This OPTIONAL plain-text file takes the same format as your server's mapcycle.txt, so it's contents would look something like this:
cs_aztec
cs_assault
de_dust
If you do not have a maps.ini file declared in the maps_file CVAR in server.cfg, all maps in the mapcycle.txt are available for vote. If this file exists and is specified in the server.cfg, it controls what maps may be voted for using Admin Mod.
How to declare the maps_file in server.cfg:
The default server.cfg that is included with Admin Mod and which is copied to your server.cfg file when you run the installation script includes an entry already for maps_file, which you can modify.
Most commonly, people will call their maps_file "maps.ini" and they declare it like this:
maps_file "maps.ini"
If you do not want to use a maps_file, you would declare as such like this:
maps_file 0
More information about setting up your server.cfg file can be found elsewhere in this chapter, in Setting up your server.cfg file.