Mac Won't Sleep? How to Find What's Keeping It Awake

A Mac that will not sleep is almost never broken. Something is holding it awake on purpose, and macOS keeps a list of exactly what. One command gives you the answer in about five seconds, which beats every piece of advice that starts with resetting things.

Ask macOS what is holding it awake

Open Terminal and run:

# everything currently preventing sleep, and which process is responsible
pmset -g assertions

Look at the block near the top. The lines that matter are:

• PreventUserIdleSystemSleep — the Mac will not sleep at all.
• PreventUserIdleDisplaySleep — the display stays on, which usually keeps the system awake too.
• PreventSystemSleep — typically a download, a backup or an app doing work on purpose.

Beside each you get a process ID and a name, and often a human-readable reason such as "video playback" or "backup in progress". That name is your answer. Usual culprits: a browser with a tab playing audio or video, a media app, a video call app left running, a download manager, or a sleep-prevention utility somebody installed years ago.

The settings that block sleep on purpose

Check what your Mac is actually configured to do:

# current power settings for each power source
pmset -g custom

Then in System Settings:

1. Lock Screen → check Turn display off times for battery and power. If this is set to Never, nothing else matters.
2. Battery → Options → Prevent automatic sleeping on power adapter when the display is off. On a Mac desktop this is exactly the setting people forget.
3. Battery → Options → Wake for network access. Set to Never if the Mac keeps waking as well as not sleeping.
4. Displays → if an external display is connected, check whether it has its own sleep behaviour.

Sharing services keep a Mac awake by design

Open System Settings → General → Sharing. Several of these prevent sleep so the service remains reachable:

• Screen Sharing and Remote Management
• Remote Login (SSH)
• File Sharing and Printer Sharing
• Media Sharing, which is on more Macs than you would expect
• Content Caching, which will hold a Mac awake indefinitely

Turn off anything you are not using. This is the most common cause after a stray app.

Peripherals that vote against sleep

Some USB devices signal activity constantly and keep the system awake. If pmset -g assertions shows nothing and the Mac still will not sleep, unplug everything, wait, and add devices back one at a time. Common offenders: some USB hubs, drawing tablets, game controllers, older printers and audio interfaces. A wireless mouse on a desk that vibrates counts too — set the mouse aside and see if the pattern changes.

Clamshell mode and external displays

On a MacBook connected to an external display, closing the lid does not sleep the Mac if it is on power and has an external keyboard or mouse available. That is deliberate — it is how clamshell mode works — and it looks exactly like a Mac refusing to sleep.

If you want the machine to sleep with the lid closed while docked, disconnect the display or use the Apple menu → Sleep command directly. And if you want the opposite, a MacBook that keeps running with the lid closed and no display attached, that needs the lid-close behaviour changed rather than sleep prevention, which is a separate setting.

If it still refuses

1. Check for a caffeinate process left running: ps aux | grep caffeinate, and end it if you find one.
2. Restart. A stuck assertion from a crashed app clears on reboot, which is why "have you tried restarting" survives as advice.
3. Test in a new user account. If sleep works there, the cause is something in your login items or a per-user app.
4. On an Intel Mac only, an SMC reset is a legitimate last step. On Apple silicon there is no SMC reset; a full shutdown and start accomplishes the same thing.