"No X11 Display Variable" - What Does It Mean

No X11 DISPLAY variable - what does it mean?

If you're on the main display, then

export DISPLAY=:0.0

or if you're using csh or tcsh

setenv DISPLAY :0.0

before running your app.

Actually, I'm surprised it isn't set automatically. Are you trying to start this application from a non-graphic terminal? If not, have you modified the default .profile, .login, .bashrc or .cshrc?

Note that setting the DISPLAY to :0.0 pre-supposes that you're sitting at the main display, as I said, or at least that the main display is logged on to your user id. If it's not logged on, or it's a different userid, this will fail.

If you're coming in from another machine, and you're at the main display of that machine and it's running X, then you can use "ssh -X hostname" to connect to that host, and ssh will forward the X display back. ssh will also make sure that the DISPLAY environment variable is set correctly (providing it isn't being messed with in the various dot files I mentioned above). In a "ssh -X" session, the DISPLAY environment variable will have a value like "localhost:11.0", which will point to the socket that ssh is tunnelling to your local box.

“No X11 DISPLAY variable” - what does it mean?

A DISPLAY is only needed if you're running this in GUI mode. Since you're running this in Mesos, you cannot use GUI mode. Add the -n option to run in CLI mode.

JMeter: Getting Started: CLI Mode

No X11 DISPLAY variable was set' trying to run Minecraft server on EC2 instance

The problem

From my understanding the issue is with your minecraft.service file.

When you are starting the service you are running the installer for the forge server.

The installer requires X unless run with the --installServer flag as you have done above in your user data script.

This is why you are experiencing the error.

The solution

I would imagine that you want to run the actual server .jar

For the version of the installer you are using I'm pretty sure that the name for the jar is:

minecraftforge-universal-1.12.2-14.23.5.2860.jar

Using this as an example you want to replace your current command with this:

/usr/bin/java -Xmx8G -Xms8G -jar minecraftforge-universal-1.12.2-14.23.5.2860.jar nogui