`cksum `**[**-o 1 **|** 2**] [***file ...***]**

sum **[**-r**] [***file ...***]**

The **cksum**(1) utility writes to the standard output three,
white-space separated fields for each input file:

*crc #_octets file_name*

These fields contain a checksum (The **sum**(1) utility writes to the standard output three,
white-space separated fields for each input file:

*crc #_blocks file_name*

These fields contain a checksum (**-crc**), the total number
of 512-byte blocks in the file (*#_blocks*), and the file
name.

**-o***n*- Use historic algorithms instead of the default one.
*n*can be either 1 or 2:- 1
- Algorithm 1 is the algorithm used by historic Berkeley Software
Distribution (BSD) systems as the
**sum**(1) algorithm, and by historic AT&T System V systems as the**sum**(1) algorithm when using the**-r**option. This is a 16-bit checksum, with a right rotation before each addition; overflow is discarded. - 2
- Algorithm 2 is the algorithm used by historic AT&T System V
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;

- 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.
**-r**- For the
**sum**(1) command, this is equivalent to:

Without the`cksum -o 1`

**-r**option, the**sum**(1) command is equivalent to:`cskum -o 2`

The default Cyclical Redundancy Checking (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: The 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.

The coefficients of R(x) are considered to be a 32-bit sequence.

The bit sequence is complemented and the result is the CRC.