Title: Simple way to use ssh tunnels in scripts

	Title: Simple way to use ssh tunnels in scripts
	Author: Solène
	Date: 15 May 2019
	Tags: ssh automation
	Description:

	While writing a script to backup a remote database, I did not know how
	to
	handle a ssh tunnel inside a script correctly/easily. A quick internet
	search
	pointed out this link to me:
	[https://gist.github.com/scy/6781836](https://gist.github.com/scy/67818
	36)

	While I'm not a huge fan of the ControlMaster solution which consists
	at
	starting a ssh connection with ControlMaster activated, and tell ssh to
	close
	it, and don't forget to put a timeout on the socket otherwise it won't
	close if
	you interrupt the script.

	But I really enjoyed a neat solution which is valid for most of the
	cases:

	$ ssh -f -L 5432:localhost:5432 user@host "sleep 5" && pg_dumpall
	-p 5432 -h localhost > file.sql

	This will create a ssh connection and make it go to background because
	of `-f`
	flag, but it will close itself after the command is run, `sleep 5` in
	this
	case. As we chain it quickly to a command using the tunnel, ssh will
	only stops
	when the tunnel is not used anymore, keeping it alive only the required
	time
	for the pg_dump command, not more. If we interrupt the script, I'm not
	sure ssh
	will stop immediately or only after it ran successfully the command
	sleep, in
	both cases ssh will stop correctly. There is no need to use a long
	sleep value
	because as I said previously, the tunnel will stay up until nothing
	uses it.

	You should note that the ControlMaster way is the only reliable way if
	you need
	to use the ssh tunnel for multiples commands inside the script.