The error log contains a record of critical errors that occurred during the server's operation, table corruption, start and stop information.
SQL errors can also be logged in a separate file using the SQL_ERROR_LOG plugin.
MariaDB always writes its error log, but the destination is configurable.
To configure the error log to be written to a file, you can set the log_error system variable. You can configure a specific file name. However, if a specific file name is not configured, then the log will be written to the ${hostname}.err file in the datadir directory by default.
The log_error system variable can be set in a server option group in an option file prior to starting up the server. For example, to write the error log to the default ${hostname}.err file, you could configure the following:
[mariadb] ... log_error
If you configure a specific file name as the log_error system variable, and if it is not an absolute path, then it will be relative to the datadir directory. For example, if you configured the following, then the error log would be written to mariadb.err in the datadir directory:
[mariadb] ... log_error=mariadb.err
If it is a relative path, then the log_error is relative to the datadir directory.
However, the log_error system variable can also be an absolute path. For example:
[mariadb] ... log_error=/var/log/mysql/mariadb.err
Another way to configure the error log file name is to set the log-basename option, which configures MariaDB to use a common prefix for all log files (e.g. general query log, slow query log, error log, binary logs, etc.). The error log file name will be built by adding a .err extension to this prefix. For example, if you configured the following, then the error log would still be written to mariadb.err in the datadir directory:
[mariadb] ... log-basename=mariadb log_error
The log-basename cannot be an absolute path. The log file name is relative to the datadir directory.
On Unix, if the log_error system variable is not set, then errors are written to stderr, which usually means that the log messages are output to the terminal that started mysqld.
If the log_error system variable was set in an option file or on the command-line, then it can still be unset by specifying --skip-log-error.
On Unix, the error log can also be redirected to the syslog. How this is done depends on how you start MariaDB.
If you start MariaDB with mysqld_safe, then the error log can be redirected to the syslog. See mysqld_safe: Configuring MariaDB to Write the Error Log to Syslog for more information.
If you start MariaDB with systemd, then the error log can also be redirected to the syslog. See Systemd: Configuring MariaDB to Write the Error Log to Syslog for more information.
systemd also has its own logging system called the journal, and some errors may get logged there instead. See Systemd:Systemd Journal for more information.
On Windows, if the console option is specified, and if the log_error system variable is not used, then errors are written to the console. If both options are specified, then the last option takes precedence.
On Windows, error log messages are also written to the Windows Event Viewer. You can find MariaDB's error log messages by browsing Windows Logs, and then selecting Application or Application Log, depending on the Windows version.
In MariaDB 10.3 and before, you can find MariaDB's error log messages by searching for the Source MySQL.
In MariaDB 10.4 and later, you can find MariaDB's error log messages by searching for the Source MariaDB.
In MariaDB 10.2.4 and later, the default value of the log_warnings system variable is 2.
In MariaDB 10.2.3 and before, the default value of the log_warnings system variable is 1.
The log_warnings system variable can be used to configure the verbosity of the error log. It can be changed dynamically with SET GLOBAL. For example:
SET GLOBAL log_warnings=3;
It can also be set either on the command-line or in a server option group in an option file prior to starting up the server. For example:
[mariadb] ... log_warnings=3
Some of the warnings are described below. For a more complete list, see the description of the log_warnings system variable.
If log_warnings is 0, then many optional warnings will not be logged. However, this does not prevent all warnings from being logged, because there are certain core warnings that will always be written to the error log. For example:
[Warning] InnoDB: Cannot add field col25 in table db1.tab because after adding it, the row size is 8477 which is greater than maximum allowed size (8126) for a record on index leaf page.
However, if InnoDB strict mode is enabled, then the same message will be logged as an error.
If log_warnings is 1, then many types of warnings are logged. Some useful warnings are:
[Note] Error reading relay log event: slave SQL thread was killed [Note] Slave SQL thread exiting, replication stopped in log 'dbserver-2-bin.000033' at position 181420; GTID position '0-263316466-368886' [Note] Slave I/O thread exiting, read up to log 'dbserver-2-bin.000034', position 642; GTID position 0-263316466-368887
[Warning] IP address '192.168.1.193' could not be resolved: Name or service not known
[Note] Event Scheduler: Loaded 0 events
[Warning] Unsafe statement written to the binary log using statement format since BINLOG_FORMAT = STATEMENT. The statement is unsafe because it uses a LIMIT clause. This is unsafe because the set of rows included cannot be predicted.
Frequent warnings about unsafe statements for statement-based replication can cause the error log to grow very large. In MariaDB 10.0.14 and later, MariaDB will automatically detect frequent duplicate warnings about unsafe statements for statement-based replication. After 10 identical warnings are detected, MariaDB will prevent that same warning from being written to the error log again for the next 5 minutes.
If log_warnings is 2, then a couple other different kinds of warnings are printed. For example:
[Warning] Access denied for user 'root'@'localhost' (using password: YES)
[Warning] Aborted connection 35 to db: 'unconnected' user: 'user1@host1' host: '192.168.1.40' (Got an error writing communication packets) [Warning] Aborted connection 36 to db: 'unconnected' user: 'user1@host2' host: '192.168.1.230' (Got an error writing communication packets) [Warning] Aborted connection 38 to db: 'db1' user: 'user2' host: '192.168.1.60' (Unknown error) [Warning] Aborted connection 51 to db: 'db1' user: 'user2' host: '192.168.1.50' (Got an error reading communication packets) [Warning] Aborted connection 52 to db: 'db1' user: 'user3' host: '192.168.1.53' (Got timeout reading communication packets)
[Warning] Can't find record in 'tab1'. [Warning] Can't write; duplicate key in table 'tab1'. [Warning] Lock wait timeout exceeded; try restarting transaction. [Warning] The number of locks exceeds the lock table size. [Warning] Update locks cannot be acquired during a READ UNCOMMITTED transaction.
master.info file or the file that is configured by the master_info_file option. relay-log.info file or the file that is configured by the relay_log_info_file system variable. [Note] Reading Master_info: '/mariadb/data/master.info' Relay_info:'/mariadb/data/relay-log.info' [Note] Initialized Master_info from '/mariadb/data/master.info' [Note] Reading of all Master_info entries succeded [Note] Deleted Master_info file '/mariadb/data/master.info'. [Note] Deleted Master_info file '/mariadb/data/relay-log.info'.
[Note] Start binlog_dump to slave_server(263316466), pos(, 4)
If log_warnings is 3, then a couple other different kinds of warnings are printed. For example:
[Warning] An old style --language value with language specific part detected: /usr/local/mysql/data/ [Warning] Use --lc-messages-dir without language specific part instead.
[Note] InnoDB: Online DDL : Start [Note] InnoDB: Online DDL : Start reading clustered index of the table and create temporary files [Note] InnoDB: Online DDL : End of reading clustered index of the table and create temporary files [Note] InnoDB: Online DDL : Start merge-sorting index PRIMARY (1 / 3), estimated cost : 18.0263 [Note] InnoDB: Online DDL : merge-sorting has estimated 33 runs [Note] InnoDB: Online DDL : merge-sorting current run 1 estimated 33 runs [Note] InnoDB: Online DDL : merge-sorting current run 2 estimated 17 runs [Note] InnoDB: Online DDL : merge-sorting current run 3 estimated 9 runs [Note] InnoDB: Online DDL : merge-sorting current run 4 estimated 5 runs [Note] InnoDB: Online DDL : merge-sorting current run 5 estimated 3 runs [Note] InnoDB: Online DDL : merge-sorting current run 6 estimated 2 runs [Note] InnoDB: Online DDL : End of merge-sorting index PRIMARY (1 / 3) [Note] InnoDB: Online DDL : Start building index PRIMARY (1 / 3), estimated cost : 27.0395 [Note] InnoDB: Online DDL : End of building index PRIMARY (1 / 3) [Note] InnoDB: Online DDL : Completed [Note] InnoDB: Online DDL : Start merge-sorting index ux1 (2 / 3), estimated cost : 5.7895 [Note] InnoDB: Online DDL : merge-sorting has estimated 2 runs [Note] InnoDB: Online DDL : merge-sorting current run 1 estimated 2 runs [Note] InnoDB: Online DDL : End of merge-sorting index ux1 (2 / 3) [Note] InnoDB: Online DDL : Start building index ux1 (2 / 3), estimated cost : 8.6842 [Note] InnoDB: Online DDL : End of building index ux1 (2 / 3) [Note] InnoDB: Online DDL : Completed [Note] InnoDB: Online DDL : Start merge-sorting index ix1 (3 / 3), estimated cost : 6.1842 [Note] InnoDB: Online DDL : merge-sorting has estimated 3 runs [Note] InnoDB: Online DDL : merge-sorting current run 1 estimated 3 runs [Note] InnoDB: Online DDL : merge-sorting current run 2 estimated 2 runs [Note] InnoDB: Online DDL : End of merge-sorting index ix1 (3 / 3) [Note] InnoDB: Online DDL : Start building index ix1 (3 / 3), estimated cost : 9.2763 [Note] InnoDB: Online DDL : End of building index ix1 (3 / 3) [Note] InnoDB: Online DDL : Completed
If log_warnings is 4, then a couple other different kinds of warnings are printed. For example:
[Warning] Aborted connection 53 to db: 'db1' user: 'user2' host: '192.168.1.50' (KILLED)
[Warning] Aborted connection 56 to db: 'db1' user: 'user2' host: '192.168.1.50' (CLOSE_CONNECTION)
completion_type is set to RELEASE: [Warning] Aborted connection 58 to db: 'db1' user: 'user2' host: '192.168.1.50' (RELEASE)
If log_warnings is 9, then some very verbose warnings are printed. For example:
[Note] Initializing built-in plugins [Note] Initializing plugins specified on the command line [Note] Initializing installed plugins
MariaDB does not support the log_error_verbosity system variable added in MySQL 5.7.
Until MariaDB 10.1.4, the format consisted of the date (yymmdd) and time, followed by the type of error (Note, Warning or Error) and the error message, for example:
160615 16:53:08 [Note] InnoDB: The InnoDB memory heap is disabled
From MariaDB 10.1.5, the date format has been extended to yyyy-mm-dd, and the thread ID has been added, for example:
2016-06-15 16:53:33 139651251140544 [Note] InnoDB: The InnoDB memory heap is disabled
Unix and Linux distributions offer the logrotate utility, which makes it very easy to rotate log files. See Rotating Logs on Unix and Linux for more information on how to use this utility to rotate the error log.
Many error messages are ready from an error messages file that contains localized error messages. If the server can't find this file when it starts up, then you might see errors like the following:
[ERROR] Can't find messagefile '/usr/share/errmsg.sys'
If this error is occurring because the file is in a custom location, then you can configure this location by setting the lc_messages_dir system variable either on the command-line or in a server option group in an option file prior to starting up the server. For example:
[mariadb] ... lc_messages_dir=/usr/share/mysql/
If you want to use a different locale for error messages, then you can also set the lc_messages system variable. For example:
[mariadb] ... lc_messages_dir=/usr/share/mysql/ lc_messages=en_US
See Setting the Language for Error Messages for more information.
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https://mariadb.com/kb/en/error-log/