Raspian Stretch and timesyncd

[bell...@gmail.com]

It seems that in Raspian Stretch, timesyncd is enabled by default. And, it too attempts to read the date/time from a file when booting. I had removed fake-hwclock, but still had some problems with the date/time on reboot. Looking into syslog I saw the following

Mar 11 15:39:47 xxxx systemd-timesyncd[342]: System clock time unset or jumped backwards, restoring from recorded timestamp: Mon 2019-03-11 15:39:46 EDT

I ended up disabling timesyncd via

sudo systemctl disable systemd-timesyncd

and installing ntpd via

sudo apt-get install ntp

On reboot I now see that weewx is "Waiting for sane time.". Hope this helps others who might not have installed an RTC.

Rich

[Thomas Keffer]

Good observation!

I added some notes to the Wiki article on RPi time.

-tk

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[vince]

On Tuesday, March 12, 2019 at 11:39:22 AM UTC-7, bell...@gmail.com wrote:

I ended up disabling timesyncd via

sudo systemctl disable systemd-timesyncd

and installing ntpd via

sudo apt-get install ntp

Yes - systemd will run its own (not so good) time sync function by default.  You really don't have to disable it, if you install ntpd systemd detects that and lets ntpd drive things re: time.

[Thomas Keffer]

But, does it still record the time and try to use that on startup?

-tk

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[vince]

On Tue, Mar 12, 2019 at 1:48 PM vince <vince...@gmail.com> wrote:

Yes - systemd will run its own (not so good) time sync function by default.  You really don't have to disable it, if you install ntpd systemd detects that and lets ntpd drive things re: time.

On Tuesday, March 12, 2019 at 3:20:15 PM UTC-7, Thomas Keffer wrote:

But, does it still record the time and try to use that on startup?

 

I don't know....

Certainly no harm in disabling it in systemd to try to make sure, but then also do the normal disabling of fake-hwclock too I guess.

Bottom line is we probably want a system with no battery-backed-up clock to power up cleanly with a time old enough so weewx does its "wait for good time before starting" thing.   That was something like 'wait until the system clock is newer than the modification date of weewx.conf' or the like, wasn't it ?

This stuff'll make you crazy.

[G Hammer]

I've been a fan of chrony.

Hasn't been a problem on any system I've installed it on, easier (for me) to configure and monitor.

[David Beach]

Someone who is a Raspian expert can correct me on this if I'm wrong: 

I seem to recall that Raspian, if stripped of fake-hwclock, etc., does NOT start up with the universal Linux Jan 1970 date but uses a date that corresponds to the release date of that version of Raspian.  This means that programs/scripts that rely on looking for an "old" date (say, pre-2000 or pre-1990) as an indication of a 'bad' time setting won't work properly.

However, I can't remember where I stumbled on this nor does a quick Google search help me. I don't want to spread bad information. Can anyone confirm/refute this?

David

[vince]

On Wednesday, March 13, 2019 at 7:29:21 AM UTC-7, David Beach wrote:

I seem to recall that Raspian, if stripped of fake-hwclock, etc., does NOT start up with the universal Linux Jan 1970 date but uses a date that corresponds to the release date of that version of Raspian.  This means that programs/scripts that rely on looking for an "old" date (say, pre-2000 or pre-1990) as an indication of a 'bad' time setting won't work properly.

However, I can't remember where I stumbled on this nor does a quick Google search help me. I don't want to spread bad information. Can anyone confirm/refute this?

 

It's pretty easy to do experimentally.   Find a sacrificial pi with just an os there.  Yank the power.  Power it up.  Check its date.

The weewx check is in engine.py at around line 845.  It waits until the system time is later than the creation time of the weewx.conf file.   So it probably doesn't really matter what time any runtime system comes up with before some ntp(ish) or realtime clock things gets the os an accurate date and time.

[bell...@gmail.com]

It does appear that removing fake-hwclock and installing ntp might enough. On a new install, I removed fake-hwclocked, installed ntp, and disabled networking. On reboot the time stayed at the "default".

My net, if you are running WeeWX on a computer without an RTC, do your homework... read the logs, test network slowness/failures, etc.  

Or just spring for a RTC ;)

rich

On Tuesday, 12 March 2019 22:44:26 UTC-4, vince wrote:

[David Beach]

I *did* spring for a hardware RTC (a 3231). However, I still had problems and, because of other commitments (like my work, etc!), I did not further investigate why this should be so. Maybe when I get more free time, I'll troubleshoot. In the meantime, I just stuck my RPi on a spare UPS to avoid reboots!

David

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