"Your system has run out of application memory": what it means and how to stop it coming back

The dialog appears without warning. It says "Your system has run out of application memory", lists your open apps, and asks you to quit some of them. Some apps in the list may be marked as paused.

The wording suggests your Mac does not have enough memory. Usually that is not the problem.

What is actually going on

A Mac does not stop when its physical memory is full. It compresses what it can, then writes the rest to disk as swap. That is slower but it keeps working, and on a healthy Mac it happens all the time without anyone noticing.

The warning appears when that safety net runs out too. There are two common ways for that to happen:

1. One app grows without limit. A leak in a browser tab, an extension, a design file or a dev tool keeps asking for memory until compression and swap cannot keep up.
2. The disk is nearly full. Swap lives on your startup disk. With only a few gigabytes free, macOS has nowhere to put it, and an ordinary workload is enough to trigger the warning.

Often it is both: a leaking app on a Mac with very little free space.

Getting out of it right now

1. Save your work in any app you can still reach.
2. In the dialog, quit the app you trust least: the one you suspect, or the one using the most memory if the dialog shows it. Paused apps cannot recover while memory is short, so quitting one is safe once you have saved.
3. If the Mac is still sluggish, restart it. A restart clears swap and gives everything a clean start.

Then work out which of the two causes you had, so it does not happen again tomorrow.

Finding the cause

Check the disk first

Open System Settings › General › Storage. If there is less than 10 to 20 GB free, that is very likely your cause, or at least half of it. It is also the easier half to fix. Mac storage almost full: where to start gives the order to free space in, and none of the steps involve guessing.

Then look for the app that grows

Open Activity Monitor, choose the Memory tab, and click the Memory column to sort by it. Look at two things:

• The pressure graph at the bottom. Green is fine. Yellow or red that stays there means the Mac is struggling.
• Swap Used, beside the graph. A few hundred megabytes is normal. Several gigabytes during ordinary work is a warning sign.

If one app sits far above the rest, especially one that should not need much memory, note it. Check again an hour later. An app whose number keeps climbing while you use it normally is leaking, and quitting it every day is the fix until its developer ships one.

Browsers deserve a closer look, because each tab and extension is its own process. Chrome's Task Manager (in the ⋮ menu, under More tools) shows which tab or extension is responsible.

Keeping it from coming back

• Keep 10 to 20 GB free, more if you work with video or large projects.
• Restart every week or two. A Mac that has been up for a month has had a month to build up leaks.
• Trim what starts at login. Every app that starts at login takes memory before you have opened anything. Look in System Settings › General › Login Items.
• Update the app you caught. Leaks get fixed, but only in new versions.

One thing will not help: "memory cleaner" apps that free inactive memory. The number looks better for a moment, but macOS would have reclaimed that memory itself when something needed it. Freeing it does nothing about a leak or a full disk.

Where SweepyMac fits

The two causes behind this warning are the two things SweepyMac's Mac Health screen watches. Its recommendations are written as sentences, and each one fires at a set threshold:

• Disk almost full when the disk is 90 percent used or has under 8 GB free.
• Memory under pressure when macOS reports it.
• Restart once the Mac has been up for 14 days.

Each recommendation has a button that opens the module that fixes it. The health score post lists every threshold.

For the disk, Space Lens shows which folders take the room while it is still measuring, Cleanup clears caches and logs to the Trash with an Undo, and Large & Old finds the files that are actually big. For memory, the Performance screen shows live CPU, memory and disk meters that refresh every three seconds, so you can see a problem build. It also has a Free up memory button, and as explained above, that is first aid, not a cure. The Login Items list there disables a login item by moving its file to the Trash, so you can undo it.

SweepyMac cannot fix a leak inside another app, and it cannot add memory. What it does is tell you which of the two problems you have and give you the tools for the disk side. It is free for three days, then from $14.99 a year or $59.96 once. Download it from its page.

If you are a developer, the app that grows is often a dev server, a forgotten node process or Docker's virtual machine. Those are what Stackyard is for. Its Guard sends a notification when memory pressure stays high, and its leak detection flags apps that grow steadily for 45 minutes. The orphans post covers how it finds them.