What to do if mysql database connection fails

MySQL is currently one of the most popular relational databases, and its stability and performance have been widely recognized and used. However, sometimes we encounter problems with the MySQL database being unable to connect. At this time, we need to analyze the cause and take corresponding solutions.

1. Check whether the MySQL service is open

If the MySQL connection fails, you first need to confirm whether the MySQL service is running. Under the Windows operating system, we can press the Win R key, enter services.msc to open the service manager, find the MySQL service, and check whether its status is "Running". Under the Linux operating system, we can view the status of the MySQL service by executing service mysql status on the command line.

If the MySQL service is not running, we need to start the service manually. Under the Windows operating system, we can find the MySQL service in the service manager, right-click and select "Start"; under the Linux operating system, we can execute service mysql start on the command line to start the service.

2. Check the MySQL configuration file

If the MySQL service is already running and the port is not occupied, the problem may lie in the MySQL configuration file. By default, the MySQL configuration file is located in /etc/mysql/my.cnf or /etc/my.cnf. On Windows systems, it is located in the MySQL installation directory.

There may be many parameters that need to be configured in the MySQL configuration file. We need to check the following parameters:

1. bind-address: Bind IP address. We need to confirm whether it is set to "0.0.0.0". If it is set to "127.0.0.1", it can only be accessed locally, not in the LAN.
2. port: The port that the MySQL service listens on. The default port is port 3306. You can check whether the port is occupied. If it is occupied, you need to modify the port number.
3. skip-networking: If this parameter is "yes", it means that MySQL does not support network connections and must be changed to "no".

3. Check the firewall settings

If you have performed the above two steps and still cannot connect to the MySQL database, we need to consider whether the firewall is blocking the connection. Firewalls are important software for protecting computer security, but sometimes they can misjudge legitimate requests.

Under the Windows operating system, we can press the Win R key and enter control.exe firewall.cpl to open the firewall management panel and confirm whether MySQL is allowed.

Under the Linux operating system, we need to first check whether the iptables firewall settings are correct. You can use the command line to execute iptables -L -n to see which ports are allowed or prohibited to access. If the port is not allowed, you can execute the following command to open the port:

iptables -A INPUT -p tcp --dport 3306 -j ACCEPT

4. Check MySQL users and permissions

If the MySQL user and permission settings are incorrect, it may also result in the inability to connect to the database. We can view the MySQL user list through the following command:

mysql> select User from mysql.user;

If we find that there is no required user, we can execute the following command to create a user:

mysql> create user 'username'@'%' identified by 'password';

Among them, % indicates that the host address for user connection is not restricted, and any host can be used to connect to the MySQL database.

When the current user connects to the MySQL database, we can execute the following command to view the permissions of the current user:

mysql> show grants;

If the user does not have the permission to connect to the database, You can use the following command to grant the user connection permission:

mysql> grant all privileges on . to 'username'@'%';

The above command will give the user Permissions on all databases and all tables.

Summary:

There are many possible reasons for MySQL database connection failure, but no matter what the reason is, you need to prescribe the right medicine first and troubleshoot the problems one by one. By troubleshooting these issues, you'll most likely be able to successfully connect to your MySQL database eventually.

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