Namenode failure

@cc1 

There can be various reasons ...starting from

• - Low disk space, Low memory ,
• - No jvm present ,
• - Insufficient resources available on the namenode host,
• - Corrupted fsimage,
• - namenode port already in use
• - Corrupted Edits log file
• - Insufficient permissions to the NN startup user,
• - Incorrect configurations ...
  ...etc such various kind of reasons. ....

Hence it will be good to first check the NameNode logs to find out what kind of error is it showing and then accordingly it can be troubleshooted.