6.1. 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); ... };
Example 6.1. A simple source statement

The following source statement receives messages on the TCP port 1999 of the interface having the IP address.

source s_demo_tcp { network(ip( port(1999)); };
Example 6.2. A source statement using two source drivers

The following source statement receives messages on the 1999 TCP port and the 1999 UDP port of the interface having the IP address.

source s_demo_two_drivers {
           network(ip( port(1999));
           network(ip( port(1999) transport("udp")); };
Example 6.3. Setting default priority and facility

If the message received by the source does not have a proper syslog header, you can use the default-facility() and default-priority() options to set the facility and priority of the messages. Note that these values are applied only to messages that do not set these parameters in their header.

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.


Sources and destinations are initialized only when they are used in a log statement. For example, syslog-ng OSE starts listening on a port or starts polling a file only if the source is used in a log statement. For details on creating log statements, see Chapter 8, Routing messages: log paths, flags, and filters.

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:

LinuxA SOCK_DGRAM unix socket named /dev/log. Newer distributions that use systemd collect log messages into a journal file.
BSD flavorsA SOCK_DGRAM unix socket named /var/run/log.
Solaris (2.5 or below)An SVR4 style STREAMS device named /dev/log.
Solaris (2.6 or above)In addition to the STREAMS device used in earlier versions, 2.6 uses a new multithreaded IPC method called door. By default the door used by syslogd is /etc/.syslog_door.
HP-UX 11 or laterHP-UX uses a named pipe called /dev/log that is padded to 2048 bytes, for example source s_hp-ux {pipe ("/dev/log" pad-size(2048)}.
AIX 5.2 and 5.3A SOCK_STREAM or SOCK_DGRAM unix socket called /dev/log.

Table 6.1. Communication methods used between the applications and syslogd

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.

Example 6.4. Source statement on a Linux based operating system

The following source statement collects the following log messages:

  • internal(): Messages generated by syslog-ng.

  • network(transport("udp")): Messages arriving to the 514/UDP port of any interface of the host.

  • unix-dgram("/dev/log");: Messages arriving to the /dev/log socket.

source s_demo {
    unix-dgram("/dev/log"); };

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

file() Opens the specified file and reads messages.
internal() Messages generated internally in syslog-ng.
network() Receives messages from remote hosts using the BSD-syslog protocol over IPv4 and IPv6. Supports the TCP, UDP, and TLS network protocols.
nodejs() Receives JSON messages from nodejs applications.
pacct() Reads messages from the process accounting logs on Linux.
pipe() Opens the specified named pipe and reads messages.
program() Opens the specified application and reads messages from its standard output.
sun-stream(), sun-streams() Opens the specified STREAMS device on Solaris systems and reads incoming messages.
syslog() Listens for incoming messages using the new IETF-standard syslog protocol.
system() Automatically detects which platform syslog-ng OSE is running on, and collects the native log messages of that platform.
systemd-journal() Collects messages directly from the journal of platforms that use systemd.
systemd-syslog() Collects messages from the journal using a socket on platforms that use systemd.
unix-dgram() Opens the specified unix socket in SOCK_DGRAM mode and listens for incoming messages.
unix-stream() Opens the specified unix socket in SOCK_STREAM mode and listens for incoming messages.

Table 6.2. Source drivers available in syslog-ng