Section: Linux Programmer's Manual (8)
Updated: 2007-07-13
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rtcwake - enter a system sleep state until specified wakeup time  


rtcwake [-hvVlua] [-d device] [-m standby_mode] {-t time_t|-s seconds}  


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
Be 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 hwclock(8) 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.
-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:
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.
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.
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 commit 87ac84f42a7a580d0dd72ae31d6a5eb4bfe04c6d.  


The rtcwake command is part of the util-linux-ng package and is available from ftp://ftp.kernel.org/pub/linux/utils/util-linux-ng/.  


The program was written by David Brownell <dbrownell@users.sourceforge.net> and improved by Bernhard Walle <bwalle@suse.de>.  


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.  


hwclock(8), date(1)