主從複製結構、半同步複製、雙主複製結構、利用SSL實現安全的MySQL主從複製
一、主從複製結構實驗
1.主服務器配置
可以先更改server_id
在/etc/my.cnf文件中，添加
server_id=11
重啓服務，在mysql命令行查看
MariaDB [(none)]> select @@server_id;
+-------------+
| @@server_id |
+-------------+
| 11 |
+-------------+
1 row in set (0.00 sec)
授權從服務器
MariaDB [(none)]> grant replication slave,replication client on . to 'repluser'@'172.16.1.10'identified by 'replpass';
Query OK, 0 rows affected (0.00 sec)
刷新
MariaDB [(none)]> flush privileges;
Query OK, 0 rows affected (0.00 sec)
2.從服務器配置
在[mysqld]段落添加
server_id=22
relay_log=/var/log/mariadb/relay-log
skip_name_resolve=ON
innodb_file_per_table=ON
重啓服務，在mysql命令行查看
MariaDB [(none)]> select @@server_id;
+-------------+
| @@server_id |
+-------------+
| 22 |
+-------------+
1 row in set (0.00 sec)
指定主服務器
MariaDB [(none)]> change master to master_host='172.16.1.4',master_user='repluser',master_password='replpass',master_log_file='binlog.000001',master_log_pos=245;
查看相關信息
MariaDB [(none)]> show slave status\G;
開啓io線程
MariaDB [(none)]> start slave io_thread;
開啓sql線程
MariaDB [(none)]> start slave sql_thread;
於是就可以在主服務器上插入信息，在從服務器上看到了。
二、半同步複製結構實驗
從MySQL5.5開始，MySQL以插件的形式支持半同步複製。如何理解半同步呢？首先我們來看看異步，全同步的概念
異步複製（Asynchronous replication）
MySQL默認的複製即是異步的，主庫在執行完客戶端提交的事務後會立即將結果返給給客戶端，並不關心從庫是否已經接收並處理，這樣就會有一個問題，主如果crash掉了，此時主上已經提交的事務可能並沒有傳到從上，如果此時，強行將從提升爲主，可能導致新主上的數據不完整。
全同步複製（Fully synchronous replication）
指當主庫執行完一個事務，所有的從庫都執行了該事務才返回給客戶端。因爲需要等待所有從庫執行完該事務才能返回，所以全同步複製的性能必然會收到嚴重的影響。
半同步複製（Semisynchronous replication）
介於異步複製和全同步複製之間，主庫在執行完客戶端提交的事務後不是立刻返回給客戶端，而是等待至少一個從庫接收到並寫到relay log中才返回給客戶端。相對於異步複製，半同步複製提高了數據的安全性，同時它也造成了一定程度的延遲，這個延遲最少是一個TCP/IP往返的時間。所以，半同步複製最好在低延時的網絡中使用。
在主從複製搭建的基礎上，做配置修改
1.主服務器：配置文件
[root@zrs6 ~]# vim /etc/my.cnf
server_id=11
relay_log=/var/log/mariadb/relay-log
skip_name_resolve=ON
innodb_file_per_table=ON
log_bin=/var/log/mariadb/binlog
重啓
[root@zrs6 ~]# systemctl restart mariadb
安裝插件
MariaDB [(none)]> install plugin rpl_semi_sync_master soname 'semisync_master';
查看相應變量
MariaDB [(none)]> show global variables like '%rpl_semi%';
+------------------------------------+-------+
| Variable_name | Value |
+------------------------------------+-------+
| rpl_semi_sync_master_enabled | OFF |
| rpl_semi_sync_master_timeout | 10000 |
| rpl_semi_sync_master_trace_level | 32 |
| rpl_semi_sync_master_wait_no_slave | ON |
+------------------------------------+-------+
查看半同步的狀態
MariaDB [(none)]> show global status like '%rpl_semi%';
+--------------------------------------------+-------+
| Variable_name | Value |
+--------------------------------------------+-------+
| Rpl_semi_sync_master_clients | 0 |
| Rpl_semi_sync_master_net_avg_wait_time | 0 |
| Rpl_semi_sync_master_net_wait_time | 0 |
| Rpl_semi_sync_master_net_waits | 0 |
| Rpl_semi_sync_master_no_times | 0 |
| Rpl_semi_sync_master_no_tx | 0 |
| Rpl_semi_sync_master_status | OFF |
| Rpl_semi_sync_master_timefunc_failures | 0 |
| Rpl_semi_sync_master_tx_avg_wait_time | 0 |
| Rpl_semi_sync_master_tx_wait_time | 0 |
| Rpl_semi_sync_master_tx_waits | 0 |
| Rpl_semi_sync_master_wait_pos_backtraverse | 0 |
| Rpl_semi_sync_master_wait_sessions | 0 |
| Rpl_semi_sync_master_yes_tx | 0 |
+--------------------------------------------+-------+
開啓半同步複製
MariaDB [(none)]> set @@global.rpl_semi_sync_master_enabled=ON;
2.從服務器：配置文件
[root@zrs5 ~]# vim /etc/my.cnf
server_id=22
relay_log=/var/log/mariadb/relay-log
skip_name_resolve=ON
innodb_file_per_table=ON
log_bin=/var/log/mariadb/bin-log
重啓
[root@zrs5 ~]# systemctl restart mariadb
安裝插件
MariaDB [(none)]> install plugin rpl_semi_sync_slave soname 'semisync_slave.so';
查看相應變量
MariaDB [(none)]> show global variables like '%rpl_semi%';
+---------------------------------+-------+
| Variable_name | Value |
+---------------------------------+-------+
| rpl_semi_sync_slave_enabled | OFF |
| rpl_semi_sync_slave_trace_level | 32 |
+---------------------------------+-------+
開啓半同步
MariaDB [(none)]> set @@global.rpl_semi_sync_slave_enabled=ON;
3.查看主服務器的狀態
MariaDB [(none)]> show global status like '%rpl_semi%';
+--------------------------------------------+-------+
| Variable_name | Value |
+--------------------------------------------+-------+
| Rpl_semi_sync_master_clients | 1 |
| Rpl_semi_sync_master_net_avg_wait_time | 0 |
| Rpl_semi_sync_master_net_wait_time | 0 |
| Rpl_semi_sync_master_net_waits | 0 |
| Rpl_semi_sync_master_no_times | 0 |
| Rpl_semi_sync_master_no_tx | 0 |
| Rpl_semi_sync_master_status | ON |
| Rpl_semi_sync_master_timefunc_failures | 0 |
| Rpl_semi_sync_master_tx_avg_wait_time | 0 |
| Rpl_semi_sync_master_tx_wait_time | 0 |
| Rpl_semi_sync_master_tx_waits | 0 |
| Rpl_semi_sync_master_wait_pos_backtraverse | 0 |
| Rpl_semi_sync_master_wait_sessions | 0 |
| Rpl_semi_sync_master_yes_tx | 0 |
+--------------------------------------------+-------+
4.當在主服務器添加數據時
MariaDB [(none)]> use zrs05;
MariaDB [zrs05]> insert into tb1 (Username,Age) values ('Zhang san',30),('Li si',27);
MariaDB [zrs05]> select * from tb1;
+-----+-----------+------+
| UID | Username | Age |
+-----+-----------+------+
| 1 | Zhang san | 30 |
| 2 | Li si | 27 |
+-----+-----------+------+
在從服務器查看，數據已經同步了。
MariaDB [(none)]> use zrs05;
MariaDB [zrs05]> select * from tb1;
+-----+-----------+------+
| UID | Username | Age |
+-----+-----------+------+
| 1 | Zhang san | 30 |
| 2 | Li si | 27 |
+-----+-----------+------+
5.驗證半同步
需要在從服務器上先停止slave io_thread
MariaDB [zrs05]> stop slave io_thread;
當在主服務器上再次插入一條信息的時候，可以看到並不能立即插入成功，過了十秒鐘後，才成功，主服務器被阻塞一段時間，說明半同步複製已經正常工作。
MariaDB [zrs05]> insert into tb1 (Username,Age) values ('Wang wu',33);
Query OK, 1 row affected (10.01 sec)
在從服務器上查看，並沒有剛纔插入的信息
MariaDB [zrs05]> select * from tb1;
+-----+-----------+------+
| UID | Username | Age |
+-----+-----------+------+
| 1 | Zhang san | 30 |
| 2 | Li si | 27 |
+-----+-----------+------+
當開啓slave io_thread後，那條信息就出現了
MariaDB [zrs05]> start slave io_thread;
MariaDB [zrs05]> select * from tb1;
+-----+-----------+------+
| UID | Username | Age |
+-----+-----------+------+
| 1 | Zhang san | 30 |
| 2 | Li si | 27 |
| 3 | Wang wu | 33 |
+-----+-----------+------+
三、主主複製模型實驗
1.兩臺服務器的配置文件
Server1：/etc/my.cnf
[mysqld]
innodb-file-per-table = ON
skip-name-resolve=ON
log_bin=/var/log/mariadb/binlog
server_id=11
relay_log=/var/log/mariadb/relaylog
auto_increment_offset=1
auto_increment_increment=2
Server2：/etc/my.cnf
[mysqld]
innodb-file-per-table = ON
skip-name-resolve=ON
log_bin=/var/log/mariadb/binlog
server_id=22
relay_log=/var/log/mariadb/relaylog
auto_increment_offset=2
auto_increment_increment=2
2.兩臺服務器的SQL語句
Server1：
mysql> grant replication slave,replication client on . to 'repluser'@'172.16.1.3' identified by 'replpass';
mysql> change master to master_host='172.16.1.3',master_user='repluser',master_password='replpass',master_log_file='bin-log.000001',master_log_pos=427;
mysql> start slave [io_thread|sql_thread];
Server2：
mysql> grant replication slave,replication client on . to 'repluser'@'172.16.1.2' identified by 'replpass';
mysql> change master to master_host='172.16.1.2',master_user='repluser',master_password='replpass',master_log_file='bin-log.000024',master_log_pos=245;
mysql> start slave [io_thread|sql_thread];
四、利用SSL實現安全的MySQL主從複製
MySQL的主從複製是直接利用明文傳輸的，如果我們在生產環境下，跨網絡傳輸會非常不安全，所以就需要基於SSL加密傳輸，提高安全性。
1.修改配置文件
在Master上：
vim /etc/my.cnf
[mysqld]
log-bin=master-bin
binlog_format=mixed
server-id=1
ssl
[root@zj07 ~]# systemctl restart mariadb
在Slave上：
vim /etc/my.cnf
[mysqld]
log-bin=slave-bin
binlog_format=mixed
server-id=10
ssl
[root@zj08 ~]# systemctl restart mariadb
2.將master服務器自己做成CA服務器
[root@zj07 ~]# cd /etc/pki/CA/
[root@zj07 CA]# (umask 077;openssl genrsa -out private/cakey.pem 2048)
Generating RSA private key, 2048 bit long modulus
...........+++
................................................................+++
e is 65537 (0x10001)
[root@zj07 CA]#
[root@zj07 CA]# openssl req -new -x509 -key private/cakey.pem -out cacert.pem -days 365
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
Country Name (2 letter code) [XX]:CN
State or Province Name (full name) []:HeBei
Locality Name (eg, city) [Default City]:QinHuangdao
Organization Name (eg, company) [Default Company Ltd]:zrs.com
Organizational Unit Name (eg, section) []:tech
Common Name (eg, your name or your server's hostname) []:master.zrs.com
Email Address []:
[root@zj07 CA]# touch index.txt
[root@zj07 CA]# echo 01 > serial
3.爲master創建證書申請並由CA服務器簽發證書
[root@zj07 CA]# mkdir -pv /usr/local/mysql/ssl
mkdir: 已創建目錄 "/usr/local/mysql"
mkdir: 已創建目錄 "/usr/local/mysql/ssl"
[root@zj07 CA]#
[root@zj07 CA]# cd /usr/local/mysql/ssl/
[root@zj07 ssl]# (umask 077;openssl genrsa -out master.key 2048)
Generating RSA private key, 2048 bit long modulus
...........................................................................................................................................+++
..............+++
e is 65537 (0x10001)
[root@zj07 ssl]# openssl req -new -key master.key -out master.csr -days 365
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
Country Name (2 letter code) [XX]:CN
State or Province Name (full name) []:HeBei
Locality Name (eg, city) [Default City]:QinHuangdao
Organization Name (eg, company) [Default Company Ltd]:zrs.com
Organizational Unit Name (eg, section) []:tech
Common Name (eg, your name or your server's hostname) []:master.zrs.com
Email Address []:
Please enter the following 'extra' attributes
to be sent with your certificate request
A challenge password []:
An optional company name []:
[root@zj07 ssl]#
[root@zj07 ssl]# openssl ca -in master.csr -out master.crt -days 365
Using configuration from /etc/pki/tls/openssl.cnf
Check that the request matches the signature
Signature ok
Certificate Details:
Serial Number: 1 (0x1)
Validity
Not Before: Jan 15 13:35:39 2018 GMT
Not After : Jan 15 13:35:39 2019 GMT
Subject:
countryName = CN
stateOrProvinceName = HeBei
organizationName = zrs.com
organizationalUnitName = tech
commonName = master.zrs.com
X509v3 extensions:
X509v3 Basic Constraints:
CA:FALSE
Netscape Comment:
OpenSSL Generated Certificate
X509v3 Subject Key Identifier:
31:F0:A8:85:CD:6C:29:EF:3A:70:E6:C8:BB:5F:B4:04:61:32:86:48
X509v3 Authority Key Identifier:
keyid:66:56:36:59:90:6D:94:DC:4E:19:A3:BA:2C:1E:53:DC:1A:8A:58:AECertificate is to be certified until Jan 15 13:35:39 2019 GMT (365 days)
Sign the certificate? [y/n]:y
1 out of 1 certificate requests certified, commit? [y/n]y
Write out database with 1 new entries
Data Base Updated
[root@zj07 ssl]#
4.爲slave服務器創建證書申請
[root@zrs08 ~]# mkdir -pv /usr/local/mysql/ssl
mkdir: 已創建目錄 "/usr/local/mysql"
mkdir: 已創建目錄 "/usr/local/mysql/ssl"
[root@zrs08 ~]# cd /usr/local/mysql/ssl/
[root@zrs08 ssl]# (umask 077;openssl genrsa -out slave.key 2048)
Generating RSA private key, 2048 bit long modulus
....+++
...................................................................................................+++
e is 65537 (0x10001)
[root@zrs08 ssl]# openssl req -new -key slave.key -out slave.csr -days 365
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
Country Name (2 letter code) [XX]:CN
State or Province Name (full name) []:HeBei
Locality Name (eg, city) [Default City]:QinHuangdao
Organization Name (eg, company) [Default Company Ltd]:zrs.com
Organizational Unit Name (eg, section) []:tech
Common Name (eg, your name or your server's hostname) []:slave.zrs.com
Email Address []:
Please enter the following 'extra' attributes
to be sent with your certificate request
A challenge password []:
An optional company name []:
[root@zrs08 ssl]#
5.爲slave服務器簽署證書
將證書申請請求拷貝到CA服務器簽署
在slave上
[root@zrs08 ssl]# scp slave.csr 172.16.1.7:/tmp/
在master上
[root@zj07 ssl]# openssl ca -in /tmp/slave.csr -out /tmp/slave.crt -days 365
Using configuration from /etc/pki/tls/openssl.cnf
Check that the request matches the signature
Signature ok
Certificate Details:
Serial Number: 2 (0x2)
Validity
Not Before: Jan 15 13:41:19 2018 GMT
Not After : Jan 15 13:41:19 2019 GMT
Subject:
countryName = CN
stateOrProvinceName = HeBei
organizationName = zrs.com
organizationalUnitName = tech
commonName = slave.zrs.com
X509v3 extensions:
X509v3 Basic Constraints:
CA:FALSE
Netscape Comment:
OpenSSL Generated Certificate
X509v3 Subject Key Identifier:
90:B1:B5:44:92:99:24:4A:50:A7:AB:3F:36:B9:CD:C7:87:1E:CE:4A
X509v3 Authority Key Identifier:
keyid:66:56:36:59:90:6D:94:DC:4E:19:A3:BA:2C:1E:53:DC:1A:8A:58:AECertificate is to be certified until Jan 15 13:41:19 2019 GMT (365 days)
Sign the certificate? [y/n]:y
1 out of 1 certificate requests certified, commit? [y/n]y
Write out database with 1 new entries
Data Base Updated
6.簽署好證書申請拷貝到slave服務器
[root@zj07 ssl]# scp /tmp/slave.crt 172.16.1.8:/usr/local/mysql/ssl
7.將CA證書拷貝到slave服務器一份併爲master拷貝一份
[root@zj07 ssl]# scp /etc/pki/CA/cacert.pem 172.16.1.8:/usr/local/mysql/ssl/
[root@zj07 ssl]# cp /etc/pki/CA/cacert.pem /usr/local/mysql/ssl/
8.修改master和slave服務器證書屬主、屬組爲"mysql"用戶
在master上
[root@zj07 ssl]# chown -R mysql.mysql /usr/local/mysql/ssl/
[root@zj07 ssl]# ll /usr/local/mysql/ssl/
總用量 20
-rw-r--r--. 1 mysql mysql 1334 1月 15 21:45 cacert.pem
-rw-r--r--. 1 mysql mysql 4471 1月 15 21:36 master.crt
-rw-r--r--. 1 mysql mysql 1013 1月 15 21:34 master.csr
-rw-------. 1 mysql mysql 1679 1月 15 21:33 master.key
在slave上
[root@zrs08 ssl]# chown -R mysql.mysql /usr/local/mysql/ssl/
[root@zrs08 ssl]# ll /usr/local/mysql/ssl/
總用量 20
-rw-r--r--. 1 mysql mysql 1334 1月 15 21:45 cacert.pem
-rw-r--r--. 1 mysql mysql 4466 1月 15 21:43 slave.crt
-rw-r--r--. 1 mysql mysql 1009 1月 15 21:38 slave.csr
-rw-------. 1 mysql mysql 1679 1月 15 21:37 slave.key
9.在master與slave服務器修改主配置文件開啓SSL加密功能
修改master數據庫配置文件
[root@zj07 ssl]# vim /etc/my.cnf
ssl_ca=/usr/local/mysql/ssl/cacert.pem
ssl_cert=/usr/local/mysql/ssl/master.crt
ssl_key=/usr/local/mysql/ssl/master.key
[root@zj07 ssl]# systemctl restart mariadb
修改slave數據庫配置文件
[root@zrs08 ssl]# vim /etc/my.cnf
ssl_ca=/usr/local/mysql/ssl/cacert.pem
ssl_cert=/usr/local/mysql/ssl/slave.crt
ssl_key=/usr/local/mysql/ssl/slave.key
[root@zrs08 ssl]# systemctl restart mariadb
10.在master服務器查看SSL加密是否開啓，然後創建授權一個基於密鑰認證的用戶
MariaDB [(none)]> show variables like '%ssl%';
+---------------+---------------------------------+
| Variable_name | Value |
+---------------+---------------------------------+
| have_openssl | YES |
| have_ssl | YES |
| ssl_ca | /usr/local/mysql/ssl/cacert.pem |
| ssl_capath | |
| ssl_cert | /usr/local/mysql/ssl/master.crt |
| ssl_cipher | |
| ssl_key | /usr/local/mysql/ssl/master.key |
+---------------+---------------------------------+
MariaDB [(none)]> grant replication client,replication slave on . to 'slave'@'172.16.1.8' identified by '12345678' require ssl;
MariaDB [(none)]> flush privileges;
11.查看master服務器二進制日誌文件和事件位置用於的slave服務器鏈接從這個位置開始複製
MariaDB [(none)]> show master status;
+-------------------+----------+--------------+------------------+
| File | Position | Binlog_Do_DB | Binlog_Ignore_DB |
+-------------------+----------+--------------+------------------+
| master-bin.000002 | 502 | | |
+-------------------+----------+--------------+------------------+
12.測試使用加密用戶指定的密鑰鏈接服務器
在slave上
[root@zrs08 ~]# mysql -uroot -p12345678 -h 172.16.1.7 --ssl-ca=/usr/local/mysql/ssl/cacert.pem --ssl-cert=/usr/local/mysql/ssl/slave.crt --ssl-key=/usr/local/mysql/ssl/slave.key
Welcome to the MariaDB monitor. Commands end with ; or \g.
Your MariaDB connection id is 41
Server version: 5.5.56-MariaDB MariaDB Server
Copyright (c) 2000, 2017, Oracle, MariaDB Corporation Ab and others.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
MariaDB [(none)]>
13.查看slave服務器SSL是否開啓並連接master服務器
查看是否開啓SSL
MariaDB [(none)]> show variables like '%ssl%';
+---------------+---------------------------------+
| Variable_name | Value |
+---------------+---------------------------------+
| have_openssl | YES |
| have_ssl | YES |
| ssl_ca | /usr/local/mysql/ssl/cacert.pem |
| ssl_capath | |
| ssl_cert | /usr/local/mysql/ssl/master.crt |
| ssl_cipher | |
| ssl_key | /usr/local/mysql/ssl/master.key |
+---------------+---------------------------------+
鏈接master服務器
MariaDB [(none)]> change master to
-> master_host='172.16.1.7',master_user='slave',master_password='12345678',
-> master_log_file='master-bin.000002',master_log_pos=502,master_ssl=1,
-> master_ssl_ca='/usr/local/mysql/ssl/cacert.pem',
-> master_ssl_cert='/usr/local/mysql/ssl/slave.crt',
-> master_ssl_key='/usr/local/mysql/ssl/slave.key';Query OK, 0 rows affected (0.04 sec)
幫助文檔
MariaDB [(none)]> help change master to;
| MASTER_SSL = {0|1} #是否使用SSL功能
| MASTER_SSL_CA = 'ca_file_name' #CA證書位置
| MASTER_SSL_CERT = 'cert_file_name' #指定自己的證書文件
| MASTER_SSL_KEY = 'key_file_name' #指定自己的密鑰文件
14.查看slave服務器的狀態
MariaDB [(none)]> start slave;
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: 172.16.1.7
Master_User: slave
Master_Port: 3306
Connect_Retry: 60
Master_Log_File: master-bin.000002
Read_Master_Log_Pos: 2028
Relay_Log_File: mariadb-relay-bin.000002
Relay_Log_Pos: 2056
Relay_Master_Log_File: master-bin.000002
Slave_IO_Running: Yes
Slave_SQL_Running: Yes
Replicate_Do_DB:
Replicate_Ignore_DB:
Replicate_Do_Table:
Replicate_Ignore_Table:
Replicate_Wild_Do_Table: Replicate_Wild_Ignore_Table:
Last_Errno: 0
Last_Error:
Skip_Counter: 0
Exec_Master_Log_Pos: 2028
Relay_Log_Space: 2352
Until_Condition: None
Until_Log_File:
Until_Log_Pos: 0
Master_SSL_Allowed: Yes
Master_SSL_CA_File: /usr/local/mysql/ssl/cacert.pem
Master_SSL_CA_Path:
Master_SSL_Cert: /usr/local/mysql/ssl/slave.crt
Master_SSL_Cipher:
Master_SSL_Key: /usr/local/mysql/ssl/slave.key
Seconds_Behind_Master: 0Master_SSL_Verify_Server_Cert: No
Last_IO_Errno: 0
Last_IO_Error:
Last_SQL_Errno: 0
Last_SQL_Error: Replicate_Ignore_Server_Ids:
Master_Server_Id: 11 row in set (0.00 sec)
15.利用SSL實現安全的MySQL主從複製
在master服務器上創建數據庫
[root@zj07 ~]# mysql -uroot -p12345678 -e 'create database this_is_a_test_db;'
[root@zj07 ~]# mysql -uroot -p12345678 -e 'show databases';
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| performance_schema |
| this_is_a_test_db |
+--------------------+
登錄slave服務器驗證slave數據庫是否存在
[root@zrs08 ~]# mysql -uroot -p12345678 -e 'show databases';
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| performance_schema |
| this_is_a_test_db |
+--------------------+