Table of Contents

KVM

Installation

Install all the required for the installation of Qemu, KVM hypervisor, and Libvirt 

# apt install qemu-system libvirt-daemon-system qemu-utils virt-manager

Verify that the virtualization daemon, libvritd-daemon, is operating before moving on. Execute the command to achieve this. 

#  systemctl status libvirtd

Output: 

● libvirtd.service - Virtualization daemon
     Loaded: loaded (/lib/systemd/system/libvirtd.service; enabled; preset: enabled)
     Active: active (running) since Sun 2023-08-06 10:57:02 CEST; 1min 30s ago
TriggeredBy: ● libvirtd-ro.socket
             ● libvirtd-admin.socket
             ● libvirtd.socket
       Docs: man:libvirtd(8)
             https://libvirt.org
   Main PID: 7999 (libvirtd)
      Tasks: 19 (limit: 32768)
     Memory: 15.7M
        CPU: 188ms
     CGroup: /system.slice/libvirtd.service
             └─7999 /usr/sbin/libvirtd --timeout 120
Aug 06 10:57:02 pcwerkkamer systemd[1]: Starting libvirtd.service - Virtualization daemon...
Aug 06 10:57:02 pcwerkkamer systemd[1]: Started libvirtd.service - Virtualization daemon.

Check if libvirtd service will start automatically at boot time. 

# systemctl is-enabled libvirtd

Output: 
enabled

If disabled run the following command to have it boot automatically: 

# systemctl enable --now libvirtd

Use the following command to determine whether the KVM modules are loaded: 

$ lsmod | grep -i kvm
kvm_intel             380928  0
kvm                  1142784  1 kvm_intel
irqbypass              16384  1 kvm

Configuration

User priviliges

In order to manage virtual machines as a regular user, that user needs to be added to the libvirt group: 

# adduser <username> libvirt
     or  (not sure if kvm group is needed)
# usermod -aG libvirt,kvm <username>

User-specific and system-wide VMs

By default, if virsh is run as a normal user it will connect to libvirt using: qemu:///session URI string. This URI allows virsh to manage only the set of VMs belonging to this particular user.

To manage the system set of VMs (i.e., VMs belonging to root) virsh should be run as root or with: qemu:///system URI: 

$ virsh --connect qemu:///system list --all

To avoid having to use the –connect flag on every command, the URI string can be set in the LIBVIRT_DEFAULT_URI environment variable: 

$ export LIBVIRT_DEFAULT_URI='qemu:///system'

Libvirt default network

If you use libvirt to manage your VMs, libvirt provides a NATed bridged network named “default/virbr0” that allows the host to communicate with the guests. 

3: virbr0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN group default qlen 1000
    link/ether 52:54:00:f5:c4:41 brd ff:ff:ff:ff:ff:ff
    inet 192.168.122.1/24 brd 192.168.122.255 scope global virbr0
       valid_lft forever preferred_lft forever

This network is available only for the system domains (that is VMs created by root or using the “qemu:system” connection URI). VMs using this network end up in 192.168.122.1/24 and DHCP is provided to them via dnsmasq. This network is not automatically started. To start it use: 

virsh --connect=qemu:///system net-start default

To make the default network start automatically use: 

virsh --connect=qemu:///system net-autostart default

Change XML configuration

Extract the xml from an existing qcow2 image by: 

virsh dumpxml Windows-11 > Windows-11.xml

Edit and modify the tags in the XML file. Undefine the XML config from the old vm to prevent an error because of a duplicate UUID: 

virsh undefine --nvram Windows-11
or
virsh undefine Windows-11

Import / define the new XML file: 

virsh define Windows-11.xml

Of course you will have to stop and start the vm for the changes to take effect: 

virsh destroy name_of_vm
virsh start name_of_vm

Error Access ISO files, etc.

Directory, that libvirt is using for storing/reading ISO and qcow2 files needs to be readable by libvirt-qemu user. In case of an error opening an ISO or image file, the “libvirt-qemu” user does not have access to the file or the directories holding the files. The “libvirt-qemu” user needs “r+x” permissions all the way up the path. You can check if unix permissions are correct by running a shell under user “libvirt-qemu” and see if you can ls along the path all the way up to the files: 

$ sudo su -s /bin/bash libvirt-qemu

If you can't ls with an account that does have access yields a result with a permission line that contains a dot such as drwxrwxr-x. meaning extended ACL permissions.

Fix 1:

Put the iso or image into one of the pool directories of libvirt manager. E.g. /var/lib/libvirt/images Or any other paths that have full r others rights.

Convert VirtualBox to KVM

qemu-img convert -f vdi -O qcow2 virtualbox-name.vdi kvm-name.qcow2

Shrink KVM qcow2 image

qemu-img convert -O qcow2 source.qcow2 shrunk.qcow2

Make SATA disk available in Windows Client

To make a SATA disk partition available in a Windows VM add the disk to the domain’s xml config file by hand. First find the id of the partition that you want to add. Rather than using /dev/sda you should use /dev/disk/by-id/ where you get from 

 ls -l /dev/disk/by-id

Now edit the /etc/libvirt/qemu/${YOUR_VM}.xml file and add a <disk> section to the <devices> section: 

# nano /etc/libvirt/qemu/${YOUR_VM}.xml

or 

virsh edit ${YOUR_VM}
----------------------------------------------
<disk type='block' device='disk'>
    <driver name='qemu' type='raw'/>
    <source dev='/dev/disk/by-id/{the-partition-id}'/>
    <target dev='vdb' bus='virtio'/>
</disk>

This will make the host’s partition available in the guest as /dev/vdb (D:). After changing a domain’s config by hand, you have to reload the config by hand. Log in to your host and issue this command: 

# virsh define /etc/libvirt/qemu/${YOUR_VM}.xml

Domain YOUR_VM defined from /etc/libvirt/qemu/${YOUR_VM}.xml