[CircleCI]pip installがたまにおかしくなる

circle.yml内で、以下のような設定を行っています。

ソースを変更していなくてもたまに、処理が通らなくなる場合があります。
pip installにsudoをつけるかどうかで回避できます。
最近は、１ヶ月に１回程度起きていますが、これ、こちら側の問題なのかな。。。

実装イメージ

circle.yml

～～～略～～～
dependencies:
  pre:
    - pip install --upgrade pip
    - pip install selenium
～～～略～～～

正常なときのログ

$ pip install --upgrade pip
Collecting pip
  Downloading pip-9.0.1-py2.py3-none-any.whl (1.3MB)
    100% |████████████████████████████████| 1.3MB 460kB/s
Installing collected packages: pip
  Found existing installation: pip 7.1.2
    Uninstalling pip-7.1.2:
      Successfully uninstalled pip-7.1.2
Successfully installed pip-9.0.1
$ pip install selenium
Collecting selenium
  Downloading selenium-3.0.1-py2.py3-none-any.whl (913kB)
    100% |████████████████████████████████| 921kB 1.4MB/s
Installing collected packages: selenium
Successfully installed selenium-3.0.1

異常なときのログ

ソースを変えていなくてもいきなり発生する場合がありました。
原因として、Permission deniedでエラーになっています。
　→sudoをつけることで正常に動くようになります。

pip install --upgrade pip
/usr/local/lib/python2.7/dist-packages/pip/_vendor/requests/packages/urllib3/util/ssl_.py:315: SNIMissingWarning: An HTTPS request has been made, but the SNI (Subject Name Indication) extension to TLS is not available on this platform. This may cause the server to present an incorrect TLS certificate, which can cause validation failures. For more information, see https://urllib3.readthedocs.org/en/latest/security.html#snimissingwarning.
  SNIMissingWarning
/usr/local/lib/python2.7/dist-packages/pip/_vendor/requests/packages/urllib3/util/ssl_.py:120: InsecurePlatformWarning: A true SSLContext object is not available. This prevents urllib3 from configuring SSL appropriately and may cause certain SSL connections to fail. For more information, see https://urllib3.readthedocs.org/en/latest/security.html#insecureplatformwarning.
  InsecurePlatformWarning
Collecting pip
  Downloading pip-9.0.1-py2.py3-none-any.whl (1.3MB)
    100% |████████████████████████████████| 1.3MB 1.0MB/s
Installing collected packages: pip
  Found existing installation: pip 8.1.1
    Uninstalling pip-8.1.1:
Exception:
Traceback (most recent call last):
  File "/usr/local/lib/python2.7/dist-packages/pip/basecommand.py", line 209, in main
    status = self.run(options, args)
  File "/usr/local/lib/python2.7/dist-packages/pip/commands/install.py", line 317, in run
    prefix=options.prefix_path,
  File "/usr/local/lib/python2.7/dist-packages/pip/req/req_set.py", line 726, in install
    requirement.uninstall(auto_confirm=True)
  File "/usr/local/lib/python2.7/dist-packages/pip/req/req_install.py", line 746, in uninstall
    paths_to_remove.remove(auto_confirm)
  File "/usr/local/lib/python2.7/dist-packages/pip/req/req_uninstall.py", line 115, in remove
    renames(path, new_path)
  File "/usr/local/lib/python2.7/dist-packages/pip/utils/__init__.py", line 267, in renames
    shutil.move(old, new)
  File "/usr/lib/python2.7/shutil.py", line 303, in move
    os.unlink(src)
OSError: [Errno 13] Permission denied: '/usr/local/bin/pip'
/usr/local/lib/python2.7/dist-packages/pip/_vendor/requests/packages/urllib3/util/ssl_.py:120: InsecurePlatformWarning: A true SSLContext object is not available. This prevents urllib3 from configuring SSL appropriately and may cause certain SSL connections to fail. For more information, see https://urllib3.readthedocs.org/en/latest/security.html#insecureplatformwarning.
  InsecurePlatformWarning
You are using pip version 8.1.1, however version 9.0.1 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.
pip install --upgrade pip returned exit code 2
Action failed: pip install --upgrade pip

上記の異常を直した後に発生したログ

sudoを付けて運用していると、数時間で、今度は、いきなり以下のようなエラーが発生するようになりました。
　→sudoを外して元のコードに戻せば、通るようになりました。

sudo pip install --upgrade pip
Downloading/unpacking pip from https://pypi.python.org/packages/b6/ac/7015eb97dc749283ffdec1c3a88ddb8ae03b8fad0f0e611408f196358da3/pip-9.0.1-py2.py3-none-any.whl#md5=297dbd16ef53bcef0447d245815f5144
  Downloading pip-9.0.1-py2.py3-none-any.whl (1.3MB): 1.3MB downloaded
Installing collected packages: pip
  Found existing installation: pip 1.5.4
    Not uninstalling pip at /usr/lib/python2.7/dist-packages, owned by OS
Successfully installed pip
Cleaning up...

なんでこうなるかは不明です。。。