How do I know if the Glassfish Java VM is running in "headless mode"?

The asadmin command line utility is an easy way to check.

# asadmin generate-jvm-report --type summary | grep awt

java.awt.graphicsenv = sun.awt.X11GraphicsEnvironment

java.awt.headless = true

java.awt.printerjob = sun.print.PSPrinterJob