The Linux kernel is highly configurable; advanced users may wish to modify the default configuration to customise it to their needs, such as enabling a new or experimental network protocol, or enabling support for new hardware.
Configuration is most commonly done through the make menuconfig interface. Alternatively, you can modify your .config file manually, but this can be more difficult for new users.
The menuconfig tool requires the ncurses development headers to compile properly. These can be installed with the following command:
$ sudo apt install libncurses5-dev
You'll also need to download and prepare your kernel sources, as described in the build guide. In particular, ensure you have installed the default configuration.
Once you've got everything set up and ready to go, you can compile and run the menuconfig utility as follows:
$ make menuconfig
If you're cross-compiling a 32-bit kernel:
make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- menuconfig
Or, if you are cross-compiling a 64-bit kernel:
make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- menuconfig
The menuconfig utility has simple keyboard navigation. After a brief compilation, you'll be presented with a list of submenus containing all the options you can configure; there's a lot, so take your time to read through them and get acquainted.
Use the arrow keys to navigate, the Enter key to enter a submenu (indicated by --->), Escape twice to go up a level or exit, and the space bar to cycle the state of an option. Some options have multiple choices, in which case they'll appear as a submenu and the Enter key will select an option. You can press h on most entries to get help about that specific option or menu.
Resist the temptation to enable or disable a lot of things on your first attempt; it's relatively easy to break your configuration, so start small and get comfortable with the configuration and build process.
Once you're done making the changes you want, press Escape until you're prompted to save your new configuration. By default, this will save to the .config file. You can save and load configurations by copying this file around.