我的服务器启用的nginx，配置了php的连接mysql的配置文件connect.php：

<?php$server="localhost";//主机$db_username="root";//你的数据库用户名$db_password="root";//你的数据库密码$dbname = "users";$conn = new mysqli($server,$db_username,$db_password);//链接数据库if($conn->connect_error){die("can't connect".$conn->connect_error);//如果链接失败输出错误}if (!mysqli_select_db($conn, 'users')) {die("选择数据库失败: " . mysqli_error($conn));}

其中一个页面include了这个文件，按理来说可以直接连接的，当然你需要在本地mysql建立这个users库和user表。

但是调试过程中 include函数并不起作用：    include('/var/www/html/phpTest/connect.php');

我们查看nginx的错误日志 cat /var/log/nginx/error.log：

下面这两个报错分别是两个不同的问题：

一、未加载php的mysqli文件

2024/10/16 15:58:08 [error] 370320#370320: *18 FastCGI sent in stderr: "PHP message: PHP Fatal error:  Uncaught Error: Class "mysqli" not found in /var/www/html/phpTest/connect.php:7
Stack trace:
#0 /var/www/html/phpTest/signup.php(32): include()
#1 {main}thrown in /var/www/html/phpTest/connect.php on line 7" while reading response header from upstream, client: 113.132.177.30, server: _, request: "POST /phpTest/signup.php HTTP/1.1", upstream: "fastcgi://unix:/run/php/php8.1-fpm.sock:", host: "116.205.127.142", referrer: "http://116.205.127.142/phpTest/signup.php"

这个是因为没有加载php的mysqli文件导致的，我们需要在服务器上下载：

sudo apt-get install php-mysqli
sudo apt-get install php8.1-mysqli //根据你的php版本选择msqli版本sudo systemctl restart php8.1-fpm  //重启fpm和nginx
sudo systemctl restart nginx

还需要确保php的配置文件php.ini中没有禁用mysqli，找到;extension=mysqli 去掉前面分号注释符，重启fpm。

二、本地数据库拒绝连接

2024/10/16 16:27:26 [error] 371624#371624: *10 FastCGI sent in stderr: "PHP message: PHP Fatal error:  Uncaught mysqli_sql_exception: Access denied for user 'root'@'localhost' in /var/www/html/phpTest/connect.php:7
Stack trace:
#0 /var/www/html/phpTest/connect.php(7): mysqli->__construct()
#1 /var/www/html/phpTest/signup.php(32): include('...')
#2 {main}thrown in /var/www/html/phpTest/connect.php on line 7" while reading response header from upstream, client: 113.132.177.30, server: _, request: "POST /phpTest/signup.php HTTP/1.1", upstream: "fastcgi://unix:/run/php/php8.1-fpm.sock:", host: "116.205.127.142", referrer: "http://116.205.127.142/phpTest/signup.php"

需要确认 root 用户是否有权限从 localhost 访问数据库。执行以下 MySQL 命令来查看权限：

登录成功后，检查用户权限：

SELECT host, user FROM mysql.user;

如果没有 root@localhost，或者 root 用户没有适当的权限，你可以通过以下命令为 root 赋予权限：

GRANT ALL PRIVILEGES ON *.* TO 'root'@'localhost' IDENTIFIED BY 'your_password';
FLUSH PRIVILEGES;

    确保 MySQL 配置文件 (/etc/mysql/my.cnf 或 /etc/mysql/mysql.conf.d/mysqld.cnf) 中允许本地连接：默认是开启的

bind-address = 127.0.0.1

修改完之后重启mysql即可

三、权限问题

确保root用户的权限

SELECT User, Host FROM mysql.user WHERE User = 'root';

mysql> SELECT User, Host FROM mysql.user WHERE User = 'root';
+------+-----------+
| User | Host      |
+------+-----------+
| root | localhost |
+------+-----------+
1 row in set (0.00 sec)

然后检查mysql认证插件：某些情况下，MySQL 可能使用了 auth_socket 插件，这会阻止使用密码登录。检查 root 是否使用 auth_socket 插件：

SELECT user, host, plugin FROM mysql.user WHERE user = 'root';

如果 plugin 显示为 auth_socket，修改为 mysql_native_password：

ALTER USER 'root'@'localhost' IDENTIFIED WITH mysql_native_password BY 'your_password';
FLUSH PRIVILEGES;

mysql> SELECT user, host, plugin FROM mysql.user WHERE user = 'root';
+------+-----------+-----------------------+
| user | host      | plugin                |
+------+-----------+-----------------------+
| root | localhost | mysql_native_password |
+------+-----------+-----------------------+
1 row in set (0.00 sec)

尤其是最后一步，如果不修改还是连不上的