X apps only work after second login

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To: secureshell@securityfocus.com
Date: Wed, 29 Jun 2005 13:53:05 -0700

My apologies if this has been addressed previously - I didn't see
anything for it in the archives.

We're in the process of upgrading to RedHat Enterprise version 4 and
are seeing a strange ssh problem. It ships with what they label as
"openssh-3.9p1-8.RHEL4.4." Telnetting to port 22 on the box indicates
SSH-1.99-OpenSSH_3.9p1.

We're using a vanilla install. The only change we've made is one
variable in sshd_config - we've got the following variable
uncommented: X11UseLocalhost no.

Here's what happens:

1) User ssh's into remote machine (machine.company.com) which is
running the new version. Tries to run an X process, say xclock. User
is told:

Error: Can't open display: machine.company.com:10.0

User keeps this session open.

2) User opens a second ssh session to the same remote machine. Runs
xclock - it works. On this second session the client has been handed
the same display (machine.company.com:10.0) as the first session.

3) User goes back to first session. Now xclock works in that session
also.

4) If user logs out of second session, X stops working on first session.

We see this behavior regardless of the ssh client used (we've tested
Linux, OSX, HP-UX). It also doesn't matter if we use X forwarding on
the client (via -X or -Y) either.

Note that if a user doesn't have concurrent ssh sessions open, X
never works.

Any suggestions?

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