CKSUM(1) General Commands Manual CKSUM(1)
cksum - display file checksums and block counts
cksum [-bcpqrtx] [-a algorithms] [-C checklist] [-h hashfile] [-s string]
The cksum utility writes to the standard output a single line for each
input file. The format of this line varies with the algorithm being used
cksum The output line consists of three whitespace separated
fields: a CRC checksum, the number of octets in the input,
and name of the file or string. If no file name is
specified, the standard input is used and no file name is
all others The output line consists of four whitespace separated fields:
the name of the algorithm used, the name of the file or
string in parentheses, an equals sign, and the cryptographic
hash of the input. If no file name is specified, the
standard input is used and only the cryptographic hash is
The options are as follows:
Use the specified algorithm(s) instead of the default (cksum).
Supported algorithms include cksum, md5, rmd160, sha1, sha224,
sha256, sha384, sha512/256, and sha512. Multiple algorithms may
be specified, separated by a comma or whitespace. Additionally,
multiple -a options may be specified on the command line. Case
is ignored when matching algorithms. The output format may be
specified on a per-algorithm basis by using a single-character
suffix, e.g. "sha256b". If the algorithm has a `b' suffix, the
checksum will be output in base64 format. If the algorithm has
an `x' suffix, the checksum will be output in hex format. If an
algorithm with the same output format is repeated, only the first
instance is used. Note that output format suffixes are not
supported for the cksum algorithm.
-b Output checksums in base64 notation, not hexadecimal by default.
A `b' or `x' suffix on the algorithm will override this default.
This option is ignored for the cksum algorithm.
Compare the checksum of each file against the checksums in the
checklist. Any specified file that is not listed in the
checklist will generate an error.
-c If this option is specified, the file options become checklists.
Each checklist should contain hash results in the normal format,
which will be verified against the specified paths. Output
consists of the digest used, the file name, and an OK, FAILED, or
MISSING for the result of the comparison. This will validate any
of the supported checksums. If no file is given, stdin is used.
The -c option may not be used in conjunction with more than a
single -a option.
Place the checksum into hashfile instead of stdout.
-p Echoes stdin to stdout and appends the checksum to stdout.
-q Only print the checksum (quiet mode) or if used in conjunction
with the -c flag, only print the failed cases.
-r Reverse the format of the hash algorithm output, making it match
the checksum output format.
Prints a checksum of the given string.
-t Runs a built-in time trial. Specifying -t multiple times results
in the number of rounds being multiplied by 10 for each
-x Runs a built-in test script.
The default CRC used is based on the polynomial used for CRC error
checking in the networking standard ISO/IEC 8802-3:1996. The other
available algorithms are described in their respective man pages in
section 3 of the manual.
The cksum utility exits 0 on success, and >0 if an error occurs.
The default calculation is identical to that given in pseudo-code in the
following ACM article:
Dilip V. Sarwate, "Computation of Cyclic Redundancy Checks Via Table
Lookup", Communications of the ACM, August 1988.
The cksum utility is compliant with the IEEE Std 1003.1-2008 ("POSIX.1")
All the flags are extensions to that specification.
The cksum utility appeared in 4.4BSD.
Do not use the cksum or md5 algorithms to verify file integrity. An
attacker can trivially produce modified payload that has the same
checksum as the original version. Use a cryptographic checksum instead.
OpenBSD 6.4 September 3, 2016 OpenBSD 6.4
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