Remove Old Kernels In Ubuntu With One Command

A while back I wrote a post on how to remove old kernels from your Ubuntu system. While that process works just fine, it is a four step process. One person who read that post left a comment with a nice command line one-liner that removes all but the currently running kernel. And whilethat one-liner works quite well, I must admit that I don't understand all the regular expressions used in it, so I decided to try and come up with my own one-liner to remove the old kernels from my system.

I'm going to take you through this step by step so you can see how the individual commands in this one-liner tie together. If you're impatient, you canskip to the end to see the final command.

Step 1) List all packages that start with "linux-"

We'll use the dpkg command with the -l switch to list the packages, whether installed or not, that start with the stringlinux-.

dpkg -l linux-*

Step 2) Filter that list to show only installed packages

To filter the list, I'm going to pipeline the output of the first command into theawk command. I'm also going to useawk to filter out everything but the package names.

dpkg -l linux-* | awk '/^ii/{ print $2 }'

Step 3) Filter out packages for the currently running kernel

OK, so now I'm down to a pretty limited number of packages, but I don't want to remove the packages for my currently running kernel. I'm going to use a few commands to do that. First off, I can determine my currently running kernel with theuname -r command. Currently on my system that command outputs:2.6.32-25-generic.

To do my package filtering, I only want the numeric portion of that output. I'll pipeline the output ofuname -r and use thecut command with a hyphen as the field delimiter. I'll cut fields 1 & 2.

uname -r | cut -f1,2 -d"-"

Now I'm going to use this result as the filter for a grep command. In Linux, to use the result of one command as an argument in another command, you enclose the command in single back-quotes ( ` that's the key to the left of the 1 on a standard US keyboard). So here's my one-liner so far.

dpkg -l linux-* | awk '/^ii/{ print $2}' | grep -v -e `uname -r | cut -f1,2 -d"-"`

This is the output so far on my system:

linux-firmware
linux-generic
linux-headers-2.6.32-24
linux-headers-2.6.32-24-generic
linux-headers-generic
linux-image-2.6.32-24-generic
linux-image-generic
linux-libc-dev
linux-sound-base

Step 4) Filter the list for only the kernel packages

So now I have a package list that excludes the packages for my current kernel. The only packages from the list above that I want to remove are:linux-headers-2.6.32-24, linux-headers-2.6.32-24-generic, linux-image-2.6.32-24-generic.

What makes these packages unique from the others in the list is that they all contain numbers. So I can usegrep again to filter the list down to only packages with numbers in their names. I'll pipeline the output of the previous command intogrep -e [0-9].

dpkg -l linux-* | awk '/^ii/{ print $2}' | grep -v -e `uname -r | cut -f1,2 -d"-"` | grep -e [0-9]

So now the output on my system is only the following:

linux-headers-2.6.32-24
linux-headers-2.6.32-24-generic
linux-image-2.6.32-24-generic

Step 5) Make sure we don't catch any stray packages

Some people have had problems with this one-liner catching the linux-libc-dev:amd64 package. Adding a

grep -E "(image|headers)"

to the string fixes the problem. Now we have

dpkg -l linux-* | awk '/^ii/{ print $2}' | grep -v -e `uname -r | cut -f1,2 -d"-"` | grep -e [0-9] | grep -E "(image|headers)"

Step 6) Putting it all together: Removing the packages

So now that I have a good list of packages I can use another pipe and the xargs command to invoke apt-get to remove the packages. First I'm going to show it using the--dry-run switch withapt-get. That way you can give it a try without actually changing your system.

dpkg -l linux-* | awk '/^ii/{ print $2}' | grep -v -e `uname -r | cut -f1,2 -d"-"` | grep -e [0-9] | grep -E "(image|headers)" | xargs sudo apt-get --dry-run remove

For aptitude, use
 dpkg -l linux-* | awk '/^ii/{ print $2}' | grep -v -e `uname -r | cut -f1,2 -d"-"` | grep -e [0-9] | grep -E "(image|headers)" | xargs sudo aptitude --simulate purge

If everything looks good after the dry run, you can go ahead and remove the old kernels with:

dpkg -l linux-* | awk '/^ii/{ print $2}' | grep -v -e `uname -r | cut -f1,2 -d"-"` | grep -e [0-9] | grep -E "(image|headers)" | xargs sudo apt-get -y purge

For aptitude, use
 dpkg -l linux-* | awk '/^ii/{ print $2}' | grep -v -e `uname -r | cut -f1,2 -d"-"` | grep -e [0-9] | grep -E "(image|headers)" | xargs sudo aptitude  -y purge

So there you have it. One command, albeit a long one, to remove the old kernels from your Ubuntu system. I imagine the same command should work on other Debian based systems as well, but I've only tested this on my 32 bit system. I'd be interested to know if it works just as well on a 64 bit system.

Update: It works just fine on 64 bit systems as well.

http://tuxtweaks.com/2010/10/remove-old-kernels-in-ubuntu-with-one-command/