Virtual Box

[melp57]

How can I get virtualbox to run on Sparky?

[paxmark1]

And where have you searched, what have you learned prior to posting this.  How much weight do you look at free oss versus non-free sources.
Also impacting your decision is whether you are in Sparky 4or 5. 

Step back,  maybe you want to go with kvm/qemu instead.   "sudo apt install virt-manager"   will install it.  Read  before you do that.  You can do "apt -s install virt-manager" and see a simulation of the start of the install.   (You do not have to use sudo to view "apt -s blah" because it is a simulation). Lots of packages - yes.  However a virtual box install would also install at least 1/3 of those.   

If things had worked out differently, that is the way I wished I had gone. 
Also, if you are going to vm's - you might want to set up with logical volume management to span drives and change size of things. lvm is nice.  I highly recommend it. 

How much memory do you have?  I would say 8 gb min, I wish I had 12gb.    What sort of extensions for virtualization are on your cpu.  I bought a specific cpu that cost a little more to obtain some benefits.   "inxi -Cf"  will give you those details.  An I3 or I5 with the right flags will run circles around an I7 without the flags.

Xen - Sparky is the one of the last distros I would use Xen for. You want a very minimal set up, almost a command line, Sparky would work well as a Xen guest.   

First stop at the Debian wiki
https://wiki.debian.org/VirtualBox#Debian_9_.22Stretch.22    updated 2018 Oct 11

"apt install virtualbox"  (Backports is enabled from the beginning in Sparky4 -there is no backports of course in Testing-5)   or  do you want to go with the ppa.  There are people in sid and stable who prefer the ppa.  If you are going to stay in a rolling release, there is good info at forums that specialize in sid- unstable Debian. 

There will be a difference between the ppa or the Debian contrib binary.  There is a history here in Debian, for that is where all things that will affect your vm install down the years  will come from.   

And definitely check out
https://wiki.debian.org/KVM

a lot of command line stuff, but there is

Managing VM guests with a GUI

Virt-manager, possibly already installed on your Sparky install.  How to install is at top. 

My parents finances are in a VM.  Backed up several ways, but I need stability. So I researched it heavily. You should too if it is going to be important to you.   

[melp57]

All great information, thanks for sharing your knowledge!

[TheFalcon]

Thank you very much paxmark1,

your excellent response to the OP included one of the best gems of info I have seen in recent times, namely inxi. How did I get by without it! When developing software it is often required that you venture down the 'alice's rabbit hole' that is hardware specs and capabilities. inxi actually transcends the hardware software divide and reports on all manner of things in a refreshingly precise and concise manner. What a great tool, and thanks once again for bringing it to the attention of sparky users. This one is most appreciative.  8)