Jenkins is Experiencing UnknownHostException

Article ID:218156717
2 minute readKnowledge base


  • 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 <my-hostname>: <my-hostname>: unknown error
    at javax.jmdns.impl.HostInfo.newHostInfo(
    at javax.jmdns.impl.JmDNSImpl.<init>(
    at javax.jmdns.JmDNS.create(
    at hudson.DNSMultiCast$
    at jenkins.util.ContextResettingExecutorService$
    at java.util.concurrent.ThreadPoolExecutor.runWorker(
    at java.util.concurrent.ThreadPoolExecutor$
Caused by: <my-hostname>: unknown error
    at Method)
    ... 9 more


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

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

2. 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 ( 56 data bytes

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

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

[...]   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
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