How to solve the problem that the database connection failed when logging in to the PHP system

In daily web development, if you use PHP, you often need to connect to the database, because a large amount of data needs to be stored in the database, and access usually needs to be controlled through a login interface. However, PHP connections to databases don't always run smoothly. The most common problem is "PHP System Login Shows Database Connection Failed" and this article will discuss how to determine the source of the problem and resolve it.

1. Check database login information

The most common reason for database connection failure is incorrect database login information. This may be caused by remembering the password, entering the wrong password, etc., so first check whether your database login information is correct. When using mysqli_connect() or PDO to connect to a database in PHP, you need to correctly specify the database address, user name, password and other information to ensure a successful connection.

2. Check the Database Service

If the database login information is correct and you are also using the same information to connect to other applications, the problem may be with the database service itself. In this case, it is best to check that the database service is running and is not blocked by the firewall. You can try to test whether the database is reachable through ping command, telnet, etc.

3. Check PHP Extensions

In addition to the above methods, you should also check if PHP has an extension to connect to the required database. Without the PHP extension, you cannot connect to the database. For example, if you want to connect to a MySQL database, you need to install the mysqli or pdo_mysql extension. If these extensions are missing, you will need to recompile PHP or install the missing extensions.

4. Check the MySQL test script

If you are using a MySQL database, you can try a simple test script to check if you can successfully connect to the database. For example, you can create a file named test.php with the following content:

<?php
$con = mysqli_connect("localhost","my_user","my_password","my_db");
if (mysqli_connect_errno())
  {
  echo "Failed to connect to MySQL: " . mysqli_connect_error();
  }
?>

Run this script and "Connected successfully" will be printed if the connection is successful; if the connection fails, an error message will be printed.

5. Check the error log

If you still cannot solve the "PHP system login shows database connection failure" problem, you need to check the error log of the server for more information . The error log is usually located in the /var/log directory and may have multiple log files, including error logs for Apache, PHP, and databases. Review these files for any error messages related to database connections and try to resolve the problem.

Summary

The above are several methods to solve "PHP system login shows database connection failure". First, you need to check the database login information, then check the database service, and confirm that the PHP extension required for the connection has been installed. , try using the MySQL test script, and finally check the error log. Using these methods, you should be able to quickly resolve database connection issues and implement PHP system login functionality.

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