[GTALUG] TIL: rtcwake / wakealarm

[Lennart Sorensen]

On Fri, Apr 09, 2021 at 10:23:10PM -0400, Stewart C. Russell via talk wrote:
> This may be old news to many of you, but today I learned you can have
> the computer's real time clock boot your machine at a specific time. The
> more proper way seems to be to use the 'rtcwake' command, but you can
> also do it by writing the timestamp of the startup time to
> /sys/class/rtc/rtc0/wakealarm
> 
> Some more details of the /sys method -
> https://www.raspberrypi.org/forums/viewtopic.php?f=63&t=309093&p=1849326&sid=ca7a14f7d160f929378be4691b1aed9e#p1849291

Yes many PCs have had an option for the RTC to turn on the machine
(could even configure it in the BIOS to always turn on the computer at
a certain time for you).  I have never used it (I don't tend to turn
the computer off in the first place).

No idea how many other platforms support it although I suspect not very
many.  I didn't think the raspberry pi even had a concept of software
power control, which would make the RTC doing anything rather unlikely,
although if it is just sleeping that would be a different story.
Although suspend and sleep have often been rather hit or miss in my
experience.

-- 
Len Sorensen