In Nokia's SR Linux, the logging architecture is composed of three main components: sources, destinations, and filters. A logging source is an entity that generates log messages. SR Linux defines two primary types of sources: its own applications/subsystems (e.g., BGP, OSPF) and the underlying Linux system's facilities (e.g., kern, daemon). A syslog filter, by contrast, is not a source of logs. It is a set of rules or a mechanism used to process log streams, selecting which messages from a source should be sent to a specific destination. Therefore, a syslog filter is a processing element, not an originator of logs.

A. Linux facility + priority: This is a valid logging source in SR Linux. It allows the system to collect and manage log messages generated by the underlying Linux kernel and system daemons, categorized by standard syslog facilities.

B. Console: This is a primary log destination in SR Linux, used for displaying log messages. It is a recipient of logs, not a source that generates them. While it is not a source, a syslog filter is a processing rule, which is a more fundamentally different concept.

C. SR Linux subsystem + priority: This is a valid logging source. It represents the native applications running within SR Linux, such as routing protocols or system management agents, which generate logs categorized by severity.

1. Nokia SR Linux System Management Guide (Release R21.6.1)

Section: Logging > Logger process

Content: This section explicitly describes the components of the logging architecture. It states, "The logger process sends log entries to one or more destinations: the console, a log file, or a remote log server." This identifies the console (Option B) as a destination. It also states, "You can create filters to control which log messages are sent to which destinations," defining a filter (Option D) as a control mechanism, not a source.

Section: Logging > Log sources

Content: This section details the valid log sources. It specifies, "Log messages are identified by the application that generated them and a severity level." (Option C) and "The logging utility can also collect messages from the Linux syslog." (Option A). This confirms that Linux facilities and SR Linux applications are the defined sources.