What is syslog protocol?

The syslog is a communication protocol standard for logging system messages in computer networks. It enables network devices, operating systems, and applications to generate messages about their activities, errors, and statuses and send them to a centralized logging server or collector.

It’s old. Originally developed in the 1980s by Eric Allman, syslog has become a fundamental component of network management, security monitoring, and troubleshooting. It uses the User Datagram Protocol (UDP) or, less commonly, the Transmission Control Protocol (TCP) for message transmission.

Syslog messages typically contain the severity level (e.g., debug, informational, warning, error, critical), timestamp, hostname, and the message itself. These messages can be used for various purposes, including system monitoring, troubleshooting, auditing, and compliance.

Syslog messages are often stored in plain text files or databases and can be analyzed using various tools and applications. They can also be forwarded to other systems for further processing, correlation, and alerting. Many network devices, operating systems, and applications support syslog natively or through third-party software or agents.

How does Syslog work?

Syslog facilitates the generation, transmission, and storage of system log messages across a network. Here's a simplified overview of how it operates:

  1. Message Generation: The process begins when a network device, operating system, or application generates a log message. This message typically includes information such as the severity level, timestamp, hostname, and the content of the message itself.

  2. Message Formatting: The log message is formatted according to the syslog protocol standards. This formatting ensures message contains necessary metadata and adheres to a specific structure that syslog-enabled systems can understand.

  3. Message Transmission: Once formatted, the syslog message is sent over the network to a centralized syslog server or collector. This transmission can occur using either the User Datagram Protocol (UDP) or, less commonly, the Transmission Control Protocol (TCP).

  4. Reception and Storage: The syslog server or collector receives the incoming log messages and stores them in files, databases, or other storage mechanisms. These messages are typically organized based on severity level, source device, or timestamp.

  5. Analysis and Monitoring: Administrators can analyze the collected syslog messages. This analysis can help identify system issues, security threats, performance bottlenecks, and other events of interest. Additionally, real-time monitoring of syslog messages can provide insights into the health and status of network devices and systems.

  6. Archiving and Retention: Syslog messages may be archived for long-term storage and compliance. Archiving practices vary depending on organizational policies, regulatory requirements, and the volume of log data generated.

  7. Alerting and Notification: Syslog servers can be configured to trigger alerts or notifications based on specific criteria, such as critical errors or security incidents. These alerts help administrators respond promptly to potential issues and mitigate risks to the network environment.

Overall, syslog provides a standardized method for collecting, storing, and analyzing log messages from diverse sources across a network, enabling efficient system monitoring, troubleshooting, and security management.

SysLog Protocol example

<14>May 29 14:30:45 myrouter.localdomain %SYS-5-CONFIG_I: Configured from console by admin

In this example:

  • <14>

    indicates the severity level (in this case, severity level 14, which corresponds to "Informational").

  • May 29 14:30:45

    is the timestamp.

  • myrouter.localdomain

    is the hostname of the device that generated the message.


    is the message ID or tag.

  • Configured from console by admin

    is the content of the message, indicating that a configuration change was made by the administrator via the console interface.