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Xen supports para-virtualization, which was built into the original GPL version of Xen and remains useful to approach "bare-metal" speed for the virtual machines.

No, para-virtualisation is no longer useful. PV is dead, kiilled by Spectre.

Much of the need for this has been reduced through the development of "docker", which can be treated much like a Xen based para-virtualized VM with instances of even lighter weight.

WHAT???? You can't compare PV with docker (no virtualisation, just process containment via namespaces). HV with accelerated IO drivers has displaced PV.

The very active CentOS Xen community has, as I've observed, been much larger and much more active than KVM in dealing with new server and guest environments.

What???? That might seem to be the case because very few people use Xen, so the CentOS Xen community it the only place there is any open-source concerted effort around Xen. But, that is because all the concerted open-source virtualisation effort is happening on Linux/KVM.

My information may be out of date: this may also just mean KVM worked well since then. But I've seen a number of clients simply give up on KVM and just switch to Xen or Citrix Xen. due to unexpected limitations and the time necessary to spend valuable engineering time tuning their own virtualization servers. It's no longer on my recommended product list.

KVM isn't a full virtualisation solution, in the same way that Xen (not XenServer) is not a full virtualisation solution. It is just the hypervisor. There are a number of full virtualisation solutions that either support KVM only, or where KVM is the first-class hypervisor, namely:
- oVirt, or if you want, the commercially supported version from Red Hat, called Red Hat Virtualisation
- Openstack
- Proxmox
- many more

If you were ever punting KVM stand-alone, you've done it a dis-service.

Indeed, for small environments, VirtualBox has proven much better due to its cross-platform services for the virtual servers and its ties to Vagrant testing tools. I'd be very surprised to see another new virtualization toolkit enter the already crowded market.

For most of the uses of vagrant (mainly used for developers to spin up dev VMs on their own machine), docker *is* probably a better tool, but Virtualbox is really not a solution for server virtualisation at all, there are so many better open-source solutions available that are community-owned (not owned by Oracle).

This page has KVM's "ToDo" list. A good number of items on that list are supported by Xen. In addition, KVM will not play well [if at all], with older CPUs made prior to extensions enabling virtualization.

KVM also doesn't work with Intel's Atom CPUs unless extensions are available.

KVM still seems the key. Start with maybe ubuntu server install and an apache web server.

Build a UI that controls all the VM's with some kind of web front end.

One of the tricks is going to viewing remote systems. There is a remote desktop variant that encodes displays as h264 or similar. That should be viewable in a web page. Better yet, if you can somehow tie into existing paravirtual drivers in common distributions, though there are some details there to work out.

This might be a good test case for web assembly as well. The main thing is to avoid having to have to have special "client" software.

Supporting software raid out of the box is a nice to have. Linux can certainly do it, though you have to boot from something else.

I'm not sure how it works, but I think encoding h264 video with nvidia cards is doable these days, or at least some of the work is offloaded. Supporting something like that out of the box, so your remove experience, even in a web browser is smooth would likely make the distribution popular more quickly.

The previous post mentions older CPUs. I don't think that would be a priority. It is going to take a lot of effort to make a good alternative, and it is important to spend it carefully.

That page hasn't been updated in over two years, though. I have no way of knowing what was fixed, but I doubt KVM development has simply stalled for that long...

This page has KVM's "ToDo" list. A good number of items on that list are supported by Xen. In addition, KVM will not play well [if at all], with older CPUs made prior to extensions enabling virtualization.

KVM also doesn't work with Intel's Atom CPUs unless extensions are available.

You should really try Linux on the desktop again.
I've used XFCE happily for years but recently Linux desktop has gone to 11.

https://ubuntubudgie.org/ What gnome3 should have been.
https://anbox.io/ android running in a container with integration with the desktop, beta but pretty frickin sweet

Also
https://www.linux-kvm.org/ (forget bootcamp)
https://en.wikipedia.org/wiki/...

And it runs really well on my Lenova x230, which I've had for years unlike the Mac mini that was perpetually stuck at 10.6 until i put Debian on it and gave it to my 7 year old. He's having a much easier time with Budgie then he did with OSX

Google KVM?

Not everybody wants to have to buy two computers, one on which to run each operating system, and use a keyboard, video, and mouse switch. It's especially impractical for laptop users.

(looks down past the ads)
Oh, you meant that KVM. How well do, for example, games and CAD run under the Virgil virtual GPU?

Google KVM?

Not everybody wants to have to buy two computers, one on which to run each operating system, and use a keyboard, video, and mouse switch. It's especially impractical for laptop users.

(looks down past the ads)
Oh, you meant that KVM. How well do, for example, games and CAD run under the Virgil virtual GPU?

KVM (Kernel-based Virtual Machine)

That is most definitely NOT what KVM stands for.

According to their own goddam fucking site, that IS precisely what it stands for, sparky.

"KVM (for Kernel-based Virtual Machine) is a full virtualization solution for Linux on x86 hardware..."

KVM (Kernel-based Virtual Machine)

That is most definitely NOT what KVM stands for. Get off my lawn, etc.

These folks seem to disagree. Moo?

Modern virtualization doesn't have the overhead the GP cited; the 20% RAM loss and 30% CPU capacity loss numbers cited by the AC you responded to are absurd fabrications. I use KVM on Debian hosts to power a large number of VMs running a variety of operating systems, and the loss of CPU bandwidth and throughput with guests is negligible due to hardware virt extensions in modern CPUs (where "modern" in fact means "most 64-bit AMD and Intel CPUs from the last few years, plus a small number of 32-bit CPUs"). Using the "host" CPU setting in guests can also directly expose all host CPU facilities, resulting in virtually no losses in capabilities for mathematically-intensive guest operations. As far as memory is concerned, far from resulting in a 20% loss of available RAM, I gain a significant amount of efficiency in overall memory utilization using KSM (again, used with KVM). On a host running many similar guests, extremely large gains in memory deduplication may be seen. Running without KSM doesn't result in significant memory consumption overhead either, as KVM itself hardly uses any RAM.

The only significant area of loss seen with modern virtualization is disk IO performance, but this may be largely mitigated through use of correctly tuned guest VM settings and updated VirtIO drivers. The poster you replied to is ignorant at best, and trolling at worst.

The clarification was almost certainly intended to disambiguate KVM switches from Linux KVM virtualization.

Apparently, you're not old enough to have ever seen a KVM switch, and your awareness of current technologies isn't keen enough to know about KVM virtualization. Neither of these conditions is a bad thing, but the snide tone of your comment was unwarranted in light of the facts.

For a beginner I would say Virtual Box. It is open sourced - GPL version 2 compliant licensing. The hypervisor is software based - so runs as an app on your existing machine; this also means you have the flexibility of turning it off - and regaining full resources for your host operating system if/when you need it (e.g. if you play high performance video games or other processing/ram intensive activities).

It allows you to manage most of the functionality of a normal virtual environment including virtual network connections, allocation of resources to VMs and so on. It supports a large number of guest OSs to varying degrees of fidelity.

Finally - I found it to be easy to install and use compared to other virtual environments.

After you've played with Virtual Box for some time and want to do something more serious on the server side - I would advise using AMD processor based systems with lots of RAM and harddrive space [or network attached storage], and upgrading to bare metal hypervisors such as KVM or VMWare.

Other VMs had source leaks, too.

Xen had a source leak.
Virtualbox had a source leak.
Even KVM had a source leak.

These VM people better get their act together!

I'm a big fan of KVM. But you can't compare it to either Hyper-V or vSphere in terms ease of use. Let's be realistic here. It's nice to have the KVM option when you want to get started with virtualization and you just don't have the budget for any software. It's also great when your needs grow huge enough to employ a full-time crew of experts to herd it. In between those extremes the cost of VMWare or Windows Server or XenServer can be worth the money for the convenience, unless you're just into that sort of thing.

http://www.linux-kvm.org/page/Enable_VT-X_on_Mac_Pro_(Early_2008)

This might help you.

I have been using KVM on my home workstation for a few months now and I can highly recommend it. I typically use it for testing different linux distros, files systems, server configurations, etc.

If your system supports VT-x or the AMD equivalent the performance is very impressive, almost no noticeable difference. The virt-manager produced by Red Hat makes creating and configuring virtual machines a snap with its friendly user interface.

It supports many useful things like, headless VNC mode (defaut), start on boot, cloning, virtual networks, and so on. However if you are using it for graphics you may want to use the virtualbox style display for faster mouse response, just select it from the list.

It's opensource so it costs you nothing to try it and the current Ubuntu kernels have support for it built in. For me it was a simple apt-get to get started.

KVM doesn't cost you a damned thing. Are you a a filthy Windows user? ...

Oh I see the problem. Bing puts http://en.wikipedia.org/wiki/KVM_switch above http://www.linux-kvm.org/page/Main_Page

You want the second one.

http://www.linux-kvm.org/page/Main_Page - It says clearly that it uses "x86 hardware containing virtualization extensions (Intel VT or AMD V)".
See also: http://www.linux-kvm.org/page/Status
On http://en.wikipedia.org/wiki/X86_virtualization it says that the AMD V instructions came up in the second generation Opteron processors (the ones with Socket F).
Furthermore, from the same Wikipedia: "All Socket 939 and only Sempron processors except Sable, Huron and Sargas do not include support for AMD-V".

If you don't believe me, do a 'cat /proc/cpuinfo' and tell me if you see any virtualization instructions over there.

http://www.linux-kvm.org/page/Main_Page - It says clearly that it uses "x86 hardware containing virtualization extensions (Intel VT or AMD V)".
See also: http://www.linux-kvm.org/page/Status
On http://en.wikipedia.org/wiki/X86_virtualization it says that the AMD V instructions came up in the second generation Opteron processors (the ones with Socket F).
Furthermore, from the same Wikipedia: "All Socket 939 and only Sempron processors except Sable, Huron and Sargas do not include support for AMD-V".

If you don't believe me, do a 'cat /proc/cpuinfo' and tell me if you see any virtualization instructions over there.

I've run windows in KVM[0] and it works fine. I wouldn't use it for something required Direct3D or OpenGL however.
KVM runs closer to the kernel so you get better efficiency over something. If you just need windows for Office or something, you could virtualize the windows instance on the Linux box and then hook up a second hard disk and
reboot using a Linux boot CD/DVD.

Once in the Linux 'Live' boot, use dd or dd_rescue to clone the install disk to the newly attached disk. make sure
cylinders/size match on the drives. The advantage to virtualizing windows in the Linux environment, is that windows
will only see the hardware as virtulized by the host (unless you use pci passthrough). Also, using KVM, you don't
have any modules or crap (Looking at you, Vmware) when you update the kernel, or system. Also, you will have less problems
booting a cloned drive in Linux than in windows - especially if hardware is grossly different.

[0] - http://www.linux-kvm.org/page/Main_Page

KVM does not do paravirtualization, it virtualizes a full x86 processor (with all its overhead)

KVM does not need to do para-virtualization, but it can do para-virtualized I/O to get better performance (see virtio).

Oh for heaven's sake. If you have an even vaguely modern x86 computer it'll have the virtualization extensions, so just run FreeDOS in a KVM instance. Works fine.

http://www.linux-kvm.org/page/Guest_Support_Status

Now they should put parted and KVM in there and we can finally be done with the whole concept of dual-booting.