the update is blocked as long as UVMM is installed on the UCS instance. You should be able to remove UVMM (which should keep the images of the virtual machines), upgrade to UCS 5.0 and use standard Debian tools like virt-manager to manage the virtual machines.
Currently there is no step-by-step guide available for the process, so please be carefull and hav backups.
I uninstalled UCS Virtual Machine Manager via the App Center.
The update still fails with the following:
The system can not be updated to UCS 5.0 due to the following reasons:
blocking_apps:
The update to 5.0 is currently not possible,
because the following Apps are not available for UCS 5.0:
* KVM virtualization server
old_packages:
WARNING: The following packages from UCS-4 are still installed, which are no longer supported with UCS-5:
univention-kvm-compat
univention-kvm-virtio Mark libvirt as manually installed "apt-mark manual libvirt-daemon" to keep virtualisation capabilities
univention-novnc
univention-virtual-machine-manager-daemon
univention-management-console-module-uvmm
univention-virtual-machine-manager-node-common
univention-virtual-machine-manager-node-kvm
Use "univention-remove --purge" with the packages as following arguments to remove them
minimum_ucs_version_of_all_systems_in_domain:
The following hosts must be upgraded to UCS 4.4-8 first:
cn=filesrv,cn=memberserver,cn=computers,dc=hvgeek,dc=lan: 4.4-5
Error: Update aborted by pre-update script of release 5.0-0
Is it safe to purge the packages:
univention-kvm-compat
univention-kvm-virtio Mark libvirt as manually installed "apt-mark manual libvirt-daemon" to keep virtualisation capabilities
univention-novnc
univention-virtual-machine-manager-daemon
univention-management-console-module-uvmm
univention-virtual-machine-manager-node-common
univention-virtual-machine-manager-node-kvm