• Hadoop distributed file system (HDFS) uses a specific permissions model for files and directories. Following user levels are used in HDFS
  • Owner
  • Group
  • Others

• For each of the user mentioned above following permissions are applicable,
  • read (r)
  • write (w)
  • execute(x)

Above mentioned permissions work differently for files and directories.

• For files
  • read (r) permission – Reading a file.
  • write (w) permission – Writing a file.

• For directories.
  • The r permission lists the contents of a specific directory.
  • The w permission creates or deletes a directory.
  • The X permission accessing a child directory.

• NameNode is the master node for processing metadata information for data blocks within the HDFS.

• DataNode is the node which acts as slave node to store the data, for processing and use by the NameNode.
• In addition to serving the client requests, the NameNode executes either of two following roles –
  • CheckpointNode.
  • BackupNode.

• It runs on a different host from the NameNode

• It is a read-only NameNode which contains file system metadata information excluding the block locations.

• This component receives processing requests and accordingly allocates to respective NodeManagers depending on processing needs.

• It executes tasks on each single Data Node.