When using the Virt-Manager it was not possible to create a virtual machine. Permission issues were the cause. Libvirtd and Qemu are started with the user nobody. So the directories are owned by this user and group kvm. At check of rights has been found that two directories did not meet these privileges. Therefore, in the directory:
/var/lib/libvirtd/qemu
run the following command
sudo chown -R nobody:kvm channel dump
There are the new rights now angwendet recursively to the two directories channel and dump. Whether I find the user in the group can be determined with the following command:
groups
and add their own user to group:
sudo usermod -a -G kvmusername
