hang on exit bug under Linux

[Nicolas Williams]

On Mon, Dec 10, 2001 at 10:50:06AM -0800, Dan Kaminsky wrote:
> > That is not a proper daemon program and therefore not a good example
> > of a problem.  Proper daemons should always close any tty file
> > descriptor, detach from any controlling terminals, call setsid() to
> > form a new process group, etc.  This is more representative of a
> > program that could loose data.
> 
> So I've got all these Windows 9x machines that won't shut down.  Have to
> power cycle them every time, or leave them on 24/7.  Rather wasteful of
> power, and you risk your file system every time you decide to go through
> with it.  It's one of the worst parts of 9x.
> 
> Look: ssh user at host "command" needs to never, ever hang.  It needs to not
> leave processes running, it needs to not break scripts, it needs to simply
> be "this command, as if it was run locally, only it's really somewhere else.
> And if I'd be staring at a prompt somewhere else, damnit, I need to be
> staring at a prompt here."
> 
> I've gotten critical pages at three in the morning from irate sysadmins half
> the world over wondering why I'm taking up most of the load on their machine
> as a side effect of this class of bugs.  Lemme tell you, stuff like that
> puts a damper on my ability to evangelize SSH :-)

This could (should?) be handled with an option to the client to close
the session as soon as possible, perhaps with a timer. Don't use a pty
so your remote command won't get SIGHUP though!

Hey, I have the same problem to deal with. I deal with it. I always put
in explicit stdio redirections to/from /dev/null. What's wrong with that?

> > Perhaps one of the reasons this issue has been hard to get agreement
> > on is that everyone is testing with different daemons and some of
> > those are ill behaved?
> 
> I think it's mostly a cross platform issue.  Ugliness always hides at the
> fringes, and the exact set of behavior that signifies "this app is closed"
> has the exact feel of a fringe.
> 
> Yours Truly,
> 
>     Dan Kaminsky
>     DoxPara Research
>     http://www.doxpara.com
> 


Cheers,

Nico
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