On some of our servers, the /boot partition get’s 100% full and then things like yum updates stop working.

Instead of attempting a dangerous and complicated manoeuvre to resize the (boot!) partition we can just take the following steps to stop the /boot partition from filling up in the first place:

Delete all old kernel versions

# dnf remove --oldinstallonly

Then edit the yum conf:

# vi /etc/yum.conf

Update the install limit to 2:

[main]
gpgcheck=1
installonly_limit=2
clean_requirements_on_remove=True
best=True
skip_if_unavailable=False