Java
MSH Zimbra Rules requires Java 21 or later. The service launchers verify the Java version on every start and refuse to run on anything older.
Checking your Java version
To check if Java is already installed and which version you have, run:
java -version
If Java 21 or higher is installed, you will see output similar to:
openjdk version "21.0.x" 20xx-xx-xx
OpenJDK Runtime Environment (build 21.0.x+x)
OpenJDK 64-Bit Server VM (build 21.0.x+x, mixed mode)
If Java is missing or the version is lower than 21, follow the instructions below for your distribution.
If you already have a Java version newer than 21, there is no need to downgrade. The application works with any Java 21 or later release.
Debian / Ubuntu
Update the package index.
sudo apt update
Install OpenJDK 21.
sudo apt install openjdk-21-jre-headless -y
Verify the installation.
java -version
RHEL / CentOS / Rocky / AlmaLinux
Install OpenJDK 21.
sudo dnf install -y java-21-openjdk-headless
Verify the installation.
java -version
Multiple Java versions on one host
If the server already runs another Java version (for example one required by other software), you do not need to change the system default. Install Java 21 alongside it and point MSH Zimbra Rules at the Java 21 binary explicitly by setting MSH_JAVA_BIN in etc/config.cf.
What's next
- Server installation - install and start the MSH Zimbra Rules services