“Fatal error: Unable to find local grunt.” when running “grunt” command

Download locally
> npm install grunt
> grunt
Command line run: Grunt, the following problem occurs:

 
 
These are referenced in Gruntfile.js and installed in turn:
npm install grunt-contrib-copy
npm install grunt-contrib-concat
NPM install grunt – contrib – uglify
NPM install grunt – CSS
 

Reproduced in: https://www.cnblogs.com/holy-amy/p/6882540.html