I'm using GNU screen for remote pair programming. Let's call the local account for the remote user 'pairpair'. I have the following lines in my .screenrc: multiuser on acladd pairpair I have run sudo chmod u+s /usr/bin/screen. However, when the remote user tries to connect to my screen with the command screen -r [my_account_name]/[pid_of_screen] I receive the following message: Attach attempt with bad pid(xxx) The pid listed in the error message matches the pid of the screen process run by the remote user. The remote user's screen process hangs; my screen session continues happily along after the error message disappears. I've tried using both the built-in screen (at /usr/bin/screen) and the screen available from MacPorts, but I get the same error in both cases. This worked on OS X 10.5 (Leopard). I've googled around for the error message, but most of the hits relate to some BSD bug from 2003 or so (which was fixed). Has anyone else seen this behavior? Does anyone have any idea how to make multiuser support in screen work in SL?