How to connect to a “Private” screen session

Question

I have a couple of machines starting screen sessions for individual users. I do this by running

su news -c "screen -d -m -S news /usr/local/bin/newstask"

Normally, I can attach to such screen using

screen -r news/newstask

However, on one machine, this produces an error:

# screen -r news/newstask
There is a screen on:
        2341.newstask   (07.08.2016 11:28:33)   (Private)
There is no screen to be attached matching newstask.

What is strange is that the session is shown as "(Private").

Typically, they are tagged "(Multi, detached"). From another machine:

# screen -ls news/
There are several suitable screens on:
        8973.newstask   (07.08.2016 11:16:46)   (Multi, detached)
        1864.newsclient        (07.08.2016 03:03:23)   (Multi, detached)
        1850.newsserver        (07.08.2016 03:03:23)   (Multi, detached)
3 Sockets in /var/run/screen/S-news.

What could be the reason for why these sessions are tagged (Private), and how can I attach to these? Or how could I avoid the sessions being private?

Thanks.

Answer 1

Maybe this https://superuser.com/questions/193798/is-it-possible-to-make-a-screen-session-private is what you hit. GNU Screen can have password protected sessions.

Answer 2

By default, screen doesn't let you attach to a session from another user. In order to do so, you have to use the commands multiuser and addacl (see the screen(1) manual page).

In your case, assuming you want user root to be able to access screens from user news, you will have to add these lines to ~news/.screenrc:

multiuser on
addacl root