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Glossary

IOPMrootDomain

The singleton IOService at the root of the power graph. Owns system-wide decisions: full sleep, display sleep, wake on packet, wake on alarm.

IOPMrootDomain is the singleton IOService at the top of macOS's power-management graph. Every other IOPM-aware driver hangs off it (directly or transitively); it owns the system-wide power decisions.

What it does:

  • Sleep decisions — full system sleep, display sleep, dim, screen-saver entry.
  • Wake decisions — process wake events from lid open, power button, network packet, Bluetooth peripheral, scheduled alarms.
  • Sleep coordination — walks the power graph backward, asking every driver to drop to its lowest state.
  • Wake coordination — walks forward, bringing every driver back up.
  • Assertion management — tracks every userspace "prevent sleep" assertion and includes them in the decision.
apple-oss-distributions/xnuiokit/Kernel/IOPMrootDomain.cppThe root power node — orchestrator of every sleep/wake transition.View on GitHub(line —)

When you close a MacBook lid, the lid-sensor driver notifies IOPMrootDomain; the root domain decides full sleep, walks the tree backward, every device drops power, finally the SoC enters its deep sleep state. Wake reverses this.

See also: IOPM, IOKit, and the power management article.