If you have worked with remote Linux servers before, I am guessing you already encountered machines that just don’t want to reboot. This is typically due screwed-up network mounts or stuck processes, so the server will hang during shutdown. But it turns out that there are other ways to reboot a server.
One of these is the “Magic SysRq key“. To reboot a server using the SysRq trigger in the kernel, use the following two commands. First, enable the trigger:
echo 1 > /proc/sys/kernel/sysrq
Then, reboot the server the magic way by typing
echo b > /proc/sysrq-trigger
Note that this will reboot the server without unmounting or syncing the filesystems! There are also other options available via the SysRq trigger, some of them are listed in the Wikipedia article above.