info > cksum

File: coreutils.info,  Node: cksum invocation,  Next: md5sum invocation,  Prev: sum invocation,  Up: Summarizing files

6.3 'cksum': Print and verify file checksums

'cksum' by default computes a 32-bit cyclic redundancy check (CRC)
checksum for each given FILE, or standard input if none are given or for
a FILE of '-'.

   cksum also supports the '-a/--algorithm' option to select the digest
algorithm to use.  'cksum' is the preferred interface to these digests,
subsuming the other standalone checksumming utilities, which can be
emulated using 'cksum -a md5 --untagged "$@"' etc.  Synopsis:

     cksum [OPTION]... [FILE]...

   'cksum' is typically used to ensure that files have not been
corrupted, by comparing the 'cksum' output for the received files with
the 'cksum' output for the original files (typically given in the
distribution).

* Menu:

* cksum output modes::          Legacy and non Legacy output formats
* cksum general options::       Options supported only by cksum
* cksum common options::        Options supported also by standalone utilities

File: coreutils.info,  Node: cksum output modes,  Next: cksum general options,  Up: cksum invocation

Legacy output format
     'cksum' by default prints the POSIX standard CRC checksum for each
     file along with the number of bytes in the file, and the file name
     unless no arguments were given.  The 32-bit CRC used is based on
     the polynomial used for CRC error checking in the ISO/IEC
     8802-3:1996 standard (Ethernet).  Similar output formats are used
     for the other legacy checksums selectable with '--algorithm=sysv'
     or '--algorithm=bsd', detailed at *note sum invocation::.

Tagged output format
     With the '--algorithm' option selecting non legacy checksums, the
     'cksum' command defaults to output of the form:
          DIGEST_NAME (FILE NAME) = DIGEST
     Note the standalone checksum utilities can select this output mode
     by using the '--tag' option.

Untagged output format
     With the '--untagged' option and the '--algorithm' option selecting
     non legacy checksums, the following output format is used.  Note
     this is the default output format of the standalone checksum
     utilities.  For each FILE, we print the checksum, a space, a flag
     indicating binary or text input mode, and the file name.  Binary
     mode is indicated with '*', text mode with ' ' (space).  Binary
     mode is the default on systems where it's significant, otherwise
     text mode is the default.

   Note without '--zero', and with non legacy output formats, if FILE
contains a backslash, newline, or carriage return, 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.  Since the backslash character itself
is escaped, any other backslash escape sequences are reserved for future
use.

File: coreutils.info,  Node: cksum general options,  Next: cksum common options,  Prev: cksum output modes,  Up: cksum invocation

'-a'
'--algorithm'
     Compute checksums using the specified digest algorithm.

     Supported legacy checksums (which are not supported by '--check'):
          'sysv'      equivalent to sum -s
          'bsd'       equivalent to sum -r
          'crc'       equivalent to cksum (the default)

     Supported more modern digest algorithms are:
          'md5'       equivalent to md5sum
          'sha1'      equivalent to sha1sum
          'sha224'    equivalent to sha224sum
          'sha256'    equivalent to sha256sum
          'sha384'    equivalent to sha384sum
          'sha512'    equivalent to sha512sum
          'blake2b'   equivalent to b2sum
          'sm3'       only available through cksum

'--base64'
     Print base64-encoded digests not hexadecimal.  This option is
     ignored with '--check'.  The format conforms to RFC 4648#4
     (https://tools.ietf.org/search/rfc4648#section-4).

     Note that each base64-encoded digest has zero, one or two trailing
     padding ('=') bytes.  The length of that padding is the
     checksum-bit-length modulo 3, and the '--check' parser requires
     precisely the same input digest string as what is output.  I.e.,
     removing or adding any '=' padding renders a digest non-matching.

'--debug'
     Output extra information to stderr, like the checksum
     implementation being used.

'-l'
'--length'
     Change (shorten) the default digest length.  This is specified in
     bits and thus must be a multiple of 8.  This option is ignored when
     '--check' is specified, as the length is automatically determined
     when checking.

'--raw'
     Print only the unencoded raw binary digest for a single input.  Do
     not output the file name or anything else.  Use network byte order
     (big endian) where applicable: for 'bsd', 'crc', and 'sysv'.  This
     option works only with a single input.  Unlike other output
     formats, 'cksum' provides no way to '--check' a '--raw' checksum.

'--untagged'
     Output using the original Coreutils format used by the other
     standalone checksum utilities like 'md5sum' for example.  This
     format has the checksum at the start of the line, and may be more
     amenable to further processing by other utilities, especially in
     combination with the '--zero' option.  Note this does not identify
     the digest algorithm used for the checksum.  *Note cksum output
     modes:: for details of this format.

File: coreutils.info,  Node: cksum common options,  Prev: cksum general options,  Up: cksum invocation

'-b'
'--binary'
     Note this option is not supported by the 'cksum' command, as it
     operates in binary mode exclusively.  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 mode as binary: the 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 standard input if no FILE was specified) and report
     whether the checksums match the contents of the named files.  The
     input to this mode is usually the output of a prior,
     checksum-generating run of the command.

     Three input formats are supported.  Either the default output
     format described above, the '--tag' output format, or the BSD
     reversed mode format which is similar to the default mode, but
     doesn't use a character to distinguish binary and text modes.

     For the 'cksum' command, the '--check' option supports
     auto-detecting the digest algorithm to use, when presented with
     checksum information in the '--tag' output format.

     Also for the 'cksum' command, the '--check' option auto-detects the
     digest encoding, accepting both standard hexadecimal checksums and
     those generated via 'cksum' with its '--base64' option.

     Output with '--zero' enabled is not supported by '--check'.

     For each such line, 'cksum' reads the named file and computes its
     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 a checksum inconsistent with the associated file, or
     if no valid line is found, 'cksum' exits with nonzero status.
     Otherwise, it exits successfully.  Note the 'cksum' command doesn't
     support '--check' with the older 'sysv', 'bsd', or 'crc'
     algorithms.

'--ignore-missing'
     This option is useful only when verifying checksums.  When
     verifying checksums, don't fail or report any status for missing
     files.  This is useful when verifying a subset of downloaded files
     given a larger list of checksums.

'--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 checksums, exit successfully.
     Otherwise exit with a status code indicating there was a failure.

'--tag'
     Output BSD style checksums, which indicate the checksum algorithm
     used.  As a GNU extension, if '--zero' is not used, file names with
     problematic characters are escaped as described above, using the
     same escaping indicator of '\' at the start of the line, as used
     with the other output format.  The '--tag' option implies binary
     mode, and is disallowed with '--text' mode as supporting that would
     unnecessarily complicate the output format, while providing little
     benefit.  *Note cksum output modes:: for details of this format.
     The 'cksum' command, uses '--tag' as its default output format.

'-t'
'--text'
     Note this option is not supported by the 'cksum' command.  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.  This mode is
     never defaulted to if '--tag' is used.

'-w'
'--warn'
     When verifying checksums, warn about improperly formatted checksum
     lines.  This option is useful only if all but a few lines in the
     checked input are valid.

'--strict'
     When verifying checksums, if one or more input line is invalid,
     exit nonzero after all warnings have been issued.

'-z'
'--zero'
     Output a zero byte (ASCII NUL) at the end of each line, rather than
     a newline.  This option enables other programs to parse the output
     even when that output would contain data with embedded newlines.
     Also file name escaping is not used.