Md5sum
Encyclopedia
md5sum is a computer program
that calculates and verifies 128-bit MD5
hashes
, as described in RFC 1321. The MD5 hash (or checksum
) 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 unlikely that any two non-identical files will have the same MD5
hash.
Virtually any change to a file will cause its MD5 hash to change; therefore md5sum is used to verify the integrity of files. Most commonly, md5sum is used to verify that a file has not changed as a result of file transfer, disk error or meddling. The md5sum program is installed by default in most Unix
, Linux
, and Unix-like
operating systems or compatibility layer
s. Other operating systems, including Microsoft Windows and BSD variants — such as Mac OS X
- have similar utilities (see external links).
md5sum file1 file2 > files.md5
47f4cc0b788002e8b264881beb4ec08b file1
beaa28899c52f9df66094c4267876e78 file2
md5sum -c files.md5
file1: OK
file2: OK
Computer program
A computer program is a sequence of instructions written to perform a specified task with a computer. A computer requires programs to function, typically executing the program's instructions in a central processor. The program has an executable form that the computer can use directly to execute...
that calculates and verifies 128-bit MD5
MD5
The MD5 Message-Digest Algorithm is a widely used cryptographic hash function that produces a 128-bit hash value. Specified in RFC 1321, MD5 has been employed in a wide variety of security applications, and is also commonly used to check data integrity...
hashes
Cryptographic hash function
A cryptographic hash function is a deterministic procedure that takes an arbitrary block of data and returns a fixed-size bit string, the hash value, such that an accidental or intentional change to the data will change the hash value...
, as described in RFC 1321. The MD5 hash (or checksum
Checksum
A checksum or hash sum is a fixed-size datum computed from an arbitrary block of digital data for the purpose of detecting accidental errors that may have been introduced during its transmission or storage. The integrity of the data can be checked at any later time by recomputing the checksum and...
) 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 unlikely that any two non-identical files will have the same MD5
MD5
The MD5 Message-Digest Algorithm is a widely used cryptographic hash function that produces a 128-bit hash value. Specified in RFC 1321, MD5 has been employed in a wide variety of security applications, and is also commonly used to check data integrity...
hash.
Virtually any change to a file will cause its MD5 hash to change; therefore md5sum is used to verify the integrity of files. Most commonly, md5sum is used to verify that a file has not changed as a result of file transfer, disk error or meddling. The md5sum program is installed by default in most Unix
Unix
Unix is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna...
, Linux
Linux
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
, and Unix-like
Unix-like
A Unix-like operating system is one that behaves in a manner similar to a Unix system, while not necessarily conforming to or being certified to any version of the Single UNIX Specification....
operating systems or compatibility layer
Compatibility layer
A compatibility layer is a term that refers to components that allow for non-native support of components.In software engineering, a compatibility layer 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...
s. Other operating systems, including Microsoft Windows and BSD variants — such as Mac OS X
Mac OS X
Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...
- have similar utilities (see external links).
Examples
- Compute the MD5 sum of two files and store it in a third one:
md5sum file1 file2 > files.md5
- This file will have one line per input file. Each line will contain an MD5 sum (32 hexadecimal digits), two spaces and the corresponding input file name. It will look like:
47f4cc0b788002e8b264881beb4ec08b file1
beaa28899c52f9df66094c4267876e78 file2
- Check for validity with:
md5sum -c files.md5
- Expected results:
file1: OK
file2: OK
See also
- GNU Core UtilitiesGNU Core UtilitiesThe GNU Core Utilities or coreutils is a package of GNU software containing many of the basic tools, such as cat, ls, and rm, needed for Unix-like operating systems...
- cksumCksumcksum' 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...
- CygwinCygwinCygwin is a Unix-like environment and command-line interface for Microsoft Windows. Cygwin provides native integration of Windows-based applications, data, and other system resources with applications, software tools, and data of the Unix-like environment...
- GnuWin32GnuWin32The GnuWin32 project provides native ports in the form of runnable computer programs, patches, and source code for various GNU and open source tools and software, much of it modified to run on the 32-bit Windows platform...
- sha1sumSha1sumsha1sum is a computer program that calculates and verifies SHA-1 hashes. It is commonly used to verify the integrity of files. It is installed by default in most Unix-like operating systems...
- Comparison of file verification software
- MD5MD5The MD5 Message-Digest Algorithm is a widely used cryptographic hash function that produces a 128-bit hash value. Specified in RFC 1321, MD5 has been employed in a wide variety of security applications, and is also commonly used to check data integrity...