I've a linux machine (Redhat - KDE3) that I usually connect to using VNC.
Example, I telnet to the machine first and run a script with following commands to open a display on hostname:45.
1. Xvnc -rfbauth /home/myusername/.vnc/passwd :45
2. setenv DISPLAY hostname:45
3. startkde&
Later I open the display using a VNC client and can work on the remote desktop.

My problem is, I want to use this (or any) display when I run an application
(as user "apache") from a webpage. For example - I have an application,
say K2, that needs a display to run (because it opens a window to draw stuff etc.).
If I invoke K2 from a webpage I get a message in apache error log - "Error: can't open a display".
I use a PHP script to run system commands (invoke K2 application) on host.

After doing a thorough google search, I found that, X doesn't allow access to a display unless the user (who is trying to access) has 1) a valid .Xauthority OR 2) X server listening to TCP connections. Since user "apache" has no valid .Xauthority I tried to find "-nolisten tcp" in the KDE config files to comment it out. But I couldn't find a file with that option listed. When I run a "ps -auxw | grep X" command on the host, I see only the Xvnc process (which I ran before to open a display), i mean, I don't see any X process running with -nolisten tcp option.

I did a "xhost +localhost" while logged into the machine with "myuserid" and later set the environment variable "DISPLAY hostname:45" in the PHP script I use to open the application (as user "apache"). But it doesn't seem to work.

In summary, how do I make a display available to the apache user when
running an application from webpage? i.e., how to fix the "Error: can't open a display" problem?


I appreciate your help.
Thanks,
Hemanth

Try setting display in the script to JUST ":45". If you set it to hostname:45, it will be seen as a remote connection. (This all, of course, requires the xhost bit as well).

Thanks David! But I still get the same error.
Anyother suggestions, pls?

- Hemanth

Hrrm, hard to say. How are you setting the DISPLAY variable? How are you executing your program? Have you tried something simple like running an xterm?

Thanks for pointing it out. Apparently, I didn't set the DISPLAY variable right.
I used PHP "exec('export DISPLAY=hostname:45')" before.
Now I changed it "putenv(DISPLAY=:45)" and it worked :-)

- Hemanth

Yeah, the exec launches a subprocess... so it can't change the env vars of the PHP process. Glad you got it working.