listing for C
cksum - Displays the checksum and byte count of a file
Interfaces documented on this reference page conform to industry standards
Refer to the standards(5) reference page for more information about
industry standards and associated tags.
The path name of a file to be checked.
If no file is specified, standard input is used.
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
[Tru64 UNIX] To maintain compatibility if the environment variable CMD_ENV
is not set, the default action of the cksum command reports the traditional
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.
The following exit values are returned:
0 All files were processed successfully.
>0 An error occurred.
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
Commands: sum(1), wc(1)
listing for C