Comment 0 for bug 1988299

I'm attempting to upgrade from 20.04 to 22.04 and my installation uses full disk encryption, so I have a separate partition for /boot.

The size of the /boot partition was set by the installer for 22.04 (to 704 MiB) and I currently have 329 MiB free after removing old kernels with apt autoremove:

  $ df -h /boot
  Filesystem Size Used Avail Use% Mounted on
  /dev/sdb2 704M 324M 329M 50% /boot

When attempting to upgrade to 22.04 it fails with:

  The upgrade has aborted. The upgrade needs a total of 787 M free
  space on disk '/boot'. Please free at least an additional 442 M of
  disk space on '/boot'. You can remove old kernels using 'sudo apt
  autoremove' and you could also set COMPRESS=xz in
  /etc/initramfs-tools/initramfs.conf to reduce the size of your
  initramfs.

So it claims to need more space than the total size of the partition (so presumably no amount of compressing initramfs will be enough!), which as noted above is the default size for /boot chosen by the 20.04 installer.

Another instance of this issue has been raised here: https://askubuntu.com/q/1423156/57751