1dd(1M) System Administration Commands dd(1M)
2
6 dd - convert and copy a file
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9 /usr/bin/dd [operand=value]...
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13 The dd utility copies the specified input file to the specified output
14 with possible conversions. The standard input and output are used by
15 default. The input and output block sizes may be specified to take
16 advantage of raw physical I/O. Sizes are specified in bytes; a number
17 may end with k, b, or w to specify multiplication by 1024, 512, or 2,
18 respectively. Numbers may also be separated by x to indicate multipli‐
19 cation.
20 The dd utility reads the input one block at a time, using the specified
23 input block size. dd then processes the block of data actually
24 returned, which could be smaller than the requested block size. dd
25 applies any conversions that have been specified and writes the result‐
26 ing data to the output in blocks of the specified output block size.
27 cbs is used only if ascii, asciib, unblock, ebcdic, ebcdicb, ibm, ibmb,
30 or block conversion is specified. In the first two cases, cbs charac‐
31 ters are copied into the conversion buffer, any specified character
32 mapping is done, trailing blanks are trimmed, and a NEWLINE is added
33 before sending the line to output. In the last three cases, characters
34 up to NEWLINE are read into the conversion buffer and blanks are added
35 to make up an output record of size cbs. ASCII files are presumed to
36 contain NEWLINE characters. If cbs is unspecified or 0, the ascii,
37 asciib, ebcdic, ebcdicb, ibm, and ibmb options convert the character
38 set without changing the input file's block structure. The unblock and
39 block options become a simple file copy.
40 After completion, dd reports the number of whole and partial input and
43 output blocks.
44
46 The following operands are supported:
47 if=file
49 Specifies the input path. Standard input is the default.
51 of=file
54 Specifies the output path. Standard output is the default. If the
56 seek=expr conversion is not also specified, the output file will be
57 truncated before the copy begins, unless conv=notrunc is specified.
58 If seek=expr is specified, but conv=notrunc is not, the effect of
59 the copy will be to preserve the blocks in the output file over
60 which dd seeks, but no other portion of the output file will be
61 preserved. (If the size of the seek plus the size of the input file
62 is less than the previous size of the output file, the output file
63 is shortened by the copy.)
64 ibs=n
67 Specifies the input block size in n bytes (default is 512).
69 obs=n
72 Specifies the output block size in n bytes (default is 512).
74 bs=n
77 Sets both input and output block sizes to n bytes, superseding ibs=
79 and obs=. If no conversion other than sync, noerror, and notrunc is
80 specified, each input block is copied to the output as a single
81 block without aggregating short blocks.
82 cbs=n
85 Specifies the conversion block size for block and unblock in bytes
87 by n (default is 0). If cbs= is omitted or given a value of 0,
88 using block or unblock produces unspecified results.
89 This option is used only if ASCII or EBCDIC conversion is speci‐
91 fied. For the ascii and asciib operands, the input is handled as
92 described for the unblock operand except that characters are con‐
93 verted to ASCII before the trailing SPACE characters are deleted.
94 For the ebcdic, ebcdicb, ibm, and ibmb operands, the input is han‐
95 dled as described for the block operand except that the characters
96 are converted to EBCDIC or IBM EBCDIC after the trailing SPACE
97 characters are added.
98 files=n
101 Copies and concatenates n input files before terminating (makes
103 sense only where input is a magnetic tape or similar device).
104 skip=n
107 Skips n input blocks (using the specified input block size) before
109 starting to copy. On seekable files, the implementation reads the
110 blocks or seeks past them. On non-seekable files, the blocks are
111 read and the data is discarded.
112 iseek=n
115 Seeks n blocks from beginning of input file before copying (appro‐
117 priate for disk files, where skip can be incredibly slow).
118 oseek=n
121 Seeks n blocks from beginning of output file before copying.
123 seek=n
126 Skips n blocks (using the specified output block size) from begin‐
128 ning of output file before copying. On non-seekable files, existing
129 blocks are read and space from the current end-of-file to the spec‐
130 ified offset, if any, is filled with null bytes. On seekable files,
131 the implementation seeks to the specified offset or reads the
132 blocks as described for non-seekable files.
133 count=n
136 Copies only n input blocks.
138 conv=value[,value...]
141 Where values are comma-separated symbols from the following list:
143 ascii Converts EBCDIC to ASCII.
145 asciib Converts EBCDIC to ASCII using BSD-compatible character
148 translations.
149 ebcdic Converts ASCII to EBCDIC. If converting fixed-length
152 ASCII records without NEWLINEs, sets up a pipeline with
153 dd conv=unblock beforehand.
154 ebcdicb Converts ASCII to EBCDIC using BSD-compatible character
157 translations. If converting fixed-length ASCII records
158 without NEWLINEs, sets up a pipeline with dd
159 conv=unblock beforehand.
160 ibm Slightly different map of ASCII to EBCDIC. If converting
163 fixed-length ASCII records without NEWLINEs, sets up a
164 pipeline with dd conv=unblock beforehand.
165 ibmb Slightly different map of ASCII to EBCDIC using BSD-com‐
168 patible character translations. If converting fixed-
169 length ASCII records without NEWLINEs, sets up a pipe‐
170 line with dd conv=unblock beforehand.
171 The ascii (or asciib), ebcdic (or ebcdicb), and ibm (or ibmb) val‐
173 ues are mutually exclusive.
174 block Treats the input as a sequence of NEWLINE-terminated or
176 EOF-terminated variable-length records independent of
177 the input block boundaries. Each record is converted to
178 a record with a fixed length specified by the conversion
179 block size. Any NEWLINE character is removed from the
180 input line. SPACE characters are appended to lines that
181 are shorter than their conversion block size to fill the
182 block. Lines that are longer than the conversion block
183 size are truncated to the largest number of characters
184 that will fit into that size. The number of truncated
185 lines is reported.
186 unblock Converts fixed-length records to variable length. Reads
189 a number of bytes equal to the conversion block size (or
190 the number of bytes remaining in the input, if less than
191 the conversion block size), delete all trailing SPACE
192 characters, and append a NEWLINE character.
193 The block and unblock values are mutually exclusive.
195 lcase Maps upper-case characters specified by the LC_CTYPE key‐
197 word tolower to the corresponding lower-case character.
198 Characters for which no mapping is specified are not modi‐
199 fied by this conversion.
200 ucase Maps lower-case characters specified by the LC_CTYPE key‐
203 word toupper to the corresponding upper-case character.
204 Characters for which no mapping is specified are not modi‐
205 fied by this conversion.
206 The lcase and ucase symbols are mutually exclusive.
208 swab Swaps every pair of input bytes. If the current input
210 record is an odd number of bytes, the last byte in the
211 input record is ignored.
212 noerror Does not stop processing on an input error. When an
215 input error occurs, a diagnostic message is written on
216 standard error, followed by the current input and output
217 block counts in the same format as used at completion.
218 If the sync conversion is specified, the missing input
219 is replaced with null bytes and processed normally. Oth‐
220 erwise, the input block will be omitted from the output.
221 notrunc Does not truncate the output file. Preserves blocks in
224 the output file not explicitly written by this invoca‐
225 tion of dd. (See also the preceding of=file operand.)
226 sync Pads every input block to the size of the ibs= buffer,
229 appending null bytes. (If either block or unblock is
230 also specified, appends SPACE characters, rather than
231 null bytes.)
232 If operands other than conv= are specified more than once, the last
237 specified operand=value is used.
238 For the bs=, cbs=, ibs=, and obs= operands, the application must supply
241 an expression specifying a size in bytes. The expression, expr, can be:
242 1. a positive decimal number
244 2. a positive decimal number followed by k, specifying multi‐
246 plication by 1024
247 3. a positive decimal number followed by b, specifying multi‐
249 plication by 512
250 4. two or more positive decimal numbers (with or without k or
252 b) separated by x, specifying the product of the indicated
253 values.
254 All of the operands will be processed before any input is read.
257
259 See largefile(5) for the description of the behavior of dd when encoun‐
260 tering files greater than or equal to 2 Gbyte ( 2^31 bytes).
261
263 Example 1 Copying from one tape drive to another
264 The following example copies from tape drive 0 to tape drive 1, using a
267 common historical device naming convention.
268 example% dd if=/dev/rmt/0h of=/dev/rmt/1h
271 Example 2 Stripping the first 10 bytes from standard input
275 The following example strips the first 10 bytes from standard input:
278 example% dd ibs=10 skip=1
281 Example 3 Reading a tape into an ASCII file
285 This example reads an EBCDIC tape blocked ten 80-byte EBCDIC card
288 images per block into the ASCII file x:
289 example% dd if=/dev/tape of=x ibs=800 cbs=80 conv=ascii,lcase
292 Example 4 Using conv=sync to write to tape
296 The following example uses conv=sync when writing to a tape:
299 example% tar cvf - . | compress | dd obs=1024k of=/dev/rmt/0 conv=sync
302
306 See environ(5) for descriptions of the following environment variables
307 that affect the execution of dd: LANG, LC_ALL, LC_CTYPE, LC_MESSAGES,
308 and NLSPATH.
309
311 The following exit values are returned:
312 0 The input file was copied successfully.
314 >0 An error occurred.
317 If an input error is detected and the noerror conversion has not been
321 specified, any partial output block will be written to the output file,
322 a diagnostic message will be written, and the copy operation will be
323 discontinued. If some other error is detected, a diagnostic message
324 will be written and the copy operation will be discontinued.
325
327 See attributes(5) for descriptions of the following attributes:
328 ┌─────────────────────────────┬─────────────────────────────┐
333 │ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
334 ├─────────────────────────────┼─────────────────────────────┤
335 │Availability │SUNWcsu │
336 ├─────────────────────────────┼─────────────────────────────┤
337 │Interface Stability │Standard │
338 └─────────────────────────────┴─────────────────────────────┘
339
341 cp(1), sed(1), tr(1), attributes(5), environ(5), largefile(5), stan‐
342 dards(5)
343
345 f+p records in(out) numbers of full and partial blocks read(written)
346
349 Do not use dd to copy files between file systems having different block
350 sizes.
351 Using a blocked device to copy a file will result in extra nulls being
354 added to the file to pad the final block to the block boundary.
355 When dd reads from a pipe, using the ibs=X and obs=Y operands, the
358 output will always be blocked in chunks of size Y. When bs=Z is used,
359 the output blocks will be whatever was available to be read from the
360 pipe at the time.
361 When using dd to copy files to a tape device, the file size must be a
364 multiple of the device sector size (for example, 512 Kbyte). To copy
365 files of arbitrary size to a tape device, use tar(1) or cpio(1).
366 For SIGINT, dd writes status information to standard error before exit‐
369 ing. It takes the standard action for all other signals.
370SunOS 5.11 16 Sep 1996 dd(1M)