IvoryMonkey is a project mainly written in Java, it's free.
Small tools and experiments for Hadoop, targeted mostly at systems and config things.
Some simple tools that work with the internals of Hadoop, HBase, File Formats, and Compression mechanics.
Not all code is guaranteed to ... work.
Checksum generator is a single threaded replica of Hadoop's internal Distributed hash-checksum mechanic.
What its actually doing is saving the CRC32 of every 512 bytes (per block) and then doing a MD5 hash on that. Then when the "getFileChecksum()" method is called, each block for a file sends its md5 hash to a collector which are gathered together and a md5 hash is calc'd for all of the block hashes.
My version includes code that can calculate the hash on the client side (but breaks things up in the same way that hdfs does and will calc it the same way).
During development, we also discovered and filed:
https://issues.apache.org/jira/browse/HDFS-772
To invoke this method, use my shell wrapper:
https://github.com/jpatanooga/IvoryMonkey/blob/master/src/tv/floe/IvoryMonkey/hadoop/fs/Shell.java