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Virtual Machines

Notes about the preparation, configuration and use of virtual machines.

Download

Useful sites for downloading qcow2 images:

Preparation of VM

Creating a new virtual network for public access

  1. Create a bridged-network.xml configuration file:
<network>
    <name>bridged-network</name>
    <forward mode="bridge" />
    <bridge name="br0" />
</network>
  1. Define as virtual network:
$ sudo virsh net-define bridged-network.xml
  1. Activate and set as auto-started:
$ sudo virsh net-start bridged-network
$ sudo virsh net-autostart bridged-network
  1. Verify
$ sudo virsh net-list
Name              State    Autostart   Persistent
----------------------------------------------------
bridged-network   active   yes         yes
default           active   yes         yes
  1. Create/Import VM with bridged-network as network:
$ sudo virt-install --name vmlab --memory 4096 --vcpus 2 --disk /var/lib/libvirt/images/vmlab.qcow2 \
--import --os-variant centos8 --network network=bridged-network --noautoconsole

Resize a qcow2 image

  • Check image info
qemu-img info image.qcow2
  • Resize image
qemu-img resize image.qcow2 +20G
  • To resize the underlying filesystems, we need to make a copy of the image, since virt-resize does not resize disk images in-place
cp image.qcow2 image-orig.qcow2

NOTE: In this example /dev/vda3 is not the /boot partition. So be careful you are growing the correct partitions on your qcow.

  • Check the partitions to ensure the filesystem to be grown
virt-filesystems --long -h --all -a image.qcow2
  • Grow /dev/vda3
virt-resize --expand /dev/vda3 image-orig.qcow2 image.qcow2
  • Inspect new disk
qemu-img info image.qcow2
  • Verify the filesystems
virt-filesystems --long -h --all -a image.qcow2

Customize a qcow2 image

  • Setting the qcow2 image
sudo virt-customize -a /var/lib/libvirt/images/image.qcow2 --hostname vm01.rootzilopochtli.lab \
--root-password password:rootpw --ssh-inject 'root:file:labkey.pub' --uninstall cloud-init \
--selinux-relabel

Configuring VM

Loading the VM

  • Installing the VM
sudo virt-install --name vm01 --memory 1024 --vcpus 1 --disk /var/lib/libvirt/images/image.qcow2 --import \
--os-type linux --os-variant generic --noautoconsole

Note: If you want to set the exact os-variant, check with the osinfo-query command:

sudo osinfo-query os

Using the VM

Access

  • Using console
sudo virsh console vm01

NOTE: To escape from console use the key combination ctrl+5.

Fix Errors

virt-customize: warning: random seed could not be set for this type of guest

This error , during customization, causes hostkeys not to be generated; therefore sshd will not start:

root@debian:~# systemctl status sshd
● ssh.service - OpenBSD Secure Shell server
     Loaded: loaded (/lib/systemd/system/ssh.service; enabled; vendor preset: e>
     Active: failed (Result: exit-code) since Thu 2022-09-08 00:35:29 UTC; 32mi>
       Docs: man:sshd(8)
             man:sshd_config(5)
    Process: 528 ExecStartPre=/usr/sbin/sshd -t (code=exited, status=1/FAILURE)
        CPU: 5ms

Sep 08 00:35:29 debian.rootzilopochtli.lab systemd[1]: ssh.service: Scheduled r>
Sep 08 00:35:29 debian.rootzilopochtli.lab systemd[1]: Stopped OpenBSD Secure S>
Sep 08 00:35:29 debian.rootzilopochtli.lab systemd[1]: ssh.service: Start reque>
Sep 08 00:35:29 debian.rootzilopochtli.lab systemd[1]: ssh.service: Failed with>
Sep 08 00:35:29 debian.rootzilopochtli.lab systemd[1]: Failed to start OpenBSD >
root@debian:~# /usr/sbin/sshd
sshd: no hostkeys available -- exiting.
  • Generate hostkeys
root@debian:~# ssh-keygen -A
ssh-keygen: generating new host keys: RSA DSA ECDSA ED25519

virsh: cannot undefine domain with NVRAM

virsh undefine centos
error: Failed to undefine domain centos 
error: Requested operation is not valid: cannot undefine domain with nvram

nvram is a device that is allowed to change its address.

  • Solution
virsh undefine --nvram centos

Export VM

  • Copy qcow2 file from /var/lib/libvirt/images to same directory on destination host

  • Create a dump xml from domain to export

sudo virsh dumpxml VMNAME > vmname.xml
  • On the destination host run
sudo virsh define vmname.xml
  • Start VM

Using cloud-init

  1. Download cloud image

  2. Resize qcow2 image

  3. With cloud-init: Configure hostname, add a user and grant him access by ssh and change the root password:

    • Create meta-data:
    cat > meta-data <<EOF
local-hostname: vm02.rootzilopochtli.lab
EOF
    • Create user-data:
    $ cat > user-data <<EOF
# cloud-config

users
users:
- name: dexter
  ssh_authorized_keys:
    - ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAACAQD...
  sudo: ['ALL=(ALL) NOPASSWD:ALL']
  groups: sudo
  shell: /bin/bash

chpasswd:
  list: |
    root:password
  expire: False

runcmd:
  - echo "AllowUsers ubuntu" >> /etc/ssh/sshd_config
  - restart ssh
EOF
    • Create a disk to attach with cloud-init configuration:
    $ sudo genisoimage  -output /var/lib/libvirt/images/vm02-cidata.iso -volid cidata -joliet -rock user-data meta-data

  4. Launch VM

$ sudo virt-install --name vm02 --memory 2048 --vcpus 2 --disk /var/lib/libvirt/images/vm02.qcow2 \
--disk /var/lib/libvirt/images/vm02-cidata.iso,device=cdrom --import --network network=default --noautoconsole

  1. Access the VM

    • Verify that the vm is running:
    $ sudo virsh list
 Id   Name     State
 ------------------------
 1    vm02     running
    • Get his IP address
    $ sudo virsh domifaddr vm02
  Name       MAC address          Protocol     Address
 -------------------------------------------------------------------------------
  vnet0      52:54:00:19:54:79    ipv4         192.168.122.186/24
    • Testing access with ssh

References