In most cases, it isn't -- running apt-get autoremove
should identify and remove old packages (including old kernels).
Ubuntu's package manager has to read from and write to the /boot
directory in order to autoremove old kernels, and if there is insufficient space to do this, the package manager will fail with rather cryptic error messages.
The sure fire remedy is to carefully find and remove the old kernels by hand and then update the boot loader, as explained in this Stack Exchange post.
Instead, you can run the included python script (requires root or sudo permission). By default, it will short circuit unless the /boot
directory is 75% or more full:
root@localhost# ./purge-kernels.py
$ df -k /boot
$ du -ks /boot
Boot partition is only 74% full
You can override this by passing a minimum percentage as an argument:
root@localhost# ./purge-kernels.py 50
$ df -k /boot
$ du -ks /boot
$ dpkg --list "linux-image*"
$ uname -r
Found: 3.13.0-57
Found: 3.13.0-58
Found: 3.13.0-59
$ ls -1 /boot/*-3.13.0-57-*
Removing:
/boot/abi-3.13.0-57-generic
/boot/config-3.13.0-57-generic
/boot/initrd.img-3.13.0-57-generic
/boot/System.map-3.13.0-57-generic
/boot/vmlinuz-3.13.0-57-generic
$ rm -rf /boot/*-3.13.0-57-*
$ update-grub