I've bought iMac 27' in 2017 since the beginning I'm having a very annoying issue with it. On average every two weeks, my mac will freeze to the point where the mouse is still moving, audio continues to play and it even advances to the next songs. Besides the moving mouse and audio in the background, I'm unable to click anything. Usually, it happens when I close an application or when I decide to install updates from apple. Rarely it just happens out of anything.

I've tried a few things like removing programs cache, unused apps, reset SMC and NVRAM but so far nothing fixed the issue. After upgrade from Sierra to High Sierra it became more often but after updates (I remember that WindowServer had memory leaks), it got back to normal so I can live with it but it's still annoying. Also, I've run Apple's diagnostics to check if everything is okay and it's.

The only thing that I've changed in my mac was RAM upgrade so I have 2x4GB (Apple) and 1x16GB (Crucial 16GB DDR4 2400 MT/s (PC4-19200)) so in total, I have 24GB of RAM.

I've MacBook pro as well which has basically the same set of applications installed and even more and it never happened it so far and I have for over 2 years.

The last time it froze was today and I've decided to enable SSH so maybe when it'll happen again I might be still able to SSH and list processes list.

Besides the issue that I just described I have no other issues.

Does anyone have an idea what's going on?

Additionally, bellow is the list of apps that I use:

- Android Studio
- PyCharm
- Goland
- Magnet
- VirtualBox
- Vagrant
- Google Chrome
- Minecraft
- iTerm
- Slack
- Discord
- Intelliji Idea
- Magnet
- Clocker

One last thing, after it froze today I've decided to check DiagnosticReports and I've noticed that the last report is about WindowServer and when I checked the date when it happened the last time there was also WindowServer. I'm starting to suspect that it might be a bug in WindowServer but what would I have to do to fix it?

  • Firstly, welcome to Ask Different! :) Have you identified any way to actually bring on this behaviour?
    – Monomeeth
    Jun 27, 2018 at 1:05
  • It's completely random, but it happens only when my mac is running without shutting down for a few days. Usually, I put my mac to sleep when I'm not using it. Thanks for the warm welcome :) Jun 27, 2018 at 19:10
  • This feels like a lack of memory and the spin is when an app wants to swap in from disk. Thus can happen when an app wants to free memory eg closing old browser tabs. Look at memory usage in activity monitor look for non green memory pressure.
    – mmmmmm
    Jun 27, 2018 at 21:44
  • I don't know if this will help, but I'm having a similar issue on my 24 GB iMac. It didn't start until a few weeks ago and I've found it seems to freeze every 4 days. You might note the delay and see if that's how long it takes between freezes. This seems to be after an OS update and I've also found reason to suspect it's tied in to WindowServer. Also, in my case, it's not a full freeze. It happens whenever I go from one window to another.
    – Tango
    Aug 7, 2018 at 4:13
  • @Tango I found the solution, I simply decided to format the hard drive and reinstall the OS using a flash drive. Before that, I tried everything: I tested my RAM using memtest, tried to fill ram and see what happens, safe mode, removed apps cache and nothing worked. Then I bought external SSD and installed Windows 10 on it and used it for 2 weeks and it worked without any issues... So then the only thing left was os reinstall and it worked! So far 1 month without any crashes :) Aug 7, 2018 at 14:43

1 Answer 1


Troubleshooting is a process of elimination and often requires patience, but since it seems you don't have a way to bring on a freeze - and because of the time in between incidents of this happening - it's going to be somewhat slower to diagnose.

While I understand your instinct that it could be a bug with WindowServer, it's actually much more likely to be an issue with how well one of your installed apps is communicating with WindowServer. I'm not familiar with all of the apps you have installed, but if you have anything that hasn't been updated in a long time it may be worth isolating that for a while (i.e. not using it) to see if that makes a difference.

One thing worth doing regardless is to boot your iMac into Safe Mode.

Boot into Safe Mode

Follow these steps to boot your iMac into Safe Mode:

  1. Fully shut down your iMac
  2. Restart your iMac
  3. Immediately press the Shift key and keep it down
  4. Let go of the Shift key when you see the login window (NOTE: If you have FileVault enabled you may need to log in twice).
  5. Now use your iMac in Safe Mode until it crashes again or until you're satisfied it's not going to crash (i.e. you may be at this step for some days). Of course, some things don't work in Safe Mode, so you may need to exit Safe Mode earlier and boot normally anyway.
  6. Exit Safe Mode by restarting your iMac as normal
  7. Once again, test to see if your iMac still crashes

Let me know how you go, although it may take you quite some time to know if doing this has helped.

NOTE: Even just booting into Safe Mode temporarily can be enough to resolve some issues, so it's still worth doing even if you can't stay in Safe Mode for too long.

  • I'll try to boot into safe mode today. Jun 27, 2018 at 19:11
  • I've added a comment to the question, since I have a similar issue. I'd try Safe Mode, but 4 days is a long time to do that!
    – Tango
    Aug 7, 2018 at 4:14

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