/usr/share/man/man3/sd_event_source_get_io_fd.3.gz is in libsystemd-dev 237-3ubuntu10.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/man/man3/sd_event_add_io.3.gz
/usr/share/man/man3/sd_event_add_io.3.gz