dd

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) and show the progress:

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

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, save it into an IMG file (can be restored later by swapping if and of), and show the progress:

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

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.