yakkety upgrade - 256MB boot partition too small to upgrade when using EFI

[Gordon Ball]

This is related to #1465050.

ubuntu-release-upgrader-core: 1:16.04.16

What I expected to happen: Attempting xenial -> yakkety upgrade, using a previously installed system with the default partitioning scheme, would succeed.

What happened:

With a 256MB /boot [1] partition on a system using EFI (having the normal two kernels [2] with initrd, vmlinuz and vmlinuz.efi.signed), `do-release-upgrade -d` exits warning insufficient space in /boot [3].

Manually working around this is fine, but I suspect this isn't that uncommon a configuration and release-upgrader might need logic to remove the backup kernel to free sufficient space?

[1]:

/dev/sda2 237M 121M 104M 54% /boot
/dev/sda1 511M 3.6M 508M 1% /boot/efi

(this was the install default for xenial beta-1, I think)

[2]:

1.2M abi-4.4.0-31-generic 180K memtest86+.bin
1.2M abi-4.4.0-34-generic 182K memtest86+.elf
187K config-4.4.0-31-generic 182K memtest86+_multiboot.bin
187K config-4.4.0-34-generic 3.8M System.map-4.4.0-31-generic
4.0K efi/ 3.8M System.map-4.4.0-34-generic
1.0K grub/ 6.8M vmlinuz-4.4.0-31-generic
 37M initrd.img-4.4.0-31-generic 6.8M vmlinuz-4.4.0-31-generic.efi.signed
 37M initrd.img-4.4.0-34-generic 6.8M vmlinuz-4.4.0-34-generic
 12K lost+found/ 6.8M vmlinuz-4.4.0-34-generic.efi.signed

[3]:

The upgrade has aborted. The upgrade needs a total of 118 M free
space on disk '/boot'. Please free at least an additional 9,134 k of
disk space on '/boot'. Empty your trash and remove temporary packages
of former installations using 'sudo apt-get clean'.