make oldconfig takes the .config and runs it through the rules of the Kconfig files and produces a .config file which is consistent with the Kconfig rules. $ grep CONFIG_DOES_NOT_EXIST .config $ ./scripts/config --enable CONFIG_DOES_NOT_EXIST $ grep CONFIG_DOES_NOT_EXIST .config CONFIG_DOES_NOT_EXIST=y $ make oldconfig # # configuration written to .config # $ grep CONFIG_DOES_NOT_EXIST .config
make olddefconfig is similar to make oldconfig, but sets new config symbols to their default values without prompting.