Unable to create the home directory '/dev/null/.hudson'

Problem :

You deploy hudson.war in Tomcat 6 and when you want to show hudson main page, you have this error :
Unable to create the home directory '/dev/null/.hudson'. This is most likely a permission problem.
To change the home directory, use HUDSON_HOME environment variable or set the
HUDSON_HOME system property. See Container-specific documentation for more details of how to do this.

Solution :

- Create a home directory for Hudson.

mkdir -p /home/hudson
chown -R tomcat:tomcat /home/hudson/

ls -al /home/hudson/
drwxr-xr-x 6 tomcat tomcat 4096 Oct 3 18:45 hudson

Note : I've notice that you must restart Tomcat for that's work.

- Add the HUDSON home directory for Tomcat in the tomcat startup script :

vi /etc/init.d/tomcat-6

Search JAVA_OPTS
Then add some line after :

JAVA_OPTS="$JAVA_OPTS -DHUDSON_HOME=/home/hudson"

Example :
...
# Activate Logging
if [ -r "${CATALINA_HOME}"/bin/tomcat-juli.jar ]; then
JAVA_OPTS="${JAVA_OPTS} -Djava.util.logging.manager=org.apache.juli.ClassLoaderLogManager \
-Djava.util.logging.config.file=${CATALINA_BASE}/conf/logging.properties"
fi
JAVA_OPTS="$JAVA_OPTS -DHUDSON_HOME=/home/hudson"
...

- Modify the Tomcat user file (vi /etc/tomcat-6/tomcat-users.xml )
cf AdministrationHudson

- Then Restart Tomcat.