What steps did you follow to get your FTB Infinity set up?
Here is a step by step of how to get infinity working (it was in the first result in the search I gave you above):
As you can see: You need to ssh inot your server to get an FTB server working. Are you sure you want FTB? If you want a plugged or modded server, the forge or bukkit servers are easier to get working. My advice of sticking to vanilla untill you are more accustomed and versed in Linux still stands.
Edit:
Remember that when you start to add plugins or mods to a server you do increase all the ways something can go wrong, and where you have to get your hands dirty with logs, SSH and googling…