Last week’s deep dive into the precision of times in the log concluded that, with the data currently available, the highest they can aspire to are microseconds, 10^-6 seconds, and not the nanoseconds given in the last build of LogUI. The aims of this new build are to deliver correctly rounded microsecond time resolution, and to adopt consistency in time zones and DST corrections.

I described in detail yesterday how I arrived at conversion of log entry dates to yield the time in microseconds. Here I’ll consider how to treat time zones correctly.

When you enter a start time in LogUI, this is assumed to be given in the local time set on your Mac, including both its time zone and any DST correction. LogUI already takes those into account, and performs any necessary adjustments.

Now that I have completely overhauled how LogUI converts the date stored for each log entry, I have changed behaviour in comparison with the default option of the log show command, and Ulbow that accepts its timestamps without question. The best way to see that is to observe log entries when the Mac’s time zone is changed.

Ulbow, and by default the log show command, uses date and time stamps adjusted for the time zone and DST setting at the time each entry is written to the log. You should therefore be prepared to see abrupt discontinuities in its timestamps. This condensed sequence of log entries from Ulbow shows what happens when you change time zone from New York to the UK during DST:
10:50:00.729672-0400 com.apple.Settings /AppleInternal/Library/BuildRoots/ … obfuscated() obfuscate output: …
10:50:00.729687-0400 com.apple.xpc.alarm Setting timer for "com.apple. …
15:50:00.730675+0100 === system wallclock time adjusted
15:50:00.730733+0100 com.apple.mobiletimer.logging … rescheduling 0 alarms
15:50:00.730754+0100 com.apple.xpc.alarm Setting timer for "com.apple.mdmclient.timer.ManualCertRenewalCheck" in 86080 seconds.

Instead, LogUI adjusts all log entries to the current time zone for consistency in reading:
15:50:00.729672+0100 com.apple.Settings /AppleInternal/Library/BuildRoots/ … obfuscated() obfuscate output: …
15:50:00.729687+0100 com.apple.xpc.alarm Setting timer for "com.apple. …
15:50:00.730675+0100 Boundary === system wallclock time adjusted
15:50:00.730733+0100 com.apple.mobiletimer.logging … rescheduling 0 alarms
15:50:00.730754+0100 com.apple.xpc.alarm Setting timer for "com.apple.mdmclient.timer.ManualCertRenewalCheck" in 86080 seconds.

If you’re using log show, you can add the --timezone local option to adopt the same behaviour.

This also solves the dilemma when you’re browsing the log through a time zone change, for example when the clock has gone forward to DST, or the reverse. In LogUI the rule is simple: enter the current time, and all log entries will be adjusted to and shown in that single time zone.

I’ve previously explained some of the confusion that can arise with DST changes, in the autumn/fall, and again in the Spring. Hopefully LogUI won’t lead to any confusion now.

LogUI 1.0 build 52 is now available from here: logui152
and from its Product Page.

Enjoy!