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 adminmod.cfg all maps in the mapcycle.txt are available. If this file exists and is specified in the adminmod.cfg, it controls what maps may be voted for using Admin Mod. If you have defined this file, but the file is not present, Admin Mod will throw a "Bad map name" error when trying to execute admin_map commands or anyother map voting plugin.
The default adminmod.cfg that is included with Admin Mod (and which is copied to your adminmod.cfg file when you run the installation script) includes an empty entry already for maps_file, which you can modify.
Most commonly, people will call their maps_file "maps.ini"
and they can declare it this way:
maps_file "addons/adminmod/config/maps.ini"
If you do not want to use a maps_file, you would declare it like this:
maps_file 0
More information about setting up your adminmod.cfg file can be found elsewhere in this chapter, in Setting up your server.cfg and adminmod.cfg files.