about the shutdown command

[bhupesh m]

Hi,
i have this question for long time,
how u will prevent urself from doing a shutdown command when u r the root?(shutdown or any dangerous command)

sometime back, when i want to run shutdown command in one box, i did that command in another box. since both are test machines, i got no problem.

and also, the shutdown command's persmission is:
-r-sr-xr-x 1 root bin 266240 Apr 12 2000 shutdown

what is the "s" in the permissions and what is meant by root and bin(next to the permission and the "1")?..is it like, the owner of this file is bin and root only can execute it???

[James R. Ferguson · Accepted solution]

Hi:

The only way to prevent yourself from doing a shutdown command when you are root is (1) *not* to do it; or (2) don't operate as 'root' unless you absolutely need to do so!

The 'shutdown' binary is owned by 'root' and has its 'setuid' bit set. That's the "s" you see in the owner's permission in place of an "x". This means that anyone who can execute the command (as given by the group and world-wide) execute permissions) can run 'shutdown' *as if* they were 'root'. That is, the executing user's effective uid becomes zero (root).

Now, that would be disasterous *if* things the code were that simple. Normally, only 'root' can perform 'shutdown'. However, if you create '/etc/shutdown.allow' you can add 'root' AND other users to the file to denote that they have the privilege to perform 'shutdown'. You must include 'root' in the file.

For a full description of how to create an '/etc/shutdown.allow' file, see the manpages for 'shutdown':

http://www.docs.hp.com/en/B2355-60127/shutdown.1M.html

Regards!

...JRF...

[bhupesh m]

Thanks JRF,
and one question i have,
from the path, if i remove /usr/sbin, then whatever sbin commands i need to use, i should use full path only, like "/usr/sbin/shutdown -r". is that will work? is that idea fine?

[Patrick Wallek]

I would not remove /usr/bin/ from your PATH. There are lots of commands and utilities in /usr/bin that you would then have to use the full path for those commands.

Your original situation, accidentally shutting down the wrong machine, is why you MUST always know which machine you are working on.

This is one reason I include the hostname in my prompt on ALL machines.