- unstable 10.3~svn296373-7
|CKSUM(1)||General Commands Manual||CKSUM(1)|
— display file checksums and block counts
cksum utility writes to the standard
output three whitespace separated fields for each input file. These fields
are a checksum CRC, the total number of octets in the file and the file
name. If no file name is specified, the standard input is used and no file
name is written.
sum utility is identical to the
cksum utility, except that it defaults to using
historic algorithm 1, as described below. It is provided for compatibility
The options are as follows:
- Use historic algorithms instead of the (superior) default one.
Algorithm 1 is the algorithm used by historic BSD systems as the sum(1) algorithm and by historic AT&T System V UNIX systems as the sum(1) algorithm when using the
-roption. This is a 16-bit checksum, with a right rotation before each addition; overflow is discarded.
Algorithm 2 is the algorithm used by historic AT&T System V UNIX systems as the default sum(1) algorithm. This is a 32-bit checksum, and is defined as follows:
s = sum of all bytes; r = s % 2^16 + (s % 2^32) / 2^16; cksum = (r % 2^16) + r / 2^16;
Algorithm 3 is what is commonly called the ‘
32bit CRC’ algorithm. This is a 32-bit checksum.
Both algorithm 1 and 2 write to the standard output the same fields as the default algorithm except that the size of the file in bytes is replaced with the size of the file in blocks. For historic reasons, the block size is 1024 for algorithm 1 and 512 for algorithm 2. Partial blocks are rounded up.
The default CRC used is based on the polynomial used for CRC error checking in the networking standard ISO 8802-3: 1989. The CRC checksum 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:
M(x) is multiplied by x^32 (i.e., shifted left 32 bits) and divided by G(x) using mod 2 division, producing a remainder R(x) of degree <= 31.
The coefficients of R(x) are considered to be a 32-bit sequence.
The bit sequence is complemented and the result is the CRC.
utilities exit 0 on success, and >0 if an error occurs.
The default calculation is identical to that given in pseudo-code in the following ACM article.
Dilip V. Sarwate, Computation of Cyclic Redundancy Checks Via Table Lookup, Communications of the Tn ACM, August 1988.
cksum utility is expected to conform
to IEEE Std 1003.2-1992
cksum utility appeared in
|April 28, 1995||Debian|