remove old debian kernels

source in #proxmox@irc.freenode.net

peetaur2> ssm2017: I wrote a script that cleans it up... debian and ubuntu always has that problem. Also I think newer ubuntu has a package to do it.
[2016-09-06 14:14:40]  ssm2017: you can simply rm the files in /boot that are for kernels you don't care about, then use apt-get to remove them properly
[2016-09-06 14:16:54]  FYI here's my script which you may test and use... maybe don't run without testing :)  https://bpaste.net/show/2a1351e92ed9 

#!/usr/bin/env bash

current=$(uname -r | grep -Eo "[0-9][0-9\.-]+[0-9]")
latest=$(dpkg -l linux-image* | awk '$1=="ii"{print $2}' | grep -Eo "[0-9][0-9\.-]+[0-9]" | sort -u | tail -n1)

# remove all kernels except the currently booted one, and the latest one
apt-get purge -y $(dpkg -l 'linux-image*' | grep -E "linux-image-[0-9\.-]+" | awk '$1 == "ii" {print $2}' | grep -vE "$current|$latest")

# remove all kernel headers packages except the currently booted one, and the latest one
apt-get purge -y $(dpkg -l 'linux-headers*' | grep -E "linux-headers-[0-9\.-]+" | awk '$1 == "ii" {print $2}' | grep -vE "$current|$latest")

apt-get remove $(dpkg -l | egrep  '^ii  (pve-)?kernel-' | awk '{print $2}' | grep -v `uname -r`)