Acpid is a daemon that executes certain actions whenever ACPI events are received. Depending on your hardware and kernel configuration, these events include closing a laptop lid, connecting to an AC power adapter, pressing buttons and more.
KISS Linux offers two options for acpid management: busybox acpid, which is installed by default, and acpid2 [1], which can be installed with the acpid package. To use either version of acpid, you will need to enable a few kernel options and enable the acpid service. See @/init/busybox.
ACPI-related kernel drivers must be enabled for acpid to function properly. In menuconfig, these options are found under Power management and ACPI options
Power Management support > ACPI support. Most of the drivers are self-explanatory, but the following notable options can be safely disabled:
CONFIG_ACPI_PROCFS_POWER This option is deprecated
CONFIG_ACPI_EC_DEBUGFS Potentially interferes with reboot
CONFIG_ACPI_TABLE_UPGRADE KISS does not use an initrd by default
CONFIG_ACPI_DEBUG Adds 50k to kernel size
CONFIG_ACPI_PCI_SLOT Usually unnecessary
CONFIG_ACPI_CUSTOM_METHOD Potential security flaw
When events are received, acpid checks /etc/acpi.map for a matching event and /etc/acpid.conf for a corresponding handler script in /etc/acpi/ to execute.
Create the files below to suspend your laptop whenever the lid is closed:
/etc/acpi.map:
EV_SW 0x05 SW_LID 0 1 button/lid LID0 00000080
/etc/acpid.conf:
LID0 LID/00000080
/etc/acpi/LID/00000080:
#!/bin/sh
printf mem > /sys/power/state
Each line in /etc/acpi.map has six space-delimited fields: 1. Type name (EV_SW), 2. Type numerical value (0x05) 3. Keycode name (SW_LID) 4. Keycode numerical value (0) 5. Value (1) 6. Description (button/lid LID0 00000080)
Event types and keycodes are listed in /usr/include/linux/input-event-codes.h. For example, a keyboard WLAN button event would use EV_KEY 0x05 and KEY_WLAN
Each line in /etc/acpid.conf has a key (LID0) and an action (LID/00000080). The key is any unique substring of the event description in /etc/acpi.map and the action is the relative path to an executable script in /etc/acpi/.
To see if a configured event is received, check /var/log/acpid.log for output lines that list the path of your handler scripts.
acpid2 is a more user-friendly version of acpid that avoids the tedious process of mapping events with flexible configuration and better documentation. The acpid package also installs acpi_listen which prints events as they occur. For example, pressing the volume mute button will print something like this:
button/mute MUTE 00000080 00000000 K
When events are received, acpid2 checks files in /etc/acpi/event/ for a matching event and a corresponding handler script to execute. Create the following files to handle the mute button event by toggling the Master audio channel:
/etc/acpi/event/anything:
event=.*
action=/etc/acpi/handler.sh %e
/etc/acpi/handler.sh:
#!/bin/sh
case $1 in
button/mute)
amixer sset Master toggle
;;
esac
Files in /etc/acpi/event/ match events using event=REGEX with an action to execute. In this example, .* matches all events and the action executes /etc/acpi/handler.sh. The argument %e expands to five event parameters: $1=button/mute, $2=MUTE, $3=00000080, $4=00000000, $5=K. The event parameters provide an easy way to handle all events in a single script instead of the more complex multi-file system used by busybox.