Mac OS X Date & Time Synchronization

Question

When I have set Mac OS X to set it's date and time automatically, how often is this really done? And is there a way I can force an update?

Answer 1

NTPd (used by Mac OSX) will sync at the speed it thinks is more appropriate - that depends on your clock skew. It will be more frequent when you first turn it on / connect to the net and then will connect at longer intervals when it has stabilized your clock enough.

It does not only sync your current time and date, but also sync the actual clock speed. That means that after some time that you have enabled it (and are connected to the internet) your clock will be very precise even if you stay disconnected from the 'net for long times.

If you want the gory details, head on to wikipedia and to the NTP site.

Answer 2

The network time daemon (ntpd) logs activity to /var/log/system.log. You can see recent activity with grep:

$ grep ntpd /var/log/system.log | grep "time reset"
Jun 18 22:28:56 mymac ntpd[28]: time reset -0.301952 s
Jun 19 10:37:26 mymac ntpd[28]: time reset -1.443661 s
Jun 20 09:46:07 mymac ntpd[28]: time reset -3.529638 s
Jun 21 09:57:43 mymac ntpd[28]: time reset -3.293325 s
Jun 21 22:25:11 mymac ntpd[28]: time reset -0.539650 s
Jun 21 22:43:12 mymac ntpd[28]: time reset +0.142553 s
Jun 22 09:24:23 mymac ntpd[28]: time reset -1.844003 s
Jun 22 09:41:59 mymac ntpd[28]: time reset -0.156320 s
Jun 23 09:06:00 mymac ntpd[28]: time reset -1.880272 s

Read the ntp.conf man page (man ntp.conf) for details on further configuring ntpd including how much info is logged and (I assume) frequency of updates.