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System Administration Commands dd(1M)
NAME
dd - convert and copy a file
SYNOPSIS
/usr/bin/dd [operand=value...]
DESCRIPTION
The dd utility copies the specified input file to the speci-
fied output with possible conversions. The standard input
and output are used by default. The input and output block
sizes may be specified to take advantage of raw physical
I/O. Sizes are specified in bytes; a number may end with k,
b, or w to specify multiplication by 1024, 512, or 2,
respectively. Numbers may also be separated by x to indicate
multiplication.
The dd utility reads the input one block at a time, using
the specified input block size. dd then processes the block
of data actually returned, which could be smaller than the
requested block size. dd applies any conversions that have
been specified and writes the resulting data to the output
in blocks of the specified output block size.
cbs is used only if ascii, asciib, unblock, ebcdic, ebcdicb,
ibm, ibmb, or block conversion is specified. In the first
two cases, cbs characters are copied into the conversion
buffer, any specified character mapping is done, trailing
blanks are trimmed, and a NEWLINE is added before sending
the line to output. In the last three cases, characters up
to NEWLINE are read into the conversion buffer and blanks
are added to make up an output record of size cbs. ASCII
files are presumed to contain NEWLINE characters. If cbs is
unspecified or 0, the ascii, asciib, ebcdic, ebcdicb, ibm,
and ibmb options convert the character set without changing
the input file's block structure. The unblock and block
options become a simple file copy.
After completion, dd reports the number of whole and partial
input and output blocks.
OPERANDS
The following operands are supported:
if=file
Specifies the input path. Standard input is the default.
of=file
Specifies the output path. Standard output is the
SunOS 5.10 Last change: 16 Sep 1996 1
System Administration Commands dd(1M)
default. If the seek=expr conversion is not also speci-
fied, the output file will be truncated before the copy
begins, unless conv=notrunc is specified. If seek=expr
is specified, but conv=notrunc is not, the effect of the
copy will be to preserve the blocks in the output file
over which dd seeks, but no other portion of the output
file will be preserved. (If the size of the seek plus
the size of the input file is less than the previous
size of the output file, the output file is shortened by
the copy.)
ibs=n
Specifies the input block size in n bytes (default is
512).
obs=n
Specifies the output block size in n bytes (default is
512).
bs=n
Sets both input and output block sizes to n bytes,
superseding ibs= and obs=. If no conversion other than
sync, noerror, and notrunc is specified, each input
block is copied to the output as a single block without
aggregating short blocks.
cbs=n
Specifies the conversion block size for block and
unblock in bytes by n (default is 0). If cbs= is omitted
or given a value of 0, using block or unblock produces
unspecified results.
This option is used only if ASCII or EBCDIC conversion
is specified. For the ascii and asciib operands, the
input is handled as described for the unblock operand
except that characters are converted to ASCII before the
trailing SPACE characters are deleted. For the ebcdic,
ebcdicb, ibm, and ibmb operands, the input is handled as
described for the block operand except that the charac-
ters are converted to EBCDIC or IBM EBCDIC after the
SunOS 5.10 Last change: 16 Sep 1996 2
System Administration Commands dd(1M)
trailing SPACE characters are added.
files=n
Copies and concatenates n input files before terminating
(makes sense only where input is a magnetic tape or
similar device).
skip=n
Skips n input blocks (using the specified input block
size) before starting to copy. On seekable files, the
implementation reads the blocks or seeks past them. On
non-seekable files, the blocks are read and the data is
discarded.
iseek=n
Seeks n blocks from beginning of input file before copy-
ing (appropriate for disk files, where skip can be
incredibly slow).
oseek=n
Seeks n blocks from beginning of output file before
copying.
seek=n
Skips n blocks (using the specified output block size)
from beginning of output file before copying. On non-
seekable files, existing blocks are read and space from
the current end-of-file to the specified offset, if any,
is filled with null bytes. On seekable files, the imple-
mentation seeks to the specified offset or reads the
blocks as described for non-seekable files.
count=n
Copies only n input blocks.
SunOS 5.10 Last change: 16 Sep 1996 3
System Administration Commands dd(1M)
conv=value[,value...]
Where values are comma-separated symbols from the fol-
lowing list:
ascii Converts EBCDIC to ASCII.
asciib Converts EBCDIC to ASCII using BSD-
compatible character translations.
ebcdic Converts ASCII to EBCDIC. If converting
fixed-length ASCII records without NEW-
LINEs, sets up a pipeline with dd
conv=unblock beforehand.
ebcdicb Converts ASCII to EBCDIC using BSD-
compatible character translations. If
converting fixed-length ASCII records
without NEWLINEs, sets up a pipeline
with dd conv=unblock beforehand.
ibm Slightly different map of ASCII to
EBCDIC. If converting fixed-length ASCII
records without NEWLINEs, sets up a
pipeline with dd conv=unblock before-
hand.
ibmb Slightly different map of ASCII to
EBCDIC using BSD-compatible character
translations. If converting fixed-length
ASCII records without NEWLINEs, sets up
a pipeline with dd conv=unblock before-
hand.
The ascii (or asciib), ebcdic (or ebcdicb), and ibm (or
ibmb) values are mutually exclusive.
SunOS 5.10 Last change: 16 Sep 1996 4
System Administration Commands dd(1M)
block Treats the input as a sequence of
NEWLINE-terminated or EOF-terminated
variable-length records independent of
the input block boundaries. Each record
is converted to a record with a fixed
length specified by the conversion block
size. Any NEWLINE character is removed
from the input line. SPACE characters
are appended to lines that are shorter
than their conversion block size to fill
the block. Lines that are longer than
the conversion block size are truncated
to the largest number of characters that
will fit into that size. The number of
truncated lines is reported.
unblock Converts fixed-length records to vari-
able length. Reads a number of bytes
equal to the conversion block size (or
the number of bytes remaining in the
input, if less than the conversion block
size), delete all trailing SPACE charac-
ters, and append a NEWLINE character.
The block and unblock values are mutually exclusive.
lcase Maps upper-case characters specified by
the LC_CTYPE keyword tolower to the
corresponding lower-case character.
Characters for which no mapping is
specified are not modified by this
conversion.
ucase Maps lower-case characters specified by
the LC_CTYPE keyword toupper to the
corresponding upper-case character.
Characters for which no mapping is
specified are not modified by this
conversion.
The lcase and ucase symbols are mutually exclusive.
swab Swaps every pair of input bytes. If the
current input record is an odd number of
SunOS 5.10 Last change: 16 Sep 1996 5
System Administration Commands dd(1M)
bytes, the last byte in the input record
is ignored.
noerror Does not stop processing on an input
error. When an input error occurs, a
diagnostic message is written on stan-
dard error, followed by the current
input and output block counts in the
same format as used at completion. If
the sync conversion is specified, the
missing input is replaced with null
bytes and processed normally. Otherwise,
the input block will be omitted from the
output.
notrunc Does not truncate the output file.
Preserves blocks in the output file not
explicitly written by this invocation of
dd. (See also the preceding of=file
operand.)
sync Pads every input block to the size of
the ibs= buffer, appending null bytes.
(If either block or unblock is also
specified, appends SPACE characters,
rather than null bytes.)
If operands other than conv= are specified more than once,
the last specified operand=value is used.
For the bs=, cbs=, ibs=, and obs= operands, the application
must supply an expression specifying a size in bytes. The
expression, expr, can be:
1. a positive decimal number
2. a positive decimal number followed by k, specifying mul-
tiplication by 1024
3. a positive decimal number followed by b, specifying mul-
tiplication by 512
SunOS 5.10 Last change: 16 Sep 1996 6
System Administration Commands dd(1M)
4. two or more positive decimal numbers (with or without k
or b) separated by x, specifying the product of the
indicated values.
All of the operands will be processed before any input is
read.
USAGE
See largefile(5) for the description of the behavior of dd
when encountering files greater than or equal to 2 Gbyte ( 2
**31 bytes).
EXAMPLES
Example 1: Copying from one tape drive to another
The following example copies from tape drive 0 to tape drive
1, using a common historical device naming convention.
example% dd if=/dev/rmt/0h of=/dev/rmt/1h
Example 2: Stripping the first 10 bytes from standard input
The following example strips the first 10 bytes from stan-
dard input:
example% dd ibs=10 skip=1
Example 3: Reading a tape into an ASCII file
This example reads an EBCDIC tape blocked ten 80-byte EBCDIC
card images per block into the ASCII file x:
example% dd if=/dev/tape of=x ibs=800 cbs=80 conv=ascii,lcase
Example 4: Using conv=sync to write to tape
The following example uses conv=sync when writing to a tape:
example% tar cvf - . | compress | dd obs=1024k of=/dev/rmt/0 conv=sync
ENVIRONMENT VARIABLES
See environ(5) for descriptions of the following environment
variables that affect the execution of dd: LANG, LC_ALL,
LC_CTYPE, LC_MESSAGES, and NLSPATH.
EXIT STATUS
The following exit values are returned:
0 The input file was copied successfully.
SunOS 5.10 Last change: 16 Sep 1996 7
System Administration Commands dd(1M)
>0 An error occurred.
If an input error is detected and the noerror conversion has
not been specified, any partial output block will be written
to the output file, a diagnostic message will be written,
and the copy operation will be discontinued. If some other
error is detected, a diagnostic message will be written and
the copy operation will be discontinued.
ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| Availability | SUNWcsu |
|_____________________________|_____________________________|
| Interface Stability | Standard |
|_____________________________|_____________________________|
SEE ALSO
cp(1), sed(1), tr(1), attributes(5), environ(5), large-
file(5), standards(5)
DIAGNOSTICS
f+p records in(out) numbers of full and partial blocks
read(written)
NOTES
Do not use dd to copy files between file systems having dif-
ferent block sizes.
Using a blocked device to copy a file will result in extra
nulls being added to the file to pad the final block to the
block boundary.
When dd reads from a pipe, using the ibs=X and obs=Y
operands, the output will always be blocked in chunks of
size Y. When bs=Z is used, the output blocks will be what-
ever was available to be read from the pipe at the time.
When using dd to copy files to a tape device, the file size
must be a multiple of the device sector size (for example,
512 Kbyte). To copy files of arbitrary size to a tape dev-
ice, use tar(1) or cpio(1).
SunOS 5.10 Last change: 16 Sep 1996 8
System Administration Commands dd(1M)
For SIGINT, dd writes status information to standard error
before exiting. It takes the standard action for all other
signals.
SunOS 5.10 Last change: 16 Sep 1996 9
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