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KVM Virtualization Tutorial 1 on Debian and Ubuntu Server.
Our aim is to install and configure a host computer for virtual machines.
This tutorial aims to bring you (and me) to a moderate level of Virtualization Administration.
KVM (Kernel-based Virtual Machine) is a loadable kernel module which supply virtualization with APIs.
QEMU (Quick EMUlator) is a virtualizer which uses KVM API. QEMU supports other virtualization solutions too.
Libvirt is a library for managing virtualization hosts. virsh command comes from Libvirt.
Libguestfs is a collection of tools for accessing and managing VM images.
virt-manager is a GUI for managing VMs. I use it on my workstation for simple tasks.
Domain: Virtual Machine (VM)
Image: A file in which a VM (or a disk of VM) is stored.
Host: A server which runs virtualization software
Guest: A VM running on a host
Snapshot: A saved state of an image. You can revert to that stage later.
https://ostechnix.com/install-and-configure-kvm-in-ubuntu-20-04-headless-server/
https://www.qemu.org/docs/master/tools/qemu-img.html
https://www.libvirt.org/manpages/virsh.html
https://docs.fedoraproject.org/en-US/Fedora/18/html/Virtualization_Administration_Guide/index.html (not working now)
https://libguestfs.org/
https://fabianlee.org/2020/02/23/kvm-testing-cloud-init-locally-using-kvm-for-an-ubuntu-cloud-image/
https://cloudinit.readthedocs.io/en/latest/reference/examples.html
ISBN: 979-10-91414-20-3 The Debian Administrator's Handbook by Raphaël Hertzog and Roland Mas
ISBN: 978-1-78829-467-6 KVM Virtualization Cookbook by Konstantin Ivanov
Install necessary packages
sudo apt update
sudo apt install libvirt-clients libvirt-daemon-system qemu-kvm \
virtinst virt-manager virt-viewer bridge-utils --yes
Add your user to libvirt group: (Change exforge to your user name)
sudo usermod -aG libvirt exforge
For the guest computers to reach a network, a bridge configuration on the host computer is needed.
Bridge Configuration differs slighty for Debian and Ubuntu. So it is better to handle them in different sections.
By default KVM creates a virtual bridge named virbr0. This bridge allows the VMs to communicate between each other and the host. But we prefer that the VMs join to our network by getting IP address from our network.
That is we will create a public filter.
First we need to disable netfilter, which is enabled on bridges by default.
sudo nano /etc/sysctl.d/bridge.conf
File is empty, add the following lines
net.bridge.bridge-nf-call-ip6tables=0
net.bridge.bridge-nf-call-iptables=0
net.bridge.bridge-nf-call-arptables=0
sudo nano /etc/udev/rules.d/99-bridge.rules
File is empty, the add following line
ACTION=="add", SUBSYSTEM=="module", KERNEL=="br_netfilter", RUN+="/sbin/sysctl -p /etc/sysctl.d/bridge.conf"
A reboot is necessary
sudo reboot
Now we need to remove the bridge created by KVM
With "ip link" command we see all the networks. KVM network is named as virbr0.
Delete and undefine KVM networks
virsh net-destroy default
virsh net-undefine default
If in any case an error occurs, you can try the following command:
sudo ip link delete virbr0 type bridge
Now if you run "ip link" again, you will see that virbr0 is removed.
When you run "ip link", take a note of your interface name(s), it must be something like enp0s0. If you have more than 1 interface there will be more than 1 name.
Backup your network configuration file
If that file does not exist, there must be another file there with yaml extension. Proceed with that file.
sudo cp /etc/netplan/50-cloud-init.yaml{,.backup}
Edit your network config file
sudo nano /etc/netplan/50-cloud-init.yaml
Remove its content , fill it as below, beware of changing enp3s0f0 to your interface name. If you have more than 1 interfaces, add them too.
Also you should add an IP address and default gateway from your local network.
Mine are 192.168.1.121 and 192.168.1.1
network:
ethernets:
enp3s0f0:
dhcp4: false
dhcp6: false
bridges:
br0:
interfaces: [enp3s0f0]
addresses:
- 192.168.1.121/24
routes:
- to: default
via: 192.168.1.1
mtu: 1500
nameservers:
addresses:
- 8.8.8.8
- 8.8.4.4
parameters:
stp: true
forward-delay: 4
dhcp4: false
dhcp6: false
version: 2
Apply the changes. If you connect through ssh, you connection may break. In this case, close the terminal and reconnect.
sudo netplan apply
If you run "ip link" now, you can see our bridge br0
By default KVM creates a virtual bridge named virbr0. This bridge allows the VMs to communicate between each other and the host. But we want the VMs join to our network by getting IP address from our network.
First we need to disable netfilter, which is enabled on bridges by default.
sudo nano /etc/sysctl.d/bridge.conf
File is empty, add following lines
net.bridge.bridge-nf-call-ip6tables=0
net.bridge.bridge-nf-call-iptables=0
net.bridge.bridge-nf-call-arptables=0
sudo nano /etc/udev/rules.d/99-bridge.rules
File is empty, add following line
ACTION=="add", SUBSYSTEM=="module", KERNEL=="br_netfilter", RUN+="/sbin/sysctl -p /etc/sysctl.d/bridge.conf"
A reboot is necessary
sudo reboot
Now it is time to create a Bridge configuration for the KVM
Backup your network configuration file
sudo cp /etc/network/interfaces{,.backup}
Edit your network config file
sudo nano /etc/network/interfaces
Remove its content , fill it as below, beware of changing enp3s0f0 to your interface name. If you have more than 1 interfaces, add them too.
Also you should add an IP address and default gateway from your local network.
Mine are 192.168.1.121 and 192.168.1.1
auto lo
iface lo inet loopback
# The primary network interface
auto enp3s0f0
#make sure we don't get addresses on our raw device
iface enp3s0f0 inet manual
#set up bridge and give it a static ip
auto br0
iface br0 inet static
address 192.168.1.121
netmask 255.255.255.0
network 192.168.1.0
broadcast 192.168.1.255
gateway 192.168.1.1
bridge_ports enp3s0f0
bridge_stp off
bridge_fd 0
bridge_maxwait 0
dns-nameservers 8.8.8.8
Apply the changes. If you connect through ssh, your connection may break. In this case, close the terminal and reconnect.
sudo systemctl restart networking.service
Adding our Bridge to KVM. We have to create an XML file for the bridge definition:
nano host-bridge.xml
Fill as below:
<network>
<name>host-bridge</name>
<forward mode="bridge"/>
<bridge name="br0"/>
</network>
Define the bridge, start it and make it autostart.
virsh net-define host-bridge.xml
virsh net-start host-bridge
virsh net-autostart host-bridge
Set places for disk images and installation isos
/srv/kvm for VM disk images
/srv/isos for installation iso images
sudo mkdir /srv/kvm /srv/isos
sudo virsh pool-create-as srv-kvm dir --target /srv/kvm
At this point, you may want to copy some installation isos to server's /srv/isos dir
Now it is time to create our first vm
It will be Ubuntu Server 22.04 LTS with 1 GB RAM and 10 GB HDD
I already copied Ubuntu server iso ubuntu-22.04.2-live-server-amd64.iso to /srv/isos
Install a VM named testkvm:
sudo virt-install --name testkvm \
--connect qemu:///system --virt-type kvm \
--memory 1024 --vcpus 1 \
--disk /srv/kvm/testkvm.qcow2,format=qcow2,size=10 \
--cdrom /srv/isos/ubuntu-22.04.2-live-server-amd64.iso \
--network bridge=br0 \
--graphics vnc,port=5901,listen=0.0.0.0 \
--os-variant ubuntu22.04 \
--noautoconsole
Debian 11 does not recognize ubuntu22.04 os variant, so you can change it as --os-variant ubuntu20.04
There are lots of OS Variant selections. You can find yours with the following command. It helps hypervisor to optimize the system for the guest OS. It can be skipped.
sudo apt install libosinfo-bin --yes
osinfo-query os
A graphical desktop is needed to connect to the VM. You can install virt-viewer package on your Debian or Ubuntu workstation and connect to the VM.
Run on your workstation:
sudo apt update
sudo apt install virt-viewer --yes
virt-viewer --connect qemu+ssh://exforge@elma/system testkvm
Remember to replace exforge with your user name on the server and elma with your server's hostname
Our server has no graphical interface (like the most servers). If you really want a graphical management, you can install virt-manager on your workstation and manage your VMs from there.
Run on your workstation:
sudo apt update
sudo apt install virt-manager --yes
virt-manager
The application is added to Applications Menu with the name "Virtual Machine Manager"
Starting a new VM and installing OS into it is a good but time consuming way. Another way would be preparing an installed image and start it as a new VM.
Most server distros supply cloud images. By adding them some necessary configurations (user and network definitions), you can use them as ready # images.
sudo apt update
sudo apt install cloud-image-utils --yes
A search for "ubuntu cloud image" in duckduck2 gives the following address:
https://cloud-images.ubuntu.com/
Following noble and current, download kvm image noble-server-cloudimg-amd64.img, and put it in the server's /srv/isos folder.
Similarly a search for "debian cloud images" in duckduck2 gives the following address:
https://cloud.debian.org/images/cloud/
Following bookworm and latest, download debian-12-generic-amd64.qcow2 and put it in the server's /srv/isos folder.
We will create new images from the images we downloaded. Image sizes will be increased to 20 GiB and the Ubuntu image will be converted to qcow2, the preferred format for KVM.
Ubuntu image:
sudo qemu-img create -b /srv/isos/noble-server-cloudimg-amd64.img \
-F qcow2 -f qcow2 /srv/kvm/ubuntusrv-cloudimg.qcow2 20G
Debian image:
sudo qemu-img create -b /srv/isos/debian-12-generic-amd64.qcow2 \
-F qcow2 -f qcow2 /srv/kvm/debiansrv-cloudimg.qcow2 20G
The next step is to crate a cloud-init config file. This file contains instructions for the cloud image. There is a wide range of instructions like; creating a user, creating and filling files, adding apt repositories, running initial commands, installing packages, reboot and poweroff after finishing, disk and configuration. See below url for details:
https://cloudinit.readthedocs.io/en/latest/reference/examples.html
Our cloud-init file will configure the following:
To add our user's password, we need to have the hash of it.
sudo apt install whois --yes
mkpasswd --method=SHA-512 --rounds=4096
Enter the user's assigned password here, it will display the hash, copy the hash, we will use it later.
Create a place for our cloud-init files. /srv/init would be fine.
sudo mkdir /srv/init
Create our ubuntu server's cloud-init file
sudo nano /srv/init/ubuntu-cloud-init.cfg
Fill as below (Remember updating password with the hash you get):
#cloud-config
hostname: ubuntu24
fqdn: ubuntu24.x386.org
manage_etc_hosts: true
groups: exforge
users:
- name: exforge
sudo: ALL=(ALL) ALL
primary_group: exforge
groups: users
home: /home/exforge
shell: /bin/bash
lock_passwd: false
passwd: $6$rounds=4096$u5D5VbBZD7NcG/8Y$sc8WH5R9YU/xx1QqjQnMzNbQJOptj33DQGJqyHHju5EzJkvGF913gPVhjw.CsL8QLX5G79C0312tAuGIhWEhf1
packages: qemu-guest-agent
Create our debian server's cloud-init file
sudo nano /srv/init/debian-cloud-init.cfg
Fill as below:
#cloud-config
hostname: debian12
fqdn: debian12.x386.org
manage_etc_hosts: true
groups: exforge
users:
- name: exforge
sudo: ALL=(ALL) ALL
primary_group: exforge
groups: users
home: /home/exforge
shell: /bin/bash
lock_passwd: false
passwd: $6$rounds=4096$u5D5VbBZD7NcG/8Y$sc8WH5R9YU/xx1QqjQnMzNbQJOptj33DQGJqyHHju5EzJkvGF913gPVhjw.CsL8QLX5G79C0312tAuGIhWEhf1
packages: qemu-guest-agent
Do not forget to change passwd value with your copied hash.
If a network configuration other than DHCP is needed, a network configuration file is necessary.
Remember to change IP addresses as needed by your VM
sudo nano /srv/init/ubuntu-network-init.cfg
Fill as below:
#cloud-config
version: 2
ethernets:
enp1s0:
dhcp4: false
addresses: [ 192.168.1.243/24 ]
gateway4: 192.168.1.1
nameservers:
addresses: [ 192.168.1.1,8.8.8.8 ]
sudo nano /srv/init/debian-network-init.cfg
Fill as below:
#cloud-config
version: 2
ethernets:
enp1s0:
dhcp4: false
addresses: [ 192.168.1.244/24 ]
gateway4: 192.168.1.1
nameservers:
addresses: [ 192.168.1.1,8.8.8.8 ]
Now we will create image files cloud-init and network-init inside.
For Ubuntu server:
sudo cloud-localds --network-config /srv/init/ubuntu-network-init.cfg \
/srv/kvm/ubuntu24-seed.qcow2 \
/srv/init/ubuntu-cloud-init.cfg
For Debian server:
sudo cloud-localds --network-config /srv/init/debian-network-init.cfg \
/srv/kvm/debian12-seed.qcow2 \
/srv/init/debian-cloud-init.cfg
Ubuntu Server:
virt-install --name ubuntu24 \
--connect qemu:///system \
--virt-type kvm --memory 2048 --vcpus 2 \
--boot hd,menu=on \
--disk path=/srv/kvm/ubuntu24-seed.qcow2,device=cdrom \
--disk path=/srv/kvm/ubuntusrv-cloudimg.qcow2,device=disk \
--graphics vnc,port=5902,listen=0.0.0.0 \
--os-variant ubuntu24.04 \
--network bridge=br0 \
--noautoconsole \
--install no_install=yes
Debian Server
virt-install --name debian12 \
--connect qemu:///system \
--virt-type kvm --memory 2048 --vcpus 2 \
--boot hd,menu=on \
--disk path=/srv/kvm/debian12-seed.qcow2,device=cdrom \
--disk path=/srv/kvm/debiansrv-cloudimg.qcow2,device=disk \
--graphics vnc,port=5903,listen=0.0.0.0 \
--os-variant debian12 \
--network bridge=br0 \
--noautoconsole \
--install no_install=yes
Ironically, on Debian 12, --os-variant debian12 gives an error. In that case, try the following command:
virt-install --name debian12 \
--connect qemu:///system \
--virt-type kvm --memory 2048 --vcpus 2 \
--boot hd,menu=on \
--disk path=/srv/kvm/debian12-seed.qcow2,device=cdrom \
--disk path=/srv/kvm/debiansrv-cloudimg.qcow2,device=disk \
--graphics vnc,port=5903,listen=0.0.0.0 \
--os-variant debian11 \
--network bridge=br0 \
--noautoconsole \
--install no_install=yes
virt-viewer --connect qemu+ssh://exforge@elma/system ubuntu24
virt-viewer --connect qemu+ssh://exforge@elma/system debian12
On your VMs run:
sudo touch /etc/cloud/cloud-init.disabled
If the file /etc/cloud/cloud-init.disabled exists, cloud-init does not run again.
virt-manager can only help with the basic management tasks. If you want to dive deep, you need the old-style shell.
There are countless options to do with virsh command. I can only list a handfull of most useful ones (IMHO) here.
For a complete list of virsh command usage, see the following web page:
https://www.libvirt.org/manpages/virsh.html
In all examples, NAME is the name of your VM.
For Debian, in order to run virsh command without sudo, we need to set an environment variable.
export LIBVIRT_DEFAULT_URI='qemu:///system'
Instead of setting everytime, we can add it to the .bashrc file:
nano ~/.bashrc
export LIBVIRT_DEFAULT_URI='qemu:///system'
virsh nodeinfo
Running VMs
virsh list
All VMs
virsh list --all
virsh start NAME
virsh shutdown NAME
virsh reboot NAME
virsh destroy NAME
virsh undefine NAME
virsh undefine NAME --remove-all-storage
virsh reboot ubuntu24
virsh suspend NAME
virsh resume NAME
virsh autostart NAME
virsh autostart --disable NAME # Disable autostart
virsh dominfo NAME
virsh domid NAME
virsh domuuid NAME
virsh domstate NAME
Display VNC connection settings of VM
virsh domdisplay NAME
VMs have 2 memory parameters: Max Memory and Used Memory.
Used memory is the amount of mem allocated to the VM.
Max memory is the max amount of mem to be allocated to the VM.
See current memory allocation:
virsh dominfo NAME
Change Max memory (Activated after shutdown and start)
virsh setmaxmem NAME 2G --config
size could be something like 2G 1536M etc
Used memory can be changed when the VM is running (decreasing is not advised).
Change memory for this session only (reverts after shutdown and start):
virsh setmem NAME 2536M
virsh setmem NAME 2536M --live
virsh setmem NAME 2536M --current
Change memory after the next shutdown and start
virsh setmem NAME 2536M --config
Activate immediately and keep the changes after the next shutdown and start
virsh setmem NAME 1536M --live --config
virsh setmem ubuntu24 2536M --live --config
Beware of Shutdown and Start. Reboots do not count.
Just like memory, VMs have 2 virtual CPU parameters. Maximum and Current.
Current is the number of vcpus that VM uses actively (on-line).
Maximum is the max number of vcpus can be allocated to the VM.
Also, there are 2 states. Config and Live.
Config is the permanent state, it will be active after shutdown and start.
Live is the running VM's state, it may not be active after shutdown and start.
A cartesian product gives us 4 values:
maximum config: Max number of vcpus, valid after shutdown and start.
maximum live: Max number of vcpus, valid now (while running).
current config: Active number of vcpus, valid after shutdown and start.
current live: Active number of vcpus, valid now (while running).
To see these values for your VM:
virsh vcpucount NAME
I keep saying shutdown and start instead of restart or reboot, because kvm, qemu or whatever it is, acts differently when you reboot or shutdown and then start the VM.
So when I say shutdown and start, I mean shutdown first, wait a while (from 0.001 miliseconds to as long as you want) and then start the VM.
There is no way (AFAIK) to change maximum live value, you can change maximum config as:
virsh setvcpus NAME NUMBER --maximum --config
virsh setvcpus ubuntu24 3 --maximum --config
To change current vcpu count for the current state (all options are valid)
virsh setvcpus NAME NUMBER
virsh setvcpus NAME NUMBER --current
virsh setvcpus NAME NUMBER --live
virsh setvcpus ubuntu24 3
virsh setvcpus ubuntu24 3 --current
virsh setvcpus ubuntu24 3 --live
To change current vcpu count for the config state
virsh setvcpus NAME NUMBER --config
virsh setvcpus ubuntu24 3 --config
To do it both together
virsh setvcpus NAME NUMBER --config --live
virsh setvcpus ubuntu24 3 --config --live
You can both increase and decrease the vcpu count. But beware that decreasing vcpu count of a running VM could be dangerous.
When you increase the current live vcpu count, the increased vcpus becomes offline. That means you cannot use them right away. At least that is what happened to me. You can see online and offline vcpu information of your VM with the following command (run it on your VM):
lscpu | head
To activate an offline cpu, first you have to know its number. cpu numbering starts from 0, so if you had 2 vcpus and increased them by 1, the number for the 3rd vcpu will be 2. You need to edit the following file # and change the 0 inside to 1:
sudo nano /sys/devices/system/cpu/cpu2/online
The number 2 after cpu means the cpu with number 2 i.e. 3rd cpu. When you change # the file, magically that vcpu will become online. For more # vcpus, you have to change that file for each vcpu you added.
When you take a snapshot, current disk and memory state is saved.
Take a live snapshot
virsh snapshot-create-as VMNAME --name SNAPSHOTNAME --description DESCRIPTION
virsh snapshot-create-as ubuntu24 --name ss1-ubuntu24 --description "First Snapshot of Ubuntu24"
The snapshot becomes the current one and everything after is built onto this snapshot. If you want to revert to that snapshot:
virsh snapshot-revert VMNAME --current
If you want to revert to a specific snapshot:
virsh snapshot-revert VMNAME --snapshotname SNAPSHOTNAME
To see which snapshot is current:
virsh snapshot-current VMNAME --name
To delete the current snapshot
virsh snapshot-delete VMNAME --current
To delete a specific snapshot
virsh snapshot-delete VMNAME --snapshotname SNAPSHOTNAME
To list all snapshots of a VM
virsh snapshot-list VMNAME
Suppose that, for our ubuntu24 VM, we need another disk of 20GB size. Because, we need to keep some data on another disk.
We need to create a new image and attach it to the VM.
Create a 20GB image in qcow2 format:
sudo qemu-img create -f qcow2 /srv/kvm/ubuntu24-disk2.qcow2 20G
Now our image is ready to be attached to our VM. Before attaching it to the VM, we have to decide its name on the VM.
VM disks are named as vda, vdb, vdc ... so on. We have to give it a name that follows the last disk name. Because my ubuntu24 VM has only one disk, name for the second one will be vdb. To see your disks on your VM, type the following command (On your VM):
lsblk -o name -d | grep vd
Most probably you will only have vda, in that case you can use the name vdb. Otherwise use a name just after the last disk name.
Add the new image as a second disk to my ubuntu24 VM:
virsh attach-disk ubuntu24 /srv/kvm/ubuntu24-disk2.qcow2 vdb --persistent
The disk is added persistently, that is it is added alive and it will be there after shutdown and and start. If you want to add the disk for the # session only, you can change --persistent to --live. Also, if you want to add the disk after shutdown and start you can change --persistent to --config.
Needless to say that, you are going to have to mount the new disk before using it.
In any case, if you want to detach the added disk, solution is easy:
virsh detach-disk ubuntu24 vdb --persistent
As in virsh attach-disk, you can change --persistent option to --live or --config.
Get the list of all virsh subcommands:
virsh --help
qemu-img allows us to manipulate images. The command is expected to work offline. That means, before you start using qemu-img, you have to shut down the VM associated with it.
Do not use qemu-img with an image of running VM
A full documentation can be found at the below site: https://www.qemu.org/docs/master/tools/qemu-img.html
qemu-img info FILENAME
FILENAME is the name of the file which is the image for the VM.
For my ubuntu24 VM's image info:
qemu-img info /srv/kvm/ubuntusrv-cloudimg.qcow2
qemu-img create -f FORMAT FILENAME SIZE
Remember, at 5.10. we created an empty disk image to add as another disk to a VM:
sudo qemu-img create -f qcow2 /srv/kvm/ubuntu24-disk2.qcow2 20G
An image also can be created by backing from another image. In that way, we will have another image from an image, differentiating its format and size:
sudo qemu-img create -b BACKINGFILENAME -F BACKINGFILEFORMAT \
-f OUTPUTFILEFORMAT OUTPUTFILENAME SIZE
Remember, at 4.2. we created a new cloud image from the cloud image we downloaded:
sudo qemu-img create -b /srv/isos/focal-server-cloudimg-amd64.img \
-F qcow2 -f qcow2 /srv/kvm/ubuntusrv-cloudimg.qcow2 20G
There are a lot of formats for images. For us, the 2 most important ones are raw and qcow2.
qemu-img convert -f SOURCEFORMAT -O DESTINATIONFORMAT SOURCEFILE DESTFILE
I have Virtualbox installed on my workstation (Ubuntu 24.04 LTS). There is a Windows 10 installed on it for testing purposes. I'll copy its image (obviously in vdi format) to my server to /srv/kvm directory, convert it to qcow2 and run it on my server using KVM.
Copy Windows 10 image to the server Run on my workstation
scp windows10.vdi exforge@elma:/tmp
On my server Convert image to qcow2
sudo qemu-img convert -f vdi -O qcow2 /tmp/windows10.vdi \
/srv/kvm/windows10.qcow2
If we want to display the progress percentage while converting the image, add -p option.
sudo qemu-img convert -p -f vdi -O qcow2 /tmp/windows10.vdi \
/srv/kvm/windows10.qcow2
Now we can add it as a KVM image
virt-install --name windows10 \
--connect qemu:///system \
--virt-type kvm --memory 2048 --vcpus 2 \
--boot hd,menu=on \
--disk path=/srv/kvm/windows10.qcow2,device=disk \
--graphics vnc,port=5904,listen=0.0.0.0 \
--os-variant win10 \
--network bridge=br0 \
--noautoconsole
If you need extra disk space for your VM, you can increase the size of the image file.
sudo qemu-img resize FILENAME +SIZE
Resize an image, FILENAME is the name of the file which is the image for the VM.
SIZE could be something like +10G. Image size will be increased by (not to) this amount. it is possible to shrink with -
You must use the parameter --shrink to shrink the image
You must use partitioning tools in the VM to resize the disk to shrinked size before shrinking.
To increase the size of my ubuntu20 VM's image by 5GB:
sudo qemu-img resize /srv/kvm/ubuntusrv-cloudimg.qcow2 +5G
qemu-img check FILENAME
In any case if you suspect the integrity of the image file
If you want to move your VM to another host, or in a way you want to backup and restore your VM; there might be a lot of ways to do it. I'm going to demonstrate a very simple method which requires shutting down the VM (you can try while it is running, but with no success guaranteed).
First of all, let's prepare a place for our backup files, /tmp/kvmbackup would be fine.
mkdir /tmp/kvmbackup
We need the definition file of our VM and the image file it is using. "virsh dumpxml" command creates the definition file in xml format, we can save it with the VM's name.
virsh dumpxml ubuntu24 > /tmp/kvmbackup/ubuntu24.xml
This file contains all the necessary metadata information about our VM.
If our VM was installed from the scratch as in 2.1. there will be only 1 image file. But if it was installed from a cloud image as we did in 4. or if another disk was added as in 5.10; there would be more than 1 images.
We need to copy all the images.
Images used by the VM is listed in the xml file. Let's find them:
grep "source file" /tmp/kvmbackup/ubuntu24.xml
For my ubuntu24 VM, output is listed below:
<source file='/srv/kvm/ubuntu24-seed.qcow2'/>
<source file='/srv/kvm/ubuntusrv-cloudimg.qcow2'/>
That means I need to prepare 2 files: /srv/kvm/ubuntu24-seed.qcow2 and /srv/kvm/ubuntusrv-cloudimg.qcow2 .
Lets copy them to our backup locations.
cp /srv/kvm/ubuntu24-seed.qcow2 /srv/kvm/ubuntusrv-cloudimg.qcow2 \
/tmp/kvmbackup
Beware: You can copy the files while the VM is running, but it is advised to shutdown (or at least suspend your VM) before copying. Continue at your own risk.
Let's package them
tar -cf /tmp/ubuntu24.tar -C /tmp/kvmbackup .
Now we have /tmp/ubuntu24.tar, it has all the necessary data to import our VM anywhere.
You have to copy this file to another server, before importing there.
Assuming we have another virtualization server and we have copied ubuntu20.tar there, we are going to import it and make it operational.
Beware: Before importing your VM to another server, you have to remove it on the original server, otherwise you would have 2 guests with the same IP and that may cause unexpected (and unpleasant) results.
ubuntu24.tar is copied to the server's /tmp directory as /tmp/ubuntu24.tar
Create a place for our import files
mkdir /tmp/import
Extract tar file there
tar -xf /tmp/ubuntu24.tar -C /tmp/import
Now we need to move our image files to their directories as in the original server. If you have a different directory structure on your new server, and you want to copy files to different directories you have to edit the xml file and change directories there.
sudo cp /tmp/import/ubuntu24-seed.qcow2 \
/tmp/import/ubuntusrv-cloudimg.qcow2 /srv/kvm
It is time to define our server. Remember the xml file? We will use it to define our ubuntu24 server.
virsh define /tmp/import/ubuntu24.xml
Now we can start it
virsh start ubuntu24
A set of commands for managing VM disks. Full documentation:
<:https://libguestfs.org/>
Normally, as a system admin, you won't need to reach to VM's disks. But there may happen a need once in a while.
I think you already understand that when you have a VPS on a cloud server, the administrators of that cloud environment can reach your VPS' data.
There are many tools, I'm going to try to explain only mounting commands.
sudo apt update
sudo apt-get --yes install libguestfs-tools
Works online (While the VM is running) Mount my VMs disk on my host's /mnt directory:
sudo guestmount -d ubuntu24 -i --ro /mnt
/mnt directory holds all the files of my VM. If you remove --ro, you can mount it with write permissions. But be very careful.
Unmount it:
sudo guestunmount /mnt
I prefer mounting with readonly permissions just to be safe.
Details for guestmount and guestunmount commands:
guestmount --help
guestunmount --help
guestfish(1) — interactive shell
guestmount(1) — mount guest filesystem in host
guestunmount(1) — unmount guest filesystem
virt-alignment-scan(1) — check alignment of virtual machine partitions
virt-builder(1) — quick image builder
virt-builder-repository(1) — create virt-builder repositories
virt-cat(1) — display a file
virt-copy-in(1) — copy files and directories into a VM
virt-copy-out(1) — copy files and directories out of a VM
virt-customize(1) — customize virtual machines
virt-df(1) — free space
virt-dib(1) — safe diskimage-builder
virt-diff(1) — differences
virt-edit(1) — edit a file
virt-filesystems(1) — display information about filesystems, devices, LVM
virt-format(1) — erase and make blank disks
virt-get-kernel(1) — get kernel from disk
virt-inspector(1) — inspect VM images
virt-list-filesystems(1) — list filesystems
virt-list-partitions(1) — list partitions
virt-log(1) — display log files
virt-ls(1) — list files
virt-make-fs(1) — make a filesystem
virt-p2v(1) — convert physical machine to run on KVM
virt-p2v-make-disk(1) — make P2V ISO
virt-p2v-make-kickstart(1) — make P2V kickstart
virt-rescue(1) — rescue shell
virt-resize(1) — resize virtual machines
virt-sparsify(1) — make virtual machines sparse (thin-provisioned)
virt-sysprep(1) — unconfigure a virtual machine before cloning
virt-tail(1) — follow log file
virt-tar(1) — archive and upload files
virt-tar-in(1) — archive and upload files
virt-tar-out(1) — archive and download files