What is the proper method to remove old kernels from a Red Hat Enterprise Linux system?

Solution Verified - Updated

Environment

  • Red Hat Enterprise Linux 3
  • Red Hat Enterprise Linux 4
  • Red Hat Enterprise Linux 5
  • Red Hat Enterprise Linux 6
  • Red Hat Enterprise Linux 7
  • Red Hat Enterprise Linux 8
  • Red Hat Enterprise Linux 9
  • Red Hat Enterprise Linux 10

Issue

  • How can I remove old kernel packages from a Red Hat Enterprise Linux system?
  • Two kernel packages are appearing in my system, how to remove the older kernel package?
  • My /boot directory is getting full, how do I remove old kernels?
# df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/mapper/VolGroup00-LogVol00
                      14804452   7006156   7046272  50% /
/dev/sda1               101086    101086         0 100% /boot
none                    127332         0    127332   0% /dev/shm

Resolution

Red Hat Enterprise Linux 8, 9, and 10

  • The preferred method is to remove a specific older kernel. This differs from RHEL 5/6/7 in that kernel-core must be targeted:
# yum remove kernel-core-<version>

NOTE: the yum command cannot remove the running kernel. If you need to remove the running kernel you must reboot to a different kernel first.

  • The YUM version 4 (based on the upstream DNF project) method for removing kernels and keeping only the latest version and running kernel:
# yum remove --oldinstallonly

Red Hat Enterprise Linux 5, 6, and 7

  • The preferred method is to remove a specific older kernel:
# yum remove kernel-<version>

NOTE: the yum command cannot remove the running kernel. If you need to remove the running kernel you must reboot to a different kernel first.

  • The package-cleanup command can be used as shown below:
# package-cleanup --oldkernels
  • From the package-cleanup man page:
     --oldkernels        Remove old kernel and kernel-devel packages
     
     --count=KERNELCOUNT
                         Number of kernel packages to keep on the system
                        (default 2)
  • The number of kernels left in place on a system can be selected using the --count flag as shown. In the example below, the intent is to keep 3 kernels installed on the system and remove any others.
# package-cleanup --oldkernels --count=3

Red Hat Enterprise Linux 3 and 4

  • The rpm command can be used to remove a specific older kernel:
# rpm -e kernel-<version>

**Warning**: the `rpm` command can remove all kernel packages, we advise only removing specific kernels and not using a wildcard.

**Warning**: Removing all kernels will render the system unbootable.

**Note**: We suggest leaving two kernels minimum for troubleshooting.

Root Cause

  • Kernels are packaged as RPMs. The underlying rpm command can be used to query and interact with the installed kernels on a system. However, due to the critical nature of the kernel for a system, the following limitations are to be noted.
  • Avoid removal of the running kernel

Doing so can cause unexpected failures to occur as kernel modules could be needed by the running kernel during runtime that are not already loaded. The attempt to load such a module that has been removed would result in inconsistent system behaviour and possible failure. It is always recommended to avoid removing the running kernel.

  • During system updates, at minimum, two kernels should be retained/installed

The update process for a system to migrate between kernel versions requires a number of complex scripts to be executed successfully. In the event that there is a failure encountered within any, the update will proceed, but the resulting kernel installation may fail during a subsequent boot.

It is recommended to retain (at minimum) two kernel installations and associated dependencies to allow a previous working kernel to be selected during boot in the event that the default version fails.

  • With these limitations in mind, using the underlying rpm commands to remove kernel versions is not recommended. The above yum based methods include safeguards based around the above limitations.

Please see the following for further details regarding installation/removal of packages:

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