try this and then try starting roonserver:
sudo echo 1048576 > /proc/sys/fs/inotify/max_user_watches
My guess is that you have something installed on the machine which is opening up a bunch of inotify watches and when RoonServer goes to startup it can’t allocate enough. The command above will increase the number of available watches significantly.
Do you have some kind of cloud-based storage software installed (crashplan, dropbox, etc)?
If the above fixes the problem then you’ll want to add the following into /etc/sysctl.conf as a long-term solution:
fs.inotify.max_user_watches=1048576