openssh unix dev - Jul 2001 - terminal hangs on solaris

Every once in a while, my terminal session with an OpenSSH server (any
version, up to and including 2.9p2) will hang indefinitely upon logout, rather
than returning to the shell on my UNIX client machine (or closing the window,
if in a M$ environment).  Unfortunately, I can't reproduce the problem, but
it
does occur frequently enough to be annoying.  When it does happen, this is what
I see on the server system (by logging in from a different terminal and
tracking down the hung-out-to-dry process):

# pstack 3296
3296:   /usr/local/sbin/sshd -f /etc/sshd_config
 ef5b7488 poll     (efffd160, 2, 64)
 ef5cd064 select   (efffd170, ef6266cc, 11e8d0, ef6266d0, 11e8d4, 11) + 280
 00034560 wait_until_can_do_something (effff24c, effff248, effff244, 64, 4, 1)
+ 2b8
 00034d74 server_loop (fb000, 0, 104000, fb000, 104000, effff240) + 20c
 00036c7c do_exec_pty (10bbcc, 11, 36634, fb400, 8a, 0) + 260
 00036704 do_authenticated1 (0, 36400, fac00, 106800, ef623700, 36014) + 60c
 00036074 do_authenticated (110fa8, efffefbc, d0710, 400, efffefc8, 0) + 80
 0002d720 do_authentication (effff418, 3, fac00, cfc00, fb000, 10e400) + 174
 0002c17c main     (1eb4, f, 1, fac00, 1eb4, 10c498) + 1418
 0002a27c _start   (0, 0, 0, 0, 0, 0) + 5c
# truss -p 3296
poll(0xEFFFD160, 2, 100)                        = 0
poll(0xEFFFD160, 2, 100)                        = 0
poll(0xEFFFD160, 2, 100)                        = 0
poll(0xEFFFD160, 2, 100)                        = 0
poll(0xEFFFD160, 2, 100)                        = 0
poll(0xEFFFD160, 2, 100)                        = 0
poll(0xEFFFD160, 2, 100)                        = 0
poll(0xEFFFD160, 2, 100)                        = 0
poll(0xEFFFD160, 2, 100)                        = 0

  Has anyone else seen this issue?  It's mostly a nuisance, but I am
struggling
to figure out exactly what causes it.  I've been able to "gcore"
the running
process, and a gdb "bt" basically shows the same thing as pstack
above.  Sadly,
this is the extent of what I know to do in gdb :-)

  Thanks in advance.

  RudeYak at yahoo.com



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Rude Yak <rudeyak at yahoo.com> writes:
> Every once in a while, my terminal session with an OpenSSH server (any
> version, up to and including 2.9p2) will hang indefinitely upon logout, ...
It's likely that when this happens, it's because you have started a
background
process from that shell which has not closed its stdout/stderr streams.  sshd
waits to receive eof on the pipes to the shell's stdout/stderr before
exiting,
and that can't happen until all references to those pipes are closed.

When you start a background process that you want to continue after you end
the SSH connection, be sure to redirect its stdout/stderr.

- Richard