I am a Linux user, and my main music app is Rhythmbox.

After reading elsewhere on the forum, I tried syncing to iTunes first, which resulted in successfully syncing one of the iTunes demo songs to my phone.

Then, I tried Rhythmbox. Again, it worked correctly. However, when I deleted the song I synced from iTunes, I lost the rest of my music. Whenever I do media sync with Rhythmbox, the music shows in Rhythmbox's browser. I know it's making it onto the phone because if you show hidden folders while connected via USB Drive mode, you can see the IPOD_Control folder, and the .mp3 files are within it.

However when accessing the music application on the phone itself, it shows no songs.