Building the Ubuntu kernel: fakeroot debian/rules

Before submitting any patch, make sure it builds inside the devel chroot (e.g. Lunar):

$ schroot -c lunar-amd64
(lunar-amd64)$ fakeroot debian/rules clean
(lunar-amd64)$ debian/rules build
# building takes some time, be patient
(lunar-amd64)$ fakeroot debian/rules binary

Depending on your build box resources (cpus, memory, disk, etc) the process could take minutes or hours, be patient.

If the build is successful, a set of .deb binary packages will be present in the parent directory: you can install these (sudo dpkg -i linux-generic-...deb linux-modules-...deb) to test the resulting kernel.

Cross compilation

Cross compiling is a matter of setting the target dpkg-architecture before starting the build (e.g. to cross-compile an arm64 kernel):

$ schroot -c lunar-amd64
(lunar-amd64)$ export $(dpkg-architecture -aarm64)
(lunar-amd64)$ fakeroot debian/rules clean
(lunar-amd64)$ debian/rules build
# build time...
(lunar-amd64)$ fakeroot debian/rules binary

These are the available dpkg-architecture targets, and the corresponding Kbuild vars:

Target architecture	ARCH	CROSS_COMPILE	dpkg-architecture
arm64	arm64	aarch64-linux-gnu-	arm64
armhf	arm	aarch64-linux-gnu-	armhf
ppc64el	powerpc	aarch64-linux-gnu-	ppc64el
riscv64	riscv	aarch64-linux-gnu-	riscv64
s390x	s390x	aarch64-linux-gnu-	s390x