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SET PERSIST  and SET PERSIST_ONLY  enable system variables to be persisted to the mysqld- auto.cnf  option file in the data directory (see Section 13.7.6.1, “SET Syntax for Variable Assignment” ). Persisting system variables enables runtime configuration changes that affect subsequent server restarts, which is convenient for remote administration not requiring direct access to MySQL server host option files. However, some system variables are nonpersistible or can be persisted only under certain restrictive conditions. 

The persist_only_admin_x509_subject  system variable specifies the SSL certificate X.509 Subject value that users must have to be able to persist system variables that are persist-restricted. The default value is the empty string, which disables the Subject check so that persist-restricted system variables cannot be persisted by any user. 

If persist_only_admin_x509_subject  is nonempty, users who connect to the server using an encrypted connection and supply an SSL certificate with the designated Subject value then can use SET PERSIST_ONLY  to persist persist-restricted system variables. For information about persist-restricted system variables and instructions for configuring MySQL to enable persist_only_admin_x509_subject , see Section 5.1.9.4, “Nonpersistible and Persist-Restricted System Variables” . 

• pid_file 

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The path name of the file in which the server writes its process ID. The server creates the file in the data directory unless an absolute path name is given to specify a different directory. If you specify this variable, you must specify a value. If you do not specify this variable, MySQL uses a default value of host_name .pid , where host_name  is the name of the host machine. 

The process ID file is used by other programs such as mysqld_safe  to determine the server’s process ID. On Windows, this variable also affects the default error log file name. See Section 5.4.2, “The Error Log” . 

• plugin_dir 

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