Overview
This article tells you how to configure your Jobs, JobServer, and a Remote Engine to use JDK 8, 11, and 17 on Linux.
How Linux distributions work with the Java binary
Linux distributions do not add JAVA_HOME/bin in the path. Instead, there is a Java executable in /usr/bin. This binary is a symbolic link to /etc/alternatives/java, which is a symbolic link to /usr/lib/jvm/JDK-version/bin/java. Setting JAVA_HOME is not required to use Java, because it works out of the box.
$ java -version
openjdk version "11.0.20" 2023-07-18 LTS
OpenJDK Runtime Environment (Red_Hat-11.0.20.0.8-1) (build 11.0.20+8-LTS)
OpenJDK 64-Bit Server VM (Red_Hat-11.0.20.0.8-1) (build 11.0.20+8-LTS, mixed mode, sharing)
$ which java
/usr/bin/java
$ ls -l /usr/bin/java
lrwxrwxrwx 1 root root 22 Oct 18 10:47 /usr/bin/java -> /etc/alternatives/java
$ ls -l /etc/alternatives/java
lrwxrwxrwx 1 root root 62 Oct 26 10:58 /etc/alternatives/java -> /usr/lib/jvm/java-11-openjdk-11.0.20.0.8-3.el9.x86_64/bin/java
To change the release to run by default, you must change the symbolic link /etc/alternatives/java by replacing it with the command update-alternatives --config java.
$sudo update-alternatives --config java
There are 2 programs which provide 'java'.
Selection Command
-----------------------------------------------
*+ 1 java-11-openjdk.x86_64 (/usr/lib/jvm/java-11-openjdk-11.0.20.0.8-3.el9.x86_64/bin/java)
2 java-17-openjdk.x86_64 (/usr/lib/jvm/java-17-openjdk-17.0.9.0.9-2.el9.x86_64/bin/java)
Enter to keep the current selection[+], or type selection number:
This implementation means that all JAR files you run with a Java command will only use the system default Java. This also works for JDK installed with a package manager (APT or YUM).
You can add manually-installed JDK using the following command:
$sudo update-alternatives --install /usr/bin/java java /opt/portable-jdk/bin/java 0
or
$sudo ln -s /opt/portable-jdk/bin/java /etc/alternatives/java
How Talend software works with Java
Talend Remote Engine
Before installing the Remote Engine, you must update
JAVA_HOME to a JDK path. JDK uses this variable to run the Remote Engine and it is stored on the
wrapper.conf file.
# more talend-remote-engine-wrapper.conf
[...]
set.default.JAVA_HOME=/usr/lib/jvm/java-17-openjdk
{...]
You can change this value to the new Java path when the Remote Engine is stopped.
JobServer
# more start_rs.sh
[...]
MY_JAVA=/usr/lib/jvm/java-17-openjdk
How to use different Java for Jobs, Remote Engines, and JobServers
In summary, when using different Java for Jobs, JobServers, and Remote Engines:
The system default Java code will be the Java that runs the Job. The
update-alternatives --config Java command makes you select the JDK to run the Jobs.
The Remote Engine uses the
JAVA_HOME variable set just before installation in the configuration file, and JobServer uses the Java in the configuration file.
This means the Jobs use
/usr/bin/java and the Remote Engine or JobServer uses
JAVA_HOME/bin/java.
