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