I just got a new machine and downloaded XCode. I used git to clone my ReactNative project from Github. I have everything ready to go. But when I run react-native run-ios I see

xcrun: error: unable to find utility "instruments", not a developer tool or in PATH

The fix for this is pretty simple but of course not intuitive.

You need to launch XCode and agree to the terms first. Then go to Preferences > Locations and you'll see a select tag for Command Line Tools. Click this select box and choose the version of XCode you'll be using.

After this you can go back to the command line and run react-native run-ios

Here is a screen shot

<img src="http://i.imgur.com/seBdpTP.png" style="width:100%" title="xcrun: error: unable to find utility "instruments", not a developer tool or in PATH" alt="xcrun: error: unable to find utility "instruments", not a developer tool or in PATH"/>