These were taken from this source.

My one-liner to remove old kernels (this also frees up disk space)

dpkg --list | grep linux-image | awk '{ print $2 }' | sort -V | sed -n '/'`uname -r`'/q;p' | xargs sudo apt-get -y purge

Explanation (remember, | uses the output of the previous command as the input to the next)

  • dpkg –list lists all installed packages
  • grep linux-image looks for the installed linux images
  • awk '{ print $2 }' just outputs the 2nd column (which is the package name)
  • sort -V puts the items in order by version number
  • sed -n '/'`uname -r`'/q;p prints the lines before the current kernel
  • xargs sudo apt-get -y purge purges the found kernels

Unwinding the sed invocation:

  • -n tells sed to be quiet

  • uname -r outputs the current installed kernel release - we include it in backticks so that the output is includes as part of the command (you might also see this as $(uname -r)

  • /something/q says stop when you match ‘something’ (in this case, something is output of uname -r) - the / surround a regular expression

  • p is print

  • the ; is the command separtor, so /something/q;p says quit when you match something, else print

  • altogether, sed -n '/'`uname -r`'/q;p' is print the lines until it matches with the current kernel name.

If you’re paranoid (like me), you can make the last part xargs echo sudo apt-get -y purge so that the command to purge the old kernels is printed, then you can check that nothing unexpected is included before you run it.

Modified version to remove headers:

dpkg --list | grep 'linux-image' | awk '{ print $2 }' | sort -V | sed -n '/'"$(uname -r | sed "s/\([0-9.-]*\)-\([^0-9]\+\)/\1/")"'/q;p' | xargs sudo apt-get -y purge

dpkg --list | grep 'linux-headers' | awk '{ print $2 }' | sort -V | sed -n '/'"$(uname -r | sed "s/\([0-9.-]*\)-\([^0-9]\+\)/\1/")"'/q;p' | xargs sudo apt-get -y purge

Note: the sed invocation is modified.

	$(uname -r | sed "s/\([0-9.-]*\)-\([^0-9]\+\)/\1/")

extracts only the version (e.g. “3.2.0-44”) , without “-generic” or similar from uname -r

All-in-one version to remove images and headers (combines the two versions above):

echo $(dpkg --list | grep linux-image | awk '{ print $2 }' | sort -V | sed -n '/'`uname -r`'/q;p') $(dpkg --list | grep linux-headers | awk '{ print $2 }' | sort -V | sed -n '/'"$(uname -r | sed "s/\([0-9.-]*\)-\([^0-9]\+\)/\1/")"'/q;p') | xargs sudo apt-get -y purge