Rebooting Linux server normally takes a long time to load the boot loader services etc but you still have an option to quick boot the server using the following command
- # reboot -f
-f Force halt or reboot, do not call shutdown(8).
You should be careful while using this command as it does not save any recent configuration changes made on GRUB and partitions. Another option to quick rebooting the server without going for traditional rebooting steps (ie..skipping the entire boot-loader stage and directly jumps into the kernel that we want to boot to and for that you need to use the kexec tool for more information refer to IBM kexec user guide