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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 conv Ns = Ns Ar value Ns Op , Ns Ar value ...
162 is one of the symbols from the following list.
163 .Bl -tag -width ".Cm unblock"
164 .It Cm ascii , oldascii
167 value except that characters are translated from
172 records are converted.
178 There are two conversion maps for
182 specifies the recommended one which is compatible with
186 specifies the one used in historic
189 .No pre- Ns Bx 4.3 reno
192 Treats the input as a sequence of newline or end-of-file terminated variable
193 length records independent of input and output block boundaries.
194 Any trailing newline character is discarded.
195 Each input record is converted to a fixed length output record where the
196 length is specified by the
199 Input records shorter than the conversion record size are padded with spaces.
200 Input records longer than the conversion record size are truncated.
201 The number of truncated input records, if any, are reported to the standard
202 error output at the completion of the copy.
203 .It Cm ebcdic , ibm , oldebcdic , oldibm
206 value except that characters are translated from
211 records are converted.
217 There are four conversion maps for
221 specifies the recommended one which is compatible with
225 is a slightly different mapping, which is compatible with the
233 are maps used in historic
236 .No pre- Ns Bx 4.3 reno
239 Transform uppercase characters into lowercase characters.
240 .It Cm pareven , parnone , parodd , parset
241 Output data with the specified parity.
242 The parity bit on input is stripped unless
246 conversions is also specified.
248 Do not stop processing on an input error.
249 When an input error occurs, a diagnostic message followed by the current
250 input and output block counts will be written to the standard error output
251 in the same format as the standard completion message.
254 conversion is also specified, any missing input data will be replaced
257 bytes (or with spaces if a block oriented conversion value was
258 specified) and processed as a normal input buffer.
261 option is specified, the fill character provided on the command line
263 the automatic selection of the fill character.
266 conversion is not specified, the input block is omitted from the output.
267 On input files which are not tapes or pipes, the file offset
268 will be positioned past the block in which the error occurred using
271 Do not truncate the output file.
272 This will preserve any blocks in the output file not explicitly written
277 value is not supported for tapes.
279 Pad the final output block to the full output block size.
280 If the input file is not a multiple of the output block size
281 after conversion, this conversion forces the final output block
282 to be the same size as preceding blocks for use on devices that require
283 regularly sized blocks to be written.
284 This option is incompatible with use of the
286 block size specification.
288 If one or more output blocks would consist solely of
290 bytes, try to seek the output file by the required space instead of
293 resulting in a sparse file.
295 Swap every pair of input bytes.
296 If an input buffer has an odd number of bytes, the last byte will be
297 ignored during swapping.
299 Pad every input block to the input buffer size.
300 Spaces are used for pad bytes if a block oriented conversion value is
305 Transform lowercase characters into uppercase characters.
307 Treats the input as a sequence of fixed length records independent of input
308 and output block boundaries.
309 The length of the input records is specified by the
312 Any trailing space characters are discarded and a newline character is
317 Where sizes are specified, a decimal, octal, or hexadecimal number of
319 If the number ends with a
327 number is multiplied by 512, 1024 (1K), 1048576 (1M), 1073741824 (1G)
328 or the number of bytes in an integer, respectively.
329 Two or more numbers may be separated by an
331 to indicate a product.
335 displays the number of complete and partial input and output blocks,
336 truncated input records and odd-length byte-swapping blocks to the
337 standard error output.
338 A partial input block is one where less than the input block size
340 A partial output block is one where less than the output block size
342 Partial output blocks to tape devices are considered fatal errors.
343 Otherwise, the rest of the block will be written.
344 Partial output blocks to character devices will produce a warning message.
345 A truncated input block is one where a variable length record oriented
346 conversion value was specified and the input line was too long to
347 fit in the conversion record or was not newline terminated.
349 Normally, data resulting from input or conversion or both are aggregated
350 into output blocks of the specified size.
351 After the end of input is reached, any remaining output is written as
353 This means that the final output block may be shorter than the output
364 signal, the current input and output block counts will
365 be written to the standard error output
366 in the same format as the standard completion message.
371 signal, the current input and output block counts will
372 be written to the standard error output
373 in the same format as the standard completion message and
379 Check that a disk drive contains no bad blocks:
381 .Dl "dd if=/dev/ad0 of=/dev/null bs=1m"
383 Do a refresh of a disk drive, in order to prevent presently
384 recoverable read errors from progressing into unrecoverable read errors:
386 .Dl "dd if=/dev/ad0 of=/dev/ad0 bs=1m"
388 Remove parity bit from a file:
390 .Dl "dd if=file conv=parnone of=file.txt"
392 Check for (even) parity errors on a file:
394 .Dl "dd if=file conv=pareven | cmp -x - file"
403 utility is expected to be a superset of the
416 values are extensions to the
420 Protection mechanisms in the
422 subsystem might prevent the super-user from writing blocks to a disk.
423 Instructions for temporarily disabling these protectsion mechanisms can be