Comment 140 for bug 798414

"a more helpful error" that the title of this bug report calls for would not free you from the need to remove kernels manually.

I made a script called linux-purge to make it easy to remove extra kernels even in tricky conditions: https://www.bountysource.com/issues/38300038-feature-request-the-command-should-work-like-this (It is designed to handle dependency problems and even problem running out of inodes - that may occur when installing a kernel - when using --fix option.)

As for preventing system from getting full of kernels automatically, unattended-upgrades provides an adequate solution for most cases. You can configure it in Ubuntu 16.04 like this:
Add line

Unattended-Upgrade::Remove-Unused-Dependencies "true";

in /etc/apt/apt.conf.d/50unattended-upgrades

(since unattended-upgrades is enabled by default in 16.04; the configuration acts as if running "apt-get autoremove" periodically.)

The default setting in 16.04 is

Unattended-Upgrade::Remove-New-Unused-Dependencies "true";

but that does not work in some cases (Bug #1624644); the former setting overrides it.

Alternatively, putting "linux-purge --yes --keep 1" as a cron job or alike could do automatic kernel purging, (if no other process has locked dpkg at the time of calling it).
It has some differences to the unattended-upgrades way:
- It works in 12.04 and 14.04, too. (unattended-upgrades cannot remove manually installed kernels that will be around, if user installs kernel using e.g. update-manager; Bug #1439769.)
- The number of kernels to keep is configurable. It keeps the given number of nearest older kernels of each installed kernel update series, e.g. linux-generic and linux-generic-lts-xenial, not necessarily the installed kernels with greatest versions. (You could use --auto-only to keep
manually installed kernels, too, but you probably would not want to use it in 12.04 and 14.04.)
- Current kernel will never be removed. (Bug #1615381)
- It removes configuration files, too. (i.e. it purges)
- It only removes versioned kernel packages whose name start by linux-.