[gridengine users] window size, qlogin and X11 forwarding

Skylar Thompson skylar2 at uw.edu
Sat May 26 22:48:12 UTC 2018


We use qsh for X11 forwarding (starts a xterm) for this reason. For the
users who don't like xterm, they can start a gnome-terminal instead:

qsh -- -e gnome-terminal

On Fri, May 25, 2018 at 06:13:50PM -0400, Stuart Barkley wrote:
> I had thought our system had been configured for qlogin X11 forwarding
> for several years now, but recently I became aware that we had never
> actually configured it.  The basics of the process are documented and
> discussed in various places, but many of them are pretty old.  I also
> have a couple of hints which make life a little easier and one pending
> problem.
> 
> See below for details on our X11 forwarding configuration.
> 
> So far the only problem I have encountered is that window size changes
> do not get successfully propagated to the compute node.  For example,
> if I am editing a file with vi and change the size of my terminal
> window vi does not know about the change and the screen starts to get
> very confused.
> 
> With some exploration it appears that the SIGWINCH signal gets ignored
> by the ssh process started by qlogin.  The 'builtin' qlogin support
> has specific code to handle SIGWINCH and propagate the new window size
> to the compute node.  For some reason I can't figure out everything
> except 'builtin' has a lot of signals ignored.
> 
> Do other people using X11 forwarding have this problem?
> 
> For reference here is my current X11 forwarding configuration
> information.  There are a few changes from the standard configuration
> given elsewhere.
> 
> Create a qlogin wrapper script and put it somewhere systems running
> qlogin can access.  I'm using /opt/sge_root/bin/qlogin-wrapper but
> other places may be better:
> 
> ==== start ====
> #!/bin/sh
> # Helper script for grid engine qlogin commands.
> 
> HOST=$1
> PORT=$2
> 
> exec /usr/bin/ssh -X -Y -o HostKeyAlias=$HOST -p $PORT $HOST
> ==== end ====
> 
> Use 'qconf -mconf' and change the qlogin_command and qlogin_daemon
> parameters from 'builtin' to:
> 
> qlogin_command               /opt/sge_root/bin/qlogin-wrapper
> qlogin_daemon                /usr/sbin/sshd -i
> 
> qlogin-wrapper needs to be available on the system running qlogin.
> 
> sshd needs to be available on the compute nodes.
> 
> xauth needs to be available on the compute node so that sshd can
> manipulate X11 authority files.
> 
> That is pretty much it and things should work.
> 
> Differences from the more common descriptions:
> 
> There is no need to test for the DISPLAY environment variable.  ssh
> will only forward X11 if DISPLAY is set on the qlogin system.
> 
> The '-X' option is needed to forward X11 sessions.  Not clearly
> documented elsewhere is that sshd will automatically turn off X11
> forwarding after about 20 minutes.
> 
> The '-Y' option turns off the 20 minute timeout and turns off some
> other X11 SECURITY support.  Study this at your own peril, but I
> believe this is not a significant issue.
> 
> The '-o HostKeyAlias=$HOST' option causes ssh to just use the hostname
> for lookups in the ssh known_hosts files.  Without this you will get
> errors/warnings for each new host/port combination that grid engine
> uses for the connections.
> 
> I have not explored the rlogin_command and rsh_command aspects but
> believe the same changes can apply there.
> 
> Stuart Barkley
> -- 
> I've never been lost; I was once bewildered for three days, but never lost!
>                                         --  Daniel Boone
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> users at gridengine.org
> https://gridengine.org/mailman/listinfo/users

-- 
-- Skylar Thompson (skylar2 at u.washington.edu)
-- Genome Sciences Department, System Administrator
-- Foege Building S046, (206)-685-7354
-- University of Washington School of Medicine



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