dd(1) General Commands Manual dd(1)

dd - Copy, and optionally convert, a file system resource

dd [-h|--help] [-V|--version] [operands]

Copy, and optionally convert, a file system resource

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[operands]

### Operands

- bs=BYTES : read and write up to BYTES bytes at a time (default: 512);
overwrites ibs and obs. - cbs=BYTES : the 'conversion block size' in bytes. Applies to the
conv=block, and conv=unblock operations. - conv=CONVS : a comma-separated list of conversion options or (for legacy
reasons) file flags. - count=N : stop reading input after N ibs-sized read operations rather
than proceeding until EOF. See iflag=count_bytes if stopping after N bytes
is preferred - ibs=N : the size of buffer used for reads (default: 512) - if=FILE : the file used for input. When not specified, stdin is used instead - iflag=FLAGS : a comma-separated list of input flags which specify how the
input source is treated. FLAGS may be any of the input-flags or general-flags
specified below. - skip=N (or iseek=N) : skip N ibs-sized records into input before beginning
copy/convert operations. See iflag=seek_bytes if seeking N bytes is preferred. - obs=N : the size of buffer used for writes (default: 512) - of=FILE : the file used for output. When not specified, stdout is used
instead - oflag=FLAGS : comma separated list of output flags which specify how the
output source is treated. FLAGS may be any of the output flags or general
flags specified below - seek=N (or oseek=N) : seeks N obs-sized records into output before
beginning copy/convert operations. See oflag=seek_bytes if seeking N bytes is
preferred - status=LEVEL : controls whether volume and performance stats are written to
stderr.


When unspecified, dd will print stats upon completion. An example is below.


plain
6+0 records in
16+0 records out
8192 bytes (8.2 kB, 8.0 KiB) copied, 0.00057009 s,
14.4 MB/s


The first two lines are the 'volume' stats and the final line is the
'performance' stats.
The volume stats indicate the number of complete and partial ibs-sized reads,
or obs-sized writes that took place during the copy. The format of the volume
stats is <complete>+<partial>. If records have been truncated (see
conv=block), the volume stats will contain the number of truncated records.


Possible LEVEL values are:
- progress : Print periodic performance stats as the copy proceeds.
- noxfer : Print final volume stats, but not performance stats.
- none : Do not print any stats.


Printing performance stats is also triggered by the INFO signal (where supported),
or the USR1 signal. Setting the POSIXLY_CORRECT environment variable to any value
(including an empty value) will cause the USR1 signal to be ignored.

### Conversion Options

- ascii : convert from EBCDIC to ASCII. This is the inverse of the ebcdic
option. Implies conv=unblock. - ebcdic : convert from ASCII to EBCDIC. This is the inverse of the ascii
option. Implies conv=block. - ibm : convert from ASCII to EBCDIC, applying the conventions for [, ]
and ~ specified in POSIX. Implies conv=block.

- ucase : convert from lower-case to upper-case. - lcase : converts from upper-case to lower-case.

- block : for each newline less than the size indicated by cbs=BYTES, remove
the newline and pad with spaces up to cbs. Lines longer than cbs are truncated. - unblock : for each block of input of the size indicated by cbs=BYTES, remove
right-trailing spaces and replace with a newline character.

- sparse : attempts to seek the output when an obs-sized block consists of
only zeros. - swab : swaps each adjacent pair of bytes. If an odd number of bytes is
present, the final byte is omitted. - sync : pad each ibs-sided block with zeros. If block or unblock is
specified, pad with spaces instead. - excl : the output file must be created. Fail if the output file is already
present. - nocreat : the output file will not be created. Fail if the output file in
not already present. - notrunc : the output file will not be truncated. If this option is not
present, output will be truncated when opened. - noerror : all read errors will be ignored. If this option is not present,
dd will only ignore Error::Interrupted. - fdatasync : data will be written before finishing. - fsync : data and metadata will be written before finishing.

### Input flags

- count_bytes : a value to count=N will be interpreted as bytes. - skip_bytes : a value to skip=N will be interpreted as bytes. - fullblock : wait for ibs bytes from each read. zero-length reads are still
considered EOF.

### Output flags

- append : open file in append mode. Consider setting conv=notrunc as well. - seek_bytes : a value to seek=N will be interpreted as bytes.

### General Flags

- direct : use direct I/O for data. - directory : fail unless the given input (if used as an iflag) or
output (if used as an oflag) is a directory. - dsync : use synchronized I/O for data. - sync : use synchronized I/O for data and metadata. - nonblock : use non-blocking I/O. - noatime : do not update access time. - nocache : request that OS drop cache. - noctty : do not assign a controlling tty. - nofollow : do not follow system links.

v0.0.27

dd 0.0.27