DD(1) OpenBSD Reference Manual DD(1)NAMEdd - convert and copy a file
SYNOPSISdd [operand ...]
DESCRIPTION
The dd utility copies the standard input to the standard output, applying
any specified conversions. 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:
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 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.
ibs=n Set the input block size to n bytes instead of the default 512.
obs=n Set the output block size to n bytes instead of the default 512.
bs=n Set both the input and output block size to n bytes, 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.
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.
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 System V.
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, 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 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.
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. 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 integer,
respectively. Two or more numbers may be separated by an `x' to indicate
a product.
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 (see the ``status'' argument for stty(1))
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. 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 occurs.
EXAMPLES
Write an OpenBSD floppy image to a floppy disk:
# dd if=floppy34.fs of=/dev/rfd0c bs=32k
Create an ISO-9660 image of a CD-ROM:
# dd if=/dev/rcd0c of=disk.iso bs=32k
SEE ALSOcp(1), mt(1), tr(1)STANDARDS
The dd utility is compliant with the IEEE Std 1003.1-2008 (``POSIX'')
specification.
The conversions ascii, ebcdic, and ibm are compliant with the X/Open
Portability Guide Issue 4 (``XPG4'') specification.
The files operand, the conversions oldascii, oldebcdic, oldibm, and
osync, and the size multipliers `m' and `w' are all extensions to those
specifications.
OpenBSD 4.9 September 3, 2010 OpenBSD 4.9
