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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
  21 
  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
  69 
  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
  86 
  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
  96 
  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
 106 
 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
 119 
 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
 140 
 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
 151 
 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
 164 
 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
 175 
 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
 185 
 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
 199 
 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
 209 
 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
 226 
 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
 236 
 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
 247 
 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
 258 
 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
 269 
 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
 281 
 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
 299 
 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
 311 
 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
 323 
 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
 334 
 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
 345 
 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
 359 
 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
 370 
 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
 381 
 382 .RE
 383 
 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
 401 
 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
 412 
 413 .RE
 414 
 415 .sp
 416 .LP
 417 If operands other than \fBconv=\fR and \fBoflag=\fR are specified more than once,
 418 the last specified \fBoperand=\fR\fIvalue\fR is used.
 419 .sp
 420 .LP
 421 For the \fBbs=\fR, \fBcbs=\fR, \fBibs=\fR, and \fBobs=\fR operands, the
 422 application must supply an expression specifying a size in bytes. The
 423 expression, \fBexpr\fR, can be:
 424 .RS +4
 425 .TP
 426 1.
 427 a positive decimal number
 428 .RE
 429 .RS +4
 430 .TP
 431 2.
 432 a positive decimal number followed by \fBk\fR, specifying multiplication by
 433 1024
 434 .RE
 435 .RS +4
 436 .TP
 437 3.
 438 a positive decimal number followed by \fBM\fR, specifying multiplication by
 439 1024*1024
 440 .RE
 441 .RS +4
 442 .TP
 443 4.
 444 a positive decimal number followed by \fBG\fR, specifying multiplication by
 445 1024*1024*1024
 446 .RE
 447 .RS +4
 448 .TP
 449 5.
 450 a positive decimal number followed by \fBT\fR, specifying multiplication by
 451 1024*1024*1024*1024
 452 .RE
 453 .RS +4
 454 .TP
 455 6.
 456 a positive decimal number followed by \fBP\fR, specifying multiplication by
 457 1024*1024*1024*1024*1024
 458 .RE
 459 .RS +4
 460 .TP
 461 7.
 462 a positive decimal number followed by \fBE\fR, specifying multiplication by
 463 1024*1024*1024*1024*1024*1024
 464 .RE
 465 .RS +4
 466 .TP
 467 8.
 468 a positive decimal number followed by \fBZ\fR, specifying multiplication by
 469 1024*1024*1024*1024*1024*1024*1024
 470 .RE
 471 .RS +4
 472 .TP
 473 9.
 474 a positive decimal number followed by \fBb\fR, specifying multiplication by
 475 512
 476 .RE
 477 .RS +4
 478 .TP
 479 10.
 480 two or more positive decimal numbers (with or without \fBk\fR or \fBb\fR)
 481 separated by \fBx\fR, specifying the product of the indicated values.
 482 .RE
 483 .sp
 484 .LP
 485 All of the operands will be processed before any input is read.
 486 .SH SIGNALS
 487 .sp
 488 .LP
 489 When \fBdd\fR receives either SIGINFO or SIGUSR1, \fBdd\fR will emit the current
 490 input and output block counts, total bytes written, total time elapsed, and the
 491 number of bytes per second to standard error. This is the same information
 492 format that \fBdd\fR emits when it successfully completes. Users may send
 493 SIGINFO via their terminal. The default character is ^T, see \fBstty\fR(1) for
 494 more information.
 495 .sp
 496 .LP
 497 For \fBSIGINT\fR, \fBdd\fR writes status information to standard error before
 498 exiting. \fBdd\fR takes the standard action for all other signals.
 499 
 500 .SH USAGE
 501 .sp
 502 .LP
 503 See \fBlargefile\fR(5) for the description of the behavior of \fBdd\fR when
 504 encountering files greater than or equal to 2 Gbyte ( 2^31 bytes).
 505 .SH EXAMPLES
 506 .LP
 507 \fBExample 1 \fRCopying from one tape drive to another
 508 .sp
 509 .LP
 510 The following example copies from tape drive \fB0\fR to tape drive \fB1\fR,
 511 using a common historical device naming convention.
 512 
 513 .sp
 514 .in +2
 515 .nf
 516 example% \fBdd if=/dev/rmt/0h  of=/dev/rmt/1h\fR
 517 .fi
 518 .in -2
 519 .sp
 520 
 521 .LP
 522 \fBExample 2 \fRStripping the first 10 bytes from standard input
 523 .sp
 524 .LP
 525 The following example strips the first 10 bytes from standard input:
 526 
 527 .sp
 528 .in +2
 529 .nf
 530 example% \fBdd ibs=10  skip=1\fR
 531 .fi
 532 .in -2
 533 .sp
 534 
 535 .LP
 536 \fBExample 3 \fRReading a tape into an ASCII file
 537 .sp
 538 .LP
 539 This example reads an \fBEBCDIC\fR tape blocked ten 80-byte \fBEBCDIC\fR card
 540 images per block into the \fBASCII\fR file \fBx\fR:
 541 
 542 .sp
 543 .in +2
 544 .nf
 545 example% \fBdd if=/dev/tape of=x ibs=800 cbs=80 conv=ascii,lcase\fR
 546 .fi
 547 .in -2
 548 .sp
 549 
 550 .LP
 551 \fBExample 4 \fRUsing conv=sync to write to tape
 552 .sp
 553 .LP
 554 The following example uses \fBconv=sync\fR when writing to a tape:
 555 
 556 .sp
 557 .in +2
 558 .nf
 559 example% \fBtar cvf - . | compress | dd obs=1024k of=/dev/rmt/0 conv=sync\fR
 560 .fi
 561 .in -2
 562 .sp
 563 
 564 .SH ENVIRONMENT VARIABLES
 565 .sp
 566 .LP
 567 See \fBenviron\fR(5) for descriptions of the following environment variables
 568 that affect the execution of \fBdd\fR: \fBLANG\fR, \fBLC_ALL\fR,
 569 \fBLC_CTYPE\fR, \fBLC_MESSAGES\fR, and \fBNLSPATH\fR.
 570 .SH EXIT STATUS
 571 .sp
 572 .LP
 573 The following exit values are returned:
 574 .sp
 575 .ne 2
 576 .na
 577 \fB\fB0\fR\fR
 578 .ad
 579 .RS 6n
 580 The input file was copied successfully.
 581 .RE
 582 
 583 .sp
 584 .ne 2
 585 .na
 586 \fB\fB>0\fR\fR
 587 .ad
 588 .RS 6n
 589 An error occurred.
 590 .RE
 591 
 592 .sp
 593 .LP
 594 If an input error is detected and the \fBnoerror\fR conversion has not been
 595 specified, any partial output block will be written to the output file, a
 596 diagnostic message will be written, and the copy operation will be
 597 discontinued. If some other error is detected, a diagnostic message will be
 598 written and the copy operation will be discontinued.
 599 .SH ATTRIBUTES
 600 .sp
 601 .LP
 602 See \fBattributes\fR(5) for descriptions of the following attributes:
 603 .sp
 604 
 605 .sp
 606 .TS
 607 box;
 608 c | c
 609 l | l .
 610 ATTRIBUTE TYPE  ATTRIBUTE VALUE
 611 _
 612 Interface Stability     Standard
 613 .TE
 614 
 615 .SH SEE ALSO
 616 .sp
 617 .LP
 618 \fBcp\fR(1), \fBsed\fR(1), \fBtr\fR(1), \fBfcntl.h\fR(3HEAD),
 619 \fBattributes\fR(5), \fBenviron\fR(5), \fBlargefile\fR(5), \fBstandards\fR(5)
 620 .SH DIAGNOSTICS
 621 .sp
 622 .ne 2
 623 .na
 624 \fB\fBf+p records in(out)\fR\fR
 625 .ad
 626 .RS 23n
 627 numbers of full and partial blocks read(written)
 628 .RE
 629 
 630 .SH NOTES
 631 .sp
 632 .LP
 633 Do not use \fBdd\fR to copy files between file systems having different block
 634 sizes.
 635 .sp
 636 .LP
 637 Using a  blocked device to copy a file will result in extra nulls being added
 638 to the file to pad the final block to the block boundary.
 639 .sp
 640 .LP
 641 When  \fBdd\fR reads from a pipe, using the  \fBibs=X\fR and  \fBobs=Y\fR
 642 operands, the output will always be blocked in chunks of size Y. When
 643 \fBbs=Z\fR is used, the output blocks will be whatever was available to be read
 644 from the pipe at the time.
 645 .sp
 646 .LP
 647 When using \fBdd\fR to copy files to a tape device, the file size must be a
 648 multiple of the device sector size (for example, 512 Kbyte).  To  copy files of
 649 arbitrary size to a tape device, use  \fBtar\fR(1) or  \fBcpio\fR(1).