How to Delete Old Unused Kernels in CentOS, RHEL and Fedora?

Kernel management is a crucial system administration task in CentOS, RHEL, and Fedora. When you install kernel updates, the old versions are kept as a safety measure, but over time these can accumulate and consume valuable disk space, potentially causing boot issues or system slowdowns.

Removing old unused kernels frees up disk space, reduces boot menu clutter, and eliminates potential security vulnerabilities in outdated kernel versions. However, it's important to always keep at least one or two recent kernels as backup in case the current kernel encounters issues.

Checking the Current Kernel Version

Before removing any kernels, you need to identify which kernel version is currently running. Use the uname command to check your current kernel ?

uname -r

This displays output similar to ?

3.10.0-1160.el7.x86_64

The kernel version format consists of ?

• Major.Minor.Patch (3.10.0) The upstream kernel version

• Build number (1160) Distribution-specific build

• Distribution tag (el7) Indicates the distribution version

• Architecture (x86_64) The processor architecture

Listing Installed Kernels

To view all installed kernel packages on your system, use the RPM package manager ?

rpm -qa kernel

This produces output showing all installed kernels ?

kernel-4.18.0-348.el8.x86_64
kernel-4.18.0-305.el8.x86_64
kernel-4.18.0-240.el8.x86_64

You can also use rpm -qa | grep kernel to see all kernel-related packages including headers and development packages.

Removing Old Kernels

Manual Removal Method

To remove a specific old kernel, use the appropriate package manager for your distribution ?

CentOS/RHEL 7 and earlier ?

sudo yum remove kernel-4.18.0-240.el8.x86_64

CentOS/RHEL 8+ and Fedora ?

sudo dnf remove kernel-4.18.0-240.el8.x86_64

Automated Cleanup

For easier management, you can configure automatic kernel cleanup. On CentOS/RHEL 8+ and Fedora, set the number of kernels to keep ?

sudo dnf install dnf-utils
sudo package-cleanup --oldkernels --count=2

To make this permanent, edit /etc/dnf/dnf.conf and add ?

installonly_limit=3

Using YUM/DNF Remove Old Kernels Plugin

On older systems, you can use the package-cleanup tool ?

sudo yum install yum-utils
sudo package-cleanup --oldkernels --count=2

Important Precautions

• Never remove the currently running kernel Always verify with uname -r first

• Keep at least 2-3 recent kernels This provides fallback options if issues occur

• Test boot after removal Ensure your system can still boot properly

• Backup important data Always maintain current backups before kernel operations

Verifying Successful Removal

After removing old kernels, verify the cleanup was successful ?

rpm -qa kernel
df -h /boot

Check your bootloader configuration to ensure removed kernels are no longer listed ?

sudo grub2-mkconfig -o /boot/grub2/grub.cfg

Distribution-Specific Examples

Conclusion

Regular kernel cleanup is essential for maintaining system health and freeing up disk space in /boot. Always keep multiple kernel versions for recovery purposes and use automated cleanup tools to streamline the process. Proper kernel management ensures your system remains secure, stable, and efficient.