====== Ubuntu - Packages - Removed Unused Kernels ======

Ubuntu does not remove kernels when they install a new one, however the /boot partition is usually relatively small.

So after only a few kernel upgrades, you can get **No Space Left On Device** errors when trying to upgrade. 

To determine which kernels can be removed run the following:

<code bash>
sudo dpkg --get-selections | grep 'linux-image.*-[0-9].*' | awk '{print $1}' | egrep -v "$(uname -r)"| while read n; do echo $n; done
</code>

To delete all these old kernels run the following.

<WRAP info>
**NOTE**:  This will only keep the very latest kernel and will delete all others, so may not be what you want:
</WRAP>


<code bash>
sudo dpkg --get-selections | grep 'linux-image.*-[0-9].*' | awk '{print $1}' | egrep -v "$(uname -r)"| while read n; do apt-get -y remove $n; done
</code>

----

===== Another Method =====

Either remove them manually, or use this one liner to automatically remove them all.

<code bash>
export KERNEL="$(uname -r | grep -Po '([0-9\.\-]*[0-9])?')"; dpkg --get-selections | grep -E "linux-(header|image).*" | grep -iw install | sort | grep -v "$KERNEL" | grep -v "lts" | sed 's/install//g' | xargs dpkg -P
</code>

Here's the command by command explanation:

<code>
export KERNEL="$(uname -r | grep -Po '([0-9\.\-]*[0-9])?')"
</code>

The first portion sets the current kernel number in a variable KERNEL.  It only takes the number, and greps out any additions like -generic or -server.

<code bash>
sudo dpkg --get-selections 
</code>

The second portion first prints out all available packages.

<code bash>
grep -E "linux-(header|image).*"
</code>

The third portion greps for all packages with either linux-header or linux-image in the name.

<code bash>
grep -iw install
</code>

The fourth portion greps out only installed packages.

<code bash>
sort
</code>

The fifth portion sorts the output.

<code bash>
grep -v "$KERNEL" | grep -v "lts"
</code>

The sixth portion filters out the current kernel and the LTS kernel package.  Removing those will cause problems.

<code bash>
sed 's/install//g'
</code>

The seventh part strips off the install part.

<code bash>
xargs dpkg -P
</code>

The last part actually removes the packages.  **xargs** send all the package names to **dpkg**.  Then **dpkg -P** purges the packages.  That means, removing them and removing their configs.