goose121 / alsd

An ambient light sensor daemon which responds to ACPI events

alsd

alsd is a relatively simple Common Lisp program (with a Rust helper) which updates the display backlight brightness in accordance with ambient light sensor values. It requires als_bus in order to function. Configuration is mainly done by setting dynamic variable values; most of the variable declarations should be near the beginnings of files.

Usage

alsd is started using either the START-DAEMON or ENTRY-POINT function. START-DAEMON is mainly meant for interactive usage, while ENTRY-POINT is the entry point for creating an executable image, which can be done by soft-linking alsd.asd to a location where ASDF can find it, then executing (asdf:make :alsd) at a REPL. The first argument to either START-DAEMON or to the generated executable should be the path to the alsd-handler executable. Note that the alsd-handler executable must have certain permissions, detailed in the Installation section.

IPC

alsd can be controlled via a socket, which is created by default as an anonymous Unix-domain socket named alsd-ctl. It currently supports 3 commands: (update-screen), which updates the screen brightness in accordance with current ambient light conditions, and writes T back on the socket; (adjust-brightness AMOUNT), which adjusts the user-supplied brightness factor (which is multiplied by the factor associated with the current ambient brightness to obtain the actual brightness percentage) by AMOUNT percentage points and writes the new brightness value back on the socket; and (stop) (aliases (quit) and (exit)), which causes the daemon to shut down gracefully. Note that it closes the socket connection with a client after each command and that the commands are not processed in parallel so it can only handle one request at a time.

Building

Building the helper

$ cd /path/to/alsd/sources
$ cd alsd-helper
$ cargo build --release

Building a standalone alsd executable (optional)

These instructions are for SBCL, but they should work for any Common Lisp implementation by simply replacing sbcl with that Lisp interpreter’s executable, and fiddling with its arguments somewhat to make it evaluate (asdf:make :alsd).

$ cd /path/to/alsd/sources
# Note: this may need to be replaced with a different path depending
# on your local value of asdf:*central-registry*
$ ln -s alsd.asd ~/common-lisp/
$ sbcl --eval "(asdf:make :alsd)"

Installation

$ cd /path/to/alsd/sources
# This can go anywhere you want; its path just needs to be passed to
# alsd as an argument
$ sudo cp alsd-helper/target/release/alsd-helper /usr/local/sbin/
# Currently this is implemented as a setuid executable; in the future,
# it may be preferable to use capabilites (specifically CAP_NET_ADMIN)
# for security reasons
$ sudo chmod u+s /usr/local/sbin/alsd-helper