GNU Screen: can not resume the screen from a broken remote session

Question

Sometimes the SSH shell featuring a active screen session to my remote server gets broken (internet line not very stable, for example) with the session still attached.

Then I SSH again into the server, and try to resume the screen session:

luis@Zarzamoro:~$ screen -r
There is a screen on:
        9166.pts-2.Zarzamoro    (12/23/15 23:47:34)     (Attached)
There is no screen to be resumed.
luis@Zarzamoro:~$ screen -r 9166.pts-2.Zarzamoro
There is a screen on:
        9166.pts-2.Zarzamoro    (12/23/15 23:47:34)     (Attached)
There is no screen to be resumed matching 9166.pts-2.Zarzamoro.

I don't know much about GNU screen. Why does this happen?
Is it possible to resume this screen session?

Answer 1

Use:

screen -r -d <pid>.<tty>.<host>

In your case:

screen -r -d 9166.pts-2.Zarzamoro

This will force detach the screen on the other end and attach.

Answer 2

Two points:

• You do not have to specify the whole pid+session name (screen accepts a reasonable abbreviation).

• You may get better results with the -x option.

From the manual page:

-r
sessionowner/[pid.sessionname]’ Resume a detached screen session.

-x
Attach to a session which is already attached elsewhere (multi-display mode). Screen refuses to attach from within itself. But when cascading multiple screens, loops are not detected; take care.

Answer 3

This happens to me occasionally as well. What I believe happens is that your tty is not properly detached from screen and therefore when you reconnect to the server you are still "attached" to the screen.

Here's what I do:

screen -d
screen -r (if you have only one screen)
screen -r <pid> (if you have more than one screen)

You can also do

screen -r -d (add <pid> if you have more than one screen)

to detach and reattach the improperly attached screen.

Also, when doing screen -r you needn't specify the entire screen's name, only the pid (four digit number).

Answer 4

You can even automate this, as shown in the here to where it will automatically reconnect to the existing screen session (or create a new screen session if none exists):

.bashrc

Add these lines at the top of ~/.bashrc on the target host:

# Auto-screen invocation. see: http://taint.org/wk/RemoteLoginAutoScreen
# if we're coming from a remote SSH connection, in an interactive session
# then automatically put us into a screen(1) session.   Only try once
# -- if $STARTED_SCREEN is set, don't try it again, to avoid looping
# if screen fails for some reason.
if [ "$PS1" != "" -a "${STARTED_SCREEN:-x}" = x -a "${SSH_TTY:-x}" != x ]
then
  STARTED_SCREEN=1 ; export STARTED_SCREEN
  [ -d $HOME/lib/screen-logs ] || mkdir -p $HOME/lib/screen-logs
  sleep 1
  screen -RR && exit 0
  # normally, execution of this rc script ends here...
  echo "Screen failed! continuing with normal bash startup"
fi
# [end of auto-screen snippet]