Introduction

KVM¹ is part of linux kernel, and QEMU² (Quick EMUlator) is an emulator. KVM by itself cannot provide the complete virtualization solution, it needs QEMU to provide full hypervisor functionality. QEMU can emulate cpu on its own, but with KVM, QEMU can achieve near native performance by executing the guest code directly on the host CPU.

So it’s best for them to work together.

tools you need

Use your own package manager to install these tools:

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# arch users
sudo pacman -Sy --needed \
        qemu \
        virt-viewer \
        libvirt \
        dnsmasq \
        ebtables \
        virt-install \
        virt-manager \

• kvm (Kernel-based Virtual Machine): Kernel module that handles CPU and memory communication
• qemu (Quick EMUlator): emulates many hardware resources – dick, network, usb…
• libvirt: an open-source API, daemon and management tool for managing platform virtualization. It can be used to manage KVM, Xen, VMware ESXi, QEMU and other virtualization technologies.
  • virsh: comes with libvirt, command-line tools for communicating with libvirt
• virt-manager: GUI alternative to virsh, albeit less capable.
• virt-install: part of virt-manager project, create new VM guests
• virt-viewer: part of virt-manager project, UI for interacting with VMs via VNC/SPICE
• dnsmasq: light-weight DNS/DHCP server. Primarily used for allocating IPs to VMs.
• ebtables: used for setting up NAT networking the host

some setup

two problems

1. by default, virt-manager talks to qemu:///system, and virsh talks to qemu:///session (unless run as sudo).
2. when talking to qemu:///system, we need to input password every time, especially unpleasant experience when a cli tool like virsh.

for the first problem, we can tell virsh to use qemu:///system by default

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cp /etc/libvirt/libvirt.conf ~/.config/libvirt/libvirt.conf
vim ~/.config/libvirt/libvirt.conf # uncomment or add: uri_default = "qemu:///system"

To solve the second problem, we can add a rule to polkit to allow our group (wheel – administrator group) to use virt-manager or vish without being asked for password.

edit /etc/polkit-1/rules.d/xxx.rules, your path may be different, put this in.

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/* Allow users in wheel group to manage the libvirt daemon without authentication */
polkit.addRule(function (action, subject) {
  if (action.id == "org.libvirt.unix.manage" && subject.isInGroup("wheel")) {
    return polkit.Result.YES;
  }
});

start services

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systemctl enable libvirtd # start on boot
systemctl enable virtstoraged # start on boot
systemctl enable virtnetworkd # start on boot
systemctl start libvirtd  # start libvirtd
systemctl start virtstoraged # start on boot
systemctl start virtnetworkd # start on boot
virsh net-autostart --network default
virsh net-start --network default # start the default network

add shrarefolders

Inside virtual machine manager, double click on one of your machine, then select view->details->Add Hardware, set something like below:

The above setting will add a new device /ctf in the virtual machine

if in ubuntu

sudo vim /etc/rc.local

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#!/bin/sh -e
#
# rc.local
#
# This script is executed at the end of each multiuser runlevel.
# Make sure that the script will "exit 0" on success or any other
# value on error.
#
# In order to enable or disable this script just change the execution
# bits.
#
# By default this script does nothing.

mount -t 9p -o trans=virtio,version=9p2000.L /ctf /home/sky/ctf

exit 0

After restarting this server, /ctf will automatically be mounted on /home/sky/ctf

To make the user (actually kvm) writing the share folder same as the user at host (vm host):
sudo vim /etc/libvirt/qemu.conf, find two lines with user=xxx and group=xxx, change them to yourself (by default, xxx should be root), then uncomment the two lines. for me, they are:

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user = "sky"
group = "sky"

You may need to restart the libvirtd.service for this to take effect.

Also, you need to chown the disk to the above user:group: sudo chown sky:sky /var/lib/libvirt/images/ubt16-server.qcow2

create a VM

• gui: virt-manager
• cli: virt-install

examples:

• Windows 11 VM with QEMU/KVM

clone a VM

• gui: virt-manager
• cli: virt-clone

useful virsh commands

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virsh list --all
virsh start ubuntu-server
virsh shutdown ubuntu-server
virsh reboot ubuntu-server

Resources

• Linux Hypervisor Setup (libvirt/qemu/kvm)
• Sharing folder with VM through libvirt, 9p, permission denied
• macOS-Simple-KVM