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.
Note that alarm functionality depends on hardware; not every RTC is able to setup an alarm up to 24 hours in the future.
The suspend setup may be interrupted by active hardware; for example wireless USB input devices that continue to send events for some fraction of a second after the return key is pressed. rtcwake tries to avoid this problem and it waits to terminal to settle down before entering a system sleep.
- -A, --adjfile file
- Specify an alternative path to the adjust file.
- -a, --auto
- Read the clock mode (whether the hardware clock is set to UTC or local time) from the adjtime file, where hwclock(8) stores that information. This is the default.
- --date timestamp
- Set the wakeup time to the value of the timestamp. Format of the timestamp
can be any of the following:
YYYYMMDDhhmmss YYYY-MM-DD hh:mm:ss YYYY-MM-DD hh:mm (seconds will be set to 00) YYYY-MM-DD (time will be set to 00:00:00) hh:mm:ss (date will be set to today) hh:mm (date will be set to today, seconds to 00) tomorrow (time is set to 00:00:00) +5min
- -d, --device device
- Use the specified 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.
- -l, --local
- Assume that the hardware clock is set to local time, regardless of the contents of the adjtime file.
- List available --mode option arguments.
- -m, --mode mode
- Go into the given standby state. Valid values for mode 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.
- The processes are frozen, all the devices are suspended and all the processors idled. This state is a general state that does not need any platform-specific support, but it saves less power than Suspend-to-RAM, because the system is still in a running state. (Available since Linux 3.9.)
- 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 it usually works.
- Don't suspend, only set the RTC wakeup time.
- Don't suspend, but read the RTC device until an alarm time appears. This mode is useful for debugging.
- Disable a previously set alarm.
- 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".
- -n, --dry-run
- This option does everything apart from actually setting up the alarm, suspending the system, or waiting for the alarm.
- -s, --seconds seconds
- Set the wakeup time to seconds in the future from now.
- -t, --time time_t
- Set 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.
- -u, --utc
- Assume that the hardware clock is set to UTC (Universal Time Coordinated), regardless of the contents of the adjtime file.
- -v, --verbose
- Be verbose.
- -V, --version
- Display version information and exit.
- -h, --help
- Display help text and exit.