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I'm trying to understand if it is possible to have a Type-1 Hypervisor (bare metal, no host OS) with the ability to view the guest(s) operating system(s) on the same machine.

i.e. I have a XenServer which hosts 2 Windows and 1 Ubuntu server. While they are all manageable remotely, they require another machine to access them.

In the event scenario that no other machine is available, I want to be able to visit the physical host, and connect directly to a guest vm.

I'm looking at the options and for my existing XenServer, it seems that I can only gain text based console view for the guest on the physical host.

It looks like KVM is a natural hybrid Type-1 and Type-2 hypervisor, and even so, might be able to save me some CPU cycles if I descend my Ubuntu VM to the host, hosting KVM.

Are there other options? I am imagining a XenServer/ESXi/Hyper-V Server that can ALT-TAB each OS by using some form of X11 + VNC.

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    I'm having a lot of trouble coming up with any realistic scenario in which no other machine is available. Maybe the aftermath of a nuclear war, but in that case you'll have more pressing concerns. May 20, 2015 at 17:06
  • @MichaelHampton, It's on a ship and regulations (and mountable space) allow only 1. ;)
    – ericosg
    Jun 4, 2015 at 6:57

4 Answers 4

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While it might not look like one, Hyper-V actually is a type-1 hypervisor, because the virtualization layer is placed below the Windows operating system and mediates all hardware access (some time ago, before hardware-assisted virtualization improved a lot, it was very common to experience really slow graphic performance on Hyper-V hosts, due to the O.S. sitting above the virtualization layer).

And of course, a Hyper-V host is perfectly capable of accessing a guest system's console (unless you choose to run the Server Core edition which has no GUI).

Some useful links:

http://en.wikipedia.org/wiki/Hypervisor
http://en.wikipedia.org/wiki/Comparison_of_platform_virtualization_software
http://www.virtualizationsoftware.com/top-5-enterprise-type-1-hypervisors

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  • In this case, Hyper-V Server (standalone) cannot provide graphic console access, as you stated since it's a server core. Using Hyper-V as you suggest requires Windows, but I didn't know that it's "bare metal". Great answer.
    – ericosg
    May 21, 2015 at 7:13
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    A full Windows installation and a Server Core one (on which Hyper-V server is based) are exactly the same system, the only difference is in GUI support; but in both cases, the hypervisor has direct hardware access and sits below the Windows OS.
    – Massimo
    May 21, 2015 at 8:30
  • What do you mean by a "Hyper-V host"? Hyper-V is the host.
    – Melab
    Feb 22 at 1:09
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No such thing as a "baremetal" hypervisor, unless it actually runs on-chip. Xen, ESXi, Hyper-V - all are a double kernel stack, where the hypervisor OS boots, and then brings up a secondary management OS. While the VMs are running on the hypervisor, it doesn't mean the hypervisor level is not an OS, as stripped down as it may be.

As for KVM, it simplifies the approach, using the Linux kernel for most things (because it already can do those things, quite often better than any hypervisor - it's been around, developed and optimized for much longer after all), but the hypervisor bits are as "baremetal" as in ESXi or Xen.

In short, the type-1/type-2 etc argument is moot, nothing but marketing to distinguish the dedicated hypervisor systems from the on-desktop virtualization software.

Now, as for recommendations, what you are asking for can be done natively with Linux/KVM and Hyper-V (full Windows edition). Or you can use one of the desktop oriented virtualization products, like Virtualbox or VMWare WS. AFAIK it is also possible with Xen on Linux, not the xenserver edition of course.

PS: with KVM, you can gain both GUI console and text console access if you don't have X installed on the hypervisor.

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  • Not my choice of a distro, especially for KVM, but that's an entirely different conversation.
    – dyasny
    May 22, 2015 at 13:37
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Perhaps you can use device passthrough on ESXi to pass a video card and USB (keyboard/mouse) to a guest VM that you then use to manage the other hosts at that same box. You would have an additional keyboard/mouse and monitor (unless you have the option of having dual inputs on your display).

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  • Interesting solution, thanks. Maybe adding a kvmp switch to this.
    – ericosg
    May 21, 2015 at 7:15
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No, what you are asking is simply not possible.

Think about that: to give you a graphical user interface, your hypothetical hypervisor need a video driver and a window system. This automatically means that it is a full-flegged OS, rather than a thin hypervisor layer.

So, no type1 hypervisor can do that. Heck, true type1 hypervisors really are firmware-based (think to IBM/Oracle partitioning and virtualization systems). On the other hand, even embedded hypervisor as ESXi are not true type1 hypervisors in the strict sense.

However, I think you overestimate the performance impact of an hybrid or type2 hypervisors: a minimal CentOS/Debian system is very light in terms of resources usage.

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    Nobody uses the original definitions of "Type 1" and "Type 2" hypervisors anymore. May 20, 2015 at 17:23
  • Very true. This is why I would not pick my choice based on "type1" vs "type2" hypervisor, rather I would base it on real-world performance, scalability and ease to manage.
    – shodanshok
    May 20, 2015 at 17:26
  • It's like hearing "Class C IP range".
    – ewwhite
    May 20, 2015 at 17:49
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    I was thinking to "true", firmware-based type1 hypervisor. With Xen and especially KVM this is surely possibile, but I would be afraid to run an entire graphical stacks (with relative kernel-level drivers, which often are not rock-solid) on a production hypervisor.
    – shodanshok
    May 21, 2015 at 7:54
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    The most famous probably is the PowerVM hypervisor, but there are others also.
    – shodanshok
    May 21, 2015 at 15:38

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