How do I enable ntpd to serve ntp clients (using High Sierra)?

I have some raspberry pi computers on a private network which do not have real time clocks and thus cannot keep time accurately after they are shut off. Because they are disconnected from the internet, they cannot use ntp to update their clocks after they sync. However, I can connect my mac to the private network and ask the raspberry pi computers to get the the current time from the mac. When I try doing this, it does not work. The ntpd launchd service is disabled on High Sierra. When I try to start it, this happens. $ sudo launchctl load -w /System/Library/LaunchDaemons/org.ntp.ntpd-legacy.plist Password: /System/Library/LaunchDaemons/org.ntp.ntpd-legacy.plist: Service is disabled I tried to enable like so, to no avail $ sudo launchctl enable system/org.ntp.ntpd-legacy $ sudo launchctl load -w /System/Library/LaunchDaemons/org.ntp.ntpd-legacy.plist Password: /System/Library/LaunchDaemons/org.ntp.ntpd-legacy.plist: Service is disabled so I have to start it manually like so: sudo /usr/sbin/ntpd When I test on the pi to see if the ntp sync is working, I get this: pi@jessie:~ $ timedatectl status Local time: Mon 2018-05-07 14:53:03 GMT+7 Universal time: Mon 2018-05-07 21:53:03 UTC RTC time: n/a Time zone: Etc/GMT+7 (GMT+7, -0700) NTP enabled: yes NTP synchronized: no RTC in local TZ: no DST active: n/a Notice that NTP synchronized is set to "no". When I test to see if the times are synchronized, this is the result: $ date; SSHPASS='pass' sshpass -e ssh pi@pi1 date Mon May 7 14:52:23 PDT 2018 Mon May 7 14:52:00 GMT+7 2018 The times are not synchronized. I am uncertain how to debug. It is not clear where the ntpd logs are stored. Ultimately, I just want to be able to start ntpd and have it respond to requests for time.