Some versions of dd have the ability to provide the open -status=progress which makes the point of this post moot. But in the case your dd doesn't have this option, read on.

I found my self needing to return a hard drive that had sensitive information on it, so of course I wanted to securely delete the contents before returning the drive.

To securely delete a drive one can run the following:

dd if=/dev/urandom of=/dev/sda bs=1M

This will write random data to the drive /dev/sda and overwrite any data that was already there.

However, the disk was 8TB and so it was going to take quite some time and I wouldn't have a clue how far along things had progressed without some status update.

It turns out you can run dd in the background and then use kill to get an update of the dd status. When I first came across this it sounded insane, because doesn't kill end processes? Well, that is true, but there are other signals that you can provide to kill which won't terminate a process. In this case we are going to use USR1 (this signal may be different on your system).

The first thing to do is run dd in the background and grab its PID:

dd if=/dev/urandom of=/dev/sda bs=1M & PID=$!

Now that we have the PID and dd is running in the background we simply issue the kill signal:

kill -USR1 $PID

Ok, but maybe I just want to look at the screen and not run a command every time I want an update. What we can do to solve this is to run the kill signal in a loop and use clear to print to the same lines by

while kill -0 $PID > /dev/null 2>&1
do
  kill -USR1 $PID
  sleep 0.5
  clear
done

The condition for the while loop is using kill with the flag -0 to see if a signal can be sent to the process $PID. A signal can only be sent if the process still exists, so this while loop should only run while $PID is still running. Next we pipe the output to /dev/null so that we aren't spammed by the result of this condition. We also don't want to see the output from stderr, so we are piping that to stdout, which in turn is piped to /dev/null

This is a bit janky, but it seems the best way to have this printed into the same area. If you don't like this options you can always go with the simpler, yet multiple output method using watch

watch -n 1 kill -USR1 $PID

The -n 1 says to run the kill signal every second. The solution here is much cleaner, but reults in many lines of output. So, it's up to you what you want here.