cksum

cksum is a command in Unix-like operating systems that generates a checksum value for a file or stream of data. The cksum command reads each file given in its arguments, or standard input if no arguments are provided, and outputs the file's CRC checksum and byte count.

The cksum command can be used to verify that files transferred by unreliable means arrived intact.^[1] However, the CRC checksum calculated by the cksum command is not cryptographically secure: While it guards against accidental corruption (it is unlikely that the corrupted data will have the same checksum as the intended data), it is not difficult for an attacker to deliberately corrupt the file in a specific way that its checksum is unchanged. Unix-like systems typically include other commands for cryptographically secure checksums, such as sha1sum.

Interoperability

The standard cksum command, as found on most UNIX-like operating systems (including GNU/Linux, *BSD, Mac OS X, and Solaris) uses a CRC algorithm based on the ethernet standard frame check and is therefore interoperable between implementations. This is in contrast to the sum command, which is not as interoperable. It is however not compatible with the CRC-32 calculation. On Tru64 operating systems, the cksum command returns a different CRC value, unless the environment variable CMD_ENV is set to “xpg4”.

Syntax

cksum [ File ... ]

Usage example

$ cksum test.txt
4038471504 75 test.txt

where "4038471504" represents the checksum value and "75" represents the file size of test.txt.

References

↑ "cksum: Print CRC checksum and byte counts". Retrieved 2015-07-05.

External links

cksum: write file checksums and sizes – Commands & Utilities Reference, The Single UNIX® Specification, Issue 7 from The Open Group

Unix command-line interface programs and shell builtins

File system	cat chmod chown chgrp cksum cmp cp dd du df file fsck fuser ln ls mkdir mount mv pax pwd rm rmdir split tee touch type umask

Processes	at bg chroot cron fg kill killall nice pgrep pkill ps pstree time top

User environment	clear env exit finger history logname mesg passwd su sudo uptime talk tput uname w wall who whoami write

Text processing	awk banner basename comm csplit cut diff dirname ed ex fmt fold head iconv join less more nl paste printf sed sort spell strings tail tr uniq vi wc xargs yes

Shell builtins	alias cd echo test unset wait

Networking	dig host ifconfig inetd netcat netstat nslookup ping rdate rlogin route ssh traceroute

Searching	find grep locate whatis whereis

Documentation	apropos help man

Miscellaneous	bc dc cal expr lp od sleep true and false

List of Unix utilities

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