Documentation / kbuild / kconfig.rst


Based on kernel version 5.17. Page generated on 2022-03-28 08:42 EST.

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===================
Kconfig make config
===================

This file contains some assistance for using `make *config`.

Use "make help" to list all of the possible configuration targets.

The xconfig ('qconf'), menuconfig ('mconf'), and nconfig ('nconf')
programs also have embedded help text.  Be sure to check that for
navigation, search, and other general help text.

General
-------

New kernel releases often introduce new config symbols.  Often more
important, new kernel releases may rename config symbols.  When
this happens, using a previously working .config file and running
"make oldconfig" won't necessarily produce a working new kernel
for you, so you may find that you need to see what NEW kernel
symbols have been introduced.

To see a list of new config symbols, use::

	cp user/some/old.config .config
	make listnewconfig

and the config program will list any new symbols, one per line.

Alternatively, you can use the brute force method::

	make oldconfig
	scripts/diffconfig .config.old .config | less

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

Environment variables for `*config`

KCONFIG_CONFIG
--------------
This environment variable can be used to specify a default kernel config
file name to override the default name of ".config".

KCONFIG_DEFCONFIG_LIST
----------------------

This environment variable specifies a list of config files which can be used
as a base configuration in case the .config does not exist yet. Entries in
the list are separated with whitespaces to each other, and the first one
that exists is used.

KCONFIG_OVERWRITECONFIG
-----------------------
If you set KCONFIG_OVERWRITECONFIG in the environment, Kconfig will not
break symlinks when .config is a symlink to somewhere else.

`CONFIG_`
---------
If you set `CONFIG_` in the environment, Kconfig will prefix all symbols
with its value when saving the configuration, instead of using the default,
`CONFIG_`.

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

Environment variables for '{allyes/allmod/allno/rand}config'

KCONFIG_ALLCONFIG
-----------------
(partially based on lkml email from/by Rob Landley, re: miniconfig)

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

The allyesconfig/allmodconfig/allnoconfig/randconfig variants can also
use the environment variable KCONFIG_ALLCONFIG as a flag or a filename
that contains config symbols that the user requires to be set to a
specific value.  If KCONFIG_ALLCONFIG is used without a filename where
KCONFIG_ALLCONFIG == "" or KCONFIG_ALLCONFIG == "1", `make *config`
checks for a file named "all{yes/mod/no/def/random}.config"
(corresponding to the `*config` command that was used) for symbol values
that are to be forced.  If this file is not found, it checks for a
file named "all.config" to contain forced values.

This enables you to create "miniature" config (miniconfig) or custom
config files containing just the config symbols that you are interested
in.  Then the kernel config system generates the full .config file,
including symbols of your miniconfig file.

This 'KCONFIG_ALLCONFIG' file is a config file which contains
(usually a subset of all) preset config symbols.  These variable
settings are still subject to normal dependency checks.

Examples::

	KCONFIG_ALLCONFIG=custom-notebook.config make allnoconfig

or::

	KCONFIG_ALLCONFIG=mini.config make allnoconfig

or::

	make KCONFIG_ALLCONFIG=mini.config allnoconfig

These examples will disable most options (allnoconfig) but enable or
disable the options that are explicitly listed in the specified
mini-config files.

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

Environment variables for 'randconfig'

KCONFIG_SEED
------------
You can set this to the integer value used to seed the RNG, if you want
to somehow debug the behaviour of the kconfig parser/frontends.
If not set, the current time will be used.

KCONFIG_PROBABILITY
-------------------
This variable can be used to skew the probabilities. This variable can
be unset or empty, or set to three different formats:

    =======================     ==================  =====================
	KCONFIG_PROBABILITY     y:n split           y:m:n split
    =======================     ==================  =====================
	unset or empty          50  : 50            33  : 33  : 34
	N                        N  : 100-N         N/2 : N/2 : 100-N
    [1] N:M                     N+M : 100-(N+M)      N  :  M  : 100-(N+M)
    [2] N:M:L                    N  : 100-N          M  :  L  : 100-(M+L)
    =======================     ==================  =====================

where N, M and L are integers (in base 10) in the range [0,100], and so
that:

    [1] N+M is in the range [0,100]

    [2] M+L is in the range [0,100]

Examples::

	KCONFIG_PROBABILITY=10
		10% of booleans will be set to 'y', 90% to 'n'
		5% of tristates will be set to 'y', 5% to 'm', 90% to 'n'
	KCONFIG_PROBABILITY=15:25
		40% of booleans will be set to 'y', 60% to 'n'
		15% of tristates will be set to 'y', 25% to 'm', 60% to 'n'
	KCONFIG_PROBABILITY=10:15:15
		10% of booleans will be set to 'y', 90% to 'n'
		15% of tristates will be set to 'y', 15% to 'm', 70% to 'n'

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

Environment variables for 'syncconfig'

KCONFIG_NOSILENTUPDATE
----------------------
If this variable has a non-blank value, it prevents silent kernel
config updates (requires explicit updates).

KCONFIG_AUTOCONFIG
------------------
This environment variable can be set to specify the path & name of the
"auto.conf" file.  Its default value is "include/config/auto.conf".

KCONFIG_AUTOHEADER
------------------
This environment variable can be set to specify the path & name of the
"autoconf.h" (header) file.
Its default value is "include/generated/autoconf.h".


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

menuconfig
----------

SEARCHING for CONFIG symbols

Searching in menuconfig:

	The Search function searches for kernel configuration symbol
	names, so you have to know something close to what you are
	looking for.

	Example::

		/hotplug
		This lists all config symbols that contain "hotplug",
		e.g., HOTPLUG_CPU, MEMORY_HOTPLUG.

	For search help, enter / followed by TAB-TAB (to highlight
	<Help>) and Enter.  This will tell you that you can also use
	regular expressions (regexes) in the search string, so if you
	are not interested in MEMORY_HOTPLUG, you could try::

		/^hotplug

	When searching, symbols are sorted thus:

	  - first, exact matches, sorted alphabetically (an exact match
	    is when the search matches the complete symbol name);
	  - then, other matches, sorted alphabetically.

	For example: ^ATH.K matches:

	    ATH5K ATH9K ATH5K_AHB ATH5K_DEBUG [...] ATH6KL ATH6KL_DEBUG
	    [...] ATH9K_AHB ATH9K_BTCOEX_SUPPORT ATH9K_COMMON [...]

	of which only ATH5K and ATH9K match exactly and so are sorted
	first (and in alphabetical order), then come all other symbols,
	sorted in alphabetical order.

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

User interface options for 'menuconfig'

MENUCONFIG_COLOR
----------------
It is possible to select different color themes using the variable
MENUCONFIG_COLOR.  To select a theme use::

	make MENUCONFIG_COLOR=<theme> menuconfig

Available themes are::

  - mono       => selects colors suitable for monochrome displays
  - blackbg    => selects a color scheme with black background
  - classic    => theme with blue background. The classic look
  - bluetitle  => a LCD friendly version of classic. (default)

MENUCONFIG_MODE
---------------
This mode shows all sub-menus in one large tree.

Example::

	make MENUCONFIG_MODE=single_menu menuconfig

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

nconfig
-------

nconfig is an alternate text-based configurator.  It lists function
keys across the bottom of the terminal (window) that execute commands.
You can also just use the corresponding numeric key to execute the
commands unless you are in a data entry window.  E.g., instead of F6
for Save, you can just press 6.

Use F1 for Global help or F3 for the Short help menu.

Searching in nconfig:

	You can search either in the menu entry "prompt" strings
	or in the configuration symbols.

	Use / to begin a search through the menu entries.  This does
	not support regular expressions.  Use <Down> or <Up> for
	Next hit and Previous hit, respectively.  Use <Esc> to
	terminate the search mode.

	F8 (SymSearch) searches the configuration symbols for the
	given string or regular expression (regex).

NCONFIG_MODE
------------
This mode shows all sub-menus in one large tree.

Example::

	make NCONFIG_MODE=single_menu nconfig

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

xconfig
-------

Searching in xconfig:

	The Search function searches for kernel configuration symbol
	names, so you have to know something close to what you are
	looking for.

	Example::

		Ctrl-F hotplug

	or::

		Menu: File, Search, hotplug

	lists all config symbol entries that contain "hotplug" in
	the symbol name.  In this Search dialog, you may change the
	config setting for any of the entries that are not grayed out.
	You can also enter a different search string without having
	to return to the main menu.


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

gconfig
-------

Searching in gconfig:

	There is no search command in gconfig.  However, gconfig does
	have several different viewing choices, modes, and options.