, so you cannot specify multiple forms. 2003 2004 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port. 2005 Format: <Controller#>[,poll interval] 2006 The controller # is the number of the ehci usb debug 2007 port as it is probed via PCI. The poll interval is 2008 optional and is the number seconds in between 2009 each poll cycle to the debug port in case you need 2010 the functionality for interrupting the kernel with 2011 gdb or control-c on the dbgp connection. When 2012 not using this parameter you use sysrq-g to break into 2013 the kernel debugger. 2014 2015 kgdboc= [KGDB,HW] kgdb over consoles. 2016 Requires a tty driver that supports console polling, 2017 or a supported polling keyboard driver (non-usb). 2018 Serial only format: <serial_device>[,baud] 2019 keyboard only format: kbd 2020 keyboard and serial format: kbd,<serial_device>[,baud] 2021 Optional Kernel mode setting: 2022 kms, kbd format: kms,kbd 2023 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 2024 2025 kgdbwait [KGDB] Stop kernel execution and enter the 2026 kernel debugger at the earliest opportunity. 2027 2028 kmac= [MIPS] korina ethernet MAC address. 2029 Configure the RouterBoard 532 series on-chip 2030 Ethernet adapter MAC address. 2031 2032 kmemleak= [KNL] Boot-time kmemleak enable/disable 2033 Valid arguments: on, off 2034 Default: on 2035 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 2036 the default is off. 2037 2038 kprobe_event=[probe-list] 2039 [FTRACE] Add kprobe events and enable at boot time. 2040 The probe-list is a semicolon delimited list of probe 2041 definitions. Each definition is same as kprobe_events 2042 interface, but the parameters are comma delimited. 2043 For example, to add a kprobe event on vfs_read with 2044 arg1 and arg2, add to the command line; 2045 2046 kprobe_event=p,vfs_read,$arg1,$arg2 2047 2048 See also Documentation/trace/kprobetrace.rst "Kernel 2049 Boot Parameter" section. 2050 2051 kpti= [ARM64] Control page table isolation of user 2052 and kernel address spaces. 2053 Default: enabled on cores which need mitigation. 2054 0: force disabled 2055 1: force enabled 2056 2057 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 2058 Default is 0 (don't ignore, but inject #GP) 2059 2060 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface. 2061 Default is false (don't support). 2062 2063 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit 2064 KVM MMU at runtime. 2065 Default is 0 (off) 2066 2067 kvm.nx_huge_pages= 2068 [KVM] Controls the software workaround for the 2069 X86_BUG_ITLB_MULTIHIT bug. 2070 force : Always deploy workaround. 2071 off : Never deploy workaround. 2072 auto : Deploy workaround based on the presence of 2073 X86_BUG_ITLB_MULTIHIT. 2074 2075 Default is 'auto'. 2076 2077 If the software workaround is enabled for the host, 2078 guests do need not to enable it for nested guests. 2079 2080 kvm.nx_huge_pages_recovery_ratio= 2081 [KVM] Controls how many 4KiB pages are periodically zapped 2082 back to huge pages. 0 disables the recovery, otherwise if 2083 the value is N KVM will zap 1/Nth of the 4KiB pages every 2084 minute. The default is 60. 2085 2086 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM. 2087 Default is 1 (enabled) 2088 2089 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU) 2090 for all guests. 2091 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode. 2092 2093 kvm-arm.vgic_v3_group0_trap= 2094 [KVM,ARM] Trap guest accesses to GICv3 group-0 2095 system registers 2096 2097 kvm-arm.vgic_v3_group1_trap= 2098 [KVM,ARM] Trap guest accesses to GICv3 group-1 2099 system registers 2100 2101 kvm-arm.vgic_v3_common_trap= 2102 [KVM,ARM] Trap guest accesses to GICv3 common 2103 system registers 2104 2105 kvm-arm.vgic_v4_enable= 2106 [KVM,ARM] Allow use of GICv4 for direct injection of 2107 LPIs. 2108 2109 kvm-intel.ept= [KVM,Intel] Disable extended page tables 2110 (virtualized MMU) support on capable Intel chips. 2111 Default is 1 (enabled) 2112 2113 kvm-intel.emulate_invalid_guest_state= 2114 [KVM,Intel] Enable emulation of invalid guest states 2115 Default is 0 (disabled) 2116 2117 kvm-intel.flexpriority= 2118 [KVM,Intel] Disable FlexPriority feature (TPR shadow). 2119 Default is 1 (enabled) 2120 2121 kvm-intel.nested= 2122 [KVM,Intel] Enable VMX nesting (nVMX). 2123 Default is 0 (disabled) 2124 2125 kvm-intel.unrestricted_guest= 2126 [KVM,Intel] Disable unrestricted guest feature 2127 (virtualized real and unpaged mode) on capable 2128 Intel chips. Default is 1 (enabled) 2129 2130 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault 2131 CVE-2018-3620. 2132 2133 Valid arguments: never, cond, always 2134 2135 always: L1D cache flush on every VMENTER. 2136 cond: Flush L1D on VMENTER only when the code between 2137 VMEXIT and VMENTER can leak host memory. 2138 never: Disables the mitigation 2139 2140 Default is cond (do L1 cache flush in specific instances) 2141 2142 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification 2143 feature (tagged TLBs) on capable Intel chips. 2144 Default is 1 (enabled) 2145 2146 l1tf= [X86] Control mitigation of the L1TF vulnerability on 2147 affected CPUs 2148 2149 The kernel PTE inversion protection is unconditionally 2150 enabled and cannot be disabled. 2151 2152 full 2153 Provides all available mitigations for the 2154 L1TF vulnerability. Disables SMT and 2155 enables all mitigations in the 2156 hypervisors, i.e. unconditional L1D flush. 2157 2158 SMT control and L1D flush control via the 2159 sysfs interface is still possible after 2160 boot. Hypervisors will issue a warning 2161 when the first VM is started in a 2162 potentially insecure configuration, 2163 i.e. SMT enabled or L1D flush disabled. 2164 2165 full,force 2166 Same as 'full', but disables SMT and L1D 2167 flush runtime control. Implies the 2168 'nosmt=force' command line option. 2169 (i.e. sysfs control of SMT is disabled.) 2170 2171 flush 2172 Leaves SMT enabled and enables the default 2173 hypervisor mitigation, i.e. conditional 2174 L1D flush. 2175 2176 SMT control and L1D flush control via the 2177 sysfs interface is still possible after 2178 boot. Hypervisors will issue a warning 2179 when the first VM is started in a 2180 potentially insecure configuration, 2181 i.e. SMT enabled or L1D flush disabled. 2182 2183 flush,nosmt 2184 2185 Disables SMT and enables the default 2186 hypervisor mitigation. 2187 2188 SMT control and L1D flush control via the 2189 sysfs interface is still possible after 2190 boot. Hypervisors will issue a warning 2191 when the first VM is started in a 2192 potentially insecure configuration, 2193 i.e. SMT enabled or L1D flush disabled. 2194 2195 flush,nowarn 2196 Same as 'flush', but hypervisors will not 2197 warn when a VM is started in a potentially 2198 insecure configuration. 2199 2200 off 2201 Disables hypervisor mitigations and doesn't 2202 emit any warnings. 2203 It also drops the swap size and available 2204 RAM limit restriction on both hypervisor and 2205 bare metal. 2206 2207 Default is 'flush'. 2208 2209 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst 2210 2211 l2cr= [PPC] 2212 2213 l3cr= [PPC] 2214 2215 lapic [X86-32,APIC] Enable the local APIC even if BIOS 2216 disabled it. 2217 2218 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline 2219 value for LAPIC timer one-shot implementation. Default 2220 back to the programmable timer unit in the LAPIC. 2221 2222 lapic_timer_c2_ok [X86,APIC] trust the local apic timer 2223 in C2 power state. 2224 2225 libata.dma= [LIBATA] DMA control 2226 libata.dma=0 Disable all PATA and SATA DMA 2227 libata.dma=1 PATA and SATA Disk DMA only 2228 libata.dma=2 ATAPI (CDROM) DMA only 2229 libata.dma=4 Compact Flash DMA only 2230 Combinations also work, so libata.dma=3 enables DMA 2231 for disks and CDROMs, but not CFs. 2232 2233 libata.ignore_hpa= [LIBATA] Ignore HPA limit 2234 libata.ignore_hpa=0 keep BIOS limits (default) 2235 libata.ignore_hpa=1 ignore limits, using full disk 2236 2237 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 2238 when set. 2239 Format: <int> 2240 2241 libata.force= [LIBATA] Force configurations. The format is comma 2242 separated list of "[ID:]VAL" where ID is 2243 PORT[.DEVICE]. PORT and DEVICE are decimal numbers 2244 matching port, link or device. Basically, it matches 2245 the ATA ID string printed on console by libata. If 2246 the whole ID part is omitted, the last PORT and DEVICE 2247 values are used. If ID hasn't been specified yet, the 2248 configuration applies to all ports, links and devices. 2249 2250 If only DEVICE is omitted, the parameter applies to 2251 the port and all links and devices behind it. DEVICE 2252 number of 0 either selects the first device or the 2253 first fan-out link behind PMP device. It does not 2254 select the host link. DEVICE number of 15 selects the 2255 host link and device attached to it. 2256 2257 The VAL specifies the configuration to force. As long 2258 as there's no ambiguity shortcut notation is allowed. 2259 For example, both 1.5 and 1.5G would work for 1.5Gbps. 2260 The following configurations can be forced. 2261 2262 * Cable type: 40c, 80c, short40c, unk, ign or sata. 2263 Any ID with matching PORT is used. 2264 2265 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 2266 2267 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 2268 udma[/][16,25,33,44,66,100,133] notation is also 2269 allowed. 2270 2271 * [no]ncq: Turn on or off NCQ. 2272 2273 * [no]ncqtrim: Turn off queued DSM TRIM. 2274 2275 * nohrst, nosrst, norst: suppress hard, soft 2276 and both resets. 2277 2278 * rstonce: only attempt one reset during 2279 hot-unplug link recovery 2280 2281 * dump_id: dump IDENTIFY data. 2282 2283 * atapi_dmadir: Enable ATAPI DMADIR bridge support 2284 2285 * disable: Disable this device. 2286 2287 If there are multiple matching configurations changing 2288 the same attribute, the last one is used. 2289 2290 memblock=debug [KNL] Enable memblock debug messages. 2291 2292 load_ramdisk= [RAM] List of ramdisks to load from floppy 2293 See Documentation/admin-guide/blockdev/ramdisk.rst. 2294 2295 lockd.nlm_grace_period=P [NFS] Assign grace period. 2296 Format: <integer> 2297 2298 lockd.nlm_tcpport=N [NFS] Assign TCP port. 2299 Format: <integer> 2300 2301 lockd.nlm_timeout=T [NFS] Assign timeout value. 2302 Format: <integer> 2303 2304 lockd.nlm_udpport=M [NFS] Assign UDP port. 2305 Format: <integer> 2306 2307 lockdown= [SECURITY] 2308 { integrity | confidentiality } 2309 Enable the kernel lockdown feature. If set to 2310 integrity, kernel features that allow userland to 2311 modify the running kernel are disabled. If set to 2312 confidentiality, kernel features that allow userland 2313 to extract confidential information from the kernel 2314 are also disabled. 2315 2316 locktorture.nreaders_stress= [KNL] 2317 Set the number of locking read-acquisition kthreads. 2318 Defaults to being automatically set based on the 2319 number of online CPUs. 2320 2321 locktorture.nwriters_stress= [KNL] 2322 Set the number of locking write-acquisition kthreads. 2323 2324 locktorture.onoff_holdoff= [KNL] 2325 Set time (s) after boot for CPU-hotplug testing. 2326 2327 locktorture.onoff_interval= [KNL] 2328 Set time (s) between CPU-hotplug operations, or 2329 zero to disable CPU-hotplug testing. 2330 2331 locktorture.shuffle_interval= [KNL] 2332 Set task-shuffle interval (jiffies). Shuffling 2333 tasks allows some CPUs to go into dyntick-idle 2334 mode during the locktorture test. 2335 2336 locktorture.shutdown_secs= [KNL] 2337 Set time (s) after boot system shutdown. This 2338 is useful for hands-off automated testing. 2339 2340 locktorture.stat_interval= [KNL] 2341 Time (s) between statistics printk()s. 2342 2343 locktorture.stutter= [KNL] 2344 Time (s) to stutter testing, for example, 2345 specifying five seconds causes the test to run for 2346 five seconds, wait for five seconds, and so on. 2347 This tests the locking primitive's ability to 2348 transition abruptly to and from idle. 2349 2350 locktorture.torture_type= [KNL] 2351 Specify the locking implementation to test. 2352 2353 locktorture.verbose= [KNL] 2354 Enable additional printk() statements. 2355 2356 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 2357 Format: <irq> 2358 2359 loglevel= All Kernel Messages with a loglevel smaller than the 2360 console loglevel will be printed to the console. It can 2361 also be changed with klogd or other programs. The 2362 loglevels are defined as follows: 2363 2364 0 (KERN_EMERG) system is unusable 2365 1 (KERN_ALERT) action must be taken immediately 2366 2 (KERN_CRIT) critical conditions 2367 3 (KERN_ERR) error conditions 2368 4 (KERN_WARNING) warning conditions 2369 5 (KERN_NOTICE) normal but significant condition 2370 6 (KERN_INFO) informational 2371 7 (KERN_DEBUG) debug-level messages 2372 2373 log_buf_len=n[KMG] Sets the size of the printk ring buffer, 2374 in bytes. n must be a power of two and greater 2375 than the minimal size. The minimal size is defined 2376 by LOG_BUF_SHIFT kernel config parameter. There is 2377 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter 2378 that allows to increase the default size depending on 2379 the number of CPUs. See init/Kconfig for more details. 2380 2381 logo.nologo [FB] Disables display of the built-in Linux logo. 2382 This may be used to provide more screen space for 2383 kernel log messages and is useful when debugging 2384 kernel boot problems. 2385 2386 lp=0 [LP] Specify parallel ports to use, e.g, 2387 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 2388 lp=reset first parallel port). 'lp=0' disables the 2389 lp=auto printer driver. 'lp=reset' (which can be 2390 specified in addition to the ports) causes 2391 attached printers to be reset. Using 2392 lp=port1,port2,... specifies the parallel ports 2393 to associate lp devices with, starting with 2394 lp0. A port specification may be 'none' to skip 2395 that lp device, or a parport name such as 2396 'parport0'. Specifying 'lp=auto' instead of a 2397 port specification list means that device IDs 2398 from each port should be examined, to see if 2399 an IEEE 1284-compliant printer is attached; if 2400 so, the driver will manage that printer. 2401 See also header of drivers/char/lp.c. 2402 2403 lpj=n [KNL] 2404 Sets loops_per_jiffy to given constant, thus avoiding 2405 time-consuming boot-time autodetection (up to 250 ms per 2406 CPU). 0 enables autodetection (default). To determine 2407 the correct value for your kernel, boot with normal 2408 autodetection and see what value is printed. Note that 2409 on SMP systems the preset will be applied to all CPUs, 2410 which is likely to cause problems if your CPUs need 2411 significantly divergent settings. An incorrect value 2412 will cause delays in the kernel to be wrong, leading to 2413 unpredictable I/O errors and other breakage. Although 2414 unlikely, in the extreme case this might damage your 2415 hardware. 2416 2417 ltpc= [NET] 2418 Format: <io>,<irq>,<dma> 2419 2420 lsm.debug [SECURITY] Enable LSM initialization debugging output. 2421 2422 lsm=lsm1,...,lsmN 2423 [SECURITY] Choose order of LSM initialization. This 2424 overrides CONFIG_LSM, and the "security=" parameter. 2425 2426 machvec= [IA-64] Force the use of a particular machine-vector 2427 (machvec) in a generic kernel. 2428 Example: machvec=hpzx1 2429 2430 machtype= [Loongson] Share the same kernel image file between different 2431 yeeloong laptop. 2432 Example: machtype=lemote-yeeloong-2f-7inch 2433 2434 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater 2435 than or equal to this physical address is ignored. 2436 2437 maxcpus= [SMP] Maximum number of processors that an SMP kernel 2438 will bring up during bootup. maxcpus=n : n >= 0 limits 2439 the kernel to bring up 'n' processors. Surely after 2440 bootup you can bring up the other plugged cpu by executing 2441 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 2442 only takes effect during system bootup. 2443 While n=0 is a special case, it is equivalent to "nosmp", 2444 which also disables the IO APIC. 2445 2446 max_loop= [LOOP] The number of loop block devices that get 2447 (loop.max_loop) unconditionally pre-created at init time. The default 2448 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 2449 of statically allocating a predefined number, loop 2450 devices can be requested on-demand with the 2451 /dev/loop-control interface. 2452 2453 mce [X86-32] Machine Check Exception 2454 2455 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.rst 2456 2457 md= [HW] RAID subsystems devices and level 2458 See Documentation/admin-guide/md.rst. 2459 2460 mdacon= [MDA] 2461 Format: <first>,<last> 2462 Specifies range of consoles to be captured by the MDA. 2463 2464 mds= [X86,INTEL] 2465 Control mitigation for the Micro-architectural Data 2466 Sampling (MDS) vulnerability. 2467 2468 Certain CPUs are vulnerable to an exploit against CPU 2469 internal buffers which can forward information to a 2470 disclosure gadget under certain conditions. 2471 2472 In vulnerable processors, the speculatively 2473 forwarded data can be used in a cache side channel 2474 attack, to access data to which the attacker does 2475 not have direct access. 2476 2477 This parameter controls the MDS mitigation. The 2478 options are: 2479 2480 full - Enable MDS mitigation on vulnerable CPUs 2481 full,nosmt - Enable MDS mitigation and disable 2482 SMT on vulnerable CPUs 2483 off - Unconditionally disable MDS mitigation 2484 2485 On TAA-affected machines, mds=off can be prevented by 2486 an active TAA mitigation as both vulnerabilities are 2487 mitigated with the same mechanism so in order to disable 2488 this mitigation, you need to specify tsx_async_abort=off 2489 too. 2490 2491 Not specifying this option is equivalent to 2492 mds=full. 2493 2494 For details see: Documentation/admin-guide/hw-vuln/mds.rst 2495 2496 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory 2497 Amount of memory to be used when the kernel is not able 2498 to see the whole system memory or for test. 2499 [X86] Work as limiting max address. Use together 2500 with memmap= to avoid physical address space collisions. 2501 Without memmap= PCI devices could be placed at addresses 2502 belonging to unused RAM. 2503 2504 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 2505 memory. 2506 2507 memchunk=nn[KMG] 2508 [KNL,SH] Allow user to override the default size for 2509 per-device physically contiguous DMA buffers. 2510 2511 memhp_default_state=online/offline 2512 [KNL] Set the initial state for the memory hotplug 2513 onlining policy. If not specified, the default value is 2514 set according to the 2515 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config 2516 option. 2517 See Documentation/admin-guide/mm/memory-hotplug.rst. 2518 2519 memmap=exactmap [KNL,X86] Enable setting of an exact 2520 E820 memory map, as specified by the user. 2521 Such memmap=exactmap lines can be constructed based on 2522 BIOS output or other requirements. See the memmap=nn@ss 2523 option description. 2524 2525 memmap=nn[KMG]@ss[KMG] 2526 [KNL] Force usage of a specific region of memory. 2527 Region of memory to be used is from ss to ss+nn. 2528 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], 2529 which limits max address to nn[KMG]. 2530 Multiple different regions can be specified, 2531 comma delimited. 2532 Example: 2533 memmap=100M@2G,100M#3G,1G!1024G 2534 2535 memmap=nn[KMG]#ss[KMG] 2536 [KNL,ACPI] Mark specific memory as ACPI data. 2537 Region of memory to be marked is from ss to ss+nn. 2538 2539 memmap=nn[KMG]$ss[KMG] 2540 [KNL,ACPI] Mark specific memory as reserved. 2541 Region of memory to be reserved is from ss to ss+nn. 2542 Example: Exclude memory from 0x18690000-0x1869ffff 2543 memmap=64K$0x18690000 2544 or 2545 memmap=0x10000$0x18690000 2546 Some bootloaders may need an escape character before '$', 2547 like Grub2, otherwise '$' and the following number 2548 will be eaten. 2549 2550 memmap=nn[KMG]!ss[KMG] 2551 [KNL,X86] Mark specific memory as protected. 2552 Region of memory to be used, from ss to ss+nn. 2553 The memory region may be marked as e820 type 12 (0xc) 2554 and is NVDIMM or ADR memory. 2555 2556 memmap=<size>%<offset>-<oldtype>+<newtype> 2557 [KNL,ACPI] Convert memory within the specified region 2558 from <oldtype> to <newtype>. If "-<oldtype>" is left 2559 out, the whole region will be marked as <newtype>, 2560 even if previously unavailable. If "+<newtype>" is left 2561 out, matching memory will be removed. Types are 2562 specified as e820 types, e.g., 1 = RAM, 2 = reserved, 2563 3 = ACPI, 12 = PRAM. 2564 2565 memory_corruption_check=0/1 [X86] 2566 Some BIOSes seem to corrupt the first 64k of 2567 memory when doing things like suspend/resume. 2568 Setting this option will scan the memory 2569 looking for corruption. Enabling this will 2570 both detect corruption and prevent the kernel 2571 from using the memory being corrupted. 2572 However, its intended as a diagnostic tool; if 2573 repeatable BIOS-originated corruption always 2574 affects the same memory, you can use memmap= 2575 to prevent the kernel from using that memory. 2576 2577 memory_corruption_check_size=size [X86] 2578 By default it checks for corruption in the low 2579 64k, making this memory unavailable for normal 2580 use. Use this parameter to scan for 2581 corruption in more or less memory. 2582 2583 memory_corruption_check_period=seconds [X86] 2584 By default it checks for corruption every 60 2585 seconds. Use this parameter to check at some 2586 other rate. 0 disables periodic checking. 2587 2588 memtest= [KNL,X86,ARM,PPC] Enable memtest 2589 Format: <integer> 2590 default : 0 <disable> 2591 Specifies the number of memtest passes to be 2592 performed. Each pass selects another test 2593 pattern from a given set of patterns. Memtest 2594 fills the memory with this pattern, validates 2595 memory contents and reserves bad memory 2596 regions that are detected. 2597 2598 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control 2599 Valid arguments: on, off 2600 Default (depends on kernel configuration option): 2601 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y) 2602 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n) 2603 mem_encrypt=on: Activate SME 2604 mem_encrypt=off: Do not activate SME 2605 2606 Refer to Documentation/virt/kvm/amd-memory-encryption.rst 2607 for details on when memory encryption can be activated. 2608 2609 mem_sleep_default= [SUSPEND] Default system suspend mode: 2610 s2idle - Suspend-To-Idle 2611 shallow - Power-On Suspend or equivalent (if supported) 2612 deep - Suspend-To-RAM or equivalent (if supported) 2613 See Documentation/admin-guide/pm/sleep-states.rst. 2614 2615 meye.*= [HW] Set MotionEye Camera parameters 2616 See Documentation/media/v4l-drivers/meye.rst. 2617 2618 mfgpt_irq= [IA-32] Specify the IRQ to use for the 2619 Multi-Function General Purpose Timers on AMD Geode 2620 platforms. 2621 2622 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 2623 the BIOS has incorrectly applied a workaround. TinyBIOS 2624 version 0.98 is known to be affected, 0.99 fixes the 2625 problem by letting the user disable the workaround. 2626 2627 mga= [HW,DRM] 2628 2629 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this 2630 physical address is ignored. 2631 2632 mini2440= [ARM,HW,KNL] 2633 Format:[0..2][b][c][t] 2634 Default: "0tb" 2635 MINI2440 configuration specification: 2636 0 - The attached screen is the 3.5" TFT 2637 1 - The attached screen is the 7" TFT 2638 2 - The VGA Shield is attached (1024x768) 2639 Leaving out the screen size parameter will not load 2640 the TFT driver, and the framebuffer will be left 2641 unconfigured. 2642 b - Enable backlight. The TFT backlight pin will be 2643 linked to the kernel VESA blanking code and a GPIO 2644 LED. This parameter is not necessary when using the 2645 VGA shield. 2646 c - Enable the s3c camera interface. 2647 t - Reserved for enabling touchscreen support. The 2648 touchscreen support is not enabled in the mainstream 2649 kernel as of 2.6.30, a preliminary port can be found 2650 in the "bleeding edge" mini2440 support kernel at 2651 http://repo.or.cz/w/linux-2.6/mini2440.git 2652 2653 mitigations= 2654 [X86,PPC,S390,ARM64] Control optional mitigations for 2655 CPU vulnerabilities. This is a set of curated, 2656 arch-independent options, each of which is an 2657 aggregation of existing arch-specific options. 2658 2659 off 2660 Disable all optional CPU mitigations. This 2661 improves system performance, but it may also 2662 expose users to several CPU vulnerabilities. 2663 Equivalent to: nopti [X86,PPC] 2664 kpti=0 [ARM64] 2665 nospectre_v1 [X86,PPC] 2666 nobp=0 [S390] 2667 nospectre_v2 [X86,PPC,S390,ARM64] 2668 spectre_v2_user=off [X86] 2669 spec_store_bypass_disable=off [X86,PPC] 2670 ssbd=force-off [ARM64] 2671 l1tf=off [X86] 2672 mds=off [X86] 2673 tsx_async_abort=off [X86] 2674 kvm.nx_huge_pages=off [X86] 2675 2676 Exceptions: 2677 This does not have any effect on 2678 kvm.nx_huge_pages when 2679 kvm.nx_huge_pages=force. 2680 2681 auto (default) 2682 Mitigate all CPU vulnerabilities, but leave SMT 2683 enabled, even if it's vulnerable. This is for 2684 users who don't want to be surprised by SMT 2685 getting disabled across kernel upgrades, or who 2686 have other ways of avoiding SMT-based attacks. 2687 Equivalent to: (default behavior) 2688 2689 auto,nosmt 2690 Mitigate all CPU vulnerabilities, disabling SMT 2691 if needed. This is for users who always want to 2692 be fully mitigated, even if it means losing SMT. 2693 Equivalent to: l1tf=flush,nosmt [X86] 2694 mds=full,nosmt [X86] 2695 tsx_async_abort=full,nosmt [X86] 2696 2697 mminit_loglevel= 2698 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this 2699 parameter allows control of the logging verbosity for 2700 the additional memory initialisation checks. A value 2701 of 0 disables mminit logging and a level of 4 will 2702 log everything. Information is printed at KERN_DEBUG 2703 so loglevel=8 may also need to be specified. 2704 2705 module.sig_enforce 2706 [KNL] When CONFIG_MODULE_SIG is set, this means that 2707 modules without (valid) signatures will fail to load. 2708 Note that if CONFIG_MODULE_SIG_FORCE is set, that 2709 is always true, so this option does nothing. 2710 2711 module_blacklist= [KNL] Do not load a comma-separated list of 2712 modules. Useful for debugging problem modules. 2713 2714 mousedev.tap_time= 2715 [MOUSE] Maximum time between finger touching and 2716 leaving touchpad surface for touch to be considered 2717 a tap and be reported as a left button click (for 2718 touchpads working in absolute mode only). 2719 Format: <msecs> 2720 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 2721 reporting absolute coordinates, such as tablets 2722 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 2723 reporting absolute coordinates, such as tablets 2724 2725 movablecore= [KNL,X86,IA-64,PPC] 2726 Format: nn[KMGTPE] | nn% 2727 This parameter is the complement to kernelcore=, it 2728 specifies the amount of memory used for migratable 2729 allocations. If both kernelcore and movablecore is 2730 specified, then kernelcore will be at *least* the 2731 specified value but may be more. If movablecore on its 2732 own is specified, the administrator must be careful 2733 that the amount of memory usable for all allocations 2734 is not too small. 2735 2736 movable_node [KNL] Boot-time switch to make hotplugable memory 2737 NUMA nodes to be movable. This means that the memory 2738 of such nodes will be usable only for movable 2739 allocations which rules out almost all kernel 2740 allocations. Use with caution! 2741 2742 MTD_Partition= [MTD] 2743 Format: <name>,<region-number>,<size>,<offset> 2744 2745 MTD_Region= [MTD] Format: 2746 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 2747 2748 mtdparts= [MTD] 2749 See drivers/mtd/cmdlinepart.c. 2750 2751 multitce=off [PPC] This parameter disables the use of the pSeries 2752 firmware feature for updating multiple TCE entries 2753 at a time. 2754 2755 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 2756 2757 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 2758 2759 boundary - index of last SLC block on Flex-OneNAND. 2760 The remaining blocks are configured as MLC blocks. 2761 lock - Configure if Flex-OneNAND boundary should be locked. 2762 Once locked, the boundary cannot be changed. 2763 1 indicates lock status, 0 indicates unlock status. 2764 2765 mtdset= [ARM] 2766 ARM/S3C2412 JIVE boot control 2767 2768 See arch/arm/mach-s3c2412/mach-jive.c 2769 2770 mtouchusb.raw_coordinates= 2771 [HW] Make the MicroTouch USB driver use raw coordinates 2772 ('y', default) or cooked coordinates ('n') 2773 2774 mtrr_chunk_size=nn[KMG] [X86] 2775 used for mtrr cleanup. It is largest continuous chunk 2776 that could hold holes aka. UC entries. 2777 2778 mtrr_gran_size=nn[KMG] [X86] 2779 Used for mtrr cleanup. It is granularity of mtrr block. 2780 Default is 1. 2781 Large value could prevent small alignment from 2782 using up MTRRs. 2783 2784 mtrr_spare_reg_nr=n [X86] 2785 Format: <integer> 2786 Range: 0,7 : spare reg number 2787 Default : 1 2788 Used for mtrr cleanup. It is spare mtrr entries number. 2789 Set to 2 or more if your graphical card needs more. 2790 2791 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 2792 2793 netdev= [NET] Network devices parameters 2794 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 2795 Note that mem_start is often overloaded to mean 2796 something different and driver-specific. 2797 This usage is only documented in each driver source 2798 file if at all. 2799 2800 nf_conntrack.acct= 2801 [NETFILTER] Enable connection tracking flow accounting 2802 0 to disable accounting 2803 1 to enable accounting 2804 Default value is 0. 2805 2806 nfsaddrs= [NFS] Deprecated. Use ip= instead. 2807 See Documentation/filesystems/nfs/nfsroot.txt. 2808 2809 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 2810 See Documentation/filesystems/nfs/nfsroot.txt. 2811 2812 nfsrootdebug [NFS] enable nfsroot debugging messages. 2813 See Documentation/filesystems/nfs/nfsroot.txt. 2814 2815 nfs.callback_nr_threads= 2816 [NFSv4] set the total number of threads that the 2817 NFS client will assign to service NFSv4 callback 2818 requests. 2819 2820 nfs.callback_tcpport= 2821 [NFS] set the TCP port on which the NFSv4 callback 2822 channel should listen. 2823 2824 nfs.cache_getent= 2825 [NFS] sets the pathname to the program which is used 2826 to update the NFS client cache entries. 2827 2828 nfs.cache_getent_timeout= 2829 [NFS] sets the timeout after which an attempt to 2830 update a cache entry is deemed to have failed. 2831 2832 nfs.idmap_cache_timeout= 2833 [NFS] set the maximum lifetime for idmapper cache 2834 entries. 2835 2836 nfs.enable_ino64= 2837 [NFS] enable 64-bit inode numbers. 2838 If zero, the NFS client will fake up a 32-bit inode 2839 number for the readdir() and stat() syscalls instead 2840 of returning the full 64-bit number. 2841 The default is to return 64-bit inode numbers. 2842 2843 nfs.max_session_cb_slots= 2844 [NFSv4.1] Sets the maximum number of session 2845 slots the client will assign to the callback 2846 channel. This determines the maximum number of 2847 callbacks the client will process in parallel for 2848 a particular server. 2849 2850 nfs.max_session_slots= 2851 [NFSv4.1] Sets the maximum number of session slots 2852 the client will attempt to negotiate with the server. 2853 This limits the number of simultaneous RPC requests 2854 that the client can send to the NFSv4.1 server. 2855 Note that there is little point in setting this 2856 value higher than the max_tcp_slot_table_limit. 2857 2858 nfs.nfs4_disable_idmapping= 2859 [NFSv4] When set to the default of '1', this option 2860 ensures that both the RPC level authentication 2861 scheme and the NFS level operations agree to use 2862 numeric uids/gids if the mount is using the 2863 'sec=sys' security flavour. In effect it is 2864 disabling idmapping, which can make migration from 2865 legacy NFSv2/v3 systems to NFSv4 easier. 2866 Servers that do not support this mode of operation 2867 will be autodetected by the client, and it will fall 2868 back to using the idmapper. 2869 To turn off this behaviour, set the value to '0'. 2870 nfs.nfs4_unique_id= 2871 [NFS4] Specify an additional fixed unique ident- 2872 ification string that NFSv4 clients can insert into 2873 their nfs_client_id4 string. This is typically a 2874 UUID that is generated at system install time. 2875 2876 nfs.send_implementation_id = 2877 [NFSv4.1] Send client implementation identification 2878 information in exchange_id requests. 2879 If zero, no implementation identification information 2880 will be sent. 2881 The default is to send the implementation identification 2882 information. 2883 2884 nfs.recover_lost_locks = 2885 [NFSv4] Attempt to recover locks that were lost due 2886 to a lease timeout on the server. Please note that 2887 doing this risks data corruption, since there are 2888 no guarantees that the file will remain unchanged 2889 after the locks are lost. 2890 If you want to enable the kernel legacy behaviour of 2891 attempting to recover these locks, then set this 2892 parameter to '1'. 2893 The default parameter value of '0' causes the kernel 2894 not to attempt recovery of lost locks. 2895 2896 nfs4.layoutstats_timer = 2897 [NFSv4.2] Change the rate at which the kernel sends 2898 layoutstats to the pNFS metadata server. 2899 2900 Setting this to value to 0 causes the kernel to use 2901 whatever value is the default set by the layout 2902 driver. A non-zero value sets the minimum interval 2903 in seconds between layoutstats transmissions. 2904 2905 nfsd.nfs4_disable_idmapping= 2906 [NFSv4] When set to the default of '1', the NFSv4 2907 server will return only numeric uids and gids to 2908 clients using auth_sys, and will accept numeric uids 2909 and gids from such clients. This is intended to ease 2910 migration from NFSv2/v3. 2911 2912 nmi_debug= [KNL,SH] Specify one or more actions to take 2913 when a NMI is triggered. 2914 Format: [state][,regs][,debounce][,die] 2915 2916 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 2917 Format: [panic,][nopanic,][num] 2918 Valid num: 0 or 1 2919 0 - turn hardlockup detector in nmi_watchdog off 2920 1 - turn hardlockup detector in nmi_watchdog on 2921 When panic is specified, panic when an NMI watchdog 2922 timeout occurs (or 'nopanic' to not panic on an NMI 2923 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set) 2924 To disable both hard and soft lockup detectors, 2925 please see 'nowatchdog'. 2926 This is useful when you use a panic=... timeout and 2927 need the box quickly up again. 2928 2929 These settings can be accessed at runtime via 2930 the nmi_watchdog and hardlockup_panic sysctls. 2931 2932 netpoll.carrier_timeout= 2933 [NET] Specifies amount of time (in seconds) that 2934 netpoll should wait for a carrier. By default netpoll 2935 waits 4 seconds. 2936 2937 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 2938 emulation library even if a 387 maths coprocessor 2939 is present. 2940 2941 no5lvl [X86-64] Disable 5-level paging mode. Forces 2942 kernel to use 4-level paging instead. 2943 2944 no_console_suspend 2945 [HW] Never suspend the console 2946 Disable suspending of consoles during suspend and 2947 hibernate operations. Once disabled, debugging 2948 messages can reach various consoles while the rest 2949 of the system is being put to sleep (ie, while 2950 debugging driver suspend/resume hooks). This may 2951 not work reliably with all consoles, but is known 2952 to work with serial and VGA consoles. 2953 To facilitate more flexible debugging, we also add 2954 console_suspend, a printk module parameter to control 2955 it. Users could use console_suspend (usually 2956 /sys/module/printk/parameters/console_suspend) to 2957 turn on/off it dynamically. 2958 2959 novmcoredd [KNL,KDUMP] 2960 Disable device dump. Device dump allows drivers to 2961 append dump data to vmcore so you can collect driver 2962 specified debug info. Drivers can append the data 2963 without any limit and this data is stored in memory, 2964 so this may cause significant memory stress. Disabling 2965 device dump can help save memory but the driver debug 2966 data will be no longer available. This parameter 2967 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP 2968 is set. 2969 2970 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien 2971 caches in the slab allocator. Saves per-node memory, 2972 but will impact performance. 2973 2974 noalign [KNL,ARM] 2975 2976 noaltinstr [S390] Disables alternative instructions patching 2977 (CPU alternatives feature). 2978 2979 noapic [SMP,APIC] Tells the kernel to not make use of any 2980 IOAPICs that may be present in the system. 2981 2982 noautogroup Disable scheduler automatic task group creation. 2983 2984 nobats [PPC] Do not use BATs for mapping kernel lowmem 2985 on "Classic" PPC cores. 2986 2987 nocache [ARM] 2988 2989 noclflush [BUGS=X86] Don't use the CLFLUSH instruction 2990 2991 nodelayacct [KNL] Disable per-task delay accounting 2992 2993 nodsp [SH] Disable hardware DSP at boot time. 2994 2995 noefi Disable EFI runtime services support. 2996 2997 noexec [IA-64] 2998 2999 noexec [X86] 3000 On X86-32 available only on PAE configured kernels. 3001 noexec=on: enable non-executable mappings (default) 3002 noexec=off: disable non-executable mappings 3003 3004 nosmap [X86,PPC] 3005 Disable SMAP (Supervisor Mode Access Prevention) 3006 even if it is supported by processor. 3007 3008 nosmep [X86,PPC] 3009 Disable SMEP (Supervisor Mode Execution Prevention) 3010 even if it is supported by processor. 3011 3012 noexec32 [X86-64] 3013 This affects only 32-bit executables. 3014 noexec32=on: enable non-executable mappings (default) 3015 read doesn't imply executable mappings 3016 noexec32=off: disable non-executable mappings 3017 read implies executable mappings 3018 3019 nofpu [MIPS,SH] Disable hardware FPU at boot time. 3020 3021 nofxsr [BUGS=X86-32] Disables x86 floating point extended 3022 register save and restore. The kernel will only save 3023 legacy floating-point registers on task switch. 3024 3025 nohugeiomap [KNL,x86,PPC] Disable kernel huge I/O mappings. 3026 3027 nosmt [KNL,S390] Disable symmetric multithreading (SMT). 3028 Equivalent to smt=1. 3029 3030 [KNL,x86] Disable symmetric multithreading (SMT). 3031 nosmt=force: Force disable SMT, cannot be undone 3032 via the sysfs control file. 3033 3034 nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1 3035 (bounds check bypass). With this option data leaks are 3036 possible in the system. 3037 3038 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for 3039 the Spectre variant 2 (indirect branch prediction) 3040 vulnerability. System may allow data leaks with this 3041 option. 3042 3043 nospec_store_bypass_disable 3044 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability 3045 3046 noxsave [BUGS=X86] Disables x86 extended register state save 3047 and restore using xsave. The kernel will fallback to 3048 enabling legacy floating-point and sse state. 3049 3050 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 3051 register states. The kernel will fall back to use 3052 xsave to save the states. By using this parameter, 3053 performance of saving the states is degraded because 3054 xsave doesn't support modified optimization while 3055 xsaveopt supports it on xsaveopt enabled systems. 3056 3057 noxsaves [X86] Disables xsaves and xrstors used in saving and 3058 restoring x86 extended register state in compacted 3059 form of xsave area. The kernel will fall back to use 3060 xsaveopt and xrstor to save and restore the states 3061 in standard form of xsave area. By using this 3062 parameter, xsave area per process might occupy more 3063 memory on xsaves enabled systems. 3064 3065 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or 3066 wfi(ARM) instruction doesn't work correctly and not to 3067 use it. This is also useful when using JTAG debugger. 3068 3069 no_file_caps Tells the kernel not to honor file capabilities. The 3070 only way then for a file to be executed with privilege 3071 is to be setuid root or executed by root. 3072 3073 nohalt [IA-64] Tells the kernel not to use the power saving 3074 function PAL_HALT_LIGHT when idle. This increases 3075 power-consumption. On the positive side, it reduces 3076 interrupt wake-up latency, which may improve performance 3077 in certain environments such as networked servers or 3078 real-time systems. 3079 3080 nohibernate [HIBERNATION] Disable hibernation and resume. 3081 3082 nohz= [KNL] Boottime enable/disable dynamic ticks 3083 Valid arguments: on, off 3084 Default: on 3085 3086 nohz_full= [KNL,BOOT,SMP,ISOL] 3087 The argument is a cpu list, as described above. 3088 In kernels built with CONFIG_NO_HZ_FULL=y, set 3089 the specified list of CPUs whose tick will be stopped 3090 whenever possible. The boot CPU will be forced outside 3091 the range to maintain the timekeeping. Any CPUs 3092 in this list will have their RCU callbacks offloaded, 3093 just as if they had also been called out in the 3094 rcu_nocbs= boot parameter. 3095 3096 noiotrap [SH] Disables trapped I/O port accesses. 3097 3098 noirqdebug [X86-32] Disables the code which attempts to detect and 3099 disable unhandled interrupt sources. 3100 3101 no_timer_check [X86,APIC] Disables the code which tests for 3102 broken timer IRQ sources. 3103 3104 noisapnp [ISAPNP] Disables ISA PnP code. 3105 3106 noinitrd [RAM] Tells the kernel not to load any configured 3107 initial RAM disk. 3108 3109 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt 3110 remapping. 3111 [Deprecated - use intremap=off] 3112 3113 nointroute [IA-64] 3114 3115 noinvpcid [X86] Disable the INVPCID cpu feature. 3116 3117 nojitter [IA-64] Disables jitter checking for ITC timers. 3118 3119 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver 3120 3121 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page 3122 fault handling. 3123 3124 no-vmw-sched-clock 3125 [X86,PV_OPS] Disable paravirtualized VMware scheduler 3126 clock and use the default one. 3127 3128 no-steal-acc [X86,KVM,ARM64] Disable paravirtualized steal time 3129 accounting. steal time is computed, but won't 3130 influence scheduler behaviour 3131 3132 nolapic [X86-32,APIC] Do not enable or use the local APIC. 3133 3134 nolapic_timer [X86-32,APIC] Do not use the local APIC timer. 3135 3136 noltlbs [PPC] Do not use large page/tlb entries for kernel 3137 lowmem mapping on PPC40x and PPC8xx 3138 3139 nomca [IA-64] Disable machine check abort handling 3140 3141 nomce [X86-32] Disable Machine Check Exception 3142 3143 nomfgpt [X86-32] Disable Multi-Function General Purpose 3144 Timer usage (for AMD Geode machines). 3145 3146 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 3147 shutdown the other cpus. Instead use the REBOOT_VECTOR 3148 irq. 3149 3150 nomodule Disable module load 3151 3152 nopat [X86] Disable PAT (page attribute table extension of 3153 pagetables) support. 3154 3155 nopcid [X86-64] Disable the PCID cpu feature. 3156 3157 norandmaps Don't use address space randomization. Equivalent to 3158 echo 0 > /proc/sys/kernel/randomize_va_space 3159 3160 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 3161 with UP alternatives 3162 3163 nordrand [X86] Disable kernel use of the RDRAND and 3164 RDSEED instructions even if they are supported 3165 by the processor. RDRAND and RDSEED are still 3166 available to user space applications. 3167 3168 noresume [SWSUSP] Disables resume and restores original swap 3169 space. 3170 3171 no-scroll [VGA] Disables scrollback. 3172 This is required for the Braillex ib80-piezo Braille 3173 reader made by F.H. Papenmeier (Germany). 3174 3175 nosbagart [IA-64] 3176 3177 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support. 3178 3179 nosmp [SMP] Tells an SMP kernel to act as a UP kernel, 3180 and disable the IO APIC. legacy for "maxcpus=0". 3181 3182 nosoftlockup [KNL] Disable the soft-lockup detector. 3183 3184 nosync [HW,M68K] Disables sync negotiation for all devices. 3185 3186 nowatchdog [KNL] Disable both lockup detectors, i.e. 3187 soft-lockup and NMI watchdog (hard-lockup). 3188 3189 nowb [ARM] 3190 3191 nox2apic [X86-64,APIC] Do not enable x2APIC mode. 3192 3193 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when 3194 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off. 3195 Some features depend on CPU0. Known dependencies are: 3196 1. Resume from suspend/hibernate depends on CPU0. 3197 Suspend/hibernate will fail if CPU0 is offline and you 3198 need to online CPU0 before suspend/hibernate. 3199 2. PIC interrupts also depend on CPU0. CPU0 can't be 3200 removed if a PIC interrupt is detected. 3201 It's said poweroff/reboot may depend on CPU0 on some 3202 machines although I haven't seen such issues so far 3203 after CPU0 is offline on a few tested machines. 3204 If the dependencies are under your control, you can 3205 turn on cpu0_hotplug. 3206 3207 nps_mtm_hs_ctr= [KNL,ARC] 3208 This parameter sets the maximum duration, in 3209 cycles, each HW thread of the CTOP can run 3210 without interruptions, before HW switches it. 3211 The actual maximum duration is 16 times this 3212 parameter's value. 3213 Format: integer between 1 and 255 3214 Default: 255 3215 3216 nptcg= [IA-64] Override max number of concurrent global TLB 3217 purges which is reported from either PAL_VM_SUMMARY or 3218 SAL PALO. 3219 3220 nr_cpus= [SMP] Maximum number of processors that an SMP kernel 3221 could support. nr_cpus=n : n >= 1 limits the kernel to 3222 support 'n' processors. It could be larger than the 3223 number of already plugged CPU during bootup, later in 3224 runtime you can physically add extra cpu until it reaches 3225 n. So during boot up some boot time memory for per-cpu 3226 variables need be pre-allocated for later physical cpu 3227 hot plugging. 3228 3229 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 3230 3231 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing. 3232 Allowed values are enable and disable 3233 3234 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 3235 'node', 'default' can be specified 3236 This can be set from sysctl after boot. 3237 See Documentation/admin-guide/sysctl/vm.rst for details. 3238 3239 of_devlink [OF, KNL] Create device links between consumer and 3240 supplier devices by scanning the devictree to infer the 3241 consumer/supplier relationships. A consumer device 3242 will not be probed until all the supplier devices have 3243 probed successfully. 3244 3245 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver. 3246 See Documentation/debugging-via-ohci1394.txt for more 3247 info. 3248 3249 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 3250 Rather than timing out after 20 ms if an EC 3251 command is not properly ACKed, override the length 3252 of the timeout. We have interrupts disabled while 3253 waiting for the ACK, so if this is set too high 3254 interrupts *may* be lost! 3255 3256 omap_mux= [OMAP] Override bootloader pin multiplexing. 3257 Format: <mux_mode0.mode_name=value>... 3258 For example, to override I2C bus2: 3259 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 3260 3261 oprofile.timer= [HW] 3262 Use timer interrupt instead of performance counters 3263 3264 oprofile.cpu_type= Force an oprofile cpu type 3265 This might be useful if you have an older oprofile 3266 userland or if you want common events. 3267 Format: { arch_perfmon } 3268 arch_perfmon: [X86] Force use of architectural 3269 perfmon on Intel CPUs instead of the 3270 CPU specific event set. 3271 timer: [X86] Force use of architectural NMI 3272 timer mode (see also oprofile.timer 3273 for generic hr timer mode) 3274 3275 oops=panic Always panic on oopses. Default is to just kill the 3276 process, but there is a small probability of 3277 deadlocking the machine. 3278 This will also cause panics on machine check exceptions. 3279 Useful together with panic=30 to trigger a reboot. 3280 3281 page_alloc.shuffle= 3282 [KNL] Boolean flag to control whether the page allocator 3283 should randomize its free lists. The randomization may 3284 be automatically enabled if the kernel detects it is 3285 running on a platform with a direct-mapped memory-side 3286 cache, and this parameter can be used to 3287 override/disable that behavior. The state of the flag 3288 can be read from sysfs at: 3289 /sys/module/page_alloc/parameters/shuffle. 3290 3291 page_owner= [KNL] Boot-time page_owner enabling option. 3292 Storage of the information about who allocated 3293 each page is disabled in default. With this switch, 3294 we can turn it on. 3295 on: enable the feature 3296 3297 page_poison= [KNL] Boot-time parameter changing the state of 3298 poisoning on the buddy allocator, available with 3299 CONFIG_PAGE_POISONING=y. 3300 off: turn off poisoning (default) 3301 on: turn on poisoning 3302 3303 panic= [KNL] Kernel behaviour on panic: delay <timeout> 3304 timeout > 0: seconds before rebooting 3305 timeout = 0: wait forever 3306 timeout < 0: reboot immediately 3307 Format: <timeout> 3308 3309 panic_print= Bitmask for printing system info when panic happens. 3310 User can chose combination of the following bits: 3311 bit 0: print all tasks info 3312 bit 1: print system memory info 3313 bit 2: print timer info 3314 bit 3: print locks info if CONFIG_LOCKDEP is on 3315 bit 4: print ftrace buffer 3316 bit 5: print all printk messages in buffer 3317 3318 panic_on_warn panic() instead of WARN(). Useful to cause kdump 3319 on a WARN(). 3320 3321 crash_kexec_post_notifiers 3322 Run kdump after running panic-notifiers and dumping 3323 kmsg. This only for the users who doubt kdump always 3324 succeeds in any situation. 3325 Note that this also increases risks of kdump failure, 3326 because some panic notifiers can make the crashed 3327 kernel more unstable. 3328 3329 parkbd.port= [HW] Parallel port number the keyboard adapter is 3330 connected to, default is 0. 3331 Format: <parport#> 3332 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 3333 0 for XT, 1 for AT (default is AT). 3334 Format: <mode> 3335 3336 parport= [HW,PPT] Specify parallel ports. 0 disables. 3337 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 3338 Use 'auto' to force the driver to use any 3339 IRQ/DMA settings detected (the default is to 3340 ignore detected IRQ/DMA settings because of 3341 possible conflicts). You can specify the base 3342 address, IRQ, and DMA settings; IRQ and DMA 3343 should be numbers, or 'auto' (for using detected 3344 settings on that particular port), or 'nofifo' 3345 (to avoid using a FIFO even if it is detected). 3346 Parallel ports are assigned in the order they 3347 are specified on the command line, starting 3348 with parport0. 3349 3350 parport_init_mode= [HW,PPT] 3351 Configure VIA parallel port to operate in 3352 a specific mode. This is necessary on Pegasos 3353 computer where firmware has no options for setting 3354 up parallel port mode and sets it to spp. 3355 Currently this function knows 686a and 8231 chips. 3356 Format: [spp|ps2|epp|ecp|ecpepp] 3357 3358 pause_on_oops= 3359 Halt all CPUs after the first oops has been printed for 3360 the specified number of seconds. This is to be used if 3361 your oopses keep scrolling off the screen. 3362 3363 pcbit= [HW,ISDN] 3364 3365 pcd. [PARIDE] 3366 See header of drivers/block/paride/pcd.c. 3367 See also Documentation/admin-guide/blockdev/paride.rst. 3368 3369 pci=option[,option...] [PCI] various PCI subsystem options. 3370 3371 Some options herein operate on a specific device 3372 or a set of devices (<pci_dev>). These are 3373 specified in one of the following formats: 3374 3375 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* 3376 pci:<vendor>:<device>[:<subvendor>:<subdevice>] 3377 3378 Note: the first format specifies a PCI 3379 bus/device/function address which may change 3380 if new hardware is inserted, if motherboard 3381 firmware changes, or due to changes caused 3382 by other kernel parameters. If the 3383 domain is left unspecified, it is 3384 taken to be zero. Optionally, a path 3385 to a device through multiple device/function 3386 addresses can be specified after the base 3387 address (this is more robust against 3388 renumbering issues). The second format 3389 selects devices using IDs from the 3390 configuration space which may match multiple 3391 devices in the system. 3392 3393 earlydump dump PCI config space before the kernel 3394 changes anything 3395 off [X86] don't probe for the PCI bus 3396 bios [X86-32] force use of PCI BIOS, don't access 3397 the hardware directly. Use this if your machine 3398 has a non-standard PCI host bridge. 3399 nobios [X86-32] disallow use of PCI BIOS, only direct 3400 hardware access methods are allowed. Use this 3401 if you experience crashes upon bootup and you 3402 suspect they are caused by the BIOS. 3403 conf1 [X86] Force use of PCI Configuration Access 3404 Mechanism 1 (config address in IO port 0xCF8, 3405 data in IO port 0xCFC, both 32-bit). 3406 conf2 [X86] Force use of PCI Configuration Access 3407 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 3408 the function, IO port 0xCFA, also 8-bit, sets 3409 bus number. The config space is then accessed 3410 through ports 0xC000-0xCFFF). 3411 See http://wiki.osdev.org/PCI for more info 3412 on the configuration access mechanisms. 3413 noaer [PCIE] If the PCIEAER kernel config parameter is 3414 enabled, this kernel boot option can be used to 3415 disable the use of PCIE advanced error reporting. 3416 nodomains [PCI] Disable support for multiple PCI 3417 root domains (aka PCI segments, in ACPI-speak). 3418 nommconf [X86] Disable use of MMCONFIG for PCI 3419 Configuration 3420 check_enable_amd_mmconf [X86] check for and enable 3421 properly configured MMIO access to PCI 3422 config space on AMD family 10h CPU 3423 nomsi [MSI] If the PCI_MSI kernel config parameter is 3424 enabled, this kernel boot option can be used to 3425 disable the use of MSI interrupts system-wide. 3426 noioapicquirk [APIC] Disable all boot interrupt quirks. 3427 Safety option to keep boot IRQs enabled. This 3428 should never be necessary. 3429 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 3430 primary IO-APIC for bridges that cannot disable 3431 boot IRQs. This fixes a source of spurious IRQs 3432 when the system masks IRQs. 3433 noioapicreroute [APIC] Disable workaround that uses the 3434 boot IRQ equivalent of an IRQ that connects to 3435 a chipset where boot IRQs cannot be disabled. 3436 The opposite of ioapicreroute. 3437 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 3438 routing table. These calls are known to be buggy 3439 on several machines and they hang the machine 3440 when used, but on other computers it's the only 3441 way to get the interrupt routing table. Try 3442 this option if the kernel is unable to allocate 3443 IRQs or discover secondary PCI buses on your 3444 motherboard. 3445 rom [X86] Assign address space to expansion ROMs. 3446 Use with caution as certain devices share 3447 address decoders between ROMs and other 3448 resources. 3449 norom [X86] Do not assign address space to 3450 expansion ROMs that do not already have 3451 BIOS assigned address ranges. 3452 nobar [X86] Do not assign address space to the 3453 BARs that weren't assigned by the BIOS. 3454 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 3455 assigned automatically to PCI devices. You can 3456 make the kernel exclude IRQs of your ISA cards 3457 this way. 3458 pirqaddr=0xAAAAA [X86] Specify the physical address 3459 of the PIRQ table (normally generated 3460 by the BIOS) if it is outside the 3461 F0000h-100000h range. 3462 lastbus=N [X86] Scan all buses thru bus #N. Can be 3463 useful if the kernel is unable to find your 3464 secondary buses and you want to tell it 3465 explicitly which ones they are. 3466 assign-busses [X86] Always assign all PCI bus 3467 numbers ourselves, overriding 3468 whatever the firmware may have done. 3469 usepirqmask [X86] Honor the possible IRQ mask stored 3470 in the BIOS $PIR table. This is needed on 3471 some systems with broken BIOSes, notably 3472 some HP Pavilion N5400 and Omnibook XE3 3473 notebooks. This will have no effect if ACPI 3474 IRQ routing is enabled. 3475 noacpi [X86] Do not use ACPI for IRQ routing 3476 or for PCI scanning. 3477 use_crs [X86] Use PCI host bridge window information 3478 from ACPI. On BIOSes from 2008 or later, this 3479 is enabled by default. If you need to use this, 3480 please report a bug. 3481 nocrs [X86] Ignore PCI host bridge windows from ACPI. 3482 If you need to use this, please report a bug. 3483 routeirq Do IRQ routing for all PCI devices. 3484 This is normally done in pci_enable_device(), 3485 so this option is a temporary workaround 3486 for broken drivers that don't call it. 3487 skip_isa_align [X86] do not align io start addr, so can 3488 handle more pci cards 3489 noearly [X86] Don't do any early type 1 scanning. 3490 This might help on some broken boards which 3491 machine check when some devices' config space 3492 is read. But various workarounds are disabled 3493 and some IOMMU drivers will not work. 3494 bfsort Sort PCI devices into breadth-first order. 3495 This sorting is done to get a device 3496 order compatible with older (<= 2.4) kernels. 3497 nobfsort Don't sort PCI devices into breadth-first order. 3498 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 3499 tuning and use the BIOS-configured MPS defaults. 3500 pcie_bus_safe Set every device's MPS to the largest value 3501 supported by all devices below the root complex. 3502 pcie_bus_perf Set device MPS to the largest allowable MPS 3503 based on its parent bus. Also set MRRS (Max 3504 Read Request Size) to the largest supported 3505 value (no larger than the MPS that the device 3506 or bus can support) for best performance. 3507 pcie_bus_peer2peer Set every device's MPS to 128B, which 3508 every device is guaranteed to support. This 3509 configuration allows peer-to-peer DMA between 3510 any pair of devices, possibly at the cost of 3511 reduced performance. This also guarantees 3512 that hot-added devices will work. 3513 cbiosize=nn[KMG] The fixed amount of bus space which is 3514 reserved for the CardBus bridge's IO window. 3515 The default value is 256 bytes. 3516 cbmemsize=nn[KMG] The fixed amount of bus space which is 3517 reserved for the CardBus bridge's memory 3518 window. The default value is 64 megabytes. 3519 resource_alignment= 3520 Format: 3521 [<order of align>@]<pci_dev>[; ...] 3522 Specifies alignment and device to reassign 3523 aligned memory resources. How to 3524 specify the device is described above. 3525 If <order of align> is not specified, 3526 PAGE_SIZE is used as alignment. 3527 A PCI-PCI bridge can be specified if resource 3528 windows need to be expanded. 3529 To specify the alignment for several 3530 instances of a device, the PCI vendor, 3531 device, subvendor, and subdevice may be 3532 specified, e.g., 12@pci:8086:9c22:103c:198f 3533 for 4096-byte alignment. 3534 ecrc= Enable/disable PCIe ECRC (transaction layer 3535 end-to-end CRC checking). 3536 bios: Use BIOS/firmware settings. This is the 3537 the default. 3538 off: Turn ECRC off 3539 on: Turn ECRC on. 3540 hpiosize=nn[KMG] The fixed amount of bus space which is 3541 reserved for hotplug bridge's IO window. 3542 Default size is 256 bytes. 3543 hpmmiosize=nn[KMG] The fixed amount of bus space which is 3544 reserved for hotplug bridge's MMIO window. 3545 Default size is 2 megabytes. 3546 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is 3547 reserved for hotplug bridge's MMIO_PREF window. 3548 Default size is 2 megabytes. 3549 hpmemsize=nn[KMG] The fixed amount of bus space which is 3550 reserved for hotplug bridge's MMIO and 3551 MMIO_PREF window. 3552 Default size is 2 megabytes. 3553 hpbussize=nn The minimum amount of additional bus numbers 3554 reserved for buses below a hotplug bridge. 3555 Default is 1. 3556 realloc= Enable/disable reallocating PCI bridge resources 3557 if allocations done by BIOS are too small to 3558 accommodate resources required by all child 3559 devices. 3560 off: Turn realloc off 3561 on: Turn realloc on 3562 realloc same as realloc=on 3563 noari do not use PCIe ARI. 3564 noats [PCIE, Intel-IOMMU, AMD-IOMMU] 3565 do not use PCIe ATS (and IOMMU device IOTLB). 3566 pcie_scan_all Scan all possible PCIe devices. Otherwise we 3567 only look for one device below a PCIe downstream 3568 port. 3569 big_root_window Try to add a big 64bit memory window to the PCIe 3570 root complex on AMD CPUs. Some GFX hardware 3571 can resize a BAR to allow access to all VRAM. 3572 Adding the window is slightly risky (it may 3573 conflict with unreported devices), so this 3574 taints the kernel. 3575 disable_acs_redir=<pci_dev>[; ...] 3576 Specify one or more PCI devices (in the format 3577 specified above) separated by semicolons. 3578 Each device specified will have the PCI ACS 3579 redirect capabilities forced off which will 3580 allow P2P traffic between devices through 3581 bridges without forcing it upstream. Note: 3582 this removes isolation between devices and 3583 may put more devices in an IOMMU group. 3584 force_floating [S390] Force usage of floating interrupts. 3585 nomio [S390] Do not use MIO instructions. 3586 3587 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power 3588 Management. 3589 off Disable ASPM. 3590 force Enable ASPM even on devices that claim not to support it. 3591 WARNING: Forcing ASPM on may cause system lockups. 3592 3593 pcie_ports= [PCIE] PCIe port services handling: 3594 native Use native PCIe services (PME, AER, DPC, PCIe hotplug) 3595 even if the platform doesn't give the OS permission to 3596 use them. This may cause conflicts if the platform 3597 also tries to use these services. 3598 dpc-native Use native PCIe service for DPC only. May 3599 cause conflicts if firmware uses AER or DPC. 3600 compat Disable native PCIe services (PME, AER, DPC, PCIe 3601 hotplug). 3602 3603 pcie_port_pm= [PCIE] PCIe port power management handling: 3604 off Disable power management of all PCIe ports 3605 force Forcibly enable power management of all PCIe ports 3606 3607 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 3608 nomsi Do not use MSI for native PCIe PME signaling (this makes 3609 all PCIe root ports use INTx for all services). 3610 3611 pcmv= [HW,PCMCIA] BadgePAD 4 3612 3613 pd_ignore_unused 3614 [PM] 3615 Keep all power-domains already enabled by bootloader on, 3616 even if no driver has claimed them. This is useful 3617 for debug and development, but should not be 3618 needed on a platform with proper driver support. 3619 3620 pd. [PARIDE] 3621 See Documentation/admin-guide/blockdev/paride.rst. 3622 3623 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 3624 boot time. 3625 Format: { 0 | 1 } 3626 See arch/parisc/kernel/pdc_chassis.c 3627 3628 percpu_alloc= Select which percpu first chunk allocator to use. 3629 Currently supported values are "embed" and "page". 3630 Archs may support subset or none of the selections. 3631 See comments in mm/percpu.c for details on each 3632 allocator. This parameter is primarily for debugging 3633 and performance comparison. 3634 3635 pf. [PARIDE] 3636 See Documentation/admin-guide/blockdev/paride.rst. 3637 3638 pg. [PARIDE] 3639 See Documentation/admin-guide/blockdev/paride.rst. 3640 3641 pirq= [SMP,APIC] Manual mp-table setup 3642 See Documentation/x86/i386/IO-APIC.rst. 3643 3644 plip= [PPT,NET] Parallel port network link 3645 Format: { parport<nr> | timid | 0 } 3646 See also Documentation/admin-guide/parport.rst. 3647 3648 pmtmr= [X86] Manual setup of pmtmr I/O Port. 3649 Override pmtimer IOPort with a hex value. 3650 e.g. pmtmr=0x508 3651 3652 pnp.debug=1 [PNP] 3653 Enable PNP debug messages (depends on the 3654 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 3655 via /sys/module/pnp/parameters/debug. We always show 3656 current resource usage; turning this on also shows 3657 possible settings and some assignment information. 3658 3659 pnpacpi= [ACPI] 3660 { off } 3661 3662 pnpbios= [ISAPNP] 3663 { on | off | curr | res | no-curr | no-res } 3664 3665 pnp_reserve_irq= 3666 [ISAPNP] Exclude IRQs for the autoconfiguration 3667 3668 pnp_reserve_dma= 3669 [ISAPNP] Exclude DMAs for the autoconfiguration 3670 3671 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 3672 Ranges are in pairs (I/O port base and size). 3673 3674 pnp_reserve_mem= 3675 [ISAPNP] Exclude memory regions for the 3676 autoconfiguration. 3677 Ranges are in pairs (memory base and size). 3678 3679 ports= [IP_VS_FTP] IPVS ftp helper module 3680 Default is 21. 3681 Up to 8 (IP_VS_APP_MAX_PORTS) ports 3682 may be specified. 3683 Format: <port>,<port>.... 3684 3685 powersave=off [PPC] This option disables power saving features. 3686 It specifically disables cpuidle and sets the 3687 platform machine description specific power_save 3688 function to NULL. On Idle the CPU just reduces 3689 execution priority. 3690 3691 ppc_strict_facility_enable 3692 [PPC] This option catches any kernel floating point, 3693 Altivec, VSX and SPE outside of regions specifically 3694 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 3695 There is some performance impact when enabling this. 3696 3697 ppc_tm= [PPC] 3698 Format: {"off"} 3699 Disable Hardware Transactional Memory 3700 3701 print-fatal-signals= 3702 [KNL] debug: print fatal signals 3703 3704 If enabled, warn about various signal handling 3705 related application anomalies: too many signals, 3706 too many POSIX.1 timers, fatal signals causing a 3707 coredump - etc. 3708 3709 If you hit the warning due to signal overflow, 3710 you might want to try "ulimit -i unlimited". 3711 3712 default: off. 3713 3714 printk.always_kmsg_dump= 3715 Trigger kmsg_dump for cases other than kernel oops or 3716 panics 3717 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3718 default: disabled 3719 3720 printk.devkmsg={on,off,ratelimit} 3721 Control writing to /dev/kmsg. 3722 on - unlimited logging to /dev/kmsg from userspace 3723 off - logging to /dev/kmsg disabled 3724 ratelimit - ratelimit the logging 3725 Default: ratelimit 3726 3727 printk.time= Show timing data prefixed to each printk message line 3728 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3729 3730 processor.max_cstate= [HW,ACPI] 3731 Limit processor to maximum C-state 3732 max_cstate=9 overrides any DMI blacklist limit. 3733 3734 processor.nocst [HW,ACPI] 3735 Ignore the _CST method to determine C-states, 3736 instead using the legacy FADT method 3737 3738 profile= [KNL] Enable kernel profiling via /proc/profile 3739 Format: [<profiletype>,]<number> 3740 Param: <profiletype>: "schedule", "sleep", or "kvm" 3741 [defaults to kernel profiling] 3742 Param: "schedule" - profile schedule points. 3743 Param: "sleep" - profile D-state sleeping (millisecs). 3744 Requires CONFIG_SCHEDSTATS 3745 Param: "kvm" - profile VM exits. 3746 Param: <number> - step/bucket size as a power of 2 for 3747 statistical time based profiling. 3748 3749 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk 3750 before loading. 3751 See Documentation/admin-guide/blockdev/ramdisk.rst. 3752 3753 psi= [KNL] Enable or disable pressure stall information 3754 tracking. 3755 Format: <bool> 3756 3757 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 3758 probe for; one of (bare|imps|exps|lifebook|any). 3759 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 3760 per second. 3761 psmouse.resetafter= [HW,MOUSE] 3762 Try to reset the device after so many bad packets 3763 (0 = never). 3764 psmouse.resolution= 3765 [HW,MOUSE] Set desired mouse resolution, in dpi. 3766 psmouse.smartscroll= 3767 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 3768 0 = disabled, 1 = enabled (default). 3769 3770 pstore.backend= Specify the name of the pstore backend to use 3771 3772 pt. [PARIDE] 3773 See Documentation/admin-guide/blockdev/paride.rst. 3774 3775 pti= [X86_64] Control Page Table Isolation of user and 3776 kernel address spaces. Disabling this feature 3777 removes hardening, but improves performance of 3778 system calls and interrupts. 3779 3780 on - unconditionally enable 3781 off - unconditionally disable 3782 auto - kernel detects whether your CPU model is 3783 vulnerable to issues that PTI mitigates 3784 3785 Not specifying this option is equivalent to pti=auto. 3786 3787 nopti [X86_64] 3788 Equivalent to pti=off 3789 3790 pty.legacy_count= 3791 [KNL] Number of legacy pty's. Overwrites compiled-in 3792 default number. 3793 3794 quiet [KNL] Disable most log messages 3795 3796 r128= [HW,DRM] 3797 3798 raid= [HW,RAID] 3799 See Documentation/admin-guide/md.rst. 3800 3801 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 3802 See Documentation/admin-guide/blockdev/ramdisk.rst. 3803 3804 random.trust_cpu={on,off} 3805 [KNL] Enable or disable trusting the use of the 3806 CPU's random number generator (if available) to 3807 fully seed the kernel's CRNG. Default is controlled 3808 by CONFIG_RANDOM_TRUST_CPU. 3809 3810 ras=option[,option,...] [KNL] RAS-specific options 3811 3812 cec_disable [X86] 3813 Disable the Correctable Errors Collector, 3814 see CONFIG_RAS_CEC help text. 3815 3816 rcu_nocbs= [KNL] 3817 The argument is a cpu list, as described above, 3818 except that the string "all" can be used to 3819 specify every CPU on the system. 3820 3821 In kernels built with CONFIG_RCU_NOCB_CPU=y, set 3822 the specified list of CPUs to be no-callback CPUs. 3823 Invocation of these CPUs' RCU callbacks will be 3824 offloaded to "rcuox/N" kthreads created for that 3825 purpose, where "x" is "p" for RCU-preempt, and 3826 "s" for RCU-sched, and "N" is the CPU number. 3827 This reduces OS jitter on the offloaded CPUs, 3828 which can be useful for HPC and real-time 3829 workloads. It can also improve energy efficiency 3830 for asymmetric multiprocessors. 3831 3832 rcu_nocb_poll [KNL] 3833 Rather than requiring that offloaded CPUs 3834 (specified by rcu_nocbs= above) explicitly 3835 awaken the corresponding "rcuoN" kthreads, 3836 make these kthreads poll for callbacks. 3837 This improves the real-time response for the 3838 offloaded CPUs by relieving them of the need to 3839 wake up the corresponding kthread, but degrades 3840 energy efficiency by requiring that the kthreads 3841 periodically wake up to do the polling. 3842 3843 rcutree.blimit= [KNL] 3844 Set maximum number of finished RCU callbacks to 3845 process in one batch. 3846 3847 rcutree.dump_tree= [KNL] 3848 Dump the structure of the rcu_node combining tree 3849 out at early boot. This is used for diagnostic 3850 purposes, to verify correct tree setup. 3851 3852 rcutree.gp_cleanup_delay= [KNL] 3853 Set the number of jiffies to delay each step of 3854 RCU grace-period cleanup. 3855 3856 rcutree.gp_init_delay= [KNL] 3857 Set the number of jiffies to delay each step of 3858 RCU grace-period initialization. 3859 3860 rcutree.gp_preinit_delay= [KNL] 3861 Set the number of jiffies to delay each step of 3862 RCU grace-period pre-initialization, that is, 3863 the propagation of recent CPU-hotplug changes up 3864 the rcu_node combining tree. 3865 3866 rcutree.use_softirq= [KNL] 3867 If set to zero, move all RCU_SOFTIRQ processing to 3868 per-CPU rcuc kthreads. Defaults to a non-zero 3869 value, meaning that RCU_SOFTIRQ is used by default. 3870 Specify rcutree.use_softirq=0 to use rcuc kthreads. 3871 3872 rcutree.rcu_fanout_exact= [KNL] 3873 Disable autobalancing of the rcu_node combining 3874 tree. This is used by rcutorture, and might 3875 possibly be useful for architectures having high 3876 cache-to-cache transfer latencies. 3877 3878 rcutree.rcu_fanout_leaf= [KNL] 3879 Change the number of CPUs assigned to each 3880 leaf rcu_node structure. Useful for very 3881 large systems, which will choose the value 64, 3882 and for NUMA systems with large remote-access 3883 latencies, which will choose a value aligned 3884 with the appropriate hardware boundaries. 3885 3886 rcutree.jiffies_till_first_fqs= [KNL] 3887 Set delay from grace-period initialization to 3888 first attempt to force quiescent states. 3889 Units are jiffies, minimum value is zero, 3890 and maximum value is HZ. 3891 3892 rcutree.jiffies_till_next_fqs= [KNL] 3893 Set delay between subsequent attempts to force 3894 quiescent states. Units are jiffies, minimum 3895 value is one, and maximum value is HZ. 3896 3897 rcutree.jiffies_till_sched_qs= [KNL] 3898 Set required age in jiffies for a 3899 given grace period before RCU starts 3900 soliciting quiescent-state help from 3901 rcu_note_context_switch() and cond_resched(). 3902 If not specified, the kernel will calculate 3903 a value based on the most recent settings 3904 of rcutree.jiffies_till_first_fqs 3905 and rcutree.jiffies_till_next_fqs. 3906 This calculated value may be viewed in 3907 rcutree.jiffies_to_sched_qs. Any attempt to set 3908 rcutree.jiffies_to_sched_qs will be cheerfully 3909 overwritten. 3910 3911 rcutree.kthread_prio= [KNL,BOOT] 3912 Set the SCHED_FIFO priority of the RCU per-CPU 3913 kthreads (rcuc/N). This value is also used for 3914 the priority of the RCU boost threads (rcub/N) 3915 and for the RCU grace-period kthreads (rcu_bh, 3916 rcu_preempt, and rcu_sched). If RCU_BOOST is 3917 set, valid values are 1-99 and the default is 1 3918 (the least-favored priority). Otherwise, when 3919 RCU_BOOST is not set, valid values are 0-99 and 3920 the default is zero (non-realtime operation). 3921 3922 rcutree.rcu_nocb_gp_stride= [KNL] 3923 Set the number of NOCB callback kthreads in 3924 each group, which defaults to the square root 3925 of the number of CPUs. Larger numbers reduce 3926 the wakeup overhead on the global grace-period 3927 kthread, but increases that same overhead on 3928 each group's NOCB grace-period kthread. 3929 3930 rcutree.qhimark= [KNL] 3931 Set threshold of queued RCU callbacks beyond which 3932 batch limiting is disabled. 3933 3934 rcutree.qlowmark= [KNL] 3935 Set threshold of queued RCU callbacks below which 3936 batch limiting is re-enabled. 3937 3938 rcutree.rcu_idle_gp_delay= [KNL] 3939 Set wakeup interval for idle CPUs that have 3940 RCU callbacks (RCU_FAST_NO_HZ=y). 3941 3942 rcutree.rcu_idle_lazy_gp_delay= [KNL] 3943 Set wakeup interval for idle CPUs that have 3944 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y). 3945 Lazy RCU callbacks are those which RCU can 3946 prove do nothing more than free memory. 3947 3948 rcutree.rcu_kick_kthreads= [KNL] 3949 Cause the grace-period kthread to get an extra 3950 wake_up() if it sleeps three times longer than 3951 it should at force-quiescent-state time. 3952 This wake_up() will be accompanied by a 3953 WARN_ONCE() splat and an ftrace_dump(). 3954 3955 rcutree.sysrq_rcu= [KNL] 3956 Commandeer a sysrq key to dump out Tree RCU's 3957 rcu_node tree with an eye towards determining 3958 why a new grace period has not yet started. 3959 3960 rcuperf.gp_async= [KNL] 3961 Measure performance of asynchronous 3962 grace-period primitives such as call_rcu(). 3963 3964 rcuperf.gp_async_max= [KNL] 3965 Specify the maximum number of outstanding 3966 callbacks per writer thread. When a writer 3967 thread exceeds this limit, it invokes the 3968 corresponding flavor of rcu_barrier() to allow 3969 previously posted callbacks to drain. 3970 3971 rcuperf.gp_exp= [KNL] 3972 Measure performance of expedited synchronous 3973 grace-period primitives. 3974 3975 rcuperf.holdoff= [KNL] 3976 Set test-start holdoff period. The purpose of 3977 this parameter is to delay the start of the 3978 test until boot completes in order to avoid 3979 interference. 3980 3981 rcuperf.nreaders= [KNL] 3982 Set number of RCU readers. The value -1 selects 3983 N, where N is the number of CPUs. A value 3984 "n" less than -1 selects N-n+1, where N is again 3985 the number of CPUs. For example, -2 selects N 3986 (the number of CPUs), -3 selects N+1, and so on. 3987 A value of "n" less than or equal to -N selects 3988 a single reader. 3989 3990 rcuperf.nwriters= [KNL] 3991 Set number of RCU writers. The values operate 3992 the same as for rcuperf.nreaders. 3993 N, where N is the number of CPUs 3994 3995 rcuperf.perf_type= [KNL] 3996 Specify the RCU implementation to test. 3997 3998 rcuperf.shutdown= [KNL] 3999 Shut the system down after performance tests 4000 complete. This is useful for hands-off automated 4001 testing. 4002 4003 rcuperf.verbose= [KNL] 4004 Enable additional printk() statements. 4005 4006 rcuperf.writer_holdoff= [KNL] 4007 Write-side holdoff between grace periods, 4008 in microseconds. The default of zero says 4009 no holdoff. 4010 4011 rcutorture.fqs_duration= [KNL] 4012 Set duration of force_quiescent_state bursts 4013 in microseconds. 4014 4015 rcutorture.fqs_holdoff= [KNL] 4016 Set holdoff time within force_quiescent_state bursts 4017 in microseconds. 4018 4019 rcutorture.fqs_stutter= [KNL] 4020 Set wait time between force_quiescent_state bursts 4021 in seconds. 4022 4023 rcutorture.fwd_progress= [KNL] 4024 Enable RCU grace-period forward-progress testing 4025 for the types of RCU supporting this notion. 4026 4027 rcutorture.fwd_progress_div= [KNL] 4028 Specify the fraction of a CPU-stall-warning 4029 period to do tight-loop forward-progress testing. 4030 4031 rcutorture.fwd_progress_holdoff= [KNL] 4032 Number of seconds to wait between successive 4033 forward-progress tests. 4034 4035 rcutorture.fwd_progress_need_resched= [KNL] 4036 Enclose cond_resched() calls within checks for 4037 need_resched() during tight-loop forward-progress 4038 testing. 4039 4040 rcutorture.gp_cond= [KNL] 4041 Use conditional/asynchronous update-side 4042 primitives, if available. 4043 4044 rcutorture.gp_exp= [KNL] 4045 Use expedited update-side primitives, if available. 4046 4047 rcutorture.gp_normal= [KNL] 4048 Use normal (non-expedited) asynchronous 4049 update-side primitives, if available. 4050 4051 rcutorture.gp_sync= [KNL] 4052 Use normal (non-expedited) synchronous 4053 update-side primitives, if available. If all 4054 of rcutorture.gp_cond=, rcutorture.gp_exp=, 4055 rcutorture.gp_normal=, and rcutorture.gp_sync= 4056 are zero, rcutorture acts as if is interpreted 4057 they are all non-zero. 4058 4059 rcutorture.n_barrier_cbs= [KNL] 4060 Set callbacks/threads for rcu_barrier() testing. 4061 4062 rcutorture.nfakewriters= [KNL] 4063 Set number of concurrent RCU writers. These just 4064 stress RCU, they don't participate in the actual 4065 test, hence the "fake". 4066 4067 rcutorture.nreaders= [KNL] 4068 Set number of RCU readers. The value -1 selects 4069 N-1, where N is the number of CPUs. A value 4070 "n" less than -1 selects N-n-2, where N is again 4071 the number of CPUs. For example, -2 selects N 4072 (the number of CPUs), -3 selects N+1, and so on. 4073 4074 rcutorture.object_debug= [KNL] 4075 Enable debug-object double-call_rcu() testing. 4076 4077 rcutorture.onoff_holdoff= [KNL] 4078 Set time (s) after boot for CPU-hotplug testing. 4079 4080 rcutorture.onoff_interval= [KNL] 4081 Set time (jiffies) between CPU-hotplug operations, 4082 or zero to disable CPU-hotplug testing. 4083 4084 rcutorture.shuffle_interval= [KNL] 4085 Set task-shuffle interval (s). Shuffling tasks 4086 allows some CPUs to go into dyntick-idle mode 4087 during the rcutorture test. 4088 4089 rcutorture.shutdown_secs= [KNL] 4090 Set time (s) after boot system shutdown. This 4091 is useful for hands-off automated testing. 4092 4093 rcutorture.stall_cpu= [KNL] 4094 Duration of CPU stall (s) to test RCU CPU stall 4095 warnings, zero to disable. 4096 4097 rcutorture.stall_cpu_holdoff= [KNL] 4098 Time to wait (s) after boot before inducing stall. 4099 4100 rcutorture.stall_cpu_irqsoff= [KNL] 4101 Disable interrupts while stalling if set. 4102 4103 rcutorture.stat_interval= [KNL] 4104 Time (s) between statistics printk()s. 4105 4106 rcutorture.stutter= [KNL] 4107 Time (s) to stutter testing, for example, specifying 4108 five seconds causes the test to run for five seconds, 4109 wait for five seconds, and so on. This tests RCU's 4110 ability to transition abruptly to and from idle. 4111 4112 rcutorture.test_boost= [KNL] 4113 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 4114 "Maybe" means test if the RCU implementation 4115 under test support RCU priority boosting. 4116 4117 rcutorture.test_boost_duration= [KNL] 4118 Duration (s) of each individual boost test. 4119 4120 rcutorture.test_boost_interval= [KNL] 4121 Interval (s) between each boost test. 4122 4123 rcutorture.test_no_idle_hz= [KNL] 4124 Test RCU's dyntick-idle handling. See also the 4125 rcutorture.shuffle_interval parameter. 4126 4127 rcutorture.torture_type= [KNL] 4128 Specify the RCU implementation to test. 4129 4130 rcutorture.verbose= [KNL] 4131 Enable additional printk() statements. 4132 4133 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL] 4134 Dump ftrace buffer after reporting RCU CPU 4135 stall warning. 4136 4137 rcupdate.rcu_cpu_stall_suppress= [KNL] 4138 Suppress RCU CPU stall warning messages. 4139 4140 rcupdate.rcu_cpu_stall_timeout= [KNL] 4141 Set timeout for RCU CPU stall warning messages. 4142 4143 rcupdate.rcu_expedited= [KNL] 4144 Use expedited grace-period primitives, for 4145 example, synchronize_rcu_expedited() instead 4146 of synchronize_rcu(). This reduces latency, 4147 but can increase CPU utilization, degrade 4148 real-time latency, and degrade energy efficiency. 4149 No effect on CONFIG_TINY_RCU kernels. 4150 4151 rcupdate.rcu_normal= [KNL] 4152 Use only normal grace-period primitives, 4153 for example, synchronize_rcu() instead of 4154 synchronize_rcu_expedited(). This improves 4155 real-time latency, CPU utilization, and 4156 energy efficiency, but can expose users to 4157 increased grace-period latency. This parameter 4158 overrides rcupdate.rcu_expedited. No effect on 4159 CONFIG_TINY_RCU kernels. 4160 4161 rcupdate.rcu_normal_after_boot= [KNL] 4162 Once boot has completed (that is, after 4163 rcu_end_inkernel_boot() has been invoked), use 4164 only normal grace-period primitives. No effect 4165 on CONFIG_TINY_RCU kernels. 4166 4167 rcupdate.rcu_task_stall_timeout= [KNL] 4168 Set timeout in jiffies for RCU task stall warning 4169 messages. Disable with a value less than or equal 4170 to zero. 4171 4172 rcupdate.rcu_self_test= [KNL] 4173 Run the RCU early boot self tests 4174 4175 rdinit= [KNL] 4176 Format: <full_path> 4177 Run specified binary instead of /init from the ramdisk, 4178 used for early userspace startup. See initrd. 4179 4180 rdrand= [X86] 4181 force - Override the decision by the kernel to hide the 4182 advertisement of RDRAND support (this affects 4183 certain AMD processors because of buggy BIOS 4184 support, specifically around the suspend/resume 4185 path). 4186 4187 rdt= [HW,X86,RDT] 4188 Turn on/off individual RDT features. List is: 4189 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, 4190 mba. 4191 E.g. to turn on cmt and turn off mba use: 4192 rdt=cmt,!mba 4193 4194 reboot= [KNL] 4195 Format (x86 or x86_64): 4196 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \ 4197 [[,]s[mp]#### \ 4198 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 4199 [[,]f[orce] 4200 Where reboot_mode is one of warm (soft) or cold (hard) or gpio 4201 (prefix with 'panic_' to set mode for panic 4202 reboot only), 4203 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 4204 reboot_force is either force or not specified, 4205 reboot_cpu is s[mp]#### with #### being the processor 4206 to be used for rebooting. 4207 4208 relax_domain_level= 4209 [KNL, SMP] Set scheduler's default relax_domain_level. 4210 See Documentation/admin-guide/cgroup-v1/cpusets.rst. 4211 4212 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory 4213 Format: <base1>,<size1>[,<base2>,<size2>,...] 4214 Reserve I/O ports or memory so the kernel won't use 4215 them. If <base> is less than 0x10000, the region 4216 is assumed to be I/O ports; otherwise it is memory. 4217 4218 reservetop= [X86-32] 4219 Format: nn[KMG] 4220 Reserves a hole at the top of the kernel virtual 4221 address space. 4222 4223 reservelow= [X86] 4224 Format: nn[K] 4225 Set the amount of memory to reserve for BIOS at 4226 the bottom of the address space. 4227 4228 reset_devices [KNL] Force drivers to reset the underlying device 4229 during initialization. 4230 4231 resume= [SWSUSP] 4232 Specify the partition device for software suspend 4233 Format: 4234 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 4235 4236 resume_offset= [SWSUSP] 4237 Specify the offset from the beginning of the partition 4238 given by "resume=" at which the swap header is located, 4239 in <PAGE_SIZE> units (needed only for swap files). 4240 See Documentation/power/swsusp-and-swap-files.rst 4241 4242 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 4243 read the resume files 4244 4245 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 4246 Useful for devices that are detected asynchronously 4247 (e.g. USB and MMC devices). 4248 4249 hibernate= [HIBERNATION] 4250 noresume Don't check if there's a hibernation image 4251 present during boot. 4252 nocompress Don't compress/decompress hibernation images. 4253 no Disable hibernation and resume. 4254 protect_image Turn on image protection during restoration 4255 (that will set all pages holding image data 4256 during restoration read-only). 4257 4258 retain_initrd [RAM] Keep initrd memory after extraction 4259 4260 rfkill.default_state= 4261 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 4262 etc. communication is blocked by default. 4263 1 Unblocked. 4264 4265 rfkill.master_switch_mode= 4266 0 The "airplane mode" button does nothing. 4267 1 The "airplane mode" button toggles between everything 4268 blocked and the previous configuration. 4269 2 The "airplane mode" button toggles between everything 4270 blocked and everything unblocked. 4271 4272 rhash_entries= [KNL,NET] 4273 Set number of hash buckets for route cache 4274 4275 ring3mwait=disable 4276 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 4277 CPUs. 4278 4279 ro [KNL] Mount root device read-only on boot 4280 4281 rodata= [KNL] 4282 on Mark read-only kernel memory as read-only (default). 4283 off Leave read-only kernel memory writable for debugging. 4284 4285 rockchip.usb_uart 4286 Enable the uart passthrough on the designated usb port 4287 on Rockchip SoCs. When active, the signals of the 4288 debug-uart get routed to the D+ and D- pins of the usb 4289 port and the regular usb controller gets disabled. 4290 4291 root= [KNL] Root filesystem 4292 See name_to_dev_t comment in init/do_mounts.c. 4293 4294 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 4295 mount the root filesystem 4296 4297 rootflags= [KNL] Set root filesystem mount option string 4298 4299 rootfstype= [KNL] Set root filesystem type 4300 4301 rootwait [KNL] Wait (indefinitely) for root device to show up. 4302 Useful for devices that are detected asynchronously 4303 (e.g. USB and MMC devices). 4304 4305 rproc_mem=nn[KMG][@address] 4306 [KNL,ARM,CMA] Remoteproc physical memory block. 4307 Memory area to be used by remote processor image, 4308 managed by CMA. 4309 4310 rw [KNL] Mount root device read-write on boot 4311 4312 S [KNL] Run init in single mode 4313 4314 s390_iommu= [HW,S390] 4315 Set s390 IOTLB flushing mode 4316 strict 4317 With strict flushing every unmap operation will result in 4318 an IOTLB flush. Default is lazy flushing before reuse, 4319 which is faster. 4320 4321 sa1100ir [NET] 4322 See drivers/net/irda/sa1100_ir.c. 4323 4324 sbni= [NET] Granch SBNI12 leased line adapter 4325 4326 sched_debug [KNL] Enables verbose scheduler debug messages. 4327 4328 schedstats= [KNL,X86] Enable or disable scheduled statistics. 4329 Allowed values are enable and disable. This feature 4330 incurs a small amount of overhead in the scheduler 4331 but is useful for debugging and performance tuning. 4332 4333 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate 4334 xtime_lock contention on larger systems, and/or RCU lock 4335 contention on all systems with CONFIG_MAXSMP set. 4336 Format: { "0" | "1" } 4337 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 4338 1 -- enable. 4339 Note: increases power consumption, thus should only be 4340 enabled if running jitter sensitive (HPC/RT) workloads. 4341 4342 security= [SECURITY] Choose a legacy "major" security module to 4343 enable at boot. This has been deprecated by the 4344 "lsm=" parameter. 4345 4346 selinux= [SELINUX] Disable or enable SELinux at boot time. 4347 Format: { "0" | "1" } 4348 See security/selinux/Kconfig help text. 4349 0 -- disable. 4350 1 -- enable. 4351 Default value is set via kernel config option. 4352 If enabled at boot time, /selinux/disable can be used 4353 later to disable prior to initial policy load. 4354 4355 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 4356 Format: { "0" | "1" } 4357 See security/apparmor/Kconfig help text 4358 0 -- disable. 4359 1 -- enable. 4360 Default value is set via kernel config option. 4361 4362 serialnumber [BUGS=X86-32] 4363 4364 shapers= [NET] 4365 Maximal number of shapers. 4366 4367 simeth= [IA-64] 4368 simscsi= 4369 4370 slram= [HW,MTD] 4371 4372 slab_nomerge [MM] 4373 Disable merging of slabs with similar size. May be 4374 necessary if there is some reason to distinguish 4375 allocs to different slabs, especially in hardened 4376 environments where the risk of heap overflows and 4377 layout control by attackers can usually be 4378 frustrated by disabling merging. This will reduce 4379 most of the exposure of a heap attack to a single 4380 cache (risks via metadata attacks are mostly 4381 unchanged). Debug options disable merging on their 4382 own. 4383 For more information see Documentation/vm/slub.rst. 4384 4385 slab_max_order= [MM, SLAB] 4386 Determines the maximum allowed order for slabs. 4387 A high setting may cause OOMs due to memory 4388 fragmentation. Defaults to 1 for systems with 4389 more than 32MB of RAM, 0 otherwise. 4390 4391 slub_debug[=options[,slabs]] [MM, SLUB] 4392 Enabling slub_debug allows one to determine the 4393 culprit if slab objects become corrupted. Enabling 4394 slub_debug can create guard zones around objects and 4395 may poison objects when not in use. Also tracks the 4396 last alloc / free. For more information see 4397 Documentation/vm/slub.rst. 4398 4399 slub_memcg_sysfs= [MM, SLUB] 4400 Determines whether to enable sysfs directories for 4401 memory cgroup sub-caches. 1 to enable, 0 to disable. 4402 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON. 4403 Enabling this can lead to a very high number of debug 4404 directories and files being created under 4405 /sys/kernel/slub. 4406 4407 slub_max_order= [MM, SLUB] 4408 Determines the maximum allowed order for slabs. 4409 A high setting may cause OOMs due to memory 4410 fragmentation. For more information see 4411 Documentation/vm/slub.rst. 4412 4413 slub_min_objects= [MM, SLUB] 4414 The minimum number of objects per slab. SLUB will 4415 increase the slab order up to slub_max_order to 4416 generate a sufficiently large slab able to contain 4417 the number of objects indicated. The higher the number 4418 of objects the smaller the overhead of tracking slabs 4419 and the less frequently locks need to be acquired. 4420 For more information see Documentation/vm/slub.rst. 4421 4422 slub_min_order= [MM, SLUB] 4423 Determines the minimum page order for slabs. Must be 4424 lower than slub_max_order. 4425 For more information see Documentation/vm/slub.rst. 4426 4427 slub_nomerge [MM, SLUB] 4428 Same with slab_nomerge. This is supported for legacy. 4429 See slab_nomerge for more information. 4430 4431 smart2= [HW] 4432 Format: <io1>[,<io2>[,...,<io8>]] 4433 4434 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 4435 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 4436 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 4437 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 4438 smsc-ircc2.ircc_irq= [HW] IRQ line 4439 smsc-ircc2.ircc_dma= [HW] DMA channel 4440 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 4441 0: Toshiba Satellite 1800 (GP data pin select) 4442 1: Fast pin select (default) 4443 2: ATC IRMode 4444 4445 smt [KNL,S390] Set the maximum number of threads (logical 4446 CPUs) to use per physical CPU on systems capable of 4447 symmetric multithreading (SMT). Will be capped to the 4448 actual hardware limit. 4449 Format: <integer> 4450 Default: -1 (no limit) 4451 4452 softlockup_panic= 4453 [KNL] Should the soft-lockup detector generate panics. 4454 Format: <integer> 4455 4456 A nonzero value instructs the soft-lockup detector 4457 to panic the machine when a soft-lockup occurs. This 4458 is also controlled by CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC 4459 which is the respective build-time switch to that 4460 functionality. 4461 4462 softlockup_all_cpu_backtrace= 4463 [KNL] Should the soft-lockup detector generate 4464 backtraces on all cpus. 4465 Format: <integer> 4466 4467 sonypi.*= [HW] Sony Programmable I/O Control Device driver 4468 See Documentation/admin-guide/laptops/sonypi.rst 4469 4470 spectre_v2= [X86] Control mitigation of Spectre variant 2 4471 (indirect branch speculation) vulnerability. 4472 The default operation protects the kernel from 4473 user space attacks. 4474 4475 on - unconditionally enable, implies 4476 spectre_v2_user=on 4477 off - unconditionally disable, implies 4478 spectre_v2_user=off 4479 auto - kernel detects whether your CPU model is 4480 vulnerable 4481 4482 Selecting 'on' will, and 'auto' may, choose a 4483 mitigation method at run time according to the 4484 CPU, the available microcode, the setting of the 4485 CONFIG_RETPOLINE configuration option, and the 4486 compiler with which the kernel was built. 4487 4488 Selecting 'on' will also enable the mitigation 4489 against user space to user space task attacks. 4490 4491 Selecting 'off' will disable both the kernel and 4492 the user space protections. 4493 4494 Specific mitigations can also be selected manually: 4495 4496 retpoline - replace indirect branches 4497 retpoline,generic - google's original retpoline 4498 retpoline,amd - AMD-specific minimal thunk 4499 4500 Not specifying this option is equivalent to 4501 spectre_v2=auto. 4502 4503 spectre_v2_user= 4504 [X86] Control mitigation of Spectre variant 2 4505 (indirect branch speculation) vulnerability between 4506 user space tasks 4507 4508 on - Unconditionally enable mitigations. Is 4509 enforced by spectre_v2=on 4510 4511 off - Unconditionally disable mitigations. Is 4512 enforced by spectre_v2=off 4513 4514 prctl - Indirect branch speculation is enabled, 4515 but mitigation can be enabled via prctl 4516 per thread. The mitigation control state 4517 is inherited on fork. 4518 4519 prctl,ibpb 4520 - Like "prctl" above, but only STIBP is 4521 controlled per thread. IBPB is issued 4522 always when switching between different user 4523 space processes. 4524 4525 seccomp 4526 - Same as "prctl" above, but all seccomp 4527 threads will enable the mitigation unless 4528 they explicitly opt out. 4529 4530 seccomp,ibpb 4531 - Like "seccomp" above, but only STIBP is 4532 controlled per thread. IBPB is issued 4533 always when switching between different 4534 user space processes. 4535 4536 auto - Kernel selects the mitigation depending on 4537 the available CPU features and vulnerability. 4538 4539 Default mitigation: 4540 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl" 4541 4542 Not specifying this option is equivalent to 4543 spectre_v2_user=auto. 4544 4545 spec_store_bypass_disable= 4546 [HW] Control Speculative Store Bypass (SSB) Disable mitigation 4547 (Speculative Store Bypass vulnerability) 4548 4549 Certain CPUs are vulnerable to an exploit against a 4550 a common industry wide performance optimization known 4551 as "Speculative Store Bypass" in which recent stores 4552 to the same memory location may not be observed by 4553 later loads during speculative execution. The idea 4554 is that such stores are unlikely and that they can 4555 be detected prior to instruction retirement at the 4556 end of a particular speculation execution window. 4557 4558 In vulnerable processors, the speculatively forwarded 4559 store can be used in a cache side channel attack, for 4560 example to read memory to which the attacker does not 4561 directly have access (e.g. inside sandboxed code). 4562 4563 This parameter controls whether the Speculative Store 4564 Bypass optimization is used. 4565 4566 On x86 the options are: 4567 4568 on - Unconditionally disable Speculative Store Bypass 4569 off - Unconditionally enable Speculative Store Bypass 4570 auto - Kernel detects whether the CPU model contains an 4571 implementation of Speculative Store Bypass and 4572 picks the most appropriate mitigation. If the 4573 CPU is not vulnerable, "off" is selected. If the 4574 CPU is vulnerable the default mitigation is 4575 architecture and Kconfig dependent. See below. 4576 prctl - Control Speculative Store Bypass per thread 4577 via prctl. Speculative Store Bypass is enabled 4578 for a process by default. The state of the control 4579 is inherited on fork. 4580 seccomp - Same as "prctl" above, but all seccomp threads 4581 will disable SSB unless they explicitly opt out. 4582 4583 Default mitigations: 4584 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl" 4585 4586 On powerpc the options are: 4587 4588 on,auto - On Power8 and Power9 insert a store-forwarding 4589 barrier on kernel entry and exit. On Power7 4590 perform a software flush on kernel entry and 4591 exit. 4592 off - No action. 4593 4594 Not specifying this option is equivalent to 4595 spec_store_bypass_disable=auto. 4596 4597 spia_io_base= [HW,MTD] 4598 spia_fio_base= 4599 spia_pedr= 4600 spia_peddr= 4601 4602 srcutree.counter_wrap_check [KNL] 4603 Specifies how frequently to check for 4604 grace-period sequence counter wrap for the 4605 srcu_data structure's ->srcu_gp_seq_needed field. 4606 The greater the number of bits set in this kernel 4607 parameter, the less frequently counter wrap will 4608 be checked for. Note that the bottom two bits 4609 are ignored. 4610 4611 srcutree.exp_holdoff [KNL] 4612 Specifies how many nanoseconds must elapse 4613 since the end of the last SRCU grace period for 4614 a given srcu_struct until the next normal SRCU 4615 grace period will be considered for automatic 4616 expediting. Set to zero to disable automatic 4617 expediting. 4618 4619 ssbd= [ARM64,HW] 4620 Speculative Store Bypass Disable control 4621 4622 On CPUs that are vulnerable to the Speculative 4623 Store Bypass vulnerability and offer a 4624 firmware based mitigation, this parameter 4625 indicates how the mitigation should be used: 4626 4627 force-on: Unconditionally enable mitigation for 4628 for both kernel and userspace 4629 force-off: Unconditionally disable mitigation for 4630 for both kernel and userspace 4631 kernel: Always enable mitigation in the 4632 kernel, and offer a prctl interface 4633 to allow userspace to register its 4634 interest in being mitigated too. 4635 4636 stack_guard_gap= [MM] 4637 override the default stack gap protection. The value 4638 is in page units and it defines how many pages prior 4639 to (for stacks growing down) resp. after (for stacks 4640 growing up) the main stack are reserved for no other 4641 mapping. Default value is 256 pages. 4642 4643 stacktrace [FTRACE] 4644 Enabled the stack tracer on boot up. 4645 4646 stacktrace_filter=[function-list] 4647 [FTRACE] Limit the functions that the stack tracer 4648 will trace at boot up. function-list is a comma separated 4649 list of functions. This list can be changed at run 4650 time by the stack_trace_filter file in the debugfs 4651 tracing directory. Note, this enables stack tracing 4652 and the stacktrace above is not needed. 4653 4654 sti= [PARISC,HW] 4655 Format: <num> 4656 Set the STI (builtin display/keyboard on the HP-PARISC 4657 machines) console (graphic card) which should be used 4658 as the initial boot-console. 4659 See also comment in drivers/video/console/sticore.c. 4660 4661 sti_font= [HW] 4662 See comment in drivers/video/console/sticore.c. 4663 4664 stifb= [HW] 4665 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 4666 4667 sunrpc.min_resvport= 4668 sunrpc.max_resvport= 4669 [NFS,SUNRPC] 4670 SunRPC servers often require that client requests 4671 originate from a privileged port (i.e. a port in the 4672 range 0 < portnr < 1024). 4673 An administrator who wishes to reserve some of these 4674 ports for other uses may adjust the range that the 4675 kernel's sunrpc client considers to be privileged 4676 using these two parameters to set the minimum and 4677 maximum port values. 4678 4679 sunrpc.svc_rpc_per_connection_limit= 4680 [NFS,SUNRPC] 4681 Limit the number of requests that the server will 4682 process in parallel from a single connection. 4683 The default value is 0 (no limit). 4684 4685 sunrpc.pool_mode= 4686 [NFS] 4687 Control how the NFS server code allocates CPUs to 4688 service thread pools. Depending on how many NICs 4689 you have and where their interrupts are bound, this 4690 option will affect which CPUs will do NFS serving. 4691 Note: this parameter cannot be changed while the 4692 NFS server is running. 4693 4694 auto the server chooses an appropriate mode 4695 automatically using heuristics 4696 global a single global pool contains all CPUs 4697 percpu one pool for each CPU 4698 pernode one pool for each NUMA node (equivalent 4699 to global on non-NUMA machines) 4700 4701 sunrpc.tcp_slot_table_entries= 4702 sunrpc.udp_slot_table_entries= 4703 [NFS,SUNRPC] 4704 Sets the upper limit on the number of simultaneous 4705 RPC calls that can be sent from the client to a 4706 server. Increasing these values may allow you to 4707 improve throughput, but will also increase the 4708 amount of memory reserved for use by the client. 4709 4710 suspend.pm_test_delay= 4711 [SUSPEND] 4712 Sets the number of seconds to remain in a suspend test 4713 mode before resuming the system (see 4714 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 4715 is set. Default value is 5. 4716 4717 svm= [PPC] 4718 Format: { on | off | y | n | 1 | 0 } 4719 This parameter controls use of the Protected 4720 Execution Facility on pSeries. 4721 4722 swapaccount=[0|1] 4723 [KNL] Enable accounting of swap in memory resource 4724 controller if no parameter or 1 is given or disable 4725 it if 0 is given (See Documentation/admin-guide/cgroup-v1/memory.rst) 4726 4727 swiotlb= [ARM,IA-64,PPC,MIPS,X86] 4728 Format: { <int> | force | noforce } 4729 <int> -- Number of I/O TLB slabs 4730 force -- force using of bounce buffers even if they 4731 wouldn't be automatically used by the kernel 4732 noforce -- Never use bounce buffers (for debugging) 4733 4734 switches= [HW,M68k] 4735 4736 sysfs.deprecated=0|1 [KNL] 4737 Enable/disable old style sysfs layout for old udev 4738 on older distributions. When this option is enabled 4739 very new udev will not work anymore. When this option 4740 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled) 4741 in older udev will not work anymore. 4742 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in 4743 the kernel configuration. 4744 4745 sysrq_always_enabled 4746 [KNL] 4747 Ignore sysrq setting - this boot parameter will 4748 neutralize any effect of /proc/sys/kernel/sysrq. 4749 Useful for debugging. 4750 4751 tcpmhash_entries= [KNL,NET] 4752 Set the number of tcp_metrics_hash slots. 4753 Default value is 8192 or 16384 depending on total 4754 ram pages. This is used to specify the TCP metrics 4755 cache size. See Documentation/networking/ip-sysctl.txt 4756 "tcp_no_metrics_save" section for more details. 4757 4758 tdfx= [HW,DRM] 4759 4760 test_suspend= [SUSPEND][,N] 4761 Specify "mem" (for Suspend-to-RAM) or "standby" (for 4762 standby suspend) or "freeze" (for suspend type freeze) 4763 as the system sleep state during system startup with 4764 the optional capability to repeat N number of times. 4765 The system is woken from this state using a 4766 wakeup-capable RTC alarm. 4767 4768 thash_entries= [KNL,NET] 4769 Set number of hash buckets for TCP connection 4770 4771 thermal.act= [HW,ACPI] 4772 -1: disable all active trip points in all thermal zones 4773 <degrees C>: override all lowest active trip points 4774 4775 thermal.crt= [HW,ACPI] 4776 -1: disable all critical trip points in all thermal zones 4777 <degrees C>: override all critical trip points 4778 4779 thermal.nocrt= [HW,ACPI] 4780 Set to disable actions on ACPI thermal zone 4781 critical and hot trip points. 4782 4783 thermal.off= [HW,ACPI] 4784 1: disable ACPI thermal control 4785 4786 thermal.psv= [HW,ACPI] 4787 -1: disable all passive trip points 4788 <degrees C>: override all passive trip points to this 4789 value 4790 4791 thermal.tzp= [HW,ACPI] 4792 Specify global default ACPI thermal zone polling rate 4793 <deci-seconds>: poll all this frequency 4794 0: no polling (default) 4795 4796 threadirqs [KNL] 4797 Force threading of all interrupt handlers except those 4798 marked explicitly IRQF_NO_THREAD. 4799 4800 topology= [S390] 4801 Format: {off | on} 4802 Specify if the kernel should make use of the cpu 4803 topology information if the hardware supports this. 4804 The scheduler will make use of this information and 4805 e.g. base its process migration decisions on it. 4806 Default is on. 4807 4808 topology_updates= [KNL, PPC, NUMA] 4809 Format: {off} 4810 Specify if the kernel should ignore (off) 4811 topology updates sent by the hypervisor to this 4812 LPAR. 4813 4814 tp720= [HW,PS2] 4815 4816 tpm_suspend_pcr=[HW,TPM] 4817 Format: integer pcr id 4818 Specify that at suspend time, the tpm driver 4819 should extend the specified pcr with zeros, 4820 as a workaround for some chips which fail to 4821 flush the last written pcr on TPM_SaveState. 4822 This will guarantee that all the other pcrs 4823 are saved. 4824 4825 trace_buf_size=nn[KMG] 4826 [FTRACE] will set tracing buffer size on each cpu. 4827 4828 trace_event=[event-list] 4829 [FTRACE] Set and start specified trace events in order 4830 to facilitate early boot debugging. The event-list is a 4831 comma separated list of trace events to enable. See 4832 also Documentation/trace/events.rst 4833 4834 trace_options=[option-list] 4835 [FTRACE] Enable or disable tracer options at boot. 4836 The option-list is a comma delimited list of options 4837 that can be enabled or disabled just as if you were 4838 to echo the option name into 4839 4840 /sys/kernel/debug/tracing/trace_options 4841 4842 For example, to enable stacktrace option (to dump the 4843 stack trace of each event), add to the command line: 4844 4845 trace_options=stacktrace 4846 4847 See also Documentation/trace/ftrace.rst "trace options" 4848 section. 4849 4850 tp_printk[FTRACE] 4851 Have the tracepoints sent to printk as well as the 4852 tracing ring buffer. This is useful for early boot up 4853 where the system hangs or reboots and does not give the 4854 option for reading the tracing buffer or performing a 4855 ftrace_dump_on_oops. 4856 4857 To turn off having tracepoints sent to printk, 4858 echo 0 > /proc/sys/kernel/tracepoint_printk 4859 Note, echoing 1 into this file without the 4860 tracepoint_printk kernel cmdline option has no effect. 4861 4862 ** CAUTION ** 4863 4864 Having tracepoints sent to printk() and activating high 4865 frequency tracepoints such as irq or sched, can cause 4866 the system to live lock. 4867 4868 traceoff_on_warning 4869 [FTRACE] enable this option to disable tracing when a 4870 warning is hit. This turns off "tracing_on". Tracing can 4871 be enabled again by echoing '1' into the "tracing_on" 4872 file located in /sys/kernel/debug/tracing/ 4873 4874 This option is useful, as it disables the trace before 4875 the WARNING dump is called, which prevents the trace to 4876 be filled with content caused by the warning output. 4877 4878 This option can also be set at run time via the sysctl 4879 option: kernel/traceoff_on_warning 4880 4881 transparent_hugepage= 4882 [KNL] 4883 Format: [always|madvise|never] 4884 Can be used to control the default behavior of the system 4885 with respect to transparent hugepages. 4886 See Documentation/admin-guide/mm/transhuge.rst 4887 for more details. 4888 4889 tsc= Disable clocksource stability checks for TSC. 4890 Format: <string> 4891 [x86] reliable: mark tsc clocksource as reliable, this 4892 disables clocksource verification at runtime, as well 4893 as the stability checks done at bootup. Used to enable 4894 high-resolution timer mode on older hardware, and in 4895 virtualized environment. 4896 [x86] noirqtime: Do not use TSC to do irq accounting. 4897 Used to run time disable IRQ_TIME_ACCOUNTING on any 4898 platforms where RDTSC is slow and this accounting 4899 can add overhead. 4900 [x86] unstable: mark the TSC clocksource as unstable, this 4901 marks the TSC unconditionally unstable at bootup and 4902 avoids any further wobbles once the TSC watchdog notices. 4903 [x86] nowatchdog: disable clocksource watchdog. Used 4904 in situations with strict latency requirements (where 4905 interruptions from clocksource watchdog are not 4906 acceptable). 4907 4908 tsx= [X86] Control Transactional Synchronization 4909 Extensions (TSX) feature in Intel processors that 4910 support TSX control. 4911 4912 This parameter controls the TSX feature. The options are: 4913 4914 on - Enable TSX on the system. Although there are 4915 mitigations for all known security vulnerabilities, 4916 TSX has been known to be an accelerator for 4917 several previous speculation-related CVEs, and 4918 so there may be unknown security risks associated 4919 with leaving it enabled. 4920 4921 off - Disable TSX on the system. (Note that this 4922 option takes effect only on newer CPUs which are 4923 not vulnerable to MDS, i.e., have 4924 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get 4925 the new IA32_TSX_CTRL MSR through a microcode 4926 update. This new MSR allows for the reliable 4927 deactivation of the TSX functionality.) 4928 4929 auto - Disable TSX if X86_BUG_TAA is present, 4930 otherwise enable TSX on the system. 4931 4932 Not specifying this option is equivalent to tsx=off. 4933 4934 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 4935 for more details. 4936 4937 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async 4938 Abort (TAA) vulnerability. 4939 4940 Similar to Micro-architectural Data Sampling (MDS) 4941 certain CPUs that support Transactional 4942 Synchronization Extensions (TSX) are vulnerable to an 4943 exploit against CPU internal buffers which can forward 4944 information to a disclosure gadget under certain 4945 conditions. 4946 4947 In vulnerable processors, the speculatively forwarded 4948 data can be used in a cache side channel attack, to 4949 access data to which the attacker does not have direct 4950 access. 4951 4952 This parameter controls the TAA mitigation. The 4953 options are: 4954 4955 full - Enable TAA mitigation on vulnerable CPUs 4956 if TSX is enabled. 4957 4958 full,nosmt - Enable TAA mitigation and disable SMT on 4959 vulnerable CPUs. If TSX is disabled, SMT 4960 is not disabled because CPU is not 4961 vulnerable to cross-thread TAA attacks. 4962 off - Unconditionally disable TAA mitigation 4963 4964 On MDS-affected machines, tsx_async_abort=off can be 4965 prevented by an active MDS mitigation as both vulnerabilities 4966 are mitigated with the same mechanism so in order to disable 4967 this mitigation, you need to specify mds=off too. 4968 4969 Not specifying this option is equivalent to 4970 tsx_async_abort=full. On CPUs which are MDS affected 4971 and deploy MDS mitigation, TAA mitigation is not 4972 required and doesn't provide any additional 4973 mitigation. 4974 4975 For details see: 4976 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 4977 4978 turbografx.map[2|3]= [HW,JOY] 4979 TurboGraFX parallel port interface 4980 Format: 4981 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 4982 See also Documentation/input/devices/joystick-parport.rst 4983 4984 udbg-immortal [PPC] When debugging early kernel crashes that 4985 happen after console_init() and before a proper 4986 console driver takes over, this boot options might 4987 help "seeing" what's going on. 4988 4989 uhash_entries= [KNL,NET] 4990 Set number of hash buckets for UDP/UDP-Lite connections 4991 4992 uhci-hcd.ignore_oc= 4993 [USB] Ignore overcurrent events (default N). 4994 Some badly-designed motherboards generate lots of 4995 bogus events, for ports that aren't wired to 4996 anything. Set this parameter to avoid log spamming. 4997 Note that genuine overcurrent events won't be 4998 reported either. 4999 5000 unknown_nmi_panic 5001 [X86] Cause panic on unknown NMI. 5002 5003 usbcore.authorized_default= 5004 [USB] Default USB device authorization: 5005 (default -1 = authorized except for wireless USB, 5006 0 = not authorized, 1 = authorized, 2 = authorized 5007 if device connected to internal port) 5008 5009 usbcore.autosuspend= 5010 [USB] The autosuspend time delay (in seconds) used 5011 for newly-detected USB devices (default 2). This 5012 is the time required before an idle device will be 5013 autosuspended. Devices for which the delay is set 5014 to a negative value won't be autosuspended at all. 5015 5016 usbcore.usbfs_snoop= 5017 [USB] Set to log all usbfs traffic (default 0 = off). 5018 5019 usbcore.usbfs_snoop_max= 5020 [USB] Maximum number of bytes to snoop in each URB 5021 (default = 65536). 5022 5023 usbcore.blinkenlights= 5024 [USB] Set to cycle leds on hubs (default 0 = off). 5025 5026 usbcore.old_scheme_first= 5027 [USB] Start with the old device initialization 5028 scheme, applies only to low and full-speed devices 5029 (default 0 = off). 5030 5031 usbcore.usbfs_memory_mb= 5032 [USB] Memory limit (in MB) for buffers allocated by 5033 usbfs (default = 16, 0 = max = 2047). 5034 5035 usbcore.use_both_schemes= 5036 [USB] Try the other device initialization scheme 5037 if the first one fails (default 1 = enabled). 5038 5039 usbcore.initial_descriptor_timeout= 5040 [USB] Specifies timeout for the initial 64-byte 5041 USB_REQ_GET_DESCRIPTOR request in milliseconds 5042 (default 5000 = 5.0 seconds). 5043 5044 usbcore.nousb [USB] Disable the USB subsystem 5045 5046 usbcore.quirks= 5047 [USB] A list of quirk entries to augment the built-in 5048 usb core quirk list. List entries are separated by 5049 commas. Each entry has the form 5050 VendorID:ProductID:Flags. The IDs are 4-digit hex 5051 numbers and Flags is a set of letters. Each letter 5052 will change the built-in quirk; setting it if it is 5053 clear and clearing it if it is set. The letters have 5054 the following meanings: 5055 a = USB_QUIRK_STRING_FETCH_255 (string 5056 descriptors must not be fetched using 5057 a 255-byte read); 5058 b = USB_QUIRK_RESET_RESUME (device can't resume 5059 correctly so reset it instead); 5060 c = USB_QUIRK_NO_SET_INTF (device can't handle 5061 Set-Interface requests); 5062 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't 5063 handle its Configuration or Interface 5064 strings); 5065 e = USB_QUIRK_RESET (device can't be reset 5066 (e.g morph devices), don't use reset); 5067 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has 5068 more interface descriptions than the 5069 bNumInterfaces count, and can't handle 5070 talking to these interfaces); 5071 g = USB_QUIRK_DELAY_INIT (device needs a pause 5072 during initialization, after we read 5073 the device descriptor); 5074 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For 5075 high speed and super speed interrupt 5076 endpoints, the USB 2.0 and USB 3.0 spec 5077 require the interval in microframes (1 5078 microframe = 125 microseconds) to be 5079 calculated as interval = 2 ^ 5080 (bInterval-1). 5081 Devices with this quirk report their 5082 bInterval as the result of this 5083 calculation instead of the exponent 5084 variable used in the calculation); 5085 i = USB_QUIRK_DEVICE_QUALIFIER (device can't 5086 handle device_qualifier descriptor 5087 requests); 5088 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device 5089 generates spurious wakeup, ignore 5090 remote wakeup capability); 5091 k = USB_QUIRK_NO_LPM (device can't handle Link 5092 Power Management); 5093 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL 5094 (Device reports its bInterval as linear 5095 frames instead of the USB 2.0 5096 calculation); 5097 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs 5098 to be disconnected before suspend to 5099 prevent spurious wakeup); 5100 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a 5101 pause after every control message); 5102 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra 5103 delay after resetting its port); 5104 Example: quirks=0781:5580:bk,0a5c:5834:gij 5105 5106 usbhid.mousepoll= 5107 [USBHID] The interval which mice are to be polled at. 5108 5109 usbhid.jspoll= 5110 [USBHID] The interval which joysticks are to be polled at. 5111 5112 usbhid.kbpoll= 5113 [USBHID] The interval which keyboards are to be polled at. 5114 5115 usb-storage.delay_use= 5116 [UMS] The delay in seconds before a new device is 5117 scanned for Logical Units (default 1). 5118 5119 usb-storage.quirks= 5120 [UMS] A list of quirks entries to supplement or 5121 override the built-in unusual_devs list. List 5122 entries are separated by commas. Each entry has 5123 the form VID:PID:Flags where VID and PID are Vendor 5124 and Product ID values (4-digit hex numbers) and 5125 Flags is a set of characters, each corresponding 5126 to a common usb-storage quirk flag as follows: 5127 a = SANE_SENSE (collect more than 18 bytes 5128 of sense data, not on uas); 5129 b = BAD_SENSE (don't collect more than 18 5130 bytes of sense data, not on uas); 5131 c = FIX_CAPACITY (decrease the reported 5132 device capacity by one sector); 5133 d = NO_READ_DISC_INFO (don't use 5134 READ_DISC_INFO command, not on uas); 5135 e = NO_READ_CAPACITY_16 (don't use 5136 READ_CAPACITY_16 command); 5137 f = NO_REPORT_OPCODES (don't use report opcodes 5138 command, uas only); 5139 g = MAX_SECTORS_240 (don't transfer more than 5140 240 sectors at a time, uas only); 5141 h = CAPACITY_HEURISTICS (decrease the 5142 reported device capacity by one 5143 sector if the number is odd); 5144 i = IGNORE_DEVICE (don't bind to this 5145 device); 5146 j = NO_REPORT_LUNS (don't use report luns 5147 command, uas only); 5148 l = NOT_LOCKABLE (don't try to lock and 5149 unlock ejectable media, not on uas); 5150 m = MAX_SECTORS_64 (don't transfer more 5151 than 64 sectors = 32 KB at a time, 5152 not on uas); 5153 n = INITIAL_READ10 (force a retry of the 5154 initial READ(10) command, not on uas); 5155 o = CAPACITY_OK (accept the capacity 5156 reported by the device, not on uas); 5157 p = WRITE_CACHE (the device cache is ON 5158 by default, not on uas); 5159 r = IGNORE_RESIDUE (the device reports 5160 bogus residue values, not on uas); 5161 s = SINGLE_LUN (the device has only one 5162 Logical Unit); 5163 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 5164 commands, uas only); 5165 u = IGNORE_UAS (don't bind to the uas driver); 5166 w = NO_WP_DETECT (don't test whether the 5167 medium is write-protected). 5168 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 5169 even if the device claims no cache, 5170 not on uas) 5171 Example: quirks=0419:aaf5:rl,0421:0433:rc 5172 5173 user_debug= [KNL,ARM] 5174 Format: <int> 5175 See arch/arm/Kconfig.debug help text. 5176 1 - undefined instruction events 5177 2 - system calls 5178 4 - invalid data aborts 5179 8 - SIGSEGV faults 5180 16 - SIGBUS faults 5181 Example: user_debug=31 5182 5183 userpte= 5184 [X86] Flags controlling user PTE allocations. 5185 5186 nohigh = do not allocate PTE pages in 5187 HIGHMEM regardless of setting 5188 of CONFIG_HIGHPTE. 5189 5190 vdso= [X86,SH] 5191 On X86_32, this is an alias for vdso32=. Otherwise: 5192 5193 vdso=1: enable VDSO (the default) 5194 vdso=0: disable VDSO mapping 5195 5196 vdso32= [X86] Control the 32-bit vDSO 5197 vdso32=1: enable 32-bit VDSO 5198 vdso32=0 or vdso32=2: disable 32-bit VDSO 5199 5200 See the help text for CONFIG_COMPAT_VDSO for more 5201 details. If CONFIG_COMPAT_VDSO is set, the default is 5202 vdso32=0; otherwise, the default is vdso32=1. 5203 5204 For compatibility with older kernels, vdso32=2 is an 5205 alias for vdso32=0. 5206 5207 Try vdso32=0 if you encounter an error that says: 5208 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 5209 5210 vector= [IA-64,SMP] 5211 vector=percpu: enable percpu vector domain 5212 5213 video= [FB] Frame buffer configuration 5214 See Documentation/fb/modedb.rst. 5215 5216 video.brightness_switch_enabled= [0,1] 5217 If set to 1, on receiving an ACPI notify event 5218 generated by hotkey, video driver will adjust brightness 5219 level and then send out the event to user space through 5220 the allocated input device; If set to 0, video driver 5221 will only send out the event without touching backlight 5222 brightness level. 5223 default: 1 5224 5225 virtio_mmio.device= 5226 [VMMIO] Memory mapped virtio (platform) device. 5227 5228 <size>@<baseaddr>:<irq>[:<id>] 5229 where: 5230 <size> := size (can use standard suffixes 5231 like K, M and G) 5232 <baseaddr> := physical base address 5233 <irq> := interrupt number (as passed to 5234 request_irq()) 5235 <id> := (optional) platform device id 5236 example: 5237 virtio_mmio.device=1K@0x100b0000:48:7 5238 5239 Can be used multiple times for multiple devices. 5240 5241 vga= [BOOT,X86-32] Select a particular video mode 5242 See Documentation/x86/boot.rst and 5243 Documentation/admin-guide/svga.rst. 5244 Use vga=ask for menu. 5245 This is actually a boot loader parameter; the value is 5246 passed to the kernel using a special protocol. 5247 5248 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. 5249 May slow down system boot speed, especially when 5250 enabled on systems with a large amount of memory. 5251 All options are enabled by default, and this 5252 interface is meant to allow for selectively 5253 enabling or disabling specific virtual memory 5254 debugging features. 5255 5256 Available options are: 5257 P Enable page structure init time poisoning 5258 - Disable all of the above options 5259 5260 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact 5261 size of <nn>. This can be used to increase the 5262 minimum size (128MB on x86). It can also be used to 5263 decrease the size and leave more room for directly 5264 mapped kernel RAM. 5265 5266 vmcp_cma=nn[MG] [KNL,S390] 5267 Sets the memory size reserved for contiguous memory 5268 allocations for the vmcp device driver. 5269 5270 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 5271 Format: <command> 5272 5273 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 5274 Format: <command> 5275 5276 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 5277 Format: <command> 5278 5279 vsyscall= [X86-64] 5280 Controls the behavior of vsyscalls (i.e. calls to 5281 fixed addresses of 0xffffffffff600x00 from legacy 5282 code). Most statically-linked binaries and older 5283 versions of glibc use these calls. Because these 5284 functions are at fixed addresses, they make nice 5285 targets for exploits that can control RIP. 5286 5287 emulate [default] Vsyscalls turn into traps and are 5288 emulated reasonably safely. The vsyscall 5289 page is readable. 5290 5291 xonly Vsyscalls turn into traps and are 5292 emulated reasonably safely. The vsyscall 5293 page is not readable. 5294 5295 none Vsyscalls don't work at all. This makes 5296 them quite hard to use for exploits but 5297 might break your system. 5298 5299 vt.color= [VT] Default text color. 5300 Format: 0xYX, X = foreground, Y = background. 5301 Default: 0x07 = light gray on black. 5302 5303 vt.cur_default= [VT] Default cursor shape. 5304 Format: 0xCCBBAA, where AA, BB, and CC are the same as 5305 the parameters of the <Esc>[?A;B;Cc escape sequence; 5306 see VGA-softcursor.txt. Default: 2 = underline. 5307 5308 vt.default_blu= [VT] 5309 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 5310 Change the default blue palette of the console. 5311 This is a 16-member array composed of values 5312 ranging from 0-255. 5313 5314 vt.default_grn= [VT] 5315 Format: <green0>,<green1>,<green2>,...,<green15> 5316 Change the default green palette of the console. 5317 This is a 16-member array composed of values 5318 ranging from 0-255. 5319 5320 vt.default_red= [VT] 5321 Format: <red0>,<red1>,<red2>,...,<red15> 5322 Change the default red palette of the console. 5323 This is a 16-member array composed of values 5324 ranging from 0-255. 5325 5326 vt.default_utf8= 5327 [VT] 5328 Format=<0|1> 5329 Set system-wide default UTF-8 mode for all tty's. 5330 Default is 1, i.e. UTF-8 mode is enabled for all 5331 newly opened terminals. 5332 5333 vt.global_cursor_default= 5334 [VT] 5335 Format=<-1|0|1> 5336 Set system-wide default for whether a cursor 5337 is shown on new VTs. Default is -1, 5338 i.e. cursors will be created by default unless 5339 overridden by individual drivers. 0 will hide 5340 cursors, 1 will display them. 5341 5342 vt.italic= [VT] Default color for italic text; 0-15. 5343 Default: 2 = green. 5344 5345 vt.underline= [VT] Default color for underlined text; 0-15. 5346 Default: 3 = cyan. 5347 5348 watchdog timers [HW,WDT] For information on watchdog timers, 5349 see Documentation/watchdog/watchdog-parameters.rst 5350 or other driver-specific files in the 5351 Documentation/watchdog/ directory. 5352 5353 watchdog_thresh= 5354 [KNL] 5355 Set the hard lockup detector stall duration 5356 threshold in seconds. The soft lockup detector 5357 threshold is set to twice the value. A value of 0 5358 disables both lockup detectors. Default is 10 5359 seconds. 5360 5361 workqueue.watchdog_thresh= 5362 If CONFIG_WQ_WATCHDOG is configured, workqueue can 5363 warn stall conditions and dump internal state to 5364 help debugging. 0 disables workqueue stall 5365 detection; otherwise, it's the stall threshold 5366 duration in seconds. The default value is 30 and 5367 it can be updated at runtime by writing to the 5368 corresponding sysfs file. 5369 5370 workqueue.disable_numa 5371 By default, all work items queued to unbound 5372 workqueues are affine to the NUMA nodes they're 5373 issued on, which results in better behavior in 5374 general. If NUMA affinity needs to be disabled for 5375 whatever reason, this option can be used. Note 5376 that this also can be controlled per-workqueue for 5377 workqueues visible under /sys/bus/workqueue/. 5378 5379 workqueue.power_efficient 5380 Per-cpu workqueues are generally preferred because 5381 they show better performance thanks to cache 5382 locality; unfortunately, per-cpu workqueues tend to 5383 be more power hungry than unbound workqueues. 5384 5385 Enabling this makes the per-cpu workqueues which 5386 were observed to contribute significantly to power 5387 consumption unbound, leading to measurably lower 5388 power usage at the cost of small performance 5389 overhead. 5390 5391 The default value of this parameter is determined by 5392 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 5393 5394 workqueue.debug_force_rr_cpu 5395 Workqueue used to implicitly guarantee that work 5396 items queued without explicit CPU specified are put 5397 on the local CPU. This guarantee is no longer true 5398 and while local CPU is still preferred work items 5399 may be put on foreign CPUs. This debug option 5400 forces round-robin CPU selection to flush out 5401 usages which depend on the now broken guarantee. 5402 When enabled, memory and cache locality will be 5403 impacted. 5404 5405 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of 5406 default x2apic cluster mode on platforms 5407 supporting x2apic. 5408 5409 x86_intel_mid_timer= [X86-32,APBT] 5410 Choose timer option for x86 Intel MID platform. 5411 Two valid options are apbt timer only and lapic timer 5412 plus one apbt timer for broadcast timer. 5413 x86_intel_mid_timer=apbt_only | lapic_and_apbt 5414 5415 xen_512gb_limit [KNL,X86-64,XEN] 5416 Restricts the kernel running paravirtualized under Xen 5417 to use only up to 512 GB of RAM. The reason to do so is 5418 crash analysis tools and Xen tools for doing domain 5419 save/restore/migration must be enabled to handle larger 5420 domains. 5421 5422 xen_emul_unplug= [HW,X86,XEN] 5423 Unplug Xen emulated devices 5424 Format: [unplug0,][unplug1] 5425 ide-disks -- unplug primary master IDE devices 5426 aux-ide-disks -- unplug non-primary-master IDE devices 5427 nics -- unplug network devices 5428 all -- unplug all emulated devices (NICs and IDE disks) 5429 unnecessary -- unplugging emulated devices is 5430 unnecessary even if the host did not respond to 5431 the unplug protocol 5432 never -- do not unplug even if version check succeeds 5433 5434 xen_legacy_crash [X86,XEN] 5435 Crash from Xen panic notifier, without executing late 5436 panic() code such as dumping handler. 5437 5438 xen_nopvspin [X86,XEN] 5439 Disables the ticketlock slowpath using Xen PV 5440 optimizations. 5441 5442 xen_nopv [X86] 5443 Disables the PV optimizations forcing the HVM guest to 5444 run as generic HVM guest with no PV drivers. 5445 This option is obsoleted by the "nopv" option, which 5446 has equivalent effect for XEN platform. 5447 5448 xen_scrub_pages= [XEN] 5449 Boolean option to control scrubbing pages before giving them back 5450 to Xen, for use by other domains. Can be also changed at runtime 5451 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. 5452 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. 5453 5454 xen_timer_slop= [X86-64,XEN] 5455 Set the timer slop (in nanoseconds) for the virtual Xen 5456 timers (default is 100000). This adjusts the minimum 5457 delta of virtualized Xen timers, where lower values 5458 improve timer resolution at the expense of processing 5459 more timer interrupts. 5460 5461 nopv= [X86,XEN,KVM,HYPER_V,VMWARE] 5462 Disables the PV optimizations forcing the guest to run 5463 as generic guest with no PV drivers. Currently support 5464 XEN HVM, KVM, HYPER_V and VMWARE guest. 5465 5466 xirc2ps_cs= [NET,PCMCIA] 5467 Format: 5468 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 5469 5470 xive= [PPC] 5471 By default on POWER9 and above, the kernel will 5472 natively use the XIVE interrupt controller. This option 5473 allows the fallback firmware mode to be used: 5474 5475 off Fallback to firmware control of XIVE interrupt 5476 controller on both pseries and powernv 5477 platforms. Only useful on POWER9 and above. 5478 5479 xhci-hcd.quirks [USB,KNL] 5480 A hex value specifying bitmask with supplemental xhci 5481 host controller quirks. Meaning of each bit can be 5482 consulted in header drivers/usb/host/xhci.h. 5483 5484 xmon [PPC] 5485 Format: { early | on | rw | ro | off } 5486 Controls if xmon debugger is enabled. Default is off. 5487 Passing only "xmon" is equivalent to "xmon=early". 5488 early Call xmon as early as possible on boot; xmon 5489 debugger is called from setup_arch(). 5490 on xmon debugger hooks will be installed so xmon 5491 is only called on a kernel crash. Default mode, 5492 i.e. either "ro" or "rw" mode, is controlled 5493 with CONFIG_XMON_DEFAULT_RO_MODE. 5494 rw xmon debugger hooks will be installed so xmon 5495 is called only on a kernel crash, mode is write, 5496 meaning SPR registers, memory and, other data 5497 can be written using xmon commands. 5498 ro same as "rw" option above but SPR registers, 5499 memory, and other data can't be written using 5500 xmon commands. 5501 off xmon is disabled. 5502