/usr/bin/dd

Copy, and optionally convert, a file system resource

Usage: dd [OPERAND]...
       dd OPTION

Arguments:
  [operands]...

Options:
  -h, --help     Print help
  -V, --version  Print version

Operands:

  - bs=BYTES : read and write up to BYTES bytes at a time (default: 512); overwrites ibs and obs.
  - cbs=BYTES : the 'conversion block size' in bytes. Applies to the conv=block, and conv=unblock
  operations.
  - conv=CONVS : a comma-separated list of conversion options or (for legacy reasons) file flags.
  - count=N : stop reading input after N ibs-sized read operations rather than proceeding until EOF.
  See iflag=count_bytes if stopping after N bytes is preferred
  - ibs=N : the size of buffer used for reads (default: 512)
  - if=FILE : the file used for input. When not specified, stdin is used instead
  - iflag=FLAGS : a comma-separated list of input flags which specify how the input source is
  treated. FLAGS may be any of the input-flags or general-flags specified below.
  - skip=N (or iseek=N) : skip N ibs-sized records into input before beginning copy/convert
  operations. See iflag=seek_bytes if seeking N bytes is preferred.
  - obs=N : the size of buffer used for writes (default: 512)
  - of=FILE : the file used for output. When not specified, stdout is used instead
  - oflag=FLAGS : comma separated list of output flags which specify how the output source is
  treated. FLAGS may be any of the output flags or general flags specified below
  - seek=N (or oseek=N) : seeks N obs-sized records into output before beginning copy/convert
  operations. See oflag=seek_bytes if seeking N bytes is preferred
  - status=LEVEL : controls whether volume and performance stats are written to stderr.

    When unspecified, dd will print stats upon completion. An example is below.

      6+0 records in
      16+0 records out
      8192 bytes (8.2 kB, 8.0 KiB) copied, 0.00057009 s,
      14.4 MB/s

    The first two lines are the 'volume' stats and the final line is the 'performance' stats. The
    volume stats indicate the number of complete and partial ibs-sized reads, or obs-sized writes
    that took place during the copy. The format of the volume stats is <complete>+<partial>. If
    records have been truncated (see conv=block), the volume stats will contain the number of
    truncated records.

    Possible LEVEL values are:
      - progress : Print periodic performance stats as the copy proceeds.
      - noxfer : Print final volume stats, but not performance stats.
      - none : Do not print any stats.

    Printing performance stats is also triggered by the INFO signal (where supported), or the USR1
    signal. Setting the POSIXLY_CORRECT environment variable to any value (including an empty value)
    will cause the USR1 signal to be ignored.

Conversion options:

  - ascii : convert from EBCDIC to ASCII. This is the inverse of the ebcdic option. Implies
  conv=unblock.
  - ebcdic : convert from ASCII to EBCDIC. This is the inverse of the ascii option. Implies
  conv=block.
  - ibm : convert from ASCII to EBCDIC, applying the conventions for [, ] and ~ specified in POSIX.
  Implies conv=block.
  - ucase : convert from lower-case to upper-case.
  - lcase : convert from upper-case to lower-case.
  - block : for each newline less than the size indicated by cbs=BYTES, remove the newline and pad
  with spaces up to cbs. Lines longer than cbs are truncated.
  - unblock : for each block of input of the size indicated by cbs=BYTES, remove right-trailing
  spaces and replace with a newline character.
  - sparse : attempts to seek the output when an obs-sized block consists of only zeros.
  - swab : swaps each adjacent pair of bytes. If an odd number of bytes is present, the final byte
  is omitted.
  - sync : pad each ibs-sided block with zeros. If block or unblock is specified, pad with spaces
  instead.
  - excl : the output file must be created. Fail if the output file is already present.
  - nocreat : the output file will not be created. Fail if the output file is not already present.
  - notrunc : the output file will not be truncated. If this option is not present, output will be
  truncated when opened.
  - noerror : all read errors will be ignored. If this option is not present, dd will only ignore
  Error::Interrupted.
  - fdatasync : data will be written before finishing.
  - fsync : data and metadata will be written before finishing.

Input flags:

  - count_bytes : a value to count=N will be interpreted as bytes.
  - skip_bytes : a value to skip=N will be interpreted as bytes.
  - fullblock : wait for ibs bytes from each read. zero-length reads are still considered EOF.

Output flags:

  - append : open file in append mode. Consider setting conv=notrunc as well.
  - seek_bytes : a value to seek=N will be interpreted as bytes.

General flags:

  - direct : use direct I/O for data.
  - directory : fail unless the given input (if used as an iflag) or output (if used as an oflag) is
  a directory.
  - dsync : use synchronized I/O for data.
  - sync : use synchronized I/O for data and metadata.
  - nonblock : use non-blocking I/O.
  - noatime : do not update access time.
  - nocache : request that OS drop cache.
  - noctty : do not assign a controlling tty.
  - nofollow : do not follow system links.