General¶

New kernel releases often introduce new config symbols. Often moreimportant, new kernel releases may rename config symbols. Whenthis happens, using a previously working .config file and running“make oldconfig” won’t necessarily produce a working new kernelfor you, so you may find that you need to see what NEW kernelsymbols have been introduced.

To see a list of new config symbols, use:

cp user/some/old.config .configmake listnewconfig

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

Alternatively, you can use the brute force method:

make oldconfigscripts/diffconfig .config.old .config | less

Environment variables¶

Environment variables for*config:

KCONFIG_CONFIG

This environment variable can be used to specify a default kernel configfile name to override the default name of “.config”.

KCONFIG_DEFCONFIG_LIST

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

KCONFIG_OVERWRITECONFIG

If you set KCONFIG_OVERWRITECONFIG in the environment, Kconfig will notbreak symlinks when .config is a symlink to somewhere else.

KCONFIG_WARN_UNKNOWN_SYMBOLS

This environment variable makes Kconfig warn about all unrecognizedsymbols in the config input.

KCONFIG_WERROR

If set, Kconfig treats warnings as errors.

CONFIG_

If you setCONFIG_ in the environment, Kconfig will prefix all symbolswith its value when saving the configuration, instead of using thedefault,CONFIG_.

Environment variables for{allyes/allmod/allno/alldef/rand}config:

KCONFIG_ALLCONFIG

The allyesconfig/allmodconfig/alldefconfig/allnoconfig/randconfig variantscan also use the environment variable KCONFIG_ALLCONFIG as a flag or afilename that contains config symbols that the user requires to be set to aspecific value. If KCONFIG_ALLCONFIG is used without a filename whereKCONFIG_ALLCONFIG == “” or KCONFIG_ALLCONFIG == “1”,make*configchecks for a file named “all{yes/mod/no/def/random}.config”(corresponding to the*config command that was used) for symbol valuesthat are to be forced. If this file is not found, it checks for afile named “all.config” to contain forced values.

This enables you to create “miniature” config (miniconfig) or customconfig files containing just the config symbols that you are interestedin. Then the kernel config system generates the full .config file,including symbols of your miniconfig file.

ThisKCONFIG_ALLCONFIG file is a config file which contains(usually a subset of all) preset config symbols. These variablesettings 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 ordisable the options that are explicitly listed in the specifiedmini-config files.

Environment variables forrandconfig:

KCONFIG_SEED

You can set this to the integer value used to seed the RNG, if you wantto 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 canbe 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 sothat:

[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 forsyncconfig:

KCONFIG_NOSILENTUPDATE

If this variable has a non-blank value, it prevents silent kernelconfig 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 in menuconfig:

The Search function searches for kernel configuration symbolnames, so you have to know something close to what you arelooking for.

Example:

/hotplugThis 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 useregular expressions (regexes) in the search string, so if youare not interested in MEMORY_HOTPLUG, you could try:

/^hotplug

When searching, symbols are sorted thus:

• first, exact matches, sorted alphabetically (an exact matchis 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 sortedfirst (and in alphabetical order), then come all other symbols,sorted in alphabetical order.

In this menu, pressing the key in the (#) prefix will jumpdirectly to that location. You will be returned to the currentsearch results after exiting this new menu.

User interface options for ‘menuconfig’:

MENUCONFIG_COLOR

It is possible to select different color themes using the variableMENUCONFIG_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 functionkeys across the bottom of the terminal (window) that execute commands.You can also just use the corresponding numeric key to execute thecommands unless you are in a data entry window. E.g., instead of F6for 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” stringsor in the configuration symbols.

Use / to begin a search through the menu entries. This doesnot support regular expressions. Use <Down> or <Up> forNext hit and Previous hit, respectively. Use <Esc> toterminate the search mode.

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

In the SymSearch, pressing the key in the (#) prefix willjump directly to that location. You will be returned to thecurrent search results after exiting this new menu.

Environment variables:

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 symbolnames, so you have to know something close to what you arelooking for.

Example:

Ctrl-F hotplug

or:

Menu: File, Search, hotplug

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

gconfig¶

Searching in gconfig:

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