acpi_available

acpi_available is not a directly executable command from the shell. It represents an internal check or API call within system software (like acpid, upower, or kernel modules) to determine the presence and functionality of the ACPI subsystem. There is no command-line syntax for acpi_available as a standalone utility.

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    As acpi_available is not a standalone command, it does not accept command-line parameters or options. Its "result" is typically an internal boolean (true/false) indicating ACPI availability, used by other programs.

acpi_available is not a standalone, user-executable Linux command in the traditional sense. Instead, it refers to a conceptual check or an internal function/variable within system utilities and the kernel to determine if the Advanced Configuration and Power Interface (ACPI) subsystem is enabled and functioning on a given hardware platform. ACPI is crucial for modern operating systems like Linux to manage power, thermal events, battery status, and other hardware configurations efficiently. When a system or an application needs to interact with ACPI-driven features (e.g., suspend, hibernate, fan control, battery reporting), it first performs an "ACPI availability check" to ensure the necessary kernel modules and interfaces (often exposed via /proc/acpi or /sys/firmware/acpi) are present and accessible. This check confirms the system's ability to leverage ACPI for power management and hardware interaction.

The most important caveat is that acpi_available is not a command you type into the terminal. If you need to programmatically check for ACPI availability in a shell script, common methods involve:

1. Checking for the existence of /proc/acpi:
if [ -d /proc/acpi ]; then ... fi

2. Checking for the existence of /sys/firmware/acpi:
if [ -d /sys/firmware/acpi ]; then ... fi

The actual implementation of an "ACPI available" check can vary depending on the specific system utility or programming language used.

While not a direct command, the concept of checking ACPI availability is vital. In shell scripting, a common way to infer ACPI support is to check for the presence of the /proc/acpi directory or the /sys/firmware/acpi directory. These directories are populated by the kernel when ACPI is active and provide interfaces to ACPI events and information. For example, a script might contain:
if [ -d /sys/firmware/acpi ]; then
  echo "ACPI is available."
else
  echo "ACPI not detected."
fi

ACPI (Advanced Configuration and Power Interface) was introduced as a successor to APM (Advanced Power Management) in 1997, aimed at providing a more flexible and robust framework for power management, Plug and Play, and configuration in operating systems. Linux adopted ACPI support early on, with its integration evolving significantly over kernel versions. The concept of acpi_available emerged implicitly with this integration, as power management tools and kernel modules needed a standardized way to ascertain if the underlying hardware and kernel support for ACPI were present and usable. This check became fundamental for modern Linux distributions to correctly manage power states, battery life, and thermal controls on diverse hardware.

acpid(8) - ACPI daemon for event handling, upower(7) - D-Bus interface for power management, proc(5) - Pseudo-filesystem providing process and kernel information, sys(5) - Pseudo-filesystem providing kernel data structures