Only allow connections if file (or special condition) is present

[Tobias Borgert]

> Better than a cron job is a udev script; just trigger for the specific FS 
> UUID, and then start/stop SSHD.

Thank you all! I'll first try the udev script. If there is interest, I can post whether it worked or not and how I maded it. But it might take until the weekend until I find time for this.

Thank you very much!