openstack-manuals/doc/image-guide/source/create-images-manually-tools-libvirt.rst

Tools: libvirt and virsh/virt-manager

depth

3

Prerequisites

Verify the libvirt default network is running

Before starting a virtual machine with libvirt, verify that the libvirt default network has started. This network must be active for your virtual machine to be able to connect out to the network. Starting this network will create a Linux bridge (usually called virbr0), iptables rules, and a dnsmasq process that will serve as a DHCP server.

To verify that the libvirt default network is enabled, use the virsh net-list command and verify that the default network is active:

# virsh net-list
Name                 State      Autostart
-----------------------------------------
default              active     yes

If the network is not active, start it by doing:

# virsh net-start default

Use the virt-manager X11 GUI

If you plan to create a virtual machine image on a machine that can run X11 applications, the simplest way to do so is to use the virt-manager GUI, which is installable as the virt-manager package on both Fedora-based and Debian-based systems. This GUI has an embedded VNC client that will let you view and interact with the guest's graphical console.

If you are building the image on a headless server, and you have an X server on your local machine, you can launch virt-manager using ssh X11 forwarding to access the GUI. Since virt-manager interacts directly with libvirt, you typically need to be root to access it. If you can ssh directly in as root (or with a user that has permissions to interact with libvirt), do:

$ ssh -X root@server virt-manager

If the account you use to ssh into your server does not have permissions to run libvirt, but has sudo privileges, do:

$ ssh -X user@server
$ sudo virt-manager

Note

The -X flag passed to ssh will enable X11 forwarding over ssh. If this does not work, try replacing it with the -Y flag.

Click the Create a new virtual machine button at the top-left, or go to File --> New Virtual Machine. Then, follow the instructions.

You will be shown a series of dialog boxes that will allow you to specify information about the virtual machine.

Note

When using qcow2 format images, you should check the option Customize configuration before install, go to disk properties and explicitly select the qcow2 format. This ensures the virtual machine disk size will be correct.

Use virt-install and connect by using a local VNC client

If you do not wish to use virt-manager (for example, you do not want to install the dependencies on your server, you do not have an X server running locally, the X11 forwarding over SSH is not working), you can use the virt-install tool to boot the virtual machine through libvirt and connect to the graphical console from a VNC client installed on your local machine.

Because VNC is a standard protocol, there are multiple clients available that implement the VNC spec, including TigerVNC (multiple platforms), TightVNC (multiple platforms), RealVNC (multiple platforms), Chicken (Mac OS X), Krde (KDE), Vinagre (GNOME).

The following example shows how to use the qemu-img command to create an empty image file, and virt-install command to start up a virtual machine using that image file. As root:

# qemu-img create -f qcow2 /tmp/centos.qcow2 10G
# virt-install --virt-type kvm --name centos --ram 1024 \
  --disk /tmp/centos.qcow2,format=qcow2 \
  --network network=default \
  --graphics vnc,listen=0.0.0.0 --noautoconsole \
  --os-type=linux --os-variant=centos7.0 \
  --location=/data/isos/CentOS-7-x86_64-NetInstall-1611.iso

Starting install...
Creating domain...                     |    0 B     00:00
Domain installation still in progress. You can reconnect to
the console to complete the installation process.

The KVM hypervisor starts the virtual machine with the libvirt name, centos, with 1024 MB of RAM. The virtual machine also has a virtual CD-ROM drive associated with the /data/isos/CentOS-7-x86_64-NetInstall-1611.iso file and a local 10 GB hard disk in qcow2 format that is stored in the host at /tmp/centos.qcow2. It configures networking to use libvirt default network. There is a VNC server that is listening on all interfaces, and libvirt will not attempt to launch a VNC client automatically nor try to display the text console (--no-autoconsole). Finally, libvirt will attempt to optimize the configuration for a Linux guest running a CentOS 7 distribution.

Note

When using the libvirt default network, libvirt will connect the virtual machine's interface to a bridge called virbr0. There is a dnsmasq process managed by libvirt that will hand out an IP address on the 192.168.122.0/24 subnet, and libvirt has iptables rules for doing NAT for IP addresses on this subnet.

Run the osinfo-query os command to see a range of allowed --os-variant options.

Use the virsh vncdisplay vm-name command to get the VNC port number.

# virsh vncdisplay centos
:1

In the example above, the guest centos uses VNC display :1, which corresponds to TCP port 5901. You should be able to connect a VNC client running on your local machine to display :1 on the remote machine and step through the installation process.