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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 generating  polyno-
       mial:

       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 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 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 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 cryptographically secure. The chances of a damaged
       file producing the same CRC as the original are  astronomically  small;
       deliberate deception is difficult, but probably not impossible.

       Although  input files to cksum can be any type, the results need not be
       what would be expected on character special device  files.  Since  this
       document  does not specify the block size used when doing input, check-
       sums 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 transforma-
       tions 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:  LANG,  LC_ALL,  LC_CTYPE,  LC_MES-
       SAGES, and NLSPATH.

EXIT STATUS
       The following exit values are returned:

       0        All files were processed successfully.



       >&gt;0       An error occurred.



ATTRIBUTES
       See attributes(5) for descriptions of the following attributes:


       tab()     allbox;     cw(2.750000i)|    cw(2.750000i)    lw(2.750000i)|
       lw(2.750000i).   ATTRIBUTE  TYPEATTRIBUTE   VALUE   AvailabilitySUNWcsu
       Interface StabilityStandard


SEE ALSO
       sum(1), attributes(5), environ(5), largefile(5), standards(5)



SunOS 5.10                        1 Feb 1995                          cksum(1)