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 1: syslog Message Facilities
| 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 2: syslog Message Severities
| 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 |
This section describes the HEADER message part of a syslog message, according to the legacy-syslog or BSD-syslog protocol.
For further details about the MSG and PRI parts of a syslog message, see the following sections:
The HEADER message part contains a timestamp and the hostname (without the domain name) or the IP address of the device. The timestamp field is the local time in the Mmm dd hh:mm:ss format, where:
-
Mmm is the English abbreviation of the month: Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, Nov, Dec.
-
dd is the day of the month on two digits. If the day of the month is less than 10, the first digit is replaced with a space. (for example, Aug 7.)
-
hh:mm:ss is the local time. The hour (hh) is represented in a 24-hour format. Valid entries are between 00 and 23, inclusive. The minute (mm) and second (ss) entries are between 00 and 59 inclusive.
NOTE: The syslog-ng Open Source Edition (syslog-ng OSE) application supports other timestamp formats as well, like ISO, or the PIX extended format. For details, see the ts-format() option in Global options.
This section describes the MSG message part of a syslog message, according to the legacy-syslog or BSD-syslog protocol.
For further details about the HEADER and PRI message parts of a syslog message, see the following sections:
The MSG part contains the name of the program or process that generated the message, and the text of the message itself. The MSG part is usually in the following format: program[pid]: message text.
This section describes the format of a syslog message, according to the IETF-syslog protocol. A syslog message consists of the following parts:
The following is a sample syslog message (source: https://tools.ietf.org/html/rfc5424):
<34>1 2003-10-11T22:14:15.003Z mymachine.example.com su - ID47 - BOM'su root' failed for lonvick on /dev/pts/8
The message corresponds to the following format:
<priority>VERSION ISOTIMESTAMP HOSTNAME APPLICATION PID MESSAGEID STRUCTURED-DATA MSG
-
Facility is 4, severity is 2, so PRI is 34.
-
The VERSION is 1.
-
The message was created on 11 October 2003 at 10:14:15pm UTC, 3 milliseconds into the next second.
-
The message originated from a host that identifies itself as "mymachine.example.com".
-
The APP-NAME is "su" and the PROCID is unknown.
-
The MSGID is "ID47".
-
The MSG is "'su root' failed for lonvick...", encoded in UTF-8.
-
In this example, the encoding is defined by the BOM:
The byte order mark (BOM) is a Unicode character used to signal the byte-order of the message text.
-
There is no STRUCTURED-DATA present in the message, this is indicated by "-" in the STRUCTURED-DATA field.
The HEADER part of the message must be in plain ASCII format, the parameter values of the STRUCTURED-DATA part must be in UTF-8, while the MSG part should be in UTF-8. The different parts of the message are explained in the following sections.
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. The Priority value is calculated by first multiplying the Facility number by 8 and then adding the numerical value of the Severity. The possible facility and severity values are presented below.
NOTE: Facility codes may slightly vary between different platforms. The syslog-ng application accepts facility codes as numerical values as well.
Table 3: syslog Message Facilities
| 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 the severity values.
Table 4: syslog Message Severities
| 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 |
The HEADER message part
The HEADER part contains the following elements:
-
VERSION: Version number of the syslog protocol standard. Currently this can only be 1.
-
ISOTIMESTAMP: The time when the message was generated in the ISO 8601 compatible standard timestamp format (yyyy-mm-ddThh:mm:ss+-ZONE), for example: 2006-06-13T15:58:00.123+01:00.
-
HOSTNAME: The machine that originally sent the message.
-
APPLICATION: The device or application that generated the message
-
PID: The process name or process ID of the syslog application that sent the message. It is not necessarily the process ID of the application that generated the message.
-
MESSAGEID: The ID number of the message.
NOTE: The syslog-ng application supports other timestamp formats as well, like ISO, or the PIX extended format. The timestamp used in the IETF-syslog protocol is derived from RFC3339, which is based on ISO8601. For details, see the ts-format() option in Global options.
The syslog-ng OSE application will truncate the following fields:
-
If APP-NAME is longer than 48 characters it will be truncated to 48 characters.
-
If PROC-ID is longer than 128 characters it will be truncated to 128 characters.
-
If MSGID is longer than 32 characters it will be truncated to 32 characters.
-
If HOSTNAME is longer than 255 characters it will be truncated to 255 characters.
The STRUCTURED-DATA message part
The STRUCTURED-DATA message part may contain meta- information about the syslog message, or application-specific information such as traffic counters or IP addresses. STRUCTURED-DATA consists of data blocks enclosed in brackets ([]). Every block includes the ID of the block, and one or more name=value pairs. The syslog-ng application automatically parses the STRUCTURED-DATA part of syslog messages, which can be referenced in macros (for details, see Macros of syslog-ng OSE). An example STRUCTURED-DATA block looks like:
[exampleSDID@0 iut="3" eventSource="Application" eventID="1011"][examplePriority@0 class="high"]
The MSG message part
The MSG part contains the text of the message itself. The encoding of the text must be UTF-8 if the BOM character is present in the message. If the message does not contain the BOM character, the encoding is treated as unknown. Usually messages arriving from legacy sources do not include the BOM character. CRLF characters will not be removed from the message.
