"reboot" or "shutdown" commands are executed daemons are gracefully stopped and storage volumes unmounted. This is usually accomplished via scripts in the /etc/init.d directory which will wait for each daemon to shut down gracefully before proceeding on to the next one. That environment triggers dead-lock situation when one of the daemons are not closing gracefully. To force the kernel to reboot the system will be adding an additional parameter "-f"

reboot -f