CKSUM(1)Commands and ApplicationsCKSUM(1)

cksum,sum- display file checksums and block counts

cksum[-o1|2|3] [file...]sum[file...]

Thecksumutility writes to the standard output three whitespace sepa- rated fields for each input file. These fields are a checksumCRC, 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. Thesumutility is identical to thecksumutility, except that it defaults to using historic algorithm 1, described below. It is pro- vided for compatibility. You can either install thesumprogram (which has the same content as thecksumprogram file) or create agsh(1)alias that invokescksum: alias sum "cksum -o 1" The program options are as follows:-oUse historic algorithms instead of the (superior) default one. Algorithm 1 is the algorithm used by historic systems as thesum(1)algorithm and by historic systems as thesumalgorithm when using the-roption. 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 defaultsumalgorithm. 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 com- monly called the32bitCRCalgorithm. 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 defaultCRCused is based on the poly- nomial used forCRCerror checking in the networking standard POSIX-3. TheCRCchecksum encoding is defined by the gener- ating 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, theCRCvalue correspond- ing to a given file is defined by the fol- lowing procedure: Thenbits to be evaluated are con- sidered to be the coefficients of a mod 2 polynomial M(x) of degreen-1. Thesenbits are the bits from the file, with the most sig- nificant 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 default calcula- tion is identical to that given in pseudo- code in the article "Computation of Cyclic Redundancy Checks Via Table Lookup" by Dilip V. Sarwate,Communica-tionsoftheACM, August 1988. Thecksumandsumutilities exit 0 on success, and >0 if an error occurs.

This manual page documentscksumversion 2.0.

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

A version ofsumtranslated 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 usecksumto calulate a checksum that matches the oldsum, usetr(1)to translate the input stream. For example, tr '\r' '\n' < filename | cksum -o 1

Thecksumutility is expected to conform to POSIX-2. GNO December 1997CKSUM(1)

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