Remove Old Kernels

When Ubuntu upgrades the kernel, a new version is installed alongside the old one. At the grub boot prompt, you can select which kernel to use.

That's great if for some reason a new kernel doesn't work as well as an old one, but there's not much use for keeping old kernels around forever. Since Ubuntu doesn't yet automatically offer obsolete kernels for uninstallation, I wrote a one-liner to remove old kernels:

sudo apt-get remove --purge `dpkg --get-selections 'linux-*.*' | awk '$2 == "install" { print $1 }' | grep -v "$(uname -r | sed 's/\(.*\)-.*/\1/')"`

Since Linux kernels can take up a lot of disk space, you should regularly clean up your system to free space by manually running the one-liner after upgrading your kernel and rebooting. Make sure that you rebooted into your new kernel once a kernel upgrade has been installed, otherwise you'd remove the new kernel instead of the old one which most likely isn't what you want.