centos7.5下添加gd庫然後mysql拓展庫沒了，mysql拓展的配置也沒問題，phpinfo中就是沒有mysql拓展。
php -v 報錯如下：
PHP Warning: PHP Startup: Unable to load dynamic library '/usr/lib64/php/modules/mysqli.so'
PHP Warning: PHP Startup: Unable to load dynamic library '/usr/lib64/php/modules/pdo_mysql.so'
[root@VM_0_14_centos modules]# php -v
PHP Warning: PHP Startup: Unable to load dynamic library '/usr/lib64/php/modules/mysqli.so' - libmysqlclient.so.18: cannot open shared object file: No such file or directory in Unknown on line 0
Warning: PHP Startup: Unable to load dynamic library '/usr/lib64/php/modules/mysqli.so' - libmysqlclient.so.18: cannot open shared object file: No such file or directory in Unknown on line 0
PHP Warning: PHP Startup: Unable to load dynamic library '/usr/lib64/php/modules/pdo_mysql.so' - libmysqlclient.so.18: cannot open shared object file: No such file or directory in Unknown on line 0
Warning: PHP Startup: Unable to load dynamic library '/usr/lib64/php/modules/pdo_mysql.so' - libmysqlclient.so.18: cannot open shared object file: No such file or directory in Unknown on line 0
PHP 5.4.16 (cli) (built: Nov 1 2019 16:04:20)
Copyright (c) 1997-2013 The PHP Group
Zend Engine v2.4.0, Copyright (c) 1998-2013 Zend Technologies
如果msyqli.so 的配置都沒問題的情況，試下卸載mysqli.so拓展, 如：yum remove php-mysqli ;然後再重新裝php-mysqli ,
yum install -y php-mysqli
重啓php-fpm：
systemctl restart php-fpm
重啓nginx服務器：
systemctl restart nginx
php -v查看有沒有報錯
以上都是在centos7.5下的命令行操作的，其他系統類似。
再通過phpinfo.php 查看有沒有mysql拓展，有則問題解決。
好像是系統本身的bug。