The error log contains information indicating when mysqld was started and stopped and also any critical errors that occur while the server is running. If mysqld notices a table that needs to be automatically checked or repaired, it writes a message to the error log.
In the following discussion, “console” means
stderr, the standard error output; this is your
terminal or console window unless the standard error output has
--log-error[=, mysqld writes error messages to an error log file. The server uses the named file if present, creating it in in the data directory unless an absolute path name is given to specify a different directory. If no file is named, the default name is
in the data directory.
In addition, on Windows, the server writes events and error
messages to the Windows Event Log within the Application log.
Entries marked as
Note are written to the Event Log, but not
informational messages such as information statements from
individual storage engines. These log entries have a source of
MySQL. You cannot disable writing information
to the Windows Event Log.
On Unix and Unix-like systems, mysqld writes error log messages as follows:
--log-error[=, mysqld writes error messages to an error log file. The server uses the named file if present, creating it in the data directory unless an absolute path name is given to specify a different directory. If no file is named, the default name is
in the data directory.
variable indicates the error log file name if error output is
written to a file.
If you flush the logs using
FLUSH LOGS or
mysqladmin flush-logs and
mysqld is writing the error log to a file (for
example, if it was started with the
--log-error option), it renames the
current log file with the suffix
creates a new empty log file. Be aware that a second log-flushing
operation thus causes the original error log file to be lost
unless you save it under a different name. For example, you can
use the following commands to save the file:
No error log renaming occurs when the logs are flushed if the server is not writing to a named file.
If you use mysqld_safe to start
mysqld, mysqld_safe arranges
for mysqld to write error messages to a log
file. If you specify a file name using
mysqld_safe or mysqld, that
file name is used. Otherwise, mysqld_safe uses
the default error log file.
--log-warnings option or
log_warnings system variable can
be used to control warning logging to the error log. The default
value is enabled (1). Warning logging can be disabled using a
value of 0. If the value is greater than 1, aborted connections
are written to the error log. See
Section B.5.2.11, “Communication Errors and Aborted Connections”.