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1 Kernel Parameters
2 ~~~~~~~~~~~~~~~~~
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3
4The following is a consolidated list of the kernel parameters as implemented
5(mostly) by the __setup() macro and sorted into English Dictionary order
6(defined as ignoring all punctuation and sorting digits before letters in a
7case insensitive manner), and with descriptions where known.
8
9Module parameters for loadable modules are specified only as the
10parameter name with optional '=' and value as appropriate, such as:
11
12 modprobe usbcore blinkenlights=1
13
14Module parameters for modules that are built into the kernel image
15are specified on the kernel command line with the module name plus
16'.' plus parameter name, with '=' and value if appropriate, such as:
17
18 usbcore.blinkenlights=1
19
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20Hyphens (dashes) and underscores are equivalent in parameter names, so
21 log_buf_len=1M print-fatal-signals=1
22can also be entered as
23 log-buf-len=1M print_fatal_signals=1
24
25
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26This document may not be entirely up to date and comprehensive. The command
27"modinfo -p ${modulename}" shows a current list of all parameters of a loadable
28module. Loadable modules, after being loaded into the running kernel, also
29reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
30parameters may be changed at runtime by the command
31"echo -n ${value} > /sys/module/${modulename}/parameters/${parm}".
32
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33The parameters listed below are only valid if certain kernel build options were
34enabled and if respective hardware is present. The text in square brackets at
35the beginning of each description states the restrictions within which a
36parameter is applicable:
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37
38 ACPI ACPI support is enabled.
c99c108a 39 AGP AGP (Accelerated Graphics Port) is enabled.
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40 ALSA ALSA sound support is enabled.
41 APIC APIC support is enabled.
42 APM Advanced Power Management support is enabled.
16290246 43 ARM ARM architecture is enabled.
e7ba176b 44 AVR32 AVR32 architecture is enabled.
1da177e4 45 AX25 Appropriate AX.25 support is enabled.
0ae53640 46 BLACKFIN Blackfin architecture is enabled.
1e435256 47 CLK Common clock infrastructure is enabled.
5c71d618 48 CMA Contiguous Memory Area support is enabled.
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49 DRM Direct Rendering Management support is enabled.
50 DYNAMIC_DEBUG Build in debug messages and enable them at runtime
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51 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
52 EFI EFI Partitioning (GPT) is enabled
53 EIDE EIDE/ATAPI support is enabled.
7102ebcd 54 EVM Extended Verification Module
1da177e4 55 FB The frame buffer device is enabled.
16290246 56 FTRACE Function tracing enabled.
2521f2c2 57 GCOV GCOV profiling is enabled.
1da177e4 58 HW Appropriate hardware is enabled.
1da177e4 59 IA-64 IA-64 architecture is enabled.
6146f0d5 60 IMA Integrity measurement architecture is enabled.
1da177e4 61 IOSCHED More than one I/O scheduler is enabled.
41e2e8be 62 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
b0f83b28 63 IPV6 IPv6 support is enabled.
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64 ISAPNP ISA PnP code is enabled.
65 ISDN Appropriate ISDN support is enabled.
66 JOY Appropriate joystick support is enabled.
84c08fd6 67 KGDB Kernel debugger support is enabled.
fef07aae 68 KVM Kernel Virtual Machine support is enabled.
11ef697b 69 LIBATA Libata driver is enabled
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70 LP Printer support is enabled.
71 LOOP Loopback device support is enabled.
72 M68k M68k architecture is enabled.
73 These options have more detailed description inside of
74 Documentation/m68k/kernel-options.txt.
1da177e4 75 MDA MDA console support is enabled.
16290246 76 MIPS MIPS architecture is enabled.
1da177e4 77 MOUSE Appropriate mouse support is enabled.
309e57df 78 MSI Message Signaled Interrupts (PCI).
c8facbb6 79 MTD MTD (Memory Technology Device) support is enabled.
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80 NET Appropriate network support is enabled.
81 NUMA NUMA support is enabled.
82 NFS Appropriate NFS support is enabled.
83 OSS OSS sound support is enabled.
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84 PV_OPS A paravirtualized kernel is enabled.
85 PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
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86 PARISC The PA-RISC architecture is enabled.
87 PCI PCI bus support is enabled.
7f785763 88 PCIE PCI Express support is enabled.
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89 PCMCIA The PCMCIA subsystem is enabled.
90 PNP Plug & Play support is enabled.
91 PPC PowerPC architecture is enabled.
92 PPT Parallel port support is enabled.
93 PS2 Appropriate PS/2 support is enabled.
94 RAM RAM disk support is enabled.
95 S390 S390 architecture is enabled.
96 SCSI Appropriate SCSI support is enabled.
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97 A lot of drivers have their options described inside
98 the Documentation/scsi/ sub-directory.
20510f2f 99 SECURITY Different security models are enabled.
1da177e4 100 SELINUX SELinux support is enabled.
c1c124e9 101 APPARMOR AppArmor support is enabled.
1da177e4 102 SERIAL Serial support is enabled.
e523d93c 103 SH SuperH architecture is enabled.
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104 SMP The kernel is an SMP kernel.
105 SPARC Sparc architecture is enabled.
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106 SWSUSP Software suspend (hibernation) is enabled.
107 SUSPEND System suspend states are enabled.
225a9be2 108 TPM TPM drivers are enabled.
1da177e4 109 TS Appropriate touchscreen support is enabled.
d4f373e5 110 UMS USB Mass Storage support is enabled.
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111 USB USB support is enabled.
112 USBHID USB Human Interface Device support is enabled.
113 V4L Video For Linux support is enabled.
81a054ce 114 VMMIO Driver for memory mapped virtio devices is enabled.
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115 VGA The VGA console has been enabled.
116 VT Virtual terminal support is enabled.
117 WDT Watchdog support is enabled.
118 XT IBM PC/XT MFM hard disk support is enabled.
cd4f0ef7 119 X86-32 X86-32, aka i386 architecture is enabled.
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120 X86-64 X86-64 architecture is enabled.
121 More X86-64 boot options can be found in
71cced6e 122 Documentation/x86/x86_64/boot-options.txt .
16290246 123 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
c1c5413a 124 XEN Xen support is enabled
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125
126In addition, the following text indicates that the option:
127
128 BUGS= Relates to possible processor bugs on the said processor.
129 KNL Is a kernel start-up parameter.
130 BOOT Is a boot loader parameter.
131
132Parameters denoted with BOOT are actually interpreted by the boot
133loader, and have no meaning to the kernel directly.
134Do not modify the syntax of boot loader parameters without extreme
954a8b81 135need or coordination with <Documentation/x86/boot.txt>.
1da177e4 136
5558870b 137There are also arch-specific kernel-parameters not documented here.
71cced6e 138See for example <Documentation/x86/x86_64/boot-options.txt>.
5558870b 139
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140Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
141a trailing = on the name of any parameter states that that parameter will
142be entered as an environment variable, whereas its absence indicates that
143it will appear as a kernel argument readable via /proc/cmdline by programs
144running once the system is up.
145
9c4751fd 146The number of kernel parameters is not limited, but the length of the
147complete command line (parameters including spaces etc.) is limited to
148a fixed number of characters. This limit depends on the architecture
149and is between 256 and 4096 characters. It is defined in the file
150./include/asm/setup.h as COMMAND_LINE_SIZE.
151
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152Finally, the [KMG] suffix is commonly described after a number of kernel
153parameter values. These 'K', 'M', and 'G' letters represent the _binary_
154multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
155bytes respectively. Such letter suffixes can also be entirely omitted.
156
9c4751fd 157
6cececfc 158 acpi= [HW,ACPI,X86]
03d926f8 159 Advanced Configuration and Power Interface
68ca4069 160 Format: { force | off | strict | noirq | rsdt }
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161 force -- enable ACPI if default was off
162 off -- disable ACPI if default was on
163 noirq -- do not use ACPI for IRQ routing
a9913044 164 strict -- Be less tolerant of platforms that are not
1da177e4 165 strictly ACPI specification compliant.
237889bf 166 rsdt -- prefer RSDT over (default) XSDT
aa2110cb 167 copy_dsdt -- copy DSDT to memory
1da177e4 168
395cf969 169 See also Documentation/power/runtime_pm.txt, pci=noacpi
1da177e4 170
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171 acpi_rsdp= [ACPI,EFI,KEXEC]
172 Pass the RSDP address to the kernel, mostly used
173 on machines running EFI runtime service to boot the
174 second kernel for kdump.
175
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176 acpi_apic_instance= [ACPI, IOAPIC]
177 Format: <int>
178 2: use 2nd APIC table, if available
179 1,0: use 1st APIC table
4e381a4f 180 default: 0
a1fdcc0d 181
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182 acpi_backlight= [HW,ACPI]
183 acpi_backlight=vendor
184 acpi_backlight=video
185 If set to vendor, prefer vendor specific driver
186 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
187 of the ACPI video.ko driver.
188
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189 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
190 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
1da177e4 191 Format: <int>
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192 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
193 debug output. Bits in debug_layer correspond to a
194 _COMPONENT in an ACPI source file, e.g.,
195 #define _COMPONENT ACPI_PCI_COMPONENT
196 Bits in debug_level correspond to a level in
197 ACPI_DEBUG_PRINT statements, e.g.,
198 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
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199 The debug_level mask defaults to "info". See
200 Documentation/acpi/debug.txt for more information about
201 debug layers and levels.
a0d84a92 202
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203 Enable processor driver info messages:
204 acpi.debug_layer=0x20000000
205 Enable PCI/PCI interrupt routing info messages:
206 acpi.debug_layer=0x400000
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207 Enable AML "Debug" output, i.e., stores to the Debug
208 object while interpreting AML:
209 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
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210 Enable all messages related to ACPI hardware:
211 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
212
213 Some values produce so much output that the system is
214 unusable. The "log_buf_len" parameter may be useful
215 if you need to capture more output.
f989106c 216
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217 acpi_force_table_verification [HW,ACPI]
218 Enable table checksum verification during early stage.
219 By default, this is disabled due to x86 early mapping
220 size limitation.
221
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222 acpi_irq_balance [HW,ACPI]
223 ACPI will balance active IRQs
224 default in APIC mode
225
226 acpi_irq_nobalance [HW,ACPI]
227 ACPI will not move active IRQs (default)
228 default in PIC mode
229
230 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
231 Format: <irq>,<irq>...
232
233 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
234 use by PCI
235 Format: <irq>,<irq>...
236
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237 acpi_no_auto_serialize [HW,ACPI]
238 Disable auto-serialization of AML methods
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239 AML control methods that contain the opcodes to create
240 named objects will be marked as "Serialized" by the
241 auto-serialization feature.
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242 This feature is enabled by default.
243 This option allows to turn off the feature.
22b5afce 244
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245 acpi_no_static_ssdt [HW,ACPI]
246 Disable installation of static SSDTs at early boot time
247 By default, SSDTs contained in the RSDT/XSDT will be
248 installed automatically and they will appear under
249 /sys/firmware/acpi/tables.
250 This option turns off this feature.
251 Note that specifying this option does not affect
252 dynamic table installation which will install SSDT
253 tables to /sys/firmware/acpi/tables/dynamic.
0cb55ad2 254
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255 acpica_no_return_repair [HW, ACPI]
256 Disable AML predefined validation mechanism
257 This mechanism can repair the evaluation result to make
258 the return objects more ACPI specification compliant.
259 This option is useful for developers to identify the
260 root cause of an AML interpreter issue when the issue
261 has something to do with the repair mechanism.
262
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263 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
264 Format: To spoof as Windows 98: ="Microsoft Windows"
265
266 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
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267 acpi_osi="string1" # add string1
268 acpi_osi="!string2" # remove string2
741d8128 269 acpi_osi=!* # remove all strings
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270 acpi_osi=! # disable all built-in OS vendor
271 strings
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272 acpi_osi= # disable all strings
273
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274 'acpi_osi=!' can be used in combination with single or
275 multiple 'acpi_osi="string1"' to support specific OS
276 vendor string(s). Note that such command can only
277 affect the default state of the OS vendor strings, thus
278 it cannot affect the default state of the feature group
279 strings and the current state of the OS vendor strings,
280 specifying it multiple times through kernel command line
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281 is meaningless. This command is useful when one do not
282 care about the state of the feature group strings which
283 should be controlled by the OSPM.
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284 Examples:
285 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
286 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
287 can make '_OSI("Windows 2000")' TRUE.
288
289 'acpi_osi=' cannot be used in combination with other
290 'acpi_osi=' command lines, the _OSI method will not
291 exist in the ACPI namespace. NOTE that such command can
292 only affect the _OSI support state, thus specifying it
293 multiple times through kernel command line is also
294 meaningless.
295 Examples:
296 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
297 FALSE.
298
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299 'acpi_osi=!*' can be used in combination with single or
300 multiple 'acpi_osi="string1"' to support specific
301 string(s). Note that such command can affect the
302 current state of both the OS vendor strings and the
303 feature group strings, thus specifying it multiple times
304 through kernel command line is meaningful. But it may
305 still not able to affect the final state of a string if
306 there are quirks related to this string. This command
307 is useful when one want to control the state of the
308 feature group strings to debug BIOS issues related to
309 the OSPM features.
310 Examples:
311 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
312 '_OSI("Module Device")' FALSE.
313 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
314 '_OSI("Module Device")' TRUE.
315 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
316 equivalent to
317 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
318 and
319 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
320 they all will make '_OSI("Windows 2000")' TRUE.
321
6cececfc 322 acpi_pm_good [X86]
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323 Override the pmtimer bug detection: force the kernel
324 to assume that this machine's pmtimer latches its value
325 and always returns good values.
326
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327 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
328 Format: { level | edge | high | low }
329
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330 acpi_skip_timer_override [HW,ACPI]
331 Recognize and ignore IRQ0/pin2 Interrupt Override.
332 For broken nForce2 BIOS resulting in XT-PIC timer.
333
334 acpi_sleep= [HW,ACPI] Sleep options
335 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
c3b0795c 336 old_ordering, nonvs, sci_force_enable }
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337 See Documentation/power/video.txt for information on
338 s3_bios and s3_mode.
339 s3_beep is for debugging; it makes the PC's speaker beep
340 as soon as the kernel's real-mode entry point is called.
341 s4_nohwsig prevents ACPI hardware signature from being
342 used during resume from hibernation.
343 old_ordering causes the ACPI 1.0 ordering of the _PTS
344 control method, with respect to putting devices into
345 low power states, to be enforced (the ACPI 2.0 ordering
346 of _PTS is used by default).
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347 nonvs prevents the kernel from saving/restoring the
348 ACPI NVS memory during suspend/hibernation and resume.
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349 sci_force_enable causes the kernel to set SCI_EN directly
350 on resume from S1/S3 (which is against the ACPI spec,
351 but some broken systems don't work without it).
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352
353 acpi_use_timer_override [HW,ACPI]
354 Use timer override. For some broken Nvidia NF5 boards
355 that require a timer override, but don't have HPET
356
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357 acpi_enforce_resources= [ACPI]
358 { strict | lax | no }
359 Check for resource conflicts between native drivers
360 and ACPI OperationRegions (SystemIO and SystemMemory
361 only). IO ports and memory declared in ACPI might be
362 used by the ACPI subsystem in arbitrary AML code and
363 can interfere with legacy drivers.
364 strict (default): access to resources claimed by ACPI
365 is denied; legacy drivers trying to access reserved
366 resources will fail to bind to device using them.
367 lax: access to resources claimed by ACPI is allowed;
368 legacy drivers trying to access reserved resources
369 will bind successfully but a warning message is logged.
370 no: ACPI OperationRegions are not marked as reserved,
371 no further checks are performed.
372
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373 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
374 kernels.
375
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376 add_efi_memmap [EFI; X86] Include EFI memory map in
377 kernel's map of available physical RAM.
378
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379 agp= [AGP]
380 { off | try_unsupported }
381 off: disable AGP support
382 try_unsupported: try to drive unsupported chipsets
383 (may crash computer or cause data corruption)
384
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385 ALSA [HW,ALSA]
386 See Documentation/sound/alsa/alsa-parameters.txt
387
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388 alignment= [KNL,ARM]
389 Allow the default userspace alignment fault handler
390 behaviour to be specified. Bit 0 enables warnings,
391 bit 1 enables fixups, and bit 2 sends a segfault.
392
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393 align_va_addr= [X86-64]
394 Align virtual addresses by clearing slice [14:12] when
395 allocating a VMA at process creation time. This option
396 gives you up to 3% performance improvement on AMD F15h
397 machines (where it is enabled by default) for a
398 CPU-intensive style benchmark, and it can vary highly in
399 a microbenchmark depending on workload and compiler.
400
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401 32: only for 32-bit processes
402 64: only for 64-bit processes
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403 on: enable for both 32- and 64-bit processes
404 off: disable for both 32- and 64-bit processes
405
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406 alloc_snapshot [FTRACE]
407 Allocate the ftrace snapshot buffer on boot up when the
408 main buffer is allocated. This is handy if debugging
409 and you need to use tracing_snapshot() on boot up, and
410 do not want to use tracing_snapshot_alloc() as it needs
411 to be done where GFP_KERNEL allocations are allowed.
412
89e0b9a3 413 amd_iommu= [HW,X86-64]
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414 Pass parameters to the AMD IOMMU driver in the system.
415 Possible values are:
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416 fullflush - enable flushing of IO/TLB entries when
417 they are unmapped. Otherwise they are
418 flushed before they will be reused, which
419 is a lot of faster
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420 off - do not initialize any AMD IOMMU found in
421 the system
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422 force_isolation - Force device isolation for all
423 devices. The IOMMU driver is not
424 allowed anymore to lift isolation
425 requirements as needed. This option
426 does not override iommu=pt
afa9fdc2 427
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428 amd_iommu_dump= [HW,X86-64]
429 Enable AMD IOMMU driver option to dump the ACPI table
430 for AMD IOMMU. With this option enabled, AMD IOMMU
431 driver will print ACPI tables for AMD IOMMU during
432 IOMMU initialization.
433
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434 amijoy.map= [HW,JOY] Amiga joystick support
435 Map of devices attached to JOY0DAT and JOY1DAT
436 Format: <a>,<b>
395cf969 437 See also Documentation/input/joystick.txt
1da177e4
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438
439 analog.map= [HW,JOY] Analog joystick and gamepad support
440 Specifies type or capabilities of an analog joystick
441 connected to one of 16 gameports
442 Format: <type1>,<type2>,..<type16>
443
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444 apc= [HW,SPARC]
445 Power management functions (SPARCstation-4/5 + deriv.)
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446 Format: noidle
447 Disable APC CPU standby support. SPARCstation-Fox does
448 not play well with APC CPU idle - disable it if you have
449 APC and your system crashes randomly.
450
ca1eda2d 451 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
c8facbb6 452 Change the output verbosity whilst booting
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LT
453 Format: { quiet (default) | verbose | debug }
454 Change the amount of debugging information output
455 when initialising the APIC and IO-APIC components.
a9913044 456
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457 autoconf= [IPV6]
458 See Documentation/networking/ipv6.txt.
459
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460 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
461 Limit apic dumping. The parameter defines the maximal
462 number of local apics being dumped. Also it is possible
463 to set it to "all" by meaning -- no limit here.
464 Format: { 1 (default) | 2 | ... | all }.
465 The parameter valid if only apic=debug or
466 apic=verbose is specified.
467 Example: apic=debug show_lapic=all
468
1da177e4 469 apm= [APM] Advanced Power Management
71f77055 470 See header of arch/x86/kernel/apm_32.c.
1da177e4 471
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472 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
473 Format: <io>,<irq>,<nodeID>
474
475 ataflop= [HW,M68k]
476
477 atarimouse= [HW,MOUSE] Atari Mouse
478
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479 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
480 EzKey and similar keyboards
481
482 atkbd.reset= [HW] Reset keyboard during initialization
483
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484 atkbd.set= [HW] Select keyboard code set
485 Format: <int> (2 = AT (default), 3 = PS/2)
1da177e4
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486
487 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
488 keyboards
489
490 atkbd.softraw= [HW] Choose between synthetic and real raw mode
491 Format: <bool> (0 = real, 1 = synthetic (default))
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492
493 atkbd.softrepeat= [HW]
494 Use software keyboard repeat
1da177e4 495
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496 audit= [KNL] Enable the audit sub-system
497 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
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498 0 - kernel audit is disabled and can not be enabled
499 until the next reboot
500 unset - kernel audit is initialized but disabled and
501 will be fully enabled by the userspace auditd.
502 1 - kernel audit is initialized and partially enabled,
503 storing at most audit_backlog_limit messages in
504 RAM until it is fully enabled by the userspace
505 auditd.
a106fb0c 506 Default: unset
f3411cb2 507
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508 audit_backlog_limit= [KNL] Set the audit queue size limit.
509 Format: <int> (must be >=0)
510 Default: 64
511
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512 baycom_epp= [HW,AX25]
513 Format: <io>,<mode>
a9913044 514
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515 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
516 Format: <io>,<mode>
517 See header of drivers/net/hamradio/baycom_par.c.
518
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519 baycom_ser_fdx= [HW,AX25]
520 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
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521 Format: <io>,<irq>,<mode>[,<baud>]
522 See header of drivers/net/hamradio/baycom_ser_fdx.c.
523
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524 baycom_ser_hdx= [HW,AX25]
525 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
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526 Format: <io>,<irq>,<mode>
527 See header of drivers/net/hamradio/baycom_ser_hdx.c.
528
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529 blkdevparts= Manual partition parsing of block device(s) for
530 embedded devices based on command line input.
531 See Documentation/block/cmdline-partition.txt
532
bfe8df3d
RD
533 boot_delay= Milliseconds to delay each printk during boot.
534 Values larger than 10 seconds (10000) are changed to
535 no delay (0).
536 Format: integer
537
35fc908d
AH
538 bootmem_debug [KNL] Enable bootmem allocator debug messages.
539
1da177e4 540 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
a9913044
RD
541 bttv.radio= Most important insmod options are available as
542 kernel args too.
1da177e4 543 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
395cf969 544 bttv.tuner=
1da177e4 545
4e89a2d8
WS
546 bulk_remove=off [PPC] This parameter disables the use of the pSeries
547 firmware feature for flushing multiple hpte entries
548 at a time.
549
1da177e4
LT
550 c101= [NET] Moxa C101 synchronous serial card
551
cd4f0ef7 552 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
1da177e4
LT
553 Sometimes CPU hardware bugs make them report the cache
554 size incorrectly. The kernel will attempt work arounds
555 to fix known problems, but for some CPUs it is not
556 possible to determine what the correct size should be.
557 This option provides an override for these situations.
558
14ff56bb
SO
559 ccw_timeout_log [S390]
560 See Documentation/s390/CommonIO for details.
1da177e4 561
8bab8dde
PM
562 cgroup_disable= [KNL] Disable a particular controller
563 Format: {name of the controller(s) to disable}
ca0bdbb5
QH
564 The effects of cgroup_disable=foo are:
565 - foo isn't auto-mounted if you mount all cgroups in
566 a single hierarchy
567 - foo isn't visible as an individually mountable
568 subsystem
569 {Currently only "memory" controller deal with this and
570 cut the overhead, others just disable the usage. So
571 only cgroup_disable=memory is actually worthy}
8bab8dde 572
1da177e4
LT
573 checkreqprot [SELINUX] Set initial checkreqprot flag value.
574 Format: { "0" | "1" }
575 See security/selinux/Kconfig help text.
a9913044
RD
576 0 -- check protection applied by kernel (includes
577 any implied execute protection).
1da177e4
LT
578 1 -- check protection requested by application.
579 Default value is set via a kernel config option.
a9913044
RD
580 Value can be changed at runtime via
581 /selinux/checkreqprot.
582
661ca0da
SO
583 cio_ignore= [S390]
584 See Documentation/s390/CommonIO for details.
1e435256
OJ
585 clk_ignore_unused
586 [CLK]
587 Keep all clocks already enabled by bootloader on,
588 even if no driver has claimed them. This is useful
589 for debug and development, but should not be
590 needed on a platform with proper driver support.
591 For more information, see Documentation/clk.txt.
661ca0da 592
cd4f0ef7 593 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
734efb46 594 [Deprecated]
3f6dee9b 595 Forces specified clocksource (if available) to be used
734efb46 596 when calculating gettimeofday(). If specified
3f6dee9b 597 clocksource is not available, it defaults to PIT.
1da177e4
LT
598 Format: { pit | tsc | cyclone | pmtmr }
599
592913ec 600 clocksource= Override the default clocksource
3d6ac984
RD
601 Format: <string>
602 Override the default clocksource and use the clocksource
603 with the name specified.
604 Some clocksource names to choose from, depending on
605 the platform:
606 [all] jiffies (this is the base, fallback clocksource)
607 [ACPI] acpi_pm
608 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
609 pxa_timer,timer3,32k_counter,timer0_1
610 [AVR32] avr32
9863c90f 611 [X86-32] pit,hpet,tsc;
3d6ac984
RD
612 scx200_hrt on Geode; cyclone on IBM x440
613 [MIPS] MIPS
614 [PARISC] cr16
615 [S390] tod
616 [SH] SuperH
617 [SPARC64] tick
618 [X86-64] hpet,tsc
619
ac72e788
AK
620 clearcpuid=BITNUM [X86]
621 Disable CPUID feature X for the kernel. See
07983f0e
RD
622 arch/x86/include/asm/cpufeature.h for the valid bit
623 numbers. Note the Linux specific bits are not necessarily
ac72e788
AK
624 stable over kernel options, but the vendor specific
625 ones should be.
626 Also note that user programs calling CPUID directly
627 or using the feature without checking anything
628 will still see it. This just prevents it from
629 being used by the kernel or shown in /proc/cpuinfo.
630 Also note the kernel might malfunction if you disable
631 some critical bits.
632
5ea3b1b2
AM
633 cma=nn[MG]@[start[MG][-end[MG]]]
634 [ARM,X86,KNL]
635 Sets the size of kernel global memory area for
636 contiguous memory allocations and optionally the
637 placement constraint by the physical address range of
c64be2bb
MS
638 memory allocations. For more information, see
639 include/linux/dma-contiguous.h
640
14f966e7
RJ
641 cmo_free_hint= [PPC] Format: { yes | no }
642 Specify whether pages are marked as being inactive
643 when they are freed. This is used in CMO environments
644 to determine OS memory pressure for page stealing by
645 a hypervisor.
646 Default: yes
647
c7909509
MS
648 coherent_pool=nn[KMG] [ARM,KNL]
649 Sets the size of memory pool for coherent, atomic dma
e9da6e99 650 allocations, by default set to 256K.
c7909509 651
6cececfc 652 code_bytes [X86] How many bytes of object code to print
a25bd949 653 in an oops report.
86c41837
CE
654 Range: 0 - 8192
655 Default: 64
656
1da177e4 657 com20020= [HW,NET] ARCnet - COM20020 chipset
a9913044
RD
658 Format:
659 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
1da177e4
LT
660
661 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
662 Format: <io>[,<irq>]
663
a9913044
RD
664 com90xx= [HW,NET]
665 ARCnet - COM90xx chipset (memory-mapped buffers)
1da177e4
LT
666 Format: <io>[,<irq>[,<memstart>]]
667
668 condev= [HW,S390] console device
669 conmode=
a9913044 670
1da177e4
LT
671 console= [KNL] Output console device and options.
672
673 tty<n> Use the virtual console device <n>.
674
675 ttyS<n>[,options]
f1a1c2dc 676 ttyUSB0[,options]
1da177e4 677 Use the specified serial port. The options are of
f1a1c2dc
RD
678 the form "bbbbpnf", where "bbbb" is the baud rate,
679 "p" is parity ("n", "o", or "e"), "n" is number of
680 bits, and "f" is flow control ("r" for RTS or
681 omit it). Default is "9600n8".
682
683 See Documentation/serial-console.txt for more
684 information. See
685 Documentation/networking/netconsole.txt for an
686 alternative.
1da177e4 687
18a8bd94
YL
688 uart[8250],io,<addr>[,options]
689 uart[8250],mmio,<addr>[,options]
1da177e4
LT
690 Start an early, polled-mode console on the 8250/16550
691 UART at the specified I/O port or MMIO address,
692 switching to the matching ttyS device later. The
693 options are the same as for ttyS, above.
a2fd6419
KRW
694 hvc<n> Use the hypervisor console device <n>. This is for
695 both Xen and PowerPC hypervisors.
1da177e4 696
f7511d5f
ST
697 If the device connected to the port is not a TTY but a braille
698 device, prepend "brl," before the device type, for instance
699 console=brl,ttyS0
700 For now, only VisioBraille is supported.
701
f324edc8
DM
702 consoleblank= [KNL] The console blank (screen saver) timeout in
703 seconds. Defaults to 10*60 = 10mins. A value of 0
704 disables the blank timer.
705
4cb0e11b
HK
706 coredump_filter=
707 [KNL] Change the default value for
708 /proc/<pid>/coredump_filter.
709 See also Documentation/filesystems/proc.txt.
710
62027aea
LB
711 cpuidle.off=1 [CPU_IDLE]
712 disable the cpuidle sub-system
713
1da177e4 714 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
a9913044
RD
715 Format:
716 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
1da177e4 717
6f21e646
AD
718 crashkernel=size[KMG][@offset[KMG]]
719 [KNL] Using kexec, Linux can switch to a 'crash kernel'
720 upon panic. This parameter reserves the physical
721 memory region [offset, offset + size] for that kernel
722 image. If '@offset' is omitted, then a suitable offset
723 is selected automatically. Check
724 Documentation/kdump/kdump.txt for further details.
dc009d92 725
fb391599
BW
726 crashkernel=range1:size1[,range2:size2,...][@offset]
727 [KNL] Same as above, but depends on the memory
728 in the running system. The syntax of range is
729 start-[end] where start and end are both
730 a memory unit (amount[KMG]). See also
6f21e646 731 Documentation/kdump/kdump.txt for an example.
fb391599 732
adbc742b 733 crashkernel=size[KMG],high
55a20ee7
YL
734 [KNL, x86_64] range could be above 4G. Allow kernel
735 to allocate physical memory region from top, so could
736 be above 4G if system have more than 4G ram installed.
737 Otherwise memory region will be allocated below 4G, if
738 available.
739 It will be ignored if crashkernel=X is specified.
adbc742b
YL
740 crashkernel=size[KMG],low
741 [KNL, x86_64] range under 4G. When crashkernel=X,high
742 is passed, kernel could allocate physical memory region
c729de8f
YL
743 above 4G, that cause second kernel crash on system
744 that require some amount of low memory, e.g. swiotlb
745 requires at least 64M+32K low memory. Kernel would
746 try to allocate 72M below 4G automatically.
747 This one let user to specify own low range under 4G
748 for second kernel instead.
749 0: to disable low allocation.
adbc742b 750 It will be ignored when crashkernel=X,high is not used
55a20ee7 751 or memory reserved is below 4G.
c729de8f 752
1da177e4
LT
753 cs89x0_dma= [HW,NET]
754 Format: <dma>
755
756 cs89x0_media= [HW,NET]
757 Format: { rj45 | aui | bnc }
a9913044 758
a9913044 759 dasd= [HW,NET]
1da177e4
LT
760 See header of drivers/s390/block/dasd_devmap.c.
761
762 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
763 (one device per port)
764 Format: <port#>,<type>
765 See also Documentation/input/joystick-parport.txt
766
a648ec05
TR
767 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
768 time. See Documentation/dynamic-debug-howto.txt for
29e36c9f 769 details. Deprecated, see dyndbg.
a648ec05 770
1da177e4
LT
771 debug [KNL] Enable kernel debugging (events log level).
772
cae2ed9a
IM
773 debug_locks_verbose=
774 [KNL] verbose self-tests
775 Format=<0|1>
776 Print debugging info while doing the locking API
777 self-tests.
778 We default to 0 (no extra messages), setting it to
779 1 will print _a lot_ more information - normally
780 only useful to kernel developers.
781
3ac7fe5a
TG
782 debug_objects [KNL] Enable object debugging
783
3e8ebb5c
KM
784 no_debug_objects
785 [KNL] Disable object debugging
786
c0a32fc5
SG
787 debug_guardpage_minorder=
788 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
789 parameter allows control of the order of pages that will
790 be intentionally kept free (and hence protected) by the
791 buddy allocator. Bigger value increase the probability
792 of catching random memory corruption, but reduce the
793 amount of memory for normal system use. The maximum
794 possible value is MAX_ORDER/2. Setting this parameter
795 to 1 or 2 should be enough to identify most random
796 memory corruption problems caused by bugs in kernel or
797 driver code when a CPU writes to (or reads from) a
798 random memory location. Note that there exists a class
799 of memory corruptions problems caused by buggy H/W or
800 F/W or by drivers badly programing DMA (basically when
801 memory is written at bus level and the CPU MMU is
802 bypassed) which are not detectable by
803 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
804 tracking down these problems.
805
d3af01f1
TG
806 debugpat [X86] Enable PAT debugging
807
2d27a966 808 decnet.addr= [HW,NET]
1da177e4
LT
809 Format: <area>[,<node>]
810 See also Documentation/networking/decnet.txt.
811
0cb55ad2
RD
812 default_hugepagesz=
813 [same as hugepagesz=] The size of the default
814 HugeTLB page size. This is the size represented by
815 the legacy /proc/ hugepages APIs, used for SHM, and
816 default size when mounting hugetlbfs filesystems.
817 Defaults to the default architecture's huge page size
818 if not specified.
55ff9780 819
1da177e4
LT
820 dhash_entries= [KNL]
821 Set number of hash buckets for dentry cache.
a9913044 822
b0f83b28
BH
823 disable= [IPV6]
824 See Documentation/networking/ipv6.txt.
825
151e0c7d
HD
826 disable_cpu_apicid= [X86,APIC,SMP]
827 Format: <int>
828 The number of initial APIC ID for the
829 corresponding CPU to be disabled at boot,
830 mostly used for the kdump 2nd kernel to
831 disable BSP to wake up multiple CPUs without
832 causing system reset or hang due to sending
833 INIT from AP to BSP.
834
4e8b0cf4
NA
835 disable_ddw [PPC/PSERIES]
836 Disable Dynamic DMA Window support. Use this if
837 to workaround buggy firmware.
838
b0f83b28
BH
839 disable_ipv6= [IPV6]
840 See Documentation/networking/ipv6.txt.
841
95ffa243 842 disable_mtrr_cleanup [X86]
95ffa243
YL
843 The kernel tries to adjust MTRR layout from continuous
844 to discrete, to make X server driver able to add WB
0cb55ad2 845 entry later. This parameter disables that.
95ffa243 846
093af8d7 847 disable_mtrr_trim [X86, Intel and AMD only]
99fc8d42
JB
848 By default the kernel will trim any uncacheable
849 memory out of your available memory pool based on
850 MTRR settings. This parameter disables that behavior,
851 possibly causing your machine to run very slowly.
852
6cececfc 853 disable_timer_pin_1 [X86]
0cb55ad2
RD
854 Disable PIN 1 of APIC timer
855 Can be useful to work around chipset bugs.
856
0cb55ad2
RD
857 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
858 this option disables the debugging code at boot.
859
860 dma_debug_entries=<number>
861 This option allows to tune the number of preallocated
862 entries for DMA-API debugging code. One entry is
863 required per DMA-API allocation. Use this if the
864 DMA-API debugging code disables itself because the
865 architectural default is too low.
866
1745de5e
JR
867 dma_debug_driver=<driver_name>
868 With this option the DMA-API debugging driver
869 filter feature can be enabled at boot time. Just
870 pass the driver to filter for as the parameter.
871 The filter can be disabled or changed to another
872 driver later using sysfs.
873
da0df92b
CE
874 drm_kms_helper.edid_firmware=[<connector>:]<file>
875 Broken monitors, graphic adapters and KVMs may
876 send no or incorrect EDID data sets. This parameter
877 allows to specify an EDID data set in the
878 /lib/firmware directory that is used instead.
879 Generic built-in EDID data sets are used, if one of
880 edid/1024x768.bin, edid/1280x1024.bin,
881 edid/1680x1050.bin, or edid/1920x1080.bin is given
882 and no file with the same name exists. Details and
883 instructions how to build your own EDID data are
884 available in Documentation/EDID/HOWTO.txt. An EDID
885 data set will only be used for a particular connector,
886 if its name and a colon are prepended to the EDID
887 name.
888
1da177e4
LT
889 dscc4.setup= [NET]
890
29e36c9f
JC
891 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
892 module.dyndbg[="val"]
893 Enable debug messages at boot time. See
894 Documentation/dynamic-debug-howto.txt for details.
895
56aeeba8
MS
896 early_ioremap_debug [KNL]
897 Enable debug messages in early_ioremap support. This
898 is useful for tracking down temporary early mappings
899 which are not unmapped.
900
0cb55ad2 901 earlycon= [KNL] Output early console device and options.
0d3c673e 902
0cb55ad2
RD
903 uart[8250],io,<addr>[,options]
904 uart[8250],mmio,<addr>[,options]
1917ac76 905 uart[8250],mmio32,<addr>[,options]
0cb55ad2
RD
906 Start an early, polled-mode console on the 8250/16550
907 UART at the specified I/O port or MMIO address.
16290246
RD
908 MMIO inter-register address stride is either 8-bit
909 (mmio) or 32-bit (mmio32).
0cb55ad2
RD
910 The options are the same as for ttyS, above.
911
0d3c673e
RH
912 pl011,<addr>
913 Start an early, polled-mode console on a pl011 serial
914 port at the specified address. The pl011 serial port
915 must already be setup and configured. Options are not
916 yet supported.
917
d50d7269
RH
918 smh Use ARM semihosting calls for early console.
919
7913ad1a 920 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
1da177e4 921 earlyprintk=vga
72548e83 922 earlyprintk=efi
2482a92e 923 earlyprintk=xen
1da177e4 924 earlyprintk=serial[,ttySn[,baudrate]]
147ea091 925 earlyprintk=serial[,0x...[,baudrate]]
ea3acb19 926 earlyprintk=ttySn[,baudrate]
9780bc41 927 earlyprintk=dbgp[debugController#]
1da177e4 928
147ea091
DH
929 earlyprintk is useful when the kernel crashes before
930 the normal console is initialized. It is not enabled by
931 default because it has some cosmetic problems.
932
a9913044 933 Append ",keep" to not disable it when the real console
1da177e4
LT
934 takes over.
935
72548e83
MF
936 Only one of vga, efi, serial, or usb debug port can
937 be used at a time.
1da177e4 938
147ea091
DH
939 Currently only ttyS0 and ttyS1 may be specified by
940 name. Other I/O ports may be explicitly specified
941 on some architectures (x86 and arm at least) by
942 replacing ttySn with an I/O port address, like this:
943 earlyprintk=serial,0x1008,115200
944 You can find the port for a given device in
945 /proc/tty/driver/serial:
946 2: uart:ST16650V2 port:00001008 irq:18 ...
1da177e4
LT
947
948 Interaction with the standard serial driver is not
949 very good.
950
72548e83
MF
951 The VGA and EFI output is eventually overwritten by
952 the real console.
1da177e4 953
2482a92e
KRW
954 The xen output can only be used by Xen PV guests.
955
c700f013
CG
956 edac_report= [HW,EDAC] Control how to report EDAC event
957 Format: {"on" | "off" | "force"}
958 on: enable EDAC to report H/W event. May be overridden
959 by other higher priority error reporting module.
960 off: disable H/W event reporting through EDAC.
961 force: enforce the use of EDAC to report H/W event.
962 default: on.
963
9731191f
JW
964 ekgdboc= [X86,KGDB] Allow early kernel console debugging
965 ekgdboc=kbd
966
25985edc 967 This is designed to be used in conjunction with
9731191f
JW
968 the boot argument: earlyprintk=vga
969
1da177e4 970 edd= [EDD]
8c4dd606 971 Format: {"off" | "on" | "skip[mbr]"}
1da177e4 972
d2f7cbe7
BP
973 efi= [EFI]
974 Format: { "old_map" }
975 old_map [X86-64]: switch to the old ioremap-based EFI
976 runtime services mapping. 32-bit still uses this one by
977 default.
978
8c58bf3e
RW
979 efi_no_storage_paranoia [EFI; X86]
980 Using this parameter you can use more than 50% of
981 your efi variable storage. Use this parameter only if
982 you are really sure that your UEFI does sane gc and
983 fulfills the spec otherwise your board may brick.
984
1da177e4
LT
985 eisa_irq_edge= [PARISC,HW]
986 See header of drivers/parisc/eisa.c.
987
cd4f0ef7 988 elanfreq= [X86-32]
1da177e4 989 See comment before function elanfreq_setup() in
71f77055 990 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1da177e4
LT
991
992 elevator= [IOSCHED]
17a9e7bb 993 Format: {"cfq" | "deadline" | "noop"}
395cf969 994 See Documentation/block/cfq-iosched.txt and
a9913044
RD
995 Documentation/block/deadline-iosched.txt for details.
996
d3bf3795 997 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
a9913044 998 Specifies physical address of start of kernel core
d3bf3795
MH
999 image elf header and optionally the size. Generally
1000 kexec loader will pass this option to capture kernel.
aac04b32 1001 See Documentation/kdump/kdump.txt for details.
1da177e4 1002
0cb55ad2
RD
1003 enable_mtrr_cleanup [X86]
1004 The kernel tries to adjust MTRR layout from continuous
1005 to discrete, to make X server driver able to add WB
1006 entry later. This parameter enables that.
1007
ca1eda2d 1008 enable_timer_pin_1 [X86]
0cb55ad2
RD
1009 Enable PIN 1 of APIC timer
1010 Can be useful to work around chipset bugs
1011 (in particular on some ATI chipsets).
1012 The kernel tries to set a reasonable default.
1013
1da177e4
LT
1014 enforcing [SELINUX] Set initial enforcing status.
1015 Format: {"0" | "1"}
1016 See security/selinux/Kconfig help text.
1017 0 -- permissive (log only, no denials).
1018 1 -- enforcing (deny and log).
1019 Default value is 0.
1020 Value can be changed at runtime via /selinux/enforce.
1021
a08f82d0
HY
1022 erst_disable [ACPI]
1023 Disable Error Record Serialization Table (ERST)
1024 support.
1025
1da177e4
LT
1026 ether= [HW,NET] Ethernet cards parameters
1027 This option is obsoleted by the "netdev=" option, which
1028 has equivalent usage. See its documentation for details.
1029
7102ebcd
MZ
1030 evm= [EVM]
1031 Format: { "fix" }
1032 Permit 'security.evm' to be updated regardless of
1033 current integrity status.
1034
de1ba09b
AM
1035 failslab=
1036 fail_page_alloc=
1037 fail_make_request=[KNL]
1038 General fault injection mechanism.
1039 Format: <interval>,<probability>,<space>,<times>
395cf969 1040 See also Documentation/fault-injection/.
de1ba09b 1041
1da177e4 1042 floppy= [HW]
31c00fc1 1043 See Documentation/blockdev/floppy.txt.
1da177e4 1044
f13ae30e
AC
1045 force_pal_cache_flush
1046 [IA-64] Avoid check_sal_cache_flush which may hang on
1047 buggy SAL_CACHE_FLUSH implementations. Using this
1048 parameter will force ia64_sal_cache_flush to call
1049 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1050
69f2366c
CB
1051 forcepae [X86-32]
1052 Forcefully enable Physical Address Extension (PAE).
1053 Many Pentium M systems disable PAE but may have a
1054 functionally usable PAE implementation.
1055 Warning: use of this parameter will taint the kernel
1056 and may cause unknown problems.
1057
d9e54076 1058 ftrace=[tracer]
2af15d6a 1059 [FTRACE] will set and start the specified tracer
d9e54076
PZ
1060 as early as possible in order to facilitate early
1061 boot debugging.
1062
cecbca96 1063 ftrace_dump_on_oops[=orig_cpu]
2af15d6a 1064 [FTRACE] will dump the trace buffers on oops.
cecbca96
FW
1065 If no parameter is passed, ftrace will dump
1066 buffers of all CPUs, but if you pass orig_cpu, it will
1067 dump only the buffer of the CPU that triggered the
1068 oops.
2af15d6a
SR
1069
1070 ftrace_filter=[function-list]
1071 [FTRACE] Limit the functions traced by the function
1072 tracer at boot up. function-list is a comma separated
1073 list of functions. This list can be changed at run
1074 time by the set_ftrace_filter file in the debugfs
16290246 1075 tracing directory.
2af15d6a
SR
1076
1077 ftrace_notrace=[function-list]
1078 [FTRACE] Do not trace the functions specified in
1079 function-list. This list can be changed at run time
1080 by the set_ftrace_notrace file in the debugfs
1081 tracing directory.
d9e54076 1082
369bc18f
SA
1083 ftrace_graph_filter=[function-list]
1084 [FTRACE] Limit the top level callers functions traced
1085 by the function graph tracer at boot up.
1086 function-list is a comma separated list of functions
1087 that can be changed at run time by the
1088 set_graph_function file in the debugfs tracing directory.
1089
1da177e4
LT
1090 gamecon.map[2|3]=
1091 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1092 support via parallel port (up to 5 devices per port)
1093 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1094 See also Documentation/input/joystick-parport.txt
1095
1096 gamma= [HW,DRM]
1097
aaf23042
YL
1098 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1099 Format: off | on
1100 default: on
1101
2521f2c2
PO
1102 gcov_persist= [GCOV] When non-zero (default), profiling data for
1103 kernel modules is saved and remains accessible via
1104 debugfs, even when the module is unloaded/reloaded.
1105 When zero, profiling data is discarded and associated
1106 debugfs files are removed at module unload time.
1107
1da177e4 1108 gpt [EFI] Forces disk with valid GPT signature but
6c5de79b
DB
1109 invalid Protective MBR to be treated as GPT. If the
1110 primary GPT is corrupted, it enables the backup/alternate
1111 GPT to be used instead.
1da177e4 1112
6cec9b07
AL
1113 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1114 the "Enable 0" bit of the configuration register.
1115 Format: 0 | 1
1116 Default: 0
1117 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1118 the "Enable 0" bit of the configuration register.
1119 Format: 0 | 1
1120 Default: 0
1121 grcan.select= [HW] Select which physical interface to use.
1122 Format: 0 | 1
1123 Default: 0
1124 grcan.txsize= [HW] Sets the size of the tx buffer.
1125 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1126 Default: 1024
1127 grcan.rxsize= [HW] Sets the size of the rx buffer.
1128 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1129 Default: 1024
1130
1da177e4
LT
1131 hashdist= [KNL,NUMA] Large hashes allocated during boot
1132 are distributed across NUMA nodes. Defaults on
16290246 1133 for 64-bit NUMA, off otherwise.
a9913044 1134 Format: 0 | 1 (for off | on)
1da177e4
LT
1135
1136 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1137
1138 hd= [EIDE] (E)IDE hard drive subsystem geometry
1139 Format: <cyl>,<head>,<sect>
1140
ea8c071c
HY
1141 hest_disable [ACPI]
1142 Disable Hardware Error Source Table (HEST) support;
1143 corresponding firmware-first mode error processing
1144 logic will be disabled.
1145
1da177e4
LT
1146 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1147 size of <nn>. This works even on boxes that have no
1148 highmem otherwise. This also works to reduce highmem
1149 size on bigger boxes.
1150
54cdfdb4
TG
1151 highres= [KNL] Enable/disable high resolution timer mode.
1152 Valid parameters: "on", "off"
1153 Default: "on"
1154
1da177e4
LT
1155 hisax= [HW,ISDN]
1156 See Documentation/isdn/README.HiSax.
1157
0cb55ad2
RD
1158 hlt [BUGS=ARM,SH]
1159
1160 hpet= [X86-32,HPET] option to control HPET usage
1161 Format: { enable (default) | disable | force |
1162 verbose }
1163 disable: disable HPET and use PIT instead
1164 force: allow force enabled of undocumented chips (ICH4,
1165 VIA, nVidia)
1166 verbose: show contents of HPET registers during setup
1167
3d035f58
PB
1168 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1169 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1170
b4718e62
AK
1171 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1172 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
0d9ea754
JT
1173 On x86-64 and powerpc, this option can be specified
1174 multiple times interleaved with hugepages= to reserve
1175 huge pages of different sizes. Valid pages sizes on
1176 x86-64 are 2M (when the CPU supports "pse") and 1G
1177 (when the CPU supports the "pdpe1gb" cpuinfo flag)
b4718e62
AK
1178 Note that 1GB pages can only be allocated at boot time
1179 using hugepages= and not freed afterwards.
6902aa84 1180
555d61d6
HB
1181 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1182 terminal devices. Valid values: 0..8
431429ff
HB
1183 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1184 If specified, z/VM IUCV HVC accepts connections
1185 from listed z/VM user IDs only.
cef7125d 1186
fdabf525
JH
1187 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1188 hardware thread id mappings.
1189 Format: <cpu>:<hwthread>
1190
7bf69395
FDN
1191 keep_bootcon [KNL]
1192 Do not unregister boot console at start. This is only
1193 useful for debugging when something happens in the window
1194 between unregistering the boot console and initializing
1195 the real console.
1196
3a853fb9 1197 i2c_bus= [HW] Override the default board specific I2C bus speed
7954763b
JN
1198 or register an additional I2C bus that is not
1199 registered from board initialization code.
3a853fb9
JN
1200 Format:
1201 <bus_id>,<clkrate>
1202
36d95739 1203 i8042.debug [HW] Toggle i8042 debug mode
1da177e4 1204 i8042.direct [HW] Put keyboard port into non-translated mode
84eb8d06
ML
1205 i8042.dumbkbd [HW] Pretend that controller can only read data from
1206 keyboard and cannot control its state
1da177e4
LT
1207 (Don't attempt to blink the leds)
1208 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
945ef0d4 1209 i8042.nokbd [HW] Don't check/create keyboard port
75d08c78
JK
1210 i8042.noloop [HW] Disable the AUX Loopback command while probing
1211 for the AUX port
1da177e4
LT
1212 i8042.nomux [HW] Don't check presence of an active multiplexing
1213 controller
1214 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1215 controllers
24775d65 1216 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1da177e4
LT
1217 i8042.reset [HW] Reset the controller during init and cleanup
1218 i8042.unlock [HW] Unlock (ignore) the keylock
1219
1220 i810= [HW,DRM]
1221
e70c9d5e
DT
1222 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1223 indicates that the driver is running on unsupported
1224 hardware.
1da177e4
LT
1225 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1226 does not match list of supported models.
1227 i8k.power_status
1228 [HW] Report power status in /proc/i8k
1229 (disabled by default)
1230 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1231 capability is set.
1232
4dca20ef 1233 i915.invert_brightness=
7bd90909
CE
1234 [DRM] Invert the sense of the variable that is used to
1235 set the brightness of the panel backlight. Normally a
4dca20ef
CE
1236 brightness value of 0 indicates backlight switched off,
1237 and the maximum of the brightness value sets the backlight
1238 to maximum brightness. If this parameter is set to 0
1239 (default) and the machine requires it, or this parameter
1240 is set to 1, a brightness value of 0 sets the backlight
1241 to maximum brightness, and the maximum of the brightness
1242 value switches the backlight off.
1243 -1 -- never invert brightness
1244 0 -- machine default
1245 1 -- force brightness inversion
7bd90909 1246
1da177e4
LT
1247 icn= [HW,ISDN]
1248 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1249
0af80c04
DF
1250 ide-core.nodma= [HW] (E)IDE subsystem
1251 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
075affcb
BZ
1252 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1253 .cdrom .chs .ignore_cable are additional options
1c10e938 1254 See Documentation/ide/ide.txt.
1da177e4 1255
0cb55ad2
RD
1256 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1257 Claim all unknown PCI IDE storage controllers.
1258
f039b754 1259 idle= [X86]
69fb3676 1260 Format: idle=poll, idle=halt, idle=nomwait
ada9cfdd
RD
1261 Poll forces a polling idle loop that can slightly
1262 improve the performance of waking up a idle CPU, but
1263 will use a lot of power and make the system run hot.
1264 Not recommended.
ada9cfdd 1265 idle=halt: Halt is forced to be used for CPU idle.
c1e3b377 1266 In such case C2/C3 won't be used again.
ada9cfdd 1267 idle=nomwait: Disable mwait for CPU C-states
a9913044 1268
79290822
IM
1269 ignore_loglevel [KNL]
1270 Ignore loglevel setting - this will print /all/
1271 kernel messages to the console. Useful for debugging.
0eca6b7c
YZ
1272 We also add it as printk module parameter, so users
1273 could change it dynamically, usually by
1274 /sys/module/printk/parameters/ignore_loglevel.
79290822 1275
1da177e4
LT
1276 ihash_entries= [KNL]
1277 Set number of hash buckets for inode cache.
1278
2fe5d6de
MZ
1279 ima_appraise= [IMA] appraise integrity measurements
1280 Format: { "off" | "enforce" | "fix" }
1281 default: "enforce"
1282
07f6a794
MZ
1283 ima_appraise_tcb [IMA]
1284 The builtin appraise policy appraises all files
1285 owned by uid=0.
1286
3323eec9 1287 ima_hash= [IMA]
e7a2ad7e
MZ
1288 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1289 | sha512 | ... }
3323eec9
MZ
1290 default: "sha1"
1291
e7a2ad7e
MZ
1292 The list of supported hash algorithms is defined
1293 in crypto/hash_info.h.
1294
5789ba3b
EP
1295 ima_tcb [IMA]
1296 Load a policy which meets the needs of the Trusted
1297 Computing Base. This means IMA will measure all
1298 programs exec'd, files mmap'd for exec, and all files
1299 opened for read by uid=0.
1300
9b9d4ce5
RS
1301 ima_template= [IMA]
1302 Select one of defined IMA measurements template formats.
1303 Formats: { "ima" | "ima-ng" }
1304 Default: "ima-ng"
1305
1da177e4
LT
1306 init= [KNL]
1307 Format: <full_path>
1308 Run specified binary instead of /sbin/init as init
1309 process.
1310
1311 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1312 for working out where the kernel is dying during
1313 startup.
1314
1315 initrd= [BOOT] Specify the location of the initial ramdisk
1316
1317 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1318 Format: <irq>
1319
6bb2ff84
FY
1320 int_pln_enable [x86] Enable power limit notification interrupt
1321
d726d8d7
MZ
1322 integrity_audit=[IMA]
1323 Format: { "0" | "1" }
1324 0 -- basic integrity auditing messages. (Default)
1325 1 -- additional integrity auditing messages.
1326
ba395927 1327 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
0cd5c3c8
KM
1328 on
1329 Enable intel iommu driver.
ba395927
KA
1330 off
1331 Disable intel iommu driver.
1332 igfx_off [Default Off]
1333 By default, gfx is mapped as normal device. If a gfx
1334 device has a dedicated DMAR unit, the DMAR unit is
1335 bypassed by not enabling DMAR with this option. In
1336 this case, gfx device will use physical address for
1337 DMA.
7d3b03ce
KA
1338 forcedac [x86_64]
1339 With this option iommu will not optimize to look
16290246 1340 for io virtual address below 32-bit forcing dual
7d3b03ce 1341 address cycle on pci bus for cards supporting greater
16290246
RD
1342 than 32-bit addressing. The default is to look
1343 for translation below 32-bit and if not available
7d3b03ce 1344 then look in the higher range.
5e0d2a6f 1345 strict [Default Off]
1346 With this option on every unmap_single operation will
1347 result in a hardware IOTLB flush operation as opposed
1348 to batching them for performance.
6dd9a7c7
YS
1349 sp_off [Default Off]
1350 By default, super page will be supported if Intel IOMMU
1351 has the capability. With this option, super page will
1352 not be supported.
2e92c7ad
MI
1353
1354 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1355 0 disables intel_idle and fall back on acpi_idle.
1356 1 to 6 specify maximum depth of C-state.
1357
6be26498
DB
1358 intel_pstate= [X86]
1359 disable
1360 Do not enable intel_pstate as the default
1361 scaling driver for the supported processors
1362
d1423d56 1363 intremap= [X86-64, Intel-IOMMU]
d1423d56
CW
1364 on enable Interrupt Remapping (default)
1365 off disable Interrupt Remapping
1366 nosid disable Source ID checking
41750d31
SS
1367 no_x2apic_optout
1368 BIOS x2APIC opt-out request will be ignored
d1423d56 1369
0cb55ad2
RD
1370 iomem= Disable strict checking of access to MMIO memory
1371 strict regions from userspace.
1372 relaxed
1373
1374 iommu= [x86]
1375 off
1376 force
1377 noforce
1378 biomerge
1379 panic
1380 nopanic
1381 merge
1382 nomerge
1383 forcesac
1384 soft
bcb71abe 1385 pt [x86, IA-64]
bcb71abe 1386
0cb55ad2
RD
1387
1388 io7= [HW] IO7 for Marvel based alpha systems
1389 See comment before marvel_specify_io7 in
1390 arch/alpha/kernel/core_marvel.c.
1391
6cececfc 1392 io_delay= [X86] I/O delay method
6e7c4025
IM
1393 0x80
1394 Standard port 0x80 based delay
1395 0xed
1396 Alternate port 0xed based delay (needed on some systems)
b02aae9c 1397 udelay
6e7c4025
IM
1398 Simple two microseconds delay
1399 none
1400 No delay
b02aae9c 1401
1da177e4 1402 ip= [IP_PNP]
dc7a0816 1403 See Documentation/filesystems/nfs/nfsroot.txt.
1da177e4
LT
1404
1405 ip2= [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
c8facbb6
RD
1406 See comment before ip2_setup() in
1407 drivers/char/ip2/ip2base.c.
1da177e4 1408
200803df
AC
1409 irqfixup [HW]
1410 When an interrupt is not handled search all handlers
1411 for it. Intended to get systems with badly broken
1412 firmware running.
1413
1414 irqpoll [HW]
1415 When an interrupt is not handled search all handlers
1416 for it. Also check all handlers each timer
1417 interrupt. Intended to get systems with badly broken
1418 firmware running.
1419
1da177e4 1420 isapnp= [ISAPNP]
a9913044 1421 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1da177e4
LT
1422
1423 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
22f2e280
DF
1424 Format:
1425 <cpu number>,...,<cpu number>
1426 or
b225d44e
LZ
1427 <cpu number>-<cpu number>
1428 (must be a positive range in ascending order)
22f2e280
DF
1429 or a mixture
1430 <cpu number>,...,<cpu number>-<cpu number>
b225d44e 1431
1da177e4
LT
1432 This option can be used to specify one or more CPUs
1433 to isolate from the general SMP balancing and scheduling
b225d44e
LZ
1434 algorithms. You can move a process onto or off an
1435 "isolated" CPU via the CPU affinity syscalls or cpuset.
1da177e4
LT
1436 <cpu number> begins at 0 and the maximum value is
1437 "number of CPUs in system - 1".
1438
1439 This option is the preferred way to isolate CPUs. The
a9913044
RD
1440 alternative -- manually setting the CPU mask of all
1441 tasks in the system -- can cause problems and
1442 suboptimal load balancer performance.
1da177e4 1443
a9913044 1444 iucv= [HW,NET]
1da177e4 1445
7d8bfa26
JR
1446 ivrs_ioapic [HW,X86_64]
1447 Provide an override to the IOAPIC-ID<->DEVICE-ID
1448 mapping provided in the IVRS ACPI table. For
1449 example, to map IOAPIC-ID decimal 10 to
1450 PCI device 00:14.0 write the parameter as:
1451 ivrs_ioapic[10]=00:14.0
1452
1453 ivrs_hpet [HW,X86_64]
1454 Provide an override to the HPET-ID<->DEVICE-ID
1455 mapping provided in the IVRS ACPI table. For
1456 example, to map HPET-ID decimal 0 to
1457 PCI device 00:14.0 write the parameter as:
1458 ivrs_hpet[0]=00:14.0
1459
1da177e4
LT
1460 js= [HW,JOY] Analog joystick
1461 See Documentation/input/joystick.txt.
1462
0cb55ad2
RD
1463 keepinitrd [HW,ARM]
1464
6cececfc 1465 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
ed7ed365
MG
1466 specifies the amount of memory usable by the kernel
1467 for non-movable allocations. The requested amount is
1468 spread evenly throughout all nodes in the system. The
1469 remaining memory in each node is used for Movable
1470 pages. In the event, a node is too small to have both
1471 kernelcore and Movable pages, kernelcore pages will
1472 take priority and other nodes will have a larger number
675217fd 1473 of Movable pages. The Movable zone is used for the
ed7ed365
MG
1474 allocation of pages that may be reclaimed or moved
1475 by the page migration subsystem. This means that
1476 HugeTLB pages may not be allocated from this zone.
1477 Note that allocations like PTEs-from-HighMem still
1478 use the HighMem zone if it exists, and the Normal
1479 zone if it does not.
1480
4fe1da4e
JW
1481 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1482 Format: <Controller#>[,poll interval]
1483 The controller # is the number of the ehci usb debug
1484 port as it is probed via PCI. The poll interval is
1485 optional and is the number seconds in between
1486 each poll cycle to the debug port in case you need
1487 the functionality for interrupting the kernel with
1488 gdb or control-c on the dbgp connection. When
1489 not using this parameter you use sysrq-g to break into
1490 the kernel debugger.
1491
84c08fd6 1492 kgdboc= [KGDB,HW] kgdb over consoles.
ada64e4c
JW
1493 Requires a tty driver that supports console polling,
1494 or a supported polling keyboard driver (non-usb).
65b5ac14
JW
1495 Serial only format: <serial_device>[,baud]
1496 keyboard only format: kbd
1497 keyboard and serial format: kbd,<serial_device>[,baud]
1498 Optional Kernel mode setting:
1499 kms, kbd format: kms,kbd
1500 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
6cdf6e06 1501
84c08fd6
JW
1502 kgdbwait [KGDB] Stop kernel execution and enter the
1503 kernel debugger at the earliest opportunity.
1504
9bed90c6
FF
1505 kmac= [MIPS] korina ethernet MAC address.
1506 Configure the RouterBoard 532 series on-chip
1507 Ethernet adapter MAC address.
1508
04f70336
CM
1509 kmemleak= [KNL] Boot-time kmemleak enable/disable
1510 Valid arguments: on, off
1511 Default: on
1512
c3ac14b2
XQ
1513 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1514 Valid arguments: 0, 1, 2
1515 kmemcheck=0 (disabled)
1516 kmemcheck=1 (enabled)
1517 kmemcheck=2 (one-shot mode)
1518 Default: 2 (one-shot mode)
1519
6cececfc 1520 kstack=N [X86] Print N words from the kernel stack
0cb55ad2
RD
1521 in oops dumps.
1522
fef07aae
AP
1523 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1524 Default is 0 (don't ignore, but inject #GP)
1525
a182d873
XG
1526 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1527 KVM MMU at runtime.
fef07aae
AP
1528 Default is 0 (off)
1529
fef07aae 1530 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
8475f94a 1531 Default is 1 (enabled)
fef07aae
AP
1532
1533 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1534 for all guests.
16290246 1535 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
fef07aae 1536
fef07aae
AP
1537 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1538 (virtualized MMU) support on capable Intel chips.
1539 Default is 1 (enabled)
1540
1541 kvm-intel.emulate_invalid_guest_state=
1542 [KVM,Intel] Enable emulation of invalid guest states
1543 Default is 0 (disabled)
1544
1545 kvm-intel.flexpriority=
1546 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1547 Default is 1 (enabled)
1548
e1a72ae2
SL
1549 kvm-intel.nested=
1550 [KVM,Intel] Enable VMX nesting (nVMX).
1551 Default is 0 (disabled)
1552
fef07aae
AP
1553 kvm-intel.unrestricted_guest=
1554 [KVM,Intel] Disable unrestricted guest feature
1555 (virtualized real and unpaged mode) on capable
1556 Intel chips. Default is 1 (enabled)
1557
1558 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1559 feature (tagged TLBs) on capable Intel chips.
1560 Default is 1 (enabled)
1561
1da177e4
LT
1562 l2cr= [PPC]
1563
a78bfbfc
RB
1564 l3cr= [PPC]
1565
cd4f0ef7 1566 lapic [X86-32,APIC] Enable the local APIC even if BIOS
a9913044 1567 disabled it.
1da177e4 1568
279f1461
SS
1569 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1570 value for LAPIC timer one-shot implementation. Default
1571 back to the programmable timer unit in the LAPIC.
1572
6cececfc 1573 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
ada9cfdd 1574 in C2 power state.
e585bef8 1575
fcb71f6f
FC
1576 libata.dma= [LIBATA] DMA control
1577 libata.dma=0 Disable all PATA and SATA DMA
1578 libata.dma=1 PATA and SATA Disk DMA only
1579 libata.dma=2 ATAPI (CDROM) DMA only
16290246 1580 libata.dma=4 Compact Flash DMA only
fcb71f6f
FC
1581 Combinations also work, so libata.dma=3 enables DMA
1582 for disks and CDROMs, but not CFs.
16290246 1583
20308871
MP
1584 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1585 libata.ignore_hpa=0 keep BIOS limits (default)
1586 libata.ignore_hpa=1 ignore limits, using full disk
fcb71f6f 1587
78e70c23
DJ
1588 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1589 when set.
1590 Format: <int>
1591
33267325
TH
1592 libata.force= [LIBATA] Force configurations. The format is comma
1593 separated list of "[ID:]VAL" where ID is
4c44f309 1594 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
33267325
TH
1595 matching port, link or device. Basically, it matches
1596 the ATA ID string printed on console by libata. If
1597 the whole ID part is omitted, the last PORT and DEVICE
1598 values are used. If ID hasn't been specified yet, the
1599 configuration applies to all ports, links and devices.
1600
1601 If only DEVICE is omitted, the parameter applies to
1602 the port and all links and devices behind it. DEVICE
1603 number of 0 either selects the first device or the
1604 first fan-out link behind PMP device. It does not
1605 select the host link. DEVICE number of 15 selects the
1606 host link and device attached to it.
1607
1608 The VAL specifies the configuration to force. As long
1609 as there's no ambiguity shortcut notation is allowed.
1610 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1611 The following configurations can be forced.
1612
1613 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1614 Any ID with matching PORT is used.
1615
1616 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1617
1618 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1619 udma[/][16,25,33,44,66,100,133] notation is also
1620 allowed.
1621
1622 * [no]ncq: Turn on or off NCQ.
1623
05944bdf
TH
1624 * nohrst, nosrst, norst: suppress hard, soft
1625 and both resets.
1626
ca6d43b0
DW
1627 * rstonce: only attempt one reset during
1628 hot-unplug link recovery
1629
43c9c591
TH
1630 * dump_id: dump IDENTIFY data.
1631
966fbe19
VP
1632 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1633
b8bd6dc3
RJ
1634 * disable: Disable this device.
1635
33267325
TH
1636 If there are multiple matching configurations changing
1637 the same attribute, the last one is used.
1638
95f72d1e 1639 memblock=debug [KNL] Enable memblock debug messages.
7c4be253 1640
1da177e4 1641 load_ramdisk= [RAM] List of ramdisks to load from floppy
31c00fc1 1642 See Documentation/blockdev/ramdisk.txt.
1da177e4 1643
a6b25b67
RD
1644 lockd.nlm_grace_period=P [NFS] Assign grace period.
1645 Format: <integer>
1da177e4 1646
a6b25b67
RD
1647 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1648 Format: <integer>
1649
1650 lockd.nlm_timeout=T [NFS] Assign timeout value.
1651 Format: <integer>
1652
1653 lockd.nlm_udpport=M [NFS] Assign UDP port.
1654 Format: <integer>
1da177e4
LT
1655
1656 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1657 Format: <irq>
1658
1659 loglevel= All Kernel Messages with a loglevel smaller than the
1660 console loglevel will be printed to the console. It can
1661 also be changed with klogd or other programs. The
1662 loglevels are defined as follows:
1663
1664 0 (KERN_EMERG) system is unusable
1665 1 (KERN_ALERT) action must be taken immediately
1666 2 (KERN_CRIT) critical conditions
1667 3 (KERN_ERR) error conditions
1668 4 (KERN_WARNING) warning conditions
1669 5 (KERN_NOTICE) normal but significant condition
1670 6 (KERN_INFO) informational
1671 7 (KERN_DEBUG) debug-level messages
1672
c756d08a
RD
1673 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1674 in bytes. n must be a power of two. The default
1675 size is set in the kernel config file.
1da177e4 1676
accaa24c
RD
1677 logo.nologo [FB] Disables display of the built-in Linux logo.
1678 This may be used to provide more screen space for
1679 kernel log messages and is useful when debugging
1680 kernel boot problems.
1681
1da177e4
LT
1682 lp=0 [LP] Specify parallel ports to use, e.g,
1683 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1684 lp=reset first parallel port). 'lp=0' disables the
1685 lp=auto printer driver. 'lp=reset' (which can be
1686 specified in addition to the ports) causes
1687 attached printers to be reset. Using
1688 lp=port1,port2,... specifies the parallel ports
1689 to associate lp devices with, starting with
1690 lp0. A port specification may be 'none' to skip
1691 that lp device, or a parport name such as
1692 'parport0'. Specifying 'lp=auto' instead of a
1693 port specification list means that device IDs
1694 from each port should be examined, to see if
1695 an IEEE 1284-compliant printer is attached; if
1696 so, the driver will manage that printer.
1697 See also header of drivers/char/lp.c.
1698
1699 lpj=n [KNL]
1700 Sets loops_per_jiffy to given constant, thus avoiding
1701 time-consuming boot-time autodetection (up to 250 ms per
1702 CPU). 0 enables autodetection (default). To determine
1703 the correct value for your kernel, boot with normal
1704 autodetection and see what value is printed. Note that
1705 on SMP systems the preset will be applied to all CPUs,
1706 which is likely to cause problems if your CPUs need
1707 significantly divergent settings. An incorrect value
1708 will cause delays in the kernel to be wrong, leading to
1709 unpredictable I/O errors and other breakage. Although
1710 unlikely, in the extreme case this might damage your
1711 hardware.
1712
1713 ltpc= [NET]
1714 Format: <io>,<irq>,<dma>
1715
16290246 1716 machvec= [IA-64] Force the use of a particular machine-vector
a9913044
RD
1717 (machvec) in a generic kernel.
1718 Example: machvec=hpzx1_swiotlb
1da177e4 1719
3209e70e
WZ
1720 machtype= [Loongson] Share the same kernel image file between different
1721 yeeloong laptop.
1722 Example: machtype=lemote-yeeloong-2f-7inch
1723
0cb55ad2
RD
1724 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1725 than or equal to this physical address is ignored.
1da177e4
LT
1726
1727 maxcpus= [SMP] Maximum number of processors that an SMP kernel
61ec7567
LB
1728 should make use of. maxcpus=n : n >= 0 limits the
1729 kernel to using 'n' processors. n=0 is a special case,
1730 it is equivalent to "nosmp", which also disables
1731 the IO APIC.
1da177e4 1732
d134b00b
KS
1733 max_loop= [LOOP] The number of loop block devices that get
1734 (loop.max_loop) unconditionally pre-created at init time. The default
1735 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1736 of statically allocating a predefined number, loop
1737 devices can be requested on-demand with the
1738 /dev/loop-control interface.
2b2c3750 1739
cd4f0ef7 1740 mce [X86-32] Machine Check Exception
1da177e4 1741
71cced6e 1742 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
909dd324 1743
1da177e4
LT
1744 md= [HW] RAID subsystems devices and level
1745 See Documentation/md.txt.
a9913044 1746
1da177e4
LT
1747 mdacon= [MDA]
1748 Format: <first>,<last>
1749 Specifies range of consoles to be captured by the MDA.
a9913044 1750
1da177e4
LT
1751 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1752 Amount of memory to be used when the kernel is not able
1753 to see the whole system memory or for test.
fbb97d87
WC
1754 [X86] Work as limiting max address. Use together
1755 with memmap= to avoid physical address space collisions.
1756 Without memmap= PCI devices could be placed at addresses
1757 belonging to unused RAM.
1da177e4 1758
cd4f0ef7 1759 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1da177e4
LT
1760 memory.
1761
6902aa84
PM
1762 memchunk=nn[KMG]
1763 [KNL,SH] Allow user to override the default size for
1764 per-device physically contiguous DMA buffers.
1765
6cececfc 1766 memmap=exactmap [KNL,X86] Enable setting of an exact
1da177e4
LT
1767 E820 memory map, as specified by the user.
1768 Such memmap=exactmap lines can be constructed based on
1769 BIOS output or other requirements. See the memmap=nn@ss
1770 option description.
1771
1772 memmap=nn[KMG]@ss[KMG]
277cba1d
RD
1773 [KNL] Force usage of a specific region of memory.
1774 Region of memory to be used is from ss to ss+nn.
1da177e4
LT
1775
1776 memmap=nn[KMG]#ss[KMG]
1777 [KNL,ACPI] Mark specific memory as ACPI data.
277cba1d 1778 Region of memory to be marked is from ss to ss+nn.
1da177e4
LT
1779
1780 memmap=nn[KMG]$ss[KMG]
1781 [KNL,ACPI] Mark specific memory as reserved.
277cba1d 1782 Region of memory to be reserved is from ss to ss+nn.
1312848e
PM
1783 Example: Exclude memory from 0x18690000-0x1869ffff
1784 memmap=64K$0x18690000
1785 or
1786 memmap=0x10000$0x18690000
1da177e4 1787
9f077871
JF
1788 memory_corruption_check=0/1 [X86]
1789 Some BIOSes seem to corrupt the first 64k of
1790 memory when doing things like suspend/resume.
1791 Setting this option will scan the memory
1792 looking for corruption. Enabling this will
1793 both detect corruption and prevent the kernel
1794 from using the memory being corrupted.
1795 However, its intended as a diagnostic tool; if
1796 repeatable BIOS-originated corruption always
1797 affects the same memory, you can use memmap=
1798 to prevent the kernel from using that memory.
1799
1800 memory_corruption_check_size=size [X86]
1801 By default it checks for corruption in the low
1802 64k, making this memory unavailable for normal
1803 use. Use this parameter to scan for
1804 corruption in more or less memory.
1805
1806 memory_corruption_check_period=seconds [X86]
1807 By default it checks for corruption every 60
1808 seconds. Use this parameter to check at some
1809 other rate. 0 disables periodic checking.
1810
caadbdce 1811 memtest= [KNL,X86] Enable memtest
c64df707 1812 Format: <integer>
c64df707 1813 default : 0 <disable>
9e5f6cf5
AH
1814 Specifies the number of memtest passes to be
1815 performed. Each pass selects another test
1816 pattern from a given set of patterns. Memtest
1817 fills the memory with this pattern, validates
1818 memory contents and reserves bad memory
1819 regions that are detected.
c64df707 1820
1da177e4
LT
1821 meye.*= [HW] Set MotionEye Camera parameters
1822 See Documentation/video4linux/meye.txt.
1823
8f36881b
AS
1824 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1825 Multi-Function General Purpose Timers on AMD Geode
1826 platforms.
1827
e6c4dc6c
WT
1828 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1829 the BIOS has incorrectly applied a workaround. TinyBIOS
1830 version 0.98 is known to be affected, 0.99 fixes the
1831 problem by letting the user disable the workaround.
1832
1da177e4
LT
1833 mga= [HW,DRM]
1834
1c207f95
RD
1835 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1836 physical address is ignored.
1837
39f45d7b
MP
1838 mini2440= [ARM,HW,KNL]
1839 Format:[0..2][b][c][t]
1840 Default: "0tb"
1841 MINI2440 configuration specification:
1842 0 - The attached screen is the 3.5" TFT
1843 1 - The attached screen is the 7" TFT
1844 2 - The VGA Shield is attached (1024x768)
1845 Leaving out the screen size parameter will not load
1846 the TFT driver, and the framebuffer will be left
1847 unconfigured.
1848 b - Enable backlight. The TFT backlight pin will be
1849 linked to the kernel VESA blanking code and a GPIO
1850 LED. This parameter is not necessary when using the
1851 VGA shield.
1852 c - Enable the s3c camera interface.
1853 t - Reserved for enabling touchscreen support. The
1854 touchscreen support is not enabled in the mainstream
1855 kernel as of 2.6.30, a preliminary port can be found
1856 in the "bleeding edge" mini2440 support kernel at
1857 http://repo.or.cz/w/linux-2.6/mini2440.git
1858
6b74ab97
MG
1859 mminit_loglevel=
1860 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1861 parameter allows control of the logging verbosity for
1862 the additional memory initialisation checks. A value
1863 of 0 disables mminit logging and a level of 4 will
1864 log everything. Information is printed at KERN_DEBUG
1865 so loglevel=8 may also need to be specified.
1866
106a4ee2
RR
1867 module.sig_enforce
1868 [KNL] When CONFIG_MODULE_SIG is set, this means that
1869 modules without (valid) signatures will fail to load.
2a039be7 1870 Note that if CONFIG_MODULE_SIG_FORCE is set, that
106a4ee2
RR
1871 is always true, so this option does nothing.
1872
1da177e4
LT
1873 mousedev.tap_time=
1874 [MOUSE] Maximum time between finger touching and
1875 leaving touchpad surface for touch to be considered
1876 a tap and be reported as a left button click (for
1877 touchpads working in absolute mode only).
1878 Format: <msecs>
1879 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
1880 reporting absolute coordinates, such as tablets
1881 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
1882 reporting absolute coordinates, such as tablets
1883
6cececfc 1884 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
0cb55ad2
RD
1885 is similar to kernelcore except it specifies the
1886 amount of memory used for migratable allocations.
1887 If both kernelcore and movablecore is specified,
1888 then kernelcore will be at *least* the specified
1889 value but may be more. If movablecore on its own
1890 is specified, the administrator must be careful
1891 that the amount of memory usable for all allocations
1892 is not too small.
1893
c5320926
TC
1894 movable_node [KNL,X86] Boot-time switch to enable the effects
1895 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
1896
1da177e4
LT
1897 MTD_Partition= [MTD]
1898 Format: <name>,<region-number>,<size>,<offset>
1899
a9913044
RD
1900 MTD_Region= [MTD] Format:
1901 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1da177e4
LT
1902
1903 mtdparts= [MTD]
c8facbb6 1904 See drivers/mtd/cmdlinepart.c.
1da177e4 1905
4e89a2d8
WS
1906 multitce=off [PPC] This parameter disables the use of the pSeries
1907 firmware feature for updating multiple TCE entries
1908 at a time.
1909
5988af23
RH
1910 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
1911
1912 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
1913
1914 boundary - index of last SLC block on Flex-OneNAND.
1915 The remaining blocks are configured as MLC blocks.
1916 lock - Configure if Flex-OneNAND boundary should be locked.
1917 Once locked, the boundary cannot be changed.
1918 1 indicates lock status, 0 indicates unlock status.
1919
9db829f4
BD
1920 mtdset= [ARM]
1921 ARM/S3C2412 JIVE boot control
1922
1923 See arch/arm/mach-s3c2412/mach-jive.c
1924
1da177e4 1925 mtouchusb.raw_coordinates=
a9913044
RD
1926 [HW] Make the MicroTouch USB driver use raw coordinates
1927 ('y', default) or cooked coordinates ('n')
1da177e4 1928
0cb55ad2 1929 mtrr_chunk_size=nn[KMG] [X86]
19f59460 1930 used for mtrr cleanup. It is largest continuous chunk
0cb55ad2
RD
1931 that could hold holes aka. UC entries.
1932
1933 mtrr_gran_size=nn[KMG] [X86]
1934 Used for mtrr cleanup. It is granularity of mtrr block.
1935 Default is 1.
1936 Large value could prevent small alignment from
1937 using up MTRRs.
1938
1939 mtrr_spare_reg_nr=n [X86]
1940 Format: <integer>
1941 Range: 0,7 : spare reg number
1942 Default : 1
1943 Used for mtrr cleanup. It is spare mtrr entries number.
1944 Set to 2 or more if your graphical card needs more.
1945
1da177e4
LT
1946 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
1947
1da177e4
LT
1948 netdev= [NET] Network devices parameters
1949 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
1950 Note that mem_start is often overloaded to mean
1951 something different and driver-specific.
a9913044
RD
1952 This usage is only documented in each driver source
1953 file if at all.
1954
58401572
KPO
1955 nf_conntrack.acct=
1956 [NETFILTER] Enable connection tracking flow accounting
1957 0 to disable accounting
1958 1 to enable accounting
d70a011d 1959 Default value is 0.
58401572 1960
306a0753 1961 nfsaddrs= [NFS] Deprecated. Use ip= instead.
dc7a0816 1962 See Documentation/filesystems/nfs/nfsroot.txt.
1da177e4
LT
1963
1964 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
dc7a0816 1965 See Documentation/filesystems/nfs/nfsroot.txt.
1da177e4 1966
306a0753
CL
1967 nfsrootdebug [NFS] enable nfsroot debugging messages.
1968 See Documentation/filesystems/nfs/nfsroot.txt.
1969
a72b4422
TM
1970 nfs.callback_tcpport=
1971 [NFS] set the TCP port on which the NFSv4 callback
1972 channel should listen.
1973
e571cbf1
TM
1974 nfs.cache_getent=
1975 [NFS] sets the pathname to the program which is used
1976 to update the NFS client cache entries.
1977
1978 nfs.cache_getent_timeout=
1979 [NFS] sets the timeout after which an attempt to
1980 update a cache entry is deemed to have failed.
1981
58df095b
TM
1982 nfs.idmap_cache_timeout=
1983 [NFS] set the maximum lifetime for idmapper cache
1984 entries.
1985
f43bf0be
TM
1986 nfs.enable_ino64=
1987 [NFS] enable 64-bit inode numbers.
1988 If zero, the NFS client will fake up a 32-bit inode
1989 number for the readdir() and stat() syscalls instead
1990 of returning the full 64-bit number.
1991 The default is to return 64-bit inode numbers.
1992
ef159e91
TM
1993 nfs.max_session_slots=
1994 [NFSv4.1] Sets the maximum number of session slots
1995 the client will attempt to negotiate with the server.
1996 This limits the number of simultaneous RPC requests
1997 that the client can send to the NFSv4.1 server.
1998 Note that there is little point in setting this
1999 value higher than the max_tcp_slot_table_limit.
2000
b064eca2 2001 nfs.nfs4_disable_idmapping=
074b1d12
TM
2002 [NFSv4] When set to the default of '1', this option
2003 ensures that both the RPC level authentication
2004 scheme and the NFS level operations agree to use
2005 numeric uids/gids if the mount is using the
2006 'sec=sys' security flavour. In effect it is
2007 disabling idmapping, which can make migration from
2008 legacy NFSv2/v3 systems to NFSv4 easier.
2009 Servers that do not support this mode of operation
2010 will be autodetected by the client, and it will fall
2011 back to using the idmapper.
2012 To turn off this behaviour, set the value to '0'.
6f2ea7f2
CL
2013 nfs.nfs4_unique_id=
2014 [NFS4] Specify an additional fixed unique ident-
2015 ification string that NFSv4 clients can insert into
2016 their nfs_client_id4 string. This is typically a
2017 UUID that is generated at system install time.
b064eca2 2018
db8ac8ba
WAA
2019 nfs.send_implementation_id =
2020 [NFSv4.1] Send client implementation identification
2021 information in exchange_id requests.
2022 If zero, no implementation identification information
2023 will be sent.
2024 The default is to send the implementation identification
2025 information.
f6de7a39
TM
2026
2027 nfs.recover_lost_locks =
2028 [NFSv4] Attempt to recover locks that were lost due
2029 to a lease timeout on the server. Please note that
2030 doing this risks data corruption, since there are
2031 no guarantees that the file will remain unchanged
2032 after the locks are lost.
2033 If you want to enable the kernel legacy behaviour of
2034 attempting to recover these locks, then set this
2035 parameter to '1'.
2036 The default parameter value of '0' causes the kernel
2037 not to attempt recovery of lost locks.
db8ac8ba 2038
e9541ce8
BF
2039 nfsd.nfs4_disable_idmapping=
2040 [NFSv4] When set to the default of '1', the NFSv4
2041 server will return only numeric uids and gids to
2042 clients using auth_sys, and will accept numeric uids
2043 and gids from such clients. This is intended to ease
2044 migration from NFSv2/v3.
db8ac8ba 2045
18d98f6c
SB
2046 objlayoutdriver.osd_login_prog=
2047 [NFS] [OBJLAYOUT] sets the pathname to the program which
2048 is used to automatically discover and login into new
2049 osd-targets. Please see:
2050 Documentation/filesystems/pnfs.txt for more explanations
2051
1e1030dc 2052 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
e7ba176b
HS
2053 when a NMI is triggered.
2054 Format: [state][,regs][,debounce][,die]
2055
6cececfc 2056 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
fef2c9bc 2057 Format: [panic,][nopanic,][num]
5dc30558 2058 Valid num: 0
5b9a0e14 2059 0 - turn nmi_watchdog off
0cb55ad2 2060 When panic is specified, panic when an NMI watchdog
fef2c9bc
DZ
2061 timeout occurs (or 'nopanic' to override the opposite
2062 default).
0cb55ad2
RD
2063 This is useful when you use a panic=... timeout and
2064 need the box quickly up again.
1da177e4 2065
bff38771
AV
2066 netpoll.carrier_timeout=
2067 [NET] Specifies amount of time (in seconds) that
2068 netpoll should wait for a carrier. By default netpoll
2069 waits 4 seconds.
2070
cd4f0ef7 2071 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
1da177e4
LT
2072 emulation library even if a 387 maths coprocessor
2073 is present.
2074
0cb55ad2
RD
2075 no_console_suspend
2076 [HW] Never suspend the console
2077 Disable suspending of consoles during suspend and
2078 hibernate operations. Once disabled, debugging
2079 messages can reach various consoles while the rest
2080 of the system is being put to sleep (ie, while
2081 debugging driver suspend/resume hooks). This may
2082 not work reliably with all consoles, but is known
2083 to work with serial and VGA consoles.
134620f7
YZ
2084 To facilitate more flexible debugging, we also add
2085 console_suspend, a printk module parameter to control
2086 it. Users could use console_suspend (usually
2087 /sys/module/printk/parameters/console_suspend) to
2088 turn on/off it dynamically.
0cb55ad2 2089
c1aee215
CL
2090 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2091 caches in the slab allocator. Saves per-node memory,
2092 but will impact performance.
3395ee05 2093
a9913044
RD
2094 noalign [KNL,ARM]
2095
1da177e4
LT
2096 noapic [SMP,APIC] Tells the kernel to not make use of any
2097 IOAPICs that may be present in the system.
2098
8ab3820f 2099 nokaslr [X86]
e2b32e67
KC
2100 Disable kernel and module base offset ASLR (Address
2101 Space Layout Randomization) if built into the kernel.
8ab3820f 2102
5091faa4
MG
2103 noautogroup Disable scheduler automatic task group creation.
2104
1da177e4
LT
2105 nobats [PPC] Do not use BATs for mapping kernel lowmem
2106 on "Classic" PPC cores.
2107
2108 nocache [ARM]
a9913044 2109
0cb55ad2
RD
2110 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2111
163ecdff
SN
2112 nodelayacct [KNL] Disable per-task delay accounting
2113
1da177e4
LT
2114 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2115
6902aa84
PM
2116 nodsp [SH] Disable hardware DSP at boot time.
2117
6cececfc 2118 noefi [X86] Disable EFI runtime services support.
8b2cb7a8 2119
1da177e4
LT
2120 noexec [IA-64]
2121
6cececfc 2122 noexec [X86]
f5a1b191 2123 On X86-32 available only on PAE configured kernels.
1da177e4 2124 noexec=on: enable non-executable mappings (default)
f5a1b191
JS
2125 noexec=off: disable non-executable mappings
2126
52b6179a
PA
2127 nosmap [X86]
2128 Disable SMAP (Supervisor Mode Access Prevention)
2129 even if it is supported by processor.
2130
de5397ad 2131 nosmep [X86]
52b6179a 2132 Disable SMEP (Supervisor Mode Execution Prevention)
de5397ad
FY
2133 even if it is supported by processor.
2134
f5a1b191
JS
2135 noexec32 [X86-64]
2136 This affects only 32-bit executables.
2137 noexec32=on: enable non-executable mappings (default)
2138 read doesn't imply executable mappings
2139 noexec32=off: disable non-executable mappings
2140 read implies executable mappings
1da177e4 2141
6902aa84
PM
2142 nofpu [SH] Disable hardware FPU at boot time.
2143
cd4f0ef7 2144 nofxsr [BUGS=X86-32] Disables x86 floating point extended
4f886511
CE
2145 register save and restore. The kernel will only save
2146 legacy floating-point registers on task switch.
1da177e4 2147
0c752a93
SS
2148 noxsave [BUGS=X86] Disables x86 extended register state save
2149 and restore using xsave. The kernel will fallback to
2150 enabling legacy floating-point and sse state.
2151
5d2bd700 2152 eagerfpu= [X86]
e0022981 2153 on enable eager fpu restore
5d2bd700 2154 off disable eager fpu restore
e0022981
SS
2155 auto selects the default scheme, which automatically
2156 enables eagerfpu restore for xsaveopt.
5d2bd700 2157
01a24d2b
PZ
2158 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2159 wfi(ARM) instruction doesn't work correctly and not to
2160 use it. This is also useful when using JTAG debugger.
a9913044 2161
1f29fae2
SH
2162 no_file_caps Tells the kernel not to honor file capabilities. The
2163 only way then for a file to be executed with privilege
2164 is to be setuid root or executed by root.
2165
1da177e4
LT
2166 nohalt [IA-64] Tells the kernel not to use the power saving
2167 function PAL_HALT_LIGHT when idle. This increases
2168 power-consumption. On the positive side, it reduces
2169 interrupt wake-up latency, which may improve performance
2170 in certain environments such as networked servers or
2171 real-time systems.
2172
79bf2bb3
TG
2173 nohz= [KNL] Boottime enable/disable dynamic ticks
2174 Valid arguments: on, off
2175 Default: on
2176
c5bfece2
FW
2177 nohz_full= [KNL,BOOT]
2178 In kernels built with CONFIG_NO_HZ_FULL=y, set
a831881b 2179 the specified list of CPUs whose tick will be stopped
0453b435
FW
2180 whenever possible. The boot CPU will be forced outside
2181 the range to maintain the timekeeping.
d1e43fa5
FW
2182 The CPUs in this range must also be included in the
2183 rcu_nocbs= set.
a831881b 2184
eeee7853
PM
2185 noiotrap [SH] Disables trapped I/O port accesses.
2186
cd4f0ef7 2187 noirqdebug [X86-32] Disables the code which attempts to detect and
1da177e4
LT
2188 disable unhandled interrupt sources.
2189
6cececfc 2190 no_timer_check [X86,APIC] Disables the code which tests for
8542b200
ZA
2191 broken timer IRQ sources.
2192
1da177e4
LT
2193 noisapnp [ISAPNP] Disables ISA PnP code.
2194
2195 noinitrd [RAM] Tells the kernel not to load any configured
2196 initial RAM disk.
2197
03ea8155
WH
2198 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2199 remapping.
d1423d56 2200 [Deprecated - use intremap=off]
03ea8155 2201
1da177e4
LT
2202 nointroute [IA-64]
2203
16290246 2204 nojitter [IA-64] Disables jitter checking for ITC timers.
0aa366f3 2205
9cf4c4fc
JK
2206 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2207
fd10cde9
GN
2208 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2209 fault handling.
2210
d910f5c1
GC
2211 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2212 steal time is computed, but won't influence scheduler
2213 behaviour
2214
cd4f0ef7 2215 nolapic [X86-32,APIC] Do not enable or use the local APIC.
1da177e4 2216
cd4f0ef7 2217 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
ad62ca2b 2218
1da177e4
LT
2219 noltlbs [PPC] Do not use large page/tlb entries for kernel
2220 lowmem mapping on PPC40x.
2221
312f1f01
H
2222 nomca [IA-64] Disable machine check abort handling
2223
cd4f0ef7 2224 nomce [X86-32] Machine Check Exception
abe37e5a 2225
83d7384f
AS
2226 nomfgpt [X86-32] Disable Multi-Function General Purpose
2227 Timer usage (for AMD Geode machines).
2228
bda62633
DZ
2229 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2230 shutdown the other cpus. Instead use the REBOOT_VECTOR
2231 irq.
2232
02608bef
DY
2233 nomodule Disable module load
2234
016ddd9b
JK
2235 nopat [X86] Disable PAT (page attribute table extension of
2236 pagetables) support.
2237
0cb55ad2
RD
2238 norandmaps Don't use address space randomization. Equivalent to
2239 echo 0 > /proc/sys/kernel/randomize_va_space
2240
bbff2168 2241 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
959b4fdf 2242
cd4f0ef7 2243 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
b7fb4af0
JF
2244 with UP alternatives
2245
7a5091d5
PA
2246 nordrand [X86] Disable kernel use of the RDRAND and
2247 RDSEED instructions even if they are supported
2248 by the processor. RDRAND and RDSEED are still
2249 available to user space applications.
49d859d7 2250
a9913044
RD
2251 noresume [SWSUSP] Disables resume and restores original swap
2252 space.
2253
1da177e4
LT
2254 no-scroll [VGA] Disables scrollback.
2255 This is required for the Braillex ib80-piezo Braille
2256 reader made by F.H. Papenmeier (Germany).
2257
2258 nosbagart [IA-64]
2259
cd4f0ef7 2260 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
4f886511 2261
61ec7567
LB
2262 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2263 and disable the IO APIC. legacy for "maxcpus=0".
1da177e4 2264
97842216
DJ
2265 nosoftlockup [KNL] Disable the soft-lockup detector.
2266
1da177e4
LT
2267 nosync [HW,M68K] Disables sync negotiation for all devices.
2268
cd4f0ef7 2269 notsc [BUGS=X86-32] Disable Time Stamp Counter
1da177e4
LT
2270
2271 nousb [USB] Disable the USB subsystem
2272
55142374 2273 nowatchdog [KNL] Disable the lockup detector (NMI watchdog).
58687acb 2274
1da177e4 2275 nowb [ARM]
a9913044 2276
2b2fd87a
WH
2277 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2278
f78cff48
FY
2279 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2280 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2281 Some features depend on CPU0. Known dependencies are:
2282 1. Resume from suspend/hibernate depends on CPU0.
2283 Suspend/hibernate will fail if CPU0 is offline and you
2284 need to online CPU0 before suspend/hibernate.
2285 2. PIC interrupts also depend on CPU0. CPU0 can't be
2286 removed if a PIC interrupt is detected.
2287 It's said poweroff/reboot may depend on CPU0 on some
2288 machines although I haven't seen such issues so far
2289 after CPU0 is offline on a few tested machines.
2290 If the dependencies are under your control, you can
2291 turn on cpu0_hotplug.
2292
16290246 2293 nptcg= [IA-64] Override max number of concurrent global TLB
a6c75b86
FY
2294 purges which is reported from either PAL_VM_SUMMARY or
2295 SAL PALO.
2296
2b633e3f
YL
2297 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2298 could support. nr_cpus=n : n >= 1 limits the kernel to
2299 supporting 'n' processors. Later in runtime you can not
2300 use hotplug cpu feature to put more cpu back to online.
2301 just like you compile the kernel NR_CPUS=n
2302
0cb55ad2
RD
2303 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2304
1a687c2e
MG
2305 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2306 Allowed values are enable and disable
2307
f0c0b2b8
KH
2308 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2309 one of ['zone', 'node', 'default'] can be specified
2310 This can be set from sysctl after boot.
2311 See Documentation/sysctl/vm.txt for details.
2312
7c4be253
RD
2313 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2314 See Documentation/debugging-via-ohci1394.txt for more
2315 info.
2316
3ef0e1f8
AS
2317 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2318 Rather than timing out after 20 ms if an EC
2319 command is not properly ACKed, override the length
2320 of the timeout. We have interrupts disabled while
2321 waiting for the ACK, so if this is set too high
2322 interrupts *may* be lost!
2323
15ac7afe
TL
2324 omap_mux= [OMAP] Override bootloader pin multiplexing.
2325 Format: <mux_mode0.mode_name=value>...
2326 For example, to override I2C bus2:
2327 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2328
1da177e4
LT
2329 oprofile.timer= [HW]
2330 Use timer interrupt instead of performance counters
2331
7e4e0bd5
RR
2332 oprofile.cpu_type= Force an oprofile cpu type
2333 This might be useful if you have an older oprofile
2334 userland or if you want common events.
8d7ff4f2
RR
2335 Format: { arch_perfmon }
2336 arch_perfmon: [X86] Force use of architectural
7e4e0bd5
RR
2337 perfmon on Intel CPUs instead of the
2338 CPU specific event set.
159a80b2
RR
2339 timer: [X86] Force use of architectural NMI
2340 timer mode (see also oprofile.timer
2341 for generic hr timer mode)
dd3c4670
AK
2342 [s390] Force legacy basic mode sampling
2343 (report cpu_type "timer")
1dcdb5a9 2344
44a4dcf7
RD
2345 oops=panic Always panic on oopses. Default is to just kill the
2346 process, but there is a small probability of
2347 deadlocking the machine.
d404ab0a
OH
2348 This will also cause panics on machine check exceptions.
2349 Useful together with panic=30 to trigger a reboot.
2350
bcfde334
RD
2351 OSS [HW,OSS]
2352 See Documentation/sound/oss/oss-parameters.txt
2353
44a4dcf7 2354 panic= [KNL] Kernel behaviour on panic: delay <timeout>
4302fbc8
HD
2355 timeout > 0: seconds before rebooting
2356 timeout = 0: wait forever
2357 timeout < 0: reboot immediately
1da177e4
LT
2358 Format: <timeout>
2359
2360 parkbd.port= [HW] Parallel port number the keyboard adapter is
2361 connected to, default is 0.
2362 Format: <parport#>
2363 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2364 0 for XT, 1 for AT (default is AT).
a9913044
RD
2365 Format: <mode>
2366
2367 parport= [HW,PPT] Specify parallel ports. 0 disables.
2368 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2369 Use 'auto' to force the driver to use any
2370 IRQ/DMA settings detected (the default is to
2371 ignore detected IRQ/DMA settings because of
2372 possible conflicts). You can specify the base
2373 address, IRQ, and DMA settings; IRQ and DMA
2374 should be numbers, or 'auto' (for using detected
2375 settings on that particular port), or 'nofifo'
2376 (to avoid using a FIFO even if it is detected).
2377 Parallel ports are assigned in the order they
2378 are specified on the command line, starting
2379 with parport0.
2380
2381 parport_init_mode= [HW,PPT]
2382 Configure VIA parallel port to operate in
2383 a specific mode. This is necessary on Pegasos
2384 computer where firmware has no options for setting
2385 up parallel port mode and sets it to spp.
2386 Currently this function knows 686a and 8231 chips.
1da177e4
LT
2387 Format: [spp|ps2|epp|ecp|ecpepp]
2388
dd287796
AM
2389 pause_on_oops=
2390 Halt all CPUs after the first oops has been printed for
2391 the specified number of seconds. This is to be used if
2392 your oopses keep scrolling off the screen.
2393
1da177e4
LT
2394 pcbit= [HW,ISDN]
2395
2396 pcd. [PARIDE]
2397 See header of drivers/block/paride/pcd.c.
31c00fc1 2398 See also Documentation/blockdev/paride.txt.
1da177e4 2399
a9913044 2400 pci=option[,option...] [PCI] various PCI subsystem options:
1cc0ca26
BH
2401 earlydump [X86] dump PCI config space before the kernel
2402 changes anything
c0115606 2403 off [X86] don't probe for the PCI bus
cd4f0ef7 2404 bios [X86-32] force use of PCI BIOS, don't access
a9913044
RD
2405 the hardware directly. Use this if your machine
2406 has a non-standard PCI host bridge.
cd4f0ef7 2407 nobios [X86-32] disallow use of PCI BIOS, only direct
a9913044
RD
2408 hardware access methods are allowed. Use this
2409 if you experience crashes upon bootup and you
2410 suspect they are caused by the BIOS.
c0115606 2411 conf1 [X86] Force use of PCI Configuration
a9913044 2412 Mechanism 1.
c0115606 2413 conf2 [X86] Force use of PCI Configuration
a9913044 2414 Mechanism 2.
7f785763
RD
2415 noaer [PCIE] If the PCIEAER kernel config parameter is
2416 enabled, this kernel boot option can be used to
2417 disable the use of PCIE advanced error reporting.
32a2eea7
JG
2418 nodomains [PCI] Disable support for multiple PCI
2419 root domains (aka PCI segments, in ACPI-speak).
6cececfc 2420 nommconf [X86] Disable use of MMCONFIG for PCI
61be6d66 2421 Configuration
12983077
AH
2422 check_enable_amd_mmconf [X86] check for and enable
2423 properly configured MMIO access to PCI
2424 config space on AMD family 10h CPU
309e57df
MW
2425 nomsi [MSI] If the PCI_MSI kernel config parameter is
2426 enabled, this kernel boot option can be used to
2427 disable the use of MSI interrupts system-wide.
a9322f64
SA
2428 noioapicquirk [APIC] Disable all boot interrupt quirks.
2429 Safety option to keep boot IRQs enabled. This
2430 should never be necessary.
9197979b
SA
2431 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2432 primary IO-APIC for bridges that cannot disable
2433 boot IRQs. This fixes a source of spurious IRQs
2434 when the system masks IRQs.
41b9eb26
SA
2435 noioapicreroute [APIC] Disable workaround that uses the
2436 boot IRQ equivalent of an IRQ that connects to
2437 a chipset where boot IRQs cannot be disabled.
2438 The opposite of ioapicreroute.
cd4f0ef7 2439 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
a9913044
RD
2440 routing table. These calls are known to be buggy
2441 on several machines and they hang the machine
2442 when used, but on other computers it's the only
2443 way to get the interrupt routing table. Try
2444 this option if the kernel is unable to allocate
2445 IRQs or discover secondary PCI buses on your
2446 motherboard.
c0115606 2447 rom [X86] Assign address space to expansion ROMs.
a9913044
RD
2448 Use with caution as certain devices share
2449 address decoders between ROMs and other
2450 resources.
c0115606 2451 norom [X86] Do not assign address space to
bb71ad88
GH
2452 expansion ROMs that do not already have
2453 BIOS assigned address ranges.
7bd1c365
MH
2454 nobar [X86] Do not assign address space to the
2455 BARs that weren't assigned by the BIOS.
c0115606 2456 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
a9913044
RD
2457 assigned automatically to PCI devices. You can
2458 make the kernel exclude IRQs of your ISA cards
2459 this way.
c0115606 2460 pirqaddr=0xAAAAA [X86] Specify the physical address
a9913044
RD
2461 of the PIRQ table (normally generated
2462 by the BIOS) if it is outside the
2463 F0000h-100000h range.
c0115606 2464 lastbus=N [X86] Scan all buses thru bus #N. Can be
a9913044
RD
2465 useful if the kernel is unable to find your
2466 secondary buses and you want to tell it
2467 explicitly which ones they are.
c0115606 2468 assign-busses [X86] Always assign all PCI bus
a9913044
RD
2469 numbers ourselves, overriding
2470 whatever the firmware may have done.
c0115606 2471 usepirqmask [X86] Honor the possible IRQ mask stored
a9913044
RD
2472 in the BIOS $PIR table. This is needed on
2473 some systems with broken BIOSes, notably
2474 some HP Pavilion N5400 and Omnibook XE3
2475 notebooks. This will have no effect if ACPI
2476 IRQ routing is enabled.
c0115606 2477 noacpi [X86] Do not use ACPI for IRQ routing
a9913044 2478 or for PCI scanning.
7bc5e3f2
BH
2479 use_crs [X86] Use PCI host bridge window information
2480 from ACPI. On BIOSes from 2008 or later, this
2481 is enabled by default. If you need to use this,
2482 please report a bug.
2483 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2484 If you need to use this, please report a bug.
a9913044
RD
2485 routeirq Do IRQ routing for all PCI devices.
2486 This is normally done in pci_enable_device(),
2487 so this option is a temporary workaround
2488 for broken drivers that don't call it.
13a6ddb0
YL
2489 skip_isa_align [X86] do not align io start addr, so can
2490 handle more pci cards
a9913044
RD
2491 firmware [ARM] Do not re-enumerate the bus but instead
2492 just use the configuration from the
2493 bootloader. This is currently used on
2494 IXP2000 systems where the bus has to be
2495 configured a certain way for adjunct CPUs.
0637a70a
AK
2496 noearly [X86] Don't do any early type 1 scanning.
2497 This might help on some broken boards which
2498 machine check when some devices' config space
2499 is read. But various workarounds are disabled
2500 and some IOMMU drivers will not work.
6b4b78fe
MD
2501 bfsort Sort PCI devices into breadth-first order.
2502 This sorting is done to get a device
2503 order compatible with older (<= 2.4) kernels.
2504 nobfsort Don't sort PCI devices into breadth-first order.
fa238712
YW
2505 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2506 tuning and use the BIOS-configured MPS defaults.
2507 pcie_bus_safe Set every device's MPS to the largest value
2508 supported by all devices below the root complex.
2509 pcie_bus_perf Set device MPS to the largest allowable MPS
2510 based on its parent bus. Also set MRRS (Max
2511 Read Request Size) to the largest supported
2512 value (no larger than the MPS that the device
2513 or bus can support) for best performance.
2514 pcie_bus_peer2peer Set every device's MPS to 128B, which
2515 every device is guaranteed to support. This
2516 configuration allows peer-to-peer DMA between
2517 any pair of devices, possibly at the cost of
2518 reduced performance. This also guarantees
2519 that hot-added devices will work.
4516a618
AN
2520 cbiosize=nn[KMG] The fixed amount of bus space which is
2521 reserved for the CardBus bridge's IO window.
2522 The default value is 256 bytes.
2523 cbmemsize=nn[KMG] The fixed amount of bus space which is
2524 reserved for the CardBus bridge's memory
2525 window. The default value is 64 megabytes.
32a9a682
YS
2526 resource_alignment=
2527 Format:
2528 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2529 Specifies alignment and device to reassign
2530 aligned memory resources.
2531 If <order of align> is not specified,
2532 PAGE_SIZE is used as alignment.
2533 PCI-PCI bridge can be specified, if resource
2534 windows need to be expanded.
43c16408
AP
2535 ecrc= Enable/disable PCIe ECRC (transaction layer
2536 end-to-end CRC checking).
2537 bios: Use BIOS/firmware settings. This is the
2538 the default.
2539 off: Turn ECRC off
2540 on: Turn ECRC on.
8c8803c5
YW
2541 hpiosize=nn[KMG] The fixed amount of bus space which is
2542 reserved for hotplug bridge's IO window.
2543 Default size is 256 bytes.
2544 hpmemsize=nn[KMG] The fixed amount of bus space which is
2545 reserved for hotplug bridge's memory window.
2546 Default size is 2 megabytes.
b55438fd
YL
2547 realloc= Enable/disable reallocating PCI bridge resources
2548 if allocations done by BIOS are too small to
2549 accommodate resources required by all child
2550 devices.
2551 off: Turn realloc off
2552 on: Turn realloc on
2553 realloc same as realloc=on
6748dcc2 2554 noari do not use PCIe ARI.
284f5f9d
BH
2555 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2556 only look for one device below a PCIe downstream
2557 port.
6b4b78fe 2558
e5665a45
CE
2559 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2560 Management.
2561 off Disable ASPM.
2562 force Enable ASPM even on devices that claim not to support it.
2563 WARNING: Forcing ASPM on may cause system lockups.
2564
7570a333
MT
2565 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2566 nomsi Do not use MSI for PCI Express Native Hotplug (this
2567 makes all PCIe ports use INTx for hotplug services).
2568
79dd9182 2569 pcie_ports= [PCIE] PCIe ports handling:
28eb5f27
RW
2570 auto Ask the BIOS whether or not to use native PCIe services
2571 associated with PCIe ports (PME, hot-plug, AER). Use
2572 them only if that is allowed by the BIOS.
2573 native Use native PCIe services associated with PCIe ports
2574 unconditionally.
79dd9182
RW
2575 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2576 ports driver.
2577
c7f48656 2578 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
c39fae14 2579 nomsi Do not use MSI for native PCIe PME signaling (this makes
28eb5f27 2580 all PCIe root ports use INTx for all services).
c7f48656 2581
1da177e4
LT
2582 pcmv= [HW,PCMCIA] BadgePAD 4
2583
39ac5ba5
TB
2584 pd_ignore_unused
2585 [PM]
2586 Keep all power-domains already enabled by bootloader on,
2587 even if no driver has claimed them. This is useful
2588 for debug and development, but should not be
2589 needed on a platform with proper driver support.
2590
1da177e4 2591 pd. [PARIDE]
31c00fc1 2592 See Documentation/blockdev/paride.txt.
1da177e4
LT
2593
2594 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2595 boot time.
2596 Format: { 0 | 1 }
2597 See arch/parisc/kernel/pdc_chassis.c
2598
f58dc01b 2599 percpu_alloc= Select which percpu first chunk allocator to use.
e933a73f
TH
2600 Currently supported values are "embed" and "page".
2601 Archs may support subset or none of the selections.
2602 See comments in mm/percpu.c for details on each
2603 allocator. This parameter is primarily for debugging
2604 and performance comparison.
fa8a7094 2605
1da177e4 2606 pf. [PARIDE]
31c00fc1 2607 See Documentation/blockdev/paride.txt.
1da177e4
LT
2608
2609 pg. [PARIDE]
31c00fc1 2610 See Documentation/blockdev/paride.txt.
1da177e4
LT
2611
2612 pirq= [SMP,APIC] Manual mp-table setup
71cced6e 2613 See Documentation/x86/i386/IO-APIC.txt.
1da177e4
LT
2614
2615 plip= [PPT,NET] Parallel port network link
2616 Format: { parport<nr> | timid | 0 }
2617 See also Documentation/parport.txt.
2618
16290246 2619 pmtmr= [X86] Manual setup of pmtmr I/O Port.
de32a243
TG
2620 Override pmtimer IOPort with a hex value.
2621 e.g. pmtmr=0x508
2622
96242116
BH
2623 pnp.debug=1 [PNP]
2624 Enable PNP debug messages (depends on the
2625 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2626 via /sys/module/pnp/parameters/debug. We always show
2627 current resource usage; turning this on also shows
2628 possible settings and some assignment information.
97ef062b 2629
1da177e4
LT
2630 pnpacpi= [ACPI]
2631 { off }
2632
2633 pnpbios= [ISAPNP]
2634 { on | off | curr | res | no-curr | no-res }
2635
2636 pnp_reserve_irq=
2637 [ISAPNP] Exclude IRQs for the autoconfiguration
2638
2639 pnp_reserve_dma=
2640 [ISAPNP] Exclude DMAs for the autoconfiguration
2641
2642 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
a9913044 2643 Ranges are in pairs (I/O port base and size).
1da177e4
LT
2644
2645 pnp_reserve_mem=
a9913044
RD
2646 [ISAPNP] Exclude memory regions for the
2647 autoconfiguration.
1da177e4
LT
2648 Ranges are in pairs (memory base and size).
2649
4af94f39
RD
2650 ports= [IP_VS_FTP] IPVS ftp helper module
2651 Default is 21.
2652 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2653 may be specified.
2654 Format: <port>,<port>....
2655
45807a1d
IM
2656 print-fatal-signals=
2657 [KNL] debug: print fatal signals
f84d49b2
NO
2658
2659 If enabled, warn about various signal handling
2660 related application anomalies: too many signals,
2661 too many POSIX.1 timers, fatal signals causing a
2662 coredump - etc.
2663
2664 If you hit the warning due to signal overflow,
2665 you might want to try "ulimit -i unlimited".
2666
45807a1d
IM
2667 default: off.
2668
c22ab332
MG
2669 printk.always_kmsg_dump=
2670 Trigger kmsg_dump for cases other than kernel oops or
2671 panics
2672 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2673 default: disabled
2674
e84845c4
RD
2675 printk.time= Show timing data prefixed to each printk message line
2676 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2677
0cb55ad2
RD
2678 processor.max_cstate= [HW,ACPI]
2679 Limit processor to maximum C-state
2680 max_cstate=9 overrides any DMI blacklist limit.
2681
2682 processor.nocst [HW,ACPI]
2683 Ignore the _CST method to determine C-states,
2684 instead using the legacy FADT method
2685
1da177e4 2686 profile= [KNL] Enable kernel profiling via /proc/profile
a9913044
RD
2687 Format: [schedule,]<number>
2688 Param: "schedule" - profile schedule points.
2689 Param: <number> - step/bucket size as a power of 2 for
2690 statistical time based profiling.
b3da2a73
MG
2691 Param: "sleep" - profile D-state sleeping (millisecs).
2692 Requires CONFIG_SCHEDSTATS
c0fe2e69 2693 Param: "kvm" - profile VM exits.
1da177e4 2694
1da177e4
LT
2695 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2696 before loading.
31c00fc1 2697 See Documentation/blockdev/ramdisk.txt.
1da177e4 2698
a9913044
RD
2699 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2700 probe for; one of (bare|imps|exps|lifebook|any).
1da177e4
LT
2701 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2702 per second.
a9913044
RD
2703 psmouse.resetafter= [HW,MOUSE]
2704 Try to reset the device after so many bad packets
1da177e4
LT
2705 (0 = never).
2706 psmouse.resolution=
2707 [HW,MOUSE] Set desired mouse resolution, in dpi.
2708 psmouse.smartscroll=
a9913044 2709 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
1da177e4
LT
2710 0 = disabled, 1 = enabled (default).
2711
dee28e72
MG
2712 pstore.backend= Specify the name of the pstore backend to use
2713
1da177e4 2714 pt. [PARIDE]
31c00fc1 2715 See Documentation/blockdev/paride.txt.
1da177e4 2716
dc8c8587
KS
2717 pty.legacy_count=
2718 [KNL] Number of legacy pty's. Overwrites compiled-in
2719 default number.
2720
7d2c502f 2721 quiet [KNL] Disable most log messages
a9913044 2722
1da177e4
LT
2723 r128= [HW,DRM]
2724
2725 raid= [HW,RAID]
2726 See Documentation/md.txt.
2727
a9913044 2728 ramdisk_blocksize= [RAM]
31c00fc1 2729 See Documentation/blockdev/ramdisk.txt.
a9913044 2730
1da177e4 2731 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
31c00fc1 2732 See Documentation/blockdev/ramdisk.txt.
1da177e4 2733
4102adab 2734 rcu_nocbs= [KNL]
3fbfbf7a
PM
2735 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
2736 the specified list of CPUs to be no-callback CPUs.
2737 Invocation of these CPUs' RCU callbacks will
a4889858
PM
2738 be offloaded to "rcuox/N" kthreads created for
2739 that purpose, where "x" is "b" for RCU-bh, "p"
2740 for RCU-preempt, and "s" for RCU-sched, and "N"
2741 is the CPU number. This reduces OS jitter on the
3fbfbf7a
PM
2742 offloaded CPUs, which can be useful for HPC and
2743 real-time workloads. It can also improve energy
2744 efficiency for asymmetric multiprocessors.
2745
4102adab 2746 rcu_nocb_poll [KNL]
3fbfbf7a
PM
2747 Rather than requiring that offloaded CPUs
2748 (specified by rcu_nocbs= above) explicitly
2749 awaken the corresponding "rcuoN" kthreads,
2750 make these kthreads poll for callbacks.
2751 This improves the real-time response for the
2752 offloaded CPUs by relieving them of the need to
2753 wake up the corresponding kthread, but degrades
2754 energy efficiency by requiring that the kthreads
2755 periodically wake up to do the polling.
2756
4102adab 2757 rcutree.blimit= [KNL]
97e63f0c
PM
2758 Set maximum number of finished RCU callbacks to
2759 process in one batch.
21a1ea9e 2760
4102adab 2761 rcutree.rcu_fanout_leaf= [KNL]
f885b7f2
PM
2762 Increase the number of CPUs assigned to each
2763 leaf rcu_node structure. Useful for very large
2764 systems.
2765
4102adab 2766 rcutree.jiffies_till_first_fqs= [KNL]
c0f4dfd4
PM
2767 Set delay from grace-period initialization to
2768 first attempt to force quiescent states.
2769 Units are jiffies, minimum value is zero,
2770 and maximum value is HZ.
2771
4102adab 2772 rcutree.jiffies_till_next_fqs= [KNL]
c0f4dfd4
PM
2773 Set delay between subsequent attempts to force
2774 quiescent states. Units are jiffies, minimum
2775 value is one, and maximum value is HZ.
2776
4102adab 2777 rcutree.qhimark= [KNL]
97e63f0c
PM
2778 Set threshold of queued RCU callbacks beyond which
2779 batch limiting is disabled.
21a1ea9e 2780
4102adab 2781 rcutree.qlowmark= [KNL]
24aaef8d
RD
2782 Set threshold of queued RCU callbacks below which
2783 batch limiting is re-enabled.
21a1ea9e 2784
4102adab 2785 rcutree.rcu_idle_gp_delay= [KNL]
c0f4dfd4
PM
2786 Set wakeup interval for idle CPUs that have
2787 RCU callbacks (RCU_FAST_NO_HZ=y).
d40011f6 2788
4102adab 2789 rcutree.rcu_idle_lazy_gp_delay= [KNL]
c0f4dfd4
PM
2790 Set wakeup interval for idle CPUs that have
2791 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
2792 Lazy RCU callbacks are those which RCU can
2793 prove do nothing more than free memory.
d40011f6 2794
4102adab 2795 rcutorture.fqs_duration= [KNL]
dabb8aa9
PM
2796 Set duration of force_quiescent_state bursts.
2797
4102adab 2798 rcutorture.fqs_holdoff= [KNL]
dabb8aa9
PM
2799 Set holdoff time within force_quiescent_state bursts.
2800
4102adab 2801 rcutorture.fqs_stutter= [KNL]
dabb8aa9
PM
2802 Set wait time between force_quiescent_state bursts.
2803
4102adab
PM
2804 rcutorture.gp_exp= [KNL]
2805 Use expedited update-side primitives.
2806
2807 rcutorture.gp_normal= [KNL]
2808 Use normal (non-expedited) update-side primitives.
2809 If both gp_exp and gp_normal are set, do both.
2810 If neither gp_exp nor gp_normal are set, still
2811 do both.
dabb8aa9 2812
4102adab 2813 rcutorture.n_barrier_cbs= [KNL]
dabb8aa9
PM
2814 Set callbacks/threads for rcu_barrier() testing.
2815
4102adab 2816 rcutorture.nfakewriters= [KNL]
dabb8aa9
PM
2817 Set number of concurrent RCU writers. These just
2818 stress RCU, they don't participate in the actual
2819 test, hence the "fake".
2820
4102adab 2821 rcutorture.nreaders= [KNL]
dabb8aa9
PM
2822 Set number of RCU readers.
2823
4102adab
PM
2824 rcutorture.object_debug= [KNL]
2825 Enable debug-object double-call_rcu() testing.
2826
2827 rcutorture.onoff_holdoff= [KNL]
dabb8aa9
PM
2828 Set time (s) after boot for CPU-hotplug testing.
2829
4102adab 2830 rcutorture.onoff_interval= [KNL]
dabb8aa9
PM
2831 Set time (s) between CPU-hotplug operations, or
2832 zero to disable CPU-hotplug testing.
2833
4102adab
PM
2834 rcutorture.rcutorture_runnable= [BOOT]
2835 Start rcutorture running at boot time.
2836
2837 rcutorture.shuffle_interval= [KNL]
dabb8aa9
PM
2838 Set task-shuffle interval (s). Shuffling tasks
2839 allows some CPUs to go into dyntick-idle mode
2840 during the rcutorture test.
2841
4102adab 2842 rcutorture.shutdown_secs= [KNL]
dabb8aa9
PM
2843 Set time (s) after boot system shutdown. This
2844 is useful for hands-off automated testing.
2845
4102adab 2846 rcutorture.stall_cpu= [KNL]
dabb8aa9
PM
2847 Duration of CPU stall (s) to test RCU CPU stall
2848 warnings, zero to disable.
2849
4102adab 2850 rcutorture.stall_cpu_holdoff= [KNL]
dabb8aa9
PM
2851 Time to wait (s) after boot before inducing stall.
2852
4102adab 2853 rcutorture.stat_interval= [KNL]
dabb8aa9
PM
2854 Time (s) between statistics printk()s.
2855
4102adab 2856 rcutorture.stutter= [KNL]
dabb8aa9
PM
2857 Time (s) to stutter testing, for example, specifying
2858 five seconds causes the test to run for five seconds,
2859 wait for five seconds, and so on. This tests RCU's
2860 ability to transition abruptly to and from idle.
2861
4102adab 2862 rcutorture.test_boost= [KNL]
dabb8aa9
PM
2863 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
2864 "Maybe" means test if the RCU implementation
2865 under test support RCU priority boosting.
2866
4102adab 2867 rcutorture.test_boost_duration= [KNL]
dabb8aa9
PM
2868 Duration (s) of each individual boost test.
2869
4102adab 2870 rcutorture.test_boost_interval= [KNL]
dabb8aa9
PM
2871 Interval (s) between each boost test.
2872
4102adab 2873 rcutorture.test_no_idle_hz= [KNL]
dabb8aa9
PM
2874 Test RCU's dyntick-idle handling. See also the
2875 rcutorture.shuffle_interval parameter.
2876
4102adab 2877 rcutorture.torture_type= [KNL]
dabb8aa9
PM
2878 Specify the RCU implementation to test.
2879
4102adab 2880 rcutorture.verbose= [KNL]
dabb8aa9
PM
2881 Enable additional printk() statements.
2882
4102adab
PM
2883 rcupdate.rcu_expedited= [KNL]
2884 Use expedited grace-period primitives, for
2885 example, synchronize_rcu_expedited() instead
2886 of synchronize_rcu(). This reduces latency,
2887 but can increase CPU utilization, degrade
2888 real-time latency, and degrade energy efficiency.
2889
2890 rcupdate.rcu_cpu_stall_suppress= [KNL]
2891 Suppress RCU CPU stall warning messages.
2892
2893 rcupdate.rcu_cpu_stall_timeout= [KNL]
2894 Set timeout for RCU CPU stall warning messages.
2895
ffdfc409
OJ
2896 rdinit= [KNL]
2897 Format: <full_path>
2898 Run specified binary instead of /init from the ramdisk,
2899 used for early userspace startup. See initrd.
2900
1b3a5d02
RH
2901 reboot= [KNL]
2902 Format (x86 or x86_64):
2903 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
2904 [[,]s[mp]#### \
2905 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
2906 [[,]f[orce]
2907 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
2908 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
2909 reboot_force is either force or not specified,
2910 reboot_cpu is s[mp]#### with #### being the processor
2911 to be used for rebooting.
1da177e4 2912
46b6d94e
PJ
2913 relax_domain_level=
2914 [KNL, SMP] Set scheduler's default relax_domain_level.
21acb9ca 2915 See Documentation/cgroups/cpusets.txt.
46b6d94e 2916
0399d4db
RW
2917 relative_sleep_states=
2918 [SUSPEND] Use sleep state labeling where the deepest
2919 state available other than hibernation is always "mem".
2920 Format: { "0" | "1" }
2921 0 -- Traditional sleep state labels.
2922 1 -- Relative sleep state labels.
2923
1da177e4
LT
2924 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
2925
cd4f0ef7 2926 reservetop= [X86-32]
461a9aff
ZA
2927 Format: nn[KMG]
2928 Reserves a hole at the top of the kernel virtual
2929 address space.
2930
9ea77bdb
PA
2931 reservelow= [X86]
2932 Format: nn[K]
2933 Set the amount of memory to reserve for BIOS at
2934 the bottom of the address space.
2935
7e96287d
VG
2936 reset_devices [KNL] Force drivers to reset the underlying device
2937 during initialization.
2938
a9913044
RD
2939 resume= [SWSUSP]
2940 Specify the partition device for software suspend
2df83fa4
MB
2941 Format:
2942 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
1da177e4 2943
ecbd0da1
RW
2944 resume_offset= [SWSUSP]
2945 Specify the offset from the beginning of the partition
2946 given by "resume=" at which the swap header is located,
2947 in <PAGE_SIZE> units (needed only for swap files).
2948 See Documentation/power/swsusp-and-swap-files.txt
2949
f126f733
BS
2950 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
2951 read the resume files
2952
6f8d7022
BS
2953 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
2954 Useful for devices that are detected asynchronously
2955 (e.g. USB and MMC devices).
2956
f996fc96
BS
2957 hibernate= [HIBERNATION]
2958 noresume Don't check if there's a hibernation image
2959 present during boot.
2960 nocompress Don't compress/decompress hibernation images.
2961
0a7b35cb
MN
2962 retain_initrd [RAM] Keep initrd memory after extraction
2963
1da177e4
LT
2964 rhash_entries= [KNL,NET]
2965 Set number of hash buckets for route cache
2966
1da177e4
LT
2967 ro [KNL] Mount root device read-only on boot
2968
2969 root= [KNL] Root filesystem
f2d34fd9 2970 See name_to_dev_t comment in init/do_mounts.c.
1da177e4
LT
2971
2972 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
2973 mount the root filesystem
2974
2975 rootflags= [KNL] Set root filesystem mount option string
2976
2977 rootfstype= [KNL] Set root filesystem type
2978
cc1ed754
PO
2979 rootwait [KNL] Wait (indefinitely) for root device to show up.
2980 Useful for devices that are detected asynchronously
2981 (e.g. USB and MMC devices).
2982
5c71d618
RT
2983 rproc_mem=nn[KMG][@address]
2984 [KNL,ARM,CMA] Remoteproc physical memory block.
2985 Memory area to be used by remote processor image,
2986 managed by CMA.
2987
1da177e4
LT
2988 rw [KNL] Mount root device read-write on boot
2989
2990 S [KNL] Run init in single mode
2991
2992 sa1100ir [NET]
2993 See drivers/net/irda/sa1100_ir.c.
2994
1da177e4 2995 sbni= [NET] Granch SBNI12 leased line adapter
a9913044 2996
f6630114
MT
2997 sched_debug [KNL] Enables verbose scheduler debug messages.
2998
5307c955
MG
2999 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3000 xtime_lock contention on larger systems, and/or RCU lock
3001 contention on all systems with CONFIG_MAXSMP set.
3002 Format: { "0" | "1" }
3003 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3004 1 -- enable.
3005 Note: increases power consumption, thus should only be
3006 enabled if running jitter sensitive (HPC/RT) workloads.
3007
0cb55ad2
RD
3008 security= [SECURITY] Choose a security module to enable at boot.
3009 If this boot parameter is not specified, only the first
3010 security module asking for security registration will be
3011 loaded. An invalid security module name will be treated
3012 as if no module has been chosen.
3013
3014 selinux= [SELINUX] Disable or enable SELinux at boot time.
1da177e4
LT
3015 Format: { "0" | "1" }
3016 See security/selinux/Kconfig help text.
3017 0 -- disable.
3018 1 -- enable.
3019 Default value is set via kernel config option.
3020 If enabled at boot time, /selinux/disable can be used
3021 later to disable prior to initial policy load.
3022
c1c124e9
JJ
3023 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3024 Format: { "0" | "1" }
3025 See security/apparmor/Kconfig help text
3026 0 -- disable.
3027 1 -- enable.
3028 Default value is set via kernel config option.
3029
cd4f0ef7 3030 serialnumber [BUGS=X86-32]
1da177e4 3031
1da177e4
LT
3032 shapers= [NET]
3033 Maximal number of shapers.
a9913044 3034
b05f78f5
YL
3035 show_msr= [x86] show boot-time MSR settings
3036 Format: { <integer> }
3037 Show boot-time (BIOS-initialized) MSR settings.
3038 The parameter means the number of CPUs to show,
3039 for example 1 means boot CPU only.
3040
1da177e4
LT
3041 simeth= [IA-64]
3042 simscsi=
a9913044 3043
1da177e4
LT
3044 slram= [HW,MTD]
3045
3df1cccd
DR
3046 slab_max_order= [MM, SLAB]
3047 Determines the maximum allowed order for slabs.
3048 A high setting may cause OOMs due to memory
3049 fragmentation. Defaults to 1 for systems with
3050 more than 32MB of RAM, 0 otherwise.
3051
f0630fff
CL
3052 slub_debug[=options[,slabs]] [MM, SLUB]
3053 Enabling slub_debug allows one to determine the
3054 culprit if slab objects become corrupted. Enabling
3055 slub_debug can create guard zones around objects and
3056 may poison objects when not in use. Also tracks the
3057 last alloc / free. For more information see
3058 Documentation/vm/slub.txt.
c1aee215
CL
3059
3060 slub_max_order= [MM, SLUB]
f0630fff
CL
3061 Determines the maximum allowed order for slabs.
3062 A high setting may cause OOMs due to memory
3063 fragmentation. For more information see
3064 Documentation/vm/slub.txt.
c1aee215
CL
3065
3066 slub_min_objects= [MM, SLUB]
f0630fff
CL
3067 The minimum number of objects per slab. SLUB will
3068 increase the slab order up to slub_max_order to
3069 generate a sufficiently large slab able to contain
3070 the number of objects indicated. The higher the number
3071 of objects the smaller the overhead of tracking slabs
3072 and the less frequently locks need to be acquired.
c1aee215
CL
3073 For more information see Documentation/vm/slub.txt.
3074
3075 slub_min_order= [MM, SLUB]
24775d65 3076 Determines the minimum page order for slabs. Must be
f0630fff 3077 lower than slub_max_order.
c1aee215
CL
3078 For more information see Documentation/vm/slub.txt.
3079
3080 slub_nomerge [MM, SLUB]
f0630fff 3081 Disable merging of slabs with similar size. May be
c1aee215 3082 necessary if there is some reason to distinguish
f0630fff
CL
3083 allocs to different slabs. Debug options disable
3084 merging on their own.
c1aee215
CL
3085 For more information see Documentation/vm/slub.txt.
3086
1da177e4
LT
3087 smart2= [HW]
3088 Format: <io1>[,<io2>[,...,<io8>]]
3089
d0d4f69b
BH
3090 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3091 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3092 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3093 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3094 smsc-ircc2.ircc_irq= [HW] IRQ line
3095 smsc-ircc2.ircc_dma= [HW] DMA channel
3096 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3097 0: Toshiba Satellite 1800 (GP data pin select)
3098 1: Fast pin select (default)
3099 2: ATC IRMode
3100
9c44bc03
IM
3101 softlockup_panic=
3102 [KNL] Should the soft-lockup detector generate panics.
44a4dcf7 3103 Format: <integer>
9c44bc03 3104
1da177e4 3105 sonypi.*= [HW] Sony Programmable I/O Control Device driver
395cf969 3106 See Documentation/laptops/sonypi.txt
1da177e4 3107
1da177e4
LT
3108 spia_io_base= [HW,MTD]
3109 spia_fio_base=
3110 spia_pedr=
3111 spia_peddr=
3112
f38f1d2a
SR
3113 stacktrace [FTRACE]
3114 Enabled the stack tracer on boot up.
3115
762e1207
SR
3116 stacktrace_filter=[function-list]
3117 [FTRACE] Limit the functions that the stack tracer
3118 will trace at boot up. function-list is a comma separated
3119 list of functions. This list can be changed at run
3120 time by the stack_trace_filter file in the debugfs
3121 tracing directory. Note, this enables stack tracing
3122 and the stacktrace above is not needed.
3123
1da177e4
LT
3124 sti= [PARISC,HW]
3125 Format: <num>
3126 Set the STI (builtin display/keyboard on the HP-PARISC
3127 machines) console (graphic card) which should be used
3128 as the initial boot-console.
3129 See also comment in drivers/video/console/sticore.c.
3130
3131 sti_font= [HW]
3132 See comment in drivers/video/console/sticore.c.
3133
3134 stifb= [HW]
3135 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3136
cbf11071
TM
3137 sunrpc.min_resvport=
3138 sunrpc.max_resvport=
3139 [NFS,SUNRPC]
3140 SunRPC servers often require that client requests
3141 originate from a privileged port (i.e. a port in the
3142 range 0 < portnr < 1024).
3143 An administrator who wishes to reserve some of these
3144 ports for other uses may adjust the range that the
3145 kernel's sunrpc client considers to be privileged
3146 using these two parameters to set the minimum and
3147 maximum port values.
3148
42a7fc4a
GB
3149 sunrpc.pool_mode=
3150 [NFS]
3151 Control how the NFS server code allocates CPUs to
3152 service thread pools. Depending on how many NICs
3153 you have and where their interrupts are bound, this
3154 option will affect which CPUs will do NFS serving.
3155 Note: this parameter cannot be changed while the
3156 NFS server is running.
3157
3158 auto the server chooses an appropriate mode
3159 automatically using heuristics
3160 global a single global pool contains all CPUs
3161 percpu one pool for each CPU
3162 pernode one pool for each NUMA node (equivalent
3163 to global on non-NUMA machines)
3164
cbf11071
TM
3165 sunrpc.tcp_slot_table_entries=
3166 sunrpc.udp_slot_table_entries=
3167 [NFS,SUNRPC]
3168 Sets the upper limit on the number of simultaneous
3169 RPC calls that can be sent from the client to a
3170 server. Increasing these values may allow you to
3171 improve throughput, but will also increase the
3172 amount of memory reserved for use by the client.
3173
07555ac1 3174 swapaccount=[0|1]
a42c390c
MH
3175 [KNL] Enable accounting of swap in memory resource
3176 controller if no parameter or 1 is given or disable
3177 it if 0 is given (See Documentation/cgroups/memory.txt)
3178
91fec0f5
JK
3179 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3180 Format: { <int> | force }
3181 <int> -- Number of I/O TLB slabs
3182 force -- force using of bounce buffers even if they
3183 wouldn't be automatically used by the kernel
a9913044 3184
1da177e4
LT
3185 switches= [HW,M68k]
3186
e52eec13
AK
3187 sysfs.deprecated=0|1 [KNL]
3188 Enable/disable old style sysfs layout for old udev
3189 on older distributions. When this option is enabled
3190 very new udev will not work anymore. When this option
3191 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3192 in older udev will not work anymore.
3193 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3194 the kernel configuration.
3195
5d6f647f
IM
3196 sysrq_always_enabled
3197 [KNL]
3198 Ignore sysrq setting - this boot parameter will
3199 neutralize any effect of /proc/sys/kernel/sysrq.
3200 Useful for debugging.
3201
1da177e4
LT
3202 tdfx= [HW,DRM]
3203
77437fd4
DB
3204 test_suspend= [SUSPEND]
3205 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3206 standby suspend) as the system sleep state to briefly
3207 enter during system startup. The system is woken from
3208 this state using a wakeup-capable RTC alarm.
3209
1da177e4
LT
3210 thash_entries= [KNL,NET]
3211 Set number of hash buckets for TCP connection
3212
f8707ec9
LB
3213 thermal.act= [HW,ACPI]
3214 -1: disable all active trip points in all thermal zones
3215 <degrees C>: override all lowest active trip points
3216
c52a7419
LB
3217 thermal.crt= [HW,ACPI]
3218 -1: disable all critical trip points in all thermal zones
22a94d79 3219 <degrees C>: override all critical trip points
c52a7419 3220
f5487145
LB
3221 thermal.nocrt= [HW,ACPI]
3222 Set to disable actions on ACPI thermal zone
3223 critical and hot trip points.
3224
72b33ef8
LB
3225 thermal.off= [HW,ACPI]
3226 1: disable ACPI thermal control
3227
a70cdc52
LB
3228 thermal.psv= [HW,ACPI]
3229 -1: disable all passive trip points
ada9cfdd
RD
3230 <degrees C>: override all passive trip points to this
3231 value
a70cdc52 3232
730ff34d
LB
3233 thermal.tzp= [HW,ACPI]
3234 Specify global default ACPI thermal zone polling rate
3235 <deci-seconds>: poll all this frequency
3236 0: no polling (default)
3237
8d32a307
TG
3238 threadirqs [KNL]
3239 Force threading of all interrupt handlers except those
24775d65 3240 marked explicitly IRQF_NO_THREAD.
8d32a307 3241
2ca62b04
KRW
3242 tmem [KNL,XEN]
3243 Enable the Transcendent memory driver if built-in.
3244
3245 tmem.cleancache=0|1 [KNL, XEN]
3246 Default is on (1). Disable the usage of the cleancache
3247 API to send anonymous pages to the hypervisor.
3248
3249 tmem.frontswap=0|1 [KNL, XEN]
3250 Default is on (1). Disable the usage of the frontswap
37d46e15
KRW
3251 API to send swap pages to the hypervisor. If disabled
3252 the selfballooning and selfshrinking are force disabled.
2ca62b04
KRW
3253
3254 tmem.selfballooning=0|1 [KNL, XEN]
3255 Default is on (1). Disable the driving of swap pages
3256 to the hypervisor.
3257
3258 tmem.selfshrinking=0|1 [KNL, XEN]
3259 Default is on (1). Partial swapoff that immediately
3260 transfers pages from Xen hypervisor back to the
3261 kernel based on different criteria.
3262
2b1a61f0
HC
3263 topology= [S390]
3264 Format: {off | on}
3265 Specify if the kernel should make use of the cpu
f65e51d7
SL
3266 topology information if the hardware supports this.
3267 The scheduler will make use of this information and
2b1a61f0 3268 e.g. base its process migration decisions on it.
c9af3fa9 3269 Default is on.
2b1a61f0 3270
1da177e4
LT
3271 tp720= [HW,PS2]
3272
225a9be2
RA
3273 tpm_suspend_pcr=[HW,TPM]
3274 Format: integer pcr id
3275 Specify that at suspend time, the tpm driver
3276 should extend the specified pcr with zeros,
3277 as a workaround for some chips which fail to
3278 flush the last written pcr on TPM_SaveState.
3279 This will guarantee that all the other pcrs
3280 are saved.
3281
9d612bef
LZ
3282 trace_buf_size=nn[KMG]
3283 [FTRACE] will set tracing buffer size.
631595fb 3284
020e5f85
LZ
3285 trace_event=[event-list]
3286 [FTRACE] Set and start specified trace events in order
3287 to facilitate early boot debugging.
3288 See also Documentation/trace/events.txt
3289
7bcfaf54
SR
3290 trace_options=[option-list]
3291 [FTRACE] Enable or disable tracer options at boot.
3292 The option-list is a comma delimited list of options
3293 that can be enabled or disabled just as if you were
3294 to echo the option name into
3295
3296 /sys/kernel/debug/tracing/trace_options
3297
3298 For example, to enable stacktrace option (to dump the
3299 stack trace of each event), add to the command line:
3300
3301 trace_options=stacktrace
3302
3303 See also Documentation/trace/ftrace.txt "trace options"
3304 section.
3305
de7edd31
SRRH
3306 traceoff_on_warning
3307 [FTRACE] enable this option to disable tracing when a
3308 warning is hit. This turns off "tracing_on". Tracing can
3309 be enabled again by echoing '1' into the "tracing_on"
3310 file located in /sys/kernel/debug/tracing/
3311
3312 This option is useful, as it disables the trace before
3313 the WARNING dump is called, which prevents the trace to
3314 be filled with content caused by the warning output.
3315
3316 This option can also be set at run time via the sysctl
3317 option: kernel/traceoff_on_warning
3318
fcf4d821
JK
3319 transparent_hugepage=
3320 [KNL]
3321 Format: [always|madvise|never]
3322 Can be used to control the default behavior of the system
3323 with respect to transparent hugepages.
3324 See Documentation/vm/transhuge.txt for more details.
3325
d3b8f889 3326 tsc= Disable clocksource stability checks for TSC.
395628ef
AK
3327 Format: <string>
3328 [x86] reliable: mark tsc clocksource as reliable, this
d3b8f889
JS
3329 disables clocksource verification at runtime, as well
3330 as the stability checks done at bootup. Used to enable
3331 high-resolution timer mode on older hardware, and in
3332 virtualized environment.
e82b8e4e
VP
3333 [x86] noirqtime: Do not use TSC to do irq accounting.
3334 Used to run time disable IRQ_TIME_ACCOUNTING on any
3335 platforms where RDTSC is slow and this accounting
3336 can add overhead.
395628ef 3337
a9913044
RD
3338 turbografx.map[2|3]= [HW,JOY]
3339 TurboGraFX parallel port interface
3340 Format:
3341 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
1da177e4
LT
3342 See also Documentation/input/joystick-parport.txt
3343
b6935f8c
CK
3344 udbg-immortal [PPC] When debugging early kernel crashes that
3345 happen after console_init() and before a proper
3346 console driver takes over, this boot options might
3347 help "seeing" what's going on.
3348
f86dcc5a
ED
3349 uhash_entries= [KNL,NET]
3350 Set number of hash buckets for UDP/UDP-Lite connections
3351
5f8364b7
AS
3352 uhci-hcd.ignore_oc=
3353 [USB] Ignore overcurrent events (default N).
3354 Some badly-designed motherboards generate lots of
3355 bogus events, for ports that aren't wired to
3356 anything. Set this parameter to avoid log spamming.
3357 Note that genuine overcurrent events won't be
3358 reported either.
3359
e3a61b0a 3360 unknown_nmi_panic
44a4dcf7 3361 [X86] Cause panic on unknown NMI.
e3a61b0a 3362
c4fc2342
CDH
3363 usbcore.authorized_default=
3364 [USB] Default USB device authorization:
3365 (default -1 = authorized except for wireless USB,
3366 0 = not authorized, 1 = authorized)
3367
b5e795f8
AS
3368 usbcore.autosuspend=
3369 [USB] The autosuspend time delay (in seconds) used
3370 for newly-detected USB devices (default 2). This
3371 is the time required before an idle device will be
3372 autosuspended. Devices for which the delay is set
eaafbc3a 3373 to a negative value won't be autosuspended at all.
b5e795f8 3374
fd7c519d
JK
3375 usbcore.usbfs_snoop=
3376 [USB] Set to log all usbfs traffic (default 0 = off).
3377
3378 usbcore.blinkenlights=
3379 [USB] Set to cycle leds on hubs (default 0 = off).
3380
3381 usbcore.old_scheme_first=
3382 [USB] Start with the old device initialization
3383 scheme (default 0 = off).
3384
3f5eb8d5
AS
3385 usbcore.usbfs_memory_mb=
3386 [USB] Memory limit (in MB) for buffers allocated by
3387 usbfs (default = 16, 0 = max = 2047).
3388
fd7c519d
JK
3389 usbcore.use_both_schemes=
3390 [USB] Try the other device initialization scheme
3391 if the first one fails (default 1 = enabled).
3392
3393 usbcore.initial_descriptor_timeout=
3394 [USB] Specifies timeout for the initial 64-byte
3395 USB_REQ_GET_DESCRIPTOR request in milliseconds
3396 (default 5000 = 5.0 seconds).
3397
1da177e4
LT
3398 usbhid.mousepoll=
3399 [USBHID] The interval which mice are to be polled at.
a9913044 3400
d4f373e5
AS
3401 usb-storage.delay_use=
3402 [UMS] The delay in seconds before a new device is
3403 scanned for Logical Units (default 5).
3404
3405 usb-storage.quirks=
3406 [UMS] A list of quirks entries to supplement or
3407 override the built-in unusual_devs list. List
3408 entries are separated by commas. Each entry has
3409 the form VID:PID:Flags where VID and PID are Vendor
3410 and Product ID values (4-digit hex numbers) and
3411 Flags is a set of characters, each corresponding
3412 to a common usb-storage quirk flag as follows:
c838ea46
AS
3413 a = SANE_SENSE (collect more than 18 bytes
3414 of sense data);
a0bb1081
AS
3415 b = BAD_SENSE (don't collect more than 18
3416 bytes of sense data);
d4f373e5
AS
3417 c = FIX_CAPACITY (decrease the reported
3418 device capacity by one sector);
5116901d
KR
3419 d = NO_READ_DISC_INFO (don't use
3420 READ_DISC_INFO command);
3421 e = NO_READ_CAPACITY_16 (don't use
3422 READ_CAPACITY_16 command);
c838ea46
AS
3423 h = CAPACITY_HEURISTICS (decrease the
3424 reported device capacity by one
3425 sector if the number is odd);
d4f373e5
AS
3426 i = IGNORE_DEVICE (don't bind to this
3427 device);
3428 l = NOT_LOCKABLE (don't try to lock and
3429 unlock ejectable media);
3430 m = MAX_SECTORS_64 (don't transfer more
3431 than 64 sectors = 32 KB at a time);
21c13a4f
AS
3432 n = INITIAL_READ10 (force a retry of the
3433 initial READ(10) command);
c838ea46
AS
3434 o = CAPACITY_OK (accept the capacity
3435 reported by the device);
eaa05dfc
NJ
3436 p = WRITE_CACHE (the device cache is ON
3437 by default);
d4f373e5
AS
3438 r = IGNORE_RESIDUE (the device reports
3439 bogus residue values);
3440 s = SINGLE_LUN (the device has only one
3441 Logical Unit);
3442 w = NO_WP_DETECT (don't test whether the
3443 medium is write-protected).
3444 Example: quirks=0419:aaf5:rl,0421:0433:rc
3445
ac1667db
SB
3446 user_debug= [KNL,ARM]
3447 Format: <int>
3448 See arch/arm/Kconfig.debug help text.
3449 1 - undefined instruction events
3450 2 - system calls
3451 4 - invalid data aborts
3452 8 - SIGSEGV faults
3453 16 - SIGBUS faults
3454 Example: user_debug=31
3455
14315592
IC
3456 userpte=
3457 [X86] Flags controlling user PTE allocations.
3458
3459 nohigh = do not allocate PTE pages in
3460 HIGHMEM regardless of setting
3461 of CONFIG_HIGHPTE.
3462
6cececfc 3463 vdso= [X86,SH]
b0b49f26
AL
3464 On X86_32, this is an alias for vdso32=. Otherwise:
3465
3466 vdso=1: enable VDSO (the default)
e6e5494c
IM
3467 vdso=0: disable VDSO mapping
3468
b0b49f26
AL
3469 vdso32= [X86] Control the 32-bit vDSO
3470 vdso32=1: enable 32-bit VDSO
3471 vdso32=0 or vdso32=2: disable 32-bit VDSO
3472
3473 See the help text for CONFIG_COMPAT_VDSO for more
3474 details. If CONFIG_COMPAT_VDSO is set, the default is
3475 vdso32=0; otherwise, the default is vdso32=1.
3476
3477 For compatibility with older kernels, vdso32=2 is an
3478 alias for vdso32=0.
3479
3480 Try vdso32=0 if you encounter an error that says:
3481 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
af65d648 3482
d080d397
YI
3483 vector= [IA-64,SMP]
3484 vector=percpu: enable percpu vector domain
3485
1da177e4
LT
3486 video= [FB] Frame buffer configuration
3487 See Documentation/fb/modedb.txt.
3488
3afe6dab
AL
3489 video.brightness_switch_enabled= [0,1]
3490 If set to 1, on receiving an ACPI notify event
3491 generated by hotkey, video driver will adjust brightness
3492 level and then send out the event to user space through
3493 the allocated input device; If set to 0, video driver
3494 will only send out the event without touching backlight
3495 brightness level.
886129a8 3496 default: 0
3afe6dab 3497
81a054ce
PM
3498 virtio_mmio.device=
3499 [VMMIO] Memory mapped virtio (platform) device.
3500
3501 <size>@<baseaddr>:<irq>[:<id>]
3502 where:
3503 <size> := size (can use standard suffixes
3504 like K, M and G)
3505 <baseaddr> := physical base address
3506 <irq> := interrupt number (as passed to
3507 request_irq())
3508 <id> := (optional) platform device id
3509 example:
3510 virtio_mmio.device=1K@0x100b0000:48:7
3511
3512 Can be used multiple times for multiple devices.
3513
cd4f0ef7 3514 vga= [BOOT,X86-32] Select a particular video mode
954a8b81 3515 See Documentation/x86/boot.txt and
a9913044 3516 Documentation/svga.txt.
1da177e4
LT
3517 Use vga=ask for menu.
3518 This is actually a boot loader parameter; the value is
3519 passed to the kernel using a special protocol.
3520
a9913044 3521 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
1da177e4
LT
3522 size of <nn>. This can be used to increase the
3523 minimum size (128MB on x86). It can also be used to
3524 decrease the size and leave more room for directly
3525 mapped kernel RAM.
3526
585c3047
PO
3527 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
3528 Format: <command>
1da177e4 3529
585c3047
PO
3530 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
3531 Format: <command>
3532
3533 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
3534 Format: <command>
a9913044 3535
3ae36655
AL
3536 vsyscall= [X86-64]
3537 Controls the behavior of vsyscalls (i.e. calls to
3538 fixed addresses of 0xffffffffff600x00 from legacy
3539 code). Most statically-linked binaries and older
3540 versions of glibc use these calls. Because these
3541 functions are at fixed addresses, they make nice
3542 targets for exploits that can control RIP.
3543
2e57ae05
AL
3544 emulate [default] Vsyscalls turn into traps and are
3545 emulated reasonably safely.
3ae36655 3546
2e57ae05 3547 native Vsyscalls are native syscall instructions.
3ae36655
AL
3548 This is a little bit faster than trapping
3549 and makes a few dynamic recompilers work
3550 better than they would in emulation mode.
3551 It also makes exploits much easier to write.
3552
3553 none Vsyscalls don't work at all. This makes
3554 them quite hard to use for exploits but
3555 might break your system.
3556
3855ae1c
CL
3557 vt.color= [VT] Default text color.
3558 Format: 0xYX, X = foreground, Y = background.
3559 Default: 0x07 = light gray on black.
3560
9ea9a886
CL
3561 vt.cur_default= [VT] Default cursor shape.
3562 Format: 0xCCBBAA, where AA, BB, and CC are the same as
3563 the parameters of the <Esc>[?A;B;Cc escape sequence;
3564 see VGA-softcursor.txt. Default: 2 = underline.
3565
0cb55ad2
RD
3566 vt.default_blu= [VT]
3567 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
3568 Change the default blue palette of the console.
3569 This is a 16-member array composed of values
3570 ranging from 0-255.
3571
3572 vt.default_grn= [VT]
3573 Format: <green0>,<green1>,<green2>,...,<green15>
3574 Change the default green palette of the console.
3575 This is a 16-member array composed of values
3576 ranging from 0-255.
3577
3578 vt.default_red= [VT]
3579 Format: <red0>,<red1>,<red2>,...,<red15>
3580 Change the default red palette of the console.
3581 This is a 16-member array composed of values
3582 ranging from 0-255.
3583
3584 vt.default_utf8=
3585 [VT]
3586 Format=<0|1>
3587 Set system-wide default UTF-8 mode for all tty's.
3588 Default is 1, i.e. UTF-8 mode is enabled for all
3589 newly opened terminals.
3590
f6c06b68
MG
3591 vt.global_cursor_default=
3592 [VT]
3593 Format=<-1|0|1>
3594 Set system-wide default for whether a cursor
3595 is shown on new VTs. Default is -1,
3596 i.e. cursors will be created by default unless
3597 overridden by individual drivers. 0 will hide
3598 cursors, 1 will display them.
3599
3855ae1c
CL
3600 vt.italic= [VT] Default color for italic text; 0-15.
3601 Default: 2 = green.
3602
3603 vt.underline= [VT] Default color for underlined text; 0-15.
3604 Default: 3 = cyan.
3605
4724ba57
RD
3606 watchdog timers [HW,WDT] For information on watchdog timers,
3607 see Documentation/watchdog/watchdog-parameters.txt
3608 or other driver-specific files in the
3609 Documentation/watchdog/ directory.
1da177e4 3610
d55262c4
TH
3611 workqueue.disable_numa
3612 By default, all work items queued to unbound
3613 workqueues are affine to the NUMA nodes they're
3614 issued on, which results in better behavior in
3615 general. If NUMA affinity needs to be disabled for
3616 whatever reason, this option can be used. Note
3617 that this also can be controlled per-workqueue for
3618 workqueues visible under /sys/bus/workqueue/.
3619
cee22a15
VK
3620 workqueue.power_efficient
3621 Per-cpu workqueues are generally preferred because
3622 they show better performance thanks to cache
3623 locality; unfortunately, per-cpu workqueues tend to
3624 be more power hungry than unbound workqueues.
3625
3626 Enabling this makes the per-cpu workqueues which
3627 were observed to contribute significantly to power
3628 consumption unbound, leading to measurably lower
3629 power usage at the cost of small performance
3630 overhead.
3631
3632 The default value of this parameter is determined by
3633 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
3634
0cb55ad2
RD
3635 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
3636 default x2apic cluster mode on platforms
3637 supporting x2apic.
3638
712b6aa8
KS
3639 x86_intel_mid_timer= [X86-32,APBT]
3640 Choose timer option for x86 Intel MID platform.
bb24c471
JP
3641 Two valid options are apbt timer only and lapic timer
3642 plus one apbt timer for broadcast timer.
712b6aa8 3643 x86_intel_mid_timer=apbt_only | lapic_and_apbt
bb24c471 3644
c1c5413a
SS
3645 xen_emul_unplug= [HW,X86,XEN]
3646 Unplug Xen emulated devices
3647 Format: [unplug0,][unplug1]
3648 ide-disks -- unplug primary master IDE devices
3649 aux-ide-disks -- unplug non-primary-master IDE devices
3650 nics -- unplug network devices
3651 all -- unplug all emulated devices (NICs and IDE disks)
1dc7ce99
IC
3652 unnecessary -- unplugging emulated devices is
3653 unnecessary even if the host did not respond to
3654 the unplug protocol
c93a4dfb 3655 never -- do not unplug even if version check succeeds
c1c5413a 3656
15a3eac0
KRW
3657 xen_nopvspin [X86,XEN]
3658 Disables the ticketlock slowpath using Xen PV
3659 optimizations.
3660
1da177e4 3661 xirc2ps_cs= [NET,PCMCIA]
a9913044
RD
3662 Format:
3663 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
1da177e4 3664
a9913044 3665______________________________________________________________________
1da177e4
LT
3666
3667TODO:
3668
1da177e4 3669 Add more DRM drivers.