This section describes the format of a syslog message, according to the legacy-syslog or BSD-syslog protocol. A syslog message consists of the following parts:
The total message cannot be longer than 1024 bytes.
The following is a sample syslog message:
<133>Feb 25 14:09:07 webserver syslogd: restart
The message corresponds to the following format:
<priority>timestamp hostname application: message
The different parts of the message are explained in the following sections.
NOTE: The syslog-ng Open Source Edition (syslog-ng OSE) application supports longer messages as well. For details, see the log-msg-size() option in Global options. However, it is not recommended to enable messages larger than the packet size when using UDP destinations.
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.
