On Fri, Aug 28, 2020, 10:06 Ulrich Windl <Ulrich.Windl@xxxxxxxxxxxxxxxxxxxx> wrote:
>>> Mark Corbin <mark@xxxxxxxxxxxx> schrieb am 27.08.2020 um 12:33 in
Nachricht
<c2edc2b5-0c6a-2d34-42ff-569c2626294a@xxxxxxxxxxxx>:
> Hello
>
> I am working on time synchronisation issues at boot for systems without
> an RTC (using balenaOS on a Raspberry Pi 3) and have some questions
> about how journald assigns timestamps to log messages.
>
> When I boot my system and look at the journal I see an initial date/time
> for kernel messages, e.g. '1 June 2020 10:00:00' followed by messages
> with the 'correct' date/time once the system time has been set from
> another source, e.g. build time, NTP, etc. This means that over several
> reboots I have lots of sets of log messages from 1 June 2020 which
> understandably confuses the 'journalctl ‑‑list‑boots' command. I found
> an issue that describes the problem here
> https://github.com/systemd/systemd/issues/662 and had assumed that there
> wasn't anything I could do about this.
"Good old UNIX" had the feature to "guess" the current time by looking at the
last update in the root filesystem (when that seemed newer than the "current
time").
One idea would be to have a "timestamp file" (much like a low-resolution
software RTC) that is updated periodically when it's known that the system time
is correct. Then after boot you would get a good guess, and time wouldn't jump
backwards, too.
I believe systemd already does that, although I keep forgetting the details – not sure if it's part of core or if it's part of systemd-timesyncd.
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