C.4.  Setting the default JDK with the /usr/sbin/alternatives Utility

/usr/sbin/alternatives is a tool for managing different software packages that provide the same functionality. Red Hat Enterprise Linux uses /usr/sbin/alternatives to ensure that only one Java Development Kit is set as the system default at one time.

Important

Installing a Java Development Kit from the Red Hat Network will normally result in an automatically configured system. However, if multiple JDKs are installed, it is possible that /usr/sbin/alternatives may contain conflicting configurations. Refer to Procedure C.4, “ Using /usr/sbin/alternatives to Set the Default JDK ” for syntax of the /usr/sbin/alternatives command.

Procedure C.4.  Using /usr/sbin/alternatives to Set the Default JDK

  1. Become the root user.

    /usr/sbin/alternatives needs to be run with root privileges. Use the su command or other mechanism to gain these privileges.
  2. Set java.

    Input this command: /usr/sbin/alternatives --config java
    Next, follow the on-screen directions to ensure that the correct version of java is selected. Table C.1, “java alternative commands” shows the relevant command settings for each of the different JDKs.

    Table C.1. java alternative commands

    JDK alternative command
    OpenJDK 1.6 /usr/lib/jvm/jre-1.6.0-openjdk/bin/java
    Sun Microsystems JDK 1.6 /usr/lib/jvm/jre-1.6.0-sun/bin/java
  3. Set javac.

    Enter this command: /usr/sbin/alternatives --config javac
    Follow the on-screen directions to ensure that the correct version of javac is selected. Table C.2, “javac alternative commands” shows the appropriate command settings for the different JDKs.

    Table C.2. javac alternative commands

    JDK alternative command
    OpenJDK 1.6 /usr/lib/jvm/java-1.6.0-openjdk/bin/javac
    Sun Microsystems JDK 1.6 /usr/lib/jvm/java-1.6.0-sun/bin/javac
  4. Extra Step: Set java_sdk_1.6.0.

    The Sun Microsystems JDK 1.6 requires an additional command be run:
    /usr/sbin/alternatives --config java_sdk_1.6.0
    Follow the on-screen directions to ensure that the correct java_sdk is selected. It is /usr/lib/jvm/java-1.6.0-sun.