Provided by: dcfldd_1.9.2-1_amd64 
NAME
dcfldd - enhanced version of dd for forensics and security
SYNOPSIS
dcfldd [OPTION]...
DESCRIPTION
Copy a file, converting and formatting according to the options.
dcfldd was initially developed at Department of Defense Computer Forensics Lab (DCFL).
This tool is based on the dd program with the following additional features:
• Hashing on-the-fly: dcfldd can hash the input data as it is being transferred, helping
to ensure data integrity.
• Status output: dcfldd can update the user of its progress in terms of the amount of
data transferred and how much longer operation will take.
• Flexible disk wipes: dcfldd can be used to wipe disks quickly and with a known pattern
if desired.
• Image/wipe verify: dcfldd can verify that a target drive is a bit-for-bit match of the
specified input file or pattern.
• Multiple outputs: dcfldd can output to multiple files or disks at the same time.
• Split output: dcfldd can split output to multiple files with more configurability than
the split command.
• Piped output and logs: dcfldd can send all its log data and output to commands as well
as files natively.
• When dd uses a default block size (bs, ibs, obs) of 512 bytes, dcfldd uses 32768 bytes
(32 KiB) which is HUGELY more efficient.
• The following options are present in dcfldd but not in dd: ALGORITHMlog:, errlog, hash,
hashconv, hashformat, hashlog, hashlog:, hashwindow, limit, of:, pattern, sizeprobe,
split, splitformat, statusinterval, textpattern, totalhashformat, verifylog,
verifylog:, vf.
dcfldd supports the following letters to specify amount of data: k for kilo, M for Mega, G
for Giga, T for Tera, P for Peta, E for Exa, Z for Zetta and Y for Yotta. E.g. 10M is
equal to 10 MiB. See the BLOCKS AND BYTES section to get other possibilities.
OPTIONS
bs=BYTES
Force ibs=BYTES and obs=BYTES. Default value is 32768 (32KiB). See BLOCKS AND BYTES
section. Warning: the block size will be created in RAM. Make sure you have
sufficient amount of free memory.
cbs=BYTES
Convert BYTES bytes at a time. (see BLOCKS AND BYTES section)
conv=KEYWORDS
Convert the file as per the comma separated keyword list.
count=BLOCKS
Copy only BLOCKS input blocks. (see BLOCKS AND BYTES section)
limit=BYTES
Similar to count but using BYTES instead of BLOCKS. (see BLOCKS AND BYTES section)
ibs=BYTES
Read BYTES bytes at a time. (see BLOCKS AND BYTES section)
if=FILE
Read from FILE instead of stdin. (see BLOCKS AND BYTES section)
obs=BYTES
Write BYTES bytes at a time. (see BLOCKS AND BYTES section)
of=FILE
Write to FILE instead of stdout. NOTE: of=FILE may be used several times to write
output to multiple files simultaneously.
of:=COMMAND
Exec and write output to process COMMAND.
seek=BLOCKS
Skip BLOCKS obs-sized blocks at start of output. (see BLOCKS AND BYTES section)
skip=BLOCKS
Skip BLOCKS ibs-sized blocks at start of input. (see BLOCKS AND BYTES section)
pattern=HEX
Use the specified binary pattern as input. You can use a byte only.
textpattern=TEXT
Use repeating TEXT as input. You can use a character only.
errlog=FILE
Send error messages to FILE as well as stderr.
hash=NAME
Do hash calculation in parallel with the disk reading. Either md5, sha1, sha256,
sha384 or sha512 can be used. Default algorithm is md5. To select multiple
algorithms to run simultaneously enter the names in a comma separated list.
hashlog=FILE
Send hash output to FILE instead of stderr. If you are using multiple hash
algorithms you can send each to a separate file using the convention
ALGORITHMlog=FILE, for example md5log=FILE1, sha1log=FILE2, etc.
hashwindow=BYTES
Perform a hash on every BYTES amount of data. The partial results will be shown in
screen. The default hash is md5 but you can use hash= option to choose other.
hashlog:=COMMAND
Exec and write hashlog to process COMMAND.
ALGORITHMlog:=COMMAND
Also works in the same fashion of hashlog:=COMMAND.
hashconv=[before|after]
Perform the hashing before or after the conversions.
hashformat=FORMAT
Display each hashwindow according to FORMAT the hash format mini-language is
described below.
totalhashformat=FORMAT
Display the total hash value according to FORMAT the hash format mini-language is
described below.
status=[on|off]
Display a continual status message on stderr. Default state is "on".
statusinterval=N
Update the status message every N blocks. Default value is 256.
sizeprobe=[if|of|BYTES]
Determine the size of the input or output file or an amount of BYTES for use with
status messages. This option gives you a percentage indicator around the sizeprobe
value. WARNING: do not use this option against a tape device. (see BLOCKS AND BYTES
section)
split=BYTES
Write every BYTES amount of data to a new file. This operation applies to any
of=FILE that follows (split= must be put before of=). (see BLOCKS AND BYTES
section)
splitformat=[TEXT|MAC|WIN]
The file extension format for split operation. You may use "a" for letters and "n"
for numbers. If you use annn, an extension started as a000 will be appended; the
last possible extension for this format will be z999. splitformat=an will provide
a0, a1, a2, a3, a4, a5, a6, a7, a8, a9, b0, b1, b2, b3... If nothing is specified
the default format is "nnn". NOTE: the split and splitformat options take effect
only for output files (option of=) specified AFTER these options appear in the
command line (e.g. split=50M splitformat=annn of=/tmp/test.iso). Likewise, you may
specify it several times for different output files within the same command line.
You may use as many digits in any combination you would like. E.g. "anaannnaana"
would be valid, but a quite insane (see BLOCKS AND BYTES section). Other possible
approach is MAC. If "MAC" is used, a suffix dmg and several dmgpart will be
appended. In other words, it will generate a partial disk image file, used by the
Mac OS X operating system. dmgpart files are usually provided with a corresponding
dmg file, which is the master file for the split archive. If dmg is opened in Mac
OS X, all dmgpart will be read too. The last option is WIN, which will
automatically output file naming of foo.001, foo.002, ..., foo.999, foo.1000, ....
vf=FILE
Verify that FILE matches the specified input.
verifylog=FILE
Send verify results to FILE instead of stderr.
verifylog:=COMMAND
Exec and write verify results to process COMMAND.
diffwr=[on|off]
Only write to output if destination block content differs. This operation applies
to any of=FILE that follows (diffwr= must be put before any of=).
--help Display a help page and exit.
--version
Output version information and exit.
BLOCKS AND BYTES
BLOCKS and BYTES may be followed by the following multiplicative suffixes: xM M, c 1, w 2,
b 512, kD 1000, k 1024, MD 1,000,000, M 1,048,576, GD 1,000,000,000, G 1,073,741,824, and
so on for T, P, E, Z, Y.
KEYWORDS
Each KEYWORD may be:
ascii From EBCDIC to ASCII.
ebcdic From ASCII to EBCDIC.
ibm From ASCII to alternated EBCDIC.
block Pad newline-terminated records with spaces to cbs-size.
unblock
Replace trailing spaces in cbs-size records with newline.
lcase Change upper case to lower case.
notrunc
Do not truncate the output file.
ucase Change lower case to upper case.
swab Swap every pair of input bytes.
noerror
Continue after read errors.
sync Pad every input block with NULs to ibs-size. When used with block or unblock, pad
with spaces rather than NULs.
FORMAT
The structure of FORMAT may contain any valid text and special variables. The built-in
variables are the following format: #variable_name#. To pass FORMAT strings to the program
from a command line, it may be
necessary to surround your FORMAT strings with "quotes."
The built-in variables are listed below:
window_start
The beginning byte offset of the hashwindow.
window_end
The ending byte offset of the hashwindow.
block_start
The beginning block (by input blocksize) of the window.
block_end
The ending block (by input blocksize) of the hash window.
hash The hash value.
algorithm
The name of the hash algorithm.
For example, the default FORMAT for hashformat and totalhashformat are:
hashformat="#window_start# - #window_end#: #hash#" totalhashformat="Total (#algorithm#): #hash#"
The FORMAT structure accepts the following escape codes:
\n Newline
\t Tab
\r Carriage return
\ Insert the '\' character
## Insert the '#' character as text, not a variable
EXAMPLES
Each following line will create a 100 MiB file containing zeros:
$ dcfldd if=/dev/zero of=test bs=1M count=100
$ dcfldd if=/dev/zero of=test bs=100M count=1
$ dcfldd if=/dev/zero of=test bs=50M count=2
$ dcfldd if=/dev/zero of=test limit=100M
To create a copy (forensics image) from a disk called /dev/sdb inside a file, using
input/output blocks of 4096 bytes (4 KiB) instead of 32 KiB (default):
$ dcfldd if=/dev/sdb bs=4096 of=sdb.img
As the last example, plus calculating MD5 and SHA256 hashes, putting the results inside
sdb.md5 and sdb.sha256. It is very useful for forensics works because the hashes will be
processed in real time, avoiding a waste of time to make something as 'dd + md5 + sha256'.
Considering that I/O disk is very slow and RAM is very fast, the hashes will be
calculated, bit per bit in memory, when the next portion of the disk is read. When all
disk was read, all hashes are now ready.
$ dcfldd if=/dev/sdb bs=4096 hash=md5,sha256 md5log=sdb.md5 sha256log=sdb.sha256 of=sdb.img
To validate the image file against the original source:
$ dcfldd if=/dev/sdb vf=sdb.img
Splitting the image in 500 MiB slices, using the default bs value (32 KiB). Note that
split= must be put before of= to work:
$ dcfldd if=/dev/sdb split=500M of=sdb.img
At the last example, using from a0000 up to z9999 as suffix for each split file:
$ dcfldd if=/dev/sdb split=500M splitformat=annnn of=sdb.img
Now, dcfldd will work byte per byte (bs=1) and will hop 1056087439 bytes. After this,
dcfldd will collect 200000 bytes and write the results to a file called airplane.jpg.
$ dcfldd if=/dev/sda3 bs=1 skip=1056087439 count=200000 of=airplane.jpg
In the last example, the same result could be obtained using "limit" instead of "count".
The main difference is that count uses 200000*bs and limit uses 200000 bytes (regardless
of the value declared in bs option):
$ dcfldd if=/dev/sda3 bs=1 skip=1056087439 limit=200000 of=airplane.jpg
To write something inside a file, you can use seek. Suppose you want to write a message
from a file called message.txt inside a file called target.iso, hopping 200000 bytes from
start of file:
$ dcfldd if=message.txt bs=1 seek=200000 of=target.iso
dcfldd also can send a result to be processed by an external command:
$ dcfldd if=text.txt of:="cat | sort -u"
To convert a file from ASCII to EBCDIC:
$ dcfldd if=text.asc conv=ebcdic of=text.ebcdic
To convert a file from EBCDIC to ASCII:
$ dcfldd if=text.ebcdic conv=ascii of=text.asc
SEE ALSO
dd(1)
REPORTING BUGS
Report bugs at https://github.com/resurrecting-open-source-projects/dcfldd/issues
AUTHORS
dcfldd was originally written by Nicholas Harbour. Currently is maintained by some
volunteers.
GNU dd was written by Paul Rubin, David MacKenzie and Stuart Kemp.
This manpage was written by dd authors, Nicholas Harbour, Joao Eriberto Mota Filho and
others.