7.4.2.8 Error Logging to the System Log

It is possible to have mysqld write the error log to the system log (the Event Log on Windows, and syslog on Unix and Unix-like systems).

This section describes how to configure error logging using the built-in filter, log_filter_internal, and the system log sink, log_sink_syseventlog, to take effect immediately and for subsequent server startups. For general information about configuring error logging, see Section 7.4.2.1, “Error Log Configuration”.

To enable the system log sink, first load the sink component, then modify the log_error_services value:

INSTALL COMPONENT 'file://component_log_sink_syseventlog';
SET PERSIST log_error_services = 'log_filter_internal; log_sink_syseventlog';

To set log_error_services to take effect at server startup, use the instructions at Section 7.4.2.1, “Error Log Configuration”. Those instructions apply to other error-logging system variables as well.

Note

Error logging to the system log may require additional system configuration. Consult the system log documentation for your platform.

On Windows, error messages written to the Event Log within the Application log have these characteristics:

Entries marked as Error, Warning, and Note are written to the Event Log, but not messages such as information statements from individual storage engines.
Event Log entries have a source of MySQL (or MySQL-tag if syseventlog.tag is defined as tag).

On Unix and Unix-like systems, logging to the system log uses syslog. The following system variables affect syslog messages:

syseventlog.facility: The default facility for syslog messages is daemon. Set this variable to specify a different facility.
syseventlog.include_pid: Whether to include the server process ID in each line of syslog output.
syseventlog.tag: This variable defines a tag to add to the server identifier (mysqld) in syslog messages. If defined, the tag is appended to the identifier with a leading hyphen.

MySQL uses the custom label “System” for important system messages about non-error situations, such as startup, shutdown, and some significant changes to settings. In logs that do not support custom labels, including the Event Log on Windows, and syslog on Unix and Unix-like systems, system messages are assigned the label used for the information priority level. However, these messages are printed to the log even if the MySQL log_error_verbosity setting normally excludes messages at the information level.

When a log sink must fall back to a label of “Information” instead of “System” in this way, and the log event is further processed outside of the MySQL server (for example, filtered or forwarded by a syslog configuration), these events may by default be processed by the secondary application as being of “Information” priority rather than “System” priority.