Recently while running Java Program on my Mac OS X, I noticed below error in Eclipse console.
java.net.UnknownHostException: LAPTOP-23876346: LAPTOP-23876346: nodename nor servname provided, or not known at java.net.InetAddress.getLocalHost(InetAddress.java:1473) at org.eclipse.rse.core.RSECorePlugin.getLocalMachineName(RSECorePlugin.java:265) at org.eclipse.rse.core.RSEPreferencesManager.getDefaultPrivateSystemProfileName(RSEPreferencesManager.java:358) at org.eclipse.rse.core.RSEPreferencesManager.initDefaults(RSEPreferencesManager.java:337) at org.eclipse.rse.internal.core.RSEPreferenceInitializer.initializeDefaultPreferences(RSEPreferenceInitializer.java:23) at org.eclipse.core.internal.preferences.PreferenceServiceRegistryHelper$1.run(PreferenceServiceRegistryHelper.java:300) at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42) .... .... .... Caused by: java.net.UnknownHostException: LAPTOP-23876346: nodename nor servname provided, or not known at java.net.Inet6AddressImpl.lookupAllHostAddr(Native Method) at java.net.InetAddress$1.lookupAllHostAddr(InetAddress.java:901) at java.net.InetAddress.getAddressesFromNameService(InetAddress.java:1293) at java.net.InetAddress.getLocalHost(InetAddress.java:1469) ... 28 more
I was literally scratching my head as I didn’t see this error anywhere on my Windows Desktop during Java development. What causes the error – java.net.UnknownHostException – How to solve UnknownHostException?
While debugging I came to know that – this came from my below Java code:
public static String returnHostName() {
String crunchifyHost = null;
try {
crunchifyHost = InetAddress.getLocalHost().getCanonicalHostName(); // This line was throwing above exception
} catch (Exception e) {
throw new RuntimeException("Error. Failed to retrive crunchifyHost:" + e);
}
return crunchifyHost;
}
Sometimes it’s very annoying to get exception on one Operating System compare to other. getCanonicalHostName() returns the fully qualified domain name for this IP address. Best effort method, meaning we may not be able to return the FQDN (Fully Qualified Domain Name) depending on the underlying system configuration. Mac OS X uses the different system configuration than windows.
Well, the solution is simple. Follow below steps and you should be good.
Step 1. Open Terminal Windows.
Step 2. Enter command sudo vi /private/etc/hosts
Step 3. You should see file content like that.
Step 4. Add below line 127.0.0.1 LAPTOP-23876346 immediately after 127.0.0.1 localhost
## # Host Database # # localhost is used to configure the loopback interface # when the system is booting. Do not change this entry. ## 127.0.0.1 localhost 127.0.0.1 LAPTOP-23876346 # added line. replace LAPTOP-23876346 with your laptop hostname 255.255.255.255 broadcasthost ::1 localhost
Step 5. Execute below command to flush the cache
bash-3.2$ dscacheutil -flushcache
Now again run the same java project and you should NOT see java.net.UnknownHostException again.