NAME
md5, sha1, sha224, sha256, sha384, sha512, md5sum, sha1sum, sha224sum, sha256sum, sha384sum, sha512sum – calculate a message-digest fingerprint (checksum) for a file
SYNOPSIS
md5 [-pqrtx] [-c string] [-s string] [file ...]
md5sum [-bctwz] [--binary] [--check] [--help] [--ignore-missing] [--quiet] [--status] [--strict] [--tag] [--text] [--version] [--warn] [--zero] [file ...]
(All other hashes have the same options and usage.)
shasum [-0bchqstUvw] [--01] [-a | --algorithm alg] [--binary] [--check] [--help] [--ignore-missing] [--quiet] [--status] [--strict] [--tag] [--text] [--UNIVERSAL] [--version] [--warn] [file ...]
DESCRIPTION
The md5, sha1, sha224, sha256, sha384, and sha512 utilities take as input a message of arbitrary length and produce as output a “fingerprint” or “message digest” of the input.
The md5sum, sha1sum, sha224sum, sha256sum, sha384sum, and sha512sum utilities do the same, but with command-line options and an output format that match those of their similary named GNU utilities.
In all cases, each file listed on the command line is processed separately. If no files are listed on the command line, or a file name is given as -, input is taken from stdin instead.
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, and SHA-512 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.
It is recommended that all new applications use SHA-512 instead of one of the other hash functions.
BSD OPTIONS
The following options are available in BSD mode, i.e. when the program is invoked with a name that does not end in “sum”:
- -c string, --check=string
-
Compare the digest of the file against this string. If combined with the -q or --quiet option, the calculated digest is printed in addition to the exit status being set. (Note that this option is not yet useful if multiple files are specified.)
- -p, --passthrough
-
Echo stdin to stdout and append the checksum to stdout. In this mode, any files specified on the command line are silently ignored.
- -q, --quiet
-
Quiet mode — only the checksum is printed out. Overrides the -r or --reverse option.
- -r, --reverse
-
Reverses the format of the output. This helps with visual diffs. Does nothing when combined with the -ptx options.
- -s string, --string=string
-
Print a checksum of the given string. In this mode, any files specified on the command line are silently ignored.
- -t, --time-trial
-
Run a built-in time trial. For the -sum versions, this is a nop for compatibility with coreutils.
- -x, --self-test
-
Run a built-in test script.
GNU OPTIONS
The following options are available in GNU mode, i.e. when the program is invoked with a name that ends in “sum”:
- -b, --binary
-
Read files in binary mode.
- -c, --check
-
The file passed as arguments must contain digest lines generated by the same digest algorithm 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 --quiet option can be used to quiesce the output unless there are mismatched entries in the digest.
- --help
-
Print a usage message and exit.
- --ignore-missing
-
When verifying checksums, ignore files for which checksums are given but which aren't found on disk.
- --quiet
-
When verifying checksums, do not print anything unless the verification fails.
- --status
-
When verifying checksums, do not print anything at all. The exit code will reflect whether verification succeeded.
- --strict
-
When verifying checksums, fail if the input is malformed.
- --tag
-
Produce BSD-style output.
- -t, --text
-
Read files in text mode. This is the default. Note that this implementation does not differentiate between binary and text mode.
- --version
-
Print version information and exit.
- -w, --warn
-
When verifying checksums, warn about malformed input.
- -z, --zero
-
Terminate output lines with NUL rather than with newline.
EXIT STATUS
The md5, sha1, sha224, sha256, sha384, and sha512 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.
The md5sum, sha1sum, sha224sum, sha256sum, sha384sum, and sha512sum utilities exit 0 on success and 1 if at least one of the input files could not be read or, when verifying checksums, does not have the expected checksum.
EXAMPLES
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
This is almost but not quite identical to the output from GNU mode:
$ md5sum /boot/loader.conf /etc/rc.conf ada5f60f23af88ff95b8091d6d67bef6 /boot/loader.conf d80bf36c332dc0fdc479366ec3fa44cd /etc/rc.conf
Note the two spaces between hash and file name. If binary mode is requested, they are instead separated by a space and an asterisk:
$ md5sum -b /boot/loader.conf /etc/rc.conf ada5f60f23af88ff95b8091d6d67bef6 */boot/loader.conf d80bf36c332dc0fdc479366ec3fa44cd */etc/rc.conf
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 ]
In GNU mode, 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 in either BSD or GNU mode. If a hash value does not match the file, “FAILED” is printed instead of “OK”.
SEE ALSO
cksum(1), md5(3), sha(3), sha256(3), sha384(3), sha512(3) R. Rivest, The MD5 Message-Digest Algorithm, RFC1321. J. Burrows, The Secure Hash Standard, FIPS PUB 180-2. D. Eastlake and P. Jones, US Secure Hash Algorithm 1, RFC 3174.
Secure Hash Standard (SHS): https://www.nist.gov/publications/secure-hash-standard-shs
ACKNOWLEDGMENTS
This utility was originally derived from a program which was placed in the public domain for free general use by RSA Data Security.
Support for SHA-1 was added by Oliver Eikemeier ⟨[email protected]⟩.
Support for SHA-2 was added by Colin Percival ⟨[email protected]⟩ and Allan Jude ⟨[email protected]⟩.
Compatibility with GNU coreutils was added by Warner Losh ⟨[email protected]⟩ and much expanded by Dag-Erling Smørgrav ⟨[email protected]⟩.