Unauthorized configuration value when ionic config

I follow this link: Ionic Docs - Ionic Documentation

but got “Unauthorized configuration value”

ionic config set x 1
Unauthorized configuration value

litingjun@litingjun-All-Series:~/IonicProjects/DuangWiFiApp$ ionic config build
An uncaught exception occurred and has been reported to Ionic

Unexpected end of input (CLI v1.6.4)

Your system information:

Cordova CLI: 5.1.1
Gulp version: CLI version 3.9.0
Gulp local:
Ionic Version: 1.1.0
Ionic CLI Version: 1.6.4
Ionic App Lib Version: 0.3.8
OS: Distributor ID: Ubuntu Description: Ubuntu 14.04.2 LTS
Node Version: v0.12.7

Where is the problem? thanks.