CKSUM(1) BSD General Commands Manual CKSUM(1)
cksum, md2, md4, md5, rmd160, sha1, sum -- display file checksums and block counts
cksum [-n] [-a algorithm [-ptx] [-s string]] [-o 1|2] [file ... | -c [-w] [sumfile]]
sum [-n] [-a algorithm [-ptx] [-s string]] [-o 1|2] [file ... | -c [-w] [sumfile]]
md2 [-nptx] [-s string] [file ... | -c [-w] [sumfile]]
md4 [-nptx] [-s string] [file ... | -c [-w] [sumfile]]
md5 [-nptx] [-s string] [file ... | -c [-w] [sumfile]]
rmd160 [-nptx] [-s string] [file ... | -c [-w] [sumfile]]
sha1 [-nptx] [-s string] [file ... | -c [-w] [sumfile]]
The cksum utility writes to the standard output three whitespace separated fields for each input file. These fields are a checksum CRC, the
total number of octets in the file and the file name. If no file name is specified, the standard input is used and no file name is written.
The sum utility is identical to the cksum utility, except that it defaults to using historic algorithm 1, as described below. It is provided
for compatibility only.
The md2, md4, md5, sha1, and rmd160 utilities compute cryptographic hash functions, and write to standard output the hexadecimal representa-
tion of the hash of their input.
The options are as follows:
When invoked as cksum, use the specified algorithm. Valid algorithms are:
Algorithm Bits Description
CRC 32 Default CRC algorithm
MD2 128 MD2, per RFC1319
MD4 128 MD4, per RFC1320
MD5 128 MD5, per RFC1321
RMD160 160 RIPEMD-160
SHA1 160 SHA-1, per FIPS PUB 180-1
SHA256 256 SHA-2
SHA384 384 SHA-2
SHA512 512 SHA-2
old1 16 Algorithm 1, per -o 1
old2 16 Algorithm 2, per -o 2
Verify (check) files against a list of checksums. The list is read from sumfile, or from stdin if no filename is given. E.g. first
md5 *.tgz > MD5
sha1 *.tgz > SHA1
to generate a list of MD5 checksums in MD5, then use the following command to verify them:
cat MD5 SHA1 | cksum -c
If an error is found during checksum verification, an error message is printed, and the program returns an error code of 1.
-o Use historic algorithms instead of the (superior) default one.
Algorithm 1 is the algorithm used by historic BSD systems as the sum(1) algorithm and by historic AT&T System V UNIX systems as the
sum(1) algorithm when using the -r option. This is a 16-bit checksum, with a right rotation before each addition; overflow is dis-
Algorithm 2 is the algorithm used by historic AT&T System V UNIX systems as the default sum(1) algorithm. This is a 32-bit checksum,
and is defined as follows:
s = sum of all bytes;
r = s % 2^16 + (s % 2^32) / 2^16;
cksum = (r % 2^16) + r / 2^16;
Both algorithm 1 and 2 write to the standard output the same fields as the default algorithm except that the size of the file in
bytes is replaced with the size of the file in blocks. For historic reasons, the block size is 1024 for algorithm 1 and 512 for
algorithm 2. Partial blocks are rounded up.
-w Print warnings about malformed checksum files when verifying checksums with -c.
The following options apply only when using the one of the message digest algorithms:
-n Print the hash and the filename in the normal sum output form, with the hash at the left and the filename following on the right.
-p Echo input from standard input to standard output, and append the selected message digest.
Print the hash of the given string string.
-t Run a built-in message digest time trial.
-x Run a built-in message digest test script. The tests that are run are supposed to encompass all the various tests in the suites that
accompany the algorithms' descriptions with the exception of the last test for the SHA-1 algorithm and the RIPEMD-160 algorithm. The
last test for these is one million copies of the lower letter a.
The default CRC used is based on the polynomial used for CRC error checking in the networking standard ISO/IEC 8802-3:1989. The CRC checksum
encoding is defined by the generating polynomial:
G(x) = x^32 + x^26 + x^23 + x^22 + x^16 + x^12 +
x^11 + x^10 + x^8 + x^7 + x^5 + x^4 + x^2 + x + 1
Mathematically, the CRC value corresponding to a given file is defined by the following procedure:
The n bits to be evaluated are considered to be the coefficients of a mod 2 polynomial M(x) of degree n-1. These n bits are the bits
from the file, with the most significant bit being the most significant bit of the first octet of the file and the last bit being the
least significant bit of the last octet, padded with zero bits (if necessary) to achieve an integral number of octets, followed by one
or more octets representing the length of the file as a binary value, least significant octet first. The smallest number of octets
capable of representing this integer are used.
M(x) is multiplied by x^32 (i.e., shifted left 32 bits) and divided by G(x) using mod 2 division, producing a remainder R(x) of degree
The coefficients of R(x) are considered to be a 32-bit sequence.
The bit sequence is complemented and the result is the CRC.
The cksum and sum utilities exit 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.
R. Rivest, The MD2 Message-Digest Algorithm, RFC 1319.
R. Rivest, The MD4 Message-Digest Algorithm, RFC 1186 and RFC 1320.
R. Rivest, The MD5 Message-Digest Algorithm, RFC 1321.
U.S. DOC/NIST, Secure Hash Standard, FIPS PUB 180-1.
The cksum utility is expected to conform to IEEE Std 1003.1-2004 (``POSIX.1'').
The cksum utility appeared in 4.4BSD. md5 was added in NetBSD 1.3. The functionality for md2, md4, sha1, and rmd160 was added in
NetBSD 1.6. Support for the SHA-2 algorithms (SHA256, SHA384, and SHA512) was added in NetBSD 3.0. The functionality to verify checksum
stored in a file (-c) first appeared in NetBSD 4.0.
June 24, 2012 BSD