On one of our devices we are allowing users to manually adjust the system time. This is because we expect that a majority of the time we wonn’t have internet connectivity.
What we did was implement an endpoint in one of our existing containers that set the system clock based on the time it receives. It uses the this node library. It works just fine to set the time and I can see the time reflected in the containers and in the host OS by using the date command. The logs also output updated timestamps as I would expect.
The issue is when the device is rebooted the time is different. For example, on my host OS after changing the time it shows:
Mon Apr 13 10:41:35 UTC 2020
Now when I reboot I get:
Mon Apr 13 15:44:31 UTC 2020
It should be noted that I’m currently in CST (UTC -5:00). Does anyone know what’s happening here?
Thanks for that information. When you reboot the device it will initially poll the NTP sources and use that time if it reaches them. (More information about that here: https://www.balena.io/docs/reference/OS/time/#chrony ) So if you are setting the time to something other than the current UTC and then rebooting, your example appears to be the expected behavior.
Hi there, chrony does have RTC support, but since most hardware (RPi) doesn’t have one on-board by default, you would need to add a RTC hardware module (via GPIO) first and configure chrony to use it. This is documented in the chronydocs.
balenaOS is already configured to use RTC, you can check the default set here. It is using rtcsync. If I understand correctly, you need to disable the chrony service in the hostOS which will prevent NTP from updating the time. Here is how you could proceed:
Use a container with dbus-send and execute the following command: DBUS_SYSTEM_BUS_ADDRESS=unix:path=/host/run/dbus/system_bus_socket dbus-send --system --dest=org.freedesktop.systemd1 --type=method_call --print-reply /org/freedesktop/systemd1 org.freedesktop.systemd1.Manager.StopUnit string:"chronyd.service" string:"replace"
This did not seem to work. I must admit it took a little bit to get it to function because I fell into this pitfall:
This is the reply from the dbus-send command:
17.04.20 09:58:00 (+0000) api method return time=1587117480.786902 sender=:1.1 -> destination=:1.6250 serial=177495 reply_serial=2
17.04.20 09:58:00 (+0000) api object path "/org/freedesktop/systemd1/job/79940"
When I changed the system time on the device, disconnected from the network, and power cycled it came up with a completely incorrect time. I thought originally that I would have to change the rtcsync directive in chrony to rtcfile, which is why I had originally asked how to edit that configuration:
The hwclock program is often set-up by default in the boot and shutdown scripts with many Linux installations. With the kernel RTC synchronisation ( rtcsync directive), the RTC will be set also every 11 minutes as long as the system clock is synchronised. If you want to use chronyd 's RTC monitoring ( rtcfile directive), it’s important to disable hwclock in the shutdown procedure. If you don’t, it will over-write the RTC with a new value, unknown to chronyd . At the next reboot, chronyd started with the -s option will compensate this (wrong) time with its estimate of how far the RTC has drifted whilst the power was off, giving a meaningless initial system time.
There is no need to remove hwclock from the boot process, as long as chronyd is started after it has run.