The Case of the Missing Nightly Reboot
For several months I have been using my Asus RT-AC66U router with DD-WRT. While looking into a recent quirk I noticed the uptime indicator and realized the router had not rebooted the previous night.
Through cron I reboot the router nightly to avoid potential bugs and quirks, usually associated with memory issues.
I had configured the router to reboot nightly at 2:34 AM. The option is in
Administration/Keep Alive/Scheduled Reboot.
I confirmed I had configured the Asus to reboot nightly. The time of day was correct and the NTP daemon was configured to run at boot.
/tmp/cron.d/check_schedules showed the following:
34 2 * * * root startservice run_rc_shutdown; /sbin/reboot
The router should have rebooted.
I knew that cron was working because I have a custom cron job installed that was running fine.
I noted the anomaly to investigate later.
As I was falling asleep that night my subconscious awakened me. The reason for the reboot failure was obvious and simple.
The day I had checked the uptime was March 12. In this area that was the day when Daylight Saving Time (DST) started. Computer clocks automatically skip the second hour, moving from 2 AM to 3 AM. For that specific day the time of 2:34 never existed.