This one is really useful if you want to take a quick backup of an entire hard drive. 
root@server.server.com:~# dd if=/dev/sda of=/backup/hdadisk.img
Of course make sure you input the correct if
and of
values where if
is the source drive and of
is the output file.  Enjoy!
This is a companion discussion topic for the original entry at https://jimmyb.ninja/post/1403931560