why must I use sometimes screen -rx and not screen -r?

Question

Sometimes to get access to screen console I need to user screen -rx and not just screen -r.

Any idea why and why this happens ?

Answer 1

-x attaches to an already running screen. Two or more terminals can share one session.

-r restores a detached session

Most probably you have to use -x when a session was not cleanly disconnected and is still considered running. The -xr is unnecessary in that case.

Answer 2

screen -rx attaches to a session that is already attached elsewhere, and allows simultaneous use of the screen session by all attached parties.

In the event that a screen -r fails with something similar to:

There is a screen on:
    10250.ttys016.ironforge (Attached)
There is no screen to be resumed.

... you can use screen -rd to force the other party to detach & allow you to attach.

Answer 3

Use -x if you want to attach to an already running screen without detaching the other sessions.

If the session hasn't disconnected cleanly, you have other options than -x:

• -d does the same than typing C-A d from the controlling terminal for the session.
• -D is the equivalent to the power detach key. (Both -d &-D are ignored, when not applicable.)
• Both of the above work in combination with -r resume and -R resume first appropriate.
• A powerful & useful combination is -D -R for attach here and now.
• For all combinations, see screen manual for command-line option -d.