caffeine

Start a caffeine server

$ caffeine

$ caffeine [[-h|--help]]

$ caffeine [[-V|--version]]

caffeine [OPTIONS]
or for some implementations:
caffeine [COMMAND]

--activate
    Activates the caffeine mode, preventing sleep and screen lock.

--deactivate
    Deactivates the caffeine mode, allowing normal power management.

--toggle
    Toggles the caffeine mode between active and inactive states.

--status
    Displays the current status of the caffeine mode (active/inactive).

--version
    Shows the version information of the caffeine utility.

--help
    Displays the help message with available options.

[COMMAND]
    Runs a specified command and keeps the system awake only while the command is running (available in some implementations).

The caffeine command on Linux is a utility designed to prevent the system from automatically entering sleep, suspension, or locking the screen due to inactivity. It's particularly useful during presentations, long downloads, media playback, or any scenario where you need your system to remain continuously active without user intervention.

While the exact implementation can vary (some are simple shell scripts, others more complex applications like caffeine-ng), the core functionality remains the same: to inhibit power management features that would otherwise put the system to sleep or lock the display. This is typically achieved by simulating minor user activity (like a key press or mouse movement), or more commonly, by interacting with desktop environment power management systems (e.g., via D-Bus calls to interfaces like org.freedesktop.ScreenSaver or org.gnome.SessionManager) to request a temporary inhibition of idle actions.

The command often runs in the background, providing a simple way to toggle this "awake" state on or off. It's an indispensable tool for users who need uninterrupted system availability without constantly moving the mouse or typing.

While highly convenient, caffeine may prevent critical system updates or scheduled tasks that rely on idle states or sleep. Prolonged use can also lead to increased power consumption, especially on laptops, and may affect battery life. Its effectiveness can vary across different desktop environments and display managers due to varying power management APIs and their implementations.

Modern caffeine utilities typically employ one or a combination of the following methods:

1. Simulated User Activity: Using tools like xdotool to generate fake keyboard presses or mouse movements, thus tricking the system into thinking a user is active.
2. D-Bus Inhibition: The most common and robust method. It sends D-Bus signals to desktop environment services (e.g., org.freedesktop.ScreenSaver, org.gnome.SessionManager, org.kde.KScreen) requesting them to temporarily inhibit idle actions like screen blanking, locking, or system suspension.
3. X Window System Control: Directly manipulating X server settings, such as using xset to disable display power management (DPMS) or screen blanking.

The need to prevent systems from sleeping or locking has existed since the early days of personal computing. Initially, users might resort to simple hacks like running continuous loops or moving the mouse periodically. With the advent of modern desktop environments and their sophisticated power management capabilities, direct interaction with X server settings (e.g., via xset) became common. However, these methods often required manual intervention or complex scripting.

The concept of a user-friendly 'caffeine' utility emerged to simplify this. Early implementations were often simple shell scripts leveraging tools like xdotool to simulate activity or xdg-screensaver to inhibit screen saving. As D-Bus became the standard for inter-process communication in Linux desktop environments, more robust caffeine applications (like caffeine-ng) began using D-Bus calls to interact directly with power management services (e.g., org.freedesktop.ScreenSaver, org.gnome.SessionManager, org.kde.KScreen), providing a more reliable and system-integrated way to prevent sleep. This evolution reflects a shift from low-level hacks to higher-level, desktop-environment-aware solutions.

xdotool(1), xdg-screensaver(1), dbus-send(1), xset(1), gnome-screensaver-command(1), power-profiles-daemon(1)