Network setting for Hadoop

OS: Ubuntu 14 LTS
Set static IP address

Click Internet at Top-right
Select "connection information" and  "Edit Connection"
The figure will be show.
Select "Ethernet" and Click "Edit" button in the Network Connection.
Change Method "Manual" and Add Address using "connection information"
Add Hosts

$sudo nano /etc/hosts

Tip: don't add 127.0.0.1 master. It cause " org.apache.hadoop.hdfs.server.datanode.DataNode: Problem connecting to server:"
Hadoop will only listen to port 9000 and 9001 on the loopback interface, which is inaccessible from any other host. Make sure fs.default.name and mapred.job.tracker refer to your machine's externally accessible host name

add datanode like figure.
Change hostname 

$sudo /etc/hostname

Change hostname like figure.