Removing old kernel

When upgrading ubuntu, sometimes it failed because of insufficient disk on boot. This could be caused by too many kernel installed on the machine.

Command to remove old kernel from here

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

dpkg –list | grep linux-image | awk ‘{ print $2 }’ | sort -V | sed -n ‘/'uname -r'/q;p’ | xargs sudo apt-get -y purgenation (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.