X11 applications don't open after XQuartz update (OS X 10.10.4) I updated X11 by installing the most recent XQuartz package, 2.7.9. Now, when opening an application that is supported by X11 (e.g., emacs), my terminal throws an error (while X11 starts in the background):

[lap0988:~] user% emacs test.txt &amp;
[1] 14071
[lap0988:~] user% Error: Couldn't find per display information


Needless to say, the application doesn't open. My hunch is that this has to do with the DISPLAY environment variable.

[lap0988:~] user% echo $DISPLAY
/private/tmp/com.apple.launchd.p7v5k8pNT7/org.macosforge.xquartz:0


Has anyone come across the problem? Can you suggest a straightforward fix for this?
I'm afraid you'll probably need to rebuild emacs.  I expect that the one you have is looking for libraries that aren't there any more following the XQuartz update.

I had the exact same problem, and solved it with brew upgrade emacs --with-x11 --with-ctags --with-glib --with-gnutls.  The relevant command-line for you will differ according to your choice of package manager and build options.