CKSUM(1)                     General Commands Manual                    CKSUM(1)

     cksum, sum – display file checksums and block counts

     cksum [-o 1 | 2 | 3] [file ...]
     sum [file ...]

     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 options are as follows:

     -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

             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;

             Algorithm 3 is what is commonly called the ‘32bit CRC’ algorithm.
             This is a 32-bit checksum.

             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 checking
     in the networking standard ISO 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 Tn ACM, August 1988.

     The cksum utility is expected to conform to IEEE Std 1003.2-1992

     The cksum utility appeared in 4.4BSD.

macOS 12.1                       April 28, 1995                       macOS 12.1