ios simulator appear with UDID in xcode 6

killall Xcode
- Kills all running Xcode processes.
sudo killall -9 com.apple.CoreSimulator.CoreSimulatorService
- Kills all running CoreSimulatorService's processes.
rm -rf ~/Library/Developer/CoreSimulator/Devices
- Removes all Simulator data, from all the Simulators.
open /Applications/Xcode.app - Opens Xcode.

The above steps from xcode 10 are invalid, please use the following steps:

xcrun simctl shutdown all
shutdown all devices

xcrun simctl list devices|grep -v "unavailable"|grep -Eo "[0-9A-F\-]{36}"
list all available devices

xcrun simctl list devices|grep -v "unavailable"|grep -Eo "[0-9A-F\-]{36}"|xargs xcrun simctl delete delete all devices(note: this is a single line)

more detail xcrun simctl help

In Xcode, go to Window -> Devices (shortcut is Cmd+!)

In the left pane, delete all the superfluous simulator devices (select in the left pane and press delete on keyboard)

Usually these are the ones that have no OS (showing iOS: n/a).

This usually happens when you try and copy older simulator versions directly in the SDK folders rather than installing them from Xcode -> Preferences.

How to fix it

Xcode uses the device version to disambiguate devices with the same name. If two devices have the same name and version number, it will use the devices' UDIDs.

You have 4 of each of a bunch of devices (eg iPhone 5s). I suspect that some of them are for the same iOS version. You should delete some of the duplicates. Check out xcrun simctl list and xcrun simctl delete or use the device manager within Xcode.app (click on the "-" to delete a device).

How to just get back to a default state

# Ensure all possible clients of CoreSimulatorService are no longer running:

killall Xcode 2> /dev/null
killall Instruments 2> /dev/null
killall 'iOS Simulator' 2> /dev/null
killall Simulator 2> /dev/null
killall 'Simulator (Watch)' 2> /dev/null
killall ibtoold 2> /dev/null
killall simctl 2> /dev/null
# There may be others

# Kill the service itself
sudo killall -9 com.apple.CoreSimulator.CoreSimulatorService

# Remove all the data and logs
rm -rf ~/Library/*/CoreSimulator

Why this might be happening:

CoreSimulatorService will monitor for the addition of new simulator runtimes in /Library/Developer/CoreSimulator/Profiles (eg, for when downloading them from Xcode -> Preferences -> Downloads). When installing a new runtime, CoreSimulatorService will create an initial set of devices for that runtime.

This problem arrises if there are multiple instances of CoreSimulatorService running at the same time. Each CoreSimulatorService instance will create its own set of devices (but its clients will only see that instances's sets at first). On subsequent launches (eg: after a reboot), both copies will be seen. One can get into a state where multiple copies of CoreSimulatorService are running at the same time due to testing beta versions of Xcode.app in the same login session as using the released Xcode.app or by having used Xcode.app before and after updating it through the App Store.

If you are aware of any other way that this bug might come about, please file a new radar at http://bugreport.apple.com