Start a session on the source by connecting to it with the command-line client, and flush all tables and block write statements by executing the FLUSH TABLES WITH READ LOCK statement:

mysql> FLUSH TABLES WITH READ LOCK;

In a different session on the source, use the SHOW BINARY LOG STATUS statement to determine the current binary log file name and position:

mysql> SHOW BINARY LOG STATUS\G
*************************** 1. row ***************************
             File: mysql-bin.000003
         Position: 73
     Binlog_Do_DB: test
 Binlog_Ignore_DB: manual, mysql
Executed_Gtid_Set: 3E11FA47-71CA-11E1-9E33-C80AA9429562:1-5
1 row in set (0.00 sec)

The File column shows the name of the log file and the Position column shows the position within the file. In this example, the binary log file is mysql-bin.000003 and the position is 73. Record these values. You need them later when you are setting up the replica. They represent the replication coordinates at which the replica should begin processing new updates from the source.

If the source has been running previously with binary logging disabled, the log file name and position values displayed by SHOW BINARY LOG STATUS or mysqldump --source-data are empty. In that case, the values that you need to use later when specifying the source's binary log file and position are the empty string ('') and 4.