Time for action – checking the presence of Java on Ubuntu

We will check JRE/JDK installation from the command line.

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

   ~ $ sudo update-alternatives --config java
   

2. If there is no Java properly configured you should see an output like the following:

   update-alternatives: error: no alternatives for java.
   

3. In case there is one or more Java installed the output will be similar to:

   There is only one alternative in link group java: /usr/lib/jvm/java-7-openjdk-amd64/jre/bin/java
   Nothing to configure.
   

   Or:

   There are 2 choices for the alternative java (providing /usr/bin/java).
   
   Selection Path Priority Status
   ————————————————————
   * 0 /usr/lib/jvm/java-6-openjdk/jre/bin/java 1061 auto mode
   1 /usr/lib/jvm/java-6-openjdk/jre/bin/java 1061 manual mode
   2 /usr/lib/jvm/java-6-sun/jre/bin/java 63 manual mode
   
   Press enter to keep the current choice[*], or type selection number:
   

What just happened?

We determined if a Java installation is already present on our machine. This...