How do I configure starting jdk for hudson(now jenkins)? - hudson

Question

I googled a lot and read through the wiki, just could not find out where setting starting jdk can be done. It needs jdk 1.5 or later. The os is centOS and I set the JAVA_HOME environment variable to a 1.6 version and add jdk bin directory into PATH environment variable, when I run the command '/etc/init.d/jenkins start' , I received below error:
Jenkins requires Java5 or later, but you are running 1.4.2 from /usr/lib/jvm/java-1.4.2-gcj-1.4.2.0/jre
java.lang.UnsupportedClassVersionError: 48.0
at Main.main(Main.java:90)
Don't know why jenkins look for jdk from path above, I don't see any environment variable containing /usr/lib/jvm/java-1.4.2-gcj-1.4.2.0/jre.
Any ideas?
========update
to firelore:
I tried to run command 'update-alternatives --install java java /home/irteam/app/jdk1.6.0_07 ',it doesn't work,prompting command parameters, like :
alternatives version 1.3.30.1 - Copyright (C) 2001 Red Hat, Inc.
This may be freely redistributed under the terms of the GNU Public License.
usage: alternatives --install <link> <name> <path> <priority>
[--initscript <service>]
[--slave <link> <name> <path>]*
alternatives --remove <name> <path>
alternatives --auto <name>
alternatives --config <name>
alternatives --display <name>
alternatives --set <name> <path>
common options: --verbose --test --help --usage --version
--altdir <directory> --admindir <directory>

Answer 1

The 1.4.2 version was bundled with your centOS install and made default. You will need to run the update-alternatives command to change your symlink to your updated jdk location.

Answer 2

Try to set both PATH and JAVA_HOME variable to new JRE which you have downloaded. If you are using slaves, I would suggest to delete the slave and recreate the same slave so you done loose the attached jobs to it. Check the console log, you should see it running with new jre.

Answer 3

You can configure it in Jenkins directly.
->Manage Jenkins -> Configure system -> Global Properties -> Environment Variables
Just add the JAVA_HOME.
Then add the JDK path in JDK section.