HowtomakediskimagewithddonLinuxorUnix

How to clone an entire hard disk

The syntax is:
dd if=/dev/input/DEVICE-HERE of=/dev/OUTPUT/DEVICE-HERE bs=64K conv=noerror,sync
To clone /dev/sdc (250G) to /dev/sdd (250G) in Linux, enter:
# dd if=/dev/sdc of=/dev/sdd bs=64K conv=noerror,sync
To clone /dev/ada0 (250G) to /dev/adb0 (250G) in FreeBSD, enter:
# dd if=/dev/ada0 of=/dev/adb0 bs=64K conv=noerror,sync
Where,

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1. if=/dev/file : Input device/file.

2. of=/dev/file : Output device/file.

3. bs=64k : Sets the block size to 64k. You can use 128k or any other value.

4. conv=noerror : Tell dd to continue operation, ignoring all read errors.

5. sync : Add input blocks with zeroes if there were any read errors, so data offsets stay in sync.

How to clone a partition

To clone /dev/sdc1 to /dev/sdd1, enter:
# dd if=/dev/sdc1 of=/dev/sdd1 bs=128K conv=noerror,sync
Sample outputs:

15874+0 records in
15873+0 records out
1040252928 bytes transferred in 3.805977 secs (273320858 bytes/sec)

dd make disk image

You can boot from a live cd. Once booted, make sure no partitions are mounted from the source hard drive disk. You can store disk image on an external USB disk. The syntax is as follows
dd if=/dev/INPUT/DEVICE-NAME-HERE conv=sync,noerror bs=64K | gzip -c > /path/to/my-disk.image.gz
In this example, create disk image for /dev/da0 i.e. cloning /dev/da0 and save in the current directory:
# dd if=/dev/da0 conv=sync,noerror bs=128K | gzip -c > centos-core-7.gz
Sample outputs:

Fig.01: dd command in action
The above command just cloned the entire hard disk, including the MBR, bootloader, all partitions, UUIDs, and data.

How to restore system (dd image)

The syntax is:
# gunzip -c IMAGE.HERE-GZ | dd of=/dev/OUTPUT/DEVICE-HERE
For example:
# gunzip -c centos-core-7.gz | dd of=/dev/da0

Tip #1: Not enough disk space locally? Use remote box

You can send the image through ssh and save it on the remove box called server1.cyberciti.biz:
# dd if=/dev/da0 conv=sync,noerror bs=128K | gzip -c | ssh vivek@server1.cyberciti.biz dd of=centos-core-7.gz

Tip #2: See progress while making an image with dd

You need to use GNU dd with coreutils version 8.24 as follows (pass the status=progress to the dd):
# dd if=/dev/sdc1 of=/dev/sdd1 bs=128K conv=noerror,sync status=progress
Sample outputs:

gdd (GNU DD) in action with progress bar running on MacOS X

Tip #3: Save extra information

• See how to save and restore MBR only.

• Not a fan of dd? See top 6 open source disk cloning and imaging softwares.

• Want to deal with corrupted disk? Try ddrescue command.