Comment 4 for bug 2027847

Right so it seems we forgot to bump the size requirements in ubuntu-release-upgrader when bumping them in the installer in bug 1959971, you probably should not have been able to upgrade. Albeit the size it seems is determined from the initramfs that is in /boot.

We also don't seem to acccount for system.map which is about 10MB per kernel

Unfortunately there isn't much else we can do here. You can of course opt to

1) set MODULES=dep in /etc/initramfs-tools/initramfs.conf - this will mean that you can't replace your mainboard or swap your disk into a different machine as the initrd will only include modules relevant to the device the system is running on

2) specify COMPRESS=xz or preferably if available a higher COMPRESSLEVEL=1 in the same file such that compression is higher.

I don't know why your initramfs are that big, presumably you are using nvidia gpus? With 3 kernels on my /boot and no out-of-kernel drivers I use 438MB.