Xt error: Can't open display, if using default DISPLAY

Question

Overview

I\'m attempting to get XQuartz to work on OSX so I can do X11 forwarding via Docker. I\'m following the instructions here. I believe my question may be answer

Answer 1

For OS X 10.6.3 and later, per XQuartz 2.7.11 instructions:

If this is your first time installing XQuartz, you may wish to logout and log back in. This will update your DISPLAY environment variable to point to XQuartz.app rather than X11.app. If you would prefer to keep using X11.app as your default server (you can still launch XQuartz.app manually), you’ll want to disable /Library/LaunchAgents/org.macosforge.xquartz.startx.plist using launchctl(1).

After installing XQuartz 2.7.11 on my macOS High Sierra, logging out of my Mac and logging in again was enough for this to work via my MacOS Terminal. However, you may avoid having to logout and log in by opening the XQuartz Terminal application (XQuartz > Applications > Terminal), and running your X application from there. For example:

and then

bash-3.2$ xclock &