The PRI message part

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:

  • [HEADER](/docs/axosyslog-core/chapter-concepts/concepts-message-structure/concepts-message-bsdsyslog/concepts-message-bsdsyslog-header/)

  • [MSG](/docs/axosyslog-core/chapter-concepts/concepts-message-structure/concepts-message-bsdsyslog/concepts-message-bsdsyslog-msg/)

The PRI message part

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).

syslog Message Facilities

The following table lists possible Facility values.

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

syslog Message Severities

The following table lists possible Severity values.

Numerical CodeSeverity
0Emergency: system is unusable
1Alert: action must be taken immediately
2Critical: critical conditions
3Error: error conditions
4Warning: warning conditions
5Notice: normal but significant condition
6Informational: informational messages
7Debug: debug-level messages
Last modified February 7, 2024: Formatting fixes (05f0c76)