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. What does the command mapred.job.tracker do?
The command mapred.job.tracker lists out which of your nodes is acting as a job tracker.
23. What does /etc /init.d do?
/etc /init.d specifies where daemons (services) are placed or to see the status of these daemons. It is very LINUX specific, and nothing to do with Hadoop.
24. How can we look for the Namenode in the browser?
If you have to look for Namenode in the browser, you don’t have to give localhost:8021, the port number to look for Namenode in the brower is 50070.
25. How to change from SU to Cloudera?
To change from SU to Cloudera just type exit.
26. Which files are used by the startup and shutdown commands?
Slaves and Masters are used by the startup and the shutdown commands.
27. What do slaves consist of?
Slaves consist of a list of hosts, one per line, that host datanode and task tracker servers.
28. What do masters consist of?
Masters contain a list of hosts, one per line, that are to host secondary namenode servers.
29. What does hadoop-env.sh do?
hadoop-env.sh provides the environment for Hadoop to run. JAVA_HOME is set over here.
30. Can we have multiple entries in the master files?
Yes, we can have multiple entries in the Master files.