Boot code tz=

[ClydeM]

Sorry to be a bother--I could probably figure this out by some simple experimenting--but by mentioning it here, maybe the powers that be will be inspired to update the docs.

The documentation provided for the "tz=" boot code confuses me, especially its use both with and without the "noutc" boot code. The F4 boot page shows the simplest example as "tz=GMT+8" which IMHO most people would interpret as Greenwich Mean Time plus eight hours, where hours count positive eastward from GMT, and negative numbers count westward. To me, the +8 here means an offset from UTC, which puts the pc in Beijing, China. This also implies tz= is being used without an accompanying "noutc". But what if "noutc" is used with "tz=GMT+8"?  If all of my assumptions are wrong, then perhaps "GMT+8" is not the best example to use on the F4 boot code page.

The description following that example confuses me further, because it implies a wholly different meaning to the "+8" in "PST+8PDT" -- what does it mean, both with and without a "noutc" ? Could it mean the number of hours ahead of the international date line where "PST" lies? Or the number of hours difference between the given normal time zone string and the given summer time zone string?


Just trying to describe my confusion at the possibilities one might deduce from these two examples of the use of tz=, with and without noutc, gives me a headache. Guide me please?

[Juanito]

First off, those nice unix people decided that GMT+8 means 8 hours behind GMT, i.e. California or somewhere like that.

Linux and mac set the BIOS clock to UTC (GMT), whereas windows sets it to local time, so you only need to use the noutc code, when you use linux on a windows machine.

[curaga]

Quick example of noutc:

1. BIOS clock is 13:37. With noutc set, it doesn't matter what timezone you specify, the time will always be 13:37 - only the name of what programs show you will change. "Beijing timezone, local time 13:37"

2. BIOS clock is 13:37, UTC time, not local time. You don't specify noutc. Now what the system shows you depends on the timezone. tz=GMT-2 would give you 15:37, "German time".

[ClydeM]

Quick example of noutc:

1. BIOS clock is 13:37. With noutc set, it doesn't matter what timezone you specify, the time will always be 13:37 - only the name of what programs show you will change. "Beijing timezone, local time 13:37"

2. BIOS clock is 13:37, UTC time, not local time. You don't specify noutc. Now what the system shows you depends on the timezone. tz=GMT-2 would give you 15:37, "German time".

So per your #2 example, with noutc not specified, what does the +8 in "PST+8PDT" mean? Is it just defining the offset from UTC for the PST time zone? If so, then where would the offset from UTC for PDT be specified? Somewhere I read that the number in between the two labels means how much difference there is between summer and winter times....

[curaga]

I think in that case the offset is 8 hours, the base name is PST but it's currently in PDT (pacific winter time?). Not sure.