If your cluster doesn't have it, add an exclude file to the cluster. Create an empty file in the NameNode and point to it from the $HADOOP_HOME/etc/hadoop/hdfs-site.xml file by adding the following property. Restart the NameNode:

<property>
<name>dfs.hosts.exclude</name>
<value>FULL_PATH_TO_THE_EXCLUDE_FILE</value>
<description>Names a file that contains a list of hosts that are not permitted to connect to the namenode. The full pathname of the file must be specified. If the value is empty, no hosts are excluded.</description>
</property>

Add the hostnames of the nodes that are to be decommissioned to the exclude file.

Run the following command...