Script to establish SSH tunnel and then run another program that uses the tunnel

Question

I am running a GUI app (Gnucash) that connects to a remote Postgres database via a secure shell session. I can use the SSH -L command to tunnel a local port and then separately run Gnucash and this works fine.

What I'd like to do is use a single shell script that sets up the tunnel and then calls Gnucash. Is that possible? If so, how do I do it? Currently, I run commands like the following in 2 separate terminal windows:

ssh -L 5433:127.0.0.1:19097 [email protected] gnucash postgres://gnucash@localhost:5433/gnucash_db

If I simply put both lines in a shell script, the first line drops me into the remote shell and the second line doesn't execute until I exit the remote shell.

TIA, Rob Hills

Solution

Use ssh -fNT -L 5433:127.0.0.1:19097 [email protected] to ask ssh to automatically background after establishing the tunnel, and then your script can move on the next command. I suggest you end the script with an exit, which will close the terminal and kill the ssh process; otherwise you must either explicitly kill it or it will exit if/when the server times it out.

Comments

[Ian B.]

How about adding a & to the end of the first line? Would that help?

[saran kumar]

I've not yet tried that, partly because I've been distracted by another task and partly because of the belief that using the & at the end would leave the tunnel process in the background, leaving the connection open. Not sure if it would close when I finished the script or if it would stay open until I shut down Ubuntu. I'll have to test this when I get a chance.

[Steve Kroon]

He wants to run gnucash on the remote server, so presumably he doesn't want -N. Not sure how the -T interacts either, but the -f should do the trick.

[Matthew Flaschen]

This does not kill the ssh process, even with the explicit exit (which has no effect, since the script is would exit at the end of code anyway).