dd

v0.0.26

dd [OPERAND]...
dd OPTION

Copy, and optionally convert, a file system resource

Options

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.
```
  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.

Examples

Make a bootable USB drive from an isohybrid file (such as archlinux-xxx.iso):

dd if={{path/to/file.iso}} of=/dev/{{usb_drive}}

Clone a drive to another drive with 4 MiB block size and flush writes before the command terminates:

dd bs={{4194304}} conv={{fsync}} if=/dev/{{source_drive}} of=/dev/{{dest_drive}}

Generate a file with a specific number of random bytes by using kernel random driver:

dd bs={{100}} count={{1}} if=/dev/urandom of={{path/to/random_file}}

Benchmark the sequential write performance of a disk:

dd bs={{1024}} count={{1000000}} if=/dev/zero of={{path/to/file_1GB}}

Create a system backup and save it into an IMG file (can be restored later by swapping if and of):

dd if={{/dev/drive_device}} of={{path/to/file.img}}

The examples are provided by the tldr-pages project under the CC BY 4.0 License.

Please note that, as uutils is a work in progress, some examples might fail.

uutils Documentation