How to set virtualenv for a crontab?

If you're using "workon" you're actually using "virtualenv wrapper" which is another layer of abstraction that sits on top of virtualenv. virtualenv alone can be activated by cd'ing to your virtualenv root directory and running:

source bin/activate

workon is a command provided by virtualenv wrapper, not virtualenv, and it does some additional stuff that is not necessarily required for plain virtualenv. All you really need to do is source the bin/activate file in your virtualenv root directory to "activate" a virtualenv.

You can setup your crontab to invoke a bash script which does this:

#! /bin/bash    
cd my/virtual/env/root/dir
source bin/activate

# virtualenv is now active, which means your PATH has been modified.
# Don't try to run python from /usr/bin/python, just run "python" and
# let the PATH figure out which version to run (based on what your
# virtualenv has configured).

python myScript.py