How to: Linux delete or remove kernel

I have multiple Linux kernel versions installed, and I need to save disk space. I am using CentOS Linux. How can I delete or remove a Linux kernel from my Linux distribution?

Linux Kernel and related files are stored in the following locations on your Linux distro:

1. /boot – Stores actual kernel and related file such system man and initrd images.
2. /etc or /boot/grub – Stores grub.conf file (most distro use /boot/grub these days).
3. /lib/modules/KERNEL-VERSION/* (/lib/modules/$(uname -r))- Linux device drivers (modules)

If the Linux kernel is installed using a binary package system such as rpm, yum, up2date, apt-get, etc., you can remove it with the following commands.

WARNING! Make sure you only remove or delete the unwanted Linux kernel. Removing the currently running Linux kernel will create a non-bootable system. Check Linux Kernel Version by tying the following command:
uname -r

Rpm based distro – Red Hat/CentOS/Fedora Core/Suse Linux

First, find out all installed kernel version with the following commands:
# rpm -qa | grep kernel-smp
# rpm -qa | grep kernel
# Use grep command/egrep command to filter out results #
# rpm -qa | grep kernel-[0-9]
Here is what I see before I delete or remove the installed Linux kernel on my system:

kernel-smp-2.6.9-42.EL
kernel-smp-2.6.9-42.0.3.EL
kernel-smp-2.6.9-42.0.8.EL

I have a total of three different kernels installed. To remove kernel-smp-2.6.9-42.EL type the rpm command:
# rpm -e kernel-smp-2.6.9-42.EL
OR
# rpm -vv -e kernel-smp-2.6.9-42.EL

Deleting or removing RHEL 8 Linux kernel

These days we use the yum command/dnf command to list installed kernels and delele them directly:
sudo dnf list --installed kernel
# get the current kernel version #
uname -r
# note down disk space using the df command #
df -H /
df -H
Now let us delete the Linux kernel version 4.18.0-240.10.1.el8_3:
sudo dnf remove kernel-4.18.0-240.10.1.el8_3.x86_64

Please note that you also need to remove kernel-headers, kernel-core-VERSION, and kernel-modules-VERSION packages too. For example, :
$ sudo dnf remove kernel-modules-4.18.0-240.10.1 \
kernel-core-4.18.0-240.10.1
I am keeping kernel-headers package as I need to compile other modules.

.deb based distro – Debian or Ubuntu Linux

Again find out all installed kernel version on your Debian or Ubuntu Linux system, run the dpkg command:
$ dpkg --list | grep kernel-image
# latest version of Debian/Ubuntu uses linux-image pkg #
$ dpkg --list | grep linux-image
Outputs from my Debian system:

ii  kernel-image-2.4.27-2-386   2.4.27-10sarge1             Linux kernel image for version 2.4.27 on 386
ii  kernel-image-2.6.8-2-686    2.6.8-16sarge1              Linux kernel image for version 2.6.8 on PPro

Now remove kernel-image-2.4.27-2-386 with the help of the apt-get command or apt command itself:
# apt-get remove kernel-image-2.4.27-2-386
OR
$ sudo apt-get remove kernel-image-2.4.27-2-386
Apart from the kernel-image or linux-image, you need to remove and delete headers and module packages too. For instance, here are packages releated to Linux kernel 5.4.0-25 on my Ubuntu Linux 20.04 LTS desktop:
$ dpkg --list | grep 5.4.0-25
List:

ii  linux-headers-5.4.0-25                     5.4.0-25.29                           all          Header files related to Linux kernel version 5.4.0
ii  linux-headers-5.4.0-25-generic             5.4.0-25.29                           amd64        Linux kernel headers for version 5.4.0 on 64 bit x86 SMP
ii  linux-image-5.4.0-25-generic               5.4.0-25.29                           amd64        Signed kernel image generic
ii  linux-modules-5.4.0-25-generic             5.4.0-25.29                           amd64        Linux kernel extra modules for version 5.4.0 on 64 bit x86 SMP

In other words, eliminate all those four packages:
$ sudo apt --purge remove linux-headers-5.4.0-25 \
linux-headers-5.4.0-25-generic \
linux-image-5.4.0-25-generic \
linux-modules-5.4.0-25-generic
See the following pages for more info:

• Ubuntu 18.04 remove all unused old kernels
• Debian / Ubuntu Linux Delete Old Kernel Images Command

A note about custom compiled Linux kernel

If you have a custom compiled Linux kernel running, you need to remove the following files/dirs:

• /boot/vmlinuz*KERNEL-VERSION*
• /boot/initrd*KERNEL-VERSION*
• /boot/System-map*KERNEL-VERSION*
• /boot/config-*KERNEL-VERSION*
• /lib/modules/*KERNEL-VERSION*/
• Update grub configuration file /etc/grub.conf or /boot/grub/menu.lst to point to correct kernel version.

Summing up

Removing the working Linux kernel may result in an unstable/non- bootable Linux server system. Hence, care must be taken while removing the older Linux kernel. Apart from disk space-saving, you can get rid of the vulnerable Linux kernel from the system to improve the system’s stability and security.

Category	List of Unix and Linux commands
File Management	cat
Firewall	Alpine Awall • CentOS 8 • OpenSUSE • RHEL 8 • Ubuntu 16.04 • Ubuntu 18.04 • Ubuntu 20.04
Network Utilities	dig • host • ip • nmap
OpenVPN	CentOS 7 • CentOS 8 • Debian 10 • Debian 8/9 • Ubuntu 18.04 • Ubuntu 20.04
Package Manager	apk • apt
Processes Management	bg • chroot • cron • disown • fg • jobs • killall • kill • pidof • pstree • pwdx • time
Searching	grep • whereis • which
User Information	groups • id • lastcomm • last • lid/libuser-lid • logname • members • users • whoami • who • w
WireGuard VPN	Alpine • CentOS 8 • Debian 10 • Firewall • Ubuntu 20.04