Never put off till tomorrow what you can avoid all together. (I love a good crash) Thus, the DISPLAY variable was set correctly in the xterm window. (like mine, unfortunately) However, my poor testuser has no shell environment. Maybe your other user's shell startup script sets the DISPLAY variable to a static value. Out of curiosity, what do you get when you execute: Thus, the main user cannot access the socket of the testuser but both can see both sockets. Xlib: connection to ':1.0' refused by server Srwxrwxrwx 1 kerby wheel 0B Dec 5 04:20 X1= Srwxrwxrwx 1 kerbaugh wheel 0B Dec 5 04:20 X0= With both me and my testuser, kerby, (the virtual crash-test dummy) running X11, I get the following outputs in the main user's shell:

The display is different for each different Xsession. It's done rather differently in Tiger, if my system is generic in that regard. The socket would act like a number of sockets, one for each per-session bootstrap namespace. Technical Note TN2083: Daemons and Agents) It would be possible to use the socket independently in different per-session namespaces. It would seem more likely that your sockets behave in a rather unPOSIX manner with respect to Mach namespaces. Can your users write to each other's X11 display with sudo? That would seem rather unlikely to be considered a satisfactory implementation. That's incredible! Are you sure? Maybe Apple did it differently in Panther but it's hard to imagine that writes to a socket can be 'pipelined' to correct 'screen' according to username. both xterms have DISPLAY set to 😮.0, yet the X11

Wireshark mac os x