Cksum

Template:Short description Template:Lowercase title {{#invoke:Infobox|infobox}}Template:Template other{{#invoke:Check for unknown parameters | check | showblankpositional=1 | unknown = Template:Main other | preview = Page using Template:Infobox software with unknown parameter "_VALUE_"|ignoreblank=y | AsOf | author | background | bodystyle | caption | collapsetext | collapsible | developer | discontinued | engine | engines | genre | included with | language | language count | language footnote | latest preview date | latest preview version | latest release date | latest release version | latest_preview_date | latest_preview_version | latest_release_date | latest_release_version | licence | license | logo | logo alt | logo caption | logo upright | logo size | logo title | logo_alt | logo_caption | logo_upright | logo_size | logo_title | middleware | module | name | operating system | operating_system | other_names | platform | programming language | programming_language | released | replaced_by | replaces | repo | screenshot | screenshot alt | screenshot upright | screenshot size | screenshot title | screenshot_alt | screenshot_upright | screenshot_size | screenshot_title | service_name | size | standard | title | ver layout | website | qid }}Template:Main other cksum is a command in Unix and 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 32-bit cyclic redundancy check (CRC) checksum and byte count.<ref name=":0" /> The CRC output by cksum is different from the CRC-32 used in zip, PNG and zlib.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

The cksum command can be used to verify that files transferred by unreliable means arrived intact.<ref name=":0">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> 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 sha256sum.

The command is available as a separate package for Microsoft Windows as part of the UnxUtils collection of native Win32 ports of common GNU Unix-like utilities.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Latest GNU Coreutils cksum provides additional checksum algorithms via -a option, as an extension beyond POSIX.<ref name=":0" />

InteroperabilityEdit

The standard cksum command, as found on most Unix and Unix-like operating systems (including Linux, *BSD,<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> macOS, and Solaris<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>) uses a CRC algorithm based on the ethernet standard frame check<ref name=":1" /> and is therefore interoperable between implementations. This is in contrast to the sum command, which is not as interoperable and 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.Template:Citation needed

AlgorithmEdit

cksum uses the generator polynomial 0x04C11DB7 and appends to the message its length in little endian representation. That length has null bytes trimmed on the right end.<ref name=":1">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>