When starting virt-manager, it asks for the root password.
It looks like virt-manager causes the libvirtd daemon to run pkcheck with a couple of arguments, which then shows this authentication dialog. So it's PolicyKit who's asking for the root password.
The official website (libvirt.org) describes how to define a PolicyKit rule to get rid of the password prompt:
$ sudo cat /etc/polkit-1/localauthority/50-local.d/50-org.example-libvirt-remote-access.pkla [libvirt Management Access] Identity=unix-group:libvirt Action=org.libvirt.unix.manage ResultAny=yes ResultInactive=yes ResultActive=yes
This package is installed on the system, plus a few DE frontends:
Apparently the example configuration on libvirt.org is outdated?
What configuration is necessary to get rid of the password prompt (for a specific user group)?