Kernel is central part of an operating system which act as a bridge between applications and hardware (This enable application to share the hardware effectively).

Every Linux system has a separate small partition for kernel installation, that is called /boot . When you update the system regularly, it will install all the updates including kernel images but it wont remove an old kernels.

After certain time you might have noticed that your /boot partition is running out of disk space which was occupied by lot of old/unused kernels which is kept it back there.

Suggested Read : 6 Methods To Check The Running Linux Kernel Version On System

If the boot partition is full, you can’t perform any upgrade on system level or you can’t even install available kernel too.

Every three months once kernel team releasing new stable kernel which comes with new features, improved hardware & system performance. At least monthly once we will get kernel patch/update from operating system for varies fix. For best practices, I would advice users to install all the updates regularly to make the system up and running without any issue.

We can easily accomplish this on RHEL, CentOS systems by installing system utility called yum-utils package & dnf-plugins-core for Fedora. yum-utils contains package-cleanup binary which allow users to remove the old kernels easily on RHEL & CentOS.

How to install yum-utils package on CentOS/RHEL

yum-utils package is part of yum package manager. It is a collection of utilities and plugins extending and supplementing yum in different ways. Use yum package manager to install yum-utils.

$ sudo yum install yum-utils

Core Plugins for DNF. This package enhances DNF with builddep, config-manager, copr, debuginfo-install, download, needs-restarting, repoquery and reposync commands. Additionally provides generate_completion_cache, noroot and protected_packages passive plugins. Use dnf package manager to install yum-utils.

$ sudo dnf install dnf-plugins-core

Run the following DF (Disk Filesystem) command on terminal to check the /boot partition usage.

$ $ df -h /boot Filesystem Size Used Avail Use% Mounted on /dev/sda1 497M 278M 220M 56% /boot

Check installed kernels

Run the following rpm command on terminal to check an installed Linux kernels.

$ rpm -q kernel kernel-4.9.12-200.fc25.x86_64 kernel-4.10.10-200.fc25.x86_64 kernel-4.10.14-200.fc25.x86_64

Check whether the system is running with latest kernel or not by running uname -a command.

$ uname -a Linux localhost.localdomain 4.10.14-200.fc25.x86_64 #1 SMP Wed May 3 22:52:30 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux

Delete/Remove old kernels in CentOS/RHEL

We have done the pre-validation check and ready to go for old/unused kernel removal. Run the following command to remove old kernels. After executing the below command the system will be left with two kernels (One is running kernel and other one is latest old kernel as a backup).

$ sudo package-cleanup --oldkernels --count=1 Loaded plugins: fastestmirror, langpacks --> Running transaction check ---> Package kernel.x86_64 0:3.10.0-327.el7 will be erased --> Finished Dependency Resolution Dependencies Resolved ================================================================================ Package Arch Version Repository Size ================================================================================ Removing: kernel x86_64 3.10.0-327.el7 @base/$releasever 136 M Transaction Summary ================================================================================ Remove 1 Package Installed size: 136 M Is this ok [y/N]: y Downloading packages: Running transaction check Running transaction test Transaction test succeeded Running transaction Erasing : kernel-3.10.0-327.el7.x86_64 1/1 Verifying : kernel-3.10.0-327.el7.x86_64 1/1 Removed: kernel.x86_64 0:3.10.0-327.el7 Complete!

Details :

package-cleanup : is a command

–oldkernels : Remove old kernel and kernel-devel packages.

–count : Number of duplicate/kernel packages to keep on the system (default 2)

When i try to re-run the command, it’s clearly says there is no old kernels to remove hence we have only two kernels.

$ sudo package-cleanup --oldkernels --count=1 Loaded plugins: fastestmirror, langpacks No old kernels to remove

Delete/Remove old kernels in Fedora

We have done the per-validation check and ready to go for old/unused kernel removal. DNF working straight forward compare with YUM because, if you want to keep two kernels (One is running kernel and other one is latest old kernel as a backup), you have to run the following command.

$ sudo dnf remove $(dnf repoquery --installonly --latest-limit -2 -q) Dependencies resolved. ================================================================================ Package Arch Version Repository Size ================================================================================ Removing: kernel x86_64 4.9.12-200.fc25 @updates 0 kernel-core x86_64 4.9.12-200.fc25 @updates 53 M kernel-debug-devel x86_64 4.9.12-200.fc25 @updates 41 M kernel-modules x86_64 4.9.12-200.fc25 @updates 22 M kernel-modules-extra x86_64 4.9.12-200.fc25 @updates 2.0 M Transaction Summary ================================================================================ Remove 5 Packages Installed size: 118 M Is this ok [y/N]: y Running transaction check Transaction check succeeded. Running transaction test Transaction test succeeded. Running transaction Erasing : kernel-4.9.12-200.fc25.x86_64 1/5 Erasing : kernel-debug-devel-4.9.12-200.fc25.x86_64 2/5 Erasing : kernel-modules-extra-4.9.12-200.fc25.x86_64 3/5 Erasing : kernel-modules-4.9.12-200.fc25.x86_64 4/5 Erasing : kernel-core-4.9.12-200.fc25.x86_64 5/5 Verifying : kernel-modules-4.9.12-200.fc25.x86_64 1/5 Verifying : kernel-core-4.9.12-200.fc25.x86_64 2/5 Verifying : kernel-modules-extra-4.9.12-200.fc25.x86_64 3/5 Verifying : kernel-debug-devel-4.9.12-200.fc25.x86_64 4/5 Verifying : kernel-4.9.12-200.fc25.x86_64 5/5 Removed: kernel.x86_64 4.9.12-200.fc25 kernel-core.x86_64 4.9.12-200.fc25 kernel-debug-devel.x86_64 4.9.12-200.fc25 kernel-modules.x86_64 4.9.12-200.fc25 kernel-modules-extra.x86_64 4.9.12-200.fc25 Complete!

When i try to re-run the command, it’s getting failed hence we have only two kernels.

$ sudo dnf remove $(dnf repoquery --installonly --latest-limit -2 -q) [sudo] password for magi: Error: Need to pass a list of pkgs to remove Mini usage: remove PACKAGE... remove a package or packages from your system alias: erase

Automatically Delete/Remove old kernels in Fedora/CentOS/RHEL

The above method is manual one, which needs to be take care every time. To automate this, just add the kernels count which you want to keep on /etc/yum.conf file.

$ sudo vi /etc/yum.conf installonly_limit=3

From your next update, this will remove all old kernels except latest three which includes live one (One is running kernel and other two is latest old kernels as a backup).