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 January 23, 2009 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 conv Ns = Ns Ar value Ns Op , Ns Ar value ... 160Where 161.Cm value 162is one of the symbols from the following list. 163.Bl -tag -width ".Cm unblock" 164.It Cm ascii , oldascii 165The same as the 166.Cm unblock 167value except that characters are translated from 168.Tn EBCDIC 169to 170.Tn ASCII 171before the 172records are converted. 173(These values imply 174.Cm unblock 175if the operand 176.Cm cbs 177is also specified.) 178There are two conversion maps for 179.Tn ASCII . 180The value 181.Cm ascii 182specifies the recommended one which is compatible with 183.At V . 184The value 185.Cm oldascii 186specifies the one used in historic 187.At 188and 189.No pre- Ns Bx 4.3 reno 190systems. 191.It Cm block 192Treats the input as a sequence of newline or end-of-file terminated variable 193length records independent of input and output block boundaries. 194Any trailing newline character is discarded. 195Each input record is converted to a fixed length output record where the 196length is specified by the 197.Cm cbs 198operand. 199Input records shorter than the conversion record size are padded with spaces. 200Input records longer than the conversion record size are truncated. 201The number of truncated input records, if any, are reported to the standard 202error output at the completion of the copy. 203.It Cm ebcdic , ibm , oldebcdic , oldibm 204The same as the 205.Cm block 206value except that characters are translated from 207.Tn ASCII 208to 209.Tn EBCDIC 210after the 211records are converted. 212(These values imply 213.Cm block 214if the operand 215.Cm cbs 216is also specified.) 217There are four conversion maps for 218.Tn EBCDIC . 219The value 220.Cm ebcdic 221specifies the recommended one which is compatible with 222.At V . 223The value 224.Cm ibm 225is a slightly different mapping, which is compatible with the 226.At V 227.Cm ibm 228value. 229The values 230.Cm oldebcdic 231and 232.Cm oldibm 233are maps used in historic 234.At 235and 236.No pre- Ns Bx 4.3 reno 237systems. 238.It Cm lcase 239Transform uppercase characters into lowercase characters. 240.It Cm pareven , parnone , parodd , parset 241Output data with the specified parity. 242The parity bit on input is stripped unless 243.Tn EBCDIC 244to 245.Tn ASCII 246conversions is also specified. 247.It Cm noerror 248Do not stop processing on an input error. 249When an input error occurs, a diagnostic message followed by the current 250input and output block counts will be written to the standard error output 251in the same format as the standard completion message. 252If the 253.Cm sync 254conversion is also specified, any missing input data will be replaced 255with 256.Dv NUL 257bytes (or with spaces if a block oriented conversion value was 258specified) and processed as a normal input buffer. 259If the 260.Cm fillchar 261option is specified, the fill character provided on the command line 262will override 263the automatic selection of the fill character. 264If the 265.Cm sync 266conversion is not specified, the input block is omitted from the output. 267On input files which are not tapes or pipes, the file offset 268will be positioned past the block in which the error occurred using 269.Xr lseek 2 . 270.It Cm notrunc 271Do not truncate the output file. 272This will preserve any blocks in the output file not explicitly written 273by 274.Nm . 275The 276.Cm notrunc 277value is not supported for tapes. 278.It Cm osync 279Pad the final output block to the full output block size. 280If the input file is not a multiple of the output block size 281after conversion, this conversion forces the final output block 282to be the same size as preceding blocks for use on devices that require 283regularly sized blocks to be written. 284This option is incompatible with use of the 285.Cm bs Ns = Ns Ar n 286block size specification. 287.It Cm sparse 288If one or more output blocks would consist solely of 289.Dv NUL 290bytes, try to seek the output file by the required space instead of 291filling them with 292.Dv NUL Ns s , 293resulting in a sparse file. 294.It Cm swab 295Swap every pair of input bytes. 296If an input buffer has an odd number of bytes, the last byte will be 297ignored during swapping. 298.It Cm sync 299Pad every input block to the input buffer size. 300Spaces are used for pad bytes if a block oriented conversion value is 301specified, otherwise 302.Dv NUL 303bytes are used. 304.It Cm ucase 305Transform lowercase characters into uppercase characters. 306.It Cm unblock 307Treats the input as a sequence of fixed length records independent of input 308and output block boundaries. 309The length of the input records is specified by the 310.Cm cbs 311operand. 312Any trailing space characters are discarded and a newline character is 313appended. 314.El 315.El 316.Pp 317Where sizes are specified, a decimal, octal, or hexadecimal number of 318bytes is expected. 319If the number ends with a 320.Dq Li b , 321.Dq Li k , 322.Dq Li m , 323.Dq Li g , 324or 325.Dq Li w , 326the 327number is multiplied by 512, 1024 (1K), 1048576 (1M), 1073741824 (1G) 328or the number of bytes in an integer, respectively. 329Two or more numbers may be separated by an 330.Dq Li x 331to indicate a product. 332.Pp 333When finished, 334.Nm 335displays the number of complete and partial input and output blocks, 336truncated input records and odd-length byte-swapping blocks to the 337standard error output. 338A partial input block is one where less than the input block size 339was read. 340A partial output block is one where less than the output block size 341was written. 342Partial output blocks to tape devices are considered fatal errors. 343Otherwise, the rest of the block will be written. 344Partial output blocks to character devices will produce a warning message. 345A truncated input block is one where a variable length record oriented 346conversion value was specified and the input line was too long to 347fit in the conversion record or was not newline terminated. 348.Pp 349Normally, data resulting from input or conversion or both are aggregated 350into output blocks of the specified size. 351After the end of input is reached, any remaining output is written as 352a block. 353This means that the final output block may be shorter than the output 354block size. 355.Pp 356If 357.Nm 358receives a 359.Dv SIGINFO 360(see the 361.Cm status 362argument for 363.Xr stty 1 ) 364signal, the current input and output block counts will 365be written to the standard error output 366in the same format as the standard completion message. 367If 368.Nm 369receives a 370.Dv SIGINT 371signal, the current input and output block counts will 372be written to the standard error output 373in the same format as the standard completion message and 374.Nm 375will exit. 376.Sh EXIT STATUS 377.Ex -std 378.Sh EXAMPLES 379Check that a disk drive contains no bad blocks: 380.Pp 381.Dl "dd if=/dev/ad0 of=/dev/null bs=1m" 382.Pp 383Do a refresh of a disk drive, in order to prevent presently 384recoverable read errors from progressing into unrecoverable read errors: 385.Pp 386.Dl "dd if=/dev/ad0 of=/dev/ad0 bs=1m" 387.Pp 388Remove parity bit from a file: 389.Pp 390.Dl "dd if=file conv=parnone of=file.txt" 391.Pp 392Check for (even) parity errors on a file: 393.Pp 394.Dl "dd if=file conv=pareven | cmp -x - file" 395.Pp 396To create an image of a Mode-1 CD-ROM, which is a commonly used format 397for data CD-ROM disks, use a block size of 2048 bytes: 398.Pp 399.Dl "dd if=/dev/acd0 of=filename.iso bs=2048" 400.Sh SEE ALSO 401.Xr cp 1 , 402.Xr mt 1 , 403.Xr tr 1 , 404.Xr geom 4 405.Sh STANDARDS 406The 407.Nm 408utility is expected to be a superset of the 409.St -p1003.2 410standard. 411The 412.Cm files 413operand and the 414.Cm ascii , 415.Cm ebcdic , 416.Cm ibm , 417.Cm oldascii , 418.Cm oldebcdic 419and 420.Cm oldibm 421values are extensions to the 422.Tn POSIX 423standard. 424.Sh BUGS 425Protection mechanisms in the 426.Xr geom 4 427subsystem might prevent the super-user from writing blocks to a disk. 428Instructions for temporarily disabling these protection mechanisms can be 429found in the 430.Xr geom 4 431manpage. 432