/etc/icinga2/conf.d/ is in icinga2-common 2.1.1-1.
This file is owned by root:root, with mode 0o755.
..
/etc/icinga2/conf.d/commands.conf
/etc/icinga2/conf.d/downtimes.conf
/etc/icinga2/conf.d/groups.conf
/etc/icinga2/conf.d/hosts/
/etc/icinga2/conf.d/hosts/localhost/
/etc/icinga2/conf.d/hosts/localhost.conf
/etc/icinga2/conf.d/hosts/localhost/apt.conf
/etc/icinga2/conf.d/hosts/localhost/disk.conf
/etc/icinga2/conf.d/hosts/localhost/http.conf
/etc/icinga2/conf.d/hosts/localhost/icinga.conf
/etc/icinga2/conf.d/hosts/localhost/load.conf
/etc/icinga2/conf.d/hosts/localhost/procs.conf
/etc/icinga2/conf.d/hosts/localhost/ssh.conf
/etc/icinga2/conf.d/hosts/localhost/swap.conf
/etc/icinga2/conf.d/hosts/localhost/users.conf
/etc/icinga2/conf.d/notifications.conf
/etc/icinga2/conf.d/services.conf
/etc/icinga2/conf.d/templates.conf
/etc/icinga2/conf.d/timeperiods.conf
/etc/icinga2/conf.d/users.conf