High Quality Content by WIKIPEDIA articles! Apcupsd (the name stands for American Power Conversion Uninterruptible Power Supply Daemon) is an application that runs on Linux, UNIX and some Windows machines (using Cygwin). It allows the computer to interact with (almost all recent) American Power Conversion (APC) Uninterruptible Power Supplies (UPS). Apcupsd also works with some Original Equipment Manufacturer (OEM) APC power supplies (e.g., Hewlett-Packard's). Apcupsd must run in daemon mode to keep a live connection with the UPS. This is needed to monitor the UPS via USB or RS232.