Simulators gone bad

Recently, some of my simulators launched and loaded just fine. Others simply went black. It didn’t seem to matter which firmware I was simulating. Some devices were just happier than others.

Naturally, I turned to the system console, which provides device-by-device logs, but I couldn’t really find anything.

I tried restarting and rebooting the sims. I tried resetting the core simulator service. I tried a lot of things. (No actual chickens were harmed.) Finally, I stumbled across a Apple Dev Forum thread about issues with the beta system. The advice offered in-thread was this:

  • Quit the simulator. (I also killed because reasons.)
  • Run xcrun simctl erase all
  • Set a framebuffer renderer hint: defaults write FramebufferRendererHint 3

It worked.

Yay! \o/

From the thread, apparently hints 1 and 2 do not work but 3 does. An Apple Engineer noted that, “hint 0 is auto (currently prefering Metal and then falling back to OpenGL if unavailable). Hint 1 prefers Metal and hint 3 prefers OpenGL. Hint 2 used to mean OpenCL, but we dropped OpenCL support.”

Upshot is that I lost many hours but I seem to have a working solution for dealing with a common problem. I hope this write-up helps you if you encounter the same issues.

Update: Guru Russ Bishop recommends against using this long term. He writes

If you (as I) have deadlines, and cannot wait for this problem to be fixed, this fix will get you back to work. Russ reminds me, though, “Use it temporarily only if you have this problem, and don’t forget to delete the pref in the future”


  • Thanks! I ran into this yesterday. iPad simulators with Xcode 9.4.1 refused to work, while Xcode 10b2 are fine. I didn’t try this yet — I’m okay with living in Xcode 10 for now — but I’ll have to remember this when I have to think about making releases again.

    • Thanks. This command resolved my problem you save my life.