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.

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