16 Clock: Date and Time

20210323 There are two clocks in a computer: the system clock and the hardware clock. The system clock is maintained by the running operating system (e.g., GNU/Linux). It is also said to be maintained by the kernel. The hardware clock is part of the actual hardware of the computer and is usually battery backed up. The current status of the clock can be found from the timedatectl command from systemd:

timedatectl status
##                Local time: Sat 2021-06-12 09:33:14 AEST  
##            Universal time: Fri 2021-06-11 23:33:14 UTC   
##                  RTC time: Fri 2021-06-11 23:33:14       
##                 Time zone: Australia/Sydney (AEST, +1000)
## System clock synchronized: yes                           
##               NTP service: active                        
##           RTC in local TZ: no

Alternatively, the date command talks to the system clock:

## Sat 12 Jun 2021 09:33:14 AEST

Meanwhile, the hwclock command talks to the hardware clock:

$ sudo hwclock
2021-03-23 07:42:20.426656+11:00

To set the system clock:

$ sudo date -s "13 Jun 2021 10:10:00"

To set the timezone:

$ sudo timedatectl set-timezone Australia/Canberra

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