syslog-ng Open Source Edition 3.25 - Administration Guide

Python code in external files

You can extend and customize syslog-ng OSE easily by writing destinations, parsers, template functions, and sources in Python.

Instead of writing Python code into your syslog-ng OSE configuration file, you can store the Python code for your Python object in an external file. That way, it is easier to write, maintain, and debug the code. You can store the Python code in any directory in your system, but make sure to include it in your Python path.

When referencing a Python class from an external file in the class() option of a Python block in the syslog-ng OSE configuration file, the class name must include the name of the Python file containing the class, without the path and the .py extension. For example, if the MyDestination class is available in the /etc/syslog-ng/etc/pythonexample.py file, use class("pythonexample.MyDestination"):

destination d_python_to_file {
    python(
        class("pythonexample.MyDestination")
    );
};
log {
    source(src);
    destination(d_python_to_file);
};

If you store the Python code in a separate Python file and only include it in the syslog-ng OSE configuration file, make sure that the PYTHON_PATH environment variable includes the path to the Python file, and export the PYTHON_PATH environment variable. For example, if you start syslog-ng OSE manually from a terminal and you store your Python files in the /opt/syslog-ng/etc directory, use the following command: export PYTHONPATH=/opt/syslog-ng/etc

In production, when syslog-ng OSE starts on boot, you must configure your startup script to include the Python path. The exact method depends on your operating system. For recent Red Hat Enterprise Linux, Fedora, and CentOS distributions that use systemd, the systemctl command sources the /etc/sysconfig/syslog-ng file before starting syslog-ng OSE. (On openSUSE and SLES, /etc/sysconfig/syslog file.) Append the following line to the end of this file: PYTHONPATH="<path-to-your-python-file>", for example, PYTHONPATH="/opt/syslog-ng/etc"

To help debugging and troubleshooting your Python code, you can send log messages to the internal() source of syslog-ng OSE. For details, see Logging from your Python code.

Logging from your Python code

You can extend and customize syslog-ng OSE easily by writing destinations, parsers, template functions, and sources in Python.

To debug and troubleshoot your Python code, syslog-ng OSE allows you to use the logger() method to send log messages to the internal() source of syslog-ng OSE. That way the diagnostic messages of your Python code are treated the same way as other such log messages of syslog-ng OSE. This has the following benefits:

• The logger() method respects the log level settings of syslog-ng OSE. You can write error, warning, info, debug, and trace level messages.

• You can follow what your Python code is doing even if syslog-ng OSE is running as a daemon in the background.

Logging to the internal() source is available in syslog-ng OSE version 3.20 and later.

To send log messages to the internal() source from Python

1. Add the following import to your Python code:

   import syslogng

2. Create a logger object:

   logger = syslogng.Logger()

3. Use the logger object in your Python code, for example:

   logger.info("This is a sample log message send from the Python code.")

   You can use the following log levels: logger.error, logger.warning, logger.info, logger.debug, logger.trace

4. Make sure that your syslog-ng OSE configuration includes the internal() source, for example:

   source s_internal { internal(); };
   destination d_internal { file("/var/log/internal.txt"); };
   log {source(s_internal); destination(d_internal); };
   

source: Read, receive, and collect log messages

How sources work

A source is where syslog-ng receives log messages. Sources consist of one or more drivers, each defining where and how messages are received.

To define a source, add a source statement to the syslog-ng configuration file using the following syntax:

source <identifier> {
    source-driver(params); source-driver(params); ...
};

source s_demo_tcp {
    network(ip(10.1.2.3) port(1999));
};

source s_demo_two_drivers {
    network(ip(10.1.2.3) port(1999));
    network(ip(10.1.2.3) port(1999) transport("udp"));
};

source headerless_messages { network(default-facility(syslog) default-priority(emerg)); };

Define a source only once. The same source can be used in several log paths. Duplicating sources causes syslog-ng to open the source (TCP/IP port, file, and so on) more than once, which might cause problems. For example, include the /dev/log file source only in one source statement, and use this statement in more than one log path if needed.

To collect log messages on a specific platform, it is important to know how the native syslogd communicates on that platform. The following table summarizes the operation methods of syslogd on some of the tested platforms:

Each possible communication mechanism has a corresponding source driver in syslog-ng. For example, to open a unix socket with SOCK_DGRAM style communication use the driver unix-dgram. The same socket using the SOCK_STREAM style — as used under Linux — is called unix-stream.

source s_demo {
    internal();
    network(transport("udp"));
    unix-dgram("/dev/log");
};

The following table lists the source drivers available in syslog-ng.