X dependency

The most important is probably the xorg requirement that Qt libs have when rendering to PDF, this is an undocumented requirement and the fix is not trivial.

The symptoms

Server chrashes after a GetPrint request with segfault, output in system logs:

1. [33988.177726] qgis_mapserv.fc[28337]: segfault at 10 ip 00007f278e78c65b sp 00007fffaabf4c78 error 4 in libQtGui.so.4.8.2[7f278e51e000+a82000]

Fix

1. sudo apt–get install xvfb

Since a configurable display number is needed (here set to 99), I’ve adapted the script setting display to 99:

1. #!/bin/sh
2. ### BEGIN INIT INFO
3. # Provides: Xvfb
4. # Required-Start: $local_fs $remote_fs
5. # Required-Stop:
6. # X-Start-Before:
7. # Default-Start: 2 3 4 5
8. # Default-Stop: 0 1 6
9. # Short-Description: Loads X Virtual Frame Buffer
10. ### END INIT INFO
11.  
12. XVFB=/usr/bin/Xvfb
13. XVFBARGS=“:99 -screen 0 1024x768x24 -ac +extension GLX +render -noreset”
14. PIDFILE=/var/run/xvfb.pid
15. case “$1” in
16. start)
17. echo –n “Starting virtual X frame buffer: Xvfb”
18. start–stop–daemon —start —quiet —pidfile $PIDFILE —make–pidfile —background —exec $XVFB — $XVFBARGS
19. echo “.”
20. ;;
21. stop)
22. echo –n “Stopping virtual X frame buffer: Xvfb”
23. start–stop–daemon —stop —quiet —pidfile $PIDFILE
24. echo “.”
25. ;;
26. restart)
27. $0 stop
28. $0 start
29. ;;
30. *)
31. echo “Usage: /etc/init.d/xvfb {start|stop|restart}”
32. exit 1
33. esac
34.  
35. exit 0

Install it with:

1. chmod +x /etc/init.d/xvfb
2. update–rc.d xvfb defaults

Fast CGI needs an environment variable DISPLAY having the same display number (99), I’ve adapted the fcgid configuration accordingly:

1. $ cat /etc/apache2/mods–enabled/fcgid.conf
2.  
3. AddHandler fcgid–script .fcgi
4. FcgidConnectTimeout 20
5. # Pass display number to QGIS MapServer instances
6. FcgidInitialEnv DISPLAY “:99”