Getting ‘java.net.UnknownHostException: LAPTOP-23876346: nodename nor servname provided, or not know

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Recently while running Java Program on my Mac OS X, I noticed below error in Eclipse console.

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java.net.UnknownHostException:LAPTOP-23876346:LAPTOP-23876346:nodenamenorservnameprovided,ornotknown
atjava.net.InetAddress.getLocalHost(InetAddress.java:1473)
atorg.eclipse.rse.core.RSECorePlugin.getLocalMachineName(RSECorePlugin.java:265)
atorg.eclipse.rse.core.RSEPreferencesManager.getDefaultPrivateSystemProfileName(RSEPreferencesManager.java:358)
atorg.eclipse.rse.core.RSEPreferencesManager.initDefaults(RSEPreferencesManager.java:337)
atorg.eclipse.rse.internal.core.RSEPreferenceInitializer.initializeDefaultPreferences(RSEPreferenceInitializer.java:23)
atorg.eclipse.core.internal.preferences.PreferenceServiceRegistryHelper$1.run(PreferenceServiceRegistryHelper.java:300)
atorg.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
....
....
....
Causedby:java.net.UnknownHostException:LAPTOP-23876346:nodenamenorservnameprovided,ornotknown
atjava.net.Inet6AddressImpl.lookupAllHostAddr(NativeMethod)
atjava.net.InetAddress$1.lookupAllHostAddr(InetAddress.java:901)
atjava.net.InetAddress.getAddressesFromNameService(InetAddress.java:1293)
atjava.net.InetAddress.getLocalHost(InetAddress.java:1469)
...28more

I was literally scratching my head as I didn’t see this error anywhere on my Windows Desktop duringJava development. What causes the error – java.net.UnknownHostException – How to solve UnknownHostException?

While debugging I came to know that – this came from my below Java code:

returnHostName()
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publicstaticStringreturnHostName(){
StringcrunchifyHost=null;
try{
crunchifyHost=InetAddress.getLocalHost().getCanonicalHostName();  // This line was throwing above exception
}catch(Exceptione){
thrownewRuntimeException("Error. Failed to retrive crunchifyHost:"+e);
}
returncrunchifyHost;
}

Sometimes it’s very annoying to get exception on one Operating System compare to other.getCanonicalHostName() returns the fully qualified domain name for this IP address. Best effort method, meaning we may not be able to return the FQDN (Fully Qualified Domain Name) depending on the underlying system configuration. Mac OS X uses the different system configuration than windows.

Well, the solution is simple. Follow below steps and you should be good.

Step 1. Open Terminal Windows.

Step 2. Enter command sudo vi /private/etc/hosts

Step 3. You should see file content like that.

Crunchify private-ect-hosts file content

Step 4. Add below line 127.0.0.1 LAPTOP-23876346 immediately after 127.0.0.1 localhost

Updated file
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##
# Host Database
#
# localhost is used to configure the loopback interface
# when the system is booting.  Do not change this entry.
##
127.0.0.1      localhost
127.0.0.1      LAPTOP-23876346    # added line. replace LAPTOP-23876346 with your laptop hostname
255.255.255.255broadcasthost
::1            localhost

Step 5. Execute below command to flush the cache

Clearing Directory Service Cache
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bash-3.2$dscacheutil-flushcache

Now again run the same java project and you should NOT seejava.net.UnknownHostException again.

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