Setting Up a UPS on a Mac: Shutdown Options and pmset

What macOS does with a USB UPS

Like Windows, macOS recognizes UPS units that implement the USB HID Power Device class, which covers most small APC, CyberPower, Eaton and Tripp Lite units with a USB data port. There is no driver to install. Once detected, macOS knows whether it is running on mains power or UPS battery, reads the UPS charge level and runtime estimate, and adds a set of UPS shutdown options to its power settings.

On a desktop Mac (iMac, Mac mini, Mac Studio, Mac Pro) this is the only "battery" macOS sees, so the UPS options are the whole story. On a MacBook, the internal battery takes priority and the UPS mostly protects peripherals.

Where the settings live

Apple has moved power settings several times, so the exact location depends on your macOS version. The options only appear while a UPS is connected.

If you cannot find the pane, search for "UPS" in the System Settings search box. On some versions the UPS section appears only after you reconnect the USB cable with the settings window closed.

The three shutdown triggers

The Shutdown Options dialog typically offers three checkboxes. Any one of them reaching its threshold starts a normal macOS shutdown.

Checking and setting UPS behavior with pmset

pmset is the command-line power management tool. It is useful for confirming what macOS sees and for scripting settings on several Macs.

# Show the current power source and the UPS charge as macOS sees it
pmset -g ps

# Show all active power management settings, including the UPS profile when a UPS is attached
pmset -g

# Show a log of power source changes (useful after an outage)
pmset -g log | grep -i "power source"

When on UPS power, pmset -g ps typically reports something like "Now drawing from 'UPS Power'" followed by the UPS name, charge percentage and state. If it always says AC Power with no UPS line, macOS is not receiving UPS data.

The UPS shutdown thresholds are stored in the UPS power profile, using settings named haltlevel (percentage), haltafter (minutes on UPS) and haltremain (minutes remaining). The pmset manual describes setting them with the -u flag:

# Shut down after 5 minutes on UPS power
sudo pmset -u haltafter 5

# Also shut down if estimated runtime falls below 4 minutes
sudo pmset -u haltremain 4

# Shut down if the UPS charge falls below 30%
sudo pmset -u haltlevel 30

Check man pmset on your macOS version before scripting, since flags and behavior have changed over the years. The graphical settings and pmset write the same values, so a quick look at the settings pane confirms the result.

Getting the Mac back up after the outage

A Mac mini running a home server, a media library or backups usually needs to restart by itself. Two pieces must line up:

1. Enable automatic startup. In recent versions the setting is called Start up automatically after a power failure and sits in the Energy settings for desktop Macs. From Terminal: sudo pmset -a autorestart 1.
2. Make sure the Mac really loses power. Auto restart fires on power restoration after a loss. If the UPS keeps its outlets live after the Mac shuts down and mains returns before the battery empties, the Mac sees no loss and stays off. Software that tells the UPS to turn its outlets off after a delay (vendor tools or NUT's shutdown sequence on a separate machine) closes this gap.

Testing the setup

1. Charge the UPS fully, save your work and leave the Mac doing its usual tasks.
2. Unplug the UPS from the wall socket (not with the UPS power button, which cuts the output).
3. Watch the menu bar battery indicator and time how long until the shutdown starts and completes.
4. Note the runtime the UPS display or pmset -g ps still reports when the Mac is fully off. You want minutes to spare, not seconds.
5. Restore power and confirm the Mac restarts by itself if you enabled that.

When the UPS does not show up

Work through the chain from the cable outward:

The USB cable supplied with a UPS sometimes has an unusual connector at the UPS end, or is an RJ45-to-USB cable on some models. A generic printer cable may fit some ports but not others. Use the original cable where possible, and see UPS not detected by computer for more checks.

Picking values: a worked example

Suppose a Mac mini, an external SSD enclosure and a monitor together draw around 60 W, and the UPS shows roughly 40 minutes of estimated runtime at that load. A shutdown on this kind of system usually takes under a minute, but an app with unsaved work can hold it up.

• Time on UPS: 5 minutes. Rides through flickers and short outages; shuts down with most of the battery intact in a long one.
• Time remaining below: 10 minutes. Rarely reached with these numbers. It exists for the day the battery has aged and the 40-minute estimate has quietly become 12.
• Battery level: off or low. The two time-based triggers already cover it.

On a heavier desktop, such as a Mac Studio driving several displays, runtime may be much shorter. Scale the time on UPS down so the shutdown still starts with at least twice the shutdown duration left. The UPS runtime calculator gives a starting estimate before you measure.

A Mac on a shared UPS

macOS has no built-in way to listen to a UPS that is connected to another machine. If your Mac shares a UPS with a NAS that owns the USB connection, you have three options:

• Network UPS Tools client. NUT builds for macOS (commonly installed through a package manager such as Homebrew) can run upsmon as a secondary and shut the Mac down when the NAS or server running the NUT server signals it. See Network UPS Tools for configuration.
• Vendor network shutdown software. Some vendor tools have macOS agents; check the current support list, as macOS support has been inconsistent over the years.
• Move the USB cable. If the Mac is the machine that matters most, let it own the UPS and let other devices fend for themselves, or give them their own UPS.

For a broader view of the tool options, see the UPS software overview. If macOS does not show the UPS at all, work through UPS not detected by computer.