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Configuring Python cx_Oracle and mod_wsgi on Oracle Linux

Christopher Jones
Senior Principal Product Manager

The Web Server Gateway Interface (WSGI) is a standardized interface between web servers and Python web frameworks or applications. Many frameworks including Django support WSGI.

This post is a brief how-to about configuring Apache's mod_wsgi with Python's cx_Oracle driver for Oracle Database. The steps are for Oracle Linux.

  1. Download Instant Client Basic & SDK ZIP files from OTN. For cx_Oracle 5.1, use the ZIPs, not the RPMs.

  2. As root, unzip the files to the same directory, e.g. /opt/oracle/instantclient_12_1:

    mkdir /opt/oracle
    cd /opt/oracle
    unzip /tmp/instantclient-basic-linux.x64-12.1.0.2.0.zip
    unzip /tmp/instantclient-sdk-linux.x64-12.1.0.2.0.zip
  3. Configure Instant Client:

    cd /opt/oracle/instantclient_12_1
    ln -s libclntsh.so.12.1 libclntsh.so
  4. Install the pip package management tool for Python by following pip.readthedocs.org/en/latest/installing.html and downloading get-pip.py. Then run:

    python get-pip.py
  5. Install cx_Oracle:

    export LD_RUN_PATH=/opt/oracle/instantclient_12_1
    export ORACLE_HOME=/opt/oracle/instantclient_12_1
    pip install cx_Oracle

    The key here is the use of LD_RUN_PATH. This obviates the need to later set LD_LIBRARY_PATH or configure ldconfig for cx_Oracle to find the Instant Client libraries. There is a cx_Oracle-specific variable FORCE_RPATH which has the same effect.

    Note the cx_Oracle installer overloads the meaning of ORACLE_HOME. This variable is not normally used with Instant Client.

    Neither ORACLE_HOME or LD_RUN_PATH need to be set at runtime.

    If you don't use LD_RUN_PATH or FORCE_RPATH during installation, you will need to make LD_LIBRARY_PATH available to the Apache process or use ldconfig to add Instant Client to the system wide library search path.

    Configuring ldconfig is an effective and commonly used solution. However it has a potential problem that if multiple Oracle products exist, with possibly differing versions of Oracle libraries on the same machine, then there might be library clashes. If you wish to use it, create a file /etc/ld.conf.so.d/oracle-instant-client.conf containing:

    /opt/oracle/instantclient_12_1

    Then update the linker cache by running:

    ldconfig

    Alternatively set LD_LIBRARY_PATH in Apache's environment file, /etc/sysconfig/httpd. In Oracle Linux 6 use:

    export LD_LIBRARY_PATH=/opt/oracle/instantclient_12_1

    In Oracle Linux 7 use:

    LD_LIBRARY_PATH=/opt/oracle/instantclient_12_1

    In Oracle Linux 7, don't reference variables on the right-hand side of the equals sign since they won't be expanded.

    [The Apache environment configuration file location varies between Linux distributions. On OpenSUSE see /etc/sysconfig/apache2. On Debian-based distributions look at /etc/apache2/envvars].

  6. Set any other Oracle environment variables in the Apache environment configuration file /etc/sysconfig/httpd. For example:

    NLS_LANG=GERMAN_GERMANY.AL32UTF8

    (Prefix any variable setting with export in Oracle Linux 6)

  7. Install mod_wsgi:

    yum install mod_wsgi
  8. Add this line to /etc/httpd/conf/httpd.conf:

    WSGIScriptAlias /wsgi_test /var/www/html/wsgi_test.py
  9. On Oracle Linux 6, start the web server with:

    service httpd start

    On Oracle Linux 7 use:

    systemctl start httpd.service
  10. Create a test file /var/www/html/wsgi_test.py that connects to your database:

    #-*- coding: utf-8 -*-
    def query():
    import cx_Oracle
    db = cx_Oracle.connect("hr", "welcome", "localhost/orcl")
    cursor = db.cursor()
    cursor.execute("select city from locations where location_id = 2200")
    return cursor.fetchone()[0]
    def wsgi_test(environ, start_response):
    output = query()
    status = '200 OK'
    headers = [('Content-type', 'text/plain'),

    ('Content-Length', str(len(output)))]
    start_response(status, headers)
    yield output
    application = wsgi_test
  11. Load http://localhost/wsgi_test in a browser. The city of the queried location id will be displayed.

That's it. Let me know how it works for you.

Information on cx_Oracle can be found here.

Information on Oracle Linux can be found here.

Information on Oracle Database can be found here.

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