Cksum is a POSIX command that reads the files specified by the File parameter and calculates a checksum, cyclic redundancy check (CRC) and the byte count for a file or files. If no files are specified, the cksum command reads standard input. The checksum, number of bytes, and file name are written to standard output. POSIX is the collective name of a family of related standards defined by the IEEE and formally designated IEEE 1003. ... A checksum is a form of redundancy check, a very simple measure for protecting the integrity of data by detecting errors in data that is sent through space (telecommunications) or time (storage). ... A cyclic redundancy check (CRC) is a type of hash function used to produce a checksum, which is a small number of bits, from a large block of data, such as a packet of network traffic or a block of a computer file, in order to detect errors in transmission... This article refers to the unit of binary information. ...

The cksum command can be used to compare a suspect file copied or communicated over noisy transmission lines against an exact copy of a trusted file. The comparison made by the cksum command may not be cryptographically secure. However, it is unlikely that an accidentally damaged file will produce the same checksum as the original file. See also: Topics in cryptography The security of all practical encryption schemes remains unproven, both for symmetric and asymmetric schemes. ...

The cksum command uses a CRC algorithm based on the ethernet standard frame check. Ethernet (this name comes from the physical concept of ether) is a frame-based computer networking technology for local area networks (LANs). ...

Syntax

 cksum [ File ... ] 

External links

• Jacksum (a program with various message verification functions, including the POSIX CRC implementation).