md5sum in Linux

A checksum is a form of redundancy check, a simple way to protect the integrity of data by detecting errors in data that are sent through space (telecommunications) or time (storage). It works by adding up the basic components of a message, typically the assorted bits, and storing the resulting value.
These types of redundancy check are useful in detecting accidental modification such as corruption to stored data or errors in a communication channel. However, they provide no security against a malicious agent as their simple mathematical structure makes them trivial to circumvent. To provide this level of integrity, the use of a cryptographic hash function, such as SHA-256,MD5 is necessary. In cryptography, MD5 (Message-Digest algorithm 5) is a widely used, partially insecure cryptographic hash function with a 128-bit hash value.

md5sum is a computer program that calculates and verifies 128-bit MD5 hashes, as described in RFC 1321. The MD5 hash (or checksum) functions as a compact digital fingerprint of a file. It is extremely unlikely that any two non-identical files existing in the real world will have the same MD5 hash (although as with all such hashing algorithms, in theory there is an unlimited number of files that will have any given MD5 hash).

In Linux, we use following command to check the checksum of a file.
md5sum -b ojdbc14.jar