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I have updated to Xcode 12.3 beta. device version is 14.2, but Xcode complaining:
Errors were encountered while preparing your device for development. Please check the Devices and Simulators Window.
Failed to prepare device for development
iPhone directly connected to MacBook.
I have tried all mumbo jumbos on the web. but no success any idea?
Unable to prepare DEVICE for development
Please check the connection to the device, and review all errors in the Devices and Simulators window.
A simple phone restart will fix it
I have had to come back to this SO question twice in the past couple weeks. First time, I did have to update my Xcode and iOS versions, which fixed the issue. Now, the issue has returned, but there are no updates. I tried disconnecting and reconnecting my phone from my laptop, but to no avail.
What fixed it the second time was merely restarting my phone. I am curious if that would have fixed it the first time too, without needing to have updated.
I know this is just echoing the other answers here, but at the very least, I would recommend just starting with a simple phone restart and seeing if that fixes your problem. Here is the specific screenshot that I encountered, in case yours is the same (pro tip: you can open up the "Devices and Simulators" window by going to Window -> Devices and Simulators shift-command-2).
This error shows because of iPhone OS version is not supported by Xcode that's why this warning popped up, so check which max ios version is supported by Xcode which you are using.
In my case, the Xcode version is 13.1 and my iOS version is 15.4 so what I did, First downloaded device support version 15.4 from here (Download according to your device version) and added this to my Xcode.
steps to add the file in Xcode:-
Go to Applications > Right click on Xcode and Select Show Package Contents > Contents > Developer > Platforms > iPhoneOS.platform > DeviceSupport.
Extract your device support file to DeviceSupport Folder.
Restart Xcode and unplug and plug in your device.
Exact same problem here, this solved the issue for me:
Delete the app from the phone
Clean the Build Folder with: ⌘ + shift + K
Delete derived data
Unpair device (from ⌘ + shift + 2 window)
Disconnect iPhone
Restart iPhone
Restart Mac
Trust
After this, it worked for me.
I restarted my iPhone(14.2); now both Xcode 12.3 beta and 12.2 can run app on my device.
I could not get the phone to authorize until I had the paired Apple Watch trust the computer as well.
A more helpful error message could be imagined.
Both the iPhone and the paired Apple Watch must trust the computer before the phone can be successfully prepared for development.
If u are looking this because, your ios 15.7 device (latest for iPdas at the moment) show this error on xcode 14.0 (latest at the moment) it is a bug related with the xcode version.
Check Here.
Update
This issue is fixed in Xcode 14.0.1
In my case was to keep the iOS version with my Xcode version in sync.
Xcode 12.3 with iOS 14.3
What worked for me was to go to Xcode Devices and Simulators window, then ...
right click on the Connected device, and select "Show Provisioning Profiles" menu item, then delete all the provisioning profiles,
right click on the Connected device, and select "Unpair Device" menu item
Unplug and reboot the phone
I tried most suggestions here. The only thing that ended up working was unpairing my phone in Xcode then unpairing my apple watch from my iPhone. Connects just fine now. iOS (14.3) Xcode (12.3)
Thanks Matt for hint:
Updating device iOS to 12.3 beta fixed the problem.
if you updated you iOS to latest beta version, you should also use latest Xcode beta version.
Exact the same problem with Xcode 12.3 beta ; for me, just have to:
Disconnect the phone
Restart the phone still on ios14.2
-> data cable off
-> data cable on
and it works :)
Solution: Update your Xcode to a newer release date than your iOS Release Date.
I experienced this problem when using the iPhone's personal hotspot on my Mac. The fix was to disconnect the phone from the computer, then disconnect from the personal hotspot and reconnect again. Apparently this makes the mac use the wifi hotspot (and not the usb hotspot on the iPhone, which messes things up when debugging).
As many people mentioned/suggested, restarting my iPhone solved the problem.
My setups are: Catalina 10.15.7, Android Studio 4.0, Flutter 2.01,and Xcode 12.4.
I think having an apple watch paired to your iphone causes some issues.
I had trusted from my apple watch, but was still having this issue. Unparing my apple watch from my iphone was the only thing that worked for me:
unpair apple watch from iphone
unpair iphone from xcode
Restart both, and don't pair apple watch until the iphone is paired.
and, if you have any other problems, and are using flutter, run flutter doctor, and ensure you have cocoapods installed.
and once again, if Flutter issues, follow the details here to ensure you have your signing setup correctly
also, if things aren't working, then do a flutter clean, and then try again.
Updating Xcode is a fix because old versions of Xcode can't talk to new versions of iOS (see https://developer.apple.com/support/xcode/ for compatibility).
If you're stuck on an old version of Xcode you can use something like https://github.com/iGhibli/iOS-DeviceSupport or https://github.com/filsv/iPhoneOSDeviceSupport which installs the newer device support files into older versions of Xcode.
I just solved my issue removing the iPhone cable and putting it back.
This solved the issue for me:
Delete the app from the phone
Clean the Build Folder with: ⌘ + shift + K
Unpair device ⌘ + shift + 2
Disconnect iPhone
cmd + shift + 2
Click the red cross to check error detail
In most cases, the error message shows your xcode supported iOS version is lower than your iPhone's iOS version.
Update your xcode.
In my case, after updating iPhone to a newer iOS version then got this issue.
The solution is needed to update XCode to the latest version and everything is ok.
If other answers don't work, try updating Xcode.
For me I was using Xcode 14.0.0. The release notes for 14.0.1 say
This update fixes an issue that prevents development with devices running iOS 15.7.
Indeed my phone is on iOS 15.7.
Nothing from the above listed helped me and also I have encountered this problem when the app was removed for a while. But turning off the phone for 10 mins solved the problem.
My Current Setting and Versions:
XCode 12.4 and iOS 14.4
I had to update XCode since my iOS was updated. This fixed the compiler error in Unity and then the same message popped up during deployment. All I did was disconnect/re-connect.
Restarting the iPad works for me every time!
We encountered this error and determined it was due to a damaged iPhone cable. New cable, problem solved.
I just had to unpair the phone from Xcode's Devices and Simulators screen and then tap Trust when connecting it to the computer to make my Watch work with Xcode
I had to change the iOs Deployment target to "iOs 15". Then it worked. After that, I just set it back to iOS 12, and everything keeps working.
If nothing worked for you, try the below steps.
Update the Xcode
Update the iOS version
Connect mac and iPhone to the same wifi
just Clean the Build Folder with: ⌘ + shift + K
Problem: I cannot simulate an Apple watch interface. Whenever I try and test my Apple watch app on the iPhone 6 simulator, Xcode successfully finishes and builds the app, attempts at opening simulator and fails with an error message which reads 'Invalid Device State'.
I believe simulator has a watch simulator that opens along with the compatible iPhone simulator models that can communicate with Apple watch (example: iPhone 6) Although I have yet to see it work. I have built a universal interface for iPad and iPhone and another for the watch, so it's not a matter of the app being for the wrong device. Whenever I test on my actual iPhone I can test the universal interface successfully.
I'm using Xcode 6.2 on iMac OS X 10.10.3
I have tried restarting Xcode/Computer. I can't seem to find any other mention of 'Invalid Device State' anywhere, hopefully due to it being an obvious thing to avoid/fix that I've overlooked. Any help would be appreciated.
Force Quit xCode and restart will resolve problem.
I had come across this issue after updating Xcode 6.4 to 7.1.
Below are fixes for this :
Clean project (cmd+shift+k) as well as clean build folder
(cmd+shift+k+option)
Quit simulator and run again
Quit Xcode and Simulator and run again
Restart your Mac.
Solution 3 worked for me!
I had the same issue. Generally it is because you just update Xcode or change its name in the Applications folder.
If you just restart your computer it will work correctly.
Hope it helps !
I observed this happening when more than one Xcode app installed.
To fix this,
Launch Xcode and click preference..,
Go to "Location" Tab, Select correct options from "Command Line Tools" dropdown
Quit Xcode and relaunch it.
Run your app.
First of all, just clean the project.
Quit your project.
Quit your Xcode.
Restart Xcode.
This happens to me when I have two different Xcode versions running at the same time. Hopefully this helps you.
No need to quit, restart or even re-install. Switch to another iOS Simulator device (6s if you were using 6s plus) and voila!
Nothing worked for me on XCode 7.3.1.
Had to reinstall it to make the simulator work.
Go to applications folder. Drag drop XCode to Dustbin.
Empty dustbin contents.
Go to App Store and install XCode.
Run XCode. The simulator should work now.
I have Xcode 7.3 and Xcode 8.0 Installed.
If a am working with Xcode7.3 and opens Xcode8.0 to get some code from Xcode8.0 project.
When i run my application on Xcode7.3 So it will give me same error.
Solution is simple ForceQuit or Quit all Xcode's and open the required one.
In my case, the simulator would show an indefinite black screen whether attempting to run a project, or running the simulator directly (which should bring you to the simulated home screen). This would happen even on a newly created simulated device.
After the existing suggestions failed, the following worked for me:
Delete the Simulator
Delete XCode
Delete the Developer folder
Reinstall XCode from the app store. This requires attempting to run XCode again so that Mac OS will realize it's no longer installed.
Jus clean the project and restart Xcode. This happens to me when I have two diffent xcode versions running at the same time.
Robust fix is Just Quit your xcode and run again, hope so it will help you. This heck work for me.
On M1 Mac I've found more than 3 open simulators can cause this error. Quit the simulator app to fix this error.
I am pretty sure that in my case the simulator was corrupt after a failed language change.
Following this answer to reset the simulator worked.
I'm running an app on my iOS device but, in Instruments, that device is greyed out.
This also means I can't attach the process (Cant launch iOS app with Instruments on device). Is it anything to do with my earlier question: Instruments > Profile - Revoke and request
Xcode: 6.1.1
iOS: 7.1.2
Any idea why?
I only had to reboot my phone (not my Mac), and then the error went away
(Xcode 9.2, iPhone X running 11.2.6).
i was having this issue and resolved it by
Unplugging my device
Turning my device off
Rebooted my mac
Turned device back on and plugged into computer after logging back in.
now it shows up in instruments. I tried unplugging device, restarting xcode, but that didn't work. rebooting everything is what did the trick for me.
I met the this problem. Xcode(Version 9.3.1 (9E501)), iphone 7, And I forcely quit the Instrument. It's work
I came across same problem today on xcode7.2.1, iOS 9.2.1, iPhone 6Sp. Resolved by rebooted my mac, my watch and the iPhone.
If your workspace contains several projects and/or several targets, it seems that XCode doesn't know which binary to profile.
Just Edit your scheme -> Profile -> Choose an Executable and it should enable the profiling option.
I had the same problem where Profile was greyed out. It turned out to be I had the device option at the top set to Generic iOS Device
// this will make Profile greyed out
Once I switched it to an actual simulator device or my actual device Profile was no longer greyed out
One other option can be to in Xcode at the top go to Help > search Edit Scheme and select it > on the left side of the screen select Profile > change Executable drop down to your_project's_name.app
I don't know which process helped but I force quit AppleMobileDeviceHelper and DTServiceHub in the Activity Monitor and then it started working again (I was able to select my phone without rebooting).
Recently, I confronted the question again on Xcode Version 10.1 (10B61), iphone 7 and Mac 10.14.1 (18B75). I resolved it by upgrading the deployment from 8.0 to 10.1. In fact, I have meet many strange Xcode bugs caused by the version, liking this one(xcode gpu shader profiler)
It turned out that my iPhone is not trusted my computer.
How to re-trust computers, see:
https://www.wikihow.com/Trust-a-Computer-on-an-iPhone
In short, you should reset Location and Privacy in settings, and then plug-in your iPhone again. And you will see 'Trust this computer' again.
My issue what that it was asking me to trust the computer every time I plugged it in.
To fix it, I had to turn on the Hotspot then turn it back off.
I cannot launch the simulator successfully. Once I launch the IOS Simulator this error appears:
"Unable to boot the IOS Simulator."
Following the IOS Simulator error, I then get an error from Xcode reading:
Unable to run app in Simulator
An error was encountered while running (Domain = DTiPhoneSimulatorErrorDomain, Code = 2)
UPDATE:
This might sound silly but I went to Xcode/preference/Downloads with intentions of seeing a IOS 8.0 Simulator but there was none. Could this be the problem? Am I suppose to have a IOS 8.0 Simulator? If so can someone direct me how to get it? Also, under the "Downloads" tab in Xcode preference I do see IOS 7.0 and 7.1 Simulators and both work fine with Xcode 5.
the trick is, to select the right command line tools!
just select it here
reboot(!) and everything is fine again :-)
Ok It's known problem. Do you see simulators list? If not
Goto Xcode Menu -> Open Developer Tool -> It will open a simulator in your Dock -> click on simulator then go to Simulator Menu: Hardware -> Device -> Manage Devices. Add needed simulators. Always try to run your app with different simulators.someone will work.
Restart your Mac. I just had that exact error after installing Xcode 6 beta 7, literally the only thing I did in response was reboot my Mac and now the iOS 8 simulator is working.
This error is common if you update Xcode without restarting afterwards.
In my case, i reset ios simulator settings fix it.
iOS Simulator -> Reset Content and Settings ...
Open Xcode 6 beta
Goto Window > Devices
Click on the little + sign at the bottom
Add (if missing) all the devices that you want, or delete and recreate if not working.
If anyone of the simulator is not working then you can delete it and then re-create it again in this menu.
I saw the same issue when I installed Xcode 6 beta 6, and deleted beta 4 and beta 5. Apparently, deleting the old betas also deleted the iOS Simulator 8 versions! Putting it back from my Trash solved the issue.
Solution: Don't delete old beta software!
Edit: #Flori's solution worked. Was able to delete the old beta software, and after a complete system reboot, it worked again.
From the xCode 6 pull down menus, Xcode > Open Developer Tool >
iOS Simulator (if you get a pop up error just dismiss it)
Once in the Simulator go to Hardware > Device > Manage Devices.
Delete everything listed under simulator.
Reboot your machine.
After that, navigate back to Manage Devices in the simulator and click the plus to add back your simulators. Then the iOS 8 simulators will show up.
Just unset DYLD_INSERT_LIBRARIES environment variable in the /etc/launchd.conf or ~/.launchd.conf file. Which you can edit by sudo vi /etc/launchd.conf command. remove the above flag save it by "ZZ" (captial Z) and reboot the system. It works like a charm.
Make sure that path in menu XCode>Preference>Locations point to XCode 6.0 (Restart Xcode after changing them). Then go to menu Window>Devices and add simulator devices you want to use.
Edit: Turns out I was getting my version of the error because I had a file (the "Empty File" type) named "Frameworks" in several of my projects, and this was causing big issues with the iOS 8 simulators. Renaming the file to be anything else, and then doing a Clean Build Folder fixed it right away.
------Deprecated Original Message Below--------
In case this helps anyone -- I was having a similar error on Xcode 6 GM, and tried everything mentioned in these Answers, but the iOS 8 simulators would never run any of my apps (no problems with iOS 7 running from Xcode 6 though).
What did sort of work was creating a new project (new project apps would run in the iOS 8 simulators, but never any luck with existing apps). Copying over files and project settings is no fun, but at least it let me do testing and see if my apps needed fixing for the iOS 8 public release.
Extended description of problem at https://devforums.apple.com/thread/246751
I tried everything mentioned above and nothing worked.
Finally the only way to make it work was unsetting DYLD_INSERT_LIBRARIES=/usr/lib/libimckit.dylib
How I did this:
Open terminal and typing "sudo vi /etc/launchd.conf"
Changing
"setenv DYLD_INSERT_LIBRARIES /usr/lib/libimckit.dylib"
to
"unsetenv DYLD_INSERT_LIBRARIES /usr/lib/libimckit.dylib"
Save changes
Reboot your system
In this post [1] explain what DYLD_INSERT_LIBRARIES is for
[1] https://stackoverflow.com/a/26053165/2091181
I got this issue when moving from Beta 6 to Beta 7. Very frustrating. I could reset content and settings on any of the iOS 8 simulators. None of my iOS 8 simulators were working at all, just a black screen. I restarted my machine during the process, but I am not sure if it did anything. Initially I had only iOS 8 Simulators. I had to remove and reinstall Xcode6Beta7. I did not get the Install More Components the first time I installed it, I am not sure if that was the missing part. I installed the iOS 7 Simulators from Settings->Downloads because my iOS8 ones were not working. After I had reinstalled and relaunched the simulator, I then had a list of iOS 6,7,& 8 simulators. None of the iOS 8 Simulators were working. I was able to launch the iOS7 simulator and then using the device menu change to an iOS 8 Simulator. Some still did not work, I had to remove them and re-add them in the devices screen.
Remove XCode6Beta from Applications.
Restart Machine (Just in case, this seems to solve some peoples issue completely)
Install XCode6Beta.
Verify the Install Additional Components ran.
Launch Xcode6Beta.
Preferences->General->Change Command Line Tools to Xcode 6.0.
Restart Xcode.
Preferences->Downloads->Download iOS 7 Simulator (If not already downloaded).
Run App on iOS 7 Simulator (Or launch iOS Simulator and switch to iOS 7 device)
If the iOS 7 Simulator is working, Hardware->Devices->Select an iOS 8 simulator.
Delete and recreate any non working iOS 8 Simulators in Window->Devices from Xcode.
I wrestled with this for a bit, with the simulator app reporting that it couldn't find the iOS8 simulator, and suggesting updating in Prefs/Downloads, which didn't work. I tried re-installing Beta 6 twice (without removing all the support files, which would have been next). The initial installation described itself as build 6A280c; a fresh download yielded build 6A280e. No luck.
Eventually, I opened Window -> Devices, and used the "+" button in the lower left to add a new simulator for iPhone 5s, iOS 8, naming it "Fresh 5s". The Schemes popup now displayed three iPhone 5S/iOS 8 options (none with the name I designated, but differentiated by UUIDs); at least one of them worked.
I'm guessing that this feature (collections of arbitrary simulator instances) will be very useful when it's baked. In the meantime, I guess I'll need to manage the list of simulators manually.
Do following steps worked for me:
1. Launch the iOS Simulator and go to iOS Simulator --> Reset Content and Settings...
2. Close all the applications and restart your mac
3. Open Xcode6.0.1 or 6.0 and test the iOS Simulator
Had the same problem after moving from Xcode 6 beta 5 to beta 6, but also for the iOS 7.1 simulator. Restarting my machine seemed to do the job. I did not need to update from Xcode 5.1.1 CLT to Xcode 6.0 CLT.
I tried all of the solutions above, and was still unable to launch the iOS8 Simulator. The iOS7 Simulators all launched fine.
Looking at the Console, I found that the launch was crashing, and the crash log complained about the dynamic library, libimckit.dylib. You can read about that here:
https://discussions.apple.com/thread/5781366?start=0&tstart=0
The quick solution, remove that and its partner library, reboot, and it loads.
Is there anything interesting in ~/Library/Logs/CoreSimulator/CoreSimulator.log?
The "Unable to boot the iOS Simulator." error message is almost always because launchd_crashed because DYLD_INSERT_LIBRARIES was set to something not compatible with the iOS Simulator runtime. Do you have any crash logs (eg: launchd_sim crashes) in ~/Library/Logs/DiagnosticReports? If so, check if they show DYLD_INSERT_LIBRARIES being set. If that's the case, your options are to either update to an OS X Yosemite host (which will deal with this issue) or unset DYLD_INSERT_LIBRARIES (likely set in /etc/launchd.conf or ~/.launchd.conf)
Force Quit All the apps including xcode and simulator
Restart MAC
Checking in the "Locations" Xcode preference, I had two items of the same version, one located in the app translocation area (/var/.../AppTranslocation/...). Also I had previously done a manual command line tools install. To resolve this in the end I had to delete /Applications/Xcode.app and remove the manual command line tools install:
sudo rm -rf /Library/Developer/CommandLineTools
Then installed Xcode anew, and rebooted. Boom! Simulator working again.
Reboot your mac os. its working correctly on xcode 11.3.x and mac os 10.14.6.
I cannot launch the simulator successfully. Once I launch the IOS Simulator this error appears:
"Unable to boot the IOS Simulator."
Following the IOS Simulator error, I then get an error from Xcode reading:
Unable to run app in Simulator
An error was encountered while running (Domain = DTiPhoneSimulatorErrorDomain, Code = 2)
UPDATE:
This might sound silly but I went to Xcode/preference/Downloads with intentions of seeing a IOS 8.0 Simulator but there was none. Could this be the problem? Am I suppose to have a IOS 8.0 Simulator? If so can someone direct me how to get it? Also, under the "Downloads" tab in Xcode preference I do see IOS 7.0 and 7.1 Simulators and both work fine with Xcode 5.
the trick is, to select the right command line tools!
just select it here
reboot(!) and everything is fine again :-)
Ok It's known problem. Do you see simulators list? If not
Goto Xcode Menu -> Open Developer Tool -> It will open a simulator in your Dock -> click on simulator then go to Simulator Menu: Hardware -> Device -> Manage Devices. Add needed simulators. Always try to run your app with different simulators.someone will work.
Restart your Mac. I just had that exact error after installing Xcode 6 beta 7, literally the only thing I did in response was reboot my Mac and now the iOS 8 simulator is working.
This error is common if you update Xcode without restarting afterwards.
In my case, i reset ios simulator settings fix it.
iOS Simulator -> Reset Content and Settings ...
Open Xcode 6 beta
Goto Window > Devices
Click on the little + sign at the bottom
Add (if missing) all the devices that you want, or delete and recreate if not working.
If anyone of the simulator is not working then you can delete it and then re-create it again in this menu.
I saw the same issue when I installed Xcode 6 beta 6, and deleted beta 4 and beta 5. Apparently, deleting the old betas also deleted the iOS Simulator 8 versions! Putting it back from my Trash solved the issue.
Solution: Don't delete old beta software!
Edit: #Flori's solution worked. Was able to delete the old beta software, and after a complete system reboot, it worked again.
From the xCode 6 pull down menus, Xcode > Open Developer Tool >
iOS Simulator (if you get a pop up error just dismiss it)
Once in the Simulator go to Hardware > Device > Manage Devices.
Delete everything listed under simulator.
Reboot your machine.
After that, navigate back to Manage Devices in the simulator and click the plus to add back your simulators. Then the iOS 8 simulators will show up.
Just unset DYLD_INSERT_LIBRARIES environment variable in the /etc/launchd.conf or ~/.launchd.conf file. Which you can edit by sudo vi /etc/launchd.conf command. remove the above flag save it by "ZZ" (captial Z) and reboot the system. It works like a charm.
Make sure that path in menu XCode>Preference>Locations point to XCode 6.0 (Restart Xcode after changing them). Then go to menu Window>Devices and add simulator devices you want to use.
Edit: Turns out I was getting my version of the error because I had a file (the "Empty File" type) named "Frameworks" in several of my projects, and this was causing big issues with the iOS 8 simulators. Renaming the file to be anything else, and then doing a Clean Build Folder fixed it right away.
------Deprecated Original Message Below--------
In case this helps anyone -- I was having a similar error on Xcode 6 GM, and tried everything mentioned in these Answers, but the iOS 8 simulators would never run any of my apps (no problems with iOS 7 running from Xcode 6 though).
What did sort of work was creating a new project (new project apps would run in the iOS 8 simulators, but never any luck with existing apps). Copying over files and project settings is no fun, but at least it let me do testing and see if my apps needed fixing for the iOS 8 public release.
Extended description of problem at https://devforums.apple.com/thread/246751
I tried everything mentioned above and nothing worked.
Finally the only way to make it work was unsetting DYLD_INSERT_LIBRARIES=/usr/lib/libimckit.dylib
How I did this:
Open terminal and typing "sudo vi /etc/launchd.conf"
Changing
"setenv DYLD_INSERT_LIBRARIES /usr/lib/libimckit.dylib"
to
"unsetenv DYLD_INSERT_LIBRARIES /usr/lib/libimckit.dylib"
Save changes
Reboot your system
In this post [1] explain what DYLD_INSERT_LIBRARIES is for
[1] https://stackoverflow.com/a/26053165/2091181
I got this issue when moving from Beta 6 to Beta 7. Very frustrating. I could reset content and settings on any of the iOS 8 simulators. None of my iOS 8 simulators were working at all, just a black screen. I restarted my machine during the process, but I am not sure if it did anything. Initially I had only iOS 8 Simulators. I had to remove and reinstall Xcode6Beta7. I did not get the Install More Components the first time I installed it, I am not sure if that was the missing part. I installed the iOS 7 Simulators from Settings->Downloads because my iOS8 ones were not working. After I had reinstalled and relaunched the simulator, I then had a list of iOS 6,7,& 8 simulators. None of the iOS 8 Simulators were working. I was able to launch the iOS7 simulator and then using the device menu change to an iOS 8 Simulator. Some still did not work, I had to remove them and re-add them in the devices screen.
Remove XCode6Beta from Applications.
Restart Machine (Just in case, this seems to solve some peoples issue completely)
Install XCode6Beta.
Verify the Install Additional Components ran.
Launch Xcode6Beta.
Preferences->General->Change Command Line Tools to Xcode 6.0.
Restart Xcode.
Preferences->Downloads->Download iOS 7 Simulator (If not already downloaded).
Run App on iOS 7 Simulator (Or launch iOS Simulator and switch to iOS 7 device)
If the iOS 7 Simulator is working, Hardware->Devices->Select an iOS 8 simulator.
Delete and recreate any non working iOS 8 Simulators in Window->Devices from Xcode.
I wrestled with this for a bit, with the simulator app reporting that it couldn't find the iOS8 simulator, and suggesting updating in Prefs/Downloads, which didn't work. I tried re-installing Beta 6 twice (without removing all the support files, which would have been next). The initial installation described itself as build 6A280c; a fresh download yielded build 6A280e. No luck.
Eventually, I opened Window -> Devices, and used the "+" button in the lower left to add a new simulator for iPhone 5s, iOS 8, naming it "Fresh 5s". The Schemes popup now displayed three iPhone 5S/iOS 8 options (none with the name I designated, but differentiated by UUIDs); at least one of them worked.
I'm guessing that this feature (collections of arbitrary simulator instances) will be very useful when it's baked. In the meantime, I guess I'll need to manage the list of simulators manually.
Do following steps worked for me:
1. Launch the iOS Simulator and go to iOS Simulator --> Reset Content and Settings...
2. Close all the applications and restart your mac
3. Open Xcode6.0.1 or 6.0 and test the iOS Simulator
Had the same problem after moving from Xcode 6 beta 5 to beta 6, but also for the iOS 7.1 simulator. Restarting my machine seemed to do the job. I did not need to update from Xcode 5.1.1 CLT to Xcode 6.0 CLT.
I tried all of the solutions above, and was still unable to launch the iOS8 Simulator. The iOS7 Simulators all launched fine.
Looking at the Console, I found that the launch was crashing, and the crash log complained about the dynamic library, libimckit.dylib. You can read about that here:
https://discussions.apple.com/thread/5781366?start=0&tstart=0
The quick solution, remove that and its partner library, reboot, and it loads.
Is there anything interesting in ~/Library/Logs/CoreSimulator/CoreSimulator.log?
The "Unable to boot the iOS Simulator." error message is almost always because launchd_crashed because DYLD_INSERT_LIBRARIES was set to something not compatible with the iOS Simulator runtime. Do you have any crash logs (eg: launchd_sim crashes) in ~/Library/Logs/DiagnosticReports? If so, check if they show DYLD_INSERT_LIBRARIES being set. If that's the case, your options are to either update to an OS X Yosemite host (which will deal with this issue) or unset DYLD_INSERT_LIBRARIES (likely set in /etc/launchd.conf or ~/.launchd.conf)
Force Quit All the apps including xcode and simulator
Restart MAC
Checking in the "Locations" Xcode preference, I had two items of the same version, one located in the app translocation area (/var/.../AppTranslocation/...). Also I had previously done a manual command line tools install. To resolve this in the end I had to delete /Applications/Xcode.app and remove the manual command line tools install:
sudo rm -rf /Library/Developer/CommandLineTools
Then installed Xcode anew, and rebooted. Boom! Simulator working again.
Reboot your mac os. its working correctly on xcode 11.3.x and mac os 10.14.6.