CKSUM(1)

NAME
cksum, sum - display file checksums and block counts

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

sum [file ...]

DESCRIPTION
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, described below. It is provided for compatibility. You can either install the sum program (which has the same content as the cksum program file) or create a gsh(1) alias that invokes cksum:
       alias sum "cksum -o 1"

The program options are as follows:

    -o  Use historic algorithms instead of the (superior) default one.

        Algorithm 1 is the algorithm used by historic systems as the sum(1) algorithm and by historic 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 is the algorithm used by historic 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;

                Algorithm 3, a 32-bit checksum, is commonly called the 32bit CRC algorithm.

                    Algorithms 1 and 2 write the same fields as the default algorithm except the size of the file is expressed 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 POSIX-3. 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 <= 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 default calculation is identical to that given in pseudo-code in the article "Computation of Cyclic Redundancy Checks Via Table Lookup" by Dilip V. Sarwate, Communications of the ACM, August 1988.

                        The cksum and sum utilities exit 0 on success, and >0 if an error occurs.

VERSION
This manual page documents cksum version 2.0.

ATTRIBUTIONS
This command was ported from FreeBSD source code for distribution with GNO/ME 2.0.6.

HISTORY
A version of sum translated from GNU code in 1991 by Marek Pawlowski was distributed with earlier releases of GNO. Unfortunately, as that version reads files it translates carriage return characters into new line characters. To use cksum to calulate a checksum that matches the old sum, use tr(1) to translate the input stream. For example,
          tr '\r' '\n' < filename | cksum -o 1

STANDARDS
The cksum utility is expected to conform to POSIX-2.