No app can run in my simulator, although building is good.
Error messsage is below:
Unable to run app in Simulator
An error was encountered while running (Domain = NSPOSIXErrorDomain, Code = 3)
In my case, I tried to run the app on a iPhone 6 simulator when I got this error. Quitted the simulator only and re-ran the app on iPhone 5s (8.1) - it worked fine.
After a while I changed the target back to iPhone 6 (without quitting it), and ran the app against it - no error shown.
As mentioned in the Xcode 6.1 Release Notes and in my sticky post in the Apple Developer Forums for the iOS Simulator, this is a known bug in iOS.
Upon installation of an app, SpringBoard will SIGKILL that app's process in order to force a relaunch of the app with the new executable. The problem is that there is a race condition whereby SpringBoard may accidentally SIGKILL a new process that we just launched rather than the old process. Which of the various error messages you get depends on exactly when in the launch process the SIGKILL was delivered. Normally, this shouldn't happen, so the advise is to just try again (sorry =/). If you find that this happes to you all the time or more frequently than you can tollerate, we are incredibly sorry. We are aware that systems with slower disk I/O will see this happen more frequently than faster systems, so if you are using an NFS home directory, you may want to create a local directory for your simulator data and setup a simlink to it from ~/Library/Developer/CoreSimulator
By Quitting the Simulator and Run the application worked for me.
For me , just Reset Content and setting in your simulator
Restart Mac can solve the problem for me.
This error is less severe than "Domain = DTiPhoneSimulatorErrorDomain, Code = 2" error that I had when I switched to Xcode 6.
For this one, I just reset and cleared contents on my Simulator...quit. Rebuilt and ran my app...and it works.
Every time this has happened to me (as of this writing, still happening on Xcode 6.1) I do not need to restart my mac to fix it. Instead I only had to restart the simulator. I exit the simulator by right-clicking on its icon in the tray and selecting the option to Quit. The I re-run my app and the simulator starts from scratch and runs my app with no error. Much quicker than re-starting the mac.
Well, I had the same error popping up, but since I force quitted the simulator then ran the project again I got it fixed and running fine. Hope that helps you :)
If this error occurs with ionic framework, make sure you have an app id given in your config.xml
please download new xcode_6 beta 4. your project will work in simulator. As i have tested as well.
Sometimes the beta version of XCode is wrongly configured to use the command line tools from the previous xcode version. This solution should fix the issue for you : https://stackoverflow.com/a/25415781/512504
来源：https://stackoverflow.com/questions/24233589/xcode6-cant-run-any-app-in-simulator-domain-nsposixerrordomain-code-3