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