title: what is the Usage Priorities between "/usr/local/cuda" in system and "cudatoolkit" in conda envs?
body: <p>I am using CUDA 10.0 in my system. But I want to use CUDA 9.0 in a certain project. 
  So I conda create one envs for this project with the packages needed, including <strong><em>cudatoolkit 9.0</em></strong>.</p>
  
  <p>I am a little confused about that when I am running the code, which cuda will be covered. "<strong><em>/usr/local/cuda</em></strong>" in system or "<strong><em>cudatoolkit 9.0</em></strong>" in my conda envs?</p>
  
  <p>Is there <strong><em>usage priority</em></strong> for "cudatoolkit 9.0" over "/usr/local/cuda"?</p>
  
  <p>And what are relations between <strong><em>GLOBAL</em></strong> system configuration and <strong><em>LOCAL</em></strong> conda envs configuration? If I am weak in this kind of questions(global vs local), what kinds of knowledge should I learn...</p>