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.\" 3. 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 March 26, 2019 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 "of=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 speed Ns = Ns Ar n 160Limit the copying speed to 161.Ar n 162bytes per second. 163.It Cm status Ns = Ns Ar value 164Where 165.Cm value 166is one of the symbols from the following list. 167.Bl -tag -width "progress" 168.It Cm noxfer 169Do not print the transfer statistics as the last line of status output. 170.It Cm none 171Do not print the status output. 172Error messages are shown; informational messages are not. 173.It Cm progress 174Print basic transfer statistics once per second. 175.El 176.It Cm conv Ns = Ns Ar value Ns Op , Ns Ar value ... 177Where 178.Cm value 179is one of the symbols from the following list. 180.Bl -tag -width "unblock" 181.It Cm ascii , oldascii 182The same as the 183.Cm unblock 184value except that characters are translated from 185.Tn EBCDIC 186to 187.Tn ASCII 188before the 189records are converted. 190(These values imply 191.Cm unblock 192if the operand 193.Cm cbs 194is also specified.) 195There are two conversion maps for 196.Tn ASCII . 197The value 198.Cm ascii 199specifies the recommended one which is compatible with 200.At V . 201The value 202.Cm oldascii 203specifies the one used in historic 204.At 205and 206.No pre- Ns Bx 4.3 reno 207systems. 208.It Cm block 209Treats the input as a sequence of newline or end-of-file terminated variable 210length records independent of input and output block boundaries. 211Any trailing newline character is discarded. 212Each input record is converted to a fixed length output record where the 213length is specified by the 214.Cm cbs 215operand. 216Input records shorter than the conversion record size are padded with spaces. 217Input records longer than the conversion record size are truncated. 218The number of truncated input records, if any, are reported to the standard 219error output at the completion of the copy. 220.It Cm ebcdic , ibm , oldebcdic , oldibm 221The same as the 222.Cm block 223value except that characters are translated from 224.Tn ASCII 225to 226.Tn EBCDIC 227after the 228records are converted. 229(These values imply 230.Cm block 231if the operand 232.Cm cbs 233is also specified.) 234There are four conversion maps for 235.Tn EBCDIC . 236The value 237.Cm ebcdic 238specifies the recommended one which is compatible with 239.At V . 240The value 241.Cm ibm 242is a slightly different mapping, which is compatible with the 243.At V 244.Cm ibm 245value. 246The values 247.Cm oldebcdic 248and 249.Cm oldibm 250are maps used in historic 251.At 252and 253.No pre- Ns Bx 4.3 reno 254systems. 255.It Cm lcase 256Transform uppercase characters into lowercase characters. 257.It Cm pareven , parnone , parodd , parset 258Output data with the specified parity. 259The parity bit on input is stripped unless 260.Tn EBCDIC 261to 262.Tn ASCII 263conversions is also specified. 264.It Cm noerror 265Do not stop processing on an input error. 266When an input error occurs, a diagnostic message followed by the current 267input and output block counts will be written to the standard error output 268in the same format as the standard completion message. 269If the 270.Cm sync 271conversion is also specified, any missing input data will be replaced 272with 273.Dv NUL 274bytes (or with spaces if a block oriented conversion value was 275specified) and processed as a normal input buffer. 276If the 277.Cm fillchar 278option is specified, the fill character provided on the command line 279will override 280the automatic selection of the fill character. 281If the 282.Cm sync 283conversion is not specified, the input block is omitted from the output. 284On input files which are not tapes or pipes, the file offset 285will be positioned past the block in which the error occurred using 286.Xr lseek 2 . 287.It Cm notrunc 288Do not truncate the output file. 289This will preserve any blocks in the output file not explicitly written 290by 291.Nm . 292The 293.Cm notrunc 294value is not supported for tapes. 295.It Cm osync 296Pad the final output block to the full output block size. 297If the input file is not a multiple of the output block size 298after conversion, this conversion forces the final output block 299to be the same size as preceding blocks for use on devices that require 300regularly sized blocks to be written. 301This option is incompatible with use of the 302.Cm bs Ns = Ns Ar n 303block size specification. 304.It Cm sparse 305If one or more output blocks would consist solely of 306.Dv NUL 307bytes, try to seek the output file by the required space instead of 308filling them with 309.Dv NUL Ns s , 310resulting in a sparse file. 311.It Cm swab 312Swap every pair of input bytes. 313If an input buffer has an odd number of bytes, the last byte will be 314ignored during swapping. 315.It Cm sync 316Pad every input block to the input buffer size. 317Spaces are used for pad bytes if a block oriented conversion value is 318specified, otherwise 319.Dv NUL 320bytes are used. 321.It Cm ucase 322Transform lowercase characters into uppercase characters. 323.It Cm unblock 324Treats the input as a sequence of fixed length records independent of input 325and output block boundaries. 326The length of the input records is specified by the 327.Cm cbs 328operand. 329Any trailing space characters are discarded and a newline character is 330appended. 331.El 332.El 333.Pp 334Where sizes or speed are specified, a decimal, octal, or hexadecimal number of 335bytes is expected. 336If the number ends with a 337.Dq Li b , 338.Dq Li k , 339.Dq Li m , 340.Dq Li g , 341.Dq Li t , 342.Dq Li p , 343or 344.Dq Li w , 345the 346number is multiplied by 512, 1024 (1K), 1048576 (1M), 1073741824 (1G), 3471099511627776 (1T), 1125899906842624 (1P) 348or the number of bytes in an integer, respectively. 349Two or more numbers may be separated by an 350.Dq Li x 351to indicate a product. 352.Pp 353When finished, 354.Nm 355displays the number of complete and partial input and output blocks, 356truncated input records and odd-length byte-swapping blocks to the 357standard error output. 358A partial input block is one where less than the input block size 359was read. 360A partial output block is one where less than the output block size 361was written. 362Partial output blocks to tape devices are considered fatal errors. 363Otherwise, the rest of the block will be written. 364Partial output blocks to character devices will produce a warning message. 365A truncated input block is one where a variable length record oriented 366conversion value was specified and the input line was too long to 367fit in the conversion record or was not newline terminated. 368.Pp 369Normally, data resulting from input or conversion or both are aggregated 370into output blocks of the specified size. 371After the end of input is reached, any remaining output is written as 372a block. 373This means that the final output block may be shorter than the output 374block size. 375.Pp 376If 377.Nm 378receives a 379.Dv SIGINFO 380(see the 381.Cm status 382argument for 383.Xr stty 1 ) 384signal, the current input and output block counts will 385be written to the standard error output 386in the same format as the standard completion message. 387If 388.Nm 389receives a 390.Dv SIGINT 391signal, the current input and output block counts will 392be written to the standard error output 393in the same format as the standard completion message and 394.Nm 395will exit. 396.Sh EXIT STATUS 397.Ex -std 398.Sh EXAMPLES 399Check that a disk drive contains no bad blocks: 400.Pp 401.Dl "dd if=/dev/ada0 of=/dev/null bs=1m" 402.Pp 403Do a refresh of a disk drive, in order to prevent presently 404recoverable read errors from progressing into unrecoverable read errors: 405.Pp 406.Dl "dd if=/dev/ada0 of=/dev/ada0 bs=1m" 407.Pp 408Remove parity bit from a file: 409.Pp 410.Dl "dd if=file conv=parnone of=file.txt" 411.Pp 412Check for (even) parity errors on a file: 413.Pp 414.Dl "dd if=file conv=pareven | cmp -x - file" 415.Pp 416To create an image of a Mode-1 CD-ROM, which is a commonly used format 417for data CD-ROM disks, use a block size of 2048 bytes: 418.Pp 419.Dl "dd if=/dev/cd0 of=filename.iso bs=2048" 420.Pp 421Write a filesystem image to a memory stick, padding the end with zeros, 422if necessary, to a 1MiB boundary: 423.Pp 424.Dl "dd if=memstick.img of=/dev/da0 bs=1m conv=noerror,sync" 425.Sh SEE ALSO 426.Xr cp 1 , 427.Xr mt 1 , 428.Xr recoverdisk 1 , 429.Xr tr 1 , 430.Xr geom 4 , 431.Xr trim 8 432.Sh STANDARDS 433The 434.Nm 435utility is expected to be a superset of the 436.St -p1003.2 437standard. 438The 439.Cm files 440and 441.Cm status 442operands and the 443.Cm ascii , 444.Cm ebcdic , 445.Cm ibm , 446.Cm oldascii , 447.Cm oldebcdic 448and 449.Cm oldibm 450values are extensions to the 451.Tn POSIX 452standard. 453.Sh HISTORY 454A 455.Nm 456command appeared in 457.At v5 . 458.Sh BUGS 459Protection mechanisms in the 460.Xr geom 4 461subsystem might prevent the super-user from writing blocks to a disk. 462Instructions for temporarily disabling these protection mechanisms can be 463found in the 464.Xr geom 4 465man page. 466