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This document is a WORK IN PROGRESS.
This is just a quick personal cheat sheet: treat its contents with caution!

dd

dd is a core utility whose primary purpose is to convert and copy a file. Similarly to cp, by default dd makes a bit-to-bit copy of the file, but with lower-level I/O flow control features.

Warning

Incorrect use of the dd command can wipe any drive connected to the system. Always backup all important data.

Reference(s)

Table of contents

Make sure some drives are not mounted

A lot of dd commands require a "source" and/or a "target" drive to not be mounted. Here, source and target drives refers to the disks you want to run dd upon.

  • Let's say that your system is on the /dev/sda device, that the source drive is on the /dev/sds device and the target drive is on the /dev/sdt device, then you might see something like bellow when running lsblk: 

    $ lsblk
  > NAME   MAJ:MIN RM   SIZE RO TYPE MOUNTPOINTS
  > sda      8:0    0 123.5G  0 disk
  > ├─sda1   8:1    0   512M  0 part /boot
  > └─sda2   8:2    0 123.0G  0 part /
  > sds      8:16   1  12.3G  0 disk
  > └─ ...
  > sdt      8:32   1  12.3G  0 disk
  > └─ ...

  • Now, depending on what dd command you are using, you might have to make sure that the source drive (on device /dev/sds) and/or the target drive (on device /dev/sdt), are not mounted: 

    $ sudo umount /dev/sds # un-mount source drive
$ sudo umount /dev/sdt # un-mount target drive

Installing/cloning an ISO image on a target drive

Tip

See https://docs.fedoraproject.org/en-US/quick-docs/creating-and-using-a-live-installation-image/

Warning

Be extremely careful when using the dd command, in particular pay attention to the of=/dev/some-device part! You really don't want to get the wrong device there or you will end up overwriting the wrong disk!

Tip

A better way to visualize the progression of dd, is to use pv (see https://askubuntu.com/questions/215505/how-do-you-monitor-the-progress-of-dd), e.g. for an .iso of 42 Go: 

$ sudo -i
# dd if=/path/to/image.iso bs=4M conv=fdatasync | pv --size 42G | dd of=/dev/sdt

(do not try with: 

$ sudo dd if=/path/to/image.iso bs=4M conv=fdatasync | sudo pv --size 42G | sudo dd of=/dev/sdt
or the output will look bad)

Tip

Another way to see the progression of dd, is to run: 

$ sudo kill -USR1 $(pgrep ^dd$)

This will display the progress in the associated dd terminal window without halting the process (by printing to its stderr stream).

If you would like to get regular updates of the dd progress, then enter: 

$ watch -n5 'sudo kill -USR1 $(pgrep ^dd$)'

Note

The dd command might take a long time to complete in order to "sync". Be patient.

Cloning a disk or a partition from a source drive to a target drive

Warning

Be extremely careful when using the dd command, in particular pay attention to the of=/dev/some-device part! You really don't want to get the wrong device there or you will end up overwriting the wrong disk!

Note

The dd command might take a long time to complete in order to "sync". Be patient.

Creating and restoring a disk (or a partition) image

Tip

See https://www.cyberciti.biz/faq/unix-linux-dd-create-make-disk-image-commands/

Creating a disk (or a partition) image from a source drive

  • Make sure your source drive (e.g. on /dev/sds) is not mounted.

  • Then use dd to create a disk image for /dev/sds, i.e cloning it to a file (sds-image.gz): 

    $ sudo -i
# dd if=/dev/sds conv=sync,noerror bs=4M | gzip -c > sds-image.gz
    Or to create a partition image for /dev/sds2, i.e. cloning it to a file (sds2-image.gz): 
    $ sudo -i
# dd if=/dev/sds2 conv=sync,noerror bs=4M | gzip -c > sds2-image.gz

  • The previous command just cloned the entire hard drive, including the MBR, bootloader, all partitions, UUIDs, and data.

Restoring a disk (or a partition) image to a target drive

  • Make sure your target drive (e.g. on /dev/sdt) is not mounted.

  • In order to restore a disk image (/path/to/sds-image.gz) to a target drive: 

    $ sudo -i
# gunzip -c /path/to/sds-image.gz | dd of=/dev/sdt
    Or to restore a partition image (/path/to/sds2-image.gz) to a target drive (e.g. /dev/sdt6): 
    $ sudo -i
# gunzip -c /path/to/sds2-image.gz | dd of=/dev/sdt6

Warning

Be extremely careful when using the dd command, in particular pay attention to the of=/dev/some-device part! You really don't want to get the wrong device there or you will end up overwriting the wrong disk!

Note

The dd command might take a long time to complete in order to "sync". Be patient.

Securely wipe a drive

Tip

See https://wiki.archlinux.org/title/Securely_wipe_disk#dd

Benchmark read and write speed

Tip

See https://wiki.archlinux.org/title/Securely_wipe_disk#dd

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