A Step-by-step guide to creating a Linux virtual machine on a Linux host with KVM,qemu,libvirt and ubuntu cloud images.

Step 1. Install KVM

“KVM” Is shorthand for several technologies primarily KVM itself, QEMU and Livbirt. Like all tasks, life is considerably easier with the right tools. I suggest installing the following.

sudo apt install -y qemu qemu-kvm libvirt-daemon libvirt-clients bridge-utils virt-manager cloud-image-utils libguestfs-tools

Though not strictly necessary – rebooting after installing the above might save you some headaches

sudo reboot

Step 2. Download a base image

Download a bootable image to create a VM clone from. I prefer ubuntu cloud images for this task. Choose your favorite flavor of a released build from the ubuntu cloud image released builds page. You will probably want the an amd64 build to download.

wget https://cloud-images.ubuntu.com/releases/bionic/release/ubuntu-18.04-server-cloudimg-amd64.img

Step 3. Set a password for the new VM

The cloud-images come pre loaded with a user named ubuntu however there is no password set for that user so it is impossible to login. To overcome this, you will need to create a text file which contains your own password – convert that to a magical image file and then pass in that image file as part of the VM creation. Don’t worry it’s easier than it sounds.

cat >user-data.txt <<EOF
#cloud-config
password: secretpassword
chpasswd: { expire: False }
ssh_pwauth: True
EOF

Then create the image file. We will use the user-data.img file in the virt-install step.

cloud-localds user-data.img user-data.txt

Step 4. Create a writable clone of the boot drive

So far we have a bootable, but read-only image file of our chosen Linux OS and a custom override file that will set a password for the ubuntu user. Next we need to create a “disk” for our VM to boot from which is writable. We also probably want our root disk to be larger than 2GB. We can do both of those things using qemu-img. In the example below is the file ubuntu-vm-disk.qcow2 that will become our boot disk. It will be 20G in size.

qemu-img create -b ubuntu-18.04-server-cloudimg-amd64.img -F qcow2 -f qcow2 ubuntu-vm-disk.qcow2 20G

Step 5. Create a running VM

Now we need to turn that disk image into a running VM. To do that we use virt-install. As part of the virt-install command line we pass in the customization disk user-data.img which contains details of the customizations we want (namely to set a password). Other things like the VM name, memory and number of CPU are set here too. As part of this command the VM will boot and present a console. You can login from here.

virt-install --name ubuntu-vm \
  --virt-type kvm --memory 2048 --vcpus 2 \
  --boot hd,menu=on \
  --disk path=ubuntu-vm-disk.qcow2,device=disk \
  --disk path=user-data.img,format=raw \
  --graphics none \
  --os-type Linux --os-variant ubuntu18.04 

Step 6. Enjoy your virtual machine

You are now the proud owner of a virtual machine. As long as the VM is running you can connect to it using the command $ virsh-console ubuntu-vm. The username is ubuntu and the password is secretpassword unless you changed the text in user-data.txt

Example

gary@dellboy:~$ mkdir vmtmp

gary@dellboy:~$ cd vmtmp

gary@dellboy:~/vmtmp$ wget https://cloud-images.ubuntu.com/releases/bionic/release/ubuntu-18.04-server-cloudimg-amd64.img
--2022-09-10 19:45:42--  https://cloud-images.ubuntu.com/releases/bionic/release/ubuntu-18.04-server-cloudimg-amd64.img
Resolving cloud-images.ubuntu.com (cloud-images.ubuntu.com)... 185.125.190.37, 185.125.190.40, 2620:2d:4000:1::1a, ...
Connecting to cloud-images.ubuntu.com (cloud-images.ubuntu.com)|185.125.190.37|:443... connected.
HTTP request sent, awaiting response... 200 OK
Length: 389349376 (371M) [application/octet-stream]
Saving to: ‘ubuntu-18.04-server-cloudimg-amd64.img’

ubuntu-18.04-server-cloudim 100%[========================================>] 371.31M  15.9MB/s    in 24s

2022-09-10 19:46:06 (15.7 MB/s) - ‘ubuntu-18.04-server-cloudimg-amd64.img’ saved [389349376/389349376]

gary@dellboy:~/vmtmp$ cat >user-data.txt <<EOF
#cloud-config
password: secretpassword
chpasswd: { expire: False }
ssh_pwauth: True
EOF

gary@dellboy:~/vmtmp$ cloud-localds user-data.img user-data.txt

gary@dellboy:~/vmtmp$ qemu-img create -b ubuntu-18.04-server-cloudimg-amd64.img -F qcow2 -f qcow2 ubuntu-vm-disk.qcow2 20G
Formatting 'ubuntu-vm-disk.qcow2', fmt=qcow2 size=21474836480 backing_file=ubuntu-18.04-server-cloudimg-amd64.img backing_fmt=qcow2 cluster_size=65536 lazy_refcounts=off refcount_bits=16

gary@dellboy:~/vmtmp$ virt-install --name ubuntu-vm \
  --virt-type kvm --memory 2048 --vcpus 2 \
  --boot hd,menu=on \
  --disk path=ubuntu-vm-disk.qcow2,device=disk \
  --disk path=user-data.img,format=raw \
  --graphics none \
  --os-type Linux --os-variant ubuntu18.04 

...VM boots....

[   13.327063] cloud-init[1160]: Cloud-init v. 22.2-0ubuntu1~18.04.3 running 'modules:final' at Sat, 10 Sep 2022 23:51:04 +0000. Up 13.18 seconds.
[   13.328572] cloud-init[1160]: Cloud-init v. 22.2-0ubuntu1~18.04.3 finished at Sat, 10 Sep 2022 23:51:05 +0000. Datasource DataSourceNoCloud [seed=/dev/vdb][dsmode=net].  Up 13.32 seconds
[  OK  ] Started Execute cloud user/final scripts.
[  OK  ] Reached target Cloud-init target.

Ubuntu 18.04.6 LTS ubuntu ttyS0

ubuntu login: ubuntu. <---- enter ubuntu as username
Password:  secretpassword <------ enter secretpassword as password
Welcome to Ubuntu 18.04.6 LTS (GNU/Linux 4.15.0-192-generic x86_64)

 * Documentation:  https://help.ubuntu.com
 * Management:     https://landscape.canonical.com
 * Support:        https://ubuntu.com/advantage

  System information as of Sat Sep 10 23:51:55 UTC 2022

  System load:  0.45              Processes:             104
  Usage of /:   5.7% of 19.20GB   Users logged in:       0
  Memory usage: 6%                IP address for enp1s0: 192.168.122.188
  Swap usage:   0%

0 updates can be applied immediately.



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the exact distribution terms for each program are described in the
individual files in /usr/share/doc/*/copyright.

Ubuntu comes with ABSOLUTELY NO WARRANTY, to the extent permitted by
applicable law.

To run a command as administrator (user "root"), use "sudo <command>".
See "man sudo_root" for details.

ubuntu@ubuntu:~$