MQTT的服务器有很多，这边暂时选择Mosquitto作为MQTT的服务器。
在/etc/yum.repos.d/目录中新建一个mosquitto.repo文件，并将以下内容写入文件中：
[home_oojah_mqtt]
name=mqtt (CentOS_CentOS-7)
type=rpm-md
baseurl=http://download.opensuse.org/repositories/home:/oojah:/mqtt/CentOS_CentOS-7/
gpgcheck=1
gpgkey=http://download.opensuse.org/repositories/home:/oojah:/mqtt/CentOS_CentOS-7//repodata/repomd.xml.key
enabled=1
首先搜索下mosquitto的可安装包
sudo yum search all mosquitto
mosquitto-clients.x86_64 : Mosquitto command line publish/subscribe clients
mosquitto-debuginfo.x86_64 : Debug information for package mosquitto
libmosquitto-devel.x86_64 : MQTT C client library development files
libmosquitto1.x86_64 : MQTT C client library
libmosquittopp-devel.x86_64 : MQTT C++ client library development files
libmosquittopp1.x86_64 : MQTT C++ client library
mosquitto.x86_64 : MQTT version 3.1/3.1.1 compatible message broker
然后选择安装mosquitto-clients和mosquitto，也就是客户端和服务端。
yum install mosquitto
yum install mosquitto-clients
打开mosquitto的配置文件/etc/mosquitto/mosquitto.conf ，我们看下面的代码：
# Place your local configuration in /etc/mosquitto/conf.d/
pid_file /var/run/mosquitto.pid
persistence true
persistence_location /var/lib/mosquitto/
#log_dest file /var/log/mosquitto/mosquitto.log
include_dir /etc/mosquitto/conf.d
从上面的代码我们可以看到，自定义的配置需要配置在/etc/mosquitto/conf.d/中，文件以.conf为扩展名。
具体可以参考/etc/mosquitto/mosquitto.conf.example
以下是两种启动方式，二选一
mosquitto -c /etc/mosquitto/mosquitto.conf -d
sudo /etc/init.d/mosquitto start
1）打开一个终端窗口，运行订阅程序。
mosquitto_sub -t mqtt
2）再打开一个终端窗口，运行发布程序。
mosquitto_pub -h localhost -t mqtt -m "hello world."
在订阅程序的那个窗口就能看到hello world.