title: Why pip cannot install package even having permissions for both user & system repository?
body: <p>When I upgrade my user's pip repository with the following command:</p>
  
  <pre><code>pip freeze --local | grep -v '^\-e' | cut -d = -f 1  | xargs pip install -U
  </code></pre>
  
  <p>I got the following error message:</p>
  
  <pre><code>Exception:
  Traceback (most recent call last):
    File "/home/peng/.local/lib/python2.7/site-packages/pip/basecommand.py", line 215, in main
      status = self.run(options, args)
    File "/home/peng/.local/lib/python2.7/site-packages/pip/commands/install.py", line 317, in run
      prefix=options.prefix_path,
    File "/home/peng/.local/lib/python2.7/site-packages/pip/req/req_set.py", line 742, in install
      **kwargs
    File "/home/peng/.local/lib/python2.7/site-packages/pip/req/req_install.py", line 831, in install
      self.move_wheel_files(self.source_dir, root=root, prefix=prefix)
    File "/home/peng/.local/lib/python2.7/site-packages/pip/req/req_install.py", line 1032, in move_wheel_files
      isolated=self.isolated,
    File "/home/peng/.local/lib/python2.7/site-packages/pip/wheel.py", line 346, in move_wheel_files
      clobber(source, lib_dir, True)
    File "/home/peng/.local/lib/python2.7/site-packages/pip/wheel.py", line 330, in clobber
      os.utime(destfile, (st.st_atime, st.st_mtime))
  OSError: [Errno 1] Operation not permitted: '/usr/local/lib/python2.7/dist-packages/easy_install.pyc'
  </code></pre>
  
  <p>However the file that triggers this error already has all permissions opened:</p>
  
  <pre><code>ls /usr/local/lib/python2.7/dist-packages/easy_install.pyc -l
  -rwxrwxrwx 1 root staff 315 Jul  5 20:47 /usr/local/lib/python2.7/dist-packages/easy_install.pyc
  </code></pre>
  
  <p>Why pip is still unable to work on it? What has to be done to fix it?</p>