Questions that relate to the Advanced Configuration and Power Interface (ACPI) specification which provides an open standard for device configuration and power management by the operating system.
ACPI is an open standard providing a platform-independent interface that allows an operating system to implement power management of devices.
Activation triggers for power saving modes such as suspend and hibernate and other power-management tasks are defined and implemented through ACPI. Several ACPI kernel modules may provide different ACPI functions in Ubuntu (see /lib/modules/$(uname -r/kernel/drivers/acpi). Users can control and configure the implementation through the systemctl interface on versions of Ubuntu with systemd or with the acpid daemon:
acpid is a flexible and extensible daemon for delivering ACPI events. These events are triggered by certain actions, such as:
Pressing the Power button
Pressing the Sleep/Suspend button
Closing a notebook lid
(Un)Plugging an AC power adapter from a notebook
acpid can be used by itself, or combined with a more robust system such as Pm-utils and Cpufrequtils to provide a more complete power management solution.
Source for acpid: Arch wiki
