In which log will the startup failure information of mysql be saved?

Mysql startup failure information will be saved in the "error log". The error log mainly records information during the startup and stop process of the MySQL server, failures and exceptions that occur during the operation of the server, etc.; if an exception occurs in the MySQL service, you can find the reason in the error log. In MySQL, you can use the SHOW command to view the directory and file name information where the error log file is located, with the syntax "SHOW VARIABLES LIKE 'log_error';".

The operating environment of this tutorial: windows7 system, mysql8 version, Dell G3 computer.

Mysql startup failure information will be saved in the "error log".

In MySQL, the error log file records information such as startup, shutdown, and running errors of the MySQL server.

The Error Log is the most commonly used log in MySQL. It mainly records information during the startup and stop process of the MySQL server, failures and exceptions that occur during the operation of the server, etc.

If an exception occurs in the MySQL service, you can find the cause in the error log.

In MySQL, you can view the directory and file name information of the error log file through the SHOW command.

mysql> SHOW VARIABLES LIKE 'log_error';
+---------------+----------------------------------------------------------------+
| Variable_name | Value                                                          |
+---------------+----------------------------------------------------------------+
| log_error     | C:\ProgramData\MySQL\MySQL Server 5.7\Data\LAPTOP-UHQ6V8KP.err |
+---------------+----------------------------------------------------------------+
1 row in set, 1 warning (0.04 sec)

The error log is stored in the form of a text file and can be viewed directly using ordinary text tools. Open it here with Notepad, and you can know the file name of the error log from above. This file opens the LAPTOP-UHQ6V8KP.err file under the default data path "C:\ProgramData\MySQL\MySQL Server 5.7\Data\". Part of the content is as follows:

190906 22:06:45 InnoDB: Completed initialization of buffer pool
190906 22:06:45 InnoDB: highest supported file format is Barracuda.
190906 22:06:45  InnoDB: Waiting for the background threads to start
190906 22:06:46 InnoDB: 5.7.29 started; log sequence number 1605345
190906 22:06:47 [Note] Server hostname (bind-address): '0.0.0.0'; port: 3306
190906 22:06:47 [Note]   - '0.0.0.0' resolves to '0.0.0.0';
190906 22:06:47 [Note] Server socket created on IP: '0.0.0.0'.
190906 22:06:47 [Note] Event Scheduler: Loaded 0 events
190906 22:06:47 [Note] /usr/sbin/mysqld: ready for connections.
Version: '5.7.29-log'  socket: '/var/lib/mysql/mysql.sock'  port: 3306  MySQL Community Server (GPL)

The above is part of the error log file , mainly records some operating errors of the system. The command can view the directory and file name information where the error log file is located.

Extended knowledge: Delete error log

In MySQL, you can use the mysqladmin command to open a new error log to ensure hard disk space on the MySQL server. The syntax of the mysqladmin command is as follows:

mysqladmin -uroot -p flush-logs

After executing this command, the MySQL server will first automatically create a new error log, and then rename the old error log to filename.err-old.

When an exception occurs on the MySQL server, the administrator can find the time and cause of the exception in the error log, and then solve the exception based on this information. For error logs from a long time ago, it is unlikely to be viewed, and these error logs can be deleted directly.

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