When I had installed Jenkins on Amazon Linux AMI following steps mentioned in http://bhargavamin.com/how-to-do/install-jenkins-on-amazon-linux-aws/
After installation I was able to open Jenkins through browser but when I selected option "Install Plugins" it showed error as "Unable to connect to Jenkins Server."
So then how to troubleshoot this issue??
The problem here is pretty simple, if you do curl http://127.0.0.1:8080 on your host machine, you should get a message stating:
Authentication required
<!--
You are authenticated as: anonymous
Groups that you are in:
Permission you need to have (but didn't): hudson.model.Hudson.Administer
-->
This means that jenkins has anonymous priviledges which is not allowing any connection.
To solve this issue, you will have to do two changes:
Add Jenkins user to root group: sudo usermod -a -G root jenkins
Make Jenkins listen to all external IPs by editing file /etc/sysconfig/jenkins and changing the JENKINS_LISTEN_ADDRESS="0.0.0.0"
Once this is done, restart the jenkins server and then try to install plugins for jenkins.
I'm using this trick https://issues.jenkins-ci.org/browse/JENKINS-45388 and it works. What I did is add passwd: as prefix of file /var/lib/jenkins/secrets/initialAdminPassword and click retry button for several times and finally it works.
1.Click on retry 2.Fill admin user name, pwd ,mail, full name 3.If filled already use pwd given in initialAdminPassword folder 4.proceed
