Linux Commands Examples

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Advanced Configuration and Power Interface event daemon

see also : sh - acpi_listen


acpid [options]

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exec /sbin/acpid -f
exec /sbin/acpid -d


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 default).

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 commandline 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 commandline 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.

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(1).

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 options.

When troubleshooting acpid, it is important to be aware that other parts of a system might be handling ACPI events. systemd(1) 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.


-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 startup.

-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 processing. 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 options.

-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/

-v, --version

Print version information and exit.

-h, --help

Show help and exit.


acpid should work on any linux kernel released since 2003.


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 following:

/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.




There are no known bugs. To file bug reports, see AUTHORS below.

see also

regcomp, sh , socket, connect, systemd, acpi_listen , kacpimon


Ted Felix (
Tim Hockin <thockin[:at:]hockin[:dot:]org>
Andrew Henroid

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