“Your system has run out of application memory.” How is that possible

memory

macOS is regularly popping up a "Force Quit Applications" dialog:

Your system has run out of application memory.

To avoid problems with your computer, quit any applications you are not using.

How is that possible if there are only a few open apps?

Best Answer

In my experience, this occurs when my main system hard drive is running low on free space. Operating Systems use the hard drive for extra memory storage, called "virtual memory". (I've definitely always wished that the OS could just reserve enough space for itself, but it just can't predict how many applications we'll be running).

On top of that, it's worth noting that regular web use now requires far more memory than it did in the past. In activity monitor, you'll notice that every single tab & window (every open web page) is it's own process, taking up a significant chunk of memory. On top of that, account for all the ads, movies, flash, scripts, plugins and 360 videos etc. that we expect to run smoothly. New OS's and new web pages just use a lot of memory to provide us with the services we expect to "just work" (eg. syncing across devices, notifications, automatic updating etc. etc.).

In short, in my experience there usually isn't a single process that's suddenly taking up a huge amount of memory (although a leaky program could indeed be a culprit - Sketchup 2016 does this to me, for example). More commonly, it's the additional functionality we expect of many programs/web plugins.

I believe restarting the computer always alleviates this problem for a short while - primarily by unloading all the webpages and apps we had launched over time. But if our expectation of the computer and hardware constraints stay the same (and we run the same number of processes without changing anything else), eventually we'll run into the problem again.

Two solutions that work for me:

1) Open fewer tabs/pages and fewer programs at one time. Close some web-pages/programs before opening the hefty apps, such as MS Office, Parallels, 3D CAD, Adobe programs etc.

2) Free up more space on the system hard drive (eg. move all your music and photos to another drive), to allow the system to handle your typical virtual memory needs. For me, this means my 1TB OS drive needs >20% free space (200GB)! Your requirements may be different. If you're on an older Apple laptop or iMac or Mini, the OWC Data-Doubler is a really fantastic way to accomplish this.

Method (1) is my temporary fix, so that when I eventually enact method (2) I will have restored the snappy performance I expect while running many heavy-duty programs simultaneously.

Basic methods

Run Console.app and check on 'All Messages' to see if anything unusual currently is happening.
Use Activity Monitor to read system memory and determine how much CPU, RAM and Disk is being used.

Alternatively run top in Terminal and hold Space to refresh - easier to find the cause problem (swapins/swapouts/disks?).
Run sudo fs_usage in Terminal to report system calls and page faults related to filesystem activity in real-time (I think this is the best option from all other). Then hit Control-C to stop it.

Action: Consider killing apps which appears frequently on the list, but you're not using them.

Learn more at: How do I debug an out-of-control “kernel_task” process?
Run sudo syscallbypid.d (or syscallbyproc.d), wait a bit, hit Control-C. Now check which process generated the most system calls in that given time (last column) and if you recognise it, consider kill it. If not, Google it and learn more about it.

Advanced methods

Use sysdiagnose command (can be triggered by hitting Shift-Control-⌥-⌘-. (period) to quickly gather system-wide diagnostic information helpful in investigating system memory/performance issues (will appear in /var/tmp) either by you or Apple guys. During analysis, try to not do anything, when done - consider uncompressing the generated file and analyse the logs.

^{See: How do you get system diagnostic files from OS X?}
Run footprint to gather detailed memory information on a per-VM-region type level and swapped bytes:
```
sudo footprint -a
```
Older version:
```
sudo footprint -all -categories -swapped -collapseSharing
```
Use spindump to profile entire system, it'll generate /tmp/spindump.txt file (including kernel and its extensions).
Use vm_stat to show virtual memory statistics. E.g.
```
vm_stat 1 # to display every second.
```
Use zprint to check information about kernel usage, it's possible by:
```
sudo zprint -t -s | head -n20
```
It'll show the most wasting kernel zones.
Use newproc.d to snoop new processes as they are executed, creatbyproc.d for files:
```
sudo newproc.d
sudo creatbyproc.d
```
Note: On newer OS X (10.11 or above) this may not work when integrity protection is enabled (check by csrutil status).
Try sar - system activity reporter which can sample and report various cumulative statistic counters maintained by the operating system.

For more useful debugging tools, check for dtrace scripts (grep dtrace /usr/bin/*). If you know the faulty process which causing the problem, you may use dtruss to debug it.

Actions

Here are some suggestions which can help you with the operating system issues.

Free up some inactive memory. In order to do this, you've to flush cache first and force disk cache to be purged:
```
sync && sudo purge
```
sync - force completion of pending disk writes (flush cache)

purge - force disk cache to be purged (flushed and emptied)

Its function is basically to terminate all the I/O pending operations which are using disk cache and then to free all the occupied disk cache, so it should free disk space to ease paging out and swapping out of main memory. It is safe to use, as it does not affect anonymous memory that has been allocated through malloc, vm_allocate, etc.
Use some 3rd party apps to clear up some overused memory such as iBoostUp, SystemPal, etc.

You may also disable temporary Spotlight:

sudo launchctl unload -w /System/Library/LaunchDaemons/com.apple.metadata.mds.plist

And consider other services by:

sudo launchctl list | grep ^[0-9]
sudo launchctl bslist | grep ^A

Quit your web browser and check if that helps. For example using Chrome is very resourceful, especially when there is some front-end processing going on in the background (e.g. Javascript) or advert-like animations are constantly rendering the content.