Commit 32643e10 authored by Randy Dunlap's avatar Randy Dunlap Committed by Jonathan Corbet
Browse files

Documentation: admin: reorganize kernel-parameters intro 



Reorganize the introduction to the kernel-parameters file to place
related paragraphs together:

- move module info together and near the beginning
- add a Special Handling section for dashes, underscores, double quotes,
  cpu lists, and metric (KMG) suffixes. Expand the KMG suffixes to
  include TPE as well.
- add a Kernel Build Options section

Signed-off-by: default avatarRandy Dunlap <rdunlap@infradead.org>
Signed-off-by: default avatarJonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20241029180320.412629-1-rdunlap@infradead.org
parent 062d98be

Documentation/admin-guide/kernel-parameters.rst

+23 −13
Original line number Diff line number Diff line
@@ -27,6 +27,16 @@ kernel command line (/proc/cmdline) and collects module parameters 
when it loads a module, so the kernel command line can be used for

loadable modules too.



This document may not be entirely up to date and comprehensive. The command

"modinfo -p ${modulename}" shows a current list of all parameters of a loadable

module. Loadable modules, after being loaded into the running kernel, also

reveal their parameters in /sys/module/${modulename}/parameters/. Some of these

parameters may be changed at runtime by the command

``echo -n ${value} > /sys/module/${modulename}/parameters/${parm}``.



Special handling

----------------



Hyphens (dashes) and underscores are equivalent in parameter names, so::



	log_buf_len=1M print-fatal-signals=1
@@ -39,8 +49,8 @@ Double-quotes can be used to protect spaces in values, e.g.:: 


	param="spaces in here"



cpu lists:

----------

cpu lists

~~~~~~~~~



Some kernel parameters take a list of CPUs as a value, e.g.  isolcpus,

nohz_full, irqaffinity, rcu_nocbs.  The format of this list is:
@@ -82,12 +92,17 @@ so that "nohz_full=all" is the equivalent of "nohz_full=0-N". 
The semantics of "N" and "all" is supported on a level of bitmaps and holds for

all users of bitmap_parselist().



This document may not be entirely up to date and comprehensive. The command

"modinfo -p ${modulename}" shows a current list of all parameters of a loadable

module. Loadable modules, after being loaded into the running kernel, also

reveal their parameters in /sys/module/${modulename}/parameters/. Some of these

parameters may be changed at runtime by the command

``echo -n ${value} > /sys/module/${modulename}/parameters/${parm}``.

Metric suffixes

~~~~~~~~~~~~~~~



The [KMG] suffix is commonly described after a number of kernel

parameter values. 'K', 'M', 'G', 'T', 'P', and 'E' suffixes are allowed.

These letters represent the _binary_ multipliers 'Kilo', 'Mega', 'Giga',

'Tera', 'Peta', and 'Exa', equaling 2^10, 2^20, 2^30, 2^40, 2^50, and

2^60 bytes respectively. Such letter suffixes can also be entirely omitted.



Kernel Build Options

--------------------



The parameters listed below are only valid if certain kernel build options

were enabled and if respective hardware is present. This list should be kept
@@ -211,10 +226,5 @@ a fixed number of characters. This limit depends on the architecture 
and is between 256 and 4096 characters. It is defined in the file

./include/uapi/asm-generic/setup.h as COMMAND_LINE_SIZE.



Finally, the [KMG] suffix is commonly described after a number of kernel

parameter values. These 'K', 'M', and 'G' letters represent the _binary_

multipliers 'Kilo', 'Mega', and 'Giga', equaling 2^10, 2^20, and 2^30

bytes respectively. Such letter suffixes can also be entirely omitted:



.. include:: kernel-parameters.txt

   :literal: