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 while that 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 can skip 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 string 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 the awk command. I'm also going to use awk to filter out everything but the package names.
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 the uname -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 of uname -r and use the cut command with a hyphen as the field delimiter. I'll cut fields 1 & 2.
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.
This is the output so far on my system:
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 use grep again to filter the list down to only packages with numbers in their names. I'll pipeline the output of the previous command into grep -e [0-9].
So now the output on my system is only the following:
Step 5) 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 with apt-get. That way you can give it a try without actually changing your system.
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.