Cksum
cksum is a in 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 if no arguments are provided, and outputs the file’s CRC checksum and count.
The cksum command can be used to verify that files transferred by unreliable means arrived intact. However, the CRC checksum calculated by the cksum 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 .
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Interoperability
The standard cksum command, as found on most UNIX-like operating systems (including GNU/Linux, *BSD, Mac OS X, and Solaris) uses a CRC algorithm based on the and is therefore interoperable between implementations. This is in contrast to the , which is not as interoperable. It is however not compatible with the CRC-32 calculation. On operating systems, the cksum command returns a different CRC value, unless the CMD_ENV is set to xpg4.
Algorithm
cksum uses the 0x04C11DB7 and appends to the message its length in representation. That length has trimmed on the right end.
Syntax
cksum [FILE]... cksum [OPTION] Usage example
$ cksum test.txt 4038471504 75 test.txt where 4038471504 represents the checksum value and 75 represents the file size of test.txt.