Ubuntu 12.04 hangs on reboot ("All processes ended within 1 seconds"); how to debug?
try change in /etc/default/grub following line:
GRUB_CMDLINE_LINUX="reboot=p"
or
reboot=b
or something else according to https://www.kernel.org/doc/Documentation/x86/x86_64/boot-options.txt
then
sudo update-grub