hadoop version
Hadoop 0.20.2-cdh3u2
Subversion file:///tmp/topdir/BUILD/hadoop-0.20.2-cdh3u2 -r 95a824e4005b2a94fe1c11f1ef9db4c672ba43cb
Compiled by root on Thu Oct 13 21:51:41 PDT 2011
From source with checksum 644e5db6c59d45bca96cec7f220dda51

[root@kcomp hadoop]# hadoop namenode -format
May not run daemons as root. Please specify HADOOP_NAMENODE_USER

[root@kcomp hadoop]# su - hadoop
id: cannot find name for group ID 501

[hadoop@kcomp ~]$ hadoop namenode -format
11/10/31 17:09:19 INFO namenode.NameNode: STARTUP_MSG: 
/************************************************************
STARTUP_MSG: Starting NameNode
STARTUP_MSG:   host = java.net.UnknownHostException: kcomp: kcomp
STARTUP_MSG:   args = [-format]
STARTUP_MSG:   version = 0.20.2-cdh3u2
STARTUP_MSG:   build = file:///tmp/topdir/BUILD/hadoop-0.20.2-cdh3u2 -r 95a824e4005b2a94fe1c11f1ef9db4c672ba43cb; compiled by 'root' on Thu Oct 13 21:51:41 PDT 2011
************************************************************/
Re-format filesystem in /tmp/hadoop-hadoop/dfs/name ? (Y or N) Y
11/10/31 17:09:23 INFO util.GSet: VM type       = 64-bit
11/10/31 17:09:23 INFO util.GSet: 2% max memory = 17.77875 MB
11/10/31 17:09:23 INFO util.GSet: capacity      = 2^21 = 2097152 entries
11/10/31 17:09:23 INFO util.GSet: recommended=2097152, actual=2097152
11/10/31 17:09:23 INFO metrics.MetricsUtil: Unable to obtain hostName
java.net.UnknownHostException: kcomp: kcomp
	at java.net.InetAddress.getLocalHost(InetAddress.java:1438)
	at org.apache.hadoop.metrics.MetricsUtil.getHostName(MetricsUtil.java:91)
	at org.apache.hadoop.metrics.MetricsUtil.createRecord(MetricsUtil.java:80)
	at org.apache.hadoop.security.UserGroupInformation$UgiMetrics.<init>(UserGroupInformation.java:99)
	at org.apache.hadoop.security.UserGroupInformation.<clinit>(UserGroupInformation.java:178)
	at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.setConfigurationParameters(FSNamesystem.java:446)
	at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.<init>(FSNamesystem.java:435)
	at org.apache.hadoop.hdfs.server.namenode.NameNode.format(NameNode.java:1113)
	at org.apache.hadoop.hdfs.server.namenode.NameNode.createNameNode(NameNode.java:1232)
	at org.apache.hadoop.hdfs.server.namenode.NameNode.main(NameNode.java:1248)
Caused by: java.net.UnknownHostException: kaulcomp
	at java.net.Inet4AddressImpl.lookupAllHostAddr(Native Method)
	at java.net.InetAddress$1.lookupAllHostAddr(InetAddress.java:866)
	at java.net.InetAddress.getAddressesFromNameService(InetAddress.java:1258)
	at java.net.InetAddress.getLocalHost(InetAddress.java:1434)
	... 9 more
11/10/31 17:09:23 INFO namenode.FSNamesystem: fsOwner=hadoop
11/10/31 17:09:23 INFO namenode.FSNamesystem: supergroup=supergroup
11/10/31 17:09:23 INFO namenode.FSNamesystem: isPermissionEnabled=true
11/10/31 17:09:23 INFO namenode.FSNamesystem: dfs.block.invalidate.limit=1000
11/10/31 17:09:23 INFO namenode.FSNamesystem: isAccessTokenEnabled=false accessKeyUpdateInterval=0 min(s), accessTokenLifetime=0 min(s)
11/10/31 17:09:23 INFO metrics.MetricsUtil: Unable to obtain hostName
java.net.UnknownHostException: kaulcomp: kcomp
	at java.net.InetAddress.getLocalHost(InetAddress.java:1438)
	at org.apache.hadoop.metrics.MetricsUtil.getHostName(MetricsUtil.java:91)
	at org.apache.hadoop.metrics.MetricsUtil.createRecord(MetricsUtil.java:80)
	at org.apache.hadoop.hdfs.server.namenode.FSDirectory.initialize(FSDirectory.java:85)
	at org.apache.hadoop.hdfs.server.namenode.FSDirectory.<init>(FSDirectory.java:80)
	at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.<init>(FSNamesystem.java:436)
	at org.apache.hadoop.hdfs.server.namenode.NameNode.format(NameNode.java:1113)
	at org.apache.hadoop.hdfs.server.namenode.NameNode.createNameNode(NameNode.java:1232)
	at org.apache.hadoop.hdfs.server.namenode.NameNode.main(NameNode.java:1248)
Caused by: java.net.UnknownHostException: kcomp
	at java.net.Inet4AddressImpl.lookupAllHostAddr(Native Method)
	at java.net.InetAddress$1.lookupAllHostAddr(InetAddress.java:866)
	at java.net.InetAddress.getAddressesFromNameService(InetAddress.java:1258)
	at java.net.InetAddress.getLocalHost(InetAddress.java:1434)
	... 8 more
11/10/31 17:09:23 INFO common.Storage: Image file of size 112 saved in 0 seconds.
11/10/31 17:09:24 INFO common.Storage: Storage directory /tmp/hadoop-hadoop/dfs/name has been successfully formatted.
11/10/31 17:09:24 INFO namenode.NameNode: SHUTDOWN_MSG: 
/************************************************************
SHUTDOWN_MSG: Shutting down NameNode at java.net.UnknownHostException: kcomp: kcomp
************************************************************/