cksum - write file checksums and sizes
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 generat-
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 coef-
ficients of a mod 2 polynomial M(x) of degree n-1. These
n bits are the bits from the file, with the most signifi-
cant bit being the most significant bit of the first
octet of the file and the last bit being the least signi-
ficant bit of the last octet, padded with zero bits (if
necessary) to achieve an integral number of octets, fol-
lowed 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
4. The bit sequence is complemented and the result is the
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.
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 cryp-
tographically secure. The chances of a damaged file produc-
ing the same CRC as the original are astronomically small;
deliberate deception is difficult, but probably not impossi-
Although input files to cksum can be any type, the results
need not be what would be expected on character special dev-
ice 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 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 transformations
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).
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.
The following exit values are returned:
0 All files were processed successfully.
>0 An error occurred.
See attributes(5) for descriptions of the following attri-
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
| Availability | SUNWcsu |
| Interface Stability | Standard |
sum(1), attributes(5), environ(5), largefile(5), stan-
Man(1) output converted with