dd(1M)
dd --
convert and copy a file
Synopsis
/u95/bin/dd [option=value] . . .
Description
dd copies the specified input file
to the specified output with possible conversions.
The standard input and output are used by default.
The input and output block sizes may be
specified to take advantage of raw physical I/O.
dd processes supplementary code set characters
according to the locale specified in the LC_CTYPE
environment variable
(see LANG on
environ(5)),
except as noted below.
option-
values
if=file-
input file name; standard input is default.
of=file-
output file name; standard output is default.
If the seek=expr conversion is not also specified,
the output file will be truncated before the copy begins, unless
conv=notrunc is specified.
If the seek=expr conversion is specified, but
conv=notrunc is not, the effect of the copy will be to
preserve the blocks in the output file over which dd
seeks, but no other portion of the output file will be preserved.
(If the size of the seek plus the size of the input file is less than the
previous size of the output file, the output file will be shortened by
the copy.)
ibs=n-
input block size n bytes (default 512).
obs=n-
output block size
n
bytes (default 512).
bs=n-
set both input and output block size,
superseding ibs and obs;
also, if no conversion is specified,
preserve the input block size instead of packing short blocks
into the output buffer
(this is particularly efficient since no in-core copy need be done).
cbs=n-
conversion buffer size (logical record length).
files=n-
copy and concatenate n
input files before terminating (makes sense only
where input is a magnetic tape or similar device).
skip=n-
skip n
input blocks before starting copy (appropriate for magnetic
tape, where iseek is undefined).
iseek=n-
seek n
blocks from beginning of input file before copying (appropriate
for disk files, where skip can be slow).
oseek=n-
seek n
blocks from beginning of output file before copying.
seek=n-
identical to oseek,
retained for backward compatibility.
count=n-
copy only n input blocks.
conv=value,...-
Perform character conversions as specified by one or more
comma-separated value arguments, as follows:
ascii-
convert EBCDIC to ASCII.
Conversion results cannot be assured when
supplementary code set characters are also subject to conversion.
Cannot be specified with ebcdic or ibm.
ebcdic-
convert ASCII to EBCDIC.
Conversion results cannot be assured when
supplementary code set characters are also subject to conversion.
Cannot be specified with ascii or ibm.
ibm-
slightly different map of ASCII to EBCDIC.
Conversion results cannot be assured when
supplementary code set characters are also subject to conversion.
Cannot be specified with ascii or ebcdic.
block-
convert new-line terminated ASCII records to fixed length.
unblock-
convert fixed length ASCII records to new-line terminated records.
lcase-
map alphabetics to lower case.
Multibyte characters are not converted.
ucase-
map alphabetics to upper case.
Multibyte characters are not converted.
swab-
swap every pair of bytes.
noerror-
do not stop processing on an error (limit of 5 consecutive errors).
notrunc-
Do not truncate the output file.
Preserve blocks in the output file not explicitly written by
this invocation of the dd utility.
(See also the preceding of=file operand.)
sync-
pad every input block to ibs, using spaces if conv=block
os also specified, otherwise NULL characters.
Where sizes are specified,
a number of bytes is expected.
A number may end with
k, b, or w
to specify multiplication by
1024, 512, or 2, respectively;
a pair of numbers may be separated by
x
to indicate multiplication.
cbs
is used only if
ascii,
ebcdic,
ibm,
block,
or
unblock
conversion is specified.
In the first two cases,
cbs
characters are copied into the conversion buffer, any specified
character mapping is done,
trailing blanks are trimmed, and a new-line is added
before sending the line to the output.
In the latter three cases, characters are read into the
conversion buffer and blanks are added to make up an
output record of size
cbs.
If cbs is unspecified or zero, the
ascii, ebcdic, and ibm
options convert the character set without changing the block
structure of the input file; the
unblock and block
options become a simple file copy.
After completion, dd
reports the number of whole and partial input and output blocks.
Files
/usr/lib/locale/locale/LC_MESSAGES/uxcore.abi-
language-specific message file
(see LANG on
environ(5)).
Usage
This command will read an EBCDIC tape blocked ten 80-byte
EBCDIC card images per tape block into the ASCII file x:
dd if=/dev/rmt of=x ibs=800 obs=8k cbs=80 conv=ascii,lcase
Note the use of raw magnetic tape.
dd
is especially suited to I/O on the raw
physical devices because it allows reading
and writing in arbitrary block sizes.
Note also that /rmt* represents the raw magnetic tape device name.
Reading from magnetic tape in any fixed-length block
length besides the block length that the media was written in
originally will cause an I/O error. If you want to read a
tape that was written using a block-length besides the default of
512, you must use the
tapecntl(1)
command to either set the
block-length of the drive to match the block length of the media or
to set the drive into variable block length mode.
Exit codes
The following messages are written to standard error.
n truncated block(s)
-
written only if n is larger than 0; if POSIX2 is set in the
current environment, then n
truncated record(s)
is written instead
f+
p records in(out)
-
numbers of full and partial blocks read(written)
References
cp(1)
Notices
Reading from magnetic tape in any fixed-length block length, besides the
block length that the media was written in originally, will cause an
I/O error.
In order to read a tape that was written using some block length besides the
default of 512, use the
tapecntl(1)
command to either set the
block length of the drive to match
the block length of the media, or to set the drive
into variable block length mode.
Do not use dd to copy files between file systems having
different block sizes.
dd does not always require block sizes that are in
multiples of 512 bytes.
Block size is device dependent.
If input data blocks are not a multiple of 512, however, the read
side will have no error messages, but the write side might have
a ``write error'' message.
dd transfers correctly if the
input data block sizes are a multiple of 512.
Using a blocked device to copy a file will result in extra
nulls being added to the file to pad the final block to the
block boundary.
Using dd with a cartridge tape is not recommended.
Using variable-length block mode when
writing magnetic tapes is discouraged because it may not
work correctly in releases before SVR4.2 MP. Magnetic tape should
always be written in fixed-length block mode, even though you are
free to change the default fixed-block length from 512 bytes to any
other fixed-block mode the tape drive supports.
This command has been updated to handle files greater than 2GB.
© 2005 The SCO Group, Inc. All rights reserved.
SCO OpenServer Release 6.0.0 - 02 June 2005