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NAME    [Toc]    [Back]

       cksum - Displays the checksum and byte count of a file

SYNOPSIS    [Toc]    [Back]

       cksum [file...]

STANDARDS    [Toc]    [Back]

       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    [Toc]    [Back]


OPERANDS    [Toc]    [Back]

       The path name of a file to be checked.

              If no file is specified, standard input is used.

DESCRIPTION    [Toc]    [Back]

       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

       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

       [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 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.  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    [Toc]    [Back]

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

EXAMPLES    [Toc]    [Back]

       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.


       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 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.  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    [Toc]    [Back]

       Commands:  sum(1), wc(1)

       Standards:  standards(5)

[ Back ]
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