Yesterday we were working on setting up our first Hadoop cluster. Though there are many online documentation on this even then we faced a few challenges getting with it. In this post I am providing details on the faced problems and solutions:

Passwordless login from NameNode to DataNode and vice versa:

Though setting paswordless login from NameNode to DataNode was easy. We had to just follow the steps mentioned at different tutorials:

ssh-keygen -t rsa .ssh/id_rsa.pub nsinfra@datanode1:~nsinfra/.ssh/authorized_keys .ssh/id_rsa.pub nsinfra@datanode2:~nsinfra/.ssh/authorized_keys We executed above three commands and assigned 700 permission on both .ssh & authorized_keys on NameNode before copying it to DataNodes. And we were able to ssh datanode from namenode without password.
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UMLGraph allows the declarative specification and drawing of UML class and sequence diagrams. The specification is done in text diagrams, that are then transformed into the appropriate graphical representations.

UMLGraph is implemented as a javadoc doclet (a program satisfying the doclet API that specifies the content and format of the output generated by the javadoc tool). Furthermore, the output of UMLGraph needs to be post-processed with the Graphviz dot program.
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With my latest assignment I have started exploring Hadoop and related technologies. When exploring HDFS and playing with it, I came across these two syntaxes of querying HDFS:

> hadoop dfs

> hadoop fs

Initally could not differentiate between the two and keep wondering why we have two different syntaxes for a common purpose.
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