Bug#755722: systemd must sync systemclock to RTC on shutdown

Michael Biebl biebl at debian.org
Mon Feb 16 15:00:36 GMT 2015

Am 04.02.2015 um 06:00 schrieb Stefan Fritsch:
> On Wednesday 04 February 2015 01:41:14, Michael Biebl wrote:
>> Am 31.01.2015 um 10:19 schrieb Stefan Fritsch:
>>> severity 755722 serious
>>> retitle 755722 systemd must sync systemclock to RTC on shutdown
>>> thanks
>>> Systemd must make sure that the system clock does not go
>>> backwards,
>>> which causes all kinds of problems, with file systems and with
>>> other software. To achieve that, systemd has to sync the system
>>> time to RTC on shutdown. Upstream's argument that the system time
>>> may not be more accurate is completely unrelated to this issue.
>> Upstream argues, that whoever changes the clock, should also make
>> sure to sync that to the RTC if so desired. E.g. if you change the
>> time using the builtin timedatectl command, it will make sure the
>> RTC is synced.
> There is also natural drift between the system clock and the RTC. Who 
> is supposed to account for that? On a system with an uptime of several 
> months, the drift may be large enough to cause the time to go 
> backwards at a reboot.

Running hwclock --systohc on shutdown does not solve the time skew problem.
You could use hwclocks drift calculation and call hwclock --adjust e.g.
via a cron job. That is ugly though and it get's easily confused in
multi-boot environments.
A better alternative is NTP.
Incidentally, systemd ships systemd-timesyncd, a SNTP client, which can
easily be enabled via "systemctl enable systemd-timesyncd.service" and
we are discussing about shipping it enabled by default.

Why is it that all of the instruments seeking intelligent life in the
universe are pointed away from Earth?

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