6.19. unix-stream, unix-dgram: Collecting messages from UNIX domain sockets

The unix-stream() and unix-dgram() drivers open an AF_UNIX socket and start listening on it for messages. The unix-stream() driver is primarily used on Linux and uses SOCK_STREAM semantics (connection oriented, no messages are lost), while unix-dgram() is used on BSDs and uses SOCK_DGRAM semantics: this may result in lost local messages if the system is overloaded.

To avoid denial of service attacks when using connection-oriented protocols, the number of simultaneously accepted connections should be limited. This can be achieved using the max-connections() parameter. The default value of this parameter is quite strict, you might have to increase it on a busy system.

Both unix-stream and unix-dgram have a single required argument that specifies the filename of the socket to create. For the list of available optional parameters, see Section 6.19.2, unix-stream() and unix-dgram() source options


unix-stream(filename [options]);
unix-dgram(filename [options]);

syslogd on Linux originally used SOCK_STREAM sockets, but some distributions switched to SOCK_DGRAM around 1999 to fix a possible DoS problem. On Linux you can choose to use whichever driver you like as syslog clients automatically detect the socket type being used.

Example 6.40. Using the unix-stream() and unix-dgram() drivers
source s_stream { unix-stream("/dev/log" max-connections(10)); };
source s_dgram { unix-dgram("/var/run/log"); };