Jenkins is Experiencing UnknownHostException

Issue

  • The Jenkins instance hangs when installing plugins
  • An UnknownHostException occurs on startup:
    2016-02-07 02:45:07.730+0000 [id=73]    WARNING javax.jmdns.impl.HostInfo#newHostInfo: Could not intialize the host network interface on nullbecause of an error: <my-hostname>: <my-hostname>: unknown errorjava.net.UnknownHostException: <my-hostname>: <my-hostname>: unknown error
    at java.net.InetAddress.getLocalHost(InetAddress.java:1484)
    at javax.jmdns.impl.HostInfo.newHostInfo(HostInfo.java:75)
    at javax.jmdns.impl.JmDNSImpl.<init>(JmDNSImpl.java:407)
    at javax.jmdns.JmDNS.create(JmDNS.java:60)
    at hudson.DNSMultiCast$1.call(DNSMultiCast.java:32)
    at jenkins.util.ContextResettingExecutorService$2.call(ContextResettingExecutorService.java:46)
    at java.util.concurrent.FutureTask.run(FutureTask.java:266)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at java.lang.Thread.run(Thread.java:745)
    Caused by: java.net.UnknownHostException: <my-hostname>: unknown error
    at java.net.Inet6AddressImpl.lookupAllHostAddr(Native Method)
    at java.net.InetAddress$2.lookupAllHostAddr(InetAddress.java:907)
    at java.net.InetAddress.getAddressesFromNameService(InetAddress.java:1302)
    at java.net.InetAddress.getLocalHost(InetAddress.java:1479)
    ... 9 more
    

Related Issue(s)

Environment

  • CloudBees Jenkins Operations Center
  • CloudBees Jenkins Enterprise
  • Jenkins

Resolution

  1. Disable DNS Discovery

This could be due to the Auto-discovering of Jenkins with DNS Multicast. If you are not using this functionality you can disable it by adding the following properties on startup and restart your instance:

-Dhudson.DNSMultiCast.disabled=true
-Dhudson.udp=-1.

If Jenkins is running on Apache Tomcat, you can add the following property to catalina.properties:

hudson.DNSMultiCast.disabled=true
hudson.udp=-1

  1. Troubleshoot your Hosts/DNS configuration

This could be a misconfiguration of your hostnames or your DNS (if using a DNS).

Use ping of telnet to check that the host can be resolved:

$ ping my-hostname
PING my-hostname (127.0.0.1): 56 data bytes
...

$ telnet my-hostname jenkins-port
Trying 127.0.0.1...
Connected to my-hostname.
Escape character is '^]'.

If you are not using a DNS, check that the is defined in /etc/hosts:

[...]

127.0.0.1   localhost my-hostname

[...]

If you are using a DNS, try to telnet on DNS port to check that the port is open (default port is 53):

$ telnet my-hostname dns-port
Trying 127.0.0.1...
Connected to my-hostname.
Escape character is '^]'.

Command like nslookup, dig and host can help you to troubleshoot DNS issues:

# Query a hostname for the default server
nslookup my-hostname

# Query a hostname for a different server
nslookup my-hostname my-dns-server

# List IP address(es) associated with a hostname/domain:
host -l my-hostname

# Query a hostname for the default server
dig my-hostname

# Query a hostname for the different server
dig @my-server my-hostname
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