I have been running into issues with screen when switching to another user:
$ su otheruser > password $ screen -x > Cannot open your terminal '/dev/ttys002' - please check.
From this post I have discovered that it was due to a permissions issue.
$ ls -l /dev/ttys002 > crw--w---- 1 user tty 16, 2 Dec 30 23:34 /dev/ttys002
To fix I had to set other permissions.
$ su otheruser $ sudo chmod go+wr /dev/ttys002
You still have to su to the owners account and therefore it is still secure. ie user can not just connect to a /dev/ttys002 currently in use by otheruser.
#As user, otheruser currently using /dev/ttys002 $ screen -x /dev/ttys002 > Must run suid root for multiuser support.
The issue has kept recurring and I have had to reset the permissions every time I wanted to connect. This could be Mac OS X specific but I edited the root crontab to fix.
$ sudo crontab -e # Added the text below # MIN HOUR MDAY MON DOW COMMAND 0,15,30,45 * * * * chmod o+wr /dev/ttys000 0,15,30,45 * * * * chmod o+wr /dev/ttys001 0,15,30,45 * * * * chmod o+wr /dev/ttys002 0,15,30,45 * * * * chmod o+wr /dev/ttys003 0,15,30,45 * * * * chmod o+wr /dev/ttys004 0,15,30,45 * * * * chmod o+wr /dev/ttys005