Cksum

cksum prints CRC checksum and byte counts of each file.

cksum can be used to check if files are transfered without error (or not corrupted during storage).

generates checksums' file. After transfer (or after a long storage) you can check if files are the same:

cksum also can be used for fast searching for duplicates. After issuing

identical files have same checksums.

Conversely, files with same chcecksums and same sizes almost always are identical. This can be checked further with diff.

Provided by
Most (all?) Linux distributions incorporate this from the GNU Coreutils: and use its man page

Related commands
These are related to summarizing the contents of files.
 * wc
 * sum
 * md5sum
 * sha1sum
 * sha2 utilities