dd - convert and copy a file
dd [operands ...]
The dd utility copies the standard input to the standard
any specified conversions. Input data is read and written
blocks. If input reads are short, input from multiple reads
to form the output block. When finished, dd displays
the number of
complete and partial input and output blocks and truncated
to the standard error output.
The following operands are available:
if=file Read input from file instead of the standard input.
of=file Write output to file instead of the standard output. Any regular
output file is truncated unless the notrunc
is specified. If an initial portion of the output
skipped (see the seek operand), the output file is
ibs=n Set the input block size to n bytes instead of the
obs=n Set the output block size to n bytes instead of the
bs=n Set both the input and output block size to n
the ibs and obs operands. If no conversion values
noerror, notrunc, or sync are specified, then each
is copied to the output as a single block without
of short blocks.
cbs=n Set the conversion record size to n bytes. The
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.
seek=n Seek n blocks from the beginning of the output before copying.
On non-tape devices, an lseek(2) operation is used.
existing blocks are read and the data discarded.
If the user
does not have read permission for the tape, it is
the tape ioctl(2) function calls. If the seek
past the end of file, space from the current end of
file to the
specified offset is filled with blocks of NUL
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
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.
Where value is one of the symbols from the following list.
The same as the unblock value except that
are translated from EBCDIC to ASCII before
are converted. (These values imply
unblock if the
operand cbs is also specified.) There are
maps for ASCII. The value ascii
recommended one which is compatible with
System V. The
value oldascii specifies the one used in
and pre-4.3BSD-reno systems.
block Treats the input as a sequence of newline
terminated variable length records
input and output block boundaries. Any
character is discarded. Each input
record is converted
to a fixed length output record
where the length
is specified by the cbs operand. Input
than the conversion record size are padded
Input records longer than the conversion
are truncated. The number of truncated
if any, is reported to the standard error
output at the
completion of the copy.
ebcdic, ibm, oldebcdic, oldibm
The same as the block value except that
translated from ASCII to EBCDIC after the
converted. (These values imply block if
cbs is also specified.) There are four
for EBCDIC. The value ebcdic specifies
one which is compatible with AT&T System V
value ibm is a slightly different mapping,
compatible with the AT&T System V UNIX ibm
values oldebcdic and oldibm are maps used
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
to the standard error output in the same
format as the
standard completion message. If the sync
also specified, any missing input data
will be replaced
with NUL bytes (or with spaces if a block
value was specified) and processed
as a normal
input buffer. If the sync conversion is
the input block is omitted from the output. On input
files which are not tapes or pipes, the
will be positioned past the block in which
occurred using lseek(2).
notrunc Do not truncate the output file. This
any blocks in the output file not explicitly written by
dd. The notrunc value is not supported
osync Pad the final output block to the full
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
blocks for use on devices that require
blocks to be written. This option is incompatible with
use of the bs=n block size specification.
swab Swap every pair of input bytes. If an input buffer has
an odd number of bytes, the last byte will
sync Pad every input block to the input buffer
are used for pad bytes if a block oriented
value is specified, otherwise NUL bytes
ucase Transform lowercase characters into uppercase characters.
unblock Treats the input as a sequence of fixed
independent of input and output block
length of the input records is specified
by the cbs
operand. Any trailing space characters
and a newline character is appended.
Where sizes are specified, a decimal number of bytes is expected. If the
number ends with a `b', `k', `m', or `w', the number is multiplied by
512, 1024 (1K), 1048576 (1M), or the number of bytes in an
Two or more numbers may be separated by an `x'
to indicate a
When finished, dd displays the number of complete and partial input and
output blocks, truncated input records, and odd-length byteswapping
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
to tape devices are considered fatal errors. Otherwise, the
rest of the
block will be written. Partial output blocks to character
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
Normally, data resulting from input or conversion or both
into output blocks of the specified size. After the end of
reached, any remaining output is written as a block. This
means that the
final output block may be shorter than the output block
If dd receives a SIGINFO (see the ``status'' argument for
the current input and output block counts will be written to the
standard error output in the same format as the standard
If dd receives a SIGINT signal, the current input and
counts will be written to the standard error output in the
same format as
the standard completion message and dd will exit.
The dd utility exits 0 on success or >0 if an error occurred.
# dd if=floppy34.fs of=/dev/rfd0c bs=32k
Write an OpenBSD floppy image to a floppy disk.
cp(1), mt(1), tr(1)
The dd utility is expected to be a superset of the IEEE Std
(``POSIX.2'') standard. The files operand and the ascii,
oldascii, oldebcdic, and oldibm values are extensions to the
OpenBSD 3.6 January 13, 1994
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