Unit libvirtd.service could not be found. on VM

[Michal Privoznik]

On 5/12/20 1:41 PM, Dana Elfassy wrote:
> if I understand correctly then I shouldn't have installed libvirt-daemon 
> on the guests VMs?
> 
> 

Just a little background to Daniel's response. Libvirt and QEMU treat 
guests as black boxes, to some extent. There are some exceptions to this 
rule, when it comes to para-virtualization (that is when the guest knows 
it is running virtualized and therefore can optimize some things). The 
perfect example is virtio (which are para-virtualized devices like NIC, 
disk, etc.). Depending on the guest the virtio drivers are either 
already installed (majority of Linux distributions including CentOS, if 
not all of them) or they have to be installed separately (Windows is 
typical example).

Then, some tasks can be performed only if there is a small program 
running inside the guest (so called guest agent), which listens for 
incoming commands, executes them and sends the result back to libvirt. 
In CentOS this is qemu-guest-agent RPM. As mentioned, guest agent needs 
a channel to talk to libvirt which can be configured through virsh 
directly [1], or in virt-manager (if not already present, but I guess 
virt-install adds it automatically): Add hardware -> Channel -> Name: 
org.qemu.guest_agent.0 -> Finish.

Some management applications have their own guest agents (e.g. 
libguestfs), but I wouldn't worry about them - the management 
application will configure them automatically; and you are not using 
them anyway.


However, on the host the set of packages needed is different (note, you 
don't need any virtio drivers - they are contained in qemu already; nor 
you need the guest agent). libvirt-daemon-driver-qemu is the package 
containing qemu driver for libvirt. However, in order to use other 
features libvirt provides I suggest installing 'libvirt-daemon-kvm' 
which drags in the rest of packages (e.g. storage driver, network 
driver, etc.)

The host is also where you need libvirtd running (systemctl enable 
libvirtd.service  or if you want to use socket activation then: 
systemctl enable libvirtd.socket)

Michal


1: https://wiki.libvirt.org/page/Qemu_guest_agent