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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 "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 "noxfer"
169 Do not print the transfer statistics as the last line of status output.
171 Do not print the status output.
172 Error messages are shown; informational messages are not.
174 .It Cm conv Ns = Ns Ar value Ns Op , Ns Ar value ...
177 is one of the symbols from the following list.
178 .Bl -tag -width "unblock"
179 .It Cm ascii , oldascii
182 value except that characters are translated from
187 records are converted.
193 There are two conversion maps for
197 specifies the recommended one which is compatible with
201 specifies the one used in historic
204 .No pre- Ns Bx 4.3 reno
207 Treats the input as a sequence of newline or end-of-file terminated variable
208 length records independent of input and output block boundaries.
209 Any trailing newline character is discarded.
210 Each input record is converted to a fixed length output record where the
211 length is specified by the
214 Input records shorter than the conversion record size are padded with spaces.
215 Input records longer than the conversion record size are truncated.
216 The number of truncated input records, if any, are reported to the standard
217 error output at the completion of the copy.
218 .It Cm ebcdic , ibm , oldebcdic , oldibm
221 value except that characters are translated from
226 records are converted.
232 There are four conversion maps for
236 specifies the recommended one which is compatible with
240 is a slightly different mapping, which is compatible with the
248 are maps used in historic
251 .No pre- Ns Bx 4.3 reno
254 Transform uppercase characters into lowercase characters.
255 .It Cm pareven , parnone , parodd , parset
256 Output data with the specified parity.
257 The parity bit on input is stripped unless
261 conversions is also specified.
263 Do not stop processing on an input error.
264 When an input error occurs, a diagnostic message followed by the current
265 input and output block counts will be written to the standard error output
266 in the same format as the standard completion message.
269 conversion is also specified, any missing input data will be replaced
272 bytes (or with spaces if a block oriented conversion value was
273 specified) and processed as a normal input buffer.
276 option is specified, the fill character provided on the command line
278 the automatic selection of the fill character.
281 conversion is not specified, the input block is omitted from the output.
282 On input files which are not tapes or pipes, the file offset
283 will be positioned past the block in which the error occurred using
286 Do not truncate the output file.
287 This will preserve any blocks in the output file not explicitly written
292 value is not supported for tapes.
294 Pad the final output block to the full output block size.
295 If the input file is not a multiple of the output block size
296 after conversion, this conversion forces the final output block
297 to be the same size as preceding blocks for use on devices that require
298 regularly sized blocks to be written.
299 This option is incompatible with use of the
301 block size specification.
303 If one or more output blocks would consist solely of
305 bytes, try to seek the output file by the required space instead of
308 resulting in a sparse file.
310 Swap every pair of input bytes.
311 If an input buffer has an odd number of bytes, the last byte will be
312 ignored during swapping.
314 Pad every input block to the input buffer size.
315 Spaces are used for pad bytes if a block oriented conversion value is
320 Transform lowercase characters into uppercase characters.
322 Treats the input as a sequence of fixed length records independent of input
323 and output block boundaries.
324 The length of the input records is specified by the
327 Any trailing space characters are discarded and a newline character is
332 Where sizes or speed are specified, a decimal, octal, or hexadecimal number of
334 If the number ends with a
344 number is multiplied by 512, 1024 (1K), 1048576 (1M), 1073741824 (1G),
345 1099511627776 (1T), 1125899906842624 (1P)
346 or the number of bytes in an integer, respectively.
347 Two or more numbers may be separated by an
349 to indicate a product.
353 displays the number of complete and partial input and output blocks,
354 truncated input records and odd-length byte-swapping blocks to the
355 standard error output.
356 A partial input block is one where less than the input block size
358 A partial output block is one where less than the output block size
360 Partial output blocks to tape devices are considered fatal errors.
361 Otherwise, the rest of the block will be written.
362 Partial output blocks to character devices will produce a warning message.
363 A truncated input block is one where a variable length record oriented
364 conversion value was specified and the input line was too long to
365 fit in the conversion record or was not newline terminated.
367 Normally, data resulting from input or conversion or both are aggregated
368 into output blocks of the specified size.
369 After the end of input is reached, any remaining output is written as
371 This means that the final output block may be shorter than the output
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.
389 signal, the current input and output block counts will
390 be written to the standard error output
391 in the same format as the standard completion message and
397 Check that a disk drive contains no bad blocks:
399 .Dl "dd if=/dev/ada0 of=/dev/null bs=1m"
401 Do a refresh of a disk drive, in order to prevent presently
402 recoverable read errors from progressing into unrecoverable read errors:
404 .Dl "dd if=/dev/ada0 of=/dev/ada0 bs=1m"
406 Remove parity bit from a file:
408 .Dl "dd if=file conv=parnone of=file.txt"
410 Check for (even) parity errors on a file:
412 .Dl "dd if=file conv=pareven | cmp -x - file"
414 To create an image of a Mode-1 CD-ROM, which is a commonly used format
415 for data CD-ROM disks, use a block size of 2048 bytes:
417 .Dl "dd if=/dev/cd0 of=filename.iso bs=2048"
419 Write a filesystem image to a memory stick, padding the end with zeros,
420 if necessary, to a 1MiB boundary:
422 .Dl "dd if=memstick.img of=/dev/da0 bs=1m conv=noerror,sync"
432 utility is expected to be a superset of the
447 values are extensions to the
456 Protection mechanisms in the
458 subsystem might prevent the super-user from writing blocks to a disk.
459 Instructions for temporarily disabling these protection mechanisms can be