Installation of qemu
As the root user, add any users that might use the KVM device to that
group:
usermod -a -G kvm <username>
Install qemu by running the following
commands:
![[Note]](../images/note.png)
Note
Qemu is capable of running many targets. The build process
is also capable of building multiple targets at one time in a
comma delimited list assigned to --target-list. Run
./configure --help to get a complete list of
available targets.
if [ $(uname -m) = i686 ]; then
QEMU_ARCH=i386-softmmu
else
QEMU_ARCH=x86_64-softmmu
fi
mkdir -vp build &&
cd build &&
../configure --prefix=/usr \
--sysconfdir=/etc \
--localstatedir=/var \
--target-list=$QEMU_ARCH \
--audio-drv-list=alsa \
--disable-pa \
--docdir=/usr/share/doc/qemu-7.2.0 &&
unset QEMU_ARCH &&
make
qemu uses ninja as
a subprocess when building. To run the tests, issue:
ninja test.
Now, as the root user:
make install
You will also need to add an Udev rule so that the KVM device gets correct
permissions. As the root user, issue:
cat > /lib/udev/rules.d/65-kvm.rules << "EOF"
KERNEL=="kvm", GROUP="kvm", MODE="0660"
EOF
Change the permissions and ownership of a helper script, which is needed
when using the “bridge” network device (see below). Again
as the root user, issue:
chgrp kvm /usr/libexec/qemu-bridge-helper &&
chmod 4750 /usr/libexec/qemu-bridge-helper
Note
For convenience you may want to create a symbolic link to run
the installed program. For instance (as the root user):
ln -sv qemu-system-`uname -m` /usr/bin/qemu
Using Qemu
Since using qemu means using a virtual computer, the steps to set up
the virtual machine are in close analogy with those to set up a real
computer. You'll need to decide about CPU, memory, disk, USB devices,
network card(s), screen size, etc. Once the “hardware” is
decided, you'll have for example to choose how to connect the machine
to internet, and/or to install an OS. In the following, we show basic
ways of performing those steps. But qemu is much more than this, and it
is strongly advised to read the qemu documentation in
/usr/share/doc/qemu-7.2.0/qemu-doc.html.
Note
It is standard practice to name the computer running qemu
“host” and the emulated machine running under qemu the
“guest”. We'll use those notations in the following.
Note
The following instructions assume the optional symbolic link,
qemu, has been created. Additionally,
qemu should be run in a graphical environment.
But it is possible to use qemu “headless” or through
SSH. See the documentation for the various possibilities.
Disk
A virtual disk may be set up in the following way:
VDISK_SIZE=50G
VDISK_FILENAME=vdisk.img
qemu-img create -f qcow2 $VDISK_FILENAME $VDISK_SIZE
The virtual disk size and filename should be adjusted as desired. The
actual size of the file will be less than specified, but will expand as
needed, so it is safe to put a high value.
Operating System
To install an operating system, download an iso image from your preferred
Linux distribution. For the purposes of this example, we'll use
Fedora-16-x86_64-Live-LXDE.iso in the current
directory. Run the following:
qemu -enable-kvm \
-drive file=$VDISK_FILENAME \
-cdrom Fedora-16-x86_64-Live-LXDE.iso \
-boot d \
-m 1G
Follow the normal installation procedures for the chosen distribution.
The -boot option specifies the boot order of
drives as a string of drive letters. Valid drive letters are: a, b
(floppy 1 and 2), c (first hard disk), d (first CD-ROM). The
-m option is the amount of memory to use for the
virtual machine. The choice depends on the load of the host. Modern
distributions should be comfortable with 1GB.
The -enable-kvm option allows hardware
acceleration. Without this switch, the emulation is much slower.
Defining the virtual hardware
The virtual machine hardware is defined by the qemu command line.
An example command is given below:
qemu -enable-kvm \
-smp 4 \
-cpu host \
-m 1G \
-drive file=$VDISK_FILENAME \
-cdrom grub-img.iso \
-boot order=c,once=d,menu=on \
-net nic,netdev=net0 \
-netdev user,id=net0 \
-device ac97 \
-vga std \
-serial mon:stdio \
-name "fedora-16"Meaning of the command line options
-enable-kvm: enable full KVM virtualization
support. On some hardware, it may be necessary to add the undocumented
-machine smm=off option in order to enable KVM.
-smp <N>: enable symmetric multiprocessing
with <N> CPUs.
-cpu <model>: simulate CPU <model>.
the list of supported models can be obtained with -cpu
help.
-drive file=<filename>: defines a virtual
disk whose image is stored in <filename>.
-cdrom grub-img.iso: defines an iso formatted file
to use as a cdrom. Here we use a grub rescue disk, which may turn handy
when something goes wrong at boot time.
-boot order=c,once=d,menu=on: defines the boot
order for the virtual BIOS.
-net nic,netdev=<netid>: defines a network
card connected to the network device with id <netid>.
-netdev user,id=<netid>: defines the
network “user” device. This is a virtual local network
with addresses 10.0.2.0/24, where the host has address 10.0.2.2 and
acts as a gateway to internet, and with a name server at address
10.0.2.3, and an smb server at address 10.0.2.4. A builtin DHCP server
can allocate addresses between 10.0.2.15 and 10.0.2.31.
-soundhw <model>: defines the soundcard
model. The list may be obtained with -soundhw help.
-vga <type>: defines the type of vga card
to emulate.
-serial mon:stdio: sends the serial port of the
guest (/dev/ttyS0 on linux guests), multiplexed with
the qemu monitor, to the standard input and output of the qemu
process.
-name <name>: sets the name of the guest.
This name is displayed in the guest window caption. It may be useful
if you run several guests at the same time.
-pflash /usr/share/qemu/edk2-x86_64-code.fd: Load a
pre-built EDK2 UEFI firmware, instead of the default PC BIOS. Use
this option if you want to boot the guest OS with UEFI.
-drive file=<filename>,if=virtio: Provide
Virtio interface to the guest kernel for accessing the disk image,
instead of simulating a real disk hardware. This can improve disk I/O
performance, but it requires a Virtio driver in guest kernel. Use
it instead of a plain -drive if the guest kernel
supports Virtio. Note that if the guest kernel is Linux, the virtual
disks using Virtio interface will be named vdx
in the devtmpfs, instead of sdx.
-net nic,netdev=net0,model=virtio-net-pci: Provide
Virtio interface to the guest kernel for accessing the network
interface, instead of simulating a real network interface card. This
can improve network I/O performance, but it requires a Virtio driver
in guest kernel. Use it instead of a plain -net if
the guest kernel supports Virtio.
Controlling the Emulated Display
It may happen that the guest window displayed by qemu does not correspond
to the full capability of the emulated vga card. For example, the vmware
card is 1600x900 capable, but only 1024x768 is displayed by default.
A suitable Xorg configuration on the guest allows to use the full size
(Note that the Xorg video driver to use is Xorg VMware Driver-13.4.0):
cat > /usr/share/X11/xorg.conf.d/20-vmware.conf << "EOF"
Section "Monitor"
Identifier "Monitor0"
# cvt 1600 900
# 1600x900 59.95 Hz (CVT 1.44M9) hsync: 55.99 kHz; pclk: 118.25 MHz
Modeline "1600x900" 118.25 1600 1696 1856 2112 900 903 908 934 -hsync +vsync
Option "PreferredMode" "1600x900"
HorizSync 1-200
VertRefresh 1-200
EndSection
Section "Device"
Identifier "VMware SVGA II Adapter"
Option "Monitor" "default"
Driver "vmware"
EndSection
Section "Screen"
Identifier "Default Screen"
Device "VMware SVGA II Adapter"
Monitor "Monitor0"
SubSection "Display"
Depth 24
Modes "1600x900" "1440x900" "1366x768" "1280x720" "800x480"
EndSubSection
EndSection
EOF
New sizes will be available besides the native ones. You need to
restart X in order to have the new sizes available.
Networking
The above solution for networking allows the guest to access the local
network through the host (and possibly to access internet through the
local routers), but the converse is not true. Not even the host can
access the guest, unless port forwarding is enabled. And in the case
several guests are running, they cannot communicate with each other.
Other network devices can be used for this purpose. For example, there
is the “socket” device, which allows several guests to
share a common virtual network. In the following, we describe in more
details how to set up the “bridge” device, which allows
the guests to appear as if connected to the local network. All the
commands below should be run as the root user.
Set up bridging with bridge-utils-1.7.1. Only the physical
interface(s) should be set up at boot. The virtual interface(s) will be
added as needed when qemu is started.
Set up a required configuration file:
install -vdm 755 /etc/qemu &&
echo allow br0 > /etc/qemu/bridge.conf
In the qemu command line above, replace the switch
-netdev user,... with
-netdev bridge,....