CKSUM(1)                System General Commands Manual                CKSUM(1)

NAME
     cksum, sum - display file checksums and block counts

SYNOPSIS
     cksum [-p | -t | -x | -c [checklist ...] | -s string | file ...]
           [-a algorithms] [-o 1 | 2]
     sum [file ...]

DESCRIPTION
     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
     as follows:

     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 written.

     sum     The output line consists of three whitespace separated fields: a
             CRC checksum, the number of kilobytes 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 written.

     sysvsum
             The output line consists of three whitespace separated fields: a
             CRC checksum, the number of 512-byte blocks 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 written.

     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 output.

     The sum utility is identical to the cksum utility, except that it
     defaults to using historic algorithm 1, as described below.  It is pro-
     vided for compatibility only.

     The options are as follows:

     -a algorithms
             Use the specified algorithm(s) instead of the default (cksum).
             Supported algorithms include cksum, md4, md5, rmd160, sha1,
             sha256, sha384, sha512, sum, and sysvsum.  Multiple algorithms
             may be specified, separated by a comma or whitespace.  Addition-
             ally, multiple -a options may be specified on the command line.
             If an algorithm is repeated, only the first instance is used.
             Case is ignored when matching algorithms.

     -c [checklist ...]
             Compares all checksums contained in the file checklist with newly
             computed checksums for the corresponding files.  Output consists
             of the digest used, the file name, and an OK or FAILED for the
             result of the comparison.  This will validate any of the sup-
             ported 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.

     -o 1 | 2
             Use historic algorithms instead of the (superior) default one
             (see below).

     -p      Echoes stdin to stdout and appends the checksum to stdout.

     -s string
             Prints a checksum of the given string.

     -t      Runs a built-in time trial.

     -x      Runs a built-in test script.

     Algorithm 1 (aka sum) is the algorithm used by historic BSD systems as
     the sum algorithm and by historic AT&T System V UNIX systems as the sum
     algorithm when using the -r option.  This is a 16-bit checksum, with a
     right rotation before each addition; overflow is discarded.

     Algorithm 2 (aka sysvsum) is the algorithm used by historic AT&T System V
     UNIX systems as the default sum 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.

     The default CRC used is based on the polynomial used for CRC error check-
     ing 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 signif-
           icant 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
           <= 31.

           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 other available algorithms are described in their respective man
     pages in section 3 of the manual.

DIAGNOSTICS
     The cksum and sum utilities exit 0 on success or >0 if an error occurred.

SEE ALSO
     md5(1), rmd160(1), sha1(1)

     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.

STANDARDS
     The cksum utility is compliant with the POSIX 1003.2-92 specification.

HISTORY
     A sum command appeared in Version 2 AT&T UNIX.  The cksum utility
     appeared in 4.4BSD.

WARNING
     Do not use the cksum, md4, sum, or sysvsum algorithms to detect hostile
     binary modifications.  An attacker can trivially produce backdoored dae-
     mons which have the same checksum as the standard versions.  Use a cryp-
     tographic checksum instead.

Interix                         June, 12, 2006                         Interix