Linux – automatically start screen upon ssh login

gnu-screenlinuxssh

I have been reading about how to automatically start a screen when I ssh to a remote server. I would like a simple one-liner to add to my .bash_profile to start screen when I ssh in, and NOT exit my remote connection when I detach the screen.

I have been looking into exec screen and pretty much every combination of -d, -r, -D and -R and cannot figure out what flags I need.

Ideally I would type ssh whatever and be logged into the server in a new screen or it can reattach an old screen, I would kind of like to know how to do both to see which I like better. Then I can either type Ctrl ad or Ctrl d and have it bring me back to the normal ssh login for that server (where you would see the motd). From there I can screen -r back into whatever screen I want, or hit Ctrl d again to log out.

Best Answer

A simple screen -R should do the trick.

To verify this, I added screen -R to my .bash_profile on a remote server, logged in, detached from screen, and was dropped back to a normal shell prompt on the remote server. Verified with .bashrc as well. Subsequent logins yielded the expected result (re-attach to screen session).

Related Solutions

Linux – ssh-agent and screen

With the following setup, you won't need any wrapper for invoking screen. Moreover, it avoids using /tmp (with the consequent security risks).

Ensure you have an ~/tmp directory:
```
mkdir ~/tmp
```
Add to .screenrc the following line:
```
setenv SSH_AUTH_SOCK "$HOME/tmp/ssh-agent-screen"
```
- This ensures that inside screen, ssh looks for the socket always in the same location, rather than a changing path.
- You must use setenv whichever shell you use, since it's a screen and not a shell command.
Add to .bash_profile the following line:
```
[ -n "$SSH_AUTH_SOCK" ] && [ "$SSH_AUTH_SOCK"!="$HOME/tmp/ssh-agent-screen" ] && ln -sf "$SSH_AUTH_SOCK" "$HOME/tmp/ssh-agent-screen"
```
- This will link from the fixed location (where ssh looks) to the real one, and must appear after starting ssh-agent.
- Using [ -n "$SSH_AUTH_SOCK" ] will properly prevent errors when SSH_AUTH_SOCK is not set.
- [ "$SSH_AUTH_SOCK"!="$HOME/tmp/ssh-agent-screen" ] will prevent screen sessions linking $HOME/tmp/ssh-agent-screen to itself, if screen sources .bash_profile.
Instead of starting ssh-agent in .bash_profile, you can consider connecting with ssh -A (to use agent forwarding and make the remote machine use your agent).

After this setup, you can just use standard screen command. You'll only need to recreate existing sessions or manually set SSH_AUTH_SOCK inside them to the fixed location of step 2.

Credits to this website for the idea; I avoided using /tmp. This answer is similar but uses extra aliases.

Start gnu screen automatically

Instead of using screen -r which tries to resume a screen session, you can use screen -R which tries to resume a screen session and creates a new one if one doesn't exist.

   -r [pid.tty.host]
   -r sessionowner/[pid.tty.host]
        resumes  a detached screen session.  No other options (except com-
        binations with -d/-D) may be specified, though an optional  prefix
        of  [pid.]tty.host  may  be needed to distinguish between multiple
        detached screen sessions.  The second form is used to  connect  to
        another  user's  screen session which runs in multiuser mode. This
        indicates that screen should look for sessions in  another  user's
        directory. This requires setuid-root.

   -R   attempts to resume the first detached screen session it finds.  If
        successful, all other command-line options  are  ignored.   If  no
        detached  session exists, starts a new session using the specified
        options, just as if -R had not been specified. The option  is  set
        by default if screen is run as a login-shell (actually screen uses
        "-xRR" in that case).  For combinations with the -d/-D option  see
        there.

Personally I tend to use screen -DRA.

   -D -R   Attach here and now. In detail this means: If a session is run-
           ning, then reattach. If necessary detach  and  logout  remotely
           first.   If  it  was not running create it and notify the user.
           This is the author's favorite.
   -A      Adapt  the  sizes of all windows to the size of the current termi-
           nal.  By default, screen tries to restore  its  old  window  sizes
           when  attaching  to  resizable  terminals  (those with "WS" in its
           description, e.g. suncmd or some xterm).

Best Answer

Related Solutions

Linux – ssh-agent and screen

Start gnu screen automatically

Related Question