Re: Four questions about examples of GNU Screen use

Hi Lars,

On Sat, Mar 05, 2016 at 08:23:42PM +0200, Lars Noodén wrote:
> 1) Here screen(1) is launched.
> 
>   ssh -l fred server.example.org screen

ssh lacks a -t option in this example (and the next one). Screen needs
a (pseudo) terminal.

> Once a screen(1) session is running, it is possible to detach it and
> close the SSH connection without disturbing the background processes it
> may be running. Then the terminal session can be reattached in progress.
> 
>   ssh -l fred server.example.org "screen -x"

"screen -x" works, but is probably not what most people use as it
connects to a screen session in addition to existing clients which
often restricts one of the clients to a smaller terminal than
available for him.

I usually use "screen -dr" for that:

-d = detach an attached session
-r = reattach the session here

What I do is usually

ssh -l fred server.example.org screen -Rd

-R = reattach if a session exists or creates a new session if no
     session exists.

That way you only need one command for both purposes listed above.
This is especially nice for making shell aliases or so.


> 2) Here ssh(1) is to assume that the connection is broken after 5
> seconds of not being able to reach the server and to exit.
> 
>  while ! ssh -t [email protected] -o 'ServerAliveInterval 5' \
>    screen -d -RR; do true; done

There's a nice tool which does this a little bit more intelligent:
http://www.harding.motd.ca/autossh/

Combined with the above, I use it in a shell function like this:

asc () {
        print -Pn "\e]0;%n@%m: autossh -t $* 'screen -RdU'\a"
        autossh -x -t "$@" 'screen -RdU'
}

asc stands for "autossh + screen"

I.e. I just call "asc [email protected]" and I do get a screen
session, either an existing one or a fresh one. In production for like
5 years now on a daily base -- also helps to survive setting the
laptop to sleep and waking it up at a different location with a
differnt IP address.

(And yes, there's also mosh. But the above has also the advance that I
can add any port forwardings or other SSH options and they're used
upon every reinstantiation of the connection again.)

HTH.

		Kind regards, Axel
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