How to remove old kernels on RHEL/CentOS

If your /boot partition is running out of disk space this is probably because you got bunch of old Linux kernels that got stockpiled there and are no longer in use or needed for system to function normally. If you’re running a WHM/cPanel you’ll get an email with subject:  DISKWARN blocks: Mount Point “/boot” 

Usually on a system update, if there is a new Linux Kernel it will get downloaded and initialized while the last one will be kept for just in case the first one fails for any reason. In couple of months or years you could already have 5-6 of them while only the latest Linux kernel would be in use and the previous one will be kept as  a backup. Removing these by hand is possible but an mistake could end up with a system that won’t boot.

To prevent that and free up disk space at /boot partition on Red Hat Linux or CentOS Linux all you need to do is simply to execute this command:

sudo yum install yum-utils && sudo package-cleanup --oldkernels --count=2

This will remove all your old kernels keeping just the last two (latest one and the previous one just in case) so you won’t get these emails or notifications anymore and you’ll keep your /boot partition with enough free space for a new kernel to be installed once released.