cksum(1)						      General Commands Manual							  cksum(1)

NAME

       cksum - Displays the checksum and byte count of a file

SYNOPSIS

       cksum [file...]

STANDARDS

       Interfaces documented on this reference page conform to industry standards as follows:

       cksum: XCU5.0

       Refer to the standards(5) reference page for more information about industry standards and associated tags.

OPTIONS

       None

OPERANDS

       The path name of a file to be checked.

	      If no file is specified, standard input is used.

DESCRIPTION

       The  cksum  command  reads  the files specified by the file argument and calculates a 32-bit checksum Cyclic Redundancy Check (CRC) and the
       byte count for each file. If no files are specified, standard input is read. The checksum, number of bytes, and file name  are  written	to
       standard output. If standard input is used, no path name is printed.

       The  cksum  command  can  be used to compare a suspect file copied or communicated over noisy transmission lines against an exact copy of a
       trusted file. The comparison made by the cksum command may not be cryptographically secure; however, it is unlikely  that  an  accidentally
       damaged file will produce the same checksum as the original file.

       [Tru64  UNIX]  The  cksum  command uses a different algorithm than the sum command to calculate the 32-bit checksum CRC.  The cksum command
       uses a CRC algorithm based on the Ethernet standard frame check.  In addition, the sum block count is an octet count in cksum.

       [Tru64 UNIX]  The IEEE Std 1003.2-1992 and X/Open CAE specifications require a slightly different method of  calculating  checksum  values.
       To obtain these new standards, set the environment variable CMD_ENV to xpg4 as follows: export CMD_ENV=xpg4

       [Tru64 UNIX]  To maintain compatibility if the environment variable CMD_ENV is not set, the default action of the cksum command reports the
       traditional checksum values.

       The CRC checksum is obtained in the following way:

       The 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  consid-
       ered  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 is used.  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 less than
       or equal to 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.

EXIT STATUS

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

EXAMPLES

       To  display  the  checksum  and	the  size, in bytes, of file1 and file2, enter: cksum file1 file2 3995432187	  1390	  file1 3266927833
       20912   file2

       This output shows that the checksum of the file1 file is 3995432187 and contains 1390 bytes, and that the checksum of  the  file2  file	is
       3266927833 and contains 20912 bytes.

ENVIRONMENT VARIABLES

       The following environment variables affect the execution of cksum: [Tru64 UNIX]	If this variable is set to xpg4, the method of calculating
       checksum values specified by IEEE Std 1003.2-1992 (POSIX.2) and X/Open CAE specifications is used.  Provides a default value for the inter-
       nationalization	variables  that  are unset or null. If LANG is unset or null, the corresponding value from the default locale is used.	If
       any of the internationalization variables contain an invalid setting, the utility behaves as if none of the variables had been defined.	If
       set  to	a  non-empty  string  value,  overrides the values of all the other internationalization variables.  Determines the locale for the
       interpretation of sequences of bytes of text data as characters (for example, single-byte as opposed to multibyte characters in arguments).
       Determines  the	locale	for  the format and contents of diagnostic messages written to standard error.	Determines the location of message
       catalogues for the processing of LC_MESSAGES.

SEE ALSO

       Commands:  sum(1), wc(1)

       Standards:  standards(5)

																	  cksum(1)