On Sun, 18 Jul 1999, Brian Servis wrote: > The -a option will allow other non-root users to shutdown the machine > with the Ctrl-Alt-Del key press. You will need to create and add the > non-root user names to the /etc/shutdown.allow file, again see the man > page for shutdown.
IIRC, -a in this case prevents anyone but root and the /etc/shutdown.allow users from shutting the system down. Without -a anyone who has physical access could press ctrl-alt-del and reboot the system, since anything called from inittab has uid=0 [root].
