Sharing terminal session to every PC in classroom

Interesting title, isn't it? It's just what you need when you have classroom full of Windows machines and yet you want to share terminal screen which you are projecting onto every screen for easy copy/paste from your Linux laptop. Can it be done?

So, what do we have?

  • presentation laptop running xterm (with white background) projecting picture to whiteboard
  • Windows PC in front of every student
  • local network
And what do we want?
  • copy/paste from session to own editor on student's computer
  • students session should be view only
At first, VNC came to mind. But, then again I didn't find easy way to relay single session to multiple computers. And I wasn't really sure how well it would work with my copy/paste requirement. And it seemed a bit too complex. And after all, it's not graphic session, but instead just terminal running presentation in vim for syntax highlighting...

Windows

Biggest requirement on Windows in minimal deployment under normal user privileges. Putty seems like perfect fit: single executable, good terminal emulation. No brainier.

Linux

On my laptop, I used screen with session sharing but with read-only twist (giving every student my account on personal laptop just... doesn't seem sane).

First I created new student user which will connect to screen which shares my session. This account has well-known password written on whiteboard together with IP address of my laptop.

student user is starting screen and attaching to my shared perl session using shell script configured in /etc/passwd as default shell. 

exec screen -x dpavlin/perl
So, to participate, students just ssh using Putty from Windows machines. So far, so good...

To make session read-only I needed to remove write permission from student user in screen. This proved to be a challenge in this solution, but not something that reading man screen can't solve: 

# screenrc
multiuser on
acladd student
aclumask student-w

After starting shared session named perl 

screen -S perl -c screenrc
everything is ready. If you can thing of simpler thing to do, I would love to hear it :-)

Unexpected consequence of this setup is my ability to switch to other screen in shared session screen on my laptop which changes projected session on whiteboard (to show table of contents or some random example in middle of presentation), but students will still see perl session with presentation.

Detailed step-by-step instructions how to setup view only screen sharing are available in my Sysadmin Cookbook.