12.1 About kexec

kexec is a fast-boot mechanism that allows a kernel to boot from inside the context of a kernel that is already running without initializing the BIOS or firmware, performing memory and device discovery, or passing through the boot-loader stage.

When you reboot a system, the init process goes to run-level 6 and runs the /etc/init.d/halt script. If you have configured kexec on the system, the script will execute the kexec -e command, and cause the system to bypass the standard boot sequence.

The total amount of time saved when rebooting is highly dependent on your server, and can range from several tens of seconds to several minutes.

Caution

As fast reboots bypass device initialization, some devices might fail to work correctly, or a device driver might malfunction if it sees a device in an unexpected state. Before enabling this feature on your systems, test it to ensure that the hardware devices and their drivers continue to behave correctly across fast reboots.