Syslog

What is syslog-ng?

From https://syslog-ng.org:

syslog-ng allows you to flexibly collect, parse, classify, and correlate logs from across your infrastructure and store or route them to log analysis tools.

How does Security Onion use syslog-ng?

Security Onion uses syslog-ng as its primary syslog collector and to send logs to ELSA.

How do I configure syslog-ng?

syslog-ng's configuration file is located at /etc/syslog-ng/syslog-ng.conf

How do I send logs from Security Onion to other systems?

Syslog-ng can be integrated with third-party systems to forward Bro, OSSEC, or IDS alerts.

Where do I go for more information about syslog-ng?

For more information about syslog-ng, please see:
https://syslog-ng.org/

syslog-ng listens on port 514 (TCP and UDP) for incoming syslog from other devices (you may need to run so-allow to allow traffic from the IP address of your syslog sender). This gives you basic log collection. If you'd like those logs collected from other devices to be analyzed, another option is to configure OSSEC to receive syslog directly on a port other than the syslog-ng port of 514:
http://ossec-docs.readthedocs.org/en/latest/syntax/head_ossec_config.remote.html
http://www.ossec.net/ossec-docs/OSSEC-book-ch3.pdf