pip broken, reinstall doesn't work. EC2
<p>I am using pip on EC2 now, python version is 2.7. 'sudo pip' suddenly doesn't work anymore.</p>

<pre class="lang-none prettyprint-override"><code>[ec2-user@ip-172-31-17-194 ~]$ sudo pip install validate_email
Traceback (most recent call last):
  File "/usr/bin/pip", line 5, in &lt;module&gt;
    from pkg_resources import load_entry_point
  File "/usr/local/lib/python2.7/site-packages/pkg_resources/__init__.py", line 3138, in &lt;module&gt;
    @_call_aside
  File "/usr/local/lib/python2.7/site-packages/pkg_resources/__init__.py", line 3124, in _call_aside
    f(*args, **kwargs)
  File "/usr/local/lib/python2.7/site-packages/pkg_resources/__init__.py", line 3151, in _initialize_master_working_set
    working_set = WorkingSet._build_master()
  File "/usr/local/lib/python2.7/site-packages/pkg_resources/__init__.py", line 663, in _build_master
    return cls._build_from_requirements(__requires__)
  File "/usr/local/lib/python2.7/site-packages/pkg_resources/__init__.py", line 676, in _build_from_requirements
    dists = ws.resolve(reqs, Environment())
  File "/usr/local/lib/python2.7/site-packages/pkg_resources/__init__.py", line 849, in resolve
    raise DistributionNotFound(req, requirers)
pkg_resources.DistributionNotFound: The 'pip==6.1.1' distribution was not found and is required by the application
[ec2-user@ip-172-31-17-194 ~]$ which pip
/usr/local/bin/pip
</code></pre>