How to Fix iOS Simulator Not Starting

In this tutorial, you'll learn about How to Fix iOS Simulator Not Starting. We cover key concepts, practical examples, and best practices.

The Problem

You click Run in Xcode and the iOS simulator fails to start:

Simulator unable to boot: Domain: NSPOSIXErrorDomain, Code: 60
"Simulator connection became invalid"

Or the simulator shows a black screen and stays frozen indefinitely.

Quick Fix

Step 1: Force quit and restart simulator

killall Simulator
open -a Simulator

This restarts the simulator process, which resolves most transient issues.

Step 2: Reset the simulator content and settings

In the Simulator menu: Device > Erase All Content and Settings.

Or via command line:

xcrun simctl erase all

Expected:

Erased all contents and settings of all devices.

Step 3: Delete and re-add the simulator

xcrun simctl delete unavailable
xcrun simctl create "iPhone 15" "iPhone 15" "iOS17.4"

This removes the simulator and creates a fresh one with a clean state.

Step 4: Shutdown all simulators

xcrun simctl shutdown all

Sometimes a simulator is stuck in a "booting" state. Shutting down all of them and restarting the one you need fixes it.

Step 5: Check Xcode version compatibility

xcodebuild -version

Expected:

Xcode 15.4
Build version 15F31d

If Xcode is outdated relative to your macOS version, download the latest from the Mac App Store.

Step 6: Clear Xcode derived data

rm -rf ~/Library/Developer/Xcode/DerivedData/*

Corrupted derived data can prevent the simulator from launching. Xcode regenerates these files on the next build.

Step 7: Check simulator runtime availability

xcrun simctl list runtimes

Expected:

iOS 17.4 (17.4 - 21F79) - Available

If the runtime is not listed as "Available", download it in Xcode: Settings > Platforms > click the + button.

Step 8: Restart Xcode and CoreSimulator service

sudo killall -9 com.apple.CoreSimulator
sudo launchctl reboot userspace

This restarts the CoreSimulator service that manages simulator lifecycles.

Step 9: Check disk space

df -h /

The simulator needs free disk space to boot. If disk space is below 10 GB, free up space by clearing caches and derived data.

Alternative Solutions

Run on a physical device instead of the simulator: connect an iPhone via USB, select it in the Xcode scheme menu, and click Run.

Prevention

• Keep Xcode and simulator runtimes updated to matching versions.
• Erase simulator content before each major test run to avoid state corruption.
• Close simulators cleanly (Cmd+Q) instead of killing the process.
• Maintain at least 20 GB of free disk space for simulator operations.