hang on exit bug under Linux

[Nicolas Williams]

On Tue, Dec 11, 2001 at 02:19:22PM +0100, Markus Friedl wrote:
> On Tue, Dec 11, 2001 at 08:12:32AM -0500, Nicolas Williams wrote:
> > Actually, now I'm convinced that even having the sshd send SIGHUP to the
> > process group when the session leader exits might not be correct.
> > 
> > Is it possible to have the client, upon reception of the session exit
> > message, choose to send SIGHUP to the session (meaning the process
> > group) and/or force the channels closed? Is this at all possible in the
> > SSHv2 protocol?
> 
> i sent a patch for signal passing. nobody did comment.
> 
> i sent a patch for SIGHUP, and got one single comment.
> 
> so i guess, nobody cares.

I'm commenting now.

The signal passing patch seems to be for passing signals received by
the ssh client. But I'm talking about the ssh client passing a SIGHUP
upon getting a session exit message from sshd. Is it possible to pass a
signal to that session that just exited at that point? The semantics
would be to killpg() the process group of the session in question - but
the session has exited, ergo there's a chicken-and-the-egg problem and
I'm not familiar enough with the protocol to know if it's even doable.

The killpg() patch, on second thought, is probably not good, on the
grounds that it should be the client that decides such things. You have
succeeded in convincing me of this :) which is why I'm suggesting that
the client have an option for passing SIGHUP to sessions as they exit
and/or close their channels as the sessions exit. E.g.,

hostA% ssh -o nohang hostB
hostB% sleep 150 &
hostB% exit
<ssh passes SIGHUP, closes channels for session, unused forwarded
 agent/x11, sshd exits>
hostA% 

Without -o nohang the behaviour would be as now.

> -m


Nico
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