You can specify the absolute path to your chrome driver in your script as such:
from selenium import webdriver
driver = webdriver.Chrome(executable_path="/path/to/driver/chromedriver")
Or you can add the path to your webdriver in the PATH
system variable as so:
export PATH=$PATH:/path/to/driver/chrome-driver
You may add the above line to your /home/<user>/.profile
file to make it permanent.
Tested on Ubuntu 17.10 running Python 2.7.14
Hope this helps!