title: Airflow webserver not starting in 1.10
body: <p>Trying to migrate from Airflow 1.9 to Airflow 1.10. After some effort I was able to install the new version but could not load the web UI. When I try to start webserver It  gives an error of file being busy. I have not started any process or operations which might be locking any file. <code>airflow initdb</code> works just fine. Error</p>
  
  <pre><code>ubuntu@ubuntu-xenial:~/airflow$ airflow webserver
  [2018-09-06 18:46:19,916] {settings.py:174} INFO - setting.configure_orm(): Using pool settings. pool_size=5, pool_recycle=3600
  /usr/local/lib/python2.7/dist-packages/psycopg2/__init__.py:144: UserWarning: The psycopg2 wheel package will be renamed from release 2.8; in order to keep installing from binary please use "pip install psycopg2-binary" instead. For details see: &lt;http://initd.org/psycopg/docs/install.html#binary-install-from-pypi&gt;.
    """)
  [2018-09-06 18:46:20,057] {__init__.py:51} INFO - Using executor LocalExecutor
    ____________       _____________
   ____    |__( )_________  __/__  /________      __
  ____  /| |_  /__  ___/_  /_ __  /_  __ \_ | /| / /
  ___  ___ |  / _  /   _  __/ _  / / /_/ /_ |/ |/ /
   _/_/  |_/_/  /_/    /_/    /_/  \____/____/|__/
  
  [2018-09-06 18:46:20,156] {logging_config.py:50} INFO - Successfully imported user-defined logging config from airflow.config_templates.airflow_local_settings.DEFAULT_LOGGING_CONFIG
  [2018-09-06 18:46:20,750] {models.py:258} INFO - Filling up the DagBag from /home/ubuntu/airflow/dags
  Running the Gunicorn Server with:
  Workers: 4 sync
  Host: 0.0.0.0:8080
  Timeout: 120
  Logfiles: - -
  =================================================================
  [2018-09-06 18:46:22,138] {settings.py:174} INFO - setting.configure_orm(): Using pool settings. pool_size=5, pool_recycle=3600
  /usr/local/lib/python2.7/dist-packages/psycopg2/__init__.py:144: UserWarning: The psycopg2 wheel package will be renamed from release 2.8; in order to keep installing from binary please use "pip install psycopg2-binary" instead. For details see: &lt;http://initd.org/psycopg/docs/install.html#binary-install-from-pypi&gt;.
    """)
  [2018-09-06 18:46:22 +0000] [26545] [INFO] Starting gunicorn 19.7.1
  Traceback (most recent call last):
    File "/usr/local/bin/gunicorn", line 11, in &lt;module&gt;
      sys.exit(run())
    File "/usr/local/lib/python2.7/dist-packages/gunicorn/app/wsgiapp.py", line 74, in run
      WSGIApplication("%(prog)s [OPTIONS] [APP_MODULE]").run()
    File "/usr/local/lib/python2.7/dist-packages/gunicorn/app/base.py", line 203, in run
      super(Application, self).run()
    File "/usr/local/lib/python2.7/dist-packages/gunicorn/app/base.py", line 72, in run
      Arbiter(self).run()
    File "/usr/local/lib/python2.7/dist-packages/gunicorn/arbiter.py", line 198, in run
      self.start()
    File "/usr/local/lib/python2.7/dist-packages/gunicorn/arbiter.py", line 139, in start
      self.pidfile.create(self.pid)
    File "/usr/local/lib/python2.7/dist-packages/gunicorn/pidfile.py", line 39, in create
      os.rename(fname, self.fname)
  OSError: [Errno 26] Text file busy
  [2018-09-06 18:48:21,760] {cli.py:755} ERROR - No response from gunicorn master within 120 seconds
  [2018-09-06 18:48:21,761] {cli.py:756} ERROR - Shutting down webserver
  </code></pre>
  
  <p>Not sure how to resolve this issue. Below is the output of pip freeze</p>
  
  <pre><code>adal==1.1.0
  alabaster==0.7.11
  alembic==0.8.10
  amqp==2.3.2
  ansible==2.6.3
  anyjson==0.3.3
  apache-airflow==1.10.0
  asn1crypto==0.24.0
  astroid==1.6.5
  atomicwrites==1.2.1
  attrs==18.2.0
  Babel==2.6.0
  backports-abc==0.5
  backports.functools-lru-cache==1.5
  bcrypt==3.1.4
  billiard==3.5.0.4
  bleach==2.1.2
  boto==2.49.0
  boto3==1.8.8
  botocore==1.11.8
  cachetools==2.1.0
  celery==4.1.1
  certifi==2018.8.24
  cffi==1.11.5
  cgroupspy==0.1.6
  chardet==3.0.4
  click==6.7
  colorama==0.3.9
  configparser==3.5.0
  cookies==2.2.1
  coverage==4.5.1
  croniter==0.3.25
  cryptography==2.3.1
  Cython==0.23.4
  defusedxml==0.5.0
  dicttoxml==1.7.4
  dill==0.2.8.2
  dnspython==1.15.0
  docutils==0.14
  ecdsa==0.13
  enum34==1.1.6
  et-xmlfile==1.0.1
  eventlet==0.24.1
  Flask==0.12.4
  Flask-Admin==1.4.1
  Flask-AppBuilder==1.11.1
  Flask-Babel==0.11.1
  Flask-Bcrypt==0.7.1
  Flask-Cache==0.13.1
  Flask-Caching==1.3.3
  Flask-Login==0.2.11
  Flask-OpenID==1.2.5
  Flask-SQLAlchemy==2.1
  flask-swagger==0.2.13
  Flask-WTF==0.14
  flower==0.9.2
  freezegun==0.3.10
  funcsigs==1.0.0
  future==0.16.0
  futures==3.2.0
  gevent==1.3.6
  gitdb2==2.0.4
  GitPython==2.1.11
  google-auth==1.5.1
  greenlet==0.4.14
  gunicorn==19.7.1
  html5lib==1.0.1
  httplib2==0.9.1
  idna==2.7
  imagesize==1.1.0
  inflection==0.3.1
  ipaddress==1.0.22
  iso8601==0.1.12
  isort==4.3.4
  itsdangerous==0.24
  JayDeBeApi==1.1.1
  jdcal==1.4
  Jinja2==2.8.1
  jira==2.0.0
  jmespath==0.9.3
  JPype1==0.6.3
  kombu==4.2.1
  kubernetes==7.0.0
  lazy-object-proxy==1.3.1
  ldap3==2.5.1
  librabbitmq==2.0.0
  linecache2==1.0.0
  lockfile==0.12.2
  lxml==3.8.0
  Mako==1.0.7
  Markdown==2.6.11
  MarkupSafe==1.0
  mccabe==0.6.1
  mock==2.0.0
  mongomock==3.11.1
  monotonic==1.5
  more-itertools==4.3.0
  moto==1.1.19
  mysqlclient==1.3.13
  nose==1.3.7
  nose-ignore-docstring==0.2
  nose-timer==0.7.3
  ntlm-auth==1.2.0
  numpy==1.15.1
  oauthlib==2.1.0
  odfpy==1.3.6
  openpyxl==2.5.6
  ordereddict==1.1
  packaging==17.1
  pandas==0.23.4
  parameterized==0.6.1
  paramiko==2.4.1
  pathlib2==2.3.2
  pbr==4.2.0
  pendulum==1.4.4
  pep8==1.7.1
  pluggy==0.7.1
  protobuf==3.6.1
  psutil==4.4.2
  psycopg2==2.7.5
  psycopg2-binary==2.7.5
  py==1.6.0
  pyaml==17.12.1
  pyasn1==0.4.4
  pyasn1-modules==0.2.2
  pycparser==2.18
  pycrypto==2.6.1
  pycurl==7.43.0
  pydevd==1.4.0
  Pygments==2.2.0
  PyJWT==1.6.4
  pylint==1.9.3
  pymssql==2.1.4
  PyNaCl==1.2.1
  pyodbc==4.0.24
  pyparsing==2.2.0
  pysftp==0.2.9
  pytest==3.8.0
  pytest-cov==2.6.0
  python-apt==1.1.0b1+ubuntu0.16.4.2
  python-daemon==2.1.2
  python-dateutil==2.6.1
  python-editor==1.0.3
  python-nvd3==0.15.0
  python-openid==2.2.5
  python-slugify==1.2.6
  pytz==2018.5
  pytzdata==2018.5
  pywinrm==0.3.0
  PyYAML==3.13
  qds-sdk==1.9.9
  rednose==1.3.0
  requests==2.19.1
  requests-mock==1.5.2
  requests-ntlm==1.1.0
  requests-oauthlib==1.0.0
  requests-toolbelt==0.8.0
  rsa==3.4.2
  s3transfer==0.1.13
  scandir==1.9.0
  sentinels==1.0.0
  setproctitle==1.1.10
  singledispatch==3.4.0.3
  six==1.11.0
  smmap2==2.0.4
  snakebite==2.11.0
  snowballstemmer==1.2.1
  Sphinx==1.7.9
  sphinx-argparse==0.2.2
  Sphinx-PyPI-upload==0.2.1
  sphinx-rtd-theme==0.4.1
  sphinxcontrib-websupport==1.1.0
  SQLAlchemy==1.2.11
  SQLAlchemy-Utils==0.33.3
  tablib==0.12.1
  tabulate==0.7.7
  tenacity==4.8.0
  termstyle==0.1.11
  testfixtures==6.3.0
  text-unidecode==1.2
  thrift==0.11.0
  tornado==5.1
  traceback2==1.4.0
  typing==3.6.6
  tzlocal==1.5.1
  unicodecsv==0.14.1
  Unidecode==1.0.22
  unittest2==1.1.0
  urllib3==1.23
  vine==1.1.4
  webencodings==0.5.1
  websocket-client==0.52.0
  Werkzeug==0.14.1
  wrapt==1.10.11
  WTForms==2.2.1
  xlrd==1.1.0
  xlwt==1.3.0
  xmltodict==0.11.0
  zope.deprecation==4.3.0
  </code></pre>
  
  <p>Any help is appreciated.</p>