Jenkins is hanging with no errors during startup

[Dustin Nielsen]

So, I've tried doing my research on this issue but it's gotten to the point where I'm no longer understanding what I'm reading.

I've installed Jenkins and Java on my server, running CentOS 6.8 and Apache 2.4. I had a few problems initially with just starting the service but have since ironed those out. Now stopping the service and starting it just gives me a nice green OK message stating that all is well with the world. When I run service jenkins status I get jenkins (pid 32178) is running.... But when I try to access my server with my server's IP address and the Port number (which I changed to 8888), it just hangs and then says the site took too long to respond.

So I looked at my jenkins logs and everything looked fine, even get this message INFO: Jenkins is fully up and running, but then just below that I get:

WARNING: Prober().run() exception
java.io.IOException: Operation not permitted
    at java.net.PlainDatagramSocketImpl.send(Native Method)
    at java.net.DatagramSocket.send(DatagramSocket.java:693)
    at javax.jmdns.impl.JmDNSImpl.send(JmDNSImpl.java:1537)
    at javax.jmdns.impl.tasks.state.DNSStateTask.run(DNSStateTask.java:131)
    at java.util.TimerThread.mainLoop(Timer.java:555)
    at java.util.TimerThread.run(Timer.java:505)

Jun 22, 2016 12:08:59 AM javax.jmdns.impl.JmDNSImpl __recover
WARNING: RECOVERING
Jun 22, 2016 12:08:59 AM javax.jmdns.impl.tasks.state.DNSStateTask run
WARNING: Canceler().run() exception
java.io.IOException: Operation not permitted
    at java.net.PlainDatagramSocketImpl.send(Native Method)
    at java.net.DatagramSocket.send(DatagramSocket.java:693)
    at javax.jmdns.impl.JmDNSImpl.send(JmDNSImpl.java:1537)
    at javax.jmdns.impl.tasks.state.DNSStateTask.run(DNSStateTask.java:131)
    at java.util.TimerThread.mainLoop(Timer.java:555)
    at java.util.TimerThread.run(Timer.java:505)

So I looked around for a solution to this and found a few options, first was to make sure that my server is listening on the port that I selected (8888). So I ran netstat -tuplen and saw :::8888 with a state of LISTEN and java as the program name. This leads me to believe the system is listening for that port, perhaps I'm wrong though. I also found a mailing list that was long and I didn't understand 75% of it, but it came down to seeing if multicast was enabled on the server, so I ran ifconfig eth0and got UP BROADCAST RUNNING MULTICAST in a big block of text, which leads me to believe multicast is enabled.

Also, my java version if openjdk 1.8.0_91, as I'm aware Jenkins doesn't like the normal java that seems to be installed on CentOS machines.

Just wondering what else could be the problem for Jenkins not running and giving that error, and what I could do to fix this. I'm for the most part a newbie with this kind of stuff, so more detailed info would be helpful.

[Dustin Nielsen]

So, when I setup Jenkins the instructions I was following made no note that there is a difference between running Jenkins on its own server and running Jenkins on a web server that was also running Apache.

After figuring out that there is indeed a difference I went a slightly different route with my jenkins configuration.

I added --prefix=/jenkins to JENKINS_ARGS in the jenkins configuration file. I also changed what port jenkins was listening on to 8081, and changed what IP address jenkins was listening on from 0.0.0.0 to 127.0.0.1

I then added:

ProxyPass         /jenkins  http://localhost:8081/jenkins nocanon
ProxyPassReverse  /jenkins  http://localhost:8081/jenkins
ProxyRequests     Off
AllowEncodedSlashes NoDecode

<Proxy http://localhost:8081/jenkins*>
  Order deny,allow
  Allow from all
</Proxy>

To my Apache configuration file. This fixed my issue and allowed me to access Jenkins.