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13 .TH DD 1M "Jan 04, 2014"
14 .SH NAME
15 dd \- convert and copy a file
16 .SH SYNOPSIS
17 .LP
18 .nf
19 \fB/usr/bin/dd\fR [\fIoperand=value\fR]...
20 .fi
22 .SH DESCRIPTION
23 .sp
24 .LP
25 The \fBdd\fR utility copies the specified input file to the specified output
26 with possible conversions. The standard input and output are used by default.
27 The input and output block sizes may be specified to take advantage of raw
28 physical I/O. Sizes are specified in bytes; a number may end with \fBk\fR,
29 \fBb\fR, or \fBw\fR to specify multiplication by 1024, 512, or 2, respectively.
30 Numbers may also be separated by \fBx\fR to indicate multiplication.
31 .sp
32 .LP
33 The \fBdd\fR utility reads the input one block at a time, using the specified
34 input block size. \fBdd\fR then processes the block of data actually returned,
35 which could be smaller than the requested block size. \fBdd\fR applies any
36 conversions that have been specified and writes the resulting data to the
37 output in blocks of the specified output block size.
38 .sp
39 .LP
40 \fBcbs\fR is used only if \fBascii\fR, \fBasciib\fR, \fBunblock\fR,
41 \fBebcdic\fR, \fBebcdicb\fR, \fBibm\fR, \fBibmb\fR, or \fBblock\fR conversion
42 is specified. In the first two cases, \fBcbs\fR characters are copied into the
43 conversion buffer, any specified character mapping is done, trailing blanks are
44 trimmed, and a \fBNEWLINE\fR is added before sending the line to output. In the
45 last three cases, characters up to \fBNEWLINE\fR are read into the conversion
46 buffer and blanks are added to make up an output record of size \fBcbs\fR.
47 \fBASCII\fR files are presumed to contain \fBNEWLINE\fR characters. If
48 \fBcbs\fR is unspecified or \fB0\fR, the \fBascii\fR, \fBasciib\fR,
49 \fBebcdic\fR, \fBebcdicb\fR, \fBibm\fR, and \fBibmb\fR options convert the
50 character set without changing the input file's block structure. The
51 \fBunblock\fR and \fBblock\fR options become a simple file copy.
52 .sp
53 .LP
54 After completion, \fBdd\fR reports the number of whole and partial input and
55 output blocks.
56 .SH OPERANDS
57 .sp
58 .LP
59 The following operands are supported:
60 .sp
61 .ne 2
62 .na
63 \fB\fBif=\fR\fIfile\fR\fR
64 .ad
65 .sp .6
66 .RS 4n
67 Specifies the input path. Standard input is the default.
68 .RE
70 .sp
71 .ne 2
72 .na
73 \fB\fBof=\fR\fIfile\fR\fR
74 .ad
75 .sp .6
76 .RS 4n
77 Specifies the output path. Standard output is the default. If the
78 \fBseek=\fR\fBexpr\fR conversion is not also specified, the output file will be
79 truncated before the copy begins, unless \fBconv=notrunc\fR is specified. If
80 \fBseek=\fR\fBexpr\fR is specified, but \fBconv=notrunc\fR is not, the effect
81 of the copy will be to preserve the blocks in the output file over which
82 \fBdd\fR seeks, but no other portion of the output file will be preserved. (If
83 the size of the seek plus the size of the input file is less than the previous
84 size of the output file, the output file is shortened by the copy.)
85 .RE
87 .sp
88 .ne 2
89 .na
90 \fB\fBibs=\fR\fIn\fR\fR
91 .ad
92 .sp .6
93 .RS 4n
94 Specifies the input block size in \fIn\fR bytes (default is \fB512\fR).
95 .RE
97 .sp
98 .ne 2
99 .na
100 \fB\fBobs=\fR\fIn\fR\fR
101 .ad
102 .sp .6
103 .RS 4n
104 Specifies the output block size in \fIn\fR bytes (default is \fB512\fR).
105 .RE
107 .sp
108 .ne 2
109 .na
110 \fB\fBbs=\fR\fIn\fR\fR
111 .ad
112 .sp .6
113 .RS 4n
114 Sets both input and output block sizes to \fIn\fR bytes, superseding \fBibs=\fR
115 and \fBobs=\fR. If no conversion other than \fBsync\fR,\fB noerror\fR, and
116 \fBnotrunc\fR is specified, each input block is copied to the output as a
117 single block without aggregating short blocks.
118 .RE
120 .sp
121 .ne 2
122 .na
123 \fB\fBcbs=\fR\fIn\fR\fR
124 .ad
125 .sp .6
126 .RS 4n
127 Specifies the conversion block size for \fBblock\fR and \fBunblock\fR in bytes
128 by \fIn\fR (default is \fB0\fR). If \fBcbs=\fR is omitted or given a value of
129 \fB0\fR, using \fBblock\fR or \fBunblock\fR produces unspecified results.
130 .sp
131 This option is used only if \fBASCII\fR or \fBEBCDIC\fR conversion is
132 specified. For the \fBascii\fR and \fBasciib\fR operands, the input is handled
133 as described for the \fBunblock\fR operand except that characters are converted
134 to \fBASCII\fR before the trailing \fBSPACE\fR characters are deleted. For the
135 \fBebcdic\fR, \fBebcdicb\fR, \fBibm\fR, and \fBibmb\fR operands, the input is
136 handled as described for the \fBblock\fR operand except that the characters are
137 converted to \fBEBCDIC\fR or IBM \fBEBCDIC\fR after the trailing \fBSPACE\fR
138 characters are added.
139 .RE
141 .sp
142 .ne 2
143 .na
144 \fB\fBfiles=\fR\fIn\fR\fR
145 .ad
146 .sp .6
147 .RS 4n
148 Copies and concatenates \fIn\fR input files before terminating (makes sense
149 only where input is a magnetic tape or similar device).
150 .RE
152 .sp
153 .ne 2
154 .na
155 \fB\fBskip=\fR\fIn\fR\fR
156 .ad
157 .sp .6
158 .RS 4n
159 Skips \fIn\fR input blocks (using the specified input block size) before
160 starting to copy. On seekable files, the implementation reads the blocks or
161 seeks past them. On non-seekable files, the blocks are read and the data is
162 discarded.
163 .RE
165 .sp
166 .ne 2
167 .na
168 \fB\fBiseek=\fR\fIn\fR\fR
169 .ad
170 .sp .6
171 .RS 4n
172 Seeks \fIn\fR blocks from beginning of input file before copying (appropriate
173 for disk files, where \fBskip\fR can be incredibly slow).
174 .RE
176 .sp
177 .ne 2
178 .na
179 \fB\fBoseek=\fR\fIn\fR\fR
180 .ad
181 .sp .6
182 .RS 4n
183 Seeks \fIn\fR blocks from beginning of output file before copying.
184 .RE
186 .sp
187 .ne 2
188 .na
189 \fB\fBseek=\fR\fIn\fR\fR
190 .ad
191 .sp .6
192 .RS 4n
193 Skips \fIn\fR blocks (using the specified output block size) from beginning of
194 output file before copying. On non-seekable files, existing blocks are read and
195 space from the current end-of-file to the specified offset, if any, is filled
196 with null bytes. On seekable files, the implementation seeks to the specified
197 offset or reads the blocks as described for non-seekable files.
198 .RE
200 .sp
201 .ne 2
202 .na
203 \fB\fBcount=\fR\fIn\fR\fR
204 .ad
205 .sp .6
206 .RS 4n
207 Copies only \fIn\fR input blocks.
208 .RE
210 .sp
211 .ne 2
212 .na
213 \fB\fBconv=\fR\fIvalue\fR[\fB,\fR\fIvalue\fR.\|.\|.\|]\fR
214 .ad
215 .sp .6
216 .RS 4n
217 Where \fIvalue\fRs are comma-separated symbols from the following list:
218 .sp
219 .ne 2
220 .na
221 \fB\fBascii\fR\fR
222 .ad
223 .RS 11n
224 Converts \fBEBCDIC\fR to \fBASCII\fR.
225 .RE
227 .sp
228 .ne 2
229 .na
230 \fB\fBasciib\fR\fR
231 .ad
232 .RS 11n
233 Converts \fBEBCDIC\fR to \fBASCII\fR using \fBBSD\fR-compatible character
234 translations.
235 .RE
237 .sp
238 .ne 2
239 .na
240 \fB\fBebcdic\fR\fR
241 .ad
242 .RS 11n
243 Converts \fBASCII\fR to \fBEBCDIC\fR. If converting fixed-length \fBASCII\fR
244 records without NEWLINEs, sets up a pipeline with \fBdd conv=unblock\fR
245 beforehand.
246 .RE
248 .sp
249 .ne 2
250 .na
251 \fB\fBebcdicb\fR\fR
252 .ad
253 .RS 11n
254 Converts \fBASCII\fR to \fBEBCDIC\fR using \fBBSD\fR-compatible character
255 translations. If converting fixed-length \fBASCII\fR records without
256 \fBNEWLINE\fRs, sets up a pipeline with \fBdd conv=unblock\fR beforehand.
257 .RE
259 .sp
260 .ne 2
261 .na
262 \fB\fBibm\fR\fR
263 .ad
264 .RS 11n
265 Slightly different map of \fBASCII\fR to \fBEBCDIC\fR. If converting
266 fixed-length \fBASCII\fR records without \fBNEWLINE\fRs, sets up a pipeline
267 with \fBdd conv=unblock\fR beforehand.
268 .RE
270 .sp
271 .ne 2
272 .na
273 \fB\fBibmb\fR\fR
274 .ad
275 .RS 11n
276 Slightly different map of \fBASCII\fR to \fBEBCDIC\fR using
277 \fBBSD\fR-compatible character translations. If converting fixed-length
278 \fBASCII\fR records without \fBNEWLINE\fRs, sets up a pipeline with \fBdd
279 conv=unblock\fR beforehand.
280 .RE
282 The \fBascii\fR (or \fBasciib\fR), \fBebcdic\fR (or \fBebcdicb\fR), and
283 \fBibm\fR (or \fBibmb\fR) values are mutually exclusive.
284 .sp
285 .ne 2
286 .na
287 \fB\fBblock\fR\fR
288 .ad
289 .RS 11n
290 Treats the input as a sequence of \fBNEWLINE\fR-terminated or
291 \fBEOF\fR-terminated variable-length records independent of the input block
292 boundaries. Each record is converted to a record with a fixed length specified
293 by the conversion block size. Any \fBNEWLINE\fR character is removed from the
294 input line. \fBSPACE\fR characters are appended to lines that are shorter than
295 their conversion block size to fill the block. Lines that are longer than the
296 conversion block size are truncated to the largest number of characters that
297 will fit into that size. The number of truncated lines is reported.
298 .RE
300 .sp
301 .ne 2
302 .na
303 \fB\fBunblock\fR\fR
304 .ad
305 .RS 11n
306 Converts fixed-length records to variable length. Reads a number of bytes equal
307 to the conversion block size (or the number of bytes remaining in the input, if
308 less than the conversion block size), delete all trailing \fBSPACE\fR
309 characters, and append a \fBNEWLINE\fR character.
310 .RE
312 The \fBblock\fR and \fBunblock\fR values are mutually exclusive.
313 .sp
314 .ne 2
315 .na
316 \fB\fBlcase\fR\fR
317 .ad
318 .RS 9n
319 Maps upper-case characters specified by the \fBLC_CTYPE\fR keyword
320 \fBtolower\fR to the corresponding lower-case character. Characters for which
321 no mapping is specified are not modified by this conversion.
322 .RE
324 .sp
325 .ne 2
326 .na
327 \fB\fBucase\fR\fR
328 .ad
329 .RS 9n
330 Maps lower-case characters specified by the \fBLC_CTYPE\fR keyword
331 \fBtoupper\fR to the corresponding upper-case character. Characters for which
332 no mapping is specified are not modified by this conversion.
333 .RE
335 The \fBlcase\fR and \fBucase\fR symbols are mutually exclusive.
336 .sp
337 .ne 2
338 .na
339 \fB\fBswab\fR\fR
340 .ad
341 .RS 11n
342 Swaps every pair of input bytes. If the current input record is an odd number
343 of bytes, the last byte in the input record is ignored.
344 .RE
346 .sp
347 .ne 2
348 .na
349 \fB\fBnoerror\fR\fR
350 .ad
351 .RS 11n
352 Does not stop processing on an input error. When an input error occurs, a
353 diagnostic message is written on standard error, followed by the current input
354 and output block counts in the same format as used at completion. If the
355 \fBsync\fR conversion is specified, the missing input is replaced with null
356 bytes and processed normally. Otherwise, the input block will be omitted from
357 the output.
358 .RE
360 .sp
361 .ne 2
362 .na
363 \fB\fBnotrunc\fR\fR
364 .ad
365 .RS 11n
366 Does not truncate the output file. Preserves blocks in the output file not
367 explicitly written by this invocation of \fBdd\fR. (See also the preceding
368 \fBof=\fR\fIfile\fR operand.)
369 .RE
371 .sp
372 .ne 2
373 .na
374 \fB\fBsync\fR\fR
375 .ad
376 .RS 11n
377 Pads every input block to the size of the \fBibs=\fR buffer, appending null
378 bytes. (If either \fBblock\fR or \fBunblock\fR is also specified, appends
379 \fBSPACE\fR characters, rather than null bytes.)
380 .RE
382 .RE
384 .sp
385 .ne 2
386 .na
387 \fB\fBoflag=\fR\fIvalue\fR[\fB,\fR\fIvalue\fR.\|.\|.\|]\fR
388 .ad
389 .sp .6
390 Where \fIvalue\fRs are comma-separated symbols from the following list which
391 affect the behavior of writing the output file:
392 .sp
393 .ne 2
394 .na
395 \fB\fBdsync\fR\fR
396 .ad
397 .RS 11n
398 The output file is opened with the \fBO_DSYNC\fR flag set. All data writes will
399 be synchronous. For more information on \fBO_DSYNC\fR see \fBfcntl.h\fR(3HEAD).
400 .RE
402 .sp
403 .ne 2
404 .na
405 \fB\fBsync\fR\fR
406 .ad
407 .RS 11n
408 The output file is opened with the \fBO_SYNC\fR flag set. All data and metadata
409 writes will be synchronous. For more information on \fBO_SYNC\fR see
410 \fBfcntl.h\fR(3HEAD).
411 .RE
413 .sp
414 .LP
415 If operands other than \fBconv=\fR and \fBoflag=\fR are specified more than once,
416 the last specified \fBoperand=\fR\fIvalue\fR is used.
417 .sp
418 .LP
419 For the \fBbs=\fR, \fBcbs=\fR, \fBibs=\fR, and \fBobs=\fR operands, the
420 application must supply an expression specifying a size in bytes. The
421 expression, \fBexpr\fR, can be:
422 .RS +4
423 .TP
424 1.
425 a positive decimal number
426 .RE
427 .RS +4
428 .TP
429 2.
430 a positive decimal number followed by \fBk\fR, specifying multiplication by
431 1024
432 .RE
433 .RS +4
434 .TP
435 3.
436 a positive decimal number followed by \fBM\fR, specifying multiplication by
437 1024*1024
438 .RE
439 .RS +4
440 .TP
441 4.
442 a positive decimal number followed by \fBG\fR, specifying multiplication by
443 1024*1024*1024
444 .RE
445 .RS +4
446 .TP
447 5.
448 a positive decimal number followed by \fBT\fR, specifying multiplication by
449 1024*1024*1024*1024
450 .RE
451 .RS +4
452 .TP
453 6.
454 a positive decimal number followed by \fBP\fR, specifying multiplication by
455 1024*1024*1024*1024*1024
456 .RE
457 .RS +4
458 .TP
459 7.
460 a positive decimal number followed by \fBE\fR, specifying multiplication by
461 1024*1024*1024*1024*1024*1024
462 .RE
463 .RS +4
464 .TP
465 8.
466 a positive decimal number followed by \fBZ\fR, specifying multiplication by
467 1024*1024*1024*1024*1024*1024*1024
468 .RE
469 .RS +4
470 .TP
471 9.
472 a positive decimal number followed by \fBb\fR, specifying multiplication by
473 512
474 .RE
475 .RS +4
476 .TP
477 10.
478 two or more positive decimal numbers (with or without \fBk\fR or \fBb\fR)
479 separated by \fBx\fR, specifying the product of the indicated values.
480 .RE
481 .sp
482 .LP
483 All of the operands will be processed before any input is read.
484 .SH SIGNALS
485 .sp
486 .LP
487 When \fBdd\fR receives either SIGINFO or SIGUSR1, \fBdd\fR will emit the current
488 input and output block counts, total bytes written, total time elapsed, and the
489 number of bytes per second to standard error. This is the same information
490 format that \fBdd\fR emits when it successfully completes. Users may send
491 SIGINFO via their terminal. The default character is ^T, see \fBstty\fR(1) for
492 more information.
493 .sp
494 .LP
495 For \fBSIGINT\fR, \fBdd\fR writes status information to standard error before
496 exiting. \fBdd\fR takes the standard action for all other signals.
498 .SH USAGE
499 .sp
500 .LP
501 See \fBlargefile\fR(5) for the description of the behavior of \fBdd\fR when
502 encountering files greater than or equal to 2 Gbyte ( 2^31 bytes).
503 .SH EXAMPLES
504 .LP
505 \fBExample 1 \fRCopying from one tape drive to another
506 .sp
507 .LP
508 The following example copies from tape drive \fB0\fR to tape drive \fB1\fR,
509 using a common historical device naming convention.
511 .sp
512 .in +2
513 .nf
514 example% \fBdd if=/dev/rmt/0h of=/dev/rmt/1h\fR
515 .fi
516 .in -2
517 .sp
519 .LP
520 \fBExample 2 \fRStripping the first 10 bytes from standard input
521 .sp
522 .LP
523 The following example strips the first 10 bytes from standard input:
525 .sp
526 .in +2
527 .nf
528 example% \fBdd ibs=10 skip=1\fR
529 .fi
530 .in -2
531 .sp
533 .LP
534 \fBExample 3 \fRReading a tape into an ASCII file
535 .sp
536 .LP
537 This example reads an \fBEBCDIC\fR tape blocked ten 80-byte \fBEBCDIC\fR card
538 images per block into the \fBASCII\fR file \fBx\fR:
540 .sp
541 .in +2
542 .nf
543 example% \fBdd if=/dev/tape of=x ibs=800 cbs=80 conv=ascii,lcase\fR
544 .fi
545 .in -2
546 .sp
548 .LP
549 \fBExample 4 \fRUsing conv=sync to write to tape
550 .sp
551 .LP
552 The following example uses \fBconv=sync\fR when writing to a tape:
554 .sp
555 .in +2
556 .nf
557 example% \fBtar cvf - . | compress | dd obs=1024k of=/dev/rmt/0 conv=sync\fR
558 .fi
559 .in -2
560 .sp
562 .SH ENVIRONMENT VARIABLES
563 .sp
564 .LP
565 See \fBenviron\fR(5) for descriptions of the following environment variables
566 that affect the execution of \fBdd\fR: \fBLANG\fR, \fBLC_ALL\fR,
567 \fBLC_CTYPE\fR, \fBLC_MESSAGES\fR, and \fBNLSPATH\fR.
568 .SH EXIT STATUS
569 .sp
570 .LP
571 The following exit values are returned:
572 .sp
573 .ne 2
574 .na
575 \fB\fB0\fR\fR
576 .ad
577 .RS 6n
578 The input file was copied successfully.
579 .RE
581 .sp
582 .ne 2
583 .na
584 \fB\fB>0\fR\fR
585 .ad
586 .RS 6n
587 An error occurred.
588 .RE
590 .sp
591 .LP
592 If an input error is detected and the \fBnoerror\fR conversion has not been
593 specified, any partial output block will be written to the output file, a
594 diagnostic message will be written, and the copy operation will be
595 discontinued. If some other error is detected, a diagnostic message will be
596 written and the copy operation will be discontinued.
597 .SH ATTRIBUTES
598 .sp
599 .LP
600 See \fBattributes\fR(5) for descriptions of the following attributes:
601 .sp
603 .sp
604 .TS
605 box;
606 c | c
607 l | l .
608 ATTRIBUTE TYPE ATTRIBUTE VALUE
609 _
610 Interface Stability Standard
611 .TE
613 .SH SEE ALSO
614 .sp
615 .LP
616 \fBcp\fR(1), \fBsed\fR(1), \fBtr\fR(1), \fBfcntl.h\fR(3HEAD),
617 \fBattributes\fR(5), \fBenviron\fR(5), \fBlargefile\fR(5), \fBstandards\fR(5)
618 .SH DIAGNOSTICS
619 .sp
620 .ne 2
621 .na
622 \fB\fBf+p records in(out)\fR\fR
623 .ad
624 .RS 23n
625 numbers of full and partial blocks read(written)
626 .RE
628 .SH NOTES
629 .sp
630 .LP
631 Do not use \fBdd\fR to copy files between file systems having different block
632 sizes.
633 .sp
634 .LP
635 Using a blocked device to copy a file will result in extra nulls being added
636 to the file to pad the final block to the block boundary.
637 .sp
638 .LP
639 When \fBdd\fR reads from a pipe, using the \fBibs=X\fR and \fBobs=Y\fR
640 operands, the output will always be blocked in chunks of size Y. When
641 \fBbs=Z\fR is used, the output blocks will be whatever was available to be read
642 from the pipe at the time.
643 .sp
644 .LP
645 When using \fBdd\fR to copy files to a tape device, the file size must be a
646 multiple of the device sector size (for example, 512 Kbyte). To copy files of
647 arbitrary size to a tape device, use \fBtar\fR(1) or \fBcpio\fR(1).