Xcode ‘Unable to boot the Simulator’: Causes and Fixes

Common causes

• The CoreSimulator service is stuck or unstable
• The data for a specific simulator device is corrupted
• The installed iOS Simulator Runtime is damaged or inconsistent
• Old caches or simulator records remain after an Xcode update
• macOS is low on free disk space or is experiencing a temporary system issue

Typical situations where the error appears

What to check first

1. Try another Simulator device

Select a different iPhone Simulator from Xcode’s run destination menu and try launching it. If another device boots normally, the original simulator’s data is likely corrupted.

2. Check available Simulator devices

xcrun simctl list devices

Look for devices marked as Unavailable.

3. Check free disk space

Simulator devices can consume several gigabytes each. If your Mac is very low on free space, remove unused simulators, runtimes, or Xcode build data before trying again.

Fix 1: Restart Simulator and Xcode

Quit Simulator and Xcode completely, then reopen Xcode and try again. If the issue persists, restart macOS.

Fix 2: Restart the CoreSimulator service

Open Terminal and run:

killall -9 com.apple.CoreSimulator.CoreSimulatorService

Then reopen Xcode and launch the Simulator again.

Fix 3: Shut down and erase the affected Simulator

First shut down all simulators:

xcrun simctl shutdown all

To reset a specific device, open Window > Devices and Simulators, select the simulator, and use Erase Contents and Settings.

To erase all simulator devices from the command line:

xcrun simctl erase all

Fix 4: Delete and recreate the broken Simulator

If only one simulator fails to boot, remove it from Devices and Simulators and create a new virtual device.

You can also remove unavailable simulator entries with:

xcrun simctl delete unavailable

Fix 5: Reinstall the Simulator Runtime

If several devices using the same iOS version fail to boot, the corresponding Simulator Runtime may be damaged.

Open Xcode settings, go to Platforms or the equivalent component management screen for your Xcode version, remove the affected iOS runtime, and download it again.

Fix 6: Clear DerivedData

If the problem appears alongside build or cache issues, clear Xcode’s DerivedData:

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

Restart Xcode and rebuild the project afterward.

Fix 7: Verify the selected Xcode developer directory

If multiple Xcode versions are installed, command-line tools may be pointing to a different Xcode installation.

xcode-select -p

If necessary, switch to the intended Xcode installation:

sudo xcode-select -s /Applications/Xcode.app/Contents/Developer

Fix 8: Update Xcode and macOS

An older Xcode version may not work correctly with a newer simulator runtime, and some Xcode releases require newer macOS versions. Update to the latest stable Xcode supported by your Mac, and update macOS when necessary.

Important notes

Summary

Unable to boot the Simulator is usually caused by a CoreSimulator service failure, corrupted virtual device data, a problematic Simulator Runtime, or stale Xcode caches.

Start by testing another simulator, then restart Xcode and CoreSimulator, reset or recreate the affected device, and check available disk space. If the problem continues, reinstall the Simulator Runtime, clear DerivedData, verify xcode-select, and update Xcode or macOS as needed.