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Screen’s Multi-User Mode

21/08/2011

In this article, I found a great tutorial of how one can set up a working environment between two or more people at different geographical areas. The solution is to use screen and ssh. Here are the steps that need to be taken:

  • The teacher starts screen in a local xterm, for example via screen -S SessionName. The -S switch gives the session a name, which makes multiple screen sessions easier to manage.
  • The student uses SSH to connect to the teacher’s computer.
  • The teacher then has to allow multiuser access in the screen session via the command Ctrl-a :multiuser on (all screen commands start with the screen escape sequence, Ctrl-a).
  • Next the teacher grants permission to the student user to access the screen session with Ctrl-a :acladd student where student is the student login ID.
  • The student can now connect to the teacher’s screen session. The syntax to connect to another user’s screen session is screen -x username/session.
  • Optionally, the teacher can also make the student’s session read-only. To do this, use the aclchg screen command to remove write access for the student: Ctrl-a :aclchg student -w "#". The student can then only observe the teacher’s actions.

As a note, I should mention author’s argument about setting screen’s setuid bit. This is a rather controversial and highly security risked operation, that I hope it’s not necessary at all. Time will show!

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From → Linux

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