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5 .\" This code is derived from software contributed to Berkeley by
6 .\" Keith Muller of the University of California, San Diego.
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32 .\" @(#)dd.1 8.2 (Berkeley) 1/13/94
33 .\" $FreeBSD: head/bin/dd/dd.1 337505 2018-08-08 21:37:02Z kevans $
40 .Nd convert and copy a file
47 utility copies the standard input to the standard output.
48 Input data is read and written in 512-byte blocks.
49 If input reads are short, input from multiple reads are aggregated
50 to form the output block.
53 displays the number of complete and partial input and output blocks
54 and truncated input records to the standard error output.
56 The following operands are available:
57 .Bl -tag -width "of=file"
58 .It Cm bs Ns = Ns Ar n
59 Set both input and output block size to
61 bytes, superseding the
66 If no conversion values other than
71 are specified, then each input block is copied to the output as a
72 single block without any aggregation of short blocks.
73 .It Cm cbs Ns = Ns Ar n
74 Set the conversion record size to
77 The conversion record size is required by the record oriented conversion
79 .It Cm count Ns = Ns Ar n
83 .It Cm files Ns = Ns Ar n
86 input files before terminating.
87 This operand is only applicable when the input device is a tape.
88 .It Cm fillchar Ns = Ns Ar c
89 When padding a block in conversion mode or due to use of
93 modes, fill with the specified
95 character, rather than using a space or
97 .It Cm ibs Ns = Ns Ar n
98 Set the input block size to
100 bytes instead of the default 512.
101 .It Cm if Ns = Ns Ar file
104 instead of the standard input.
105 .It Cm iseek Ns = Ns Ar n
106 Seek on the input file
109 This is synonymous with
110 .Cm skip Ns = Ns Ar n .
111 .It Cm obs Ns = Ns Ar n
112 Set the output block size to
114 bytes instead of the default 512.
115 .It Cm of Ns = Ns Ar file
118 instead of the standard output.
119 Any regular output file is truncated unless the
121 conversion value is specified.
122 If an initial portion of the output file is seeked past (see the
125 the output file is truncated at that point.
126 .It Cm oseek Ns = Ns Ar n
127 Seek on the output file
130 This is synonymous with
131 .Cm seek Ns = Ns Ar n .
132 .It Cm seek Ns = Ns Ar n
135 blocks from the beginning of the output before copying.
136 On non-tape devices, an
139 Otherwise, existing blocks are read and the data discarded.
140 If the user does not have read permission for the tape, it is positioned
144 If the seek operation is past the end of file, space from the current
145 end of file to the specified offset is filled with blocks of
148 .It Cm skip Ns = Ns Ar n
151 blocks from the beginning of the input before copying.
152 On input which supports seeks, an
155 Otherwise, input data is read and discarded.
156 For pipes, the correct number of bytes is read.
157 For all other devices, the correct number of blocks is read without
158 distinguishing between a partial or complete block being read.
159 .It Cm speed Ns = Ns Ar n
160 Limit the copying speed to
163 .It Cm status Ns = Ns Ar value
166 is one of the symbols from the following list.
167 .Bl -tag -width ".Cm progress"
169 Do not print the status output.
170 Error messages are shown; informational messages are not.
172 Do not print the transfer statistics as the last line of status output.
174 Print basic transfer statistics once per second.
176 .It Cm conv Ns = Ns Ar value Ns Op , Ns Ar value ...
179 is one of the symbols from the following list.
180 .Bl -tag -width "unblock"
181 .It Cm ascii , oldascii
184 value except that characters are translated from
189 records are converted.
195 There are two conversion maps for
199 specifies the recommended one which is compatible with
203 specifies the one used in historic
206 .No pre- Ns Bx 4.3 reno
209 Treats the input as a sequence of newline or end-of-file terminated variable
210 length records independent of input and output block boundaries.
211 Any trailing newline character is discarded.
212 Each input record is converted to a fixed length output record where the
213 length is specified by the
216 Input records shorter than the conversion record size are padded with spaces.
217 Input records longer than the conversion record size are truncated.
218 The number of truncated input records, if any, are reported to the standard
219 error output at the completion of the copy.
220 .It Cm ebcdic , ibm , oldebcdic , oldibm
223 value except that characters are translated from
228 records are converted.
234 There are four conversion maps for
238 specifies the recommended one which is compatible with
242 is a slightly different mapping, which is compatible with the
250 are maps used in historic
253 .No pre- Ns Bx 4.3 reno
256 Transform uppercase characters into lowercase characters.
257 .It Cm pareven , parnone , parodd , parset
258 Output data with the specified parity.
259 The parity bit on input is stripped unless
263 conversions is also specified.
265 Do not stop processing on an input error.
266 When an input error occurs, a diagnostic message followed by the current
267 input and output block counts will be written to the standard error output
268 in the same format as the standard completion message.
271 conversion is also specified, any missing input data will be replaced
274 bytes (or with spaces if a block oriented conversion value was
275 specified) and processed as a normal input buffer.
278 option is specified, the fill character provided on the command line
280 the automatic selection of the fill character.
283 conversion is not specified, the input block is omitted from the output.
284 On input files which are not tapes or pipes, the file offset
285 will be positioned past the block in which the error occurred using
288 Do not truncate the output file.
289 This will preserve any blocks in the output file not explicitly written
294 value is not supported for tapes.
296 Pad the final output block to the full output block size.
297 If the input file is not a multiple of the output block size
298 after conversion, this conversion forces the final output block
299 to be the same size as preceding blocks for use on devices that require
300 regularly sized blocks to be written.
301 This option is incompatible with use of the
303 block size specification.
305 If one or more output blocks would consist solely of
307 bytes, try to seek the output file by the required space instead of
310 resulting in a sparse file.
312 Swap every pair of input bytes.
313 If an input buffer has an odd number of bytes, the last byte will be
314 ignored during swapping.
316 Pad every input block to the input buffer size.
317 Spaces are used for pad bytes if a block oriented conversion value is
322 Transform lowercase characters into uppercase characters.
324 Treats the input as a sequence of fixed length records independent of input
325 and output block boundaries.
326 The length of the input records is specified by the
329 Any trailing space characters are discarded and a newline character is
334 Where sizes or speed are specified, a decimal, octal, or hexadecimal number of
336 If the number ends with a
346 number is multiplied by 512, 1024 (1K), 1048576 (1M), 1073741824 (1G),
347 1099511627776 (1T), 1125899906842624 (1P)
348 or the number of bytes in an integer, respectively.
349 Two or more numbers may be separated by an
351 to indicate a product.
355 displays the number of complete and partial input and output blocks,
356 truncated input records and odd-length byte-swapping blocks to the
357 standard error output.
358 A partial input block is one where less than the input block size
360 A partial output block is one where less than the output block size
362 Partial output blocks to tape devices are considered fatal errors.
363 Otherwise, the rest of the block will be written.
364 Partial output blocks to character devices will produce a warning message.
365 A truncated input block is one where a variable length record oriented
366 conversion value was specified and the input line was too long to
367 fit in the conversion record or was not newline terminated.
369 Normally, data resulting from input or conversion or both are aggregated
370 into output blocks of the specified size.
371 After the end of input is reached, any remaining output is written as
373 This means that the final output block may be shorter than the output
384 signal, the current input and output block counts will
385 be written to the standard error output
386 in the same format as the standard completion message.
391 signal, the current input and output block counts will
392 be written to the standard error output
393 in the same format as the standard completion message and
399 Check that a disk drive contains no bad blocks:
401 .Dl "dd if=/dev/da0 of=/dev/null bs=1m"
403 Do a refresh of a disk drive, in order to prevent presently
404 recoverable read errors from progressing into unrecoverable read errors:
406 .Dl "dd if=/dev/da0 of=/dev/da0 bs=1m"
408 Remove parity bit from a file:
410 .Dl "dd if=file conv=parnone of=file.txt"
412 Check for (even) parity errors on a file:
414 .Dl "dd if=file conv=pareven | cmp -x - file"
416 To create an image of a Mode-1 CD-ROM, which is a commonly used format
417 for data CD-ROM disks, use a block size of 2048 bytes:
419 .Dl "dd if=/dev/cd0 of=filename.iso bs=2048"
421 Write a filesystem image to a memory stick, padding the end with zeros,
422 if necessary, to a 1MiB boundary:
424 .Dl "dd if=memstick.img of=/dev/da8 bs=1m conv=noerror,sync"
432 utility is expected to be a superset of the
447 values are extensions to the