Virtualization – Getting Started

Jan Kuparinen Версія F34 onwards Last review: 2020-11-28 Needs Review!

Fedora uses the libvirt family of tools as its virtualization solution.

Enabling hardware virtualization support

This section covers setting up libvirt on your system. After setting up libvirt, you can create virtualized guest operating systems, also known as virtual machines.

System requirements

To run virtualization on Fedora, you need:

At least 600MB of hard disk storage per guest. A minimal command-line Fedora system requires 600MB of storage. Standard Fedora desktop guests require at least 3GB of space.
At least 256MB of RAM per guest, plus 256MB for the base operating system. At least 756MB is recommended for each guest of a modern operating system. A good way to estimate this is to think about how much memory is required for the operating system normally, and allocate that amount to the virtualized guest.

KVM requires a CPU with virtualization extensions, found on most consumer CPUs. These extensions are called Intel VT or AMD-V. To check whether you have CPU support, run the following command:

$ grep -E '^flags.*(vmx|svm)' /proc/cpuinfo

If this command results in nothing printed, your system does not support the relevant virtualization extensions. You can still use QEMU/KVM, but the emulator will fall back to software virtualization, which is much slower.

Installing virtualization software

When installing Fedora, you can install the virtualization packages by selecting Virtualization in the Base Group in the installer.

For existing Fedora installations, you can install the virtualization tools via the command line using the Virtualization Package Group. To view the packages, run:

$ dnf groupinfo virtualization

Group: Virtualization
 Description: These packages provide a graphical virtualization environment.
 Mandatory Packages:
   virt-install
 Default Packages:
   libvirt-daemon-config-network
   libvirt-daemon-kvm
   qemu-kvm
   virt-manager
   virt-viewer
 Optional Packages:
   libguestfs-tools
   python3-libguestfs
   virt-top

Run the following command to install the mandatory and default packages in the virtualization group:
```
# sudo dnf install @virtualization
```
Alternatively, to install the mandatory, default, and optional packages, run:
```
# sudo dnf group install --with-optional virtualization
```
After the packages install, start the libvirtd service:
```
# sudo systemctl start libvirtd
```
To start the service on boot, run:
```
# sudo systemctl enable libvirtd
```
To verify that the KVM kernel modules are properly loaded:
```
$ lsmod | grep kvm
kvm_amd               114688  0
kvm                   831488  1 kvm_amd
```
If this command lists kvm_intel or kvm_amd, KVM is properly configured.

Networking Support

By default, libvirt will create a private network for your guests on the host machine. This private network will use a 192.168.x.x subnet and not be reachable directly from the network the host machine is on. However, virtual guests can use the host machine as a gateway and can connect out via it. If you need to provide services on your guests that are reachable via other machines on your host network you can use iptables DNAT rules to forward in specific ports, or you can set up a bridged environment.

See the libvirt networking setup page for more information on how to setup a bridged network.

Creating virtual machines

The installation of Fedora guests using Anaconda is supported. The installation can be started on the command-line using the virt-install program or in the user interface program virt-manager.

Creating a guest with virt-install

virt-install is a command-line based tool for creating virtualized guests. Execute virt-install --help for command line help, or you can find the manual page at man 1 virt-install.

To use the virt-install command, you should first download an ISO of the Fedora version you wish to install. You can find the latest Fedora images at https://fedoraproject.org. This ISO is only needed during Fedora installation, and can be deleted to free up storage space afterwards if desired.

In this example we’ll use Fedora Workstation.

Planning VM Resources

Adjust the ram, vcpus, and disk size parameters according to the resources you have available.

Storage: An easy way to check your disk size from a bash shell is using the df(1)` utility from the shell:
```
# df -h
```
Memory: You can check your available memory from the shell using free(1):
```
# free -m
```
VCPU: You can check your processor information using lscpu(1):
```
# lscpu
```

When allocating resources to your VM, keep in mind the minimum system requirements for the version of Fedora you are installing as well as your use case requirements. For Fedora 41, you can find this in the Release Notes.

Create Storage for the VM

The libvirt default storage pool is located at `/var/lib/libvirt/images - which is the parent file path we use in this example. For individuals who are lacking enough storage in that path, you can simply mount a new disk or partition to that directory path (from the BASH shell, type man 1 mount) or select a new path. In the example virt-install command below, the disk did not exist prior to running virt-install. When the specified disk is not pre-existing, you must specify the size so virt-install can create a disk for you. If your disk already exists, you can safely remove the ,size=20 parameter from the disk argument.

You have several disk storage options for your VM. While it’s outside the scope of this article to discuss these in detail, the following are a few common options. These examples use 20G as the upper limit for disk size, but you can adjust this size to fit your needs.

Again, you do not need to manually allocate storage using the example options shown below if you specify the size parameter in the virt-install example shown below.

Raw File (Non-Sparse)

To create a fully allocated (non-sparse) raw file:

# sudo dd if=/dev/zero of=/var/lib/libvirt/images/guest.img bs=1M count=20480

you can also use fallocate(1):

# sudo fallocate -l 20480M /var/lib/libvirt/images/guest.img

Raw File (Sparse)

To create a dynamically allocated (sparse) raw file:

# sudo rm -f /var/lib/libvirt/images/guest.img
# sudo truncate --size=20480M /var/lib/libvirt/images/guest.img

QCOW2

To create a new qcow2-formatted disk separately, you can use qemu-img (the example below specifies a disk size of 20G):

# sudo qemu-img create -f qcow2 /var/lib/libvirt/images/guest.qcow2 20480

More information about libvirt storage options can be found at https://libvirt.org/storage.html.

Finally, run the virt-install command using the following format (adjusting parameters as needed):

# sudo virt-install --name Fedora41 \
--description 'Fedora 41 Workstation' \
--ram 4096 \
--vcpus 2 \
--disk path=/var/lib/libvirt/images/Fedora-Workstation-41/Fedora-Workstation-41-20180518.0.x86_64.qcow2,size=20 \
--os-type linux \
--os-variant fedora41 \
--network bridge=virbr0 \
--graphics vnc,listen=127.0.0.1,port=5901 \
--cdrom /var/lib/libvirt/images/Fedora-Workstation-41/Fedora-Workstation-Live-x86-64-41-1.1.iso \
--noautoconsole

Note: For the graphics parameter, we’re setting the vnc listener to localhost because it’s more secure to tunnel your VNC connection through SSH so that you don’t expose VNC to everyone with access to the network.

virt-install can use kickstart files, for example, virt-install -x ks=kickstart-file-name.ks.

If graphics were enabled, a VNC window will open and present the graphical installer. If graphics were not enabled, a text installer will appear. Proceed with the Fedora installation.

Creating a guest with virt-manager

Start Virtual Machine Manager by navigating to Applications System Tools, or by running the following command:
```
# sudo virt-manager
```
Open a connection to a hypervisor by navigating to File Add connection.
Choose qemu for KVM, or Xen for Xen.
Choose local or select a method to connect to a remote hypervisor.
After a connection is opened, click the new icon next to the hypervisor, or right-click on the active hypervisor and select New.
Configure the virtual machine following the steps in the New VM wizard.
Click Finish at the end of the wizard to provision the guest operating system. After a few moments a VNC window will appear. Proceed with the Fedora installation.

Managing virtual machines

When the installation of the guest operating system is complete, it can be managed using the virt-manager program or via command line using virsh.

Managing guests with virt-manager

Start the Virtual Machine Manager by navigating to menu:[Applications]System Tools, or run:
```
# virt-manager
```
If you are not root, you will be prompted to enter the root password.
Choose the host you wish to manage and click Connect in the Open Connection dialog window.
The list of virtual machines is displayed in the main window. Guests that are running will display a ">" icon. Guests that are not running will be greyed out.
To manage a particular guest, double click on it, or right click and select Open.
A new window for the guest will open that will allow you to use its console, see information about its virtual hardware and start, stop, and pause it.

For further information about virt-manager, see RedHat virt-manager guide.

Bugs in the virt-manager tool should be reported in Bugzilla against the virt-manager component.

Managing guests with virsh

The virsh command-line utility allows you to manage virtual machines on the command line. The virsh utility is built around the libvirt management API:

virsh has a stable set of commands whose syntax and semantics are preserved across updates to the underlying virtualization platform.
virsh can be used as an unprivileged user for read-only operations (e.g. listing domains, listing domain statistics).
virsh can manage domains running under Xen, QEMU/KVM, ESX, or other back-ends with no perceptible difference to the user.

To start a virtual machine:

# virsh create <name of virtual machine>

To list the virtual machines currently running:

# virsh list

To list all virtual machines, running or not:

# virsh list --all

To gracefully power off a guest:

# virsh shutdown <virtual machine (name | id | uuid)>

To non gracefully power off a guest:

# virsh destroy <virtual machine (name | id | uuid)>

To save a snapshot of the machine to a file:

# virsh save <virtual machine (name | id | uuid)> <filename>

To restore a previously saved snapshot:

# virsh restore <filename>

To export the configuration file of a virtual machine:

# virsh dumpxml <virtual machine (name | id | uuid)

For a complete list of commands available for use with virsh:

# virsh help

Or consult the manual page: man virsh.

Bugs in the virsh tool should be reported in Bugzilla against the libvirt component.

Remote management

The following remote management options are available:

If using non-root users via SSH, see the setup instructions in https://wiki.libvirt.org/page/SSHSetup
If using root for access via SSH, then create SSH keys for root, and use ssh-agent and ssh-add before launching virt-manager.
To use TLS, set up a local certificate authority and issue x509 certs to all servers and clients. For information on configuring this option, see https://wiki.libvirt.org/page/TLSSetup.

Other virtualization options

QEMU/KVM without libvirt

QEMU/KVM can be invoked directly without libvirt, however you cannot to use tools such as virt-manager, virt-install, or virsh. Plain QEMU (without KVM) can also virtualize other processor architectures like ARM or PowerPC.

Xen

Fedora can run as a Xen guest operating system and also be used as a Xen host (with the latter being true from Fedora 16; for using an earlier version of Fedora as a Xen host, check out the experimental repo available at https://myoung.fedorapeople.org/dom0). For a guide on how to install and setup a Fedora Xen host, see Fedora Host Installation page on the Xen Project wiki.

OpenStack

OpenStack consists of a number of services for running infrastructure as a service (IaaS) clouds. They are the Object Store (Swift), Compute (Nova), and Image (Glance) services.

OpenNebula

OpenNebula is an open source toolkit for data center virtualization.

oVirt

The oVirt project is an open virtualization project providing a end-to-end, server virtualization management system with advanced capabilities for hosts and guests, including high availability, live migration, storage management, system scheduler, and more.

Troubleshooting and known issues

First take a look at the well-known common issues. Replace the version number by the version you are actually using.

For troubleshooting tips, see Virtualization – How to Debug Issues

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