确定当前系统是不是RHEL 7系统：
[root@lao ~]# cat /etc/redhat-release
Red Hat Enterprise Linux Server release 7.6 (Maipo)systemctl管理服务的启动、重启、停止、重载、查看状态等常用命令
启动服务
service foo start
systemctl start foo.service 重启服务
service foo restart
systemctl restart foo.service 停止服务
service foo stop
systemctl stop foo.service 重新加载配置文件（不终止服务）
service foo reload
systemctl reload foo.service
查看服务状态
service foo status
systemctl status foo.service 开机自动启动
chkconfig foo on
systemctl enable foo.service 开机不自动启动
chkconfig foo off
systemctl disable foo.service查看特定服务是否为开机自启动
chkconfig foo
systemctl is-enabled foo.service查看各个级别下服务的启动与禁用情况
chkconfig --list
systemctl list-unit-files --type=service