dd - dd
NAME SYNOPSIS DESCRIPTION Arguments: OPTIONSNAME
dd − dd
SYNOPSIS
dd [OPERAND]...
DESCRIPTION
Copy, and optionally convert, a file system resource
dd OPTION
Arguments:
[operands]...
OPTIONS
−h, −−help
Print help
−V, −−version
Print version
### 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.