Since the Raspberry Pi 3 doesn’t come with a battery-powered real time clock, it will only show the correct time once it has Internet connectivity (thanks to the NTP daemon). If the Raspberry Pi 3 is not connected to the Internet, you might want to add a hardware clock to set the current date. Here’s how to add a DS3231 real time clock GPIO module to the Raspberry Pi 3 in Raspbian Jessy Lite:
- Get a DS3231 real time clock module and install it on the GPIO header of the Raspberry Pi 3 on pin 1
- Add the following line at the end of /boot/config.txt in Raspbian Jessy:
dtoverlay=i2c-rtc,ds3231
- We don’t need fake-hwclock anymore:
apt-get purge fake-hwclock
- Check/set the current system time and write the system time to the RTC module using:
hwclock -w
- Set the correct time zone using:
dpkg-reconfigure tzdata
- Edit /etc/rc.local and add the hwclock command above the line that says “exit 0”:
/sbin/hwclock -s
- The /etc/init.d/hwclock.sh shell scripts tends to corrupt this RTC clock module. In my case, the RTC clock was set to 2066/01/01 after every reboot. To prevent this from happening, edit /etc/default/hwclock and set HWCLOCKACCESS to no:
HWCLOCKACCESS=no
- Reboot
- Done! Raspbian will now set the time from the RTC clock during boot even if there is no Internet connectivity available.
- If RTC corruption is still happening, you may have to get rid of the NTP daemon as well using:
apt-get purge ntp apt-get install ntpdate
- After the NTP daemon has been removed, you can still sync the system clock using
ntpdate-debianwhich you might add to/etc/rc.localas well (after the hwclock command though) – just in case there is an Internet connection available during boot. And/or add it to/etc/cron.dailyfor example.
Raspbian Jessy Lite will detect the DS3231 real time clock module automatically (as a DS1307 module but nevermind), there’s no need to whitelist or blacklist any I2C modules. There’s no need to run the i2cdetect command from the i2c-tools package. Once the clock module is detected, this line should be visible using dmesg:
# dmesg | grep rtc [ 6.640799] rtc-ds1307 1-0068: rtc core: registered ds3231 as rtc0
Check /proc/driver/rtc for more data on the RTC:
# cat /proc/driver/rtc rtc_time : 19:26:18 rtc_date : 2016-03-25 alrm_time : 00:00:00 alrm_date : 1970-01-01 alarm_IRQ : no alrm_pending : no update IRQ enabled : no periodic IRQ enabled : no periodic IRQ frequency : 1 max user IRQ frequency : 64 24hr : yes
