How to build and install the kernel

 Sources:

• https://wiki.ubuntu.com/Kernel/BuildYourOwnKernel#apt-get
• https://www.maketecheasier.com/build-custom-kernel-ubuntu/
• https://stackoverflow.com/a/75622441

The algorithm:

1. Make source directory (I have named it 'lab') and go there: `mkdir ~/lab; cd ~/lab` 
2. Download linux sources of your distributes: `apt-get source linux-image-unsigned-$(uname -r)`
3. Download linux sources from git repository: `git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git`
4. Go to the Linus' source directory: `cd ~/lab/linux`
5. Copy your distribution's config: `cp /boot/config-$(uname -r) .config`
6. Apply the config: `make olddefconfig`
7. Copy a directory of your distribution's source in order to sign your build: `cp -avr ~/lab/linux-hwe-5.15-5.15.0/debian ~/lab/linux/debian`
8. Build the kernel: `make clean && make -j8`
9. Build deb-package: `make deb-pkg LOCALVERSION=-custom`
10. Install deb-packages: `sudo dpkg -i ~/lab/linux-*.deb`
11. Reboot your system with a new kernel =)