Have information about a running process

I recently had to backup my hard drive using "dd".
I had 110 Go to backup and it takes a while.

Then, someone made me discover the magic command to get some information about the status of the process.
Typing in another console :

$ killall -USR1 dd

gave me all the information I need (number of Go copied, etc...).

Great tip !

Even better:

$ watch -n 10 killall -USR1 dd

will execute the command every 10 seconds.
Command line is great.