syslogd is the daemon that collects log messages from programs using syslog. It can be configured to sort log data by facility or priority into separate log files or forward log data to other logging servers, including the ability to ignore specified data. It collects data via a UNIX-domain socket (typically how it gets data from the syslog function) or a UDP socket (to collect log messages forwarded from other syslogds on remote hosts).
The main configuration file for syslogd is typically /etc/syslog.conf. This file contains lines of the form:
facility.priority destination
where facility and priority are names of facilities and priority levels described previously for syslog, and destination specifies where to place the log data.
Normally specifying a priority implies that syslogd should log all messages with that priority and above. If you want it to collect log messages for only that priority, you can typically precede the priority name with =, as in mail.=info. * can be used to wildcard facility or priority names, and one can group multiple facillity.priority specifications with ;.
The destination for log messages can be a file specified with an absolute pathname such as /var/log/syslog, a remote syslogd on a given host specified with @hostname, and possibly other kinds of destinations. Some other characters may precede the destination to specify things like whether to buffer log messages (for performance) or write each message immediately to disk.
Full information on the format of syslogd.conf for your system is typically available in man syslogd or man 5 syslogd.conf.