CentOS/RHEL: Removing old unused Linux kernels

After OS updates, old Linux kernels begin to accumulate in the boot partition, taking up extra space. To remove them from the system, follow these steps:

1. Determine the current kernel under which the system is loaded:
uname -a 

Output:
Linux clear-centos8.rc.nbrb.by 4.18.0-80.7.1.el8_0.x86_64 #1 SMP Sat Aug 3 15:14:00 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux

2. Checking available kernels:
rpm -q kernel

Output:
kernel-4.18.0-80.7.1.el8_0.x86_64
kernel-4.18.0-80.el8_0.x86_64

3. Run to clean up "kernel-4.18.0-80.el8_0.x86_64" kernel:
yum remove kernel-4.18.0-80.el8_0.x86_64

4. Remove kernel from grub:
ls /boot/vmlinuz*

Determine which file corresponds to the removed kernel.
vmlinuz-0-rescue-40f768414b694ee0a57971f91b470de0
vmlinuz-4.18.0-80.7.1.el8_0.x86_64
vmlinuz-4.18.0-80.el8.x86_64

In example it's "vmlinuz-4.18.0-80.el8.x86_64".

Run:
grubby --remove-kernel=/boot/vmlinuz-4.18.0-80.el8.x86_64

5. Clear the boot section from the old image and its configuration files:
rm /boot/*-4.18.0-80.el8.x86_64*

In our case, we use the filter according to the kernel version ("-4.18.0-80.el8_0.x86_64").

P.S. There is another less flexible, but faster way to automatically clean old kernels: "yum autoremove kernel".