[tz] Hard copy of TZdata2023?

Guy Harris gharris at sonic.net
Fri Oct 20 21:32:09 UTC 2023

On Oct 20, 2023, at 2:04 PM, Alexandre Petrescu via tz <tz at iana.org> wrote:

> Le 20/10/2023 à 22:40, Doug Ewell a écrit :
>> Alexandre Petrescu wrote:
>>> Should be used when Internet is not available.
>> I would guess that very few systems depend on Internet connectivity to access the current tz database. Storing it locally seems much more sensible.
> Sure.  It should come from the Internet and stored locally.

On my system, running macOS, the tzdb originally came pre-installed.  Both operating system updates and tzdb data updates do, indeed, come from the Internet, and are stored locally.

> One would like to store it locally once one sees an email declaration from a gov't on this list, and not necessarily fast continuous updates.

The tzdb isn't continuously updated.  New versions are produced as necessary; the tzdb home page:


indicated that the current official is 2023c, released 2023-03-28, so the last update was almost 7 months ago.

> But in that, one assumes Internet access is readily available when one needs it.

"When one needs it" is "when the tzdb is updated"; that, as noted, hasn't happened for almost 7 months.  As there aren't continuous updates to the tzdb, continuous Internet access is not necessary.

> This might not be the case.  One might need to know now the date of some place, without having Internet access.

	<turns Wi-Fi off to completely remove Internet access>
	<goes to a Terminal.app window>
	<types TZ=Europe/Berlin date>

	Fri Oct 20 23:13:58 CEST 2023

So, yes, indeed, at least if you know the tzid for the tzdb region containing that place, you can know the date and time at that place without having Internet access.

With additional local data and software to let you look up the place and get the tzid, it would be even easier, but "place -> tzid" is not part of the scope of the tzdb.

The Clock app on my Mac, running Ventura, has a "World Clock" pane that lets me select a city, from a list that includes more than just the cities used to form tzids (but that doesn't, for example, include Christchurch, New Zealand, for some reason, even though it includes the city in which I live).  It works even with my Internet access turned off.  The same applies to the Clock app on my iPhone, even with both wi-fi and cellular data turned off.

The same may apply to third-party apps for both platforms, as well as built-in and third-party apps on Android and various clock apps for other platforms.

> Additionally, one might not have a usable computer to store that data to.

That's a different issue.  If you don't have a usable computer (where "computer" includes "smartphone", as per the above), you probably lack Internet access, and also probably lack anything that could *use* the data, so, yes, a printed table would be necessary. 

> So all one could do is to rely on printed tables of most recent timezone data that was available when Internet was last available.

As per my other mail, what you would want is a printed table of *compiled versions of* recent timezone data.  The tzdb does *not* consist of a list of time transitions, it consists of a list of rule and zone information from which the transitions can be calculated.  The zic command compiles those into binary lists of transitions, and, as has been noted here, current versions of the zdump command can dump out those lists in a somewhat human-readable form.

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