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SunOS man pages : cksum (1)

User Commands                                            cksum(1)

NAME

cksum - write file checksums and sizes

SYNOPSIS

cksum [ file ... ]

DESCRIPTION

The cksum command calculates and writes to standard output a cyclic redundancy check (CRC) for each input file, and also writes to standard output the number of octets in each file. For each file processed successfully, cksum will write in the following format: "%u %d %s\n" <checksum>, <# of octets>, <path name> If no file operand was specified, the path name and its leading space will be omitted. The CRC used is based on the polynomial used for CRC error checking in the referenced Ethernet standard. The encoding for the CRC checksum is defined by the generat- ing 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: 1. The n bits to be evaluated are considered to be the coef- ficients of a mod 2 polynomial M(x) of degree n-1. These n bits are the bits from the file, with the most signifi- cant bit being the most significant bit of the first octet of the file and the last bit being the least signi- ficant bit of the last octet, padded with zero bits (if necessary) to achieve an integral number of octets, fol- lowed 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 is used. 2. M(x) is multiplied by x**32 (that is, shifted left 32 bits) and divided by G(x) using mod 2 division, producing a remainder R(x) of degree < 31. 3. The coefficients of R(x) are considered to be a 32-bit sequence. 4. The bit sequence is complemented and the result is the SunOS 5.8 Last change: 1 Feb 1995 1 User Commands cksum(1) CRC.

OPERANDS

The following operand is supported: file A path name of a file to be checked. If no file operands are specified, the standard input is used.

USAGE

The cksum command is typically used to quickly compare a suspect file against a trusted version of the same, such as to ensure that files transmitted over noisy media arrive intact. However, this comparison cannot be considered cryp- tographically secure. The chances of a damaged file produc- ing the same CRC as the original are astronomically small; deliberate deception is difficult, but probably not impossi- ble. Although input files to cksum can be any type, the results need not be what would be expected on character special dev- ice files. Since this document does not specify the block size used when doing input, checksums of character special files need not process all of the data in those files. The algorithm is expressed in terms of a bitstream divided into octets. If a file is transmitted between two systems and undergoes any data transformation (such as moving 8-bit characters into 9-bit bytes or changing "Little Endian" byte ordering to "Big Endian"), identical CRC values cannot be expected. Implementations performing such transformations may extend cksum to handle such situations. See largefile(5) for the description of the behavior of cksum when encountering files greater than or equal to 2 Gbyte ( 2**31 bytes).

ENVIRONMENT VARIABLES

See environ(5) for descriptions of the following environment variables that affect the execution of cksum: LC_CTYPE, LC_MESSAGES, and NLSPATH.

EXIT STATUS

The following exit values are returned: 0 All files were processed successfully. >0 An error occurred.

ATTRIBUTES

See attributes(5) for descriptions of the following attri- butes: SunOS 5.8 Last change: 1 Feb 1995 2 User Commands cksum(1) ____________________________________________________________ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | |_____________________________|_____________________________| | Availability | SUNWcsu | |_____________________________|_____________________________|

SEE ALSO

sum(1), attributes(5), environ(5), largefile(5) SunOS 5.8 Last change: 1 Feb 1995 3