Linux Java Runtime Environment Access

# Run with java explicitly java -jar myapp.jar chmod +x myapp.jar 10.5 "UnsupportedClassVersionError" Cause : JAR compiled with newer Java than your JRE.

# Check JAR's required version javap -verbose MyClass.class | grep "major version" # 52 = Java 8, 55 = Java 11, 61 = Java 17, 65 = Java 21 Minimal Dockerfile using Alpine + OpenJDK JRE : linux java runtime environment

: Use OpenJDK (distro package) or Adoptium for most Linux servers. 3. Installing JRE on Major Linux Distributions 3.1 Debian / Ubuntu / Linux Mint # Update package index sudo apt update Install JRE (OpenJDK 17 LTS) sudo apt install openjdk-17-jre Alternative: JRE 11 sudo apt install openjdk-11-jre Check installation java -version # Run with java explicitly java -jar myapp

sudo useradd -r -s /bin/false javauser sudo chown -R javauser:javauser /opt/myapp sudo -u javauser java -jar /opt/myapp/app.jar 10.1 "java: command not found" Cause : JRE not installed or PATH not set. Installing JRE on Major Linux Distributions 3

# Reduce heap size java -Xmx256m -jar app.jar free -h 10.3 "No X11 DISPLAY variable" (headless GUI error) Fix : Run in headless mode: