Authentication Plugin ‘***’ Cannot Be Loaded: MySQL如何检查client端插件的

当MySQL客户端连接到MySQL Server，会使用到身份验证插件。在Server端，根据选项plugin-dir的设置加载插件到目录下，默认是$base/lib/plugin。

然后，在客户端也要加载身份验证插件。用户客户化安装的mysql，在尝试连接的时候会遇到错误，需要使用单独的client library。

比如，来设置一下使用测试验证插件进行用户认证。

mysql> INSTALL PLUGIN test_plugin_server SONAME 'auth_test_plugin.so';         
Query OK, 0 rows affected (0,01 sec)
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mysql> CREATE USER 'sveta'@'%' IDENTIFIED WITH test_plugin_server;
Query OK, 0 rows affected (0,01 sec)

不使用--plugin-dir选项，直接使用mysql客户端连接数据库会报错：

$ mysql -usveta
ERROR 2059 (HY000): Authentication plugin 'auth_test_plugin' cannot be loaded: /usr/local/Percona-Server-8.0.25-15-Linux.x86_64.glibc2.17/lib/plugin/auth_test_plugin.so: cannot open shared object file: No such file or directory

为了避免这个错误，需要指定--plugin-dir(在参数文件中、或命令行)：

$ mysql -usveta --plugin-dir=/home/sveta/mysqlpackages/Percona-Server-8.0.25-15-Linux.x86_64.glibc2.17/lib/plugin
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 28
Server version: 8.0.25-15 Percona Server (GPL), Release 15, Revision a558ec2
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Copyright (c) 2009-2021 Percona LLC and/or its affiliates
Copyright (c) 2000, 2021, Oracle and/or its affiliates.
​
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
​
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
​
mysql> \q
Bye

包含PAM authentication plugin在内，所有的plugins都要求客户端加载一个外部库。否则会报错：

 ERROR 2059 (HY000): Authentication plugin 'dialog' cannot be loaded: /usr/local/Percona-Server-8.0.25-15-Linux.x86_64.glibc2.17/lib/plugin/dialog.so: cannot open shared object file: No such file or directory

Oracle兼容的auth_pam_compat插件没有遇到这个问题，因为它使用了内嵌的mysql_clear_password，而不是dialog.so插件