openssh bugs - Mar 2012 - [Bug 1988] New: ControlPersist causes stderr to be left open until the master connection times out

https://bugzilla.mindrot.org/show_bug.cgi?id=1988

             Bug #: 1988
           Summary: ControlPersist causes stderr to be left open until the
                    master connection times out
    Classification: Unclassified
           Product: Portable OpenSSH
           Version: 5.8p2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: ssh
        AssignedTo: unassigned-bugs at mindrot.org
        ReportedBy: amcnabb at mcnabbs.org


As has been noted previously, when ControlPersist is set, the
background process hangs on to stderr until it terminates:

https://bugzilla.mindrot.org/show_bug.cgi?id=1330#c1
https://lwn.net/Articles/401651/

This means that any script that uses stderr from an ssh script will
hang until the master connection eventually times out. I'm opening this
bug because a user noticed that this makes pssh hang:

http://code.google.com/p/parallel-ssh/issues/detail?id=67

If the background ssh process were to close stderr, then pssh would not
hang.

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https://bugzilla.mindrot.org/show_bug.cgi?id=1988

Adam Spiers <mindrot at adamspiers.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mindrot at adamspiers.org

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Damien Miller <djm at mindrot.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |djm at mindrot.org

--- Comment #1 from Damien Miller <djm at mindrot.org> 2012-03-09 10:15:12
EST ---
Closing stderr in the backgrounded process would lose any output from
it (usually visiable at loglevel verbose or higher)

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https://bugzilla.mindrot.org/show_bug.cgi?id=1988

--- Comment #2 from Andrew McNabb <amcnabb at mcnabbs.org> 2012-03-09
10:46:36 EST ---
(In reply to comment #1)
> Closing stderr in the backgrounded process would lose any output from
> it (usually visiable at loglevel verbose or higher)
But if loglevel is not verbose, there's nothing to lose, right?

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--- Comment #3 from Damien Miller <djm at mindrot.org> 2012-03-30 11:39:32
EST ---
not necessarily - e.g. messages sent at loglevel fatal() or error()

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https://bugzilla.mindrot.org/show_bug.cgi?id=1988

--- Comment #4 from Andrew McNabb <amcnabb at mcnabbs.org> 2012-04-01
03:35:25 EST ---
If ssh has forked a background daemon, the user can't reasonably expect
to see messages on stderr anyway. For example, they might close the
terminal in which the original ssh connection was created. Furthermore,
such messages might not even be welcome. After all, the user is
probably running some other application.

Any fatal errors would be relevant to other foreground ssh processes,
but not to a terminal window that is no longer running any ssh
processes.

Might the best long-term solution be to send any logging messages to
foreground ssh processes? In any case, I think it's incorrect to send
logging messages to a now-unrelated tty. Especially since this can make
scripts hang.

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