acpid Man page

acpid(8) System Manager’s Manual acpid(8)


acpid – Advanced Configuration and Power Interface event daemon


acpid [options]


acpid is designed to notify user-space programs of ACPI events. acpid
should be started during the system boot, and will run as a background
process, by default. It will open an events file (/proc/acpi/event by
default) and attempt to read whole lines which represent ACPI events.
If the events file does not exist, acpid will attempt to connect to the
Linux kernel via the input layer and netlink. When an ACPI event is
received from one of these sources, acpid will examine a list of rules,
and execute the rules that match the event. acpid will ignore all
incoming ACPI events if a lock file exists (/var/lock/acpid by

Rules are defined by simple configuration files. acpid will look in a
configuration directory (/etc/acpi/events by default), and parse all
regular files with names that consist entirely of upper and lower case
letters, digits, underscores, and hyphens (similar to run-parts(8)).
Each file must define two things: an event and an action. Any blank
lines, or lines where the first character is a hash (‘#’) are ignored.
Extraneous lines are flagged as warnings, but are not fatal. Each line
has three tokens: the key, a literal equal sign, and the value. The
key can be up to 63 characters, and is case-insensitive (but whitespace
matters). The value can be up to 511 characters, and is case and
whitespace sensitive.

The event value is a regular expression (see regcomp(3)), against which
events are matched.

The action value is a commandline, which will be invoked via /bin/sh
whenever an event matching the rule in question occurs. The command‐
line may include shell-special characters, and they will be preserved.
The only special characters in an action value are “%” escaped. The
string “%e” will be replaced by the literal text of the event for which
the action was invoked. This string may contain spaces, so the comman‐
dline must take care to quote the “%e” if it wants a single token. The
string “%%” will be replaced by a literal “%”. All other “%” escapes
are reserved, and will cause a rule to not load.

This feature allows multiple rules to be defined for the same event
(though no ordering is guaranteed), as well as one rule to be defined
for multiple events. To force acpid to reload the rule configuration,
send it a SIGHUP.

The pseudo-action causes the event to be dropped completely and
no further processing undertaken; clients connecting via the UNIX
domain socket (see below) will not be notified of the event. This may
be useful on some machines, such as certain laptops which generate spu‐
rious battery events at frequent intervals. The name of this pseudo-
action may be redefined with a commandline option.

In addition to rule files, acpid also accepts connections on a UNIX
domain socket (/var/run/acpid.socket by default). Any application may
connect to this socket. Once connected, acpid will send the text of
all ACPI events to the client. The client has the responsibility of
filtering for messages about which it cares. acpid will not close the
client socket except in the case of a SIGHUP or acpid exiting.

For faster startup, this socket can be passed in as stdin so that acpid
need not create the socket. In addition, if a socket is passed in as
stdin, acpid will not daemonize. It will be run in foreground. This
behavior is provided to support systemd.

acpid will log all of its activities, as well as the stdout and stderr
of any actions, to syslog.

All the default files and directories can be changed with commandline


-c, –confdir directory
This option changes the directory in which acpid looks for
rule configuration files. Default is /etc/acpi/events.

-C, –clientmax number
This option changes the maximum number of non-root socket
connections which can be made to the acpid socket. Default
is 256.

-d, –debug This option increases the acpid debug level by one. If the
debug level is non-zero, acpid will run in the foreground,
and will log to stderr, in addition to the regular syslog.

-e, –eventfile filename
This option changes the event file from which acpid reads
events. Default is /proc/acpi/event.

-n, –netlink
This option forces acpid to use the Linux kernel input
layer and netlink interface for ACPI events.

-f, –foreground
This option keeps acpid in the foreground by not forking at

-l, –logevents
This option tells acpid to log information about all events
and actions.

-L, –lockfile filename
This option changes the lock file used to stop event pro‐
cessing. Default is /var/lock/acpid.

-g, –socketgroup groupname
This option changes the group ownership of the UNIX domain
socket to which acpid publishes events.

-m, –socketmode mode
This option changes the permissions of the UNIX domain
socket to which acpid publishes events. Default is 0666.

-s, –socketfile filename
This option changes the name of the UNIX domain socket
which acpid opens. Default is /var/run/acpid.socket.

-S, –nosocket filename
This option tells acpid not to open a UNIX domain socket.
This overrides the -s option, and negates all other socket

-p, –pidfile filename
This option tells acpid to use the specified file as its
pidfile. If the file exists, it will be removed and over-
written. Default is /var/run/

-r, –dropaction action
This option defines the pseudo-action which tells acpid to
abort all processing of an event, including client notifi‐
cations. Default is .

-t, –tpmutefix
This option enables special handling of the mute button for
certain ThinkPad models with mute LEDs that get out of sync
with the mute state when the mute button is held down.
With this option, the mute button will generate the follow‐
ing events in sync with the number of presses (and, by
extension, the state of the LED):

button/mute MUTE (key pressed) K
button/mute MUTE (key released) K

-v, –version
Print version information and exit.

-h, –help Show help and exit.

This example will shut down your system if you press the power button.

Create a file named /etc/acpi/events/power that contains the following:

action=/etc/acpi/ “%e”

Then create a file named /etc/acpi/ that contains the follow‐

/sbin/shutdown -h now “Power button pressed”

Now, when acpid is running, a press of the power button will cause the
rule in /etc/acpi/events/power to trigger the script in
/etc/acpi/ The script will then shut down the system.

acpid is a simple program that runs scripts in response to ACPI events
from the kernel. When there’s trouble, the problem is rarely with
acpid itself. The following are some suggestions for finding the most
common sources of ACPI-related problems.

When troubleshooting acpid, it is important to be aware that other
parts of a system might be handling ACPI events. systemd is capable
of handling the power switch and various other events that are commonly
handled by acpid. See the description of HandlePowerKey in
logind.conf(5) for more. Some window managers also take over acpid’s
normal handling of the power button and other events.

kacpimon(8) can be used to verify that the expected ACPI events are
coming in. See the man page for kacpimon(8) for the proper procedure.
If the events aren’t coming in, you’ve probably got a kernel driver

If the expected events are coming in, then you’ll need to check and see
if your window manager is responsible for handling these events. Some
are, some aren’t. (E.g. in Ubuntu 14.04 (Unity/GNOME), there are set‐
tings for the laptop lid in the System Settings > Power > “When the lid
is closed” fields.) If your window manager is responsible for handling
the problematic event, and you’ve got it configured properly, then you
may have a window manager issue.

Lastly, take a look in /etc/acpi/events (see above). Is there a con‐
figuration file in there for the event in question (e.g.
/etc/acpi/events/lidbtn for laptop lid open/close events)? Is it prop‐
erly connected to a script (e.g. /etc/acpi/ Is that script
working? It’s not unusual for an acpid script to check and see if
there is a window manager running, then do nothing if there is. This
means it is up to the window manager to handle this event.

acpid should work on any linux kernel released since 2003.



There are no known bugs. To file bug reports, see PROJECT WEBSITE


regcomp(3), sh, socket(2), connect(2), init(1), systemd,
acpi_listen(8), kacpimon(8)


Ted Felix
Tim Hockin Andrew Henroid


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