Xcode beta 6 iOS 8: Simulator not working - ios

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.

Related

Xcode 9 iOS Simulator becoming black screen after installing Xcode 10 beta

I know that so many people have asked this question earlier. But I think my situation is different. In my case Xcode 9.2 was already installed and I upgraded macOS from 10.13.2 to 10.13.5. Then I installed Xcode 10 beta. Now when I'm running any project on Xcode 9.2 and try to use simulator, its becoming black though I can see the xcode logs. Things I have tried so far,
Uninstalled Xcode 10 Beta
Uninstalling & reinstalling Xcode 9.2
Uninstall Xcode 9.2 and install Xcode 9.4
Reset Content & Settings from simulator menu
Restart Device from simulator menu
Resizing simulator.
Followed this post and cleaned DerivedData, CoreSimulator, iOSDeviceSupport
Re add simulators from devices & simulators section
Now what should I do now?
Try running defaults write com.apple.CoreSimulator.IndigoFramebufferServices FramebufferRendererHint 3 in Terminal (source). Note that this will force Simulator to use OpenGL instead of Metal, so you'll want to re-run it with 0 once this gets fixed.
try workaround, delete Library/Developer folder and start it again
Another option that occurred for me. I subclassed UIWindow and called .init(frame: .zero). Changing to .init(frame: UIScreen.main.bounds) fixed it.
Open up XCode 9 and go to add additional simulators(pictured below) re-add iOS 10 and iOS 11 simulators
You seem to have tried everything except changing the iOS simulator version you are trying to run.
Maybe the problem lies with that specific version of iOS simulator eg. iOS 11.x iPhone 6. Change that and it may run OK.
If you do not have desired version with you, go to XCode->Preferences->Components, and download one of the older iOS simulators available at the time of XCode 9.x.
Then, go to XCode->Windows->Devices and Simulators. Press + sign at the bottom left of the screen. Add your desired simulator version (give your desired name), so that this newer simulator appears in runnable scheme list of XCode.
This is just for the users that failed trying everything to save Xcode 10 and then reinstalled Xcode 9.4.1 and the simulator still not working.
Here is what I did to give Xcode 9.4.1 back running.
After I got this problem after upgraded to Xcode 10.
I tried that famous FramebufferRendererHint, didn't work for me.
I have found out the Xcode 10.1 beta release didn't fix the problem for someone else, so I didn't bother to try 10.1 beta.
From the online research I know the problem is in /Library/Developer/PrivateFrameworks/CoreSimulator.framework.
Without Xcode even installed on your Mac /Library/Developer doesn't exist.
So it is installed by Xcode when your first time run Xcode. You would notice a screen showing "Installing Components"
But after you installed Xcode 10 and then install/run Xcode 9.4.1 it won't touch that folder anymore. So problem stays even you put Xcode 9.4.1 back
That's why after I downloaded Xcode 9.4.1 expanded and ran it. Problem still there.
I didn't backup my Mac. So I decided to start from scratch. Restored my MacBook from Internet, downloaded Xcode 9.4.1 again. and now everything is back to normal.
I can keep releasing the App to App Store now.
In my case (xcode 10), I just left the computer for 10 minutes or so (out of frustration!) and when I came back I found it at the starting screen! .... I guess for the first time it takes time

Xcode 8 | iOS 10 simulator "Error returned in reply: Connection invalid"

While I am try to run an app in the iOS 10 simulator using xcode8 I get these alerts frequently. They randomly appear two at a time and it is not apparent what is triggering them.
Below is Image for Error I got.
I tried Following things.
Clean & Rebuild an app
Restart xcode & Simulator
Clear Derived Data & Rebuild application.
Even I was getting the same error. Issue in my case was I was working on xcode 7.3 and its simulator was open, later on I closed xcode 7 and opened xcode 8 and tried running app and got the above error.
I guess its happening because of both the simulator were open, it got solved when I closed my older simulator. Seem to be some problem while xcode 8 was trying to establish connection with simulator.
You just follow these steps to remove this error it's working fine in my side and i hope these steps work to you also just try it.
i)Remove multiple xcode versions.
ii)Quit all Xcode and simulators.
iii)Only one version you opened.
iv)Go to Xcode -> Preferences
v)Go to Location
vi) Set proper version for command line tools (your Xcode version)
vii)click on Derived Data
viii)Then go to Derived data and delete that folder. see below image
ix) Click on Simulator reset content settings and just quit xcode and simulator and open clear and build the xcode and run it.
Without deleting "Derived data" folder
The same rules as in the past apply to switching between Xcode 8 and
Xcode 9:
Quit Xcode, Instruments, Simulator.app, and Console
xcode-select the version you want to work with
Start the version of Xcode you want to use
If these steps don't resolve the problem for you, you can repeat the steps above > but after #2 add "sudo killall -9 com.apple.CoreSimulator.CoreSimulatorService".
from this https://forums.developer.apple.com/thread/79301
The Same issue I have faced when I have two Xcode version, but the issue was when we are opening the two instances of simulator we will get the same error, the best way to solve this issue is run command
rm -rf ~/Library/Developer/Xcode/DerivedData
to remove the derived data.
None of the above worked for me.
Instead of choosing the simulator and hitting "run" i solved it by opening the simulator form "Open Developer Tool" menu first. After that all worked fine.
I had a similar issue, despite not launching a second instance of the simulator, due to using SimPholders and having the XCode Command Line Tools set to a different version of XCode. To resolve this, open up XCode preferences, and under the Locations tab ensure that the Command Line Tools version matches what version of XCode you're currently working in.
I had the similar issue shown in below screenshot.
Got it solved by closing Xcode 7 and its simulator.
It seems that when you are working on Xcode 8 and its simulator then Xcode 7 simulator should not remain open.
Below is screenshot of simulator state for Xcode 7 when you're working on Xcode 8.
In my case,
I was open a project a Xcode 8, and the emulator for this version, then open this project on Xcode 7.3.1, when I create an emulator it shows the alert.
My Solution: Close all version of Xcode => Clear Derived Data => Quit Xcode => Open Xcode => Choose File => Open Recent.
Force Quit.. Xcode and simulator. This kind of issue happned because maybe you are try to run more than one different version Xcode at same time.
I just had this issue when attempting to debug an iOS application from Xamarin, which uses Xcode to run apps in the simulator. I was initially targeting a 9.7" iPad Pro, attempted to change the simulated device to an iPad Air 2 (still on iOS 10), but the simulator didn't respond. After quitting and relaunching the simulator it appeared to load okay, so I changed back to the previous device - not sure whether changing devices actually did anything but I haven't seen the error message in the few times I've run my app since.
Solved it by closing all xcode and simulator. Don't ask me why. It was happening on the beta version for me
I had similar issue, what I did is I closed the simulator and all the Xcode and I went to the terminal and typed to see any Xcode application running then I killed it. I had one Xcode running in the background.
Command to see if Xcode is running,
ps -e | grep -i xcode
Use kill comment to kill any runing Xcode app, I used
kill -9 <pid>
The Same issue I have faced
in my case i stopped all applications and restarted my mac
and every thing is OK
Simple And fast Remedies..
1.Quit all xCode and reopen the xCode which you need to work...
I had this problem too, but I did below process it's working fine.
You have both Xcode 8.x.x and 9 running on your Mac, which causes the problem. Only run one Xcode at a time (Quit another Xcode, don't let another Xcode runing in background!).
This can occur when you have more than one version of Xcode installed on your computer. Make sure you QUIT (not just close) all versions of Xcode first.
Changing the device seems to have worked for me after doing the other stuff. Didn't have to restart my computer.

Invalid Device State - Xcode/iOS Simulator error

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.

Why have my Xcode 6.1.1 simulator options all disappeared?

I recently tried to run a simulation of a new iOS 7 app on Xcode 6.1.1 using my MacBook Pro during a visit to Indonesia. The app was based on AddMusic and made iOS 7 compatible. When I tried to run the simulator abroad iOS simulation targets available while testing in Australia had simply disappeared from the pulldown menu in Xcode. Moreover since I came home these simulators only reappeared when I removed, downloaded and reinstalled Xcode.
Until I reinstalled Xcode the only option Xcode offered was to run the app on an iOS device but I wasn't prepared to do this in front of clients without first being able to test a revision on a simulator.
Thankfully on this occasion I was able to demonstrate earlier versions I had installed on an iPhone 4 and iPhone 5 C before I left home. But it would be really good to know what I might be able to do to avoid this situation during my next visit abroad.
I suspect the issue may have been brought on by differences between my Internet connections at home and abroad.
Has anyone else experienced a similar problem that might be related ?
Top to your Right Click on
Window > Devices
You will see that no devices will be showing Do the following
Bottom Left
Click on the +
And then start adding your devices.
Just closing the projects from the File Menu, quitting Xcode and restarting Xcode worked for me
the version is the latest Xcode 7
Some things which might help you
Check deployment target in your project settings. Switching to lower versions of OS might help you get back all simulators.
Check your xcode version used in the command line tools. Go to Xcode -> Preferences -> Locations -> Command line tools
Quit Xcode and restart your system.
Hope these things help !!

unable to boot the ios simulator XCode 6 iOS 8 [duplicate]

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.

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