Preventing Sleep

Open Activity Monitor, click the Energy tab, and click the Preventing Sleep column to sort by it. Apps showing Yes are holding the Mac awake.

For more detail, run pmset -g assertions in Terminal. It lists each active assertion and the process that owns it, which also covers background processes.

If the app has a good reason, such as a download in progress, let it finish. If it does not, quitting the app normally releases the assertion. Browser tabs playing media, including muted ones, are a common cause.

For a one line answer, run pmset -g and look at the sleep line. If something is holding the Mac awake, it ends with the words sleep prevented by and a list of process names.

pmset -g assertions gives the details. The top half is a summary of assertion types, and the section called Listed by owning process shows each process, how long it has held the assertion, and a name the app gave it. The types you will see most:

• PreventUserIdleSystemSleep: the Mac will not sleep on its own, but the display can still turn off.
• PreventUserIdleDisplaySleep: the display stays on. Video players and presentation apps use this.
• PreventSystemSleep: the Mac is kept from sleeping at all. The caffeinate -s version of this only works on power.
• NoIdleSleepAssertion: another name some apps use when they keep the Mac from idle sleep.
• powerd holding an assertion named Prevent sleep while display is on: normal while you are using the Mac.

Sometimes the owner in pmset -g assertions is a system process, such as coreaudiod, holding the assertion for another app. In that case the entry has a line that says Created for PID followed by a number. That number is the app you are looking for.

1. Run pmset -g assertions and find the Created for PID line under the system process.
2. Run ps -p <PID> -o comm=, replacing <PID> with that number, to print the app's name.
3. Stop what that app is doing with audio, such as a paused video, an open call or a recording, or quit the app.
4. Run pmset -g assertions again to confirm the entry is gone.

• A browser tab or app with audio or video open, even if it is paused or muted.
• A video call app that still has the microphone or camera open.
• Downloads, uploads, cloud sync and backups that have not finished.
• Apps reading from a disk. Apple gives Music playing songs as an example.
• People using services your Mac shares, such as a connected printer or shared files.
• An active terminal session, such as a remote login. The pmset setting ttyskeepawake prevents idle sleep while one is in use. Run pmset -g | grep ttyskeepawake to check it, where 1 means on.
• A caffeinate command or a keep awake utility you started and forgot about.

If your Mac sleeps but wakes up again, the power log records why. Run pmset -g log | grep -e " Sleep " -e " Wake " -e " DarkWake " | tail -20 to see the most recent sleeps and wakes. The text after due to names the cause, such as the lid, a keyboard or trackpad, or a scheduled task.

DarkWake lines are short wakes with the display off, which macOS uses for background tasks. A few of these overnight are normal.