How to Safely Remove old kernels in CentOS, RHEL and Fedora

Introduction

Learn how to safely remove old kernels on CentOS, RHEL, and Fedora to free up space and improve system performance. Step-by-step guide with best practices for maintaining your Linux system.

As you continue to update and upgrade your Linux system, particularly on distributions like CentOS, RHEL, and Fedora, old kernels can accumulate over time. While these kernels are essential for booting your system, having too many can clutter your boot menu and consume valuable disk space. This guide will walk you through the process of safely removing old kernels from your system without risking stability, ensuring that your Linux machine runs smoothly and efficiently.

Why Should You Remove Old Kernels?

The Problem with Accumulating Kernels

Linux kernels are the core of the operating system, responsible for managing hardware and system processes. Every time you update your system, a new kernel may be installed, but the old ones aren't automatically removed. This can lead to several issues:

• Disk Space Consumption: Old kernels can take up significant disk space, which could be used for other important data or applications.
• Cluttered Boot Menu: With multiple kernels installed, your boot menu becomes crowded, making it harder to select the correct version.
• System Maintenance: Regular system maintenance, including removing old kernels, keeps your system optimized and free of unnecessary files.

When is it Safe to Remove Old Kernels?

It's generally safe to remove old kernels as long as you keep the current one and one previous version as a fallback. The current kernel is usually the one your system is running on, and having one older kernel ensures that you have a backup in case something goes wrong with the latest version.

How to Check Installed Kernels on CentOS, RHEL, and Fedora

Before removing any kernels, it's important to know which ones are currently installed on your system. You can do this by using the following command in your terminal:

rpm -q kernel

This command will list all the installed kernels on your system. The output will look something like this:

kernel-3.10.0-693.el7.x86_64
kernel-3.10.0-862.el7.x86_64
kernel-3.10.0-957.el7.x86_64

The highest number represents the most recent kernel, while the lower numbers represent older versions.

Removing Old Kernels Using Package Manager

Automatic Removal with Yum/DNF

CentOS, RHEL, and Fedora use package managers like Yum or DNF, which can automatically remove old kernels. To remove old kernels and keep only the latest two, you can use the following command:

sudo package-cleanup --oldkernels --count=2

This command keeps the latest two kernels (including the one currently in use) and removes the rest. It's a safe and efficient way to manage your kernels.

Manual Removal of Specific Kernels

If you prefer to manually remove specific kernels, you can do so by using the yum or dnf commands, depending on your distribution. First, identify the kernel you want to remove, then execute the following command:

sudo yum remove kernel-3.10.0-693.el7.x86_64

Or, if you’re using Fedora or a newer version of RHEL/CentOS with DNF:

sudo dnf remove kernel-3.10.0-693.el7.x86_64

Replace kernel-3.10.0-693.el7.x86_64 with the actual kernel version you want to remove. Ensure that you do not remove the currently active kernel.

Cleaning Up Grub Configurations

After removing old kernels, you should clean up your Grub configuration to remove any references to the deleted kernels. Run the following command:

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

This command will regenerate your Grub configuration file, ensuring that only the available kernels are listed in the boot menu.

Frequently Asked Questions

Is it risky to remove old kernels?

No, it is not risky as long as you keep the current kernel and at least one previous version as a fallback. Ensure that you do not accidentally remove the kernel currently in use.

Can I automate the process of removing old kernels?

Yes, you can automate this process by configuring your package manager to keep only a specified number of kernels. For example, on systems using DNF, you can set the number of kernels to keep by editing the /etc/dnf/dnf.conf file and adding the line:

installonly_limit=2

This ensures that only the latest two kernels are retained, and older ones are automatically removed during system updates.

The result, to keep two kernel as below:

What happens if I remove all the kernels?

If you remove all the kernels, your system will be unable to boot, as there will be no kernel to manage the hardware and processes. Always ensure that at least one kernel remains installed on your system.

How much disk space can I free up by removing old kernels?

The amount of disk space freed up by removing old kernels depends on how many are installed and their individual sizes. Typically, each kernel can take up between 50MB to 200MB of space. Removing multiple old kernels can free up several hundred megabytes or more.

Conclusion

Maintaining a clean and efficient Linux system requires regular housekeeping, including the removal of old kernels. By following the steps outlined in this guide, you can safely remove unnecessary kernels from CentOS, RHEL, and Fedora, freeing up disk space and keeping your boot menu uncluttered. Remember to keep the current kernel and one previous version as a fallback to ensure that your system remains stable and functional. Regular kernel management is a simple yet effective way to optimize your Linux experience. Thank you for reading the huuphan.com page!