Cksum

codice_1 is a command in Unix and Unix-like operating systems that generates a checksum value for a file or stream of data. The cksum command reads each file given in its arguments, or standard input if no arguments are provided, and outputs the file's CRC-32 checksum and byte count.
The codice_1 command can be used to verify that files transferred by unreliable means arrived intact. However, the CRC checksum calculated by the codice_1 command is not cryptographically secure: While it guards against "accidental" corruption (it is unlikely that the corrupted data will have the same checksum as the intended data), it is not difficult for an attacker to "deliberately" corrupt the file in a specific way that its checksum is unchanged. Unix-like systems typically include other commands for cryptographically secure checksums, such as sha256sum.
Interoperability.
The standard codice_1 command, as found on most Unix-like operating systems (including Linux, *BSD, macOS, and Solaris) uses a CRC algorithm based on the ethernet standard frame check and is therefore interoperable between implementations. This is in contrast to the sum command, which is not as interoperable and not compatible with the CRC-32 calculation. On Tru64 operating systems, the codice_1 command returns a different CRC value, unless the environment variable codice_6 is set to codice_7.
Algorithm.
codice_1 uses the generator polynomial 0x04C11DB7 and appends to the message its length in little endian representation. That length has null bytes trimmed on the right end.
Syntax.
cksum [FILE]...
cksum [OPTION]
Usage example.
$ cksum test.txt
4038471504 75 test.txt
where codice_9 represents the checksum value and codice_10 represents the file size of codice_11.