Topic: Direct reboot sys-rq alternative
Very rarely the Raspberry PI might hang even the reboot command has been given.
If you still have shell access you can try the following:
Enable function if not already the case:
echo "1" > /proc/sys/kernel/sysrq
Sync disks to not loose data
echo "s" > /proc/sysrq-trigger
Unmount and mount read only to not damage image
echo "u" > /proc/sysrq-trigger
Do the actual reboot
echo "b" > /proc/sysrq-trigger
Hope it helps.