How to Wake Your Computer with 'rtcwake' (with examples)
- Linux
- December 17, 2024
The rtcwake
command is a useful utility in Linux environments to manage a computer’s power state. It allows users to set alarm clocks that can wake the system up from various sleep states at specified times, utilizing the real-time clock (RTC) in the BIOS. This can be extremely useful for automating tasks that need to occur at specific intervals without having to keep the computer running continuously.
Use case 1: Show whether an alarm is set or not
Code:
sudo rtcwake -m show -v
Motivation:
When managing system tasks that require scheduled wakeups, it’s important to know if there’s already a wakeup alarm set. This command allows administrators or users to verify the current state of the system’s RTC alarm settings. Knowing whether an alarm is set helps in managing upcoming tasks and ensuring no conflicts or misconfigurations in system scheduling.
Explanation:
sudo
: Runs the command with superuser privileges necessary for accessing system devices and configurations.rtcwake
: The command used to manage RTC wakeups.-m show
: Specifies the “show” mode, which queries the system to display the current wakeup time if set.-v
: Provides verbose output, offering detailed information about the status of the RTC.
Example Output:
Enabled RTC wakeup alarm:
time: Mon 2022-11-21 08:00:00 UTC
Increment: +1 hour
Use case 2: Suspend to RAM and wakeup after 10 seconds
Code:
sudo rtcwake -m mem -s 10
Motivation:
This use case is ideal for testing and quick demonstrations of the system’s ability to enter and leave low-power states. Suspending to RAM (also known as “Sleep” mode) preserves the session in memory, allowing for quick resumption by waking up the system after a brief period, for instance, 10 seconds.
Explanation:
sudo
: Executes the command with the necessary permissions.rtcwake
: The tool used to enable system wakeup.-m mem
: Indicates that the system should suspend to RAM, saving the current state to memory.-s 10
: Sets a timer for 10 seconds before the system wakes up again. This is a relative time offset.
Example Output:
RTC alarm armed for Mon 2022-11-21 08:00:10 UTC; current time is Mon 2022-11-21 08:00:00 UTC
Use case 3: Suspend to disk and wakeup 15 minutes later
Code:
sudo rtcwake -m disk --date +15min
Motivation:
Suspending to disk, often referred to as “Hibernate” mode, saves the system state to disk and powers off the device. This is particularly useful when you want to save energy over longer periods compared to suspending to RAM. It allows the system to be restored to its prior state upon waking 15 minutes later.
Explanation:
sudo
: Necessary for elevated permissions.rtcwake
: The main command to set RTC alarms.-m disk
: Specifies that the system should suspend to disk, achieving higher power savings.--date +15min
: Uses a human-readable time format to set the wakeup time at 15 minutes from the current time.
Example Output:
RTC alarm intended for Mon 2022-11-21 08:15:00 UTC; current time is Mon 2022-11-21 08:00:00 UTC
System will enter disk sleep state
Use case 4: Freeze the system and wakeup at a given date and time
Code:
sudo rtcwake -m freeze --date YYYYMMDDhhmm
Motivation:
Freezing the system allows for efficient power conservation, even more so than suspending to RAM, while requiring Linux kernel version 3.9 or newer. This use case is particularly beneficial for scheduling wakeup at a very specific future date and time, such as for routine maintenance or updates.
Explanation:
sudo
: Executes the command with administrative privileges.rtcwake
: Tool to control RTC wake functions.-m freeze
: Requests the system to enter the “Freeze” state, an efficient power-saving mode.--date YYYYMMDDhhmm
: Specifies an exact date and time format for when the system should wake up.
Example Output:
RTC alarm set for Tue 2022-11-22 09:30:00 UTC; current time is Mon 2022-11-21 08:00:00 UTC
Use case 5: Disable a previously set alarm
Code:
sudo rtcwake -m disable
Motivation:
Disabling alarms is crucial when a scheduled wakeup is no longer needed. By clearing the set alarm, users avoid unintentional wakeups that could interfere with other tasks or result in unwanted power consumption.
Explanation:
sudo
: Required for superuser access.rtcwake
: Command tool for managing system alarms and power states.-m disable
: Mode option to disable any previously set RTC wakeup alarms.
Example Output:
RTC wakeup alarm was disabled.
Use case 6: Perform a dry run to wake up the computer at a given time
Code:
sudo rtcwake -m on --date hh:ss
Motivation:
A dry run in rtcwake
allows users to test the set wakeup time without actually putting the computer into a sleep state. This practice ensures that the intended alarms are exact and correct, thereby averting any misconfiguration or potential errors.
Explanation:
sudo
: Ensures that the command is run with the required privileges.rtcwake
: The utility used to set and manage wakeup alarms.-m on
: This mode initiates a dry run, where the system calculates but does not execute the power-off command.--date hh:ss
: Sets an exact time for simulation purposes, using hour and seconds format.
Example Output:
This is a dry-run. The rtc alarm will be set to Sat 2022-11-21 10:45:00. Current time is now Sat 2022-11-21 10:00:00.
Conclusion
By leveraging rtcwake
, Linux users can efficiently manage their systems’ power states to save energy and automate important tasks. Each use case above illustrates how versatile this command is, ranging from checking the RTC alarm status to conducting dry runs for testing. Understanding and utilizing these options can greatly enhance time and energy management on personal and enterprise systems alike.