"Upgraded" from El Capitan to Sierra.

Removed old XQuartz 2.7.11 install following instructions here (just something I found via google): https://gist.github.com/pwnsdx/d127873e24cef159d4d603accaf37ee4

Installed XQuartz 2.7.11 from pkg.

Restarted computer.

Now, when I run XQuartz by clicking its icon in the Applications/Utilities folder, it starts to launch, and then quits. Then it keeps doing that, until I restart the computer.

Each time it runs it produces a new log file. The only thing that's different on each run is the time stamp and the socket name:

X11.app: main(): argc=2
	argv[0] = /Applications/Utilities/XQuartz.app/Contents/MacOS/X11.bin
	argv[1] = --listenonly
Waiting for startup parameters via Mach IPC.
X11.app: Listening on socket for fd handoff:  (5) /var/tmp/tmp.0.fHH4Av
X11.app: Thread created for handoff.  Returning success to tell caller to connect and push the fd.
X11.app Handing off fd to server thread via DarwinListenOnOpenFD(7)
DarwinListenOnOpenFD: 7
X11.app: do_start_x11_server(): argc=7
	argv[0] = /opt/X11/bin/Xquartz
	argv[1] = :0
	argv[2] = -nolisten
	argv[3] = tcp
	argv[4] = -iglx
	argv[5] = -auth
	argv[6] = /Users/tom/.serverauth.6813
[1546224.009] Xquartz starting:
[1546224.009] X.Org X Server 1.18.4
[1546224.009] Build Date: 20161025
[1546224.013] x: 1280, y: 22, w: 1440, h: 2538
[1546224.013] x: 0, y: 1008, w: 1280, h: 800
[1546224.013] x: 2720, y: 0, w: 1440, h: 2560
[1546224.027] (II) GLX: Initialized Core OpenGL GL provider for screen 0
[1546224.110] X11.app: DarwinProcessFDAdditionQueue_thread: Sleeping to allow xinitrc to catchup.
[1546224.125] (EE) Error loading keymap /tmp/server-0.xkm
[1546224.125] (EE) XKB: Failed to load keymap. Loading default keymap instead.
[1546226.801] (II) Server terminated successfully (0). Closing log file.