You can compile the Linux client without the GUI component by using
./configure --enable-headless
when compiling.
Once installed and running you can configure the Linux client from the server web interface (use the default directories to debug to configure the backup paths).
Internet mode
If you want to configure the client as internet client, you need to supply the server name, port and the authkey (assuming there already is an internet client with the name `hostname`. See http://www.urbackup.org/Administration_Manual.php#x1-200006.2) via:
echo "internet_server=example.com internet_server_port=55415 internet_authkey=foobar internet_mode_enabled=true" > /usr/local/var/urbackup/data/settings.cfg
You can start the client via
start_urbackup_client --no_daemon --loglevel debug
to see if it can establish the connection sucessfully. You have to wait 3 min till the first try.