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.


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


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


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.


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


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'


(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.


KCONFIG_ALLCONFIG=custom-notebook.config make allnoconfig


KCONFIG_ALLCONFIG=mini.config make allnoconfig


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'


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.


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


y:n split

y:m:n split

unset or empty

50 : 50

33 : 33 : 34


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]


        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'
        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'
        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'


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


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


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".


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).


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


make NCONFIG_MODE=single_menu nconfig


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.


Ctrl-F hotplug


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.


Searching in gconfig:

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