different times for last boot between last and uptime -s

[Tom Mitchell]

On Tue, Dec 6, 2022 at 6:08 PM Tom Mitchell <niftyubuntu at niftyegg.com> wrote:
>
> On Mon, Dec 5, 2022 at 1:36 AM Lentes, Bernd
> <bernd.lentes at helmholtz-muenchen.de> wrote:
> >
> > Hi guys,
> >
> > i just realized a strange behaviour. I had to find out the last boot procedure
> > for an Ubuntu 20.04.3 LTS.
> > uptime -s says:
> > root at crispor-server:/var/log/atop# uptime -s
> > 2022-12-02 21:37:18
> >
> > last says:
> > reboot   system boot  5.4.0-91-generic Fri Dec  2 22:37   still running
> >
> > The current date and time is correct, timezone is Berlin/Europe.
> >
> > This difference makes debugging more complicated.
> > Does anyone know the reason ?
>
> Recall that windows keeps local time on the RTC.
> Unix and Linux keep the UTC as the anchor time.
> and all dates are times are computed from UTC.
> WindowsPC dual boot was a pain with clocks until date time
> could cope with local time on the RTC.
>
> Thus there are corrections to cause things to
> Double check:
> NAME
>        hwclock - time clocks utility
> ...
>      -l, --localtime; -u, --utc
>            Indicate which timescale the Hardware Clock is set to.
>
>            The Hardware Clock may be configured to use either the UTC
> or the local timescale, but nothing in the clock itself says which
> alternative is being used.
>            The --localtime or --utc options give this information to
> the hwclock command. If you specify the wrong one (or specify neither
> and take a wrong default),
>            both setting and reading the Hardware Clock will be incorrect.
>
>            If you specify neither --utc nor --localtime then the one
> last given with a set function (--set, --systohc, or --adjust), as
> recorded in /etc/adjtime, will
>            be used. If the adjtime file doesn’t exist, the default is UTC.
>
>            Note: daylight saving time changes may be inconsistent when
> the Hardware Clock is kept in local time. See the discussion below,
> under LOCAL vs UTC

It is valuable to look at the newer interface..

# timedatectl -a
               Local time: Wed 2022-12-07 15:52:37 PST
           Universal time: Wed 2022-12-07 23:52:37 UTC
                 RTC time: Wed 2022-12-07 23:52:37
                Time zone: America/Los_Angeles (PST, -0800)
System clock synchronized: yes
              NTP service: n/a
          RTC in local TZ: no