How to configure Jenkins to run on port 80

1. Go to /etc/default folder --> Open the file "jenkins"
2. Modify the line HTTP_PORT=8080 as HTTP_PORT=80
3. Start jenkins as root by using the command: sudo /etc/init.d/jenkins start
4. Open a browser and browse as localhost:80

that's it

Give a try to 'authbind':

sudo apt-get install authbind
sudo touch /etc/authbind/byport/80
sudo chmod 500 /etc/authbind/byport/80 
sudo chown jenkins /etc/authbind/byport/80

Then modify the script above to have (add authbind before the $JAVA_HOME/bin/java part):

exec daemon --name=jenkins --inherit --output=$JENKINS_LOG/jenkins.log \
--user=$USER -- authbind $JAVA_HOME/bin/java $JAVA_OPTS \
-jar $JENKINS_ROOT/jenkins.war $JENKINS_ARGS \
--preferredClassLoader=java.net.URLClassLoader

For newer Jenkins installations (1.598) on newer Ubuntu installations (14.04) edit /etc/init.d/jenkins and add authbind before $JAVA

$SU -l $JENKINS_USER --shell=/bin/bash -c "$DAEMON $DAEMON_ARGS -- authbind $JAVA $JAVA_ARGS -jar $JENKINS_WAR $JENKINS_ARGS" || return 2

As mentioned by Alan (see comment below) if you need IPv6 and your system is lower than Quantal you can instead of using apt-get to install authbind download a higher version. Make sure you have libc6 and libc6-udeb installed. Here is authbind version 2.1.1 from Ubuntu:

• amd64
• i386

Then execute:

sudo dpkg -i authbind_2.1.1_amd64.deb
# or sudo dpkg -i authbind_2.1.1_i386.deb

sudo touch /etc/authbind/byport/80
sudo chmod 500 /etc/authbind/byport/80 
sudo chown jenkins /etc/authbind/byport/80

Another solution is to simply use iptables to reroute incoming traffic from 80 to 8080. The rules would look like:

-A INPUT -i eth0 -p tcp --dport 80 -j ACCEPT
-A INPUT -i eth0 -p tcp --dport 8080 -j ACCEPT
-A PREROUTING -t nat -i eth0 -p tcp --dport 80 -j REDIRECT --to-port 8080

Reformatted as an iptables.rules file:

*filter
:INPUT ACCEPT [100:100000]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [95:9000]
-A INPUT -i eth0 -p tcp --dport 80 -j ACCEPT
-A INPUT -i eth0 -p tcp --dport 8080 -j ACCEPT
COMMIT

*nat
-A PREROUTING -i eth0 -p tcp --dport 80 -j REDIRECT --to-port 8080
COMMIT

The advantage of a iptable.rules file is the rules can persist after reboots. Just make sure to integrate any other current iptable rules into the same file!

On Redhat/CentOS this file can go in /etc/sysconfig/iptables.

On Debian/Ubuntu systems they can be saved in /etc/iptables/rules.v4 by using the iptables-persistent package. Or the iptable.rules can be called by modifying /etc/network/interfaces or hooking into if-up/if-down scripts. The Ubuntu Community wiki has a great page explaining these methods.

As is usually the case with networking, there's a lot of different ways to accomplish the same result. Use what works best for you!