File: coreutils.info, Node: md5sum invocation, Next: sha1sum invocation, Prev: cksum invocation, Up: Summarizing files 6.4 `md5sum': Print or check MD5 digests ======================================== `md5sum' computes a 128-bit checksum (or "fingerprint" or "message-digest") for each specified FILE. Note: The MD5 digest is more reliable than a simple CRC (provided by the `cksum' command) for detecting accidental file corruption, as the chances of accidentally having two files with identical MD5 are vanishingly small. However, it should not be considered truly secure against malicious tampering: although finding a file with a given MD5 fingerprint, or modifying a file so as to retain its MD5 are considered infeasible at the moment, it is known how to produce different files with identical MD5 (a "collision"), something which can be a security issue in certain contexts. For more secure hashes, consider using SHA-1 or SHA-2. *Note sha1sum invocation::, and *note sha2 utilities::. If a FILE is specified as `-' or if no files are given `md5sum' computes the checksum for the standard input. `md5sum' can also determine whether a file and checksum are consistent. Synopsis: md5sum [OPTION]... [FILE]... For each FILE, `md5sum' outputs the MD5 checksum, a flag indicating a binary or text input file, and the file name. If FILE contains a backslash or newline, the line is started with a backslash, and each problematic character in the file name is escaped with a backslash, making the output unambiguous even in the presence of arbitrary file names. If FILE is omitted or specified as `-', standard input is read. The program accepts the following options. Also see *note Common options::. `-b' `--binary' Treat each input file as binary, by reading it in binary mode and outputting a `*' flag. This is the inverse of `--text'. On systems like GNU that do not distinguish between binary and text files, this option merely flags each input file as binary: the MD5 checksum is unaffected. This option is the default on systems like MS-DOS that distinguish between binary and text files, except for reading standard input when standard input is a terminal. `-c' `--check' Read file names and checksum information (not data) from each FILE (or from stdin if no FILE was specified) and report whether the checksums match the contents of the named files. The input to this mode of `md5sum' is usually the output of a prior, checksum-generating run of `md5sum'. Each valid line of input consists of an MD5 checksum, a binary/text flag, and then a file name. Binary files are marked with `*', text with ` '. For each such line, `md5sum' reads the named file and computes its MD5 checksum. Then, if the computed message digest does not match the one on the line with the file name, the file is noted as having failed the test. Otherwise, the file passes the test. By default, for each valid line, one line is written to standard output indicating whether the named file passed the test. After all checks have been performed, if there were any failures, a warning is issued to standard error. Use the `--status' option to inhibit that output. If any listed file cannot be opened or read, if any valid line has an MD5 checksum inconsistent with the associated file, or if no valid line is found, `md5sum' exits with nonzero status. Otherwise, it exits successfully. `--quiet' This option is useful only when verifying checksums. When verifying checksums, don't generate an 'OK' message per successfully checked file. Files that fail the verification are reported in the default one-line-per-file format. If there is any checksum mismatch, print a warning summarizing the failures to standard error. `--status' This option is useful only when verifying checksums. When verifying checksums, don't generate the default one-line-per-file diagnostic and don't output the warning summarizing any failures. Failures to open or read a file still evoke individual diagnostics to standard error. If all listed files are readable and are consistent with the associated MD5 checksums, exit successfully. Otherwise exit with a status code indicating there was a failure. `-t' `--text' Treat each input file as text, by reading it in text mode and outputting a ` ' flag. This is the inverse of `--binary'. This option is the default on systems like GNU that do not distinguish between binary and text files. On other systems, it is the default for reading standard input when standard input is a terminal. `-w' `--warn' When verifying checksums, warn about improperly formatted MD5 checksum lines. This option is useful only if all but a few lines in the checked input are valid. An exit status of zero indicates success, and a nonzero value indicates failure.