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.
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.