Todd,   thanks for the details information. However, I still can't figure it out. (except to reboot the node)   my cluster has three nodes: the /etc/hosts are identical as:   127.0.0.1   localhost.localdomain localhost 10.122.195.196   hdfs001.demai.com hdfs001 10.122.195.197   hdfs002.demai.com hdfs002 10.122.195.198   hdfs003.demai.com hdfs003 I tested hostname in the following ways: [ptadm@hdfs001 work-demai]$ hostname hdfs001.demai.com [ptadm@hdfs001 work-demai]$ hostname -f hdfs001.demai.com [ptadm@hdfs001 work-demai]$ python -c "import socket; print socket.getfqdn(); print socket.gethostbyname(socket.getfqdn())" hdfs001.demai.com 10.122.195.196 I turned of selinux, and tested: $selinuxenabled && echo enabled || echo disabled disable       ... View more