Solution? (was Re: hang on exit bug under Linux)

[Nicolas Williams]

On Thu, Dec 13, 2001 at 01:34:32PM +1100, carl at bl.echidna.id.au wrote:
> 
> > From: Peter Stuge <stuge at cdy.org>
> > 
> > The true solution is considered to be one of two things:
> > 
> > 1. All daemons shall behave.  (ie. close std*)
> 
> Ideally, but not likely :(
> 
> > 2. The user knows what he/she wants.  (ie. to exit, loosing data)
> > 
> > I actually want both.  I want to be able to tell sloppy daemon programmers
> > that they should clean up their code.  But I also want my users to not have
> > to deal with sloppy daemon programmers, unless they choose to do so.
> > This is tough.
> 
> Could it be done at the command line?  ssh -bad-daemon foohost ?

I think the solution is to have a client-side option to specify the
behaviour of the client when the number of live sessions goes down to 0.
The behaviour could be any of:

 - wait for channels to close ("hang")
 - background the client
 - pass SIGHUP to the session(s) that still have open channels (sshd
   should do a killpg() in response)
 - force the closure of remaining channels and exit, possibly doing this
   after the expiration of a timer

The key thing to understand here is that SSHv2 is *very* different from
SSHv1.

SSHv2 allows the use of multiple sessions in one SSH connection. And
even when there are no live sessions the client could still initiate new
ones. Thus, to fully suport the protocol, the server must not
unilaterally drop SSHv2 connections.

So what is needed to satisfy the howlers is to provide an option as
described above.

DISCLAIMER: I'm not an expert on SSHv2, nor am I involved in the
OpenSSH effort other than as a user and occasional contributor on this
list -- so I may be wrong. Ben? Markus?

> Is it too hard to have a command line switch (or config option) to say
> "lossy/not lossy" ?  It's because of this problem that I'm still stuck
> with a lot of firewalls still running ssh v1 :(

No, I don't think it is too much. The key though, is to undersand that
this is an issue of the client's behaviour. An option to say "hey, I'd
do an ~. when the session leader exits, so just do it and save me the
bother".

> Carl


Cheers,

Nico
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