Q: Could not execute command lessc on MacOS Sierra I installed odoo v9 on my macOS Sierra, but when I run it I get the infamous could not execute command lessc.  I have node 7.2.0 and npm 3.10.9 and python 2.7.12.  Ive looked at similar questions on SO but have not found any solution for mine.  
Ive tried installing npm install -g less-plugin-clean-css but still get the lessc error.

A: install npm install -g less-plugin-clean-css  and 
npm install -g less

you have to provid the two of them than restart the computer you may have some sites showing you how to do this but in windows i had to install this two package and restart the computer too because there are some system variable needed to be added hope that helps you
