I see that Microsoft has a utility that (apparently) can read a running system and create an image that can then be imported and run on Virtualbox.
https://docs.microsoft.com/en-us/sysinternals/downloads/disk2vhd
"You can even have Disk2vhd create the VHDs on local volumes, even ones being converted (though performance is better when the VHD is on a disk different than ones being converted)."
Is there anything that does the same thing for Linux, and can image a system like that while it's actually running?