Virtual Machinery on GNU/Linux

I finally got around to testing KVM. I usually use VirtualBox. The test was very easy. Everything worked. The only real difficulty I had was getting an .iso to boot. It turns out there is a “connect” button I did not notice far to the right in the configuration widget. My eyes? User interface? I don’t know but it turns out to be every bit as easy to use the GUI for KVM as VirtualBox. I even ran KVM inside VirtualBox. Everything worked.

apt-get install qemu-kvm virt-manager in Squeeze

adduser me libvirt

Then I loaded the driver (avoiding a reboot) and ran virt-manager and it was very similar to VirtualBox from there.

From now on I will prefer KVM over VirtualBox thanks to the shenanigans of Oracle v Google etc. If KVM is solid enough for RedHat, it is solid enough for me.
“KVM is included in the mainline linux kernel since 2.6.20 and is stable and fast for most workloads.” There are technical reasons to use KVM as well. Now being in the Linux kernel means it should be continually available. I have no confidence that Oracle will be smooth with VirtualBox. Parts of VB (“extensions”) are already non-free (“free for personal use”…).

see TheVarGuy for a review/comparison earlier. My first experience with KVM was much better than his but that may be because KVM was evolving rapidly back then. Phoronix did some benchmarking with peculiar results (some virtualization was faster than native… clock error? caching?) but it is clear that KVM and VB give similar performance in many cases.

About Robert Pogson

I am a retired teacher in Canada. I taught in the subject areas where I have worked for almost forty years: maths, physics, chemistry and computers. I love hunting, fishing, picking berries and mushrooms, too.
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5 Responses to Virtual Machinery on GNU/Linux

  1. On my big box VMs work very well. On this notebook without the virtualization hardware I emulate and it’s very slow but usable. I suffer 25% speed reduction on I/O, for instance.

  2. Dann says:

    I’m very much a user of VirtualBox. It’s easy to install generally and the proprietary version has usb connectivity.

    I’ve been meaning to migrate to a more free platform and it seems KVM will be my next virtualization solution.

    Thanks for looking out for our freedoms.

    @ oldman

    Then conversly, there is no comparison between KVM licensing and VMWare licensing. KVM: LGPL and GPL 2+

    I’ve used VMware a few times over the past 5 years. I haven’t used the more proprietary workstation version, so this is a biased comment, but it’s never really worked well for me.

    For example: Virtualizing Windows XP at college on VMware totalled the performance on my machine (running kubuntu 9.x or 10.04 at the time).
    There were massive slowdowns from the very launch. When I switched between vmware and other apps, it felt like molasses. Granted, the performance in the machine itself was decent. Maybe moreso than VirtualBox. But VB didn’t max out my ram when I ran it.
    That’s my experience.

  3. I am aware that KVM is newer than VMware and may lack some features but it has really come a long way quickly and seems quite usable to me. I had previously been put off with the virsh stuff but the GUI in virt-manager is very similar to VirtualBox and works well.

    There may be no comparison in your mind but people are putting KVM to work successfully. There are issues of performance but it is amazingly flexible. For instance, this thing I am using does not have the CPU-flags vt or smv flags but I run it on top of VirtualBox. Performance is dreadful with emulated emulation but everything works. I may fire up my AMD64 Phenom X4 just to give KVM a proper home. My wife will probably notice the surge in the electrical bill.

    IBM recently adopted KVM for its cloud.


    IBM tests a lot of stuff but they don’t provide it to customers without having confidence in its suitability.

  4. ChrisTX says:

    “Parts of VB (“extensions”) are already non-free (“free for personal use”…).”

    They merged the OSE and the PUEL editions and the difference is now available as extension. Don’t expect Oracle to not to try to make money out of it. But so did Sun.

    “but it is clear that KVM and VB give similar performance in many cases.”

    KVM should be faster than VB. Xen, however, will be faster than KVM. (a Type-1 HV is theoretically always a better choice than a Type-2 one) Simply because of the depth of the implementation.

    “Phoronix did some benchmarking with peculiar results”
    Phoronix’s ‘benchmarks’ are done so much unprofessional, don’t even bother to listen to them.

  5. oldman says:


    Welcome to the world of KVM. If you havent already found it I would check out the KVM site especially

    This will help your to manage your VM’s more easily.

    I do however have a bone to pick with you. While KVM may be evolving into the “best” of the open source virtualization environments available. It has a long way to go before it can be called the equivalent of the commercial offering from EMC/VMWARE. In fact there is just no comparison.

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