Alright, some progress... Vincent asked me privately to try switching to sysvinit. When I did that, chronyd started successfully on boot. So that narrows it down to some kind of systemd interaction problem.
I messed around with the chronyd.service file, and commenting out the Conflicts line resulted in chronyd starting at boot with systemd: dilinger@e7450:~$ uptime 00:51:51 up 1 min, 1 user, load average: 0.23, 0.08, 0.03 dilinger@e7450:~$ sudo systemctl status chrony ● chrony.service - chrony, an NTP client/server Loaded: loaded (/lib/systemd/system/chrony.service; enabled; vendor preset: enabled) Active: active (running) since Tue 2017-12-05 00:50:59 PST; 53s ago Docs: man:chronyd(8) man:chronyc(1) man:chrony.conf(5) Process: 558 ExecStart=/usr/sbin/chronyd (code=exited, status=0/SUCCESS) Main PID: 572 (chronyd) Tasks: 1 (limit: 4915) CGroup: /system.slice/chrony.service └─572 /usr/sbin/chronyd Dec 05 00:50:59 e7450 systemd[1]: Starting chrony, an NTP client/server... Dec 05 00:50:59 e7450 chronyd[572]: chronyd version 3.0 starting (+CMDMON +NTP +REFCLOCK +RTC +PRIVDROP +SCFILTER +SECHASH +SIGND +ASYNCDNS +IPV6 -DEBUG) Dec 05 00:50:59 e7450 chronyd[572]: Frequency 0.000 +/- 1000000.000 ppm read from /var/lib/chrony/chrony.drift Dec 05 00:50:59 e7450 systemd[1]: Started chrony, an NTP client/server. Dec 05 00:51:10 e7450 chronyd[572]: Selected source 192.207.62.39 Dec 05 00:51:11 e7450 chronyd[572]: Selected source 108.61.73.243 Dec 05 00:51:13 e7450 chronyd[572]: Source 192.207.62.39 replaced with 2604:a880:400:d0::8a0:a000 dilinger@e7450:~$ cat /etc/systemd/system/chronyd.service [Unit] Description=chrony, an NTP client/server Documentation=man:chronyd(8) man:chronyc(1) man:chrony.conf(5) #Conflicts=systemd-timesyncd.service openntpd.service After=network.target ConditionCapability=CAP_SYS_TIME [Service] Type=forking PIDFile=/run/chronyd.pid ExecStart=/usr/sbin/chronyd PrivateTmp=yes ProtectHome=yes ProtectSystem=full [Install] Alias=chronyd.service WantedBy=multi-user.target
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