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32 .\" @(#)dd.1 8.2 (Berkeley) 1/13/94
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 ".Cm of Ns = Ns Ar 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 status Ns = Ns Ar value
162 is one of the symbols from the following list.
163 .Bl -tag -width ".Cm noxfer"
165 Do not print the transfer statistics as the last line of status output.
167 Do not print the status output.
168 Error messages are shown; informational messages are not.
170 .It Cm conv Ns = Ns Ar value Ns Op , Ns Ar value ...
173 is one of the symbols from the following list.
174 .Bl -tag -width ".Cm unblock"
175 .It Cm ascii , oldascii
178 value except that characters are translated from
183 records are converted.
189 There are two conversion maps for
193 specifies the recommended one which is compatible with
197 specifies the one used in historic
200 .No pre- Ns Bx 4.3 reno
203 Treats the input as a sequence of newline or end-of-file terminated variable
204 length records independent of input and output block boundaries.
205 Any trailing newline character is discarded.
206 Each input record is converted to a fixed length output record where the
207 length is specified by the
210 Input records shorter than the conversion record size are padded with spaces.
211 Input records longer than the conversion record size are truncated.
212 The number of truncated input records, if any, are reported to the standard
213 error output at the completion of the copy.
214 .It Cm ebcdic , ibm , oldebcdic , oldibm
217 value except that characters are translated from
222 records are converted.
228 There are four conversion maps for
232 specifies the recommended one which is compatible with
236 is a slightly different mapping, which is compatible with the
244 are maps used in historic
247 .No pre- Ns Bx 4.3 reno
250 Transform uppercase characters into lowercase characters.
251 .It Cm pareven , parnone , parodd , parset
252 Output data with the specified parity.
253 The parity bit on input is stripped unless
257 conversions is also specified.
259 Do not stop processing on an input error.
260 When an input error occurs, a diagnostic message followed by the current
261 input and output block counts will be written to the standard error output
262 in the same format as the standard completion message.
265 conversion is also specified, any missing input data will be replaced
268 bytes (or with spaces if a block oriented conversion value was
269 specified) and processed as a normal input buffer.
272 option is specified, the fill character provided on the command line
274 the automatic selection of the fill character.
277 conversion is not specified, the input block is omitted from the output.
278 On input files which are not tapes or pipes, the file offset
279 will be positioned past the block in which the error occurred using
282 Do not truncate the output file.
283 This will preserve any blocks in the output file not explicitly written
288 value is not supported for tapes.
290 Pad the final output block to the full output block size.
291 If the input file is not a multiple of the output block size
292 after conversion, this conversion forces the final output block
293 to be the same size as preceding blocks for use on devices that require
294 regularly sized blocks to be written.
295 This option is incompatible with use of the
297 block size specification.
299 If one or more output blocks would consist solely of
301 bytes, try to seek the output file by the required space instead of
304 resulting in a sparse file.
306 Swap every pair of input bytes.
307 If an input buffer has an odd number of bytes, the last byte will be
308 ignored during swapping.
310 Pad every input block to the input buffer size.
311 Spaces are used for pad bytes if a block oriented conversion value is
316 Transform lowercase characters into uppercase characters.
318 Treats the input as a sequence of fixed length records independent of input
319 and output block boundaries.
320 The length of the input records is specified by the
323 Any trailing space characters are discarded and a newline character is
328 Where sizes are specified, a decimal, octal, or hexadecimal number of
330 If the number ends with a
338 number is multiplied by 512, 1024 (1K), 1048576 (1M), 1073741824 (1G)
339 or the number of bytes in an integer, respectively.
340 Two or more numbers may be separated by an
342 to indicate a product.
346 displays the number of complete and partial input and output blocks,
347 truncated input records and odd-length byte-swapping blocks to the
348 standard error output.
349 A partial input block is one where less than the input block size
351 A partial output block is one where less than the output block size
353 Partial output blocks to tape devices are considered fatal errors.
354 Otherwise, the rest of the block will be written.
355 Partial output blocks to character devices will produce a warning message.
356 A truncated input block is one where a variable length record oriented
357 conversion value was specified and the input line was too long to
358 fit in the conversion record or was not newline terminated.
360 Normally, data resulting from input or conversion or both are aggregated
361 into output blocks of the specified size.
362 After the end of input is reached, any remaining output is written as
364 This means that the final output block may be shorter than the output
375 signal, the current input and output block counts will
376 be written to the standard error output
377 in the same format as the standard completion message.
382 signal, the current input and output block counts will
383 be written to the standard error output
384 in the same format as the standard completion message and
390 Check that a disk drive contains no bad blocks:
392 .Dl "dd if=/dev/ada0 of=/dev/null bs=1m"
394 Do a refresh of a disk drive, in order to prevent presently
395 recoverable read errors from progressing into unrecoverable read errors:
397 .Dl "dd if=/dev/ada0 of=/dev/ada0 bs=1m"
399 Remove parity bit from a file:
401 .Dl "dd if=file conv=parnone of=file.txt"
403 Check for (even) parity errors on a file:
405 .Dl "dd if=file conv=pareven | cmp -x - file"
407 To create an image of a Mode-1 CD-ROM, which is a commonly used format
408 for data CD-ROM disks, use a block size of 2048 bytes:
410 .Dl "dd if=/dev/acd0 of=filename.iso bs=2048"
412 Write a filesystem image to a memory stick, padding the end with zeros,
413 if necessary, to a 1MiB boundary:
415 .Dl "dd if=memstick.img of=/dev/da0 bs=1m conv=noerror,sync"
425 utility is expected to be a superset of the
440 values are extensions to the
449 Protection mechanisms in the
451 subsystem might prevent the super-user from writing blocks to a disk.
452 Instructions for temporarily disabling these protection mechanisms can be