1.\"- 2.\" Copyright (c) 1990, 1993 3.\" The Regents of the University of California. All rights reserved. 4.\" 5.\" This code is derived from software contributed to Berkeley by 6.\" Keith Muller of the University of California, San Diego. 7.\" 8.\" Redistribution and use in source and binary forms, with or without 9.\" modification, are permitted provided that the following conditions 10.\" are met: 11.\" 1. Redistributions of source code must retain the above copyright 12.\" notice, this list of conditions and the following disclaimer. 13.\" 2. Redistributions in binary form must reproduce the above copyright 14.\" notice, this list of conditions and the following disclaimer in the 15.\" documentation and/or other materials provided with the distribution. 16.\" 4. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" @(#)dd.1 8.2 (Berkeley) 1/13/94 33.\" $FreeBSD$ 34.\" 35.Dd February 4, 2016 36.Dt DD 1 37.Os 38.Sh NAME 39.Nm dd 40.Nd convert and copy a file 41.Sh SYNOPSIS 42.Nm 43.Op Ar operands ... 44.Sh DESCRIPTION 45The 46.Nm 47utility copies the standard input to the standard output. 48Input data is read and written in 512-byte blocks. 49If input reads are short, input from multiple reads are aggregated 50to form the output block. 51When finished, 52.Nm 53displays the number of complete and partial input and output blocks 54and truncated input records to the standard error output. 55.Pp 56The following operands are available: 57.Bl -tag -width ".Cm of Ns = Ns Ar file" 58.It Cm bs Ns = Ns Ar n 59Set both input and output block size to 60.Ar n 61bytes, superseding the 62.Cm ibs 63and 64.Cm obs 65operands. 66If no conversion values other than 67.Cm noerror , 68.Cm notrunc 69or 70.Cm sync 71are specified, then each input block is copied to the output as a 72single block without any aggregation of short blocks. 73.It Cm cbs Ns = Ns Ar n 74Set the conversion record size to 75.Ar n 76bytes. 77The conversion record size is required by the record oriented conversion 78values. 79.It Cm count Ns = Ns Ar n 80Copy only 81.Ar n 82input blocks. 83.It Cm files Ns = Ns Ar n 84Copy 85.Ar n 86input files before terminating. 87This operand is only applicable when the input device is a tape. 88.It Cm fillchar Ns = Ns Ar c 89When padding a block in conversion mode or due to use of 90.Cm noerror 91and 92.Cm sync 93modes, fill with the specified 94.Tn ASCII 95character, rather than using a space or 96.Dv NUL . 97.It Cm ibs Ns = Ns Ar n 98Set the input block size to 99.Ar n 100bytes instead of the default 512. 101.It Cm if Ns = Ns Ar file 102Read input from 103.Ar file 104instead of the standard input. 105.It Cm iseek Ns = Ns Ar n 106Seek on the input file 107.Ar n 108blocks. 109This is synonymous with 110.Cm skip Ns = Ns Ar n . 111.It Cm obs Ns = Ns Ar n 112Set the output block size to 113.Ar n 114bytes instead of the default 512. 115.It Cm of Ns = Ns Ar file 116Write output to 117.Ar file 118instead of the standard output. 119Any regular output file is truncated unless the 120.Cm notrunc 121conversion value is specified. 122If an initial portion of the output file is seeked past (see the 123.Cm oseek 124operand), 125the output file is truncated at that point. 126.It Cm oseek Ns = Ns Ar n 127Seek on the output file 128.Ar n 129blocks. 130This is synonymous with 131.Cm seek Ns = Ns Ar n . 132.It Cm seek Ns = Ns Ar n 133Seek 134.Ar n 135blocks from the beginning of the output before copying. 136On non-tape devices, an 137.Xr lseek 2 138operation is used. 139Otherwise, existing blocks are read and the data discarded. 140If the user does not have read permission for the tape, it is positioned 141using the tape 142.Xr ioctl 2 143function calls. 144If the seek operation is past the end of file, space from the current 145end of file to the specified offset is filled with blocks of 146.Dv NUL 147bytes. 148.It Cm skip Ns = Ns Ar n 149Skip 150.Ar n 151blocks from the beginning of the input before copying. 152On input which supports seeks, an 153.Xr lseek 2 154operation is used. 155Otherwise, input data is read and discarded. 156For pipes, the correct number of bytes is read. 157For all other devices, the correct number of blocks is read without 158distinguishing between a partial or complete block being read. 159.It Cm status Ns = Ns Ar value 160Where 161.Cm value 162is one of the symbols from the following list. 163.Bl -tag -width ".Cm noxfer" 164.It Cm noxfer 165Do not print the transfer statistics as the last line of status output. 166.It Cm none 167Do not print the status output. 168Error messages are shown; informational messages are not. 169.El 170.It Cm conv Ns = Ns Ar value Ns Op , Ns Ar value ... 171Where 172.Cm value 173is one of the symbols from the following list. 174.Bl -tag -width ".Cm unblock" 175.It Cm ascii , oldascii 176The same as the 177.Cm unblock 178value except that characters are translated from 179.Tn EBCDIC 180to 181.Tn ASCII 182before the 183records are converted. 184(These values imply 185.Cm unblock 186if the operand 187.Cm cbs 188is also specified.) 189There are two conversion maps for 190.Tn ASCII . 191The value 192.Cm ascii 193specifies the recommended one which is compatible with 194.At V . 195The value 196.Cm oldascii 197specifies the one used in historic 198.At 199and 200.No pre- Ns Bx 4.3 reno 201systems. 202.It Cm block 203Treats the input as a sequence of newline or end-of-file terminated variable 204length records independent of input and output block boundaries. 205Any trailing newline character is discarded. 206Each input record is converted to a fixed length output record where the 207length is specified by the 208.Cm cbs 209operand. 210Input records shorter than the conversion record size are padded with spaces. 211Input records longer than the conversion record size are truncated. 212The number of truncated input records, if any, are reported to the standard 213error output at the completion of the copy. 214.It Cm ebcdic , ibm , oldebcdic , oldibm 215The same as the 216.Cm block 217value except that characters are translated from 218.Tn ASCII 219to 220.Tn EBCDIC 221after the 222records are converted. 223(These values imply 224.Cm block 225if the operand 226.Cm cbs 227is also specified.) 228There are four conversion maps for 229.Tn EBCDIC . 230The value 231.Cm ebcdic 232specifies the recommended one which is compatible with 233.At V . 234The value 235.Cm ibm 236is a slightly different mapping, which is compatible with the 237.At V 238.Cm ibm 239value. 240The values 241.Cm oldebcdic 242and 243.Cm oldibm 244are maps used in historic 245.At 246and 247.No pre- Ns Bx 4.3 reno 248systems. 249.It Cm lcase 250Transform uppercase characters into lowercase characters. 251.It Cm pareven , parnone , parodd , parset 252Output data with the specified parity. 253The parity bit on input is stripped unless 254.Tn EBCDIC 255to 256.Tn ASCII 257conversions is also specified. 258.It Cm noerror 259Do not stop processing on an input error. 260When an input error occurs, a diagnostic message followed by the current 261input and output block counts will be written to the standard error output 262in the same format as the standard completion message. 263If the 264.Cm sync 265conversion is also specified, any missing input data will be replaced 266with 267.Dv NUL 268bytes (or with spaces if a block oriented conversion value was 269specified) and processed as a normal input buffer. 270If the 271.Cm fillchar 272option is specified, the fill character provided on the command line 273will override 274the automatic selection of the fill character. 275If the 276.Cm sync 277conversion is not specified, the input block is omitted from the output. 278On input files which are not tapes or pipes, the file offset 279will be positioned past the block in which the error occurred using 280.Xr lseek 2 . 281.It Cm notrunc 282Do not truncate the output file. 283This will preserve any blocks in the output file not explicitly written 284by 285.Nm . 286The 287.Cm notrunc 288value is not supported for tapes. 289.It Cm osync 290Pad the final output block to the full output block size. 291If the input file is not a multiple of the output block size 292after conversion, this conversion forces the final output block 293to be the same size as preceding blocks for use on devices that require 294regularly sized blocks to be written. 295This option is incompatible with use of the 296.Cm bs Ns = Ns Ar n 297block size specification. 298.It Cm sparse 299If one or more output blocks would consist solely of 300.Dv NUL 301bytes, try to seek the output file by the required space instead of 302filling them with 303.Dv NUL Ns s , 304resulting in a sparse file. 305.It Cm swab 306Swap every pair of input bytes. 307If an input buffer has an odd number of bytes, the last byte will be 308ignored during swapping. 309.It Cm sync 310Pad every input block to the input buffer size. 311Spaces are used for pad bytes if a block oriented conversion value is 312specified, otherwise 313.Dv NUL 314bytes are used. 315.It Cm ucase 316Transform lowercase characters into uppercase characters. 317.It Cm unblock 318Treats the input as a sequence of fixed length records independent of input 319and output block boundaries. 320The length of the input records is specified by the 321.Cm cbs 322operand. 323Any trailing space characters are discarded and a newline character is 324appended. 325.El 326.El 327.Pp 328Where sizes are specified, a decimal, octal, or hexadecimal number of 329bytes is expected. 330If the number ends with a 331.Dq Li b , 332.Dq Li k , 333.Dq Li m , 334.Dq Li g , 335.Dq Li t , 336.Dq Li p , 337or 338.Dq Li w , 339the 340number is multiplied by 512, 1024 (1K), 1048576 (1M), 1073741824 (1G), 3411099511627776 (1T), 1125899906842624 (1P) 342or the number of bytes in an integer, respectively. 343Two or more numbers may be separated by an 344.Dq Li x 345to indicate a product. 346.Pp 347When finished, 348.Nm 349displays the number of complete and partial input and output blocks, 350truncated input records and odd-length byte-swapping blocks to the 351standard error output. 352A partial input block is one where less than the input block size 353was read. 354A partial output block is one where less than the output block size 355was written. 356Partial output blocks to tape devices are considered fatal errors. 357Otherwise, the rest of the block will be written. 358Partial output blocks to character devices will produce a warning message. 359A truncated input block is one where a variable length record oriented 360conversion value was specified and the input line was too long to 361fit in the conversion record or was not newline terminated. 362.Pp 363Normally, data resulting from input or conversion or both are aggregated 364into output blocks of the specified size. 365After the end of input is reached, any remaining output is written as 366a block. 367This means that the final output block may be shorter than the output 368block size. 369.Pp 370If 371.Nm 372receives a 373.Dv SIGINFO 374(see the 375.Cm status 376argument for 377.Xr stty 1 ) 378signal, the current input and output block counts will 379be written to the standard error output 380in the same format as the standard completion message. 381If 382.Nm 383receives a 384.Dv SIGINT 385signal, the current input and output block counts will 386be written to the standard error output 387in the same format as the standard completion message and 388.Nm 389will exit. 390.Sh EXIT STATUS 391.Ex -std 392.Sh EXAMPLES 393Check that a disk drive contains no bad blocks: 394.Pp 395.Dl "dd if=/dev/ada0 of=/dev/null bs=1m" 396.Pp 397Do a refresh of a disk drive, in order to prevent presently 398recoverable read errors from progressing into unrecoverable read errors: 399.Pp 400.Dl "dd if=/dev/ada0 of=/dev/ada0 bs=1m" 401.Pp 402Remove parity bit from a file: 403.Pp 404.Dl "dd if=file conv=parnone of=file.txt" 405.Pp 406Check for (even) parity errors on a file: 407.Pp 408.Dl "dd if=file conv=pareven | cmp -x - file" 409.Pp 410To create an image of a Mode-1 CD-ROM, which is a commonly used format 411for data CD-ROM disks, use a block size of 2048 bytes: 412.Pp 413.Dl "dd if=/dev/acd0 of=filename.iso bs=2048" 414.Pp 415Write a filesystem image to a memory stick, padding the end with zeros, 416if necessary, to a 1MiB boundary: 417.Pp 418.Dl "dd if=memstick.img of=/dev/da0 bs=1m conv=noerror,sync" 419.Sh SEE ALSO 420.Xr cp 1 , 421.Xr mt 1 , 422.Xr recoverdisk 1 , 423.Xr tr 1 , 424.Xr geom 4 425.Sh STANDARDS 426The 427.Nm 428utility is expected to be a superset of the 429.St -p1003.2 430standard. 431The 432.Cm files 433and 434.Cm status 435operands and the 436.Cm ascii , 437.Cm ebcdic , 438.Cm ibm , 439.Cm oldascii , 440.Cm oldebcdic 441and 442.Cm oldibm 443values are extensions to the 444.Tn POSIX 445standard. 446.Sh BUGS 447Protection mechanisms in the 448.Xr geom 4 449subsystem might prevent the super-user from writing blocks to a disk. 450Instructions for temporarily disabling these protection mechanisms can be 451found in the 452.Xr geom 4 453manpage. 454