This program is used to enter a system sleep state until specified wakeup time.
This uses cross-platform Linux interfaces to enter a system sleep state, and
leave it no later than a specified time. It uses any RTC framework driver that
supports standard driver model wakeup flags.
This is normally used like the old apmsleep utility, to wake from a suspend
state like ACPI S1 (standby) or S3 (suspend-to-RAM). Most platforms can
implement those without analogues of BIOS, APM, or ACPI.
On some systems, this can also be used like nvram-wakeup, waking from states
like ACPI S4 (suspend to disk). Not all systems have persistent media that are
appropriate for such suspend modes.
-v | --verbose
-h | --help
Display a short help message that shows how to use the program.
-V | --version
Displays version information and exists.
-a | --auto
Reads the clock mode (whether the hardware clock is set to UTC or local time)
from /etc/adjtime. That's the location where the
stores that information.
-l | --local
Assumes that the hardware clock is set to local time, regardless of the
contents of /etc/adjtime.
-u | --utc
Assumes that the hardware clock is set to UTC (Universal Time Coordinated),
regardless of the contents of /etc/adjtime.
-ddevice | --devicedevice
Uses device instead of rtc0 as realtime clock. This option
is only relevant if your system has more than one RTC. You may specify
rtc1, rtc2, ... here.
-sseconds | --secondsseconds
Sets the wakeup time to seconds in future from now.
-ttime_t | --timetime_t
Sets the wakeup time to the absolute time time_t. time_t
is the time in seconds since 1970-01-01, 00:00 UTC. Use the
tool to convert between human-readable time and time_t.
-mmode | --modemode
Use standby state mode. Valid values are:
ACPI state S1. This state offers minimal, though real, power savings, while
providing a very low-latency transition back to a working system. This is the
ACPI state S3 (Suspend-to-RAM). This state offers significant power savings as
everything in the system is put into a low-power state, except for memory,
which is placed in self-refresh mode to retain its contents.
ACPI state S4 (Suspend-to-disk). This state offers the greatest power savings,
and can be used even in the absence of low-level platform support for power
management. This state operates similarly to Suspend-to-RAM, but includes a
final step of writing memory contents to disk.
ACPI state S5 (Poweroff). This is done by calling '/sbin/shutdown'.
Not officially supported by ACPI, but usually working.
Don't suspend. The rtcwake command sets RTC wakeup time only.
Don't suspend, but read RTC device until alarm time appears. This mode is
useful for debugging.
Some PC systems can't currently exit sleep states such as mem
using only the kernel code accessed by this driver.
They need help from userspace code to make the framebuffer work again.
The program was posted several times on LKML and other lists
before appearing in kernel commit message for Linux 2.6 in the GIT