UnknownHostException in hadoop on CentOS

I received this error when I tried to run the dfsadmin command:

bash-4.2# bin/hdfs dfsadmin -report
report: java.net.UnknownHostException: locahost
Usage: hdfs dfsadmin [-report] [-live] [-dead] [-decommissioning]

Please note there seems to be a typo: locahost instead of localhost

I just started leaing hadoop, can anyone tell me where do I start my troubleshooting? Thank you very much.