Hadoop

41. Do we need to give a password, even if the key is added in SSH? Yes, password is still required even if the key is added in SSH. 42. …

31. Where is hadoop-env.sh file present? hadoop-env.sh file is present in the conf location. 32. In Hadoop_PID_DIR, what does PID stands for? PID stands for ‘Process ID’.

21. How can we check whether Namenode is working or not? To check whether Namenode is working or not, use the command /etc/init.d/hadoop-0.20-namenode status or as simple as jps. 22. …

11. How to exit the Vi editor? To exit the Vi Editor, press ESC and type :q and then press enter. 12. What is a spill factor with respect to …

1. Which are the three modes in which Hadoop can be run? The three modes in which Hadoop can be run are: 1. standalone (local) mode 2. Pseudo-distributed mode 3. …

41.What does “file could only be replicated to 0 nodes, instead of 1” mean? The namenode does not have any available DataNodes.

31.Default replication factor to a file is 3. Use ‘-setrep’ command to change replication factor of a file to 2. hadoop fs -setrep -w 2 apache_hadoop/sample.txt

21.What is a ‘block’ in HDFS? A ‘block’ is the minimum amount of data that can be read or written. In HDFS, the default block size is 64 MB as …

11.What is Fault Tolerance? Suppose you have a file stored in a system, and due to some technical problem that file gets destroyed. Then there is no chance of getting …

1.What does ‘jps’ command do? It gives the status of the deamons which run Hadoop cluster. It gives the output mentioning the status of namenode, datanode , secondary namenode, Jobtracker …