If you hit CTRL-ALT-DEL on a vSphere console, the server will reboot even if there are running VMs and it has not been put in Maintenance Mode. This has been disabled by editing /etc/inittab,so these two lines are remarked out.
# Trap CTRL-ALT-DELETE
# ca::ctrlaltdel:/sbin/shutdown -t3 -r no
Hope it helps