How to debug "msProcessProjection(): Projection library error. no system list, errno: 2" error in mapserver?

A couple of thoughts. It is somewhat difficult to diagnose this without looking at your mapfile, but here goes:

1. You should try setting your PROJ_LIB variable to /some/place/share/proj/nad/ That is where the epsg file should be located.

2. Enable debugging. Set it to level 5. You will need to set up an error log file too. See more info her in the MapServer docs http://mapserver.org/mapfile/map.html

I am guessing that either the path to the epsg database is wrong or your user doesn't have rights to read it.

I this isn't the problem, I would look at whether you have set all of the layer and map level metadata in your MapFile that is necessary to serve as a WMS server. More info here: http://mapserver.org/ogc/wms_server.html Make sure that you have set a valid SRS/CRS in your WMS metadata.

I just ran into this issue and found that the problem was because I had not installed the ‘proj-epsg’ package.

yum install proj-epsg

You can run the mapserv program directly from the command line (use su to switch to the apache user first) - running it through strace should help determine how libraries are being loaded and functions are being called.

You should set your specific environment variables manually before invoking mapserv to properly reflect your Apache configuration.

Also, you can set other enviroment variables to simulate running as a CGI script:

http://www.cgi101.com/book/ch3/text.html

QUERY_STRING is going to be useful.