Using System Variables SET @@PERSIST_ONLY.back_log = 1000; RESET PERSIST; RESET PERSIST  system_var_name ; RESET PERSIST IF EXISTS  system_var_name ; Like  PERSIST ,  PERSIST_ONLY  writes the variable setting to  mysqld-auto.cnf . However, unlike  PERSIST ,  PERSIST_ONLY  does not modify the global variable runtime value. This makes PERSIST_ONLY  suitable for configuring read-only system variables that can be set only at server startup. For more information about  SET , see Section 13.7.6.1, “SET Syntax for Variable Assignment” . These  RESET PERSIST  syntax options are available for removing persisted system variables: This includes plugin system variables, even if the plugin is not currently installed. If the variable is not present in the file, an error occurs. For more information about  RESET PERSIST , see Section 13.7.8.7, “RESET PERSIST Statement” . Using  SET  to persist a global system variable to a value of  DEFAULT  or to its literal default value assigns the variable its default value and adds a setting for the variable to  mysqld-auto.cnf . To remove the variable from the file, use  RESET PERSIST . Some system variables cannot be persisted. See Section 5.1.9.4, “Nonpersistible and Persist-Restricted System Variables” . A system variable implemented by a plugin can be persisted if the plugin is installed when the  SET statement is executed. Assignment of the persisted plugin variable takes effect for subsequent server restarts if the plugin is still installed. If the plugin is no longer installed, the plugin variable does not exist when the server reads the  mysqld-auto.cnf  file. In this case, the server writes a warning to the error log and continues: The Performance Schema  persisted_variables  table provides an SQL interface to the  mysqld- auto.cnf  file, enabling its contents to be inspected at runtime using  SELECT  statements. See Section 27.12.14.1, “Performance Schema persisted_variables Table” . The Performance Schema  variables_info  table contains information showing when and by which user each system variable was most recently set. See Section 27.12.14.2, “Performance Schema variables_info Table” . RESET PERSIST  affects the contents of the  persisted_variables  table because the table contents correspond to the contents of the  mysqld-auto.cnf  file. On the other hand, because  RESET PERSIST 940 Obtaining Information About Persisted System Variables currently unknown variable ’ var_name ’ was read from the persisted config file •To remove a specific persisted variable from  mysqld-auto.cnf , but produce a warning rather than an error if the variable is not present in the file, add an  IF EXISTS  clause to the previous syntax: •To remove a specific persisted variable from  mysqld-auto.cnf , name it in the statement: •To remove all persisted variables from  mysqld-auto.cnf , use  RESET PERSIST  without naming any system variable: