I think the patch presented at https://bugs.launchpad.net/ubuntu/+source/initramfs-tools/+bug/1678187/comments/8
might give more helpful error message, since it avoids filling /boot as long as possible, thus the system is unlikely to run out of space while running mkinitramfs, but finds out, if the system lacks free space, and if it does, it tells the URL of the documentation page concerning removing old kernels.
I think the patch presented at https:/ /bugs.launchpad .net/ubuntu/ +source/ initramfs- tools/+ bug/1678187/ comments/ 8
might give more helpful error message, since it avoids filling /boot as long as possible, thus the system is unlikely to run out of space while running mkinitramfs, but finds out, if the system lacks free space, and if it does, it tells the URL of the documentation page concerning removing old kernels.
P.S. The URL could be https:/ /help.ubuntu. com/community/ LowDiskOnBoot alternatively. (Luke W Faraone uses that in his merge proposal, and it redirects to the same document currently.)