If you install linux kernel by building it yourself, then you cannot manage it via apt. Then if you need to remove old version of linux kernels, then you have to do it manually.
Note that these information bases on Ubuntu 20.04 with grub version 2.04-1ubuntu26.13. Core thing is we cannot just directly edit grub entries at /boot/grub/grub.cfg as it is clearly marked with “DO NOT EDIT THIS FILE”.
The workflow to update grub entries is to edit files in /etc/grub.d and settings from /etc/default/grub then execute command update-grub to make it taken into effect.
Anyway for us, scripts inside /etc/grub.d already took care of automatically detecting newly installed linux kernels placed at /boot if you followed my written steps.
In short, this means after completing manual build steps for linux kernel, we just need to update grub.
Follow these steps
/boot/config-<kernel-version>/boot/initrd.img-<kernel-version>/boot/System.map-<kernel-version>/boot/vmlinuz-<kernel-version>sudo update-grubNow we can test by rebooting the system then inspect the grub entries, or just directly inspect /boot/grub/grub.cfg file. It should be properly updated according to related files we have in /boot directory.
First published on October, 22, 2021
Written by Wasin Thonkaew
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