This section describes the PRI message part of a syslog message, according to the legacy-syslog or BSD-syslog protocol.

For further details about the HEADER and MSG parts of a syslog message, see the following sections:

The PRI part of the syslog message (known as Priority value) represents the Facility and Severity of the message. Facility represents the part of the system sending the message, while Severity marks its importance.

PRI formula

The Priority value is calculated using the following formula:

<PRI> = ( <facility> * 8) + <severity>

That is, you first multiply the Facility number by 8, and then add the numerical value of the Severity to the multiplied sum.

Example: the correlation between facility value, severity value, and the Priority value in the PRI message part

The following example illustrates a sample syslog message with a sample PRI field (that is, Priority value): 

<133> Feb 25 14:09:07 webserver syslogd: restart

In this example, <133> represents the PRI field (Priority value). The syslog message's Facility value is 16, and the Severity value is 5.

Substituting the numerical values into the <PRI> = ( <facility> * 8) + <severity> formula, the results match the Priority value in our example:

<133> = ( <16> * 8) + <5>.

Facility and Severity values

The possible Facility values (between 0 and 23) and Severity values (between 0 and 7) each correspond to a message type (see Table 1: syslog Message Facilities), or a message importance level (see Table 2: syslog Message Severities).

NOTE: Facility codes may slightly vary between different platforms. The syslog-ng Open Source Edition (syslog-ng OSE) application accepts Facility codes as numerical values as well.

The following table lists possible Facility values.

Table 10: syslog Message Facilities
Numerical Code Facility
0 kernel messages
1 user-level messages
2 mail system
3 system daemons
4 security/authorization messages
5 messages generated internally by syslogd
6 line printer subsystem
7 network news subsystem
8 UUCP subsystem
9 clock daemon
10 security/authorization messages
11 FTP daemon
12 NTP subsystem
13 log audit
14 log alert
15 clock daemon
16-23 locally used facilities (local0-local7)

The following table lists possible Severity values.

Table 11: syslog Message Severities
Numerical Code Severity
0 Emergency: system is unusable
1 Alert: action must be taken immediately
2 Critical: critical conditions
3 Error: error conditions
4 Warning: warning conditions
5 Notice: normal but significant condition
6 Informational: informational messages
7 Debug: debug-level messages