KVM

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Resource

libvirt

  • https://en.wikipedia.org/wiki/Libvirt. libvirt is an open-source API, daemon and management tool for managing platform virtualization.[3] It can be used to manage KVM, Xen, VMware ESXi, QEMU and other virtualization technologies.
  • https://libvirt.org/
  • Check libvirt version: sudo head -n2 /var/log/libvirt/qemu/ubuntu2004.log # on Ubuntu 20.04 it shows 6.0.0

"virt-install" to install or delete a VM

$ virt-install --help | grep graphics
$ osinfo-query os 

$ sudo virt-install  -n ubuntu2004 --os-type=Linux  \
  --os-variant=ubuntu18.04  --ram=2096  --vcpus=2  \
  --disk size=20  \
  --network network=br0 \
  --graphics vnc,listen=0.0.0.0  \
  --location Downloads/ubuntu-20.04.1-desktop-amd64.iso

$ sudo virt-install --name=centos7server \
  --os-type=Linux \
  --os-variant=centos7.0 \
  --vcpu=2 --ram=2048 \
  --disk size=20 \
  --graphics vnc \
  --location=/tmp/CentOS-7-x86_64-DVD-2009.iso

# Running locally
$ sudo virt-install  -n ubuntu20043 --os-type=Linux  \
  --os-variant=ubuntu20.04  \
  --ram=4096  --vcpus=2  \
  --disk size=20  \
  --network network=default  \
  --cdrom ~/Downloads/ubuntu-20.04.3-desktop-amd64.iso

NB

  • If we just run a live session and power off the VM, it will automatically reject the installation medium (iso file) and reboot. So eventually it showed a message "No bootable device."
  • Using the Virtual Machine Manager GUI I found after I tried to delete a VM it won't actually delete the image file created in /var/lib/libvirt/images. Be careful when deleting files there. See How to delete KVM VM guest using virsh command & Removing and deleting a VM from RedHat. 
    $ virsh list --all
 Id   Name                State
------------------------------------
 39   ubuntu20043         running

$ virsh dumpxml --domain ubuntu20043 | grep 'source file' 
      <source file='/var/lib/libvirt/images/ubuntu20043.qcow2' index='2'/>

$ sudo virsh destroy ubuntu20043  # SHUT DOWN

# "sudo virsh undefine ubuntu20043" WILL LEAVE qcow2

$ sudo virsh undefine ubuntu20043 --remove-all-storage 
Domain 'ubuntu20043' has been undefined
Volume 'vda'(/var/lib/libvirt/images/ubuntu20043.qcow2) removed.

$ sudo ls -lt /var/lib/libvirt/images/

Check if running in VM

9 things to do in your first 10 minutes on a Linux server 

$ cat /sys/class/dmi/id/sys_vendor 
QEMU

$ sudo dmidecode -s system-manufacturer 
QEMU

On VirtualBox + CentOS vm, it returns "innotek GmbH".

On VMware + CentOS vm, it returns "VMware, Inc".

Guest additions

It seems QEUM/KVM does not have that to download.

QEMU vs. KVM

QEMU vs. KVM: Which Should You Use for Virtualization? QEMU uses full system emulation, allowing it to emulate a complete computer system, including the processor, memory, storage, and peripheral devices. This flexibility makes QEMU an excellent choice for cross-platform virtualization since it supports a wide range of architectures.

Bridge network

  • There are different ways to configure the network in Ubuntu.
    • If we are using a Ubuntu server, we will use the Netplan method.
    • If we are using a Ubuntu desktop, we will use the Network manager command line nmcli method or the GUI tool nm-connection-editor.
  • Use nmcli to add a bridge network and a bridge slave interface 
    sudo nmcli con add ifname br0 type bridge con-name br0
sudo nmcli con add ifname eno1 type bridge-slave master br0
  • Use nmcli to bring down a wired network and bring up a bridge network 
    sudo nmcli con down "Wired connection 1"
sudo nmcli con up br0
  • Use nmcli to delete unused bridge networks 
    sudo nmcli device show
sudo nmcli con show
sudo nmcli con del "br0"

Install

Install on Ubuntu

  • Virtualization - The Debian Administrator's Handbook
  • How to install KVM on Ubuntu 14.04 LTS Headless Server from cyberciti
  • Simple Virtualization With Ubuntu 16.04 Linux and KVM from linuxconfig
  • KVM virtualization on a home PC with Linux Mint
  • How to Install and Configure KVM on Ubuntu 18.04 LTS Server. I skip step 4: Configure Network Bridge for KVM virtual Machines.
  • How to bring down br0 and delete it? After some messing up I need to delete br0. 
    sudo ip link set br0 down  # ifconfig command is not found anymore
sudo brctl delbr br0
  • Ubuntu 20.04 Essentials (book) → Creating an Ubuntu 20.04 KVM Networked Bridge Interface. It is based on a Ubuntu Desktop environment. The description is quite detailed. Have not tried yet!
  • How to Install KVM on Ubuntu 20.04
    • qemu: qemu
    • qemu-kvm: ovmf, qemu-block-extra, qemu-system-common, qemu-system-data, qemu-system-gui, qemu-system-x86, qemu-utils, seabios, sharutils
    • libvritd-daemon: libvirt0, libvirt-daemon, libvirt-daemon-driver-qemu, ...
    • virt-manager: qemu-block-extra, qemu-utils, virt-viewer, virtinst, ...
    sudo apt install -y qemu qemu-kvm libvirt-daemon \
         libvirt-clients bridge-utils virt-manager
sudo systemctl status libvirtd
# enable it to start on boot 
sudo systemctl enable --now libvirtd
lsmod | grep -i kvm
ip a
# I got two new: virbr0, virbr0-nic
# Click the superkey (Windows) and search/launch "Virtual Machine Manager"

    Click the "Create a new virtual machine" button will result in an error: No active connection to install on. Rebooting does not help. But when I use the command line to create a new VM it works (It seems sudo helps). 

    sudo virt-install --name=ubuntu2004 \
  --os-type=Linux \
  --os-variant=ubuntu20.04 \
  --vcpu=2 --ram=2048 \
  --graphics vnc \
  --location=ubuntu-20.04.1-desktop-amd64.iso

    Add --network bridge:br0 if we have added a new bridge network (br0) in the host (eg using netplan or nmcli or nm-connection-editor GUI Tool in Ubuntu). See some resource below.

  • How to install KVM server on Debian 9/10 Headless Server
  • How to install KVM on Ubuntu 20.04 LTS Headless Server.
    • IP 192.168.2.25 is the new static IP for the bridge network (not virtual machine) and 192.168.2.254 is the gateway current ethernet is using.
    • Note according to How to add network bridge with nmcli (NetworkManager) on Linux, WiFi is not possible. It only works with Ethernet. Confirmed! The bridge network can be pinged from another computer.
    • How to create wireless bridge connection with nmcli. Ans: This is not possible.
    • I follow this How to add network bridge with nmcli (NetworkManager) on Linux disable STP, turn off “Wired connection 1” and turn on br0.
    • Question: Do I need to turn off "Wired connection 1". It will lose the original host's static IP. The new bridge IP will become the host's IP. The guest machine still obtain a new IP via DHCP. This is not what I expect?
    • Before turn off “Wired connection 1” and turn on br0: 
      $ nmcli connection show --active
NAME                UUID   TYPE      DEVICE  
Wired connection 1  XXX    ethernet  eno1    
docker0             XXX    bridge    docker0 
virbr0              XXX    bridge    virbr0
    • After turn off “Wired connection 1” and turn on br0: 
      $ nmcli connection show --active
NAME               UUID   TYPE      DEVICE  
br0                xxx    bridge    br0     
docker0            XXX    bridge    docker0 
virbr0             XXX    bridge    virbr0  
bridge-slave-eno1  XXX    ethernet  eno1    
vnet0              XXX    tun       vnet0
    • I am not able to use remmina to VNC to the bridge VM. Not sure if this is because my host OS is a desktop (not headless).
  • os-variant list in virt-install 
    $ osinfo-query os


Where are image files saved

/var/lib/libvirt/images (/var/lib/docker for Docker)

From what I can see, the directory contains many large qcow2 files that should be deleted once I delete the VM.

VNC

  • KVM/QEMU 以 virt-install 指令建立虛擬機器、VNC 顯示畫面教學 
    sudo virt-install --virt-type kvm --name ubuntu1804 --ram 2048 
  --disk /home/seal/kvm/ubuntu1804.qcow2,format=qcow2 
  --network network=default 
  --graphics vnc,listen=0.0.0.0,password=YOUR_PASSWORD 
  --noautoconsole 
  --os-type=linux --os-variant=ubuntu17.10 
  --cdrom=/home/seal/Downloads/ubuntu-18.10-desktop-amd64.iso

virsh vncdisplay ubuntu1804 #  127.0.0.1:1
                            # pay attention to the port number
                            # :0  --> 5900 in ssh
                            # :1  --> 5901 in ssh
sudo ufw disable

# Another machine. 
# Suppose the host machine has an IP 192.168.0.3
ssh -NL 5901:localhost:5901 [email protected]
ssh -NL 5901:127.0.0.1:5901 [email protected]

vncviewer 127.0.0.1:1 # from a different machine

    NOTE: I have to use local port forwarding. If I try to directly connect to the VM in RealVNC, it will show The connection was refused by the computer. A limit by KVM?

The question is how do we know the client's IP? I guess cockpit method is better.

Install qemu-system-arm in Ubuntu

  • sudo apt install qemu-system-arm
  • How to emulate Raspberry Pi in QEMU which is based on qemu-rpi-kernel-Qemu kernel for emulating Rpi on QEMU. 
    mkdir rpi-vm && cd rpi-vm
git clone https://github.com/dhruvvyas90/qemu-rpi-kernel.git

# Download Raspbian Buster Lite
# from https://www.raspberrypi.org/downloads/raspberry-pi-os/
dd if=/dev/zero bs=1M count=4096 >> 2020-08-20-raspios-buster-armhf-lite.img

sudo losetup -f -P --show 2020-08-20-raspios-buster-armhf-lite.img

sudo mount -o rw /dev/loopXp2 /mnt

sudo nano /mnt/etc/fstab

sudo nano /etc/ld.so.preload # Comment out the line and save the file. 
# Then unmount with the following commands:
# sudo umount /mnt
# sudo losetup -d /dev/loopX

qemu-system-arm \
  -M versatilepb \
  -cpu arm1176 \
  -m 256 \
  -kernel qemu-rpi-kernel/kernel-qemu-4.19.50-buster \
  -hda 2020-08-20-raspios-buster-armhf-lite.img \
  -append "dwc_otg.lpm_enable=0 root=/dev/sda2 console=tty1 rootfstype=ext4 elevator=deadline rootwait" \
  -dtb qemu-rpi-kernel/versatile-pb-buster.dtb \
  -no-reboot \
  -serial stdio

# We can install a desktop. See 
# https://www.raspberrypi.org/forums/viewtopic.php?t=133691

Install on CentOS

qemu-system-x86_64

qemu-system-x86_64 -name debian \
  -vnc 146.20.141.254:0 -m 1024 \
  -drive format=raw,index=2,file=debian.img \
  -enable-kvm -daemonize
If we use Virtual Machine Manager program, you need to have KVM (lsmod | grep kvm) installed on your system for this to work.

Install using qcow2 image

Running a virtual machine from a ramdisk

  • List of RAM drive software
  • How to Create a RAM Drive in Linux 
    if [ "$(mount | grep -o "/mnt/ram")" != "/mnt/ram" ]; then
  sudo mkdir -p /mnt/ram
  sudo mount -t ramfs -o size=1g ramfs /mnt/ram
  sudo chown -R $(whoami):$(whoami) /mnt/ram
fi
mount | grep ram

sudo umount /mnt/ram
  • https://youtu.be/fOaWrhLoVK0
  • Libvirt In-Memory Storage
  • (Windows only) USE A RAM DISK TO GET EXTREME PERFORMANCE FROM TEMPORARY VIRTUAL MACHINES
  • How to Easily Create RAM Disk on Debian, Ubuntu, Linux Mint, CentOS. How to Create a RAM Disk in Any Linux Distro. 
    sudo mkdir /tmp/ramdisk
sudo chmod 777 /tmp/ramdisk
htop  # check free ram
sudo mount -t tmpfs -o size=1G myramdisk /tmp/ramdisk
            # myramdisk is the device name I gave to it
mount | tail -n 1
sudo umount /tmp/ramdisk/

    Test RAM speed 

    # test write speed
sudo dd if=/dev/zero of=/tmp/ramdisk/zero bs=4k count=100000
## 409600000 bytes (410 MB, 391 MiB) copied, 0.734813 s, 557 MB/s  # SATA SSD
## 409600000 bytes (410 MB, 391 MiB) copied, 0.18296 s, 2.2 GB/s   # NVME

# test read speed
sudo dd if=/tmp/ramdisk/zero of=/dev/null bs=4k count=100000
## 409600000 bytes (410 MB, 391 MiB) copied, 0.410809 s, 997 MB/s  # SATA SSD
## 409600000 bytes (410 MB, 391 MiB) copied, 0.139487 s, 2.9 GB/s  # NVME

    Auto-mount on System Boot 

    sudo nano /etc/fstab
## myramdisk  /tmp/ramdisk  tmpfs  defaults,size=1G,x-gvfs-show  0  0

## To mount it immediately without reboot, run the following command.
sudo mount -a

    How to Run VirtualBox VM on RAM Disk. You should set the machine folder to the RAM disk directory (/tmp/ramdisk/).

kvm command

snapshot

  • How to Create, Revert and Delete KVM Virtual machine (domain) snapshot with virsh command, How to create snapshot in Linux KVM VM/Domain 
    $ sudo su
# virsh list --all

# virsh snapshot-create-as --domain win10 --name win10_snap --description "Windows 10 snapshot"    # Create a snapshot
# virsh snapshot-list win10
# virsh snapshot-info --domain win10 --snapshotname win10_snap

# virsh snapshot-revert win10 win10_snap    # Restore

# virsh snapshot-delete --domain win10 --snapshotname win10_snap
  • To create a snapshot using the GUI, open virtualization manager window. In the VM properties, click on the icon (two displays overlapped) which is on the right of the menu, which says Manage VM snapshots.
  • To restore a snapshot using Virtual Machine Manager, right click on a snapshot and select "Start snapshot".

GUI

Virtual Machine Manager/virt-manager, Cockpit, virt-viewer, remote-viewer

sudo apt install cockpit cockpit-machines
  • Creating Ubuntu 20.04 KVM Virtual Machines using Cockpit and virt-manager*.
    • It shows how to handle the error of cannot opening the ISO file.
    • It shows how to use virt-viewer to connect to a VM (virt-viewer)
    • remote-viewer will be used if we change the Console type from 'VNC' to 'Graphics Console in Desktop Viewer' and click the 'Launch Remote Viewer' button. A text file called 'download' will be downloaded. If we click it, it will launch remote-viewer. An interesting thing is the file will be automatically deleted once we click on it:)
  • Consider running a VM on a remote machine with cockpit version 215.
    • For Ubuntu 20.04.1 Desktop. If I increase the display resolution from 1024x768 (4:3) to others without keeping the same ratio, the mouse calibration has a problem:( Maybe it's better not to change the resolution. The VNC method works.
    • For Windows 10, we need to unplug ethernet first in order to create a local account. I've not found a way to use virt-viewer or remote-viewer to view the desktop locally. I can still use cockpit web interface (Consoles) to use the Windows desktop. I am able to increase the display resolution to 1280x800 from 1024x768 which makes the interface easy for my eyes. One problem is the machine will freeze for some unknown reason.

Network Install in virtual machine manager

Share folders

How to quit full screen

How to exit full screen mode in qemu virt-manager ( RHEL / CentOS 7). Hint: click the first of two icons shown at the top-center screen.

Windows VM

How to Create a Windows Virtual Machine in Linux With KVM

Windows VM by docker

Running Windows in a Docker Container!

GNOME Boxes

Network

Find out the IP of the guest machine

# Method 1:
$ virsh list
$ virsh domifaddr centos8

# Method 2:
$ sudo apt install net-tools   # Debian
$ sudo dnf install net-tools   # CentOS
$ arp -n               # find the rows with virbr0 adapter

# Method 3:
# KVM -> Info -> NIC

Backup and restore images

How to KVM Backup and Restore in Linux 

# Backup 
virsh list --all
virsh dumpxml win10 > /MyBackup/win10.xml
sudo cp /var/lib/libvirt/images/win10.qcow2 /MyBackup/win10.qcow2
sudo chown $USER:$USER /MyBackup/*.qcow2

# Restore Making
sudo virsh undefine win10
ls -l /etc/libvirt/qemu
virsh list --all
sudo rm /var/lib/libvirt/images/win10.qcow2
sudo cp /MyBackup/win10.qcow2 /var/lib/libvirt/images/
sudo virsh define --file /MyBackup/win10.xml
# virsh start win10

Cheat sheet

KVM Cheatsheet

Vagrant

How to Use Virtualbox VMs on KVM In Linux

How to Use Virtualbox VMs on KVM In Linux

Run macOS on KVM / QEMU

Run SteamOS on QEMU

Running the Steam Deck’s OS in a virtual machine using QEMU

QuickEMU

Some lessons:

  • By default new folders are created when we create/download guest machine in the home folder. We can create a new folder for managing these guest machines.
  • Use Ctrl+Alt+g to release the mouse. The hint is at the top of window.
  • Change boot="legacy" in windows-11.conf helps to show the Windows installation process (See Simple shell script to "manage" Qemu virtual machines.). But it still failed Windows could not create a partition on disk 0. The error occurred while applying the unattend answer file's <DiskConfiguration> setting. Error code: 0x80042565.
  • When I tried to install quickemu on another freshly installed xubuntu 20.04 focal fossa (Core2 Quad CPU), the installation went through without any problem.
  • The app running the guest machine is spicy.
  • I can install macOS Catalina, Windows 11, etc. The trick to install macOS is manually reboot the guest machine a couple times. Also it is useful to play the "Options -> Scale display" option in "spicy" to better see the text when we install macOS. Then it works.
  • I need to use Shift + F12 (see the hint at the bottom of spicy window) to release mouse (or exit full display) in spicy (the GUI where the guest machine is running) on my Ubuntu. When installing macOS, I need to use my keyboard (mouse does not work) to select the hdd for booting macOS (or just wait a few seconds & the 1st drive will be used to boot).
  • It helps to drag and enlarge the guest machine window (by default 'Scale display' option is checked).
  • When installing macOS, the screen says "About X minutes remaining". But it seems it stuck there (the minutes is not changed) though the CPU is busy. If I closed the window, shutdown the guest machine and reboot it, installation continues. Doing this a few times and eventually a new window ("Select Your Country or Region") will come up. In order to monitor the download, I open another terminal and run something like watch du -s ~/macos-big-sur. This will help me to decide when to restart the VM. For big-sur, the folder size stops at 26655436 and after I reboot the VM, the folder size keep increasing and stops at 32565600. For the 3rd reboot, it still downloads something and needs 2 internal reboots. So I think the problem is the data needs to be downloaded from Apple server is TOO large.
  • macos-big-sur & macos-monterey took about 32G & 34G space.
  • Every time I boot macOS, I shall use the right arrow to select the 2nd icon and press the Enter button to start.
  • macOS Catalina asks at least 4 characters for the password (I choose 6)
  • For macOS Catalina/Monterey guest machine, it automatically allocates 2 CPUs(?), 4/8GB RAM (depending on the host total RAM?), 100GB storage by default. After installing macOS, 75GB will still be available.
  • (Maybe related to Ubuntu 22.04 host using wayland). Whenever I start macOS vm, it pops up a window "Allow inhibiting shortcuts. The application spicy wants to inhibit shortcuts. You can restore shortcuts by pressing Super+Escape." I choose the default "Allow" and it seems to be OK. PS: I need to do this action quickly or the macOS window will go to black and not responds to my keyboard/mouse.
  • For Windows 11 guest machine, it allocates 2 CPUs, 4/8GB RAM, 64GB storage with 43GB free.
  • For Lubuntu guest machine (much better speed than macOS/Windows VM, fill full screen, Qt/KDE based), it allocates 2 CPUs, 4GB RAM, 16GB storage with 8.4GB free.

Build QEMU from source

Nested KVM

How to Enable Nested KVM Virtualization

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