"No X11 DISPLAY Variable" Error in Java Application

Java applications rely on the X Window System (X11) for graphical user interface (GUI) functionality. The "No X11 DISPLAY variable was set" error indicates that the application cannot access the X11 display environment.

To resolve this issue, set the X11 DISPLAY environment variable. The value to set depends on your display configuration.

On the Main Display

If you are using the main display, set the DISPLAY variable as follows:

For Bash or Bourne shell:

export DISPLAY=:0.0

For C shell or TC shell:

setenv DISPLAY :0.0

On Remote or Secondary Displays

If you are using a remote or secondary display, the DISPLAY variable value will be different. The value should be in the format:

DISPLAY=hostname:displaynumber.screen

For example, if the remote hostname is "host1" and the display number is "11" with screen "0", the DISPLAY variable would be:

DISPLAY=host1:11.0

Setting the DISPLAY Variable

Set the DISPLAY variable before running your Java application. This can be done by adding the following line to the start of your application's script:

export DISPLAY=:0.0

Or

setenv DISPLAY :0.0

For the appropriate display configuration.

Additional Notes

If the DISPLAY variable is not set automatically, check if you have modified the default shell configuration files (e.g., .profile, .bashrc, .cshrc). SSH sessions often set the DISPLAY variable correctly, allowing remote access to X11 applications.