Server System Variables • offline_mode •Connected client users who do not have the  CONNECTION_ADMIN  privilege (or the deprecated  SUPER privilege) are disconnected on the next request, with an appropriate error. Disconnection includes terminating running statements and releasing locks. Such clients also cannot initiate new connections, and receive an appropriate error. •Connected client users who have the  CONNECTION_ADMIN  or  SUPER  privilege are not disconnected, and can initiate new connections to manage the server. •Replication threads are permitted to keep applying data to the server. • old Only users who have the  SYSTEM_VARIABLES_ADMIN  or  SUPER  privilege can control offline mode. To put a server in offline mode, change the value of the  offline_mode  system variable from  OFF  to  ON . To resume normal operations, change  offline_mode  from  ON  to  OFF . In offline mode, clients that are refused access receive an  ER_SERVER_OFFLINE_MODE  error. old  is a compatibility variable. It is disabled by default, but can be enabled at startup to revert the server to behaviors present in older versions. When  old  is enabled, it changes the default scope of index hints to that used prior to MySQL 5.1.17. That is, index hints with no  FOR  clause apply only to how indexes are used for row retrieval and not to resolution of  ORDER BY  or  GROUP BY  clauses. (See Section 8.9.4, “Index Hints” .) Take care about enabling this in a replication setup. With statement-based binary logging, having different modes for the source and replicas might lead to replication errors. • old_alter_table Command-Line Format --offline-mode[={OFF|ON}] System Variable offline_mode Scope Global Dynamic Yes SET_VAR  Hint Applies No Type Boolean Default Value OFF Whether the server is in “offline mode” , which has these characteristics: Command-Line Format --old[={OFF|ON}] System Variable old Scope Global Dynamic No SET_VAR  Hint Applies No Type Boolean Default Value OFF Command-Line Format --old-alter-table[={OFF|ON}] System Variable old_alter_table 846