libvirt

we gonna use root for KVM here,otherwise we need a kvm-user like this:
$ usermod -a -G libvirt _non_root_user_
instead we will use this user: root@kvm.mapping.com, disable root-ssh login and login via local root password later on

install

$ su root

create the folders needed for libvirt and the ssh keys

$ mkdir /usr/share/foreman/.ssh

the user needs to be foreman and it should be fully writable:
$ chmod 700 /usr/share/foreman/.ssh
$ chown foreman:foreman /usr/share/foreman/.ssh

(not sure if that was required)

$ mkdir /usr/share/foreman/.cache
$ mkdir /usr/share/foreman/.cache/libvirt
$ mkdir /usr/share/foreman/.cache/libvirt/virsh
$ chown foreman:foreman /usr/share/foreman/.cache/libvirt/virsh
$ chmod 700 -R /usr/share/foreman/.cache 
$ chown foreman:foreman /usr/share/foreman/.cache

install libvirt:

$ dnf install qemu-kvm libvirt virt-install virt-viewer

$ for drv in qemu network nodedev nwfilter secret storage interface; do systemctl start virt${drv}d{,-ro,-admin}.socket; done

validate:

$ virt-host-validate

If all virt-host-validate checks return a PASS value, your system is prepared for creating VMs.

see the red hat guide Chapter 2. Enabling virtualization for troubleshooting

enable and start libvirt:

$ systemctl start libvirtd

install virtmanager: *(optional)*

$ virt-manager

check if the Virtual Bridge 0” interface was created

$ ifconfig

enp2s0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
       inet 192.168.2.100  netmask 255.255.255.0  broadcast 192.168.2.255
...
virbr0: flags=4099<UP,BROADCAST,MULTICAST>  mtu 1500
       inet 192.168.122.1  netmask 255.255.255.0  broadcast 192.168.122.255
...
the ip of the Interface we are looking for: 192.168.122.1

what is virbr0?

The virbr0, or “Virtual Bridge 0” interface is used for NAT (Network Address Translation). It is provided by the libvirt library, and virtual environments sometimes use it to connect to the outside network.

whether you need to create a network bridge with virbr0 depends on your specific networking requirements and how you intend to manage network connections for your virtual machines (VMs).

In many setups, especially those involving libvirt and virtualization management tools like Foreman, a default bridge (virbr0) is often automatically created and managed by these systems. The virbr0 bridge is typically configured to allow VMs managed by libvirt to communicate with external networks, acting as a gateway for them.

However, if you have specific networking needs that require custom configurations beyond what virbr0 offers, such as bonding, VLAN tagging, or other advanced features, you might choose to manually create and configure a network bridge yourself.

config

add a host mapping

edit the /etc/hosts file and add a mapping for our libvirt service

    ... 
 192.168.2.100 cc.speedport.ip     # NIC`s main Ip used for this mapping - remember we had range of 100 
 1192.168.122.1 kvm.mapping.com   # mapping for the virtual NIC we just created called vibr0

edit /etc/ssh/sshd_config:

...
Include /etc/ssh/sshd_config.d/*.conf
PermitRootLogin yes
the tricky part here is:

we permit root login via ssh, but we use the root user for KVM

i think the reason why PermitRootLogin yes doesnt work is either the kvm-user, or the foreman user

both users dont have a pass, nor are there in the sudoers file

but anway blocking root ssl login is best practise, but i still dont know the true cause

so we just accept this for now and be happy that it works

dont forget to restart sshd!

login to foreman:

$ su foreman -s /bin/bash

add ssh key:

bash-5.1$ ssh-keygen

copy the key (thats where we need root):

bash-5.1$ ssh-copy-id root@kvm.mapping.com

 ...
 root@kvm.mapping.com's password:  <<------- ROOT
 Number of key(s) added: 1
 Now try logging into the machine, with:   "ssh 'root@kvm.mapping.com'"
 and check to make sure that only the key(s) you wanted were added.

try the ssh connection:

 bash-5.1$ 'root@kvm.mapping.com'

test the kvm-hypervisor connection:

bash-5.1$ virsh -c qemu+ssh://root@kvm.mapping.com/system

Willkommen bei virsh, dem interaktiven Virtualisierungsterminal.
Tippen Sie:  'help' für eine Hilfe zu den Befehlen
     'quit' zum Beenden
virsh # 

exit the shell:

bash-5.1$ exit

try to add the libvirt compute resource in foreman:

open the dashboard, and try to add a computeresource like this:
I had to restart my computer at before that because the libvirtd-admin.socket service stopped
you can check that by using systemctl:
  $ systemctl status libvirtd
  ● libvirtd.service - libvirt legacy monolithic daemon
  Loaded: loaded (/usr/lib/systemd/system/libvirtd.service; disabled; preset>
  Active: active (running) since Mon 2024-05-27 16:21:53 CEST; 1s ago
  TriggeredBy:
    ● libvirtd-admin.socket
    ● libvirtd-ro.socket
        ● libvirtd.socket

Creating and Configuring a Network Bridge on Linux Using nmcli (OPTIONAL)

The commands you executed are part of the process to create and configure a network bridge on a Linux system. This setup allows virtual machines (VMs) to communicate directly with the physical network, as if they were directly connected to the network via a physical network interface. Here’s a comprehensive guide translated into English and formatted in Markdown:

Step 1: Create a Network Bridge

$ sudo nmcli conn add type bridge con-name br0 ifname br0

This command creates a new network bridge named br0. A network bridge acts like a virtual switch, connecting multiple network interfaces, allowing traffic to be forwarded from one side of the network to another without passing through the physical device it arrived on.

Step 2: Add a Physical Interface as a Slave to the Bridge

$ sudo nmcli conn add type ethernet slave-type bridge con-name bridge-br0 ifname enp2s0 master br0

With this command, the physical network interface enp2s0 is added as a slave to the bridge br0. This connects the physical interface with the bridge, routing traffic passing through the bridge over the physical interface enp2s0.

Step 3: Activate the Bridge

$ sudo nmcli conn up br0

This command activates the bridge br0, enabling it to function and forward traffic between connected interfaces.

Step 4: Assign an IP Address to the Bridge (Optional)

$ sudo nmcli conn modify br0 ipv4.addresses "192.168.200.100/24" ipv4.method manual sudo nmcli conn up br0

These steps are optional and serve to assign a specific IP address to the bridge or virtual machine. In this example, the bridge br0 is assigned the address 192.168.200.100 within the subnet 192.168.200.0/24. After assigning the IP address, the bridge is reactivated to ensure the changes take effect.

This configuration enables virtual machines running over the bridge br0 to communicate directly with the physical network, as if they were directly connected to the network via the physical network interface enp2s0. This setup is particularly useful for creating an isolated environment for virtual machines while still providing access to the physical network.

Knowledge Base

Install

Discovery and Provisioning

libvirt

proxmox

external DNS&DHCP

diskless pxe-boot using zfs

RHEL_9_Foreman_Guide

libvirt

install

config

Creating and Configuring a Network Bridge on Linux Using nmcli (OPTIONAL)