
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 Eth
ernet standard.
The encoding for the CRC checksum 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 n1. 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 <= 31.
3. The coefficients of R(x) are considered to be a 32bit 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 stan
dard 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, checksums 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
8bit characters into 9bit bytes or changing "Little Endian" byte ordering to "Big
Endian"), identical CRC values cannot be expected. Implementations performing such trans
formations 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_MESSAGES, and NLSPATH.
EXIT STATUS
The following exit values are returned:
0 All files were processed successfully.
>0 An error occurred.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+++
 ATTRIBUTE TYPE  ATTRIBUTE VALUE 
+++
Availability SUNWcsu 
+++
Interface Stability Standard 
+++
SEE ALSO
digest(1), sum(1), bart(1M), attributes(5), environ(5), largefile(5), standards(5)
SunOS 5.11 1 Feb 1995 cksum(1) 
