Manual Pages  — MD5

md5, skein256, md5sum, sha512t256sum – calculate a message-digest fingerprint (checksum) for a file

SYNOPSIS DESCRIPTION EXIT STATUS EXAMPLES SEE ALSO BUGS ACKNOWLEDGMENTS

md5 [-pqrtx] [-c string] [-s string] [file ...]

md5sum [-pqrtx] [-c file] [-s string] [file ...]

(All other hashes have the same options and usage.)

The md5 skein256, and skein1024 utilities take as input a message of arbitrary length and produce as output a "fingerprint" or "message digest" of the input. The md5sum, sha512t256sum, and skein1024sum utilities do the same, but default to the reversed format of the -r flag. It is conjectured that it is computationally infeasible to produce two messages having the same message digest, or to produce any message having a given prespecified target message digest. The SHA-224, SHA-256, SHA-384, SHA-512, RIPEMD-160, and SKEIN algorithms are intended for digital signature applications, where a large file must be "compressed" in a secure manner before being encrypted with a private (secret) key under a public-key cryptosystem such as RSA.

The MD5 and SHA-1 algorithms have been proven to be vulnerable to practical collision attacks and should not be relied upon to produce unique outputs, nor should they be used as part of a cryptographic signature scheme. As of 2017-03-02, there is no publicly known method to reverse either algorithm, i.e. to find an input that produces a specific output.

SHA-512t256 is a version of SHA-512 truncated to only 256 bits. On 64-bit hardware, this algorithm is approximately 50% faster than SHA-256 but with the same level of security. The hashes are not interchangeable.

It is recommended that all new applications use SHA-512 or SKEIN-512 instead of one of the other hash functions.

The following options may be used in any combination and must precede any files named on the command line. The hexadecimal checksum of each file listed on the command line is printed after the options are processed.

-b
	Make the -sum programs separate hash and digest with a blank followed by an asterisk instead of by 2 blank characters for full compatibility with the output generated by the coreutils versions of these programs.
-c string
	If the program was called with a name that does not end in sum, compare the digest of the file against this string. (Note that this option is not yet useful if multiple files are specified.)
-c file
	If the program was called with a name that does end in sum, the file passed as argument must contain digest lines generated by the same digest algorithm with or without the -r option (i.e. in either classical BSD format or in GNU coreutils format). A line with the file name followed by a colon ":" and either OK or FAILED is written for each well-formed line in the digest file. If applicable, the number of failed comparisons and the number of lines that were skipped since they were not well-formed are printed at the end. The -q option can be used to quiesce the output unless there are mismatched entries in the digest.
-s string
	Print a checksum of the given string.
-p
	Echo stdin to stdout and append the checksum to stdout.
-q
	Quiet mode — only the checksum is printed out. Overrides the -r option.
-r
	Reverses the format of the output. This helps with visual diffs. Does nothing when combined with the -ptx options.
-t
	Run a built-in time trial. For the -sum versions, this is a nop for compatibility with coreutils.
-x
	Run a built-in test script.

The md5, skein256 and skein1024 utilities exit 0 on success, 1 if at least one of the input files could not be read, and 2 if at least one file does not have the same hash as the -c option. <<<<<<< HEAD =======

Calculate the MD5 checksum of the string "Hello".

$ md5 -s Hello
MD5 ("Hello") = 8b1a9953c4611296a827abf8c47804d7

Same as above, but note the absence of the newline character in the input string:

$ echo -n Hello | md5
8b1a9953c4611296a827abf8c47804d7

Calculate the checksum of multiple files reversing the output:

$ md5 -r /boot/loader.conf /etc/rc.conf
ada5f60f23af88ff95b8091d6d67bef6 /boot/loader.conf
d80bf36c332dc0fdc479366ec3fa44cd /etc/rc.conf

.Pd 
The
-sum
variants put 2 blank characters between hash and file name for full compatibility
with the coreutils versions of these commands.

Write the digest for /boot/loader.conf in a file named digest. Then calculate the checksum again and validate it against the checksum string extracted from the digest file:

$ md5 /boot/loader.conf > digest && md5 -c $(cut -f2 -d= digest) /boot/loader.conf
MD5 (/boot/loader.conf) = ada5f60f23af88ff95b8091d6d67bef6

Same as above but comparing the digest against an invalid string ("randomstring"), which results in a failure.

$ md5 -c randomstring /boot/loader.conf
MD5 (/boot/loader.conf) = ada5f60f23af88ff95b8091d6d67bef6 [ Failed ]

If invoked with a name ending in -sum the -c option does not compare against a hash string passed as parameter. Instead, it expects a digest file, as created under the name digest for /boot/loader.conf in the example above.

$ md5 -c digest /boot/loader.conf
/boot/loader.conf: OK

The digest file may contain any number of lines in the format generated with or without the -r option (i.e. in either classical BSD format or in GNU coreutils format). If a hash value does not match the file, FAILED is printed instead of OK. >>>>>>> c2870e576bd2 (sbin/md5: improve compatibility with coreutils -c option)

All of the utilities that end in 'sum' are intended to be compatible with the GNU coreutils programs. However, the long option functionality is not provided.

This program is placed in the public domain for free general use by RSA Data Security.

Support for SHA-1 and RIPEMD-160 has been added by Oliver Eikemeier <Mt eik@FreeBSD.org>.