DD(1) General Commands Manual DD(1)

# [NAME](#NAME)

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

# [SYNOPSIS](#SYNOPSIS)

**dd** \[OPERAND]...  
**dd** OPTION

# [DESCRIPTION](#DESCRIPTION)

Copy, and optionally convert, a file system resource

# [OPTIONS](#OPTIONS)

[**-h**, **--help**](#h)

Print help

[**-V**, **--version**](#V)

Print version

\[*operands*]

# [EXTRA](#EXTRA)

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 : convert 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 is 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.

# [VERSION](#VERSION)

v(uutils coreutils) 0.12.0

2026-10-12

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Document: dd(1) from uutils 0.12.0-r3 (Chainguard OS)
Source: https://github.com/uutils/coreutils