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I am on Mac mini M1 with OSX 11.6.4. I live in an area where occasional blackouts occur especially during winter. In order to avoid dirty shutdowns and abrupt power loss to my Mac I've purchased APC UPS with data port support. It's a usb cable from UPS to Mac to signal if there is a power loss to automatically shut it down using built-in tools. The UPS will provide a runtime between 15-30min at most. I did not buy it to work during blackouts but rather to allow time for clean shutdown. I've opted for UPS for a bit more running time in case there is a task such as an update or in case Mac draws more power than usual.

What concerns me is the following. Sometimes apps would prevent Mac from shutting down. I have configured my Mac to shutdown during the night. However, in a number of instances, an app, such as Visual Studio Code or iTerm would prevent that from happening. I know that someone will suggest a workaround to manually close apps before leaving the Mac, but it has 2 major disadvantages:

  • user error: one can easily forget to close active apps, especially after a long-day
  • inconvenience: if I need to leave my Mac during the day, it would be super inconvenient to close all apps and re-open them, plus it ties with previous point where if something urgent comes up, one will easily forget to close all running apps

My question:

Does anyone know or can confirm how Mac will shutdown when entering a battery mode in UPS and when one of the thresholds for shutting down is reached?

My concern is that if it is a request rather than forced shutdown, and an actively running app will prevent a shutdown, the Mac will continue to run on UPS battery until it is drained and dirty/abrupt power loss occurs.

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  • If third party tools are a possibility, see how Power Manager manages Shutting Down Your Mac Safely and How to Shut Down When UPS Power Drops. Commented Nov 27, 2023 at 6:35
  • I am open to the possibility of third party software. As long as that software is known, reputable and/or peer reviewed, I am fine with it. Thank you for the suggestion! I'll have a look. Commented Nov 27, 2023 at 9:03
  • I wrote Power Manager, so consider the suggestion bias. You can check the company's history at dssw.co.uk/about Commented Nov 27, 2023 at 9:12

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How macOS will attempt to shut down the Mac when the UPS fails is not documented by Apple. The behaviour may also change between versions of macOS.

Scheduled shut downs by macOS can be blocked by applications presenting modal dialogs.

In Power Manager, we implemented a safer multi-step shut down process to avoid these problems. The risk then becomes loosing unsaved work.

The best approach is to test the behaviour on your Mac, using the applications you are concerned about.

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  • Power Manager app looks really good! In order to use the safe multi-step approach you've described, I believe I would need to disable built-in scheduled shutdown as well as shutdown conditions for UPS configured in Energy Saver Preferences? Commented Nov 28, 2023 at 8:29
  • Yes, you are right. You can use both but only Power Manager's scheduled events will use the safer shut down approach, see dssw.co.uk/blog/2023-04-21-power-manager-and-pmset There is also a thirty day demonstration, so you can ensure it works for your situation. Commented Nov 28, 2023 at 8:38

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