1select @@global.pid_file; 2@@global.pid_file 3MYSQLTEST_VARDIR/run/mysqld.1.pid 4select @@session.pid_file; 5ERROR HY000: Variable 'pid_file' is a GLOBAL variable 6show global variables like 'pid_file'; 7Variable_name Value 8pid_file MYSQLTEST_VARDIR/run/mysqld.1.pid 9show session variables like 'pid_file'; 10Variable_name Value 11pid_file MYSQLTEST_VARDIR/run/mysqld.1.pid 12select * from information_schema.global_variables where variable_name='pid_file'; 13VARIABLE_NAME VARIABLE_VALUE 14PID_FILE MYSQLTEST_VARDIR/run/mysqld.1.pid 15select * from information_schema.session_variables where variable_name='pid_file'; 16VARIABLE_NAME VARIABLE_VALUE 17PID_FILE MYSQLTEST_VARDIR/run/mysqld.1.pid 18set global pid_file=1; 19ERROR HY000: Variable 'pid_file' is a read only variable 20set session pid_file=1; 21ERROR HY000: Variable 'pid_file' is a read only variable 22