实验前的注意：
如果要启用级联复制,需要在从服务器启用以下配置；
[mysqld]
log_bin
log_slave_updates
log_slave_updates的作用：
因为默认从主服务器过来的二进制日志保存在从服务器的中继日志；并应用到本地数据库；
但是中间这个从服务器是即便是开启二进制日志的记录功能，他也是不记录到本地的二进制日志，
那么也就不能将对数据库的操作再传输到从的从服务器上去。当log_slave_updates启用后，
从服务器也就能将对主服务器的二进制日志在本地执行后，也记录到自己的二进制日志中；
删除数据库就可以干净做实验；
[root@master ~]$systemctl stop mariadb
[root@master ~]$rm -fr /var/lib/mysql/*
[root@master ~]$systemctl start mariadb主、从、二级从服务器的配置：
[root@master ~]$cat /etc/my.cnf
[mysqld]
datadir=/var/lib/mysql
socket=/var/lib/mysql/mysql.sock
# Disabling symbolic-links is recommended to prevent assorted security risks
symbolic-links=0
innodb_file_per_table
log_bin
server-id=1
[root@slave ~]$cat /etc/my.cnf
[mysqld]
datadir=/var/lib/mysql
socket=/var/lib/mysql/mysql.sock
# Disabling symbolic-links is recommended to prevent assorted security risks
symbolic-links=0
# Settings user and group are ignored when systemd is used.
innodb_file_per_table
server_id=2
read_only
log_bin
log_slave_updates
[root@slave2 ~]$cat /etc/my.cnf
[mysqld]
datadir=/var/lib/mysql
socket=/var/lib/mysql/mysql.sock
# Disabling symbolic-links is recommended to prevent assorted security risks
symbolic-links=0
server_id=3主服务器和从服务器实现主从复制，配置和授权：
主服务器：
MariaDB [(none)]> grant replication slave on *.* to repluser@'192.168.27.%' identified by 'centos';
Query OK, 0 rows affected (0.00 sec)
MariaDB [(none)]> show master logs;
+--------------------+-----------+
| Log_name | File_size |
+--------------------+-----------+
| mariadb-bin.000001 | 264 |
| mariadb-bin.000002 | 401 |
+--------------------+-----------+
2 rows in set (0.00 sec)
中间的从服务器：
CHANGE MASTER TO
MASTER_HOST='192.168.27.7',
MASTER_USER='repluser',
MASTER_PASSWORD='centos',
MASTER_LOG_FILE='mariadb-bin.000001',
MASTER_LOG_POS=245;
MariaDB [(none)]> CHANGE MASTER TO
-> MASTER_HOST='192.168.27.7',
-> MASTER_USER='repluser',
-> MASTER_PASSWORD='centos',
-> MASTER_LOG_FILE='mariadb-bin.000001',
-> MASTER_LOG_POS=245;
Query OK, 0 rows affected (0.02 sec)
MariaDB [(none)]> start slave;
Query OK, 0 rows affected (0.00 sec)
MariaDB [(none)]> show slave status\G
*************************** 1. row ***************************
Slave_IO_State: Waiting for master to send event
Master_Host: 192.168.27.7
Master_User: repluser
Master_Port: 3306
Connect_Retry: 60
Master_Log_File: mariadb-bin.000002
Read_Master_Log_Pos: 401
Relay_Log_File: mariadb-relay-bin.000003
Relay_Log_Pos: 687
Relay_Master_Log_File: mariadb-bin.000002
Slave_IO_Running: Yes
Slave_SQL_Running: Yes
Exec_Master_Log_Pos: 401
Relay_Log_Space: 1269
Until_Condition: None
Until_Log_File:
Until_Log_Pos: 0
Master_SSL_Allowed: No
Master_SSL_CA_File:
Master_SSL_CA_Path:
Master_SSL_Cert:
Master_SSL_Cipher:
Master_SSL_Key:
Seconds_Behind_Master: 0
MariaDB [(none)]> select user from mysql.user;
+----------+
| user |
+----------+
| root |
| repluser |
| root |
| |
| root |
| |
| root |
+----------+
7 rows in set (0.00 sec)
MariaDB [(none)]> show master logs;
+--------------------+-----------+
| Log_name | File_size |
+--------------------+-----------+
| mariadb-bin.000001 | 401 |
+--------------------+-----------+
1 row in set (0.00 sec)二级从服务器上的配置：
在从的从服务器上执行：
[mysqld]
innodb_file_per_table
read-only
server-id=3
CHANGE MASTER TO
MASTER_HOST='192.168.27.17',
MASTER_USER='repluser',
MASTER_PASSWORD='centos',
MASTER_LOG_FILE='mariadb-bin.000001',
MASTER_LOG_POS=401;
