NAME¶
rtcwake - enter a system sleep state until specified wakeup time
SYNOPSIS¶
rtcwake [
-hvVluan] [
-d device] [
-m
standby_mode] {
-t time_t|
-s seconds}
DESCRIPTION¶
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.
Options¶
- -v | --verbose
- Be verbose.
- -h | --help
- Display a short help message that shows how to use the
program.
- -V | --version
- Displays version information and exists.
- -n | --dry-run
- This option does everything but actually setup alarm,
suspend system or wait for the alarm.
- -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
hwclock(8) stores that information. This is the default.
- -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.
- -d device | --device
device
- 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.
- -s seconds | --seconds
seconds
- Sets the wakeup time to seconds in future from
now.
- -t time_t | --time time_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
date(1) tool to convert between human-readable time and
time_t.
- -m mode | --mode mode
- Use standby state mode. Valid values are:
- standby
- 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 default mode.
- mem
- 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.
- disk
- 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.
- off
- ACPI state S5 (Poweroff). This is done by calling
'/sbin/shutdown'. Not officially supported by ACPI, but usually
working.
- no
- Don't suspend. The rtcwake command sets RTC wakeup time
only.
- on
- Don't suspend, but read RTC device until alarm time
appears. This mode is useful for debugging.
- disable
- Disable previously set alarm.
- show
- Print alarm information in format: "alarm: off|on
<time>". The time is in ctime() output format, e.g.
"alarm: on Tue Nov 16 04:48:45 2010".
NOTES¶
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.
HISTORY¶
The program was posted several times on LKML and other lists before appearing in
kernel commit message for Linux 2.6 in the GIT commit
87ac84f42a7a580d0dd72ae31d6a5eb4bfe04c6d.
AVAILABILITY¶
The rtcwake command is part of the util-linux package and is available from
ftp://ftp.kernel.org/pub/linux/utils/util-linux/.
AUTHOR¶
The program was written by David Brownell
<dbrownell@users.sourceforge.net> and improved by Bernhard Walle
<bwalle@suse.de>.
COPYRIGHT¶
This is free software. You may redistribute copies of it under the terms of the
GNU General Public License <
http://www.gnu.org/licenses/gpl.html>. There
is NO WARRANTY, to the extent permitted by law.
SEE ALSO¶
hwclock(8),
date(1)
