ERROR dfs.NameNode: java.io.IOException: Cannot lock storage /tmp/hadoop-hadoop-user/dfs/name. The directory is already locked

The following is the error occurred while formatting the namenode.
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hadoop-user@hadoop-desk:~/hadoop$ bin/hadoop namenode -format
14/09/14 18:53:27 INFO dfs.NameNode: STARTUP_MSG:
/************************************************************
STARTUP_MSG: Starting NameNode
STARTUP_MSG:   host = hadoop-desk/127.0.1.1
STARTUP_MSG:   args = [-format]
STARTUP_MSG:   version = 0.18.0
STARTUP_MSG:   build = http://svn.apache.org/repos/asf/hadoop/core/branches/branch-0.18 -r 686010; comp                                                                                      iled by 'hadoopqa' on Thu Aug 14 19:48:33 UTC 2008
************************************************************/
Re-format filesystem in /tmp/hadoop-hadoop-user/dfs/name ? (Y or N) Y
14/09/14 18:53:35 INFO fs.FSNamesystem: fsOwner=hadoop-user,hadoop-user,adm,dialout,cdrom,floppy,audio,                                                                                      dip,video,plugdev,fuse,lpadmin,admin
14/09/14 18:53:35 INFO fs.FSNamesystem: supergroup=supergroup
14/09/14 18:53:35 INFO fs.FSNamesystem: isPermissionEnabled=true
14/09/14 18:53:35 INFO dfs.Storage: Cannot lock storage /tmp/hadoop-hadoop-user/dfs/name. The directory                                                                                       is already locked.
14/09/14 18:53:35 ERROR dfs.NameNode: java.io.IOException: Cannot lock storage /tmp/hadoop-hadoop-user/                                                                                      dfs/name. The directory is already locked.
        at org.apache.hadoop.dfs.Storage$StorageDirectory.lock(Storage.java:447)
        at org.apache.hadoop.dfs.FSImage.format(FSImage.java:930)
        at org.apache.hadoop.dfs.FSImage.format(FSImage.java:949)
        at org.apache.hadoop.dfs.NameNode.format(NameNode.java:741)
        at org.apache.hadoop.dfs.NameNode.createNameNode(NameNode.java:822)
        at org.apache.hadoop.dfs.NameNode.main(NameNode.java:839)
14/09/14 18:53:35 INFO dfs.NameNode: SHUTDOWN_MSG:
/************************************************************
SHUTDOWN_MSG: Shutting down NameNode at hadoop-desk/127.0.1.1
************************************************************/
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The username with which you are trying to format the name node might not have necessary privileges on the namenode and datanode directories that are listed in the hadoop-site.xml configuration file. Provide the necessary privileges on all directories and sub-directories of name node and data node directories and rerun the command to format.