About dd
The dd command copies a file, converting the format of the data in the process, according to the operands specified.
Instead of taking a backup of the hard disk, you can create an image file of the hard disk and save it in other storage devices.There are many advantages to backing up your data to a disk image, one being the ease of use. This method is typically faster than other types of backups, enabling you to quickly restore data following an unexpected catastrophe.
# dd if=/dev/hda of=~/hdadisk.img
The above creates the image of a harddisk /dev/hda
Example 5. Backup a Partition
You can use the device name of a partition in the input file, and in the output either you can specify your target path or image file as shown in the dd command example below.
The dd command copies a file, converting the format of the data in the process, according to the operands specified.
Syntax of ‘dd’ command.
dd if=<source file name> of=<target file name> [Options]
dd [OPERAND]...
dd OPTION
dd OPTION
Operands
bs=BYTES : read and write BYTES bytes at a time (also see ibs=,obs=)
cbs=BYTES : convert BYTES bytes at a time
conv=CONVS : convert the file as per the comma separated symbol list. Each symbol may be one of the following, and represents a specific type of conversion:
bs=BYTES : read and write BYTES bytes at a time (also see ibs=,obs=)
cbs=BYTES : convert BYTES bytes at a time
conv=CONVS : convert the file as per the comma separated symbol list. Each symbol may be one of the following, and represents a specific type of conversion:
ascii
from EBCDIC to ASCII
ebcdic
from ASCII to EBCDIC
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
nocreat
do not create the output file
excl
fail if the output file already exists
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,
noatime
do not update access time
noctty
do not assign controlling terminal from file
nofollow
do not follow symlinks.
obs=BYTES : write BYTES bytes at a time (default: 512)
of=FILE : write to FILE instead of stdout
oflag=FLAGS : write as per the comma separated symbol list
seek=BLOCKS : skip BLOCKS obs-sized blocks at start of output
skip=BLOCKS : skip BLOCKS ibs-sized blocks at start of input
status=noxfer : suppress transfer statistics
Options
--help : Display help and exit.
--version : Display version information and exit.
Numerical Suffixes
BLOCKS 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 (terabytes), P (petabytes), E (exabytes), Z (zettabytes), and Y (yottabytes).
This tool can be used for:
• Backing up and restoring an entire hard drive or a partition.
• Copy regions of raw device files like backing up MBR (master boot record).
• Converting data formats like ASCII to EBCDIC.
• Converting lowercase to uppercase and vice versa.
• Creating files with fixed size.
Create an img file of the /dev/sda hard drive. To restore that image type: dd if=disk1.img of=/dev/sda
Copy the contents from the if= drive /dev/sda to the of= drive /dev/sdb.
Related commands
cp — Copy files and directories.
fdisk — A disk partioning utility.
To backup an entire copy of a hard disk to another hard disk connected to the same system, execute the dd command as shown below. In this dd command example, the UNIX device name of the source hard disk is /dev/hda, and device name of the target hard disk is /dev/hdb.
from EBCDIC to ASCII
ebcdic
from ASCII to EBCDIC
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
nocreat
do not create the output file
excl
fail if the output file already exists
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
fdatasync
physically write output file data before finishing
fsync
likewise, but also write metadata.
count=BLOCKS : copy only BLOCKS input blocks
ibs=BYTES : read BYTES bytes at a time (default: 512)
if=FILE : read from FILE instead of stdin
iflag=FLAGS : read as per the comma separated symbol list. Each symbol may be
fdatasync
physically write output file data before finishing
fsync
likewise, but also write metadata.
count=BLOCKS : copy only BLOCKS input blocks
ibs=BYTES : read BYTES bytes at a time (default: 512)
if=FILE : read from FILE instead of stdin
iflag=FLAGS : read as per the comma separated symbol list. Each symbol may be
one of the following:
append
append mode (makes sense only for output; conv=notrunc suggested)
direct
use direct I/O for data
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
likewise, but also for metadata
fullblock
accumulate full blocks of input (iflag only)
nonblock
use non-blocking I/O
fail unless a directory
dsync
use synchronized I/O for data
sync
likewise, but also for metadata
fullblock
accumulate full blocks of input (iflag only)
nonblock
use non-blocking I/O
noatime
do not update access time
noctty
do not assign controlling terminal from file
nofollow
do not follow symlinks.
obs=BYTES : write BYTES bytes at a time (default: 512)
of=FILE : write to FILE instead of stdout
oflag=FLAGS : write as per the comma separated symbol list
seek=BLOCKS : skip BLOCKS obs-sized blocks at start of output
skip=BLOCKS : skip BLOCKS ibs-sized blocks at start of input
status=noxfer : suppress transfer statistics
Options
--help : Display help and exit.
--version : Display version information and exit.
Numerical Suffixes
BLOCKS 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 (terabytes), P (petabytes), E (exabytes), Z (zettabytes), and Y (yottabytes).
This tool can be used for:
• Backing up and restoring an entire hard drive or a partition.
• Copy regions of raw device files like backing up MBR (master boot record).
• Converting data formats like ASCII to EBCDIC.
• Converting lowercase to uppercase and vice versa.
• Creating files with fixed size.
dd examples
Caution: Use dd cautiously — improper usage or entering the wrong values could inadvertently wipe, destroy, or overwrite the data on your hard drive.
Caution: Use dd cautiously — improper usage or entering the wrong values could inadvertently wipe, destroy, or overwrite the data on your hard drive.
dd if=/dev/sr0 of=/home/hope/exampleCD.iso bs=2048 conv=noerror,sync
Create a ISO disc image from the CD in the computer.
Create a ISO disc image from the CD in the computer.
dd if=/dev/sda of=~/disk1.img
Create an img file of the /dev/sda hard drive. To restore that image type: dd if=disk1.img of=/dev/sda
dd if=/dev/sda of=/dev/sdb
Copy the contents from the if= drive /dev/sda to the of= drive /dev/sdb.
Related commands
cp — Copy files and directories.
fdisk — A disk partioning utility.
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Example 1. Backup Entire Harddisk
To backup an entire copy of a hard disk to another hard disk connected to the same system, execute the dd command as shown below. In this dd command example, the UNIX device name of the source hard disk is /dev/hda, and device name of the target hard disk is /dev/hdb.
# dd if=/dev/sda of=/dev/sdb
- “if” represents inputfile, and “of” represents output file. So the exact copy of /dev/sda will be available in /dev/sdb.
- If there are any errors, the above command will fail. If you give the parameter “conv=noerror” then it will continue to copy if there are read errors.
- Input file and output file should be mentioned very carefully, if you mention source device in the target and vice versa, you might loss all your data.
# dd if=/dev/sda of=/dev/sdb conv=noerror,sync
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Example 2. Create an Image of a Hard Disk
Instead of taking a backup of the hard disk, you can create an image file of the hard disk and save it in other storage devices.There are many advantages to backing up your data to a disk image, one being the ease of use. This method is typically faster than other types of backups, enabling you to quickly restore data following an unexpected catastrophe.
# dd if=/dev/hda of=~/hdadisk.img
The above creates the image of a harddisk /dev/hda
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Example 3. Restore using Hard Disk Image
To restore a hard disk with the image file of an another hard disk, use the following dd command example.
To restore a hard disk with the image file of an another hard disk, use the following dd command example.
# dd if=hdadisk.img of=/dev/hdb
The image file hdadisk.img file, is the image of a /dev/hda, so the above command will restore the image of /dev/hda to /dev/hdb.
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Example 4. Creating a Floppy Image
Using dd command, you can create a copy of the floppy image very quickly. In input file, give the floppy device location, and in the output file, give the name of your floppy image file as shown below.
# dd if=/dev/fd0 of=myfloppy.img
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You can use the device name of a partition in the input file, and in the output either you can specify your target path or image file as shown in the dd command example below.
# dd if=/dev/hda1 of=~/partition1.img
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Example 6. CDROM Backup
dd command allows you to create an iso file from a source file. So we can insert the CD and enter dd command to create an iso file of a CD content.
dd command allows you to create an iso file from a source file. So we can insert the CD and enter dd command to create an iso file of a CD content.
# dd if=/dev/cdrom of=tgsservice.iso bs=2048
dd command reads one block of input and process it and writes it into an output file. You can specify the block size for input and output file. In the above dd command example, the parameter “bs” specifies the block size for the both the input and output file. So dd uses 2048bytes as a block size in the above command.
Note: If CD is auto mounted, before creating an iso image using dd command, its always good if you unmount the CD device to avoid any unnecessary access to the CD ROM.dd command reads one block of input and process it and writes it into an output file. You can specify the block size for input and output file. In the above dd command example, the parameter “bs” specifies the block size for the both the input and output file. So dd uses 2048bytes as a block size in the above command.
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Thanks John...:-)
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