kernel-parameters.rst 8.1 KB

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  1. .. _kernelparameters:
  2. The kernel's command-line parameters
  3. ====================================
  4. The following is a consolidated list of the kernel parameters as
  5. implemented by the __setup(), core_param() and module_param() macros
  6. and sorted into English Dictionary order (defined as ignoring all
  7. punctuation and sorting digits before letters in a case insensitive
  8. manner), and with descriptions where known.
  9. The kernel parses parameters from the kernel command line up to "``--``";
  10. if it doesn't recognize a parameter and it doesn't contain a '.', the
  11. parameter gets passed to init: parameters with '=' go into init's
  12. environment, others are passed as command line arguments to init.
  13. Everything after "``--``" is passed as an argument to init.
  14. Module parameters can be specified in two ways: via the kernel command
  15. line with a module name prefix, or via modprobe, e.g.::
  16. (kernel command line) usbcore.blinkenlights=1
  17. (modprobe command line) modprobe usbcore blinkenlights=1
  18. Parameters for modules which are built into the kernel need to be
  19. specified on the kernel command line. modprobe looks through the
  20. kernel command line (/proc/cmdline) and collects module parameters
  21. when it loads a module, so the kernel command line can be used for
  22. loadable modules too.
  23. Hyphens (dashes) and underscores are equivalent in parameter names, so::
  24. log_buf_len=1M print-fatal-signals=1
  25. can also be entered as::
  26. log-buf-len=1M print_fatal_signals=1
  27. Double-quotes can be used to protect spaces in values, e.g.::
  28. param="spaces in here"
  29. cpu lists:
  30. ----------
  31. Some kernel parameters take a list of CPUs as a value, e.g. isolcpus,
  32. nohz_full, irqaffinity, rcu_nocbs. The format of this list is:
  33. <cpu number>,...,<cpu number>
  34. or
  35. <cpu number>-<cpu number>
  36. (must be a positive range in ascending order)
  37. or a mixture
  38. <cpu number>,...,<cpu number>-<cpu number>
  39. Note that for the special case of a range one can split the range into equal
  40. sized groups and for each group use some amount from the beginning of that
  41. group:
  42. <cpu number>-cpu number>:<used size>/<group size>
  43. For example one can add to the command line following parameter:
  44. isolcpus=1,2,10-20,100-2000:2/25
  45. where the final item represents CPUs 100,101,125,126,150,151,...
  46. This document may not be entirely up to date and comprehensive. The command
  47. "modinfo -p ${modulename}" shows a current list of all parameters of a loadable
  48. module. Loadable modules, after being loaded into the running kernel, also
  49. reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
  50. parameters may be changed at runtime by the command
  51. ``echo -n ${value} > /sys/module/${modulename}/parameters/${parm}``.
  52. The parameters listed below are only valid if certain kernel build options were
  53. enabled and if respective hardware is present. The text in square brackets at
  54. the beginning of each description states the restrictions within which a
  55. parameter is applicable::
  56. ACPI ACPI support is enabled.
  57. AGP AGP (Accelerated Graphics Port) is enabled.
  58. ALSA ALSA sound support is enabled.
  59. APIC APIC support is enabled.
  60. APM Advanced Power Management support is enabled.
  61. ARM ARM architecture is enabled.
  62. ARM64 ARM64 architecture is enabled.
  63. AX25 Appropriate AX.25 support is enabled.
  64. CLK Common clock infrastructure is enabled.
  65. CMA Contiguous Memory Area support is enabled.
  66. DRM Direct Rendering Management support is enabled.
  67. DYNAMIC_DEBUG Build in debug messages and enable them at runtime
  68. EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
  69. EFI EFI Partitioning (GPT) is enabled
  70. EIDE EIDE/ATAPI support is enabled.
  71. EVM Extended Verification Module
  72. FB The frame buffer device is enabled.
  73. FTRACE Function tracing enabled.
  74. GCOV GCOV profiling is enabled.
  75. HW Appropriate hardware is enabled.
  76. IA-64 IA-64 architecture is enabled.
  77. IMA Integrity measurement architecture is enabled.
  78. IOSCHED More than one I/O scheduler is enabled.
  79. IP_PNP IP DHCP, BOOTP, or RARP is enabled.
  80. IPV6 IPv6 support is enabled.
  81. ISAPNP ISA PnP code is enabled.
  82. ISDN Appropriate ISDN support is enabled.
  83. ISOL CPU Isolation is enabled.
  84. JOY Appropriate joystick support is enabled.
  85. KGDB Kernel debugger support is enabled.
  86. KVM Kernel Virtual Machine support is enabled.
  87. LIBATA Libata driver is enabled
  88. LP Printer support is enabled.
  89. LOOP Loopback device support is enabled.
  90. M68k M68k architecture is enabled.
  91. These options have more detailed description inside of
  92. Documentation/m68k/kernel-options.rst.
  93. MDA MDA console support is enabled.
  94. MIPS MIPS architecture is enabled.
  95. MOUSE Appropriate mouse support is enabled.
  96. MSI Message Signaled Interrupts (PCI).
  97. MTD MTD (Memory Technology Device) support is enabled.
  98. NET Appropriate network support is enabled.
  99. NUMA NUMA support is enabled.
  100. NFS Appropriate NFS support is enabled.
  101. OF Devicetree is enabled.
  102. OSS OSS sound support is enabled.
  103. PV_OPS A paravirtualized kernel is enabled.
  104. PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
  105. PARISC The PA-RISC architecture is enabled.
  106. PCI PCI bus support is enabled.
  107. PCIE PCI Express support is enabled.
  108. PCMCIA The PCMCIA subsystem is enabled.
  109. PNP Plug & Play support is enabled.
  110. PPC PowerPC architecture is enabled.
  111. PPT Parallel port support is enabled.
  112. PS2 Appropriate PS/2 support is enabled.
  113. RAM RAM disk support is enabled.
  114. RDT Intel Resource Director Technology.
  115. S390 S390 architecture is enabled.
  116. SCSI Appropriate SCSI support is enabled.
  117. A lot of drivers have their options described inside
  118. the Documentation/scsi/ sub-directory.
  119. SECURITY Different security models are enabled.
  120. SELINUX SELinux support is enabled.
  121. APPARMOR AppArmor support is enabled.
  122. SERIAL Serial support is enabled.
  123. SH SuperH architecture is enabled.
  124. SMP The kernel is an SMP kernel.
  125. SPARC Sparc architecture is enabled.
  126. SWSUSP Software suspend (hibernation) is enabled.
  127. SUSPEND System suspend states are enabled.
  128. TPM TPM drivers are enabled.
  129. TS Appropriate touchscreen support is enabled.
  130. UMS USB Mass Storage support is enabled.
  131. USB USB support is enabled.
  132. USBHID USB Human Interface Device support is enabled.
  133. V4L Video For Linux support is enabled.
  134. VMMIO Driver for memory mapped virtio devices is enabled.
  135. VGA The VGA console has been enabled.
  136. VT Virtual terminal support is enabled.
  137. WDT Watchdog support is enabled.
  138. XT IBM PC/XT MFM hard disk support is enabled.
  139. X86-32 X86-32, aka i386 architecture is enabled.
  140. X86-64 X86-64 architecture is enabled.
  141. More X86-64 boot options can be found in
  142. Documentation/x86/x86_64/boot-options.rst.
  143. X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
  144. X86_UV SGI UV support is enabled.
  145. XEN Xen support is enabled
  146. In addition, the following text indicates that the option::
  147. BUGS= Relates to possible processor bugs on the said processor.
  148. KNL Is a kernel start-up parameter.
  149. BOOT Is a boot loader parameter.
  150. Parameters denoted with BOOT are actually interpreted by the boot
  151. loader, and have no meaning to the kernel directly.
  152. Do not modify the syntax of boot loader parameters without extreme
  153. need or coordination with <Documentation/x86/boot.rst>.
  154. There are also arch-specific kernel-parameters not documented here.
  155. See for example <Documentation/x86/x86_64/boot-options.rst>.
  156. Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
  157. a trailing = on the name of any parameter states that that parameter will
  158. be entered as an environment variable, whereas its absence indicates that
  159. it will appear as a kernel argument readable via /proc/cmdline by programs
  160. running once the system is up.
  161. The number of kernel parameters is not limited, but the length of the
  162. complete command line (parameters including spaces etc.) is limited to
  163. a fixed number of characters. This limit depends on the architecture
  164. and is between 256 and 4096 characters. It is defined in the file
  165. ./include/asm/setup.h as COMMAND_LINE_SIZE.
  166. Finally, the [KMG] suffix is commonly described after a number of kernel
  167. parameter values. These 'K', 'M', and 'G' letters represent the _binary_
  168. multipliers 'Kilo', 'Mega', and 'Giga', equaling 2^10, 2^20, and 2^30
  169. bytes respectively. Such letter suffixes can also be entirely omitted:
  170. .. include:: kernel-parameters.txt
  171. :literal:
  172. Todo
  173. ----
  174. Add more DRM drivers.