Why can't mysql be used? How to deal with it?

MySQL is an open source relational database management system that is widely used in various network applications and websites. But sometimes, we may encounter situations where MySQL cannot be used. At this time, we need to find out the cause of the problem and take appropriate measures to solve it. This article will introduce some reasons why MySQL cannot be used and the corresponding solutions.

1. Port number is occupied

The default port number used by MySQL is 3306. If the port number is occupied by other programs, MySQL cannot start. In order to solve this problem, we can modify the port number by modifying the MySQL configuration file. Open the my.cnf file, find the [mysqld] section, and change port=3306 to another port number, such as 3307. After saving the changes, restart the MySQL service.

2. MySQL service does not start

If the MySQL service does not start normally, then we cannot use it. In Linux systems, we can use the systemctl status mysql command to check whether the MySQL service has been started. If the service is not started, we can use the systemctl start mysql command to start it. In Windows systems, we can manually start the MySQL service in "Services".

3. Database file damage

In MySQL, data is stored in the database file. If these files are damaged, MySQL will become unusable. We can try the following methods to solve this problem:

(1) Use the repair tool that comes with MySQL to repair the database file. First stop the MySQL service, and then enter mysqlcheck -r dbname at the command line, where dbname is the name of the database. This command will automatically repair damaged database files.

(2) If the repair tool that comes with MySQL cannot repair the database file, we can manually delete the damaged file and restore the backup file. Before deleting the files, we need to back up the database files to avoid data loss. After deleting the damaged files, restore the backup files to the MySQL data directory, and then restart the MySQL service.

4. Wrong username or password

If we cannot connect to MySQL with the correct username and password, then we cannot use it. You can try the following methods to solve this problem:

(1) Check whether the username and password are correct. Enter mysql -u root -p in the MySQL command line, where root is the user name and -p indicates that a password is required. If the password is correct, you can enter the MySQL command line tool.

(2) Reset the password of root user. If you forget the password of the root user, you can try the following method to reset it:

a. 停止 MySQL 服务。
b. 使用 mysqld_safe --skip-grant-tables & 命令启动 MySQL。
c. 进入 MySQL 命令行工具，使用 UPDATE mysql.user SET password = PASSWORD('newpassword') WHERE user = 'root'; 命令来重置密码。
d. 重启 MySQL 服务，然后使用新密码登录 MySQL。

Summary

The above are the common problems that cause MySQL to be unusable and the corresponding solutions. In the daily use of MySQL, we should pay more attention to these problems so that we can discover and solve them in time to ensure the normal operation of MySQL.

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