Como você pode ver em screen -list , essa sessão de tela está conectada no momento. Você não pode se conectar a ele de outro lugar sem desanexá-lo primeiro. Você pode fazer isso adicionando a opção -d , como screen -d -r 2101.pts-0.ubuntu . Há mais informações no manual do GNU Screen . Aqui está um trecho:
-r [pid.tty.host]
-r sessionowner/[pid.tty.host]
resumes a detached screen session. No other options (except combinations 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-d|-D [pid.tty.host]
does not start screen, but detaches the elsewhere running screen session. It has the same effect as typing "C-a d" from screen's controlling terminal. -D is the equivalent to the power detach key. If no session can be detached, this option is ignored. In combination with the -r/-R option more powerful effects can be achieved:-d -r Reattach a session and if necessary detach it first.
-d -R Reattach a session and if necessary detach or even create it first.
-d -RR Reattach a session and if necessary detach or create it. Use the first session if more than one session is available.
-D -r Reattach a session. If necessary detach and logout remotely first.
-D -R Attach here and now. In detail this means: If a session is running, 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.
-D -RR Attach here and now. Whatever that means, just do it.
-x Attach to a not detached screen session. (Multi display mode).
Note: It is always a good idea to check the status of your sessions by means of "screen -list".