Date: Mon, 30 Oct 2000 02:12:42 -0600 (CST) From: Ryan Thompson <ryan@sasknow.com> To: andrew@ugh.net.au Cc: freebsd-hackers@FreeBSD.ORG Subject: Re: Logging users out Message-ID: <Pine.BSF.4.21.0010300200220.86769-100000@ren.sasknow.com> In-Reply-To: <Pine.BSF.4.21.0010301452030.2043-100000@starbug.ugh.net.au>
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andrew@ugh.net.au wrote to freebsd-hackers@FreeBSD.ORG:
> Hi,
>
> What is the best way to go about logging a user out given their tty? I had
> a couple of ideas:
>
> (a) open their tty and set the baud rate to 0
Probably wouldn't be very effective.
> (b) use tcgetpgrp to get the process group id of the foreground process
> group on that tty, then with that info use libkvm to find the session
> leader's pid and send it a SIGHUP
Why not just kill their controlling shell? That's about all a logout will
do, anyway. If they have processes detatched from the controlling
terminal, the user typing "logout" will not stop them.
Recall that "background" and "foreground" are shell concepts, not
properties of any given process.
> (c) use tcgetpgrp to get the process group id of the foreground process
> group on that tty then using killpg to kill all the members of that
> process group. I would need to do this in a loop to catch background
> process groups that come to the foreground after a process group is
> killed.
>
> Whenever sending a signal I will have to verify the process exited,
> possibly sending TERM and KILL until it does.
>
> Problems:
>
> (a) a doesn't seem to work...I'm guessing it only works on serial lines.
>
> (b) b would be quite unportable I would guess (although thats not a
> tragedy I would like to avoid it if it isn't too hard). Also if the
> session leader dies is there any guarentee everything else in the session
> goes as well? Or would I have to go through and kill every process group
> in the session?
Never any guarantee.. user programs can set up signal handlers to catch or
ignore any signal but SIGKILL. Then again, a user typing "logout" will
not clean up absolutely everything, either.
> (c) c just seemed to be a bit of a hack (assuming you haven't just read
> b). Out of all of them it seems the best so far however.
>
> Does anyone have any suggestions or comments? Is there a "proper" way to
> do this?
a) Kill the controlling shell. This will leave some processes behind that
are no longer part of the user's session (like programs that have
detatched from the terminal and become daemons), and processes that
were never part of the user's session (like processes that they started
on a different terminal)
b) kill -<signal> `ps -axo user,pid | grep user | awk '{print $2}'`
Kills every process owned by ``user''. Sending SIGKILL does so
in a non-catchable way.
c) /sbin/halt is pretty much guaranteed to do the trick ;-)
>
> Thanks,
>
> Andrew
>
>
>
>
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--
Ryan Thompson <ryan@sasknow.com>
Network Administrator, Accounts
Phone: +1 (306) 664-1161
SaskNow Technologies http://www.sasknow.com
#106-380 3120 8th St E Saskatoon, SK S7H 0W2
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