Chrome OS Power Management

The Chrome OS power manager consists of several components:

• powerd: C++ system daemon running as the power user that initiates dimming the screen, suspending the system, etc.
• powerd_setuid_helper: setuid root binary used by powerd to perform actions requiring additional privileges.
• powerd_dbus_suspend: shell script executed by powerd (by way of powerd_setuid_helper) to suspend and resume the system.
• send_metrics_on_resume: shell script executed by powerd_suspend and by the send-boot-metrics Upstart job to report suspend-related metrics.

Documentation

The docs/ subdirectory contains additional documentation. Along with answers to frequently-asked questions, the following information is available:

• Battery Notifications describes when low-battery notifications are shown by the UI.
• Inactivity Delays describes powerd's logic for taking action (e.g. dimming the backlight or suspending) when the user is inactive.
• Input describes how powerd handles input events.
• Keyboard Backlight describes powerd's logic for controlling the keyboard backlight.
• Logging describes where and how powerd logs informative messages.
• Power Buttons describes how power buttons work.
• Power Supplies describes powerd's logic for determining the state of power supplies (e.g. batteries or line power).
• Screen Brightness describes powerd's logic for controlling the display backlight.
• Shutdown and Reboot describes why and how Chrome OS systems shut down and reboot.
• Suspend and Resume describes powerd's process for suspending and resuming the system.
• Thermal describes how powerd monitors system thermal state to provide thermal hinting to Chrome.
• udev Usage describes how powerd uses the udev system to learn about hardware changes.

Code Overview

This repository contains the following subdirectories:

Subdirectory	Description
common	Code shared between powerd and tools
dbus	D-Bus policy configuration files
default_prefs	Default pref files installed to /usr/share/power_manager
docs	Detailed documentation in Markdown format
init/shared	Scripts shared between Upstart and systemd
init/systemd	systemd-specific config files
init/upstart	Upstart-specific config files installed to /etc/init
optional_prefs	Pref files conditionally installed based on USE flags
powerd	Power manager daemon
powerd/policy	High-level parts of powerd that make policy decisions
powerd/system	Low-level parts of powerd that communicate with the kernel
tools	Utility programs; may depend on powerd code
udev	udev configuration files and scripts