is a

computer program A computer program is a sequence or set of instructions in a programming language for a computer to Execution (computing), execute. It is one component of software, which also includes software documentation, documentation and other intangibl ...

that calculates and verifies 128-bit

MD5 The MD5 message-digest algorithm is a widely used hash function producing a 128-bit hash value. MD5 was designed by Ronald Rivest in 1991 to replace an earlier hash function MD4, and was specified in 1992 as Request for Comments, RFC 1321. MD5 ...

hashes, as described in RFC 1321. The MD5 hash functions as a compact digital fingerprint of a file. As with all such hashing algorithms, there is theoretically an unlimited number of files that will have any given MD5 hash. However, it is very unlikely that any two non-identical files in the real world will have the same MD5 hash, unless they have been specifically created to have the same hash. The underlying MD5 algorithm is no longer deemed secure. Thus, while is well-suited for identifying known files in situations that are not security related, it should not be relied on if there is a chance that files have been purposefully and maliciously tampered. In the latter case, the use of a newer hashing tool such as sha256sum is recommended. is used to verify the integrity of files, as virtually any change to a file will cause its MD5 hash to change. Most commonly, is used to verify that a file has not changed as a result of a faulty file transfer, a disk error or non-malicious meddling. The program is included in most

Unix-like A Unix-like (sometimes referred to as UN*X, *nix or *NIX) operating system is one that behaves in a manner similar to a Unix system, although not necessarily conforming to or being certified to any version of the Single UNIX Specification. A Uni ...

operating systems An operating system (OS) is system software that manages computer hardware and software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ...

compatibility layer In software engineering, a compatibility layer is an interface that allows binaries for a legacy or foreign system to run on a host system. This translates system calls for the foreign system into native system calls for the host system. With s ...

s such as

Cygwin Cygwin ( ) is a free and open-source Unix-like environment and command-line interface (CLI) for Microsoft Windows. The project also provides a software repository containing open-source packages. Cygwin allows source code for Unix-like operati ...

. The original C code was written by Ulrich Drepper and extracted from a 2001 release of .

Examples

All of the following files are assumed to be in the current directory.

Create MD5 hash file hash.md5

$ md5sum filetohashA.txt filetohashB.txt filetohashC.txt > hash.md5

File produced

File contains hash and filename pairs: $ cat hash.md5 595f44fec1e92a71d3e9e77456ba80d1 filetohashA.txt 71f920fa275127a7b60fa4d4d41432a3 filetohashB.txt 43c191bf6d6c3f263a8cd0efd4a058ab filetohashC.txt Please note: * There must be two spaces or a space and an asterisk between each value and filename to be compared (the second space indicates text mode, the asterisk binary mode). Otherwise, the following error will result: no properly formatted MD5 checksum lines found. Many programs don't distinguish between the two modes, but some utils do. * The file must be also be UNIX line ending formatted, otherwise this will be seen: md5sum: WARNING: x listed files could not be read. will convert it quickly if it is DOS/Windows formatted.

Check MD5

$ md5sum -c hash.md5 filetohashA.txt: OK filetohashB.txt: OK filetohashC.txt: OK

Check single MD5

$ echo 'D43F2404CA13E22594E5C8B04D3BBB81 filetohashA.txt' , md5sum -c filetohashA.txt: OK

On non-GNU systems

is specific to systems that use GNU coreutils or a clone such as

BusyBox BusyBox is a software suite that provides several List of Unix commands, Unix utilities in a single executable file. It runs in a variety of POSIX environments such as Linux, Android (operating system), Android, and FreeBSD, although many of the ...

. On

FreeBSD FreeBSD is a free-software Unix-like operating system descended from the Berkeley Software Distribution (BSD). The first version was released in 1993 developed from 386BSD, one of the first fully functional and free Unix clones on affordable ...

and

OpenBSD OpenBSD is a security-focused operating system, security-focused, free software, Unix-like operating system based on the Berkeley Software Distribution (BSD). Theo de Raadt created OpenBSD in 1995 by fork (software development), forking NetBSD ...

the utilities are called , , , and . These versions offer slightly different options and features. Additionally, FreeBSD offers the "SKEIN" family of message digests.

References

External links

* {{Core Utilities commands Unix security-related software Unix file system-related software