The three modes in which Hadoop can be run are:
1. standalone (local) mode
2. Pseudo-distributed mode
3. Fully distributed mode
2. What are the features of Stand alone (local) mode?
In stand-alone mode there are no daemons, everything runs on a single JVM. It has no DFS and utilizes the local file system. Stand-alone mode is suitable only for running MapReduce programs during development. It is one of the most least used environments.
3. What are the features of Pseudo mode?
Pseudo mode is used both for development and in the QA environment. In the Pseudo mode all the daemons run on the same machine.
4. Can we call VMs as pseudos?
No, VMs are not pseudos because VM is something different and pesudo is very specific to Hadoop.
5. What are the features of Fully Distributed mode?
Fully Distributed mode is used in the production environment, where we have ‘n’ number of machines forming a Hadoop cluster. Hadoop daemons run on a cluster of machines.
There is one host onto which Namenode is running and another host on which datanode is running and then there are machines on which task tracker is running. We have separate masters and separate slaves in this distribution.
6. Does Hadoop follows the UNIX pattern?
Yes, Hadoop closely follows the UNIX pattern. Hadoop also has the ‘conf‘ directory as in the case of UNIX.
7. In which directory Hadoop is installed?
Cloudera and Apache has the same directory structure. Hadoop is installed in cd/usr/lib/hadoop-0.20/.
8. What are the port numbers of Namenode, job tracker and task tracker?
The port number for Namenode is ’70′, for job tracker is ’30′ and for task tracker is ’60′.
9. What is the Hadoop-core configuration?
Hadoop core is configured by two xml files:
1. hadoop-default.xml which was renamed to 2. hadoop-site.xml.
These files are written in xml format. We have certain properties in these xml files, which consist of name and value. But these files do not exist now.
10. What are the Hadoop configuration files at present?
There are 3 configuration files in Hadoop:
These files are located in the conf/ subdirectory.