Checking the presence of Java on your Linux machine

We will check the JRE/JDK installation from the command line as follows:

1. Log in to your server and run this command:

      ~ $ sudo update-alternatives --config java  

1. If there is no Java properly configured, you should see the following output:

      update-alternatives: error: no alternatives for java.  

1. In case there is only one Java installed, the output will be similar to the following command line:

      There is only one alternative in link group java (providing
           /usr/bin/java):   
          /usr/lib/jvm/java-8-openjdk-i386/jre/bin/java
          Nothing to configure.
  

1. If you have more than one Java, for example, Oracle JRE and OpenJDK, the output will be similar to this:

    There are 2 choices for the alternative java (providing /usr/bin/java).
    
    Selection   Path                               Priority    Status
    -----------------------------------------------------------------
    * 0        /usr/lib/jvm/java-8-openjdk-i386      1081      auto mode 
                 /jre/bin/java                           
      1        /opt/java/jre1.8.0_121/bin/java        1        manual  
                                                               mode
      2        /usr/lib/jvm/java-8-openjdk-i386      1081      maunal
                 /jre/bin/java                                 mode 
                                                          
       Press <enter> to keep the current choice[*], or
          type selection number:

We determined if a Java installation is already present on your machine. As we mentioned earlier, this is a basic requirement for our installation. We had the opportunity to check if the installed release, in case we found it, is suitable for running GeoServer, which is a version 8.x.

Now we will go through the installation of JRE and the servlet container. You can skip the following steps in case you already found a JRE/JDK installed.