Useful suggestion, but be aware, there is an annoying modal popup if go to the original page.
This is much safer way to restart your frozen Linux. To do this, you need to press:
Ctrl + Alt + PrtSc (SysRq) + reisub
Just to make it clear. You need to press and hold Ctrl, Alt and PrtSc(SysRq) buttons, and while holding them, you need to press r, e, i, s, u, b
And a nice trick from many commenters:
reisub = Reboot Even If System Utterly Broken