What are Syslog Facilities and Levels?

 What are Syslog Facilities and Levels?

Syslog Facilities

The facility represents the machine process that created the syslog event. For example, is the event created by the kernel, by the mail system, by security/authorization processes, etc.? In the context of this field, the facility represents a kind of filter, instructing SMS to forward to the remote Syslog Server only those events whose facility matches the one defined in this field. So by changing the facility number and/or the severity level you change the amount of alerts (messages) that are sent to the remote syslog server

The Facility value is a way of determining which process of the machine created the message. Since the Syslog protocol was originally written on BSD Unix, the Facilities reflect the names of UNIX processes and Daemons.

List of available Facilities as per RFC5424:

Facility Number	Facility Description	Facility Number	Facility Description
0	kernel messages	12	NTP subsystem
1	user-level messages	13	log audit
2	mail system	14	log alert
3	system daemons	15	clock daemon
4	**security/authorization messages	16	local use 0 (local0)
5	messages generated internally by syslog	17	local use 1 (local1)
6	line printer subsystem	18	local use 2 (local2)
7	network news subsystem	19	local use 3 (local3)
8	UUCP subsystem	20	local use 4 (local4)
9	clock daemon	21	local use 5 (local5)
10	security/authorization messages	22	local use 6 (local6)
11	FTP daemon	23	local use 7 (local7)
** SMS default Note: Items in yellow are the facility numbers available on the SMS.

If you are receiving messages from a UNIX system, it is suggested you use the “User” Facility as your first choice. Local0 through to Local7 are not used by UNIX and are traditionally used by networking equipment. Cisco routers for example use Local6 or Local7.

Syslog Severity Levels

Recommended practice is to use the Notice or Informational level for normal messages.

Explanation of the severity Levels:

 

https://success.trendmicro.com/solution/TP000086250-What-are-Syslog-Facilities-and-Levels

SEVERITY LEVEL		EXPLANATION
**	SEVERITY IN EVENT	Default SMS setting for Syslog Security option. This setting will send all events to remote Syslog system
0	EMERGENCY	A "panic" condition - notify all tech staff on call? (Earthquake? Tornado?) - affects multiple apps/servers/sites.
1	ALERT	Should be corrected immediately - notify staff who can fix the problem - example is loss of backup ISP connection.
2	CRITICAL	Should be corrected immediately, but indicates failure in a primary system - fix CRITICAL problems before ALERT - example is loss of primary ISP connection.
3	ERROR	Non-urgent failures - these should be relayed to developers or admins; each item must be resolved within a given time.
4	WARNING	Warning messages - not an error, but indication that an error will occur if action is not taken, e.g. file system 85% full - each item must be resolved within a given time.
5	NOTICE	Events that are unusual but not error conditions - might be summarized in an email to developers or admins to spot potential problems - no immediate action required.
6	INFORMATIONAL	Normal operational messages - may be harvested for reporting, measuring throughput, etc. - no action required.
7	DEBUG	Info useful to developers for debugging the app, not useful during operations.