In Safe Mode, the HDFS cluster is read-only. After completion of block replication maintenance activity, the name node leaves safe mode automatically.
If you try to delete files in safe mode, the following exception may raise:
org.apache.hadoop.ipc.RemoteException(org.apache.hadoop.hdfs.server.namenode.SafeModeException): Cannot delete /user/hadoop/sqoop_test/blogs. Name node is in safe mode.
The above exception occurred because I was using Sqoop to load files into HDFS while deleting existing files.
We can also manually leave safe mode by using the following command:
hadoop@hdp-master:/hadoop> hdfs dfsadmin -safemode leave
Safe mode is OFF