What is acpi?
"In computing, the Advanced Configuration and Power Interface (ACPI) specification provides an open standard for device configuration and power management by the operating system." [(http://en.wikipedia.org/wiki/Advanced_Configuration_and_Power_Interface Wikipedia)]
What is acpid?
"ACPID is a completely flexible, totally extensible daemon for delivering ACPI events. It listens on a file (/proc/acpi/event) and when an event occurs, executes programs to handle the event. The programs it executes are configured through a set of configuration files, which can be dropped into place by packages or by the admin." [(http://acpid.sourceforge.net/ acpid Sourceforge)]
To install acpid, run this command:
# emerge -av acpid
Adding to rc
# rc-update add acpid default
Then, run the following to start rc: