GPL and LGPL licenses
Starting with version 4 F1, the syslog-ng Premium Edition application is based on the syslog-ng Open Source Edition application, and includes elements that are licensed under the LGPL or GPL licenses. You can download the core of syslog-ng PE here. The components located under the /lib directory are licensed under the GNU Lesser General Public License Version 2.1 license, while the rest of the codebase is licensed under the GNU General Public License Version 2 license. External libraries and other dependencies used by syslog-ng PE have their own licenses, typically GPL, LGPL, MIT, or BSD.
Third-party contributions includes the text of the licenses applicable to syslog-ng Premium Edition.
High availability support
Multiple syslog-ng servers can be run in fail-over mode. The syslog-ng application does not include any internal support for this, as clustering support must be implemented on the operating system level. A tool that can be used to create UNIX clusters is Heartbeat (for details, see this page).
One Identity also has a log server appliance called syslog-ng Store Box that supports high-availability. For details, see the syslog-ng Store Box Product Page.
The structure of a log message
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
-
The Enterprise-wide message model or EWMM allows you to deliver structured messages between syslog-ng nodes: see Enterprise-wide message model (EWMM)
-
How messages are represented in syslog-ng PE: see Message representation in syslog-ng PE.
BSD-syslog or legacy-syslog messages
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 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. |
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. |
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 message part
The HEADER 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 application supports other timestamp formats as well, like ISO, or the PIX extended format. For details, see ts-format(). |
The MSG message part
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.