Why did my RHEL system reboot?

The best way to reliably diagnose the most common root causes for an unknown system reboot of Red Hat Enterprise Linux (RHEL) is to review the information that is generated by a fully configured kdump, which is a reliable kernel crash-dumping mechanism that ships with Red Hat Enterprise Linux (RHEL) 6, RHEL 7, RHEL 8, RHEL 9, and RHEL 10.

To determine if kdump is already installed, verify that the kexec-tools package is installed:

# rpm -q kexec-tools

If kdump was not installed and configured prior to your unexpected reboot, it may not be possible to determine the cause of the reboot.

To learn more about kdump, including how to configure it, please review this comprehensive guide to installation, configuration, and usage of the kdump tool.

Red Hat also provides a Kdump Helper application to help you set up kdump in RHEL 5 and later. You can input a minimum amount of information and the tool will generate an all-in-one script for you to set up kdump with the basic configuration, or you can generate a script to set up kdump with extended configurations for a number of particular scenarios like system hangs, processes stuck in D-state, or CPU Soft Lockups.

Please note that there are some reboot triggers that are not captured by kdump. For example, kdump will not be able to inform your system administrator about a power outage or intentional reboot. Although these kinds of root causes may be unknown in the first few minutes after a system reboot they are often revealed quickly.

Configuring kdump is an important step to ensuring that your linux installation can be maintained.