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
When configuring YARN and MapReduce in Hadoop cluster, it is very important to configure the memory and virtual processors correctly. If the configurations are incorrect, the nodes may not be able to start properly and the applications may not be able to run successfully. For example...View detail
Are you a Windows/.NET developer and willing to learn big data concepts and tools in your Windows? If yes, you can follow the links below to install them in your PC. The installations are usually easier to do in Linux/UNIX but they are not difficult to implement in Windows either since the...View detail
This page summarizes the default ports used by Hadoop services. It is useful when configuring network interfaces in a cluster. Hadoop 3.1.0 HDFS The secondary namenode http/https server address and port. ...View detail