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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 iflag Ns = Ns Ar value Ns Op , Ns Ar value ...
108 is one of the symbols from the following list.
109 .Bl -tag -width "fullblock"
111 Reading from the input file may not obtain a full block.
112 When a read returns short, continue reading to fill the block.
115 limits the number of times
117 is called on the input rather than the number of blocks copied in full.
118 May not be combined with
121 Set the O_DIRECT flag on the input file to make reads bypass any local caching.
123 .It Cm iseek Ns = Ns Ar n
124 Seek on the input file
127 This is synonymous with
128 .Cm skip Ns = Ns Ar n .
129 .It Cm obs Ns = Ns Ar n
130 Set the output block size to
132 bytes instead of the default 512.
133 .It Cm of Ns = Ns Ar file
136 instead of the standard output.
137 Any regular output file is truncated unless the
139 conversion value is specified.
140 If an initial portion of the output file is seeked past (see the
143 the output file is truncated at that point.
144 .It Cm oflag Ns = Ns Ar value Ns Op , Ns Ar value ...
147 is one of the symbols from the following list.
148 .Bl -tag -width "direct"
150 Set the O_FSYNC flag on the output file to make writes synchronous.
152 Set the O_SYNC flag on the output file to make writes synchronous.
153 This is synonymous with the
157 Set the O_DIRECT flag on the output file to make writes bypass any local caching.
159 .It Cm oseek Ns = Ns Ar n
160 Seek on the output file
163 This is synonymous with
164 .Cm seek Ns = Ns Ar n .
165 .It Cm seek Ns = Ns Ar n
168 blocks from the beginning of the output before copying.
169 On non-tape devices, an
172 Otherwise, existing blocks are read and the data discarded.
173 If the user does not have read permission for the tape, it is positioned
177 If the seek operation is past the end of file, space from the current
178 end of file to the specified offset is filled with blocks of
181 .It Cm skip Ns = Ns Ar n
184 blocks from the beginning of the input before copying.
185 On input which supports seeks, an
188 Otherwise, input data is read and discarded.
189 For pipes, the correct number of bytes is read.
190 For all other devices, the correct number of blocks is read without
191 distinguishing between a partial or complete block being read.
192 .It Cm speed Ns = Ns Ar n
193 Limit the copying speed to
196 .It Cm status Ns = Ns Ar value
199 is one of the symbols from the following list.
200 .Bl -tag -width "progress"
202 Do not print the transfer statistics as the last line of status output.
204 Do not print the status output.
205 Error messages are shown; informational messages are not.
207 Print basic transfer statistics once per second.
209 .It Cm conv Ns = Ns Ar value Ns Op , Ns Ar value ...
212 is one of the symbols from the following list.
213 .Bl -tag -width "unblock"
214 .It Cm ascii , oldascii
217 value except that characters are translated from
222 records are converted.
228 There are two conversion maps for
232 specifies the recommended one which is compatible with
236 specifies the one used in historic
239 .No pre- Ns Bx 4.3 reno
242 Treats the input as a sequence of newline or end-of-file terminated variable
243 length records independent of input and output block boundaries.
244 Any trailing newline character is discarded.
245 Each input record is converted to a fixed length output record where the
246 length is specified by the
249 Input records shorter than the conversion record size are padded with spaces.
250 Input records longer than the conversion record size are truncated.
251 The number of truncated input records, if any, are reported to the standard
252 error output at the completion of the copy.
253 .It Cm ebcdic , ibm , oldebcdic , oldibm
256 value except that characters are translated from
261 records are converted.
267 There are four conversion maps for
271 specifies the recommended one which is compatible with
275 is a slightly different mapping, which is compatible with the
283 are maps used in historic
286 .No pre- Ns Bx 4.3 reno
291 on the output file before closing it.
295 on the output file before closing it.
297 Transform uppercase characters into lowercase characters.
298 .It Cm pareven , parnone , parodd , parset
299 Output data with the specified parity.
300 The parity bit on input is stripped unless
304 conversions is also specified.
306 Do not stop processing on an input error.
307 When an input error occurs, a diagnostic message followed by the current
308 input and output block counts will be written to the standard error output
309 in the same format as the standard completion message.
312 conversion is also specified, any missing input data will be replaced
315 bytes (or with spaces if a block oriented conversion value was
316 specified) and processed as a normal input buffer.
319 option is specified, the fill character provided on the command line
321 the automatic selection of the fill character.
324 conversion is not specified, the input block is omitted from the output.
325 On input files which are not tapes or pipes, the file offset
326 will be positioned past the block in which the error occurred using
329 Do not truncate the output file.
330 This will preserve any blocks in the output file not explicitly written
335 value is not supported for tapes.
337 Pad the final output block to the full output block size.
338 If the input file is not a multiple of the output block size
339 after conversion, this conversion forces the final output block
340 to be the same size as preceding blocks for use on devices that require
341 regularly sized blocks to be written.
342 This option is incompatible with use of the
344 block size specification.
346 If one or more output blocks would consist solely of
348 bytes, try to seek the output file by the required space instead of
351 resulting in a sparse file.
353 Swap every pair of input bytes.
354 If an input buffer has an odd number of bytes, the last byte will be
355 ignored during swapping.
357 Pad every input block to the input buffer size.
358 Spaces are used for pad bytes if a block oriented conversion value is
363 Transform lowercase characters into uppercase characters.
365 Treats the input as a sequence of fixed length records independent of input
366 and output block boundaries.
367 The length of the input records is specified by the
370 Any trailing space characters are discarded and a newline character is
375 Where sizes or speed are specified, a decimal, octal, or hexadecimal number of
377 If the number ends with a
387 number is multiplied by 512, 1024 (1K), 1048576 (1M), 1073741824 (1G),
388 1099511627776 (1T), 1125899906842624 (1P)
389 or the number of bytes in an integer, respectively.
390 Two or more numbers may be separated by an
392 to indicate a product.
396 displays the number of complete and partial input and output blocks,
397 truncated input records and odd-length byte-swapping blocks to the
398 standard error output.
399 A partial input block is one where less than the input block size
401 A partial output block is one where less than the output block size
403 Partial output blocks to tape devices are considered fatal errors.
404 Otherwise, the rest of the block will be written.
405 Partial output blocks to character devices will produce a warning message.
406 A truncated input block is one where a variable length record oriented
407 conversion value was specified and the input line was too long to
408 fit in the conversion record or was not newline terminated.
410 Normally, data resulting from input or conversion or both are aggregated
411 into output blocks of the specified size.
412 After the end of input is reached, any remaining output is written as
414 This means that the final output block may be shorter than the output
425 signal, the current input and output block counts will
426 be written to the standard error output
427 in the same format as the standard completion message.
432 signal, the current input and output block counts will
433 be written to the standard error output
434 in the same format as the standard completion message and
440 Check that a disk drive contains no bad blocks:
442 .Dl "dd if=/dev/ada0 of=/dev/null bs=1m"
444 Do a refresh of a disk drive, in order to prevent presently
445 recoverable read errors from progressing into unrecoverable read errors:
447 .Dl "dd if=/dev/ada0 of=/dev/ada0 bs=1m"
449 Remove parity bit from a file:
451 .Dl "dd if=file conv=parnone of=file.txt"
453 Check for (even) parity errors on a file:
455 .Dl "dd if=file conv=pareven | cmp -x - file"
457 To create an image of a Mode-1 CD-ROM, which is a commonly used format
458 for data CD-ROM disks, use a block size of 2048 bytes:
460 .Dl "dd if=/dev/cd0 of=filename.iso bs=2048"
462 Write a filesystem image to a memory stick, padding the end with zeros,
463 if necessary, to a 1MiB boundary:
465 .Dl "dd if=memstick.img of=/dev/da0 bs=1m conv=noerror,sync"
476 utility is expected to be a superset of the
491 values are extensions to the
500 Protection mechanisms in the
502 subsystem might prevent the super-user from writing blocks to a disk.
503 Instructions for temporarily disabling these protection mechanisms can be