AutoSSH, for All Your <CONNECTION LOST>

I love SSH. I mean, I really, really love SSH. It's by far the most versatile, useful, amazingly powerful tool in my system administration quiver. One of the problems with SSH, however, is that when it dies, it doesn't automatically recover. Don't get me wrong. It's easy to recover with SSH, especially if you've set up public/private keypairs for authentication (I show you how to do that over here). But if the SSH connection dies, it's difficult to reestablish.

In the past, I've done something like enclosing the SSH command in an endless WHILE loop so that if it disconnects, it simply starts over. (I talk about WHILE loops in this month's Open-Source Classroom.) With AutoSSH, however, even if an SSH session is still active, but not actually connected, it will disconnect the zombie session and reconnect a fresh one, without any interaction.

Image Credit: AllenMcC, Wikipedia User

I personally use AutoSSH to keep reverse tunnels active inside a remote data center that is behind a double NAT. Getting into the data center remotely is very difficult, but if I can establish a tunnel from inside the double-NAT'd private network to my local server, getting in and out is a breeze. If that SSH tunnel dies, however, I'm locked out. In my particular case, the data center is an entire continent away, so driving over isn't an option. With AutoSSH, if something goes wrong, it will keep attempting to reestablish a connection until it succeeds. The program has saved my bacon more than once, and because it's so incredibly useful, AutoSSH takes this month's Editors' Choice award. It's most likely already in your distribution's repositories, but you can check out the Web site at http://www.harding.motd.ca/autossh.

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Shawn Powers is an Associate Editor for Linux Journal. You might find him chatting on the IRC channel, or Twitter

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