How to troubleshoot simulator errors?

Most iOS Simulator errors trace back to a small set of causes: corrupted simulator state, a stuck CoreSimulator service, a missing or mismatched runtime, low disk space, or an out-of-date Xcode. The fast path is to shut the device down and erase it (xcrun simctl shutdown all then xcrun simctl erase all), restart the CoreSimulator service, free disk space, and update Xcode and the Command Line Tools. Below, each common error is mapped to its exact fix. If you want to skip local simulator failures entirely, you can run your app on a real device cloud instead.

Common iOS Simulator Errors (and What Causes Them)

Before reaching for a fix, identify which error you are actually seeing. The table below maps the most common Simulator error messages to their usual root cause so you can jump straight to the right section.

Quick First Steps That Fix Most Errors

Work through these in order. They resolve the large majority of Simulator errors before you ever need to touch CoreSimulator internals:

• Quit and relaunch: fully quit the Simulator and Xcode, then reopen them. A stale process is the single most common cause of a one-off error.
• Erase content and settings: in the Simulator menu choose Device > Erase All Content and Settings, or run the terminal commands below to wipe every device.
• Restart the Mac: a reboot clears a stuck shared cache and any orphaned CoreSimulator services that a relaunch alone will not.
• Update Xcode and the Command Line Tools: mismatched tooling is a frequent source of boot and install failures, especially after a macOS update.

xcrun simctl shutdown all
xcrun simctl erase all

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

"Unable to Boot the Simulator" / "Failed to Launch"

This pair of errors almost always means the simulator's device data is corrupt or the CoreSimulator service is wedged. Escalate through these steps:

• Shut down then erase: run the shutdown and erase commands from the previous section first; they fix a surprising number of boot failures on their own.
• Kill and restart the CoreSimulator service: force-quit the background service so it respawns cleanly.
• Clear corrupt device data: remove the offending device folder, or every device, under the CoreSimulator directory and let Xcode recreate them.
• Check disk space: simulators fail to boot silently when the volume is nearly full, so confirm you have headroom.
• Update to the latest point release: Xcode 16 and iOS 18.x carry boot regressions such as launchd_sim could not bind to session; the newest patch usually resolves them.

xcrun simctl shutdown all
sudo killall -9 com.apple.CoreSimulator.CoreSimulatorService

# delete one device by UDID
rm -rf ~/Library/Developer/CoreSimulator/Devices/<UDID>

# nuclear option: remove all simulator devices
rm -rf ~/Library/Developer/CoreSimulator/Devices/*

df -h /

"Unable to Boot Device in Current State"

This error is a state mismatch rather than corruption. You asked to boot a device that is already booted, or to erase one that is still running. The fix is to always check state and shut down first:

xcrun simctl list devices        # find the UDID and current state
xcrun simctl shutdown <UDID>     # shut the target device down
xcrun simctl erase <UDID>        # then erase it safely

React Native and Expo users: a launcher that auto-boots the most recently used simulator can collide with the device your tooling is starting. In the Simulator settings, turn off "boot most recently used simulator" to stop the two from racing.

Reset Everything With simctl Cleanup Commands

When you want a clean slate, keep this reference handy. Each command targets a specific layer of simulator state, from running devices to orphaned ones to diagnostic logs:

xcrun simctl shutdown all          # stop all booted devices
xcrun simctl erase all             # wipe content and settings
xcrun simctl delete unavailable    # remove broken or orphaned devices
xcrun simctl list devices          # verify the remaining devices
xcrun simctl diagnose              # collect logs for a bug report

For a heavier reset that deletes every simulator and lets Xcode or your CI tooling recreate them from scratch, use xcrun simctl delete all. Fastlane users can achieve the same with fastlane snapshot reset_simulators.

App Won't Install, Black Screen, or White Screen

These symptoms point at the build or the device rather than the service itself:

• "Failed to install... bundle was not found": verify the .app path you are pointing at and rebuild specifically for the simulator destination, not a device.
• Black or white screen, or a frozen Apple logo: erase the device, restart the CoreSimulator service, and reboot the Mac to clear a hung boot.
• Build-for-simulator failures on Apple Silicon (arm64): in your target's build settings, add arm64 to Excluded Architectures for the iOS Simulator SDK only when a dependency forces it, then clean and clear DerivedData.

Clean the build folder with Product > Clean Build Folder (Cmd+Shift+K), then remove stale derived data:

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

Missing Runtimes and Runtime Download Failures

If the Simulator reports "no devices registered" or you cannot find a particular iOS version, the runtime is missing. Open Xcode > Settings > Components (or Platforms) and install the runtime you need. When the in-app download fails, often with DVTDownloadableErrorDomain Code 41 or a bad-URL error, download the runtime DMG manually from Apple and import it:

xcodebuild -importPlatform ~/Downloads/iOS_18.2_Simulator_Runtime.dmg

Apple Silicon and Permissions Gotchas

A handful of errors are specific to Apple Silicon Macs and file permissions:

• Rosetta missing: some tooling needs Rosetta to run x86 binaries; install it once and the dependent errors disappear.
• "Operation not permitted": reset ownership and permissions on the CoreSimulator directory so the service can read and write its own data.
• After every macOS update: re-run your fixes; OS updates routinely reintroduce boot and permission errors until the toolchain is reconciled.

softwareupdate --install-rosetta
chmod -R u+rwX ~/Library/Developer/CoreSimulator

The Android Emulator Equivalent (Brief)

If you hit the same class of "won't boot / won't launch" failures on the Android side, the causes differ: they are usually a missing hardware accelerator or a system image that does not match your CPU. Enable the hypervisor (AEHD, WHPX, or Hyper-V on Windows, KVM on Linux, Hypervisor.framework on macOS), use an x86_64 image on Intel or an arm64 image on Apple Silicon, and prefer Quick Boot. For a deeper walkthrough, see the related question on Troubleshoot Emulator Errors.

Skip Local Simulator Errors With a Real Device Cloud

Local simulators break in ways a managed cloud does not: stuck CoreSimulator services, runtime download failures, disk pressure, and version regressions all eat into your day. TestMu AI's Real Device Cloud runs your app on thousands of real iPhones and iPads with OS versions already provisioned, so there are no local boot errors and no CoreSimulator resets to manage. When you simply need a quick environment, you can also spin up an iOS Simulator Online in the browser instead of debugging your local install.

Frequently Asked Questions

How do I fix "Unable to boot the Simulator"?

Shut every device down and erase it with xcrun simctl shutdown all then xcrun simctl erase all, kill the CoreSimulator service with sudo killall -9 com.apple.CoreSimulator.CoreSimulatorService, clear corrupt device data under ~/Library/Developer/CoreSimulator/Devices, and update Xcode and the Command Line Tools. Restarting the Mac afterwards clears any stuck shared cache.

What does "Unable to boot device in current state" mean?

It means you tried to boot a device that is already booted, or erase one that is still running. List the devices and their state with xcrun simctl list devices, shut the target device down with xcrun simctl shutdown <UDID>, and only then boot or erase it.

How do I completely reset the iOS Simulator?

Run xcrun simctl shutdown all followed by xcrun simctl erase all to wipe content and settings on every device, then xcrun simctl delete unavailable to remove orphaned or broken devices. For a heavier reset, xcrun simctl delete all removes every simulator so Xcode can recreate them.

Why does my app crash or fail to install on the simulator?

The most common causes are a wrong .app bundle path or an architecture mismatch on Apple Silicon. Verify the build is targeted at the simulator, run Product > Clean Build Folder, clear DerivedData, and read the console output for the real error before retrying the install.

Why won't the iOS 18 or Xcode 16 simulator boot?

Recent Xcode 16 and iOS 18 releases have known runtime regressions and download failures such as launchd_sim could not bind to session and DVTDownloadableErrorDomain Code 41. Update to the latest point release and, if the runtime is broken, reinstall it manually with xcodebuild -importPlatform.

My simulator boots but is very slow. Is that an error?

No. Lag, jank, and high RAM or CPU usage are performance problems rather than boot or crash errors, and they have different fixes such as choosing a smaller device, disabling slow animations, and freeing memory. See How to Handle Performance Issues with the Simulator? for those.

• How to Handle Performance Issues with the Simulator?
• How to Configure Simulators Settings?
• How to Install iOS Simulators?
• Troubleshoot Emulator Errors
• How Does Real Device Testing Improve App Reliability Compared to Emulators and Simulators?