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Alphabetical listing for C

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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
  file
      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:

   1.  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 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
       less than or equal to 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 CRC.

EXIT STATUS
  The following exit values are returned:

  0   All files were processed successfully.

  >0  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:

  CMD_ENV
      [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.

  LANG
      Provides a default value for the internationalization 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.

  LC_ALL
      If set to a non-empty string value, overrides the values of all the
      other internationalization variables.

  LC_CTYPE
      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).

  LC_MESSAGES
      Determines the locale for the format and contents of diagnostic
      messages written to standard error.

  NLSPATH
      Determines the location of message catalogues for the processing of
      LC_MESSAGES.

SEE ALSO
  Commands:  sum(1), wc(1)

  Standards:  standards(5)

Index for Section 1

Alphabetical listing for C

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