[SLUG] shutdown: you must be root to do that!

[Gavin Baker]

Q: How do you give permission to shutdown(8) the machine to regular
users? 

Without patching the shutdown code to either link it to libpam or check
your UID/GID, there are 2 simple ways.

Option 1: SUID ROOT

On debian, a distro which hates setuid root anything, /sbin/shutdown's
default permissions are -rwxr-xr-x. If we make it setuid root

	$ chmod u+s /sbin/shutdown  (giving  -rwsr-xr-x)

anyone and everyone can run /sbin/shutdown, and it will run as root. So
everyone can shutdown the machine (ouch).

If we only want users from a special group to be able to execute it, we
can just make it only executable by the owner and group

	$ chmod g-wrx /sbin/shutdown (giving -rwsr-x---)

and then change the group owner to our special group. Debian has an adm
group, which seems appropriate. (but we could just create a new
shutdown, or wheel group of course).

	$ chown root.adm /sbin/shutdown 

-rwsr-x---  1 root  adm   16632 2002-05-28 12:27 /sbin/shutdown

So anyone we want to let shutdown the machine, we can just add to the
adm group.

	$ adduser fred adm



Options 2: sudo

If you use sudo, then 

	fred   ALL=(root) /sbin/shutdown

in your sudoers file would let the user fred run shutdown as root.
Without setuid root'ing anything! You can change "fred" for "%adm" or
"%shutdown" to indicate a member of that %group.


sudo logs everything and doesn't need you to change any file
permissions. 


I guess the distro's that do allow anyone to shutdown the machine use
setuid root binaries. Not as elegant as sudo, but they both work.

Gav

(ps, based on a conversation with Al)	

-- 
Gavin Baker <gav at supercowpowers.org>