WARN ipc.Client: Exception encountered while connecting to the server

While Running hadoop 0.20.S, when I run this command "hadoop dfs -ls" I got this error

WARN ipc.Client: Exception encountered while connecting to the server : javax.security.sasl.SaslException: GSS initiate failed [Caused by GSSException: No valid credentials provided (Mechanism level: Failed to find any Kerberos tgt)]
Bad connection to FS. command aborted. exception: Call to localhost/127.0.0.1:8020 failed on local exception: java.io.IOException: javax.security.sasl.SaslException: GSS initiate failed [Caused by GSSException: No valid credentials provided (Mechanism level: Failed to find any Kerberos tgt)]

after some googling I run this command
kinit username
and enter the password of kinit
eg my username is hadoop-user

so final command is
kinit hadoop-user
now enter password for kinit (note this password is not same as your username password)