Intro To 'cksum' Command In Linux

2024-05-16 - By Robert Elder

     I use the 'cksum' command to compute a cyclic redundancy check checksum of a file or stream:

cat example.txt

Hello World!

cksum example.txt

2116921653 13 example.txt

Purpose Of 'cksum' Command

     The purpose of this command is for detecting data corruption that can occur during network communication, or due to failing storage media:

info cksum

   ‘cksum’ is typically used to ensure that files transferred by
unreliable means (e.g., netnews) have not been corrupted, by comparing
the ‘cksum’ output for the received files with the ‘cksum’ output for
the original files (typically given in the distribution).

Reading The Output Of 'cksum' Command

     If I run the 'cksum' command an a file like this:

cksum data.dat

     I'll see the CRC checksum value (in this case 3779003720), followed by the number of bytes in the file (in this case 26):

3779003720 26 data.dat

How The 'cksum' Value Is Calculated

     According to the POSIX specification, the CRC checksum value is calculated using the following generator polynomial:

G(x)=x32+x26+x23+x22+x16+x12+x11+x10+x8+x7+x5+x4+x2+x+1

     This polynomial is based on similar one used by an error checking algorithm described in a 1996 telecommunications standard for Ethernet communication.

     The checksum calculated by the 'cksum' command is not cryptographically secure, and should only be used for detecting accidental, rather than deliberate data corruption.

     And that's why the 'cksum' command is my favourite Linux command.

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