The following sections describe the structure of log messages. Currently there are two standard syslog message formats:
The old standard described in RFC 3164 (also called the BSD-syslog or the legacy-syslog protocol): see BSD-syslog or legacy-syslog messages
The new standard described in RFC 5424 (also called the IETF-syslog protocol): see IETF-syslog messages
This section describes the format of a syslog message, according to the legacy-syslog or BSD-syslog protocol (see RFC 3164). A syslog message consists of the following parts:
The total message must be shorter than 1024 bytes.
The following example 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 application supports longer messages as well. For details, see the Message size option. However, it is not recommended to enable messages larger than the packet size when using UDP destinations.
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 following table lists the facility values.
The following table lists the severity values.
| 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 |
The HEADER part contains a time stamp and the hostname (without the domain name) or the IP address of the device. The time stamp 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 in 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.
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