The Linux Kernel-based Virtual Machine (KVM) is free, open source virtualization software for Linux based on the Intel VT-X and AMD-V hardware virtualization extensions and a modified version of QEMU (work is underway to get the required changes upstream). KVM—in the form of kvm.ko, a loadable kernel module that provides the core virtualization infrastructure and processor-specific modules kvm-intel.ko and kvm-amd.ko—is designed to enable full hardware emulation as far as needed to boot many PC operating systems in unmodified form.
Using KVM, you can run multiple virtual machines that themselves are running unmodified Linux or Windows® or Mac OS® X images. Each virtual machine has private virtualized hardware such as a network card, disk, graphics adapter, etc.
For this article, I used an IBM® Blade Server HS21 with SUSE 11 as the operating system. The HS21 supports the Intel VT extension and the kernel version of SUSE 11 is 22.214.171.124, which already contains KVM (KVM is included in Linux kernel versions from 2.6.20).
The three main steps to get your virtual server going are:
- Install the operating system and required software.
- Create the virtual server.
- Configure the virtual server network.
Step 1. Install the OS and required software
This section covers:
- Installing the operating system and required software
- Determining whether the CPU supports KVM
- Making sure the software is installed correctly
Install operating system and software
After you install the operating system, you can find the installed version of the Linux kernel with the following command:
kvm:~ # uname -a Linux kvm 126.96.36.199-1-pae #1 SMP 2009-01-27 13:41:16 +0100 i686 i686 i386 GNU/Linux
Then select and install the kvm and kvm-kmp-default packages (which already include a modified QEMU for I/O hardware emulation). As shown in Figure 1, select these packages and click Accept to install them:
Figure 1. Finding the installed kernel
Now, the kvm-kmp-default version should be 78_188.8.131.52_1-11.3. (78 is the KVM version, and the rest of the information indicates the kernel version.)
A typical KVM installation consists of these components:
- A device driver for managing the virtualization hardware; this driver exposes its capabilities via a character device /dev/kvm
- A user-space component for emulating PC hardware; currently, this is handled in the user space and is a lightly modified QEMU process
- The I/O model, which is directly derived from QEMU's model with support for copy-on-write disk images and other QEMU features
Determine whether the CPU supports KVM
KVM depends on the x86 virtualization extensions. To check for
compatibility, run the command
grep vmx /proc/cpuinfo (on AMD, run the command
grep svm /proc/cpuinfo). If the output is
similar to Listing 1, then the CPU supports KVM; otherwise, your CPU does
not support KVM.
Listing 1. Checking CPU for KVM support
kvm:~ # grep vmx /proc/cpuinfo flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe lm constant_tsc arch_perfmon pebs bts pni monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr dca lahf_lm flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe lm constant_tsc arch_perfmon pebs bts pni monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr dca lahf_lm flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe lm constant_tsc arch_perfmon pebs bts pni monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr dca lahf_lm flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe lm constant_tsc arch_perfmon pebs bts pni monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr dca lahf_lm
Determine that the software is successfully installed
Run the command
lsmod | grep kvm to check
whether the KVM module is installed successfully. If the result is similar
to this output, then the KVM module is installed successfully:
kvm:~ # lsmod | grep kvm kvm_intel 42604 0 kvm 150264 1 kvm_intel
Step 2. Create the virtual server
This section covers:
- Creating the raw disk image
- Installing the OS on this image
- Firing up the virtual server
Create a raw disk image
To create a raw disk image, use this command:
dd if=/dev/zero of=/mnt/kvmtest.img bs=1024 count=0 seek=$[10*1024*1024]
With this command, you'll create a 10GB image with the name of kvmtest.img.
Install the operating system on this image
To get the operating system installed on this image, use this command:
/usr/bin/qemu-kvm -hda /mnt/kvmtest.img -boot d -cdrom /mnt/SLES-11-DVD-i586-RC3-DVD1.iso -m 1024
Since you're installing a KVM package and not building KVM yourself from
source, you can use
qemu-kvm but not
-boot d means we will make the virtual server
boot from the CDROM.
-m 1024 means we specify
1GB memory for the virtual server.
After running this command, the operating system installation screen should look like Figure 2:
Figure 2. The OS installation screen
Next, install the operating system as you normally would.
Now, fire up your virtual server
After the operating system is successfully installed, you can start the virtual server with this command:
/usr/bin/qemu-kvm -hda /mnt/kvmtest.img -m 1024
Your server should run just like a normal server running on the physical hardware.
Step 3. Configure the virtual server network
You've now seen how to successfully create a virtual server, but not the network for the virtual server. Now I'll show you how to create a bridge network for the virtual server:
- Installing the bridge-util package
- Creating the bridge network interface
- Creating the script for network control
- Starting the guest operating system network
- Configuring the guest operating system network
The bridge-util package install
We need to create a bridge network, so we need to install the bridge-util package in the software management section of the operating system. Figure 3 shows where to select and install the package.
Figure 3. Installing the bridge-util package
Build the bridge network interface
In the network configuration screen of the operating system, click Add a new network interface (see Figure 4):
Figure 4. Adding a new network interface
You should get a Hardware Dialog as shown in Figure 5:
Figure 5. The hardware dialog for new network interface
Choose the Bridge device type; click Next to continue the network configuration. You'll see the configuration screen shown in Figure 6:
Figure 6. Network configuration screen
Choose eth0 under "Bridged Devices" and configure a static IP for the bridge interface, which is the same configuration of eth0 (see Figure 7).
Figure 7. Configuring a static IP for the bridge interface
After you do that, the eth0 configuration will be cleared, so click Next to continue, and you are back to the network configuration screen. You can see a new bridge network interface has been created and the eth0 configuration is cleared.
Build the network control script
The content for a network control script should look something like Listing 2:
Listing 2. Network control script
#!/bin/sh set -x switch=br0 if [ -n "$1" ];then tunctl -u `whoami` -t $1 ip link set $1 up sleep 0.5s brctl addif $switch $1 exit 0 else echo "Error: no interface specified" exit 1 fi
Start the guest operating system
Start the guest operating system with a network interface using the command:
/usr/bin/qemu-kvm -hda /mnt/kvmtest.img -m 1024 -net nic,macaddr=52:54:00:12:34:56 -net tap,script=/etc/qemu-ifup
You'll specify a network interface when you start the virtual server.
Configure the guest operating system network
After the guest operating system is booted, configure its network as you would normally.
Congratulations! You've successfully created a virtual server built on KVM.
- Learn more about QEMU, the generic and open source machine emulator and virtualizer.
- Get details on KVM too.
- The developerWorks podcast "David Ashley on a build environment with the Linux KVM" (developerWorks, July 2009) talks about crafting an on-demand software build service using the flexible KVM.
- Two good sources for using KVM are "Discover the Linux Kernel Virtual Machine" (developerWorks, April 2007), which discusses the KVM architecture and how its tight integration with the kernel can change the way you use Linux; and "Create an ooRexx build environment on Linux KVM" (developerWorks, July 2009), a hands-on experience that shows you how to use KVM to build a build system (goes with the podcast mentioned in the previous resource).
- In the developerWorks Linux zone, find more resources for Linux developers, and scan our most popular articles and tutorials.
- See all Linux articles and Linux tutorials on developerWorks.
- Stay current with developerWorks technical events and webcasts.
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