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gnu-screenmulti-usersuid

Is running GNU Screen suid root the only way to make multiuser mode work?

I'm running Ubuntu 11.10 and GNU Screen version "4.00.03jw4", and I'm trying to use multiuser mode.

The following process works for me:

as user "first_user"
> sudo chmod u+s /usr/bin/screen
> sudo chmod 755 /var/run/screen

and only after that can you do
> screen -S session_name
or if you've already created a screen session,
> screen -r session_name

and inside of screen:
>^A:multiuser on
>^A:acladd second_user "#?"

and if you want second_user to only be an observer
>^A:aclchg second_user -w "#?"

now you can, as user "second_user", do
> screen -x first_user/
to connect 

when you're all done, do 
> sudo chmod u-s /usr/bin/screen
> sudo chmod 775 /var/run/screen

because running screen suid root is a security risk

This is depressing. I've been searching diligently, but I can't find a better way. Is there one?

Update:

  • There is a bug in screen 4.06. Users can connect to a shared session, but can't send a command over it like: screen -S shared_session_name -X stuff "comands\n".
  • In the screen 4.09 it is fixed
Solution

  • You are right. This is the only way to get multiuser screen running.

    However, unless your box is very exposed, I don't think that leaving the suid bit on is a huge security risk.