/usr/include/collectd/ is in collectd-dev 5.4.0-3ubuntu2.
This file is owned by root:root, with mode 0o755.
..
/usr/include/collectd/core/
/usr/include/collectd/core/collectd.h
/usr/include/collectd/core/common.h
/usr/include/collectd/core/config.h
/usr/include/collectd/core/configfile.h
/usr/include/collectd/core/cpython.h
/usr/include/collectd/core/filter_chain.h
/usr/include/collectd/core/madwifi.h
/usr/include/collectd/core/meta_data.h
/usr/include/collectd/core/network.h
/usr/include/collectd/core/pinba.pb-c.h
/usr/include/collectd/core/plugin.h
/usr/include/collectd/core/riemann.pb-c.h
/usr/include/collectd/core/types_list.h
/usr/include/collectd/core/utils_avltree.h
/usr/include/collectd/core/utils_cache.h
/usr/include/collectd/core/utils_cmd_flush.h
/usr/include/collectd/core/utils_cmd_getval.h
/usr/include/collectd/core/utils_cmd_listval.h
/usr/include/collectd/core/utils_cmd_putnotif.h
/usr/include/collectd/core/utils_cmd_putval.h
/usr/include/collectd/core/utils_complain.h
/usr/include/collectd/core/utils_db_query.h
/usr/include/collectd/core/utils_dns.h
/usr/include/collectd/core/utils_fbhash.h
/usr/include/collectd/core/utils_format_graphite.h
/usr/include/collectd/core/utils_format_json.h
/usr/include/collectd/core/utils_heap.h
/usr/include/collectd/core/utils_ignorelist.h
/usr/include/collectd/core/utils_latency.h
/usr/include/collectd/core/utils_llist.h
/usr/include/collectd/core/utils_match.h
/usr/include/collectd/core/utils_mount.h
/usr/include/collectd/core/utils_parse_option.h
/usr/include/collectd/core/utils_random.h
/usr/include/collectd/core/utils_rrdcreate.h
/usr/include/collectd/core/utils_subst.h
/usr/include/collectd/core/utils_tail.h
/usr/include/collectd/core/utils_tail_match.h
/usr/include/collectd/core/utils_time.h
/usr/include/collectd/core/utils_vl_lookup.h
/usr/include/collectd/liboconfig/
/usr/include/collectd/liboconfig/oconfig.h