syslog-ng Open Source Edition 3.30 - Administration Guide

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.

default-network-drivers: Receive and parse common syslog messages

The default-network-drivers() source is a special source that uses multiple source drivers to receive and parse several different types of syslog messages from the network. Available in version 3.16 and later.

To use the default-network-drivers() source, the scl.conf file must be included in your syslog-ng OSE configuration:

@include "scl.conf"

Also, make sure that your SELinux, AppArmor, and firewall settings permit syslog-ng Open Source Edition to access the ports where you want to receive messages, and that no other application is using these ports. By default, the default-network-drivers() source accepts messages on the following ports:

• 514, both TCP and UDP, for RFC3164 (BSD-syslog) formatted traffic

• 601 TCP, for RFC5424 (IETF-syslog) formatted traffic

• 6514 TCP, for TLS-encrypted traffic

In addition to receiving messages on different ports and in different formats, this source tries to parse the messages automatically. If successful, it sets the ${.app.name} name-value pair to the name of the application that sent the log message. Currently it uses the following procedures.

source s_network {
    default-network-drivers();
};

source s_network {
    default-network-drivers(
        tls(
            key-file("/path/to/ssl-private-key")
            cert-file("/path/to/ssl-cert")
		)
    );
};

default-network-drivers() source options

The systemd-journal() driver has the following options.

ca-dir()

Description: The name of a directory that contains a set of trusted CA certificates in PEM format. The CA certificate files have to be named after the 32-bit hash of the subject's name. This naming can be created using the c_rehash utility in openssl. For an example, see Configuring TLS on the syslog-ng clients. The syslog-ng OSE application uses the CA certificates in this directory to validate the certificate of the peer.

This option can be used together with the optional ca-file() option.

ca-file()

Description: Optional. The name of a file that contains a set of trusted CA certificates in PEM format. The syslog-ng OSE application uses the CA certificates in this file to validate the certificate of the peer.

Example format in configuration:

ca-file("/etc/pki/tls/certs/ca-bundle.crt")

flags()

Description: Specifies the log parsing options of the source.

• assume-utf8: The assume-utf8 flag assumes that the incoming messages are UTF-8 encoded, but does not verify the encoding. If you explicitly want to validate the UTF-8 encoding of the incoming message, use the validate-utf8 flag.

• empty-lines: Use the empty-lines flag to keep the empty lines of the messages. By default, syslog-ng OSE removes empty lines automatically.

• expect-hostname: If the expect-hostname flag is enabled, syslog-ng OSE will assume that the log message contains a hostname and parse the message accordingly. This is the default behavior for TCP sources. Note that pipe sources use the no-hostname flag by default.

• guess-timezone: Attempt to guess the timezone of the message if this information is not available in the message. Works when the incoming message stream is close to real time, and the timezone information is missing from the timestamp.

• kernel: The kernel flag makes the source default to the LOG_KERN | LOG_NOTICE priority if not specified otherwise.

• no-hostname: Enable the no-hostname flag if the log message does not include the hostname of the sender host. That way syslog-ng OSE assumes that the first part of the message header is ${PROGRAM} instead of ${HOST}. For example:

  source s_dell {
      network(
          port(2000)
          flags(no-hostname)
      );
  };

• no-multi-line: The no-multi-line flag disables line-breaking in the messages: the entire message is converted to a single line. Note that this happens only if the underlying transport method actually supports multi-line messages. Currently the file() and pipe() drivers support multi-line messages.

• no-parse: By default, syslog-ng OSE parses incoming messages as syslog messages. The no-parse flag completely disables syslog message parsing and processes the complete line as the message part of a syslog message. The syslog-ng OSE application will generate a new syslog header (timestamp, host, and so on) automatically and put the entire incoming message into the MESSAGE part of the syslog message (available using the ${MESSAGE} macro). This flag is useful for parsing messages not complying to the syslog format.

  If you are using the flags(no-parse) option, then syslog message parsing is completely disabled, and the entire incoming message is treated as the ${MESSAGE} part of a syslog message. In this case, syslog-ng OSE generates a new syslog header (timestamp, host, and so on) automatically. Note that since flags(no-parse) disables message parsing, it interferes with other flags, for example, disables flags(no-multi-line).

• dont-store-legacy-msghdr: By default, syslog-ng stores the original incoming header of the log message. This is useful if the original format of a non-syslog-compliant message must be retained (syslog-ng automatically corrects minor header errors, for example, adds a whitespace before msg in the following message: Jan 22 10:06:11 host program:msg). If you do not want to store the original header of the message, enable the dont-store-legacy-msghdr flag.

• sanitize-utf8: When using the sanitize-utf8 flag, syslog-ng OSE converts non-UTF-8 input to an escaped form, which is valid UTF-8.

• store-raw-message: Save the original message as received from the client in the ${RAWMSG} macro. You can forward this raw message in its original form to another syslog-ng node using the syslog-ng() destination, or to a SIEM system, ensuring that the SIEM can process it. Available only in 3.16 and later.

• syslog-protocol: The syslog-protocol flag specifies that incoming messages are expected to be formatted according to the new IETF syslog protocol standard (RFC5424), but without the frame header. Note that this flag is not needed for the syslog driver, which handles only messages that have a frame header.

• validate-utf8: The validate-utf8 flag enables encoding-verification for messages formatted according to the new IETF syslog standard (for details, see IETF-syslog messages). If the BOM1 character is missing, but the message is otherwise UTF-8 compliant, syslog-ng automatically adds the BOM character to the message.

log-msg-size()

Description: Maximum length of an incoming message in bytes. This length includes the entire message (the data structure and individual fields). The maximal value that can be set is 268435456 bytes (256 MiB).

For messages using the IETF-syslog message format (RFC5424), the maximal size of the value of an SDATA field is 64 KiB.

For details on how encoding affects the size of the message, see Message size and encoding.

Uses the value of the global option if not specified.

source s_network {
    default-network-drivers(
        tls(
            key-file("/path/to/ssl-private-key")
            cert-file("/path/to/ssl-cert")
        )
    );
};

tls()

Description: This option sets various options related to TLS encryption, for example, key/certificate files and trusted CA locations. TLS can be used only with tcp-based transport protocols. For details, see TLS options.