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Using GNU Screen with SSH

This post is probably old news to experienced UNIX sys admins, but I thought the information might be useful to less knowledgeable folks like me. I also hope that the resulting conversation will help uncover even more knowledge we can all put to good use.

I’ve messed around with the screen utility off and on for a while. One thing I’d never quite figured out, though, was how using screen helped with SSH sessions. I kept seeing references to using screen to help keep things running when you needed to disconnect from an SSH session. That seems like a useful feature, so I decided to dig into it and see what I could figure out.

In the end, what I figured out was this:

  • I needed to install screen on the remote host(s). In my case, the remote hosts were OpenBSD (I removed the secret back doors), so a quick pkg_add corrected that issue.

  • I had to recreate my .screenrc file on the remote host(s). Fortunately, my .screenrc is very simple—it only enables the ability to use the iTerm2/Terminal scrollbar to scroll back and increases the scrollback buffer—so that was no big deal.

With these changes in place, you can then use this command to connect to a remote host:

ssh -t <> screen -R

On the first connection, this command will create a new screen session. When you’re done with this SSH session and want to disconnect, just detach from the screen session (typically using Ctrl-a d). That also disconnects the SSH session, but here’s the kicker: your screen session is still running—as are any processes you had running in that session.

When you go to reconnect, use the same command again and it will reconnect you to your existing screen session and you’ll be right back where you left off. Pretty handy!

<aside>By the way, the -t in the SSH command is necessary; without it, you’ll get a “Must be connected to a terminal” error message and it won’t work properly.<aside>

I’m sure this barely scratches the surface of the useful tricks one could perform using screen, so I challenge any and all readers to submit other useful tricks in the comments below. Or, if there is a better way of doing what I’m discussing in this article, please speak up!

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