Data Duplicator, convert and copy a file, write disk headers, boot records, create a boot floppy. dd can make an exact clone of an (unmounted) disk, this will include all blank space so the output destination must be at least as large as the input.
Syntax
dd [operands ...]
operands
bs=n Set both input and output block size to n bytes, superseding the
ibs and obs operands. If no conversion values other than
noerror, notrunc or sync are specified, then each input block is
copied to the output as a single block without any aggregation
of short blocks.
cbs=n Set the conversion record size to n bytes. The conversion
record size is required by the record oriented conversion values.
conv=CONV[,CONV ...]
Convert the file as per the comma separated symbol list, see CONVs.
count=n Copy only n input blocks.
ibs=n Set the input block size to n bytes instead of the default 512.
if=file Read input from file instead of the standard input.
iflag=flag[,flag...]
See FLAGs
iseek=n Seek on the input file n blocks. This is synonymous with skip=n.
obs=n Set the output block size to n bytes instead of the default 512.
of=file Write output to file instead of the standard output. Any regular
output file is truncated unless the notrunc conversion value
is specified. If an initial portion of the output file is
seeked past (see the oseek operand), the output file is truncated
at that point.
oflag=flag[,flag...]
See FLAGs
oseek=n Seek on the output file n blocks.
This is synonymous with seek=n.
seek=n Seek n blocks from the beginning of the output before copying. On non-tape devices,
an lseek(2) operation is used. Otherwise, existing blocks are read and the
data discarded. If the user does not have read permission for the tape, it is positioned
using the tape ioctl(2) function calls. If the seek operation is past the end of file,
space from the current end of file to the specified offset is filled with blocks of NUL bytes.
skip=n Skip n blocks from the beginning of the input before copying. On input which supports seeks,
an lseek(2) operation is used. Otherwise, input data is read and discarded. For pipes, the
correct number of bytes is read. For all other devices, the correct number of blocks is
read without distinguishing between a partial or complete block being read.
status=value
Where value is one of the following:
noxfer Do not print the transfer statistics as the last line of status output.
none Do not print the status output.
Error messages are shown; informational messages are not.
progress Print basic transfer statistics once per second.
Each FLAG symbol may be:
append append mode (makes sense only for output; conv=notrunc suggested).
direct use direct I/O for data.
directory fail unless a directory.
dsync use synchronized I/O for data.
sync Use synchronized I/O for data, but also for metadata.
direct Set F_NOCACHE on the output file to make writes bypass any local caching.
fullblock Accumulate full blocks of input (iflag only).
nonblock use non-blocking I/O.
noatime do not update access time.
nocache Request to drop cache. See also oflag=sync
noctty Do not assign controlling terminal from file.
nofollow Do not follow symlinks.
Each CONV symbol may be:
ascii From EBCDIC to ASCII.
ebcdic From ASCII to EBCDIC.
excl Fail if the output file already exists.
ibm From ASCII to alternate 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.
ucase Change lower case to upper case.
nocreat Do not create the output file.
notrunc Do not truncate the output file.
noerror Continue after read errors.
fdatasync Physically write output file data before finishing.
fsync Physically write output file data before finishing, but also write metadata.
sparse Try to seek rather than write all-NUL output blocks.
swab Swap every pair of input bytes.
sync Pad every input block with NULs to ibs-size; when used with block or unblock,
pad with spaces rather than NULs.
The numeric-valued options (N and BYTES) may be followed by the following multiplicative suffixes: c=1, w=2, b=512, kB=1000, K=1024, MB=1000*1000, M=1024*1024, xM=M, GB=1000*1000*1000, G=1024*1024*1024, and so on for T, P, E, Z, Y, R, Q.
Binary prefixes can be used, too: KiB=K, MiB=M, and so on. If N ends in 'B', it counts bytes not blocks.
When finished, dd displays the number of complete and partial input and output blocks, truncated input records and odd-length byte-swapping blocks to the standard error output. A partial input block is one where less than the input block size was read. A partial output block is one where less than the output block size was written. Partial output blocks to tape devices are considered fatal errors. Otherwise, the rest of the block will be written. Partial output blocks to character devices will produce a warning message. A truncated input block is one where a variable length record oriented conversion value was specified and the input line was too long to fit in the conversion record or was not newline ter- minated.
Normally, data resulting from input or conversion or both are aggregated into output blocks of the specified size. After the end of input is reached, any remaining output is written as a block. This means that the final output block might be shorter than the output block size.
The name dd is thought to be an allusion to the DD statement found in IBM’s Job Control Language (JCL), where the acronym stands for "Data Description". The lack of any confirmation prompt before truncating the output file has popularised the jocular name 'Data Destroyer'.
If dd receives a SIGINFO signal, the current input and output block counts will be written to the standard error output in the same format as the standard completion message. If dd receives a SIGINT signal, the current input and output block counts will be written to the standard error output in the same format as the standard completion message and dd will exit.
dd can copy a smaller drive to a larger one, but can’t copy a larger drive to a smaller one.
When cloning a disk drive, its a good idea to list the partitions before and afterwards using sudo fdisk –l
An empty/unformatted drive will appear as "Disk dev/sdn doesn’t contain a vaild partition table".
The dd utility exits 0 on success, and >0 if an error occurs.
Clone the drive sda onto drive sdb:
$ dd if=/dev/sda of=/dev/sdb
Clone the drive hda onto an image file:
$ dd if=/dev/hda of=/image.img
Copy a CD or DVD disc to a .iso image file, first unmounting the disc:
sudo umount /dev/dvd-device
dd if=/dev/dvd-device of=dvd.iso bs=2048 conv=sync,notrunc
# dvd-device will typically be dvd for a dvd disc or cdrom for a cdrom disc.
Clone a hard drive to a zipped image file in 100Mb blocks:
$ dd if=/dev/hda bs=100M | gzip -c > /image.img
Create a 10 KB file filled with random data (10 x 1K blocks):
$ dd if=/dev/random of=random.bin bs=1024 count=10
Create an 8 GB empty file (also known as "sparse file") called spacer.img:
$ dd if=/dev/zero of=spacer.img bs=1 count=0 seek=8G
Completely wipe the hard drive hdz by overwriting it with random data:
$ dd if=/dev/urandom of=/dev/hdz
Create a boot floppy:
$ dd if=boot.img of=/dev/fd0 bs=1440
“All of my servers have an 8GB empty spacer.img file that does absolutely nothing except take up space. That way in a moment of full-disk crisis I can simply delete it and buy myself some critical time” ~ Brian Schrader
CodeCoffee.com - dd examples.
cp - Copy one or more files to another location.
cpio - Copy files to and from archives.
ddrescue - Data recovery tool.
install - Copy files and set attributes.
lsblk - List block devices.
mtools - Manipulate MS-DOS files.
sum - Print a checksum for a file.
tr - Translate, squeeze, and/or delete characters.
Equivalent Windows command: FSUTIL file setzerodata, or bbcopy