SET @old_log_timestamps     = @@global.log_timestamps;

# log_timestamps -- values UTC|SYSTEM
SET GLOBAL  log_timestamps=UTC;
SELECT      @@global.log_timestamps;
SET GLOBAL  log_timestamps=SYSTEM;
SELECT      @@global.log_timestamps;

# sess var
--error ER_GLOBAL_VARIABLE
SET SESSION log_timestamps=UTC;

# wrong value
--error ER_WRONG_VALUE_FOR_VAR
SET GLOBAL  log_timestamps=ON;
--error ER_WRONG_VALUE_FOR_VAR
SET GLOBAL  log_timestamps=2;


# log_timestamps -- default UTC
SET GLOBAL  log_timestamps=DEFAULT;
SELECT      @@global.log_timestamps;

SET GLOBAL log_timestamps      = @old_log_timestamps;