Once you have enabled fast reboots, running reboot will cause the system to shut down all services and then directly execute the kernel image.

If you want to execute the new kernel immediately without shutting down any services, use the following commands.

# sync; umount -a; kexec -e

To re-enable fast reboots of the current kernel at any time, enter:

# service runkexec restart

Alternatively, specify a different kernel that you want the system to reboot into by entering the following command:

# kexec -l --append="kernel_options" --initrd=initial_ramdisk_image kernel_path

where kernel_options are the options that you want to specify to the kernel, and initial_ramdisk_image and kernel_path are the paths to the initial ramdisk image and the kernel that you want to use.

To unload a target kernel, enter:

# service runkexec stop

Alternatively, you can enter:

# kexec -u