Re: Virtual Machines: Newbie / novice questions

On May 14, 2017 06:51, <rhkramer@gmail.com> wrote:

* Is it right to consider that there is somehow a base OS and the other VMs somehow are set up on top of it--you boot into that base OS first, and then have the ability to switch to another VM. OK, I'm thinking that is not the case--I think I've heard of things like a hypervisor (??), and now I'm guessing that the machine boots first into the hypervisor and then from there boot into any of one or more VMS, one of which would contain what I consider my main or base OS?

I'm unsure about the hypervisor route, but in my case, I'm running Debian Sid on a 12 MiB Dell with a TB SSD. Then on top of that I'm running VirtualBox (aptitude install virtualbox). Within that app, I've created several virtual machines (4 GiB RAM, 120 GiB drive, 64M video RAM, etc). For each one, you turn it on, and it's just like turning on a physical PC (with a VirtualBox firmware (BIOS/UEFI) instead of a Dell firnware). The firmware splashscreen comes up, and complains that it can't find an OS to boot. I then load a Windows7 or 10 or XP or DOS or Debian netinstall or etc .ISO (or similar) file into the virtual machine's virtual CD drive (or a real CD into the real drive, mapping that to the VB's virtual CD drive), and boot and install that OS. Now I can boot into that OS at will, in a window (or full-screen), and have a fully-functioning second (or third, or tenth, with enough resources) sitting on top of my Debian Sid base. I can leave those VMs running, or shut them down, or suspend them, as I wish. With VirtualBox I can share a folder/partition, and/or the clipboard for cut/paste, either direction.

* I know (or I'm 99.9% sure) that the software for a VM is on separate
partitions (except maybe some are or could be shared between the VM and the
"base" machine, such as for my documents and such (things that I'd want to be
accessible from any of the VMs).

Not necessarily a separate partition. The virtual machine is really just a few files, but the main file is essentially the entire VM. You can move it to a separate partition, but no need. You can copy/move/backup that file to copy/move/restore the entire virtual machine, even to another physical box.

* Can I keep a VM in a running state for instant switching to it? (I
presume that in that case, it will be using RAM, on the other hand, it could
be in a non-running (either non-booted or suspended-to-disk) and not be using
RAM?

Yes.

* I presume that booting a VM takes about the same amount of time, maybe a
little longer than booting the base machine / OS (well, unless the OS in the
VM is significantly "smaller" in terms of footprint and services started at
boot)?

Pretty close to the same amount of time as physical hardware, with a little bit of overhead.

* Can I C&P between (applicatons in) different VMs and/or the base OS?

With VirtualBox, yes. VMWare, also, if I recall correctly. I'm not sure about other vm apps, like Qemu.

Thanks!

Lots of RAM and a roomy SSD make virtual machines handy to have around. A lack of those resources might present you with a miserable experience.

Kent