At my condo, which I visit monthly, I have a 2010 MBA (High Sierra?) that runs a webcam and performs various other periodic tasks. I don't have an UPS for it, but the internal battery usually lasts long enough to handle power outages. However, this week the condo scheduled an all-day outage in order to do maintenance on the electrical systems. I have the MBA scheduled to "Start up or wake" every morning. (This MBA does not have "Start up automatically after a power failure".) As expected, the MBA's battery went dead during the power outage. I expected that the battery would charge up after power was resumed and that the MBA would start up on schedule. It did not and remains shut off.

What should I have done differently?

At home I have a 2017 iMac running Catalina. It has a UPS with a battery that lasts about an hour after a power outage. When the battery gets low, the UPS sends a shutdown command to the Mac. During a long outage the UPS shuts the Mac down and then turns itself off when the battery dies. When power resumes, the Mac starts up automatically. ("Start up automatically after a power failure" is enabled.)

However, this week, while I was away, there was a power outage. The outage lasted long enough for the UPS to shut down the Mac, but power resumed before the UPS shut itself off. So, power to the Mac was never lost. As a result, it stayed shut down and required manual intervention to start up.

What should I have done differently?

  • 1
    That's a tricky one… I've always just let mine go down when the power does, then auto-boot when it returns. Had a Mac Pro ran like that 24/7/365 for 10 years with no ill-effects. My nix gateway/server still does the same. Never tried it with a laptop.
    – Tetsujin
    Sep 19, 2020 at 11:19
  • Yeah, probably worth considering. Kind of defeats the purpose of having UPS software, but probably a better solution.
    – Buadhai
    Sep 20, 2020 at 23:45

1 Answer 1


You might want to consider replacing the MBA with a Mac Mini, perhaps a previously owned model from OWC which as some real inexpensive models. Your needs don't seem to require a superlative machine with lots of RAM & etc. The Mini should be able to provide the startup after power failure option because it is a desktop Mac.

For the problem of starting up the iMac in the circumstances you described, you should consider creating a series of Terminal pmset commands which wakes or restarts your Mac with a frequency you find amenable.

This example should attempt to wake from sleep or power on the Mac on an hourly basis every day:

pmset repeat wakeorpoweron MTWRFSU 01:00:00
pmset repeat wakeorpoweron MTWRFSU 02:00:00
pmset repeat wakeorpoweron MTWRFSU 03:00:00
pmset repeat wakeorpoweron MTWRFSU 24:00:00

If the Mac is already up and running, these commands have no effect. A wealth of information is found in man pmset.

The app Power Manager may also be helpful as it provides a GUI method for setting the same commands.

Disclaimer: I have no financial or other ties to the developers of Power Manager, nor in Other World Computing, Inc.

  • Thanks. Great answer. I will play with pmset on the iMac. I had no idea. As for the MBA, I was already in the process of replacing it with a Pi 4. Of course, it started right up after the power outage and continues to run well and perform all the tasks (but one) previously assigned to the MBA.
    – Buadhai
    Sep 20, 2020 at 23:50
  • It seems that pmset will only let you set one repeating event at a time: MrMuscle:bin mnewman$ pmset -g sched Repeating power events: wakepoweron at 7:00AM every day Scheduled power events: [0] wake at 09/25/20 00:46:40 by 'com.bombich.ccchelper' [1] wake at 09/26/20 01:09:40 by 'com.bombich.ccchelper' You can see how Bombich has had to work around this by creating separate non-repeating wake events for each scheduled ccc backup.
    – Buadhai
    Sep 21, 2020 at 1:13

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