Warning: /proc/acpi is being replaced by interfaces in /sys and new software should not look in /proc.
If implemented, the Real Time Clock (RTC) alarm must
generate a hardware wake event when in the sleeping state. The RTC can
be programmed to generate an alarm. An enabled RTC alarm can be used to
generate a wake event when the system is in a sleeping state. ACPI
provides for additional hardware to support OSPM in determining that the
RTC was the source of the wake event: the RTC_STS and RTC_EN optional
bits.
If the RTC_STS and RTC_EN bits are not supported,
OSPM will attempt to identify the RTC as a possible wake source;
however, it might miss certain wake events. If implemented the RTC wake
feature is required to work in the following sleeping states: S1-S3. S4
wake is optional and supported through the RTC_S4 flag within the FADT
(if set, then the platform supports RTC wake in the S4 state).
The user-space interface can be found in GNU/Linux at /proc/acpi/alarm
.
echo yyyy-mm-dd hh:mm:ss > alarm
where the characters denote the appropriate elements of a date, for instance:
echo 2004-02-22 15:00:00 > alarm
Afterwards you might put the system to sleep with:
echo 5 > /proc/acpi/sleep
but be careful to stop any services, file systems, etc. before powering off, e.g. use /sbin/halt
instead.