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syslog-ng Open Source Edition 3.19 - Administration Guide

Preface Introduction to syslog-ng The concepts of syslog-ng Installing syslog-ng The syslog-ng OSE quick-start guide The syslog-ng OSE configuration file source: Read, receive, and collect log messages
How sources work default-network-drivers: Receive and parse common syslog messages internal: Collecting internal messages file: Collecting messages from text files wildcard-file: Collecting messages from multiple text files linux-audit: Collecting messages from Linux audit logs network: Collecting messages using the RFC3164 protocol (network() driver) nodejs: Receiving JSON messages from nodejs applications mbox: Converting local e-mail messages to log messages osquery: Collect and parse osquery result logs pipe: Collecting messages from named pipes pacct: Collecting process accounting logs on Linux program: Receiving messages from external applications python: writing server-style Python sources python-fetcher: writing fetcher-style Python sources snmptrap: Read Net-SNMP traps sun-streams: Collecting messages on Sun Solaris syslog: Collecting messages using the IETF syslog protocol (syslog() driver) system: Collecting the system-specific log messages of a platform systemd-journal: Collecting messages from the systemd-journal system log storage systemd-syslog: Collecting systemd messages using a socket tcp, tcp6, udp, udp6: Collecting messages from remote hosts using the BSD syslog protocol— OBSOLETE unix-stream, unix-dgram: Collecting messages from UNIX domain sockets stdin: Collecting messages from the standard input stream
destination: Forward, send, and store log messages
amqp: Publishing messages using AMQP elasticsearch: Sending messages directly to Elasticsearch version 1.x (DEPRECATED) elasticsearch2: Sending logs directly to Elasticsearch and Kibana 2.0 or higher file: Storing messages in plain-text files graphite: Sending metrics to Graphite Sending logs to Graylog hdfs: Storing messages on the Hadoop Distributed File System (HDFS) Posting messages over HTTP http: Posting messages over HTTP without Java kafka: Publishing messages to Apache Kafka loggly: Using Loggly logmatic: Using Logmatic.io mongodb: Storing messages in a MongoDB database network: Sending messages to a remote log server using the RFC3164 protocol (network() driver) osquery: Sending log messages to osquery's syslog table pipe: Sending messages to named pipes program: Sending messages to external applications pseudofile() python: writing custom Python destinations redis: Storing name-value pairs in Redis riemann: Monitoring your data with Riemann slack: Sending alerts and notifications to a Slack channel smtp: Generating SMTP messages (e-mail) from logs Splunk: Sending log messages to Splunk sql: Storing messages in an SQL database stomp: Publishing messages using STOMP syslog: Sending messages to a remote logserver using the IETF-syslog protocol syslog-ng: Forwarding messages and tags to another syslog-ng node tcp, tcp6, udp, udp6: Sending messages to a remote log server using the legacy BSD-syslog protocol (tcp(), udp() drivers) Telegram: Sending messages to Telegram unix-stream, unix-dgram: Sending messages to UNIX domain sockets usertty: Sending messages to a user terminal: usertty() destination Write your own custom destination in Java or Python Client-side failover
log: Filter and route log messages using log paths, flags, and filters Global options of syslog-ng OSE TLS-encrypted message transfer template and rewrite: Format, modify, and manipulate log messages parser: Parse and segment structured messages db-parser: Process message content with a pattern database (patterndb) Correlating log messages Enriching log messages with external data Statistics of syslog-ng Multithreading and scaling in syslog-ng OSE Troubleshooting syslog-ng Best practices and examples The syslog-ng manual pages Third-party contributions Creative Commons Attribution Non-commercial No Derivatives (by-nc-nd) License About us

pseudofile()

The pseudofile() destination driver is a very simple driver, aimed at delivering messages to special files such as files in the /proc, /dev or /sys directories. It opens and closes the file after each write operation, instead of keeping it open. It does not append further data. It does not support templates in the filename, and does not have a queue, processing is performed immediately as read by the source. Therefore, no loss is possible, but it takes CPU time from the source, so it is not adequate in high traffic situations.

Declaration:
pseudofile(filename options());

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pseudofile() destination options

The pseudofile() destination has the following options:

file()
Type: filename with path
Default:

Description: The file to write messages to, including the path.

hook-commands()

Description: This option makes it possible to execute external programs when the relevant driver is initialized or torn down. The hook-commands() can be used with all source and destination drivers with the exception of the usertty() and internal() drivers.

NOTE: The syslog-ng OSE application must be able to start and restart the external program, and have the necessary permissions to do so. For example, if your host is running AppArmor or SELinux, you might have to modify your AppArmor or SELinux configuration to enable syslog-ng OSE to execute external applications.

Using the hook-commands() when syslog-ng OSE starts or stops

To execute an external program when syslog-ng OSE starts or stops, use the following options:

startup()
Type: string
Default: N/A

Description: Defines the external program that is executed as syslog-ng OSE starts.

shutdown()
Type: string
Default: N/A

Description: Defines the external program that is executed as syslog-ng OSE stops.

Using the hook-commands() when syslog-ng OSE reloads

To execute an external program when the syslog-ng OSE configuration is initiated or torn down, for example, on startup/shutdown or during a syslog-ng OSE reload, use the following options:

setup()
Type: string
Default: N/A

Description: Defines an external program that is executed when the syslog-ng OSE configuration is initiated, for example, on startup or during a syslog-ng OSE reload.

teardown()
Type: string
Default: N/A

Description: Defines an external program that is executed when the syslog-ng OSE configuration is stopped or torn down, for example, on shutdown or during a syslog-ng OSE reload.

Example: Using the hook-commands() with a network source

In the following example, the hook-commands() is used with the network() driver and it opens an iptables port automatically as syslog-ng OSE is started/stopped.

The assumption in this example is that the LOGCHAIN chain is part of a larger ruleset that routes traffic to it. Whenever the syslog-ng OSE created rule is there, packets can flow, otherwise the port is closed.

source {
   network(transport(udp)
	hook-commands(
          startup("iptables -I LOGCHAIN 1 -p udp --dport 514 -j ACCEPT")
          shutdown("iptables -D LOGCHAIN 1")
        )
     );
};
template()
Type: string
Default: A format conforming to the default logfile format.

Description: Specifies a template defining the logformat to be used in the destination. Macros are described in Macros of syslog-ng OSE. Please note that for network destinations it might not be appropriate to change the template as it changes the on-wire format of the syslog protocol which might not be tolerated by stock syslog receivers (like syslogd or syslog-ng itself). For network destinations make sure the receiver can cope with the custom format defined.


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python: writing custom Python destinations

The Python destination allows you to write your own destination in Python. You can import external Python modules to process the messages, and send them to other services or servers. Since many services have a Python library, the Python destination makes integrating syslog-ng OSE very easy and quick.

    The following points apply to using Python blocks in syslog-ng OSE in general.

  • Python parsers and template functions are available in syslog-ng OSE version 3.10 and later.

    Python destinations and sources are available in syslog-ng OSE version 3.18 and later.

  • Supported Python versions: 2.7 and 3.4+ (if you are using pre-built binaries, check the dependencies of the package to find out which Python version it was compiled with)

  • The Python block must be a top-level block in the syslog-ng OSE configuration 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"

  • The Python object is initiated every time when syslog-ng OSE is started or reloaded.

    Caution:

    If you reload syslog-ng OSE, existing Python objects are destroyed, therefore the context and state information of Python blocks is lost. Log rotation and updating the configuration of syslog-ng OSE typically involves a reload.

  • The Python block can contain multiple Python functions.

  • Using Python code in syslog-ng OSE can significantly decrease the performance of syslog-ng OSE, especially if the Python code is slow. In general, the features of syslog-ng OSE are implemented in C, and are faster than implementations of the same or similar features in Python.

  • Validate and lint the Python code before using it. The syslog-ng OSE application does not do any of this.

  • Python error messages are available in the internal() source of syslog-ng OSE.

  • You can access the name-value pairs of syslog-ng OSE directly through a message object or a dict.

Declaration:

Python destinations consist of two parts. The first is a syslog-ng OSE destination object that you define in your syslog-ng OSE configuration and use in the log path. This object references a Python class, which is the second part of the Python destination. The Python class processes the log messages it receives, and can do virtually anything that you can code in Python. You can either embed the Python class into your syslog-ng OSE configuration file, or store it in an external Python file.

destination <name_of_the_python_destination>{
    python(
        class("<name_of_the_python_class_executed_by_the_destination>")
    );
};

python {
class <name_of_the_python_class_executed_by_the_destination>(object):

    def open(self):
        """Open a connection to the target service

        Should return False if opening fails"""
        return True

    def close(self):
        """Close the connection to the target service"""
        pass

    def is_opened(self):
        """Check if the connection to the target is able to receive messages"""
        return True

    def init(self, options):
        """This method is called at initialization time

        Should return false if initialization fails"""
        return True

    def deinit(self):
        """This method is called at deinitialization time"""
        pass

    def send(self, msg):
        """Send a message to the target service

        It should return True to indicate success. False will suspend the
        destination for a period specified by the time-reopen() option."""
        return True
};

Methods of the python() destination

init(self, options) method (optional)

The syslog-ng OSE application initializes Python objects every time when it is started or reloaded. The init method is executed as part of the initialization. You can perform any initialization steps that are necessary for your source to work.

Caution:

If you reload syslog-ng OSE, existing Python objects are destroyed, therefore the context and state information of Python blocks is lost. Log rotation and updating the configuration of syslog-ng OSE typically involves a reload.

When this method returns with False, syslog-ng OSE does not start. It can be used to check options and return False when they prevent the successful start of the source.

options: This optional argument contains the contents of the options() parameter of the syslog-ng OSE configuration object as a Python dict.

is_opened(self) method (optional)

Checks if the connection to the target is able to receive messages, and should return True if it is. For details, see Error handling in the python() destination.

open(self) method (optional)

The open(self) method opens the resources required for the destination, for example, it initiates a connection to the target service. It is called after init() when syslog-ng OSE is started or reloaded. If send() returns with an error, syslog-ng OSE calls close() and open() before trying to send again.

If open() fails, it should return the False value. In this case, syslog-ng OSE retries it every time-reopen() seconds. By default, this is 1 second for Python sources and destinations, the value of time-reopen() is not inherited from the global option. For details, see Error handling in the python() destination.

send(self, message) method (mandatory)

The send method sends a message to the target service. It should return True to indicate success.

This is the only mandatory method of the destination.

If a message cannot be delivered after the number of times set in retries() (by default: 3), syslog-ng OSE drops the message and continues with the next message. For details, see Error handling in the python() destination.

close(self) method (optional)

Close the connection to the target service. Usually it is called right before deinit() when stopping or reloading syslog-ng OSE. It is also called when send() fails.

The deinit(self) method (optional)

This method is executed when syslog-ng OSE is stopped or reloaded. This method does not return a value.

Caution:

If you reload syslog-ng OSE, existing Python objects are destroyed, therefore the context and state information of Python blocks is lost. Log rotation and updating the configuration of syslog-ng OSE typically involves a reload.

Error handling in the python() destination

The Python destination handles errors as follows.

  1. Currently syslog-ng OSE ignores every error from the open method until the first log message arrives to the Python destination. If the fist message has arrived and there was an error in the open method, syslog-ng OSE starts calling the open method every time-reopen() second, until opening the destination succeeds.

  2. If the open method returns without error, syslog-ng OSE calls the send method to send the first message.

  3. If the send method returns with an error, syslog-ng OSE calls the is_opened method.

    • If the is_opened method returns an error, syslog-ng OSE starts calling the open method every time-reopen() second, until opening the destination succeeds.

    • Otherwise, syslog-ng OSE calls the send method again.

  4. If the send method has returned with an error retries() times and the is_opened method has not returned any errors, syslog-ng OSE drops the message and attempts to process the next message.

Example: Write logs into a file

The purpose of this example is only to demonstrate the basics of the Python destination, if you really want to write log messages into text files, use the file destination instead.

The following sample code writes the body of log messages into the /tmp/example.txt file. Only the send() method is implemented, meaning that syslog-ng OSE opens and closes the file for every message.

destination d_python_to_file {
    python(
        class("TextDestination")
    );
};
log {
    source(src);
    destination(d_python_to_file);
};
python {
class TextDestination(object):
    def send(self, msg):
        self.outfile = open("/tmp/example.txt", "a")
        self.outfile.write("MESSAGE = %s\n" % msg["MESSAGE"])
        self.outfile.flush()
        self.outfile.close();
        return True
};

The following code is similar to the previous example, but it opens and closes the file using the open() and close() methods.

destination d_python_to_file {
    python(
        class("TextDestination")
    );
};
log {
    source(src);
    destination(d_python_to_file);
};
python {
class TextDestination(object):
    def open(self):
        try:
            self.outfile = open("/tmp/example.txt", "a")
            return True
        except:
            return False

    def send(self, msg):
        self.outfile.write("MESSAGE = %s\n" % msg["MESSAGE"])
        self.outfile.flush()
        return True

    def close(self):
        try:
            self.outfile.flush()
            self.outfile.close();
            return True
        except:
            return False
};

For a more detailed example about sending log messages to an MQTT (Message Queuing Telemetry Transport) server, see the Writing Python destination in syslog-ng: how to send log messages to MQTT blog post.

For the list of available optional parameters, see python() destination options.


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python() destination options

The Python destination allows you to write your own destination in Python. The python() destination has the following options. The class() option is mandatory. For details on writing destinations in Python, see python: writing custom Python destinations.

class()
Type: string
Default: N/A

Description: The name of the Python class that implements the destination, for example:

python(
    class("MyPythonDestination")
);

If you want to store the Python code in an external Python file, the class() option must include the name of the Python file containing the class, without the path and the .py extension, for example:

python(
    class("MyPythonfilename.MyPythonDestination")
);

For details, see Python code in external files

disk-buffer()

Description: This option enables putting outgoing messages into the disk buffer of the destination to avoid message loss in case of a system failure on the destination side. It has the following options:

reliable()
Type: yes|no
Default: no

Description: If set to yes, syslog-ng OSE cannot lose logs in case of reload/restart, unreachable destination or syslog-ng OSE crash. This solution provides a slower, but reliable disk-buffer option. It is created and initialized at startup and gradually grows as new messages arrive. If set to no, the normal disk-buffer will be used. This provides a faster, but less reliable disk-buffer option.

Caution:

Hazard of data loss! If you change the value of reliable() option when there are messages in the disk-buffer, the messages stored in the disk-buffer will be lost.

dir()
Type: string
Default: N/A

Description: Defines the folder where the disk-buffer files are stored.

Caution:

When creating a new dir() option for a disk buffer, or modifying an existing one, make sure you delete the persist file.

syslog-ng OSE creates disk-buffer files based on the path recorded in the persist file. Therefore, if the persist file is not deleted after modifying the dir() option, then following a restart, syslog-ng OSE will look for or create disk-buffer files in their old location. To ensure that syslog-ng OSE uses the new dir() setting, the persist file must not contain any information about the destinations which the disk-buffer file in question belongs to.

disk-buf-size()
Type: number (bytes)
Default:

Description: This is a required option. The maximum size of the disk-buffer in bytes. The minimum value is 1048576 bytes. If you set a smaller value, the minimum value will be used automatically. It replaces the old log-disk-fifo-size() option.
mem-buf-length()
Type: number (messages)
Default: 10000
Description: Use this option if the option reliable() is set to no. This option contains the number of messages stored in overflow queue. It replaces the old log-fifo-size() option. It inherits the value of the global log-fifo-size() option if provided. If it is not provided, the default value is 10000 messages. Note that this option will be ignored if the option reliable() is set to yes.
mem-buf-size()
Type: number (bytes)
Default: 163840000
Description: Use this option if the option reliable() is set to yes. This option contains the size of the messages in bytes that is used in the memory part of the disk buffer. It replaces the old log-fifo-size() option. It does not inherit the value of the global log-fifo-size() option, even if it is provided. Note that this option will be ignored if the option reliable() is set to no.
qout-size()
Type: number (messages)
Default: 64
Description: The number of messages stored in the output buffer of the destination. Note that if you change the value of this option and the disk-buffer already exists, the change will take effect when the disk-buffer becomes empty.

Options reliable() and disk-buf-size() are required options.

Example: Examples for using disk-buffer()

In the following case reliable disk-buffer() is used.

destination d_demo {
    network(
        "127.0.0.1"
        port(3333)
        disk-buffer(
            mem-buf-size(10000)
            disk-buf-size(2000000)
            reliable(yes)
            dir("/tmp/disk-buffer")
        )
    );
};

In the following case normal disk-buffer() is used.

destination d_demo {
    network(
        "127.0.0.1"
        port(3333)
           disk-buffer(
            mem-buf-length(10000)
            disk-buf-size(2000000)
            reliable(no)
            dir("/tmp/disk-buffer")
        )
    );
};
frac-digits()
Type: number
Default: 0

Description: The syslog-ng application can store fractions of a second in the timestamps according to the ISO8601 format. The frac-digits() parameter specifies the number of digits stored. The digits storing the fractions are padded by zeros if the original timestamp of the message specifies only seconds. Fractions can always be stored for the time the message was received. Note that syslog-ng can add the fractions to non-ISO8601 timestamps as well.

loaders()
Type: list of python modules
Default: empty list

Description: The syslog-ng OSE application imports Python modules specified in this option, before importing the code of the Python class. This option has effect only when the Python class is provided in an external Python file. This option has no effect when the Python class is provided within the syslog-ng OSE configuration file (in a python{} block). You can use the loaders() option to modify the import mechanism that imports Python class. For example, that way you can use hy in your Python class.

python(class(usermodule.HyParser) loaders(hy))
log-fifo-size()
Type: number
Default: Use global setting.

Description: The number of messages that the output queue can store.

on-error()
Accepted values:

drop-message|drop-property|fallback-to-string|

silently-drop-message|silently-drop-property|silently-fallback-to-string

Default: Use the global setting (which defaults to drop-message)

Description: Controls what happens when type-casting fails and syslog-ng OSE cannot convert some data to the specified type. By default, syslog-ng OSE drops the entire message and logs the error. Currently the value-pairs() option uses the settings of on-error().

  • drop-message: Drop the entire message and log an error message to the internal() source. This is the default behavior of syslog-ng OSE.

  • drop-property: Omit the affected property (macro, template, or message-field) from the log message and log an error message to the internal() source.

  • fallback-to-string: Convert the property to string and log an error message to the internal() source.

  • silently-drop-message: Drop the entire message silently, without logging the error.

  • silently-drop-property: Omit the affected property (macro, template, or message-field) silently, without logging the error.

  • silently-fallback-to-string: Convert the property to string silently, without logging the error.

options()
Type: string
Default: N/A

Description: This option allows you to pass custom values from the configuration file to the Python code. Enclose both the option names and their values in double-quotes. The Python code will receive these values during initialization as the options dictionary. For example, you can use this to set the IP address of the server from the configuration file, so it is not hard-coded in the Python object.

python(
    class("MyPythonClass")
    options(
        "host" "127.0.0.1"
        "port" "1883"
        "otheroption" "value")
);

For example, you can refer to the value of the host field in the Python code as options["host"]. Note that the Python code receives the values as strings, so you might have to cast them to the type required, for example: int(options["port"])

persist-name()
Type: string
Default:

Description:If you receive the following error message during syslog-ng OSE startup, set the persist-name() option of the duplicate drivers:

Error checking the uniqueness of the persist names, please override it with persist-name option. Shutting down.

This error happens if you use identical drivers in multiple sources, for example, if you configure two file sources to read from the same file. In this case, set the persist-name() of the drivers to a custom string, for example, persist-name("example-persist-name1").

throttle()
Type: number
Default: 0

Description: Sets the maximum number of messages sent to the destination per second. Use this output-rate-limiting functionality only when using disk-buffer as well to avoid the risk of losing messages. Specifying 0 or a lower value sets the output limit to unlimited.

value-pairs()
Type: parameter list of the value-pairs() option
Default:
scope("selected-macros" "nv-pairs")

Description: The value-pairs() option creates structured name-value pairs from the data and metadata of the log message. For details on using value-pairs(), see Structuring macros, metadata, and other value-pairs.

NOTE:

Empty keys are not logged.

You can use this option to limit which name-value pairs are passed to the Python code for each message. Note that if you use the value-pairs() option, the Python code receives the specified value-pairs as a Python dict. Otherwise, it receives the message object. In the following example, only the text of the log message is passed to Python.

destination d_python_to_file {
    python(
        class("pythonexample.TextDestination")
        value-pairs(key(MESSAGE))
    );
};

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