Master-slave replication, adding slave servers
Three mysql servers. One is the master and one is the slave, realizing automatic backup. Add a new slave server
System: CentOS 7.6
mariadb: 5.5.60

Primary server:

[root@Centos7 ~]#vim /etc/my.cnf
[mysqld]
server_id=7     #Set server ID 
log_bin         #Open binary log

Start mysql, View binary location information, and create users that the slave server can use

[root@Centos7 ~]#systemctl start mariadb
[root@Centos7 ~]#mysql
MariaDB [(none)]> show master logs;
+--------------------+-----------+
| Log_name           | File_size |
+--------------------+-----------+
| mariadb-bin.000001 |      245 |
+--------------------+-----------+
1 row in set (0.00 sec)
MariaDB [(none)]> grant replication slave on *.* to repluser@'192.168.37.%' identified by 'centos';
Query OK, 0 rows affected (0.01 sec)

Master server setup complete

from server

[root@Centos7 ~]#vim /etc/my.cnf

[mysqld]
server_id=17   #Set server ID
read_only      #Recommended from server, read only

Configure synchronization information: use the user provided by the master service to copy the data from the master server to the local machine

[root@Centos7 ~]#mysql
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MariaDB [(none)]> CHANGE MASTER TO   
    -> MASTER_HOST='192.168.37.7',           #Primary server IP
    -> MASTER_USER='repluser',               #user
    -> MASTER_PASSWORD='centos',             #Password
    -> MASTER_PORT=3306,                     #port
    -> MASTER_LOG_FILE='mariadb-bin.000001', #Binary
    -> MASTER_LOG_POS=245;                   #Where to start copying
Query OK, 0 rows affected (0.03 sec)

MariaDB [(none)]> start slave;               #Start slave thread
MariaDB [(none)]> show slave status\G        #View state
*************************** 1. row ***************************
               Slave_IO_State: Waiting for master to send event
                  Master_Host: 192.168.37.7  #Primary server IP
                  Master_User: repluser      #Users used
                  Master_Port: 3306          #Use port
                Connect_Retry: 60
              Master_Log_File: mariadb-bin.000001
          Read_Master_Log_Pos: 400
               Relay_Log_File: mariadb-relay-bin.000002
                Relay_Log_Pos: 686
        Relay_Master_Log_File: mariadb-bin.000001
             Slave_IO_Running: Yes            #Synchronous success
            Slave_SQL_Running: Yes            #Synchronous success
        .
        .
        .
  Replicate_Ignore_Server_Ids: 
             Master_Server_Id: 7             #Primary server ID
1 row in set (0.00 sec)
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Test: add, delete and change data on the master server, and automatically synchronize data on the slave server

Add a slave server to the primary server with existing data

MariaDB [(none)]> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| hellodb            |
| mysql              |
| performance_schema |
| testdb1            |
| testdb2            |
| testdb3            |
+--------------------+
7 rows in set (0.00 sec)

Fully back up the data of the primary server, view the logging location of the primary server, and deliver it to the new secondary server

[root@Centos7 ~]#mysqldump -A --single-transaction -F --master-data=1 > /data/backup/all.sql
[root@Centos7 ~]#scp -r /data/backup/* 192.168.37.27:/data/
[root@Centos7 ~]#mysql
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MariaDB [(none)]> show master logs;
+--------------------+-----------+
| Log_name           | File_size |
+--------------------+-----------+
| mariadb-bin.000001 |      8436 |
| mariadb-bin.000002 |       245 |   #Sync from the latest location,
+--------------------+-----------+

New slave settings

[root@Centos7 ~]#vim /etc/my.cnf
[mysqld]
server_id=37
read_only
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Set the backup file delivered by the primary server, plus the synchronization information of the primary service

[root@Centos7 ~]#vim /data/all.sql
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CHANGE MASTER TO   
MASTER_HOST='192.168.36.7',
MASTER_USER='repluser',
MASTER_PASSWORD='centos',
MASTER_PORT=3306,
MASTER_LOG_FILE='mariadb-bin.000002', 
MASTER_LOG_POS=245; 
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Start the MySQL service, import the backed up data, enter mysql, and start the slave thread

[root@Centos7 ~]#systemctl start mariadb
[root@Centos7 ~]#mysql < /data/all.sql 
[root@Centos7 ~]#mysql
MariaDB [(none)]> start slave;  #Open thread
Query OK, 0 rows affected (0.02 sec)
MariaDB [(none)]> show slave status\G
*************************** 1. row ***************************
               Slave_IO_State: Waiting for master to send event
                  Master_Host: 192.168.37.7
                  Master_User: repluser
                  Master_Port: 3306
                Connect_Retry: 60
              Master_Log_File: mariadb-bin.000002
          Read_Master_Log_Pos: 245
               Relay_Log_File: mariadb-relay-bin.000002
                Relay_Log_Pos: 531
        Relay_Master_Log_File: mariadb-bin.000002
             Slave_IO_Running: Yes   #Success
            Slave_SQL_Running: Yes   #Success
                            .
                            .
                            .
             Master_Server_Id: 7
1 row in set (0.00 sec)

Test to add, delete and modify data on the main server to see if it can be automatically synchronized