The NI-DAQmx 20.1 installer for openSUSE Leap 15.1 requires the "insserv" command, however not all openSUSE installations include that command. If you install openSUSE in the text-only "Server" configuration, you will need to install the insserv-compat package (e.g. zypper install -y insserv-compat) before installing NI-DAQmx. This problem may exist in other configurations as well, you'll get installer errors if it can't find insserv.
