I have my home computer A and a work computer C that I want to synchronise using unison. In the middle is a work computer B. A can communicate with B and B can communicate with C directly but A and C can't directly connect to each other. In fact the communication diagram looks like A->B<->C. That is A can connect to B but B can't connect to A.
To give an example how I use this setup, I currently do the following if I want to ssh from A to C
ssh -t -X -C me_B@B ssh -X me_C@C
How can I run unison from A and sync with C, maybe using ssh port forwarding?
To make it a little clearer, C has unfiltered outgoing connectivity to the Internet. B has unfiltered in and outgoing connectivity to both C and the Internet. A is my home computer.
Update
The following command line works for me to at least copy files from A to C
scp -oProxyCommand="ssh me_B@B nc -v %h %p" foo/* me_C@C:foo
Is there some way to use this idea to get unison to work?
Yes, ssh port forwarding can be used for that. Use the following command on A if you want to forward ssh on port 22 at C to the local port 3000 (for example):
# Create the tunnel
ssh -L 3000:C:22 userB@B -N
After you have issued the command, you can login into C from A using:
# Connect using the tunnel
ssh -p 3000 userC@localhost
Note: During the discussion below it turned out, that in OP's network, the connection trough the tunnel can only be established using the following command:
ssh -p 3000 -l userC localhost
Note that I'm using -l userC instead of userC@.
Now you can use unison like this:
unison directory ssh://userC@localhost:3000 directory