-u user[:group]
Specify a user, and optionally a group, to switch to. This
option is only available if the OS supports running the server
without full root privileges. Currently, this option is sup‐
ported under NetBSD (configure with --enable-clockctl) and
Linux (configure with --enable-linuxcaps).
我猜测在这种特殊情况下它意味着
user
并且ntp:ntp
意味着用户 ntp 和组 ntp。我希望它是特定于应用程序的。来自 ntpd(8) 手册页