On Thu, Jun 20, 2024 at 12:52 AM <to...@tuxteam.de> wrote: > > On Wed, Jun 19, 2024 at 01:01:44PM -0400, Jeffrey Walton wrote: > > On Wed, Jun 19, 2024 at 7:09 AM Greg Wooledge <g...@wooledge.org> wrote: > > [...] > > > > I strongly disagree. The system clock is kept on "epoch time", which > > > is the number of seconds since midnight, January 1, 1970 UTC. > > > > > > The system clock doesn't have a time zone of its own. It just gets > > > converted to a time and date within any given time zone on demand. > > > > ++. > > > > The sharp edge is how the RTC clock is set - UTC or localtime. Also > > see <https://wiki.debian.org/DateTime>. > > Please don't mix those three things, that makes them just more confusing. > > The original topic was the system's time zone. This hasn't anything > to do with the RTC clock, and only peripherally with "the system's > time zone" (of which some, me included, say "there's no such thing", > and others disagree :) > > You have > > - the RTC clock. This is *only* looked at at boot time, to init > the system clock (and when you, as an admin, do "hwclock"). > During those operations, it's important to know which timezone > the RTC is in, since this one /is/ in "human format. It was > intended to be read and set by humans, like your kitchen clock, > back then. > > - the system clock: it boringly counts seconds. Since Epoch. > Since it has't hours or minutes, let alone weeks or months, > time zones don't even make sense to it. Sometimes it does > a leap second, but experts are torn on whether this was a > good idea at all. Have a look at [1] for an entrance to yet > another deep time rabbit hole. > > - timezones and stuff: those happen whenever you want to convert > the system clock to hours, minutes, days, and other human > related stuff and back. > > (if you have good net connectivity, reading the RTC at boot can > be shunned completely, you don't need it anymore).
Don't forget boottime and the delta between boottime and the monotonic clock. You'll need them to explain this: $ TZ=America/New_York dmesg -T | head -1 [Wed Jun 19 01:50:14 2024] Linux version 6.9.4-200.fc40.x86_64 (mockbuild@d372fa 1a67e347178b7bd422ead09b96) (gcc (GCC) 14.1.1 20240607 (Red Hat 14.1.1-5), GNU l d version 2.41-37.fc40) #1 SMP PREEMPT_DYNAMIC Wed Jun 12 13:33:34 UTC 2024 $ TZ=America/California dmesg -T | head -1 [Wed Jun 19 05:50:14 2024] Linux version 6.9.4-200.fc40.x86_64 (mockbuild@d372fa 1a67e347178b7bd422ead09b96) (gcc (GCC) 14.1.1 20240607 (Red Hat 14.1.1-5), GNU l d version 2.41-37.fc40) #1 SMP PREEMPT_DYNAMIC Wed Jun 12 13:33:34 UTC 2024 > Please, keep those three at a safe distance I'm not sure how you can disgorge them given they contribute to a human readable time. Jeff
