Re: Does Dimdows Know What Time It Is?

On Sat, 28 Sep 2024 22:40:24 -0000 (UTC), Lawrence D'Oliveiro
<ldo@nz.invalid> wrote in <vda0ko$1e457$1@dont-email.me>:

Something Unix did that was different from most other OSes was, its
system clock kept time in UTC (or GMT, in pre-UTC days). Linux does the
same.
When you use a command like “date” to see what the current date and time
is, it converts that UTC time to a local time in some specified
timezone. Changing the timezone is as easy as specifying a new value for
the TZ environment variable.
 
Windows, on the other hand, keeps its system clock in local time, in
some specific time zone that is assumed to apply systemwide.
 
This is a particularly dumb idea when you realize how much it
complicates things if your time zone has daylight saving time. We have
seen this sort of thing happen on Windows systems before, where they
might forget to adjust the clock to start/stop daylight saving, or even
adjust it twice so you end up being an hour off in the opposite
direction.
 
This can’t happen on Linux systems, because there is no turning daylight
saving “on” or “off” as such: there is simply a table of local time
offsets (from the “tzdata” files), and the correct offset to apply
depends only on the actual UTC time value, not on the current setting of
any system flag.
 
This also makes it easy to convert between UTC and local times at any
time in the past, for any time zone.

$ echo $TZ

$ ls -l /etc/localtime
lrwxrwxrwx 1 root root 39 Jul 16 07:50 /etc/localtime -> /usr/share/zoneinfo/America/Los_Angeles

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