cksum(1) - osol9

1cksum(1)                         User Commands                        cksum(1)
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NAME

6       cksum - write file checksums and sizes
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SYNOPSIS

9       cksum [file]...
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DESCRIPTION

13       The  cksum  command  calculates  and writes to standard output a cyclic
14       redundancy check (CRC) for each input file, and also writes to standard
15       output the number of octets in each file.
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18       For each file processed successfully, cksum will write in the following
19       format:
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22       "%u %d %s\n" <checksum>, <# of octets>, <path name>
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25       If no file operand was specified, the path name and its  leading  space
26       will be omitted.
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29       The  CRC used is based on the polynomial used for CRC error checking in
30       the referenced Ethernet standard.
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33       The encoding for the CRC checksum is defined by the generating  polyno‐
34       mial:
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37       G(x)  =  x^32  + x^26 + x^23 + x^22 + x^16 + x^12 + x^11 + x^10 + x^8 +
38       x^7 + x^5 + x^4 + x^2 + x + 1
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41       Mathematically, the CRC value corresponding to a given file is  defined
42       by the following procedure:
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44           1.     The  n bits to be evaluated are considered to be the coeffi‐
45                  cients of a mod 2 polynomial M(x) of  degree  n−1.  These  n
46                  bits  are  the bits from the file, with the most significant
47                  bit being the most significant bit of the first octet of the
48                  file and the last bit being the least significant bit of the
49                  last octet, padded with zero bits (if necessary) to  achieve
50                  an integral number of octets, followed by one or more octets
51                  representing the length of the file as a binary value, least
52                  significant octet first. The smallest number of octets capa‐
53                  ble of representing this integer is used.
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55           2.     M(x) is multiplied by x ^32 (that is, shifted left 32  bits)
56                  and  divided  by  G(x)  using  mod  2  division, producing a
57                  remainder R(x) of degree ≤ 31.
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59           3.     The coefficients of R(x)  are  considered  to  be  a  32-bit
60                  sequence.
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62           4.     The bit sequence is complemented and the result is the CRC.
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OPERANDS

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

72       The cksum command is typically used to quickly compare a  suspect  file
73       against  a  trusted  version  of the same, such as to ensure that files
74       transmitted over noisy media arrive intact.  However,  this  comparison
75       cannot be considered cryptographically secure. The chances of a damaged
76       file producing the same CRC as the original are  astronomically  small;
77       deliberate deception is difficult, but probably not impossible.
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80       Although  input files to cksum can be any type, the results need not be
81       what would be expected on character special device  files.  Since  this
82       document  does not specify the block size used when doing input, check‐
83       sums of character special files need not process all  of  the  data  in
84       those files.
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87       The algorithm is expressed in terms of a bitstream divided into octets.
88       If a file is transmitted between two systems  and  undergoes  any  data
89       transformation  (such  as  moving  8-bit characters into 9-bit bytes or
90       changing "Little Endian" byte ordering to "Big Endian"), identical  CRC
91       values  cannot be expected. Implementations performing such transforma‐
92       tions may extend cksum to handle such situations.
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95       See largefile(5) for the description of  the  behavior  of  cksum  when
96       encountering files greater than or equal to 2 Gbyte ( 2^31 bytes).
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ENVIRONMENT VARIABLES

99       See  environ(5) for descriptions of the following environment variables
100       that affect the execution of cksum:  LANG,  LC_ALL,  LC_CTYPE,  LC_MES‐
101       SAGES, and NLSPATH.
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EXIT STATUS

104       The following exit values are returned:
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106       0     All files were processed successfully.
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109       >0    An error occurred.
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ATTRIBUTES

113       See attributes(5) for descriptions of the following attributes:
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118       ┌─────────────────────────────┬─────────────────────────────┐
119       │      ATTRIBUTE TYPE         │      ATTRIBUTE VALUE        │
120       ├─────────────────────────────┼─────────────────────────────┤
121       │Availability                 │SUNWcsu                      │
122       ├─────────────────────────────┼─────────────────────────────┤
123       │Interface Stability          │Standard                     │
124       └─────────────────────────────┴─────────────────────────────┘
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