3. Start HDFS

Start HDFS.

To start HDFS, run commands as the $HDFS_USER.

Start the NameNode. On the NameNode host machine, execute the following command:

su $HDFS_USER
export HADOOP_LIBEXEC_DIR=/usr/lib/hadoop/libexec
/usr/lib/hadoop/sbin/hadoop-daemon.sh start namenode -upgrade

On a large system, this can take a long time to complete.

	Note
	Run this command with the -upgrade option only once. After you have completed this step, you can bring up the NameNode using this command without including the -upgrade option.

Verify that the NameNode is up and running:
```
ps -ef|grep -i NameNode
```
Start the Secondary NameNode. On the Secondary NameNode host machine, execute the following command:
```
su $HDFS_USER
export HADOOP_LIBEXEC_DIR=/usr/lib/hadoop/libexec
/usr/lib/hadoop/sbin/hadoop-daemon.sh start secondarynamenode 
```
Verify that the Secondary NameNode is up and running:
```
ps -ef|grep  SecondaryNameNode
```
Note
If you are working on a non-secure DataNode, use $HDFS_USER. For a secure DataNode, use root.
Start DataNodes. On all the DataNodes, execute the following command:
```
export HADOOP_LIBEXEC_DIR=/usr/lib/hadoop/libexec 
/usr/lib/hadoop/sbin/hadoop-daemon.sh start datanode              
```
Verify that the DataNode process is up and running:
```
ps -ef|grep DataNode
```
Verify that NameNode can go out of safe mode.
```
hdfs dfsadmin -safemode wait
Safemode is OFF
```
In general, it takes 5-10 minutes to get out of safemode. For thousands of nodes with millions of data blocks, getting out of safemode could take up to 45 minutes.

	Note
	If you are working on a non-secure DataNode, use $HDFS_USER. For a secure DataNode, use root.