using unison on server to sync with machine inside a network

ad_meis

Dear Gentoo Forums,

I have the following issue. I have a laptop that I carry with me and a desktop in the office.
Whenever I go to the office daily I sync the laptop and the desktop with unison.
However it happens that I have more and more days of work out of the office, and when not in the office, it is not possible to directly sync laptop (A) to desktop (B). I have the possibility to ssh connect to a third machine, a server (C) from which I can access my office desktop, however I am granted very limited disk space on the server (I cannot use it for backup). My question is: can I sync A and B taking advantage of ssh connection with the server (but without actually saving data on the server)?

Hope this is clear. I am now familiar with using unison, but I am of course open to other solutions.

thanks for your help

VinzC · Posted: Tue Jul 31, 2012 6:25 pm Post subject:

If you know which port unison uses for synchronization (if it uses just one port) you can setup an SSH tunnel at your server machine C, will act like a VPN.
_________________
Gentoo addict: tomorrow I quit, I promise!... Just one more emerge...
1739!

jormartr · Apprentice Joined: 02 Jan 2008 Posts: 174

As VinzC says, use a ssh port forward (example: 2222), and unison like

unison /local/path ssh://localhost:2222//remote/path.

ad_meis · Posted: Tue Jul 31, 2012 6:34 pm Post subject:

Thanks, I ll look into this. And let you know

ad_meis · Posted: Wed Aug 01, 2012 7:43 am Post subject:

I am having trouble with the correct number for the port.
Is there a way to discover what port is unison using for the synchronization?

VinzC · Posted: Wed Aug 01, 2012 8:58 am Post subject:

jormartr · Apprentice Joined: 02 Jan 2008 Posts: 174

I think it should work doing a port forward within ssh, like:

office desktop lan ip: 10.0.0.2
office server lan ip: 10.0.0.1
office server public ip: 1.2.3.4

then, from home

ssh user@1.2.3.4 -L 2222:10.0.0.2:22
unison /local/path ssh://localhost:2222//remote/path

I write this without any test, I think its a way to make it.

ad_meis · Posted: Thu Aug 02, 2012 11:31 am Post subject:

Thanks again. I cannot have it working. But it could be a mistake on my side.

The first line with the ssh connection goes fine. Troubles are with the second line. Say that username is mike on all machine, and I want to sync /home/mike on laptop and office desktop, then your last line becomes:

unison /home/mike ssh://localhost:2222//home/mike

I have tried both with "localhost" and by substituting it with what set into /etc/hosts.

This is the error message I get

jormartr · Apprentice Joined: 02 Jan 2008 Posts: 174

Take a look at some documentation or these:

http://www.debianadmin.com/howto-use-ssh-local-and-remote-port-forwarding.html
https://help.ubuntu.com/community/SSH/OpenSSH/PortForwarding

you are interested in local port forwarding.

ad_meis · Posted: Sat Aug 11, 2012 11:34 am Post subject:

Thanks again. I have read the two links, but cannot have it working yet

jormartr · Apprentice Joined: 02 Jan 2008 Posts: 174

Try running "ssh office_public_ip -L local_port_to_bind:local_workstation_address_on_office:office_workstation_ssh_port -v", that is, with verbose option.

and then connect to your office workstation with ssh localhost -p local_port_to_bind, and read the messages on the first command, and maybe you find something useful, like server is not forwarding ports, or something else.