List out all Configursation entries in the Hadoop instance.

This is an extremely simple code that will give us a more straight view of what Hadoop Configuration object is. Extremely simple lines of code as below lists out entries of your hadoop instance's Configuraiton object. This tiny code could help me to figure out the configruation of a new Hadoop instance. Probably, I should expand this to be a real HadoopInfo.java that is similar as phpinfo.php.

import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;

import org.apache.hadoop.conf.Configuration;


public class HadoopInfo {
 
 public static void main(String[] args) throws Exception {
     Configuration conf = new Configuration();
     Iterator< Entry< String, String > > entries = conf.iterator();
     System.out.println("< table border=\"1\" width=\"760\" style=\"word-break:break-all;\" >" +
       "< caption>Hadoop defaul Configruation keys and values< /caption >  " +
       "< tr >< th >Key< /th >< th >Value< /th >< /tr >");
     while(entries.hasNext()){
      Map.Entry< String, String> en = (Map.Entry < String, String >)entries.next();    
      System.out.println("< tr >< td width=\"350\"> " + en.getKey() + " < /td >< td >" + en.getValue() + "< /td >< /tr >");
     }
     System.out.println("< / table >");
 } 
}

Sample output for a fresh standalone Hadoop instance.

Hadoop defaul Configruation keys and values

Key	Value
io.seqfile.compress.blocksize	1000000
hadoop.http.authentication.signature.secret.file	${user.home}/hadoop-http-auth-signature-secret
io.skip.checksum.errors	false
fs.checkpoint.size	67108864
hadoop.http.authentication.kerberos.principal	HTTP/localhost@LOCALHOST
fs.s3n.impl	org.apache.hadoop.fs.s3native.NativeS3FileSystem
fs.s3.maxRetries	4
webinterface.private.actions	false
hadoop.http.authentication.simple.anonymous.allowed	true
fs.s3.impl	org.apache.hadoop.fs.s3.S3FileSystem
hadoop.native.lib	true
fs.checkpoint.edits.dir	${fs.checkpoint.dir}
ipc.server.listen.queue.size	128
fs.default.name	file:///
hadoop.http.authentication.kerberos.keytab	${user.home}/hadoop.keytab
ipc.client.idlethreshold	4000
hadoop.tmp.dir	/tmp/hadoop-${user.name}
fs.hsftp.impl	org.apache.hadoop.hdfs.HsftpFileSystem
fs.checkpoint.dir	${hadoop.tmp.dir}/dfs/namesecondary
fs.s3.block.size	67108864
hadoop.security.authorization	false
io.serializations	org.apache.hadoop.io.serializer.WritableSerialization
hadoop.util.hash.type	murmur
io.seqfile.lazydecompress	true
io.file.buffer.size	4096
io.mapfile.bloom.size	1048576
fs.s3.buffer.dir	${hadoop.tmp.dir}/s3
hadoop.logfile.size	10000000
fs.webhdfs.impl	org.apache.hadoop.hdfs.web.WebHdfsFileSystem
ipc.client.kill.max	10
io.compression.codecs	org.apache.hadoop.io.compress.DefaultCodec,org.apache.hadoop.io.compress.GzipCodec,org.apache.hadoop.io.compress.BZip2Codec,org.apache.hadoop.io.compress.SnappyCodec
topology.script.number.args	100
fs.har.impl	org.apache.hadoop.fs.HarFileSystem
io.seqfile.sorter.recordlimit	1000000
fs.trash.interval	0
hadoop.security.authentication	simple
local.cache.size	10737418240
hadoop.security.group.mapping	org.apache.hadoop.security.ShellBasedUnixGroupsMapping
ipc.server.tcpnodelay	false
hadoop.security.token.service.use_ip	true
fs.ramfs.impl	org.apache.hadoop.fs.InMemoryFileSystem
ipc.client.connect.max.retries	10
hadoop.rpc.socket.factory.class.default	org.apache.hadoop.net.StandardSocketFactory
fs.kfs.impl	org.apache.hadoop.fs.kfs.KosmosFileSystem
fs.checkpoint.period	3600
topology.node.switch.mapping.impl	org.apache.hadoop.net.ScriptBasedMapping
hadoop.http.authentication.token.validity	36000
hadoop.security.use-weak-http-crypto	false
hadoop.logfile.count	10
hadoop.security.uid.cache.secs	14400
fs.ftp.impl	org.apache.hadoop.fs.ftp.FTPFileSystem
fs.file.impl	org.apache.hadoop.fs.LocalFileSystem
fs.hdfs.impl	org.apache.hadoop.hdfs.DistributedFileSystem
ipc.client.connection.maxidletime	10000
io.mapfile.bloom.error.rate	0.005
io.bytes.per.checksum	512
fs.har.impl.disable.cache	true
ipc.client.tcpnodelay	false
fs.hftp.impl	org.apache.hadoop.hdfs.HftpFileSystem
hadoop.relaxed.worker.version.check	false
fs.s3.sleepTimeSeconds	10
hadoop.http.authentication.type	simple