Memos when dealing with ARM boxes

External RTC

To use the rtc1 as the default RTC device, set a udev rule like this:

   1 # /etc/udev/rules.d/99-rtc1.rules
   2 KERNEL=="rtc1", SUBSYSTEM=="rtc", DRIVER=="", ATTR{name}=="ds1307", SYMLINK="rtc", MODE="0666"

The key and values can be found by udevadm info -a -p /sys/class/rtc/rtc1.

Ref

1. How can the link target of /dev/rtc be changed?