I’ve installed acpid on my system some time ago (Gentoo package: sys-power/acpid). However, each time I tried to start it, it complained:
acpid: can't open /proc/acpi/event: No such file or directory
Apparently, acpid requires you to enable ACPI_PROC_EVENT, which in its label states “Deprecated /proc/acpi/event support.” I really wonder why such a tool only supports the deprecated way of receiving ACPI events.