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DD(1)                       General Commands Manual                      DD(1)

NAME
     dd -- convert and copy a file

SYNOPSIS
     dd [operand ...]

DESCRIPTION
     The dd utility copies the standard input to the standard output.  Input
     data is read and written in 512-byte blocks.  If input reads are short,
     input from multiple reads are aggregated to form the output block.  When
     finished, dd displays the number of complete and partial input and output
     blocks and truncated input records to the standard error output.

     The following operands are available:

     bs=n     Set both input and output block size, superseding the ibs and
              obs operands.  If no conversion values other than noerror,
              notrunc or sync are specified, then each input block is copied
              to the output as a single block without any aggregation of short
              blocks.

     cbs=n    Set the conversion record size to n bytes.  The conversion
              record size is required by the record oriented conversion
              values.

     count=n  Copy only n input blocks.

     files=n  Copy n input files before terminating.  This operand is only
              applicable when the input device is a tape.

     ibs=n    Set the input block size to n bytes instead of the default 512.

     if=file  Read input from file instead of the standard input.

     iflag=flags
              Use comma-separated flags when calling open(2) for the input
              file.  The possible values are O_ flags documented in open(2),
              specified as lowercase and with the leading O_ removed.  Default
              value is rdonly.

     iseek=n  Seek on the input file n blocks.  This is synonymous with
              skip=n.

     msgfmt=fmt
              Specify the message format fmt to be used when writing
              information to standard output.  Possible values are:
                    quiet  turns off information summary report except for
                           errors and progress.
                    posix  default information summary report as specified by
                           POSIX.
                    human  default information summary report extended with
                           human-readable values.

              When fmt does not correspond to any value given above, it
              contains a string that will be used as format specifier for the
              information summary output.  Each conversion specification is
              introduced by the character %.  The following ones are
              available:
                    b   total number of bytes transferred
                    B   total number of bytes transferred in
                        humanize_number(3) format
                    e   speed transfer
                    E   speed transfer in humanize_number(3) format
                    i   number of partial input block(s)
                    I   number of full input block(s)
                    o   number of partial output block(s)
                    O   number of full output block(s)
                    s   time elapsed since the beginning in ``seconds.ms''
                        format
                    p   number of sparse output blocks
                    t   number of truncated blocks
                    w   number of odd-length swab blocks
                    P   singular/plural of ``block'' depending on number of
                        sparse blocks
                    T   singular/plural of ``block'' depending on number of
                        truncated blocks
                    W   singular/plural of ``block'' depending on number of
                        swab blocks

     obs=n    Set the output block size to n bytes instead of the default 512.

     of=file  Write output to file instead of the standard output.  Any
              regular output file is truncated unless the notrunc conversion
              value is specified.  If an initial portion of the output file is
              skipped (see the seek operand) the output file is truncated at
              that point.

     oflag=flags
              Same as iflag but for the call to open(2) on the output file.
              The default value is creat, which should be explicitly added in
              oflag in order to output to a nonexistent file.  The default or
              specified value is or'ed with rdwr for a first attempt, then on
              failure with wronly on a second attempt.  In both cases, trunc
              is automatically added if none of oseek, seek, or conv=notrunc
              operands are used,

     oseek=n  Seek on the output file n blocks.  This is synonymous with
              seek=n.

     seek=n   Seek n blocks from the beginning of the output before copying.
              On non-tape devices, an lseek(2) operation is used.  Otherwise,
              existing blocks are read and the data discarded.  If the user
              does not have read permission for the tape, it is positioned
              using the tape ioctl(2) function calls.  If the seek operation
              is past the end of file, space from the current end of file to
              the specified offset is filled with blocks of NUL bytes.

     skip=n   Skip n blocks from the beginning of the input before copying.
              On input which supports seeks, an lseek(2) operation is used.
              Otherwise, input data is read and discarded.  For pipes, the
              correct number of bytes is read.  For all other devices, the
              correct number of blocks is read without distinguishing between
              a partial or complete block being read.

     progress=n
              Switch on display of progress if n is set to any non-zero value.
              This will cause a ``.'' to be printed (to the standard error
              output) for every n full or partial blocks written to the output
              file.

     conv=value[,value...]
              Where value is one of the symbols from the following list.

              ascii, oldascii
                       The same as the unblock value except that characters
                       are translated from EBCDIC to ASCII before the records
                       are converted.  (These values imply unblock if the
                       operand cbs is also specified.)  There are two
                       conversion maps for ASCII.  The value ascii specifies
                       the recommended one which is compatible with AT&T
                       System V UNIX.  The value oldascii specifies the one
                       used in historic AT&T and pre- 4.3BSD-Reno systems.

              block    Treats the input as a sequence of newline or end-of-
                       file terminated variable length records independent of
                       input and output block boundaries.  Any trailing
                       newline character is discarded.  Each input record is
                       converted to a fixed length output record where the
                       length is specified by the cbs operand.  Input records
                       shorter than the conversion record size are padded with
                       spaces.  Input records longer than the conversion
                       record size are truncated.  The number of truncated
                       input records, if any, are reported to the standard
                       error output at the completion of the copy.

              ebcdic, ibm, oldebcdic, oldibm
                       The same as the block value except that characters are
                       translated from ASCII to EBCDIC after the records are
                       converted.  (These values imply block if the operand
                       cbs is also specified.)  There are four conversion maps
                       for EBCDIC.  The value ebcdic specifies the recommended
                       one which is compatible with AT&T System V UNIX.  The
                       value ibm is a slightly different mapping, which is
                       compatible with the AT&T System V UNIX ibm value.  The
                       values oldebcdic and oldibm are maps used in historic
                       AT&T and pre 4.3BSD-Reno systems.

              lcase    Transform uppercase characters into lowercase
                       characters.

              noerror  Do not stop processing on an input error.  When an
                       input error occurs, a diagnostic message followed by
                       the current input and output block counts will be
                       written to the standard error output in the same format
                       as the standard completion message.  If the sync
                       conversion is also specified, any missing input data
                       will be replaced with NUL bytes (or with spaces if a
                       block oriented conversion value was specified) and
                       processed as a normal input buffer.  If the sync
                       conversion is not specified, the input block is omitted
                       from the output.  On input files which are not tapes or
                       pipes, the file offset will be positioned past the
                       block in which the error occurred using lseek(2).

              notrunc  Do not truncate the output file.  This will preserve
                       any blocks in the output file not explicitly written by
                       dd.  The notrunc value is not supported for tapes.

              osync    Pad the final output block to the full output block
                       size.  If the input file is not a multiple of the
                       output block size after conversion, this conversion
                       forces the final output block to be the same size as
                       preceding blocks for use on devices that require
                       regularly sized blocks to be written.  This option is
                       incompatible with use of the bs=n block size
                       specification.

              sparse   If one or more non-final output blocks would consist
                       solely of NUL bytes, try to seek the output file by the
                       required space instead of filling them with NULs.  This
                       results in a sparse file on some file systems.

              swab     Swap every pair of input bytes.  If an input buffer has
                       an odd number of bytes, the last byte will be ignored
                       during swapping.

              sync     Pad every input block to the input buffer size.  Spaces
                       are used for pad bytes if a block oriented conversion
                       value is specified, otherwise NUL bytes are used.

              ucase    Transform lowercase characters into uppercase
                       characters.

              unblock  Treats the input as a sequence of fixed length records
                       independent of input and output block boundaries.  The
                       length of the input records is specified by the cbs
                       operand.  Any trailing space characters are discarded
                       and a newline character is appended.

     Where sizes are specified, a decimal number of bytes is expected.  Two or
     more numbers may be separated by an ``x'' to indicate a product.  Each
     number may have one of the following optional suffixes:
           b    Block; multiply by 512
           k    Kibi; multiply by 1024 (1 KiB)
           m    Mebi; multiply by 1048576 (1 MiB)
           g    Gibi; multiply by 1073741824 (1 GiB)
           t    Tebi; multiply by 1099511627776 (1 TiB)
           w    Word; multiply by the number of bytes in an integer

     When finished, dd displays the number of complete and partial input and
     output blocks, truncated input records and odd-length byte-swapping
     blocks to the standard error output.  A partial input block is one where
     less than the input block size was read.  A partial output block is one
     where less than the output block size was written.  Partial output blocks
     to tape devices are considered fatal errors.  Otherwise, the rest of the
     block will be written.  Partial output blocks to character devices will
     produce a warning message.  A truncated input block is one where a
     variable length record oriented conversion value was specified and the
     input line was too long to fit in the conversion record or was not
     newline terminated.

     Normally, data resulting from input or conversion or both are aggregated
     into output blocks of the specified size.  After the end of input is
     reached, any remaining output is written as a block.  This means that the
     final output block may be shorter than the output block size.

     If dd receives a SIGINFO signal (see the status argument for stty(1)),
     the current input and output block counts will be written to the standard
     error output in the same format as the standard completion message.  If
     dd receives a SIGINT signal, the current input and output block counts
     will be written to the standard error output in the same format as the
     standard completion message and dd will exit.

EXIT STATUS
     The dd utility exits 0 on success and >0 if an error occurred.

EXAMPLES
     To print summary information in human-readable form:

           dd if=/dev/zero of=/dev/null count=1 msgfmt=human

     To customize the information summary output and print it through
     unvis(3):

           dd if=/dev/zero of=/dev/null count=1 \
                msgfmt='speed:%E, in %s seconds\n' 2>&1 | unvis

SEE ALSO
     cp(1), mt(1), tr(1)

STANDARDS
     The dd utility is expected to be a superset of the IEEE Std 1003.2
     (``POSIX.2'') standard.  The files and msgfmt operands and the ascii,
     ebcdic, ibm, oldascii, oldebcdic and oldibm values are extensions to the
     POSIX standard.

NetBSD 7.1.2                    March 18, 2015                    NetBSD 7.1.2