A hardware calendar is a battery-powered clock available on some Cisco devices. It preserves calendar time while the device is powered off and can provide the initial value for the software clock during boot. section 2.1.2
Use these privileged EXEC commands to inspect or synchronize the two clocks:
- show calendar displays the hardware calendar; calendar set hh:mm:ss month day year changes it. section 2.1.2
- clock read-calendar copies calendar time to the software clock; clock update-calendar copies software-clock time to the calendar. section 2.1.2
- Both synchronization commands operate once; neither keeps the clocks continuously synchronized. section 2.1.2
Verify the time source
show clock detail can report “Time source is hardware calendar.” An asterisk before the time indicates that the software-clock value is not authoritative.
R1# show clock detail *08:56:18.831 UTC Mon Aug 28 2023 #1 Time source is hardware calendar #2 #1 The asterisk (*) indicates that the time is not authoritative. #2 R1 learned the date and time from its hardware calendar.
Inspect annotated Cisco output showing the hardware calendar supplying the software clock and the meaning of the asterisk. section 2.1.2
