Where does the Raspberry Pi get the time from?
I don't have to set the clock (besides the timezone) on the Raspberry Pi. Where is it getting the time from? About how accurate is it?
Fresh installs have it pick up time from a variety of sources. For details, and for the reason why you should change it to time.nist.gov, see this Q&A: https://raspberrypi.stackexchange.com/questions/68811/how-do-i-set-raspbian-to-use-the-primary-time-server-time-nist-gov
Raspbian gets the time from an NTP Server (a "time server").
Unplug your Raspberry Pi completely, pull out the network cable and start the Raspberry Pi up again. You will see that the date and time are incorrect.
If you want/need the date and time to not be reset without being plugged into the internet, you'll need a Real Time Clock (RTC) - for example, something like this - which will keep the time current, by using a battery to run a clock. This is, also, how your computer keeps the time when it is not being powered.
UPDATE Just a side note that the above RTC clock is not the only way to keep the time accurate between power losses. You could also use a GPS module and hook that up to the GPIO pins.
Accuracy It's pretty accurate, although if your clock's time is off by quite a bit. It may take up to 3 hours to correct itself, as changes from the server are applied gradually to your local clock. Network stability has the biggest impact on the accuracy, as a unpredictable network (something more wireless, like 3G) will make it very hard to be accurate. To put it simply: The accuracy is pretty good, the time difference between your computer and the actual time (from the NTP Server) is normally less than 100ms.
Nice answer; it could be improved by mentioning the accuracy of the NTP protocol.
@AlexChamberlain Thanks for the heads up, I was going to add it but it completely slipped my mind. I've added it now.
While my Pi is network connected, I'm noticing that time has drifted by 30mins now. Is the ntpd enabled by default or do I need to do this manually?
Maybe so, until Raspberry Pi 3. I bought one two months ago and NTP time update is screwed, well at least on official Raspbian Jessie. I opened three threads with that problem and everyone are clueless. I had to buy hardware module for time keeping to solve the problem.
Upvote. And make sure you are reaching a Stratum-1 server instead of the default Stratum-16 pools that come with stock Raspbian and most ubuntu and Windows installs. Whenever you see the word pool you know there are a lot of computers between you and the Master Clock. So do this instead: https://raspberrypi.stackexchange.com/questions/68811/how-do-i-set-raspbian-to-use-the-primary-time-server-time-nist-gov/68812#68812
While ntp servers are still used in Raspbian Stretch to update the time, systemd now takes care of this rather than the ntp application.
Morgan's answer gave me the hint I needed to solve the problem.
Go to http://support.ntp.org/bin/view/Servers/NTPPoolServers
Select your region, then your country and a list of servers will be display.
Edit your /etc/ntp.conf file e.g.
sudo vim /etc/ntp.conf
Replace the list of servers with the one you found in the webpage. e.g.
server 0.dk.pool.ntp.org iburst
server 1.dk.pool.ntp.org iburst
server 2.dk.pool.ntp.org iburst
server 3.dk.pool.ntp.org iburst
Save and exit.
Restart the ntp deamon.
sudo /etc/init.d/ntp restart
check that the date is correct.
Thu Jun 20 13:39:20 CEST 2013
In one of my servers the date was changed inmediately. In the other I had to wait a couple of minuts.
If you're in the UK (or another country) then you can just change the two letter country code to suit .e.g. `server 0.uk.pool.ntp.org iburst`
Step 4 did not work for me until after about 15 minutes. Or perhaps because I ran `ntpq -p`. I am using: "Raspbian GNU/Linux 7 (wheezy)" and "Linux raspberrypi 4.1.7+ #817 PREEMPT Sat Sep 19 15:25:36 BST 2015 armv6l GNU/Linux"
Perhaps `hwclock` or `fake-hwclock` is interfering (but the "/etc/rc.conf" part is out of date)
The `ntpq -p` part is from an answer to *How is time kept on the Raspberry Pi?*.
And after a 5 minute shutdown it was 5 minutes behind (`ntpq -p` did not make a difference).
Forget the pool servers. Use time.nist.gov to get is from the horse's mouth: https://raspberrypi.stackexchange.com/questions/68811/how-do-i-set-raspbian-to-use-the-primary-time-server-time-nist-gov/68812
If you have the
fake-hwclockpackage, it will also do a timestamp saving trick to prevent the clock from being reset. That won't advance time while the device is off, so it will lag behind. The internal clock will also drift a tiny bit while on.
If you have an Internet connection (or lan with a server) and run ntp (ntpd/ntpdate), you can get the time over network, as other answers point out. When synchronized, it is really quite accurate. Online servers will also give you the consensus "world time".
interesting about `fake-hwclock`. Why would someone want to freeze the clock when the machine is off? I can't think of a use case for that. Is there?
@Scoop Because the alternative is forgetting the time, so it will reset. This will cause any recorded timestamps appear to be from the future etc. "Freezing" the clock makes sure time keeps moving forward, even if the count is off :)
Having ntp or other way to set the clock of course will still work and fake-hwclock only runs at boot and shutdown.
for `fake-hwclock` on Arch Linux, use http://archplusplus.co.uk/post/40202081414/fake-hwclock-for-arch-linux-arm-on-raspberry-pi-using
The Raspberry Pi doesn't have an integrated real time clock (RTC) for cost-effectiveness: see the question "Why is there no real time clock (RTC)?" in the official FAQ. It means that when you unplug the Raspberry Pi, it loses its time. When you power it back, the time is initialized to 1 January 1970 (aka Unix epoch).
The Raspberry Pi sets its time over the network with NTP, a protocol for clock synchronization between computers. This protocol is widely used over the Internet to make sure the computers have the same time and is highly reliable since some machines are dedicated to the time calculation with atomic clocks.
ntpdis a daemon (a software in background) launched a boot time, and it is responsible for synchronizing time using the NTP protocol.
ntpdcan be configured with the file
/etc/ntp.conf. For instance, this is where you can set the servers to request the time.
Doesn't it remember the last time? I shutdown a Raspberry Pi a week ago and `date` now shows that week-old date plus, I think, some extra hours from the uptime yesterday and today (after some restarts yesterday and today). (Raspbian, corresponding to mid 2015).
Run `cat /etc/fake-hwclock.data` and you will see the last time `fake-hwclock` saved the time (obviously, at shutdown time). `fake-hwclock` is used on the RPi to mimic a real clock. I think you booted your RPi without Internet access or without `ntpd` started to update the time. Can you confirm that?
Raspbian Stretch: NTP not installed by default
It would appear that there was a bit of change-up with Raspbian Stretch. In short, ntp is no longer installed. Running
dpkg -l | grep ntpreturns nothing.
Apparently, Stretch abandoned the
ntpapplication in favor of systemd. Check the
man timesyncdentry for specifics on configuration settings.
timesyncdstill uses ntp servers to update the time. If you want to configure these servers manually, you can do so in the
After doing the edit, restart the service by `sudo systemctl restart timesyncd` and after that check the logs by `journalctl -u timesyncd -f` sometimes corporate firewalls blocks the port. In such cases, use the provided corporate ntp server URL.
If logging or keeping time when offline is what you're looking for, you may want to add a Real Time Clock chip, like the DS1307.
There's fairly reasonable RTC solutions like this to buy e.g. http://www.cjemicros.co.uk/micros/individual/newprodpages/prodinfo.php?prodcode=4D-RaspberryPi-RealTimeClock-RTC