alf.mollerud
Posts: 1
Joined: Sat Oct 19, 2019 8:32 am

Time resets at boot

Sat Oct 19, 2019 8:42 am

I am running two raspberries (installed from NOOB) as dataloggers in a proof of concept, and I rely on timing for timestamping data-entries, and of course for running cronjobs. The berries are running without any internet connection.

Now - recently I noticed one of them had set the system time 3 months back - and moreover I discovered that it resat the time on every boot.
By playing round a little, I found that if I did timedatectl set-ntp false - it would NOT reset the time, but rather keep ticking.

What is the recommended (surefire) way of ensuring correct system time ?

AM.

alphanumeric
Posts: 2115
Joined: Tue Jan 19, 2016 2:17 pm
Location: Sydney, Nova Scotia, Canada

Re: Time resets at boot

Sat Oct 19, 2019 1:02 pm

The Raspberry Pi doesn't have a Real Time Clock, like a PC does. Thus, it will lose time when shut down. With no Internet connection it has no way to sync its time with a Time server. Normally it will remember the time when it was shut down. And then update that with the correct time retrieved from the internet time service when it gets an internet connection..
You can add a RTC, I've done it on several of my Pi's. Two of which run headless with no Internet connection. Once I set it correctly its maintained even when I shut down. The RTC has a battery backup like the ones in a PC do.

User avatar
DougieLawson
Posts: 36329
Joined: Sun Jun 16, 2013 11:19 pm
Location: Basingstoke, UK
Contact: Website Twitter

Re: Time resets at boot

Sat Oct 19, 2019 1:30 pm

fake-hwclock is supposed to store the time every 17 minutes past the hour. When the system restarts fake-hwclock loads the last stored time until your RPi can sync with the internets.

If it can't sync, you should consider adding a battery powered RTC.

If fake-hwclock can't write its status file you either a) have a read-only filesystem or b) have a knackered SDCard. Most likely reason is b).

For a read-only filesystem with no access to the internets you MUST have a RTC.

Test it, take a look at /etc/fake-hwclock.data
Run sudo fake-hwclock save
Take another look.

Code: Select all

pi@intrepid:~$ cat /etc/fake-hwclock.data
2019-10-19 13:17:00
pi@intrepid:~$ sudo fake-hwclock save
pi@intrepid:~$ cat /etc/fake-hwclock.data
2019-10-19 13:29:47
pi@intrepid:~$
Then reboot and take another look at it.
Note: Having anything humorous in your signature is completely banned on this forum. Wear a tin-foil hat and you'll get a ban.

Any DMs sent on Twitter will be answered next month.

This is a doctor free zone.

Return to “Troubleshooting”