/usr/share/nbd-server/nbd-server.conf.tmpl is in nbd-server 1:2.9.25-2ubuntu1.1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10
[generic] # If you want to run everything as root rather than the nbd user, you # may either say "root" in the two following lines, or remove them # altogether. Do not remove the [generic] section, however. user = nbd group = nbd includedir = /etc/nbd-server/conf.d # What follows are export definitions. You may create as much of them as # you want, but the section header has to be unique.