different times for last boot between last and uptime -s

[gene heskett]

On 12/6/22 05:25, Ralf Mardorf via ubuntu-users wrote:
> On Tue, 2022-12-06 at 07:11 +0000, Colin Law wrote:
>> Do you dual boot with windows? I believe that Windows sets the RTC to
>> local time, Linux sets it to UTC.
> 
> This...
> 
> On Mon, 2022-12-05 at 23:38 +0100, Lentes, Bernd wrote:
>> root at crispor-server:~# timedatectl show --all
>> Timezone=Europe/Berlin
>> LocalRTC=no
>> [snip]
>> TimeUSec=Mon 2022-12-05 23:10:39 CET
>> RTCTimeUSec=Mon 2022-12-05 23:10:40 CET
> 
> ...shows that the OP's battery buffered hardware clock (RTC) is set to
> UTC when running timedatectl.
> RTCTimeUSec=Mon 2022-12-05 23:10:40 CET means that
> at this moment the RTC is  22:10:40 UTC.
> 
> If another operating system would set the RTC to CET, then at startup,
> before the system clock is initialized, there wouldn't be a hour
> missing. It's behind for an hour, since the RTC is set correctly to the
> wanted UTC and no other operating system does set it to CET. If another
> operating system would set the RTC to CET, then the clock wouldn't be a
> hour behind, it would be +- 0.
> 
> On Tue, 2022-12-06 at 00:05 -0500, gene heskett wrote:
>> Actually Ralf, the OP could have an erronious Locale entry, or a very
>> stale tzdata file. I much prefer the HWclock is on UTC and the tzdata
>> file is updated when apt wants to update it, then if Locale is correct,
>> the date query should return the local time, with the HWClock on UIC.
>> And everything Just Works.
> 
> Gene, I'm in the same time zone as the OP. Actually everything seems to
> work correctly. My RTC is set to use CET instead of UTC and I get
> 
> [rocketmouse at archlinux ~]$ last -3
> rocketmo pts/0        :0               Thu Dec  1 09:53 - 11:22  (01:28)
> rocketmo tty7         :0               Fri Nov 25 15:03    gone - no
> logout
> reboot   system boot  4.19.265-rt117-0 Fri Nov 25 15:02   still running
> 
> wtmp begins Thu Apr  4 12:47:25 2019
> [rocketmouse at archlinux ~]$ timedatectl show --all
> Timezone=Europe/Berlin
> LocalRTC=yes
> CanNTP=yes
> NTP=no
> NTPSynchronized=no
> TimeUSec=Tue 2022-12-06 10:42:59 CET
> RTCTimeUSec=Tue 2022-12-06 11:42:57 CET
> 
> "last" does show the correct time for the system boot in CET on my
> machine (I compared it with handwritten notes), while for the OP it is 1
> hour behind since the OP's RTC is set to UTC. This is expected. Btw. it
> might not be related to the system clock initialized or not initialized,
> that the OP's "last" does report to be a hour behind. Probably "last"
> does report the RTC and not the system clock time even after
> initialisation, taking a look at  man last ,  man wtmp ,  man rtc  etc.
> might or might not reveal the reason.
> 
> However, as you can see on my machine TimeUSec shows 10:42 CET, but
> RTCTimeUSec does show 11:42 CET. Actually the RTC on my machine is not
> at 11:42 it is on 10:42. The command assumes UTC for the RTC, hence an
> hour gets added.
> 
> So everything is ok on the OP's and on my machine (assuming timedatectl
> and last on Ubuntu and Arch don't differ). It's just a misinterpretation
> of the reported times, that does cause the confusion.
> 
> We know similar issues for other commands, when it's not clear if sizes
> are e.g. reported in GB or GiB.
> 
> [rocketmouse at archlinux ~]$ man ls | grep "The  SIZE"
>         The  SIZE  argument  is  an integer and optional unit (example:
> 10K is 10*1024).  Units are K,M,G,T,P,E,Z,Y (powers of 1024) or
> KB,MB,... (powers of 1000).  Binary prefixes can be
> 
> IOW if ls shows GB, it's for real GiB and not for real GB.
> 
> If Windows would cause such confusion, we wouldn't be reserved with
> criticism. Actually Linux isn't that perfect, too.
> 
> Btw. my machine is a Linux multi-boot only, no Windows install on bare
> metal is involved.
> 
> Regards,
> Ralf
> 
Agreed Ralf, both ways work if properly setup. That is the key 
provision. ntp solves it for 99%, but there seems to be that 1% who 
insist on doing it their way. I had a woof like that, 40+ years ago.
Never wrong, even when she was. I've had the ultimate revenge, outliving 
her. As for winders here? Target practice, and I'm a good shot. My 
/etc/hosts file just gained 4 more entries, all linux based, I'm 
building a 3d printer farm. Pretty good for an old coot that turned 88 a 
couple months back

Take care & stay well now old friend.

Cheers, Gene Heskett.
-- 
"There are four boxes to be used in defense of liberty:
  soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author, 1940)
If we desire respect for the law, we must first make the law respectable.
  - Louis D. Brandeis
Genes Web page <http://geneslinuxbox.net:6309/>