(on Wikipedia)
https://www.gnu.org/software/coreutils/

A ubiquitous byte-copying tool.

I use this for copying disks, partitions and ISOs.

• Part of GNU's "coreutils"

---

• To try - http://dcfldd.sourceforge.net/ -- an enhanced version of GNU dd with features useful for forensics and security.

  • Likely abandoned, as it was last updated 10 years ago.
• 2020-01-09 - 8.26 on Debian 9.9.0-i386-xfce-CD-1
• 2016-03-28 - 8.21 on Slackware 14.1
• 2016-03-26 - 8.21 on Lubuntu 14.04.4 LTS

• As dd is part of coreutils, and coreutils is included with almost every Linux distribution, I've had it for a long time.

Checking dd progress ∞

watch-dd.sh

No, don't bother to use that specialized piece of software, or other dd.

1) Begin your dd

2) In another terminal, run

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

watch and pgrep should be found in most places. sudo in most places too. If they don't exist, it should still be doable to do:

\killall  -USR1  dd

If you don't have watch, you can do:

until [ 1 = 0 ]; do \killall  -USR1  dd; sleep 10 ; done

Testing a device's speed ∞

Tested for USB sticks, but these should work with disks or whatever other storage.

Reading ∞

This is safe. It will not create any files or overwrite any data.

1) Begin your dd

\sudo  \dd  bs=1M  count=1024  if=/dev/sdx  of=/dev/null

2) In another terminal, run

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

Give it some time, and it will start giving a consistent speed.

Writing (DOES NOT WORK) ∞

• TODO - this doesn't work, because the system will do write caching.

  • I know about dropping caches, but investigate this some more.
    - https://www.binarytides.com/linux-test-drive-speed/

This is not safe! It will overwrite a drive!

• For a safer thing to do, mount the device and point your dd of= to some file on a partition on that device.

1) Begin your dd

\sudo  \dd  bs=1M  count=1024  if=/dev/zero  of=/dev/sdx

2) In another terminal, run

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

Give it some time, and it will start giving a consistent speed.

Don't dd an entire drive ∞

I believe this is what I did:

1. dd if=/dev/sda of=/dev/sdb
2. turn off sdb
3. boot into sda
4. auto-mount partitions from sda
5. turn on sdb

6. now \df will report things mounted from sdb

It would make more sense if I had sdb on when I booted up, but I'm certain that was not the case.

This is because the dd also cloned the UUIDs. That's very very bad.

Now I have leftovers from sdb presumed to be mounted, but they're actually sda! I can turn off sdb and there's no change, and I can read/write from my supposedly-sdb-mounted partition. Yeargh.

This did "do something", but did not change the output of df:

\mount  -oremount /dev/sdx1

Fiddling with inserting/removing USB stick seems to have resolved it. Turning the drive on assigns it to /dev/sdc now.

Copying an MBR from one drive to another ∞

source='/dev/sda'
target='/dev/sdb'

\dd  \
  if="$source"  \
  of="$target"  \
  bs=446  \
  count=1

Last updated 2020-06-16 at 13:16:35