6.3 cksum: Print and verify file checksums

cksum by default computes a cyclic redundancy check (CRC) checksum for each given file, or standard input if none are given or for a file of ‘-’.

cksum also supports the -a/--algorithm option to select the digest algorithm to use. cksum is the preferred interface to these digests, subsuming the other standalone checksumming utilities, which can be emulated using cksum -a md5 --untagged "$@" etc. Synopsis:

cksum [option]… [file]…

cksum is typically used to ensure that files have not been corrupted, by comparing the cksum output for the received files with the cksum output for the original files (typically given in the distribution).

cksum by default prints the POSIX standard CRC checksum for each file along with the number of bytes in the file, and the file name unless no arguments were given.

The same usage and options as the b2sum command are supported. See b2sum: Print or check BLAKE2 digests. In addition cksum supports the following options.

‘-a’ ¶

‘--algorithm’

Compute checksums using the specified digest algorithm.

Supported legacy checksums (which are not supported by --check):

‘sysv’      equivalent to sum -s
‘bsd’       equivalent to sum -r
‘crc’       equivalent to cksum (the default)

Supported more modern digest algorithms are:

‘md5’       equivalent to md5sum
‘sha1’      equivalent to sha1sum
‘sha224’    equivalent to sha224sum
‘sha256’    equivalent to sha256sum
‘sha384’    equivalent to sha384sum
‘sha512’    equivalent to sha512sum
‘blake2b’   equivalent to b2sum
‘sm3’       only available through cksum

‘-b’ ¶

‘--base64’

Print base64-encoded digests not hexadecimal. This option is ignored with --check. The format conforms to RFC 4648#4.

Note that each base64-encoded digest has zero, one or two trailing padding (‘=’) bytes. The length of that padding is the checksum-bit-length modulo 3, and the --check parser requires precisely the same input digest string as what is output. I.e., removing or adding any ‘=’ padding renders a digest non-matching.

‘--debug’ ¶

Output extra information to stderr, like the checksum implementation being used.

‘--raw’ ¶

Print only the unencoded raw binary digest for a single input. Do not output the file name or anything else. Use network byte order (big endian) where applicable: for ‘bsd’, ‘crc’, and ‘sysv’. This option works only with a single input. Unlike other output formats, cksum provides no way to --check a --raw checksum.

‘--untagged’ ¶

Output using the original Coreutils format used by the other standalone checksum utilities like md5sum for example. This format has the checksum at the start of the line, and may be more amenable to further processing by other utilities, especially in combination with the --zero option. Note this does not identify the digest algorithm used for the checksum. See md5sum: Print or check MD5 digests for details of this format.