i just started to make my first native cordova app from cordova official tutorial, and when I run
ayam@laptop:~/Documents/learn/hello$ cordova requirements
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This problem arises when there is no virtual device set up in the system (No target version or no target device). I am not sure if that is a must. You can add a device using SDK manager.
In SDK manager, Add an android repository (For example - Android 5.0.1 API 21) and all dependencies like SDK Tools etc.
Then try cordova requirements. If you are able to run an instance of emulator then this error will go off..(It worked for me that way!)
Hope this helps..