[Linux] How to reinstall shutdown / reboot

First of all, check where they are :

which shutdown 
/sbin/shutdown

which reboot
/sbin/reboot

After, check the package :

$ dpkg -S /sbin/shutdown
upstart: /sbin/shutdown

$ dpkg -S /sbin/reboot
upstart: /sbin/reboot




Now we can reinstall :

sudo apt-get install --reinstall upstart

Source : http://askubuntu.com/questions/631929/reboot-and-shutdown-executables-missing