xdmcp script don't work with a remote server

[Andrey de Oliveira]

Hi,

PROBLEM:

I tried use xdmcp (startx) script in LTSP to connect in a remote X server and it not work. Although using the package for Ubuntu, I checked that the same occurs in the packet with the ltsp 5.4.5 source code, independent of the distribution.

lts.conf

[00:11:22:AA:BB:CC]
SCREEN_07=xdmcp
XDM_SERVER=x.x.x.x

When thinclient boot, the XDM_SERVER value is ignored.

I found a bug in screen_session script, line 78 (or was it in bash?). It calls a script with $args variable as argument between double quotes:

78: "$script_path" "$args"

In xdmcp script lines 19-23, exists a condition, based in number of arguments:

19: if [ $# -lt 1 ]; then
20: X_ARGS="$X_ARGS -query ${XDM_SERVER}"
21: else
22: X_ARGS="$X_ARGS $*"
23: fi

Even without arguments, in this case, $args empty, bash/sh return 1 as total arguments in $# variable, because of the double quotes used in screen_session script.

So the condition will always be FALSE, ignoring XDM_SERVER value.

SOLUTION:

change session script line 78 to:
78: "$script_path" $args
or
78: eval "$script_path" "$args"

Regards,

Andrey de Oliveira
LPIC-1

[Rüdiger Kupper (ruediger.kupper)]

The same problem appears whith ssh session script (bug #1020113). It is (as you correctly found out), caused by wrong quoting of arguments in line 78 of /opt/ltsp/i386/usr/share/ltsp/screen_session.
Bug report #1020113 contains a patch that seems to fix the problem (I confirm it works for the ssh session script), but it has not (yet) made it into the release.
Marking as duplicate.

[Vagrant Cascadian (vagrantc)]

On 2013-05-02 09:05:16 -0500, Andrey de Oliveira wrote:
> When thinclient boot, the XDM_SERVER value is ignored.
...
> In xdmcp script lines 19-23, exists a condition, based in number of
> arguments:
>
> 19: if [ $# -lt 1 ]; then
> 20: X_ARGS="$X_ARGS -query ${XDM_SERVER}"
> 21: else
> 22: X_ARGS="$X_ARGS $*"
> 23: fi
>
> Even without arguments, in this case, $args empty, bash/sh return 1 as
> total arguments in $# variable, because of the double quotes used in
> screen_session script.

Wouldn't a viable option be:

diff --git a/client/share/ltsp/screen.d/xdmcp b/client/share/ltsp/screen.d/xdmcp
index 26924c0..d9e31a0 100755
--- a/client/share/ltsp/screen.d/xdmcp
+++ b/client/share/ltsp/screen.d/xdmcp
@@ -16,7 +16,7 @@

 XDM_SERVER=${XDM_SERVER:-${SERVER}}

-if [ $# -lt 1 ]; then
+if [ -z "$1" ]; then
     X_ARGS="$X_ARGS -query ${XDM_SERVER}"
 else
     X_ARGS="$X_ARGS $*"

That seems more meaningful than checking the number of arguments
anyways. I guess you could get passed an empty argument...

live well,
  vagrant

[Vagrant Cascadian (vagrantc)]

Fixed/worked around in:

https://bazaar.launchpad.net/~ltsp-upstream/ltsp/ltsp-trunk/revision/2598