MD5 Checksum

The MD5 checksum of a file is simply a 128-bit number that is mathematically derived from the contents of the file. The MD5 algorithm was designed by Ron Rivest, the "R" in the popular RSA public-key encryption algorithm. The "MD" in "MD5" stands for Message Digest, which is a pretty accurate description of what it does.

Unlike literary digests, an MD5 checksum conveys no information about the contents of the original file. However, it possesses one unique trait:

Any change to the file, no matter how small, results in a change to the MD5 checksum. [2]

Generating MD5 Checksum of a file with md5sum

md5sum -b filename > filename.checksum

This will store the MD5 checkup of "filename" in "filename.checksum.

Varify MD5 Checksum of a file with md5sum

(put the checksum file in same directory where actual file is located)
md5sum -c test.checksum