centos7开始使得以往老版本系统服务的/etc/init.d的启动脚本的方式就此改变，在centos7中所有对服务的管理都集中到了systemctl当中。
systemctl是一个系统管理守护进程、工具和库的集合，用于取代以往的System V、service和chkconfig命令。

创建用于启动MySQL的配置文件
[root@localhost ~]# touch /usr/lib/systemd/system/mysqld.service
[root@localhost ~]# cd /usr/lib/systemd/system

编辑mysqld.service文件，加入如下内容:
[root@localhost system]# vi mysqld.service
[Unit]
Description=MySQL Server
Documentation=man:mysqld(8)
Documentation=http://dev.mysql.com/doc/refman/en/using-systemd.html
After=network.target
After=syslog.target

[Install]
WantedBy=multi-user.target

[Service]
User=mysql
Group=mysql
ExecStart=/opt/mysql-5.7.18/bin/mysqld --defaults-file=/etc/my.cnf
LimitNOFILE = 5000
保存退出

备注:ExecStart=/opt/mysql-5.7.18/bin/mysqld (此处请对应修改为MySQL程序所在的路径)
查找mysqld路径,例如:
[root@localhost system]# which mysqld
/opt/mysql-5.7.18/bin/mysqld


通过systemctl方式启动mysql5.7:
[root@localhost system]# systemctl start mysqld


检查MySQL运行状态:
[root@localhost system]# mysql -p
Enter password:
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 6
Server version: 5.7.18-log MySQL Community Server (GPL)


Copyright (c) 2000, 2017, Oracle and/or its affiliates. All rights reserved.


Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.


Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.


mysql>
mysql>
mysql> \s
--------------
mysql Ver 14.14 Distrib 5.7.18, for linux-glibc2.5 (x86_64) using EditLine wrapper


Connection id:6
Current database:
Current user:root@localhost
SSL:Not in use
Current pager:stdout
Using outfile:''
Using delimiter:;
Server version:5.7.18-log MySQL Community Server (GPL)
Protocol version:10
Connection:Localhost via UNIX socket
Server characterset:latin1
Db characterset:latin1
Client characterset:utf8
Conn. characterset:utf8
UNIX socket:/tmp/mysql.sock
Uptime:45 sec


Threads: 3 Questions: 6 Slow queries: 0 Opens: 108 Flush tables: 1 Open tables: 101 Queries per second avg: 0.133
--------------

mysql>

关闭防火墙:
[root@localhost system]# systemctl stop firewalld.service
[root@localhost system]# systemctl disable firewalld.service
Removed symlink /etc/systemd/system/multi-user.target.wants/firewalld.service.
Removed symlink /etc/systemd/system/dbus-org.fedoraproject.FirewallD1.service.

设置mysql的开机启动：
[root@localhost system]# systemctl enable mysqld
Created symlink from /etc/systemd/system/multi-user.target.wants/mysqld.service to /usr/lib/systemd/system/mysqld.service.
[root@localhost system]# systemctl list-unit-files | grep mysqld
mysqld.serviceenabled


取消mysql的开机自启动:
[root@localhost system]# systemctl disable mysqld
Removed symlink /etc/systemd/system/multi-user.target.wants/mysqld.service.
[root@localhost system]# systemctl list-unit-files | grep mysqld
mysqld.servicedisabled