Odamex (Online Doom Multiplayer Experience) is a modification of DOOM
to allow players to compete with each other over the Internet using the
client/server architecture.

To hear in-game music, install either eawpats or freepats.

You'll also need the game data (WAD file) from one of the following:

Shareware Doom v1.9 (DOOM1.WAD)
Ultimate Doom v1.9 (DOOM.WAD)
Doom II v1.9 (DOOM2.WAD)
Final Doom: TNT Evilution v1.9 (TNT.WAD)
Final Doom: The Plutonia Experiment v1.9 (PLUTONIA.WAD)
FreeDoom v0.6.2 (FREEDOOM.WAD)

Place the WAD file(s) in /usr/share/games/doom. The filenames can be
all lowercase (doom.wad) or all uppercase (DOOM.WAD).