Unable to access Jenkins (Centos 7)

Question

I've just installed Jenkins with its default configs on a Centos 7 physical box.

Port 8080 is open on the firewall:

sudo iptables -L -n
[...]
ACCEPT     tcp  --  0.0.0.0/0            0.0.0.0/0            tcp dpt:8080
[...]

It also looks like Jenkins is actually listening on all interfaces:

sudo netstat -an | grep "LISTEN "
[...]
tcp6       0      0 :::8080                 :::*                    LISTEN
[...]

I can curl localhost:8080 locally (from the Centos box) without a problem, but from anywhere else in the network I get a Connection refused.

Am I missing something?

Solution 1

The above looks like Jenkins is defaulting to ipv6 only.

Try the following, this will probably fix your problem:

run: $ /sbin/sysctl net.ipv6.bindv6only

You will probably get an output with value net.ipv6.bindv6only = 1.

If this is the case, you will need to disable the setting:

sudo /sbin/sysctl net.ipv6.bindv6only=0

After the command above you will get an answer like net.ipv6.bindv6only = 0, restart Jenkins: sudo systemctl restart jenkins and try to connect to Jenkins again.

If this worked for you, you should put this in a sysctl config-file. Because this is not a persistent fix. After a reboot the setting you just have modified will be defaulted to 1 again.

Check /etc/sysctl.conf and /etc/sysctl.d/* and add net.ipv6.bindv6only = 0 in order to make this setting permanent and run sudo sysctl -p or restart after changing it.

Solution 2

@panos : it worked after setting JENKINS_JAVA_OPTIONS="$JENKINS_JAVA_OPTIONS -Djava.net.preferIPv4Stack=true" in /etc/sysconfig/jenkins then sudo systemctl restart jenkins. also i removed ipv6 entries in /etc/hosts not sure if the file needs to be edited, later i checked "netstat -tulpen" can see java is listening on tcp..

Comments

[natxo asenjo]

looks like it's only listening in ipv6.

[Panos]

It's listening on IPV4 now. Still can't connect.

[natxo asenjo]

could you disable selinux and try again? setenforce 0 as root sets it in permissive mode temporarily.

[Elias]

In Centos the bind can only show ipv6 entry while it is in reality bound to both ipv4 and ipv6.

[Panos]

Apparently Java was configured to use IPV6 by default, so I forced it to use IPV4 by adding JENKINS_JAVA_OPTIONS="$JENKINS_JAVA_OPTIONS -Djava.net.preferIPv4Stack=true" to /etc/sysconfig/jenkins and now I do get the correct answer from netstat: tcp 0 0 0.0.0.0:8080 0.0.0.0:* LISTEN . I still can't connect to Jenkins, though. Do I need to specify a hostname for Jenkins or does it listen on 8080 regardless of the hostname?

[Panos]

I'm coming to the conclusion that the culprit here is the firewall/IP tables, no Jenkins. Even when I spin up a web server on port 8081 (or even 80) I don't get connection from the outside.

[Bombaci]

@Panos since it is a Centos 7 machine, could you try the following (unless you disabled the firewalld service and use plain iptables): firewall-cmd --zone=public --add-port=8080/tcp --permanent firewall-cmd --zone=public --add-service=http --permanent firewall-cmd --reload

[Panos]

Nothing :( Neither 80 nor 8080 working. Actually, even with the firewall down and iptables disabled I still don't get to connect through those ports. I can still ping the server and ssh into it... This is insane...

[Bombaci]

@Panos, so: 1. Jenkins is loaded systemctl status jenkins: systemd[1]: Started LSB: Jenkins Automation Server. 2. Java listens to port 8080, lsof -u jenkins -a -i :8080 -P: java 5124 jenkins 161u IPv4 74141 0t0 TCP *:8080 (LISTEN) 3. You disabled the firewall and still not working. 4. You can SSH and Ping to the server, trough the same IP. I installed Jenkins on a fresh machine, first it didn't work also, used the steps above and it worked. Maybe an external firewall not allowing 80 or 8080 to that IP?

[Panos]

So, I ended up doing a sudo firewall-cmd --zone=public --add-service=http and got to open port 80, at least. I'm clueless as to why this didn't work when I had firewalld down... Gosh, Centos... [I'll go back to the Jenkins part tomorrow, cause this whole firewall thing was a killer]

[Bombaci]

This is a good article in order to install Jenkins and Centos 7, this also can help you further: How to install Jenkins on Centos 7

[gkephorus]

In case of an Ubuntu based machine the Jenkins settings will be on /etc/default/jenkins