yum版本号前有:冒号 指的是依赖版本号，默认0不显示

官方介绍：http://rpm-packaging-guide.github.io/#epoch

[root@CentOs7 ～]# yum list docker --showduplicates   
已加载插件：fastestmirror, priorities
Loading mirror speeds from cached hostfile
28 packages excluded due to repository priority protections
可安装的软件包
docker.x86_64                      2:1.12.6-55.gitc4618fb.el7.centos                       c7-media

　看到版本号前是2:1.12.6，1.12.6是版本号，是常见的，但是2:是什么意思，google了一下，发现这个是rpm包的命名规范，即使不写也会默认为0，是指的依赖版本号

中文RPM包信息： 看到  "时期 ：2"

[root@CentOs7 ～]# yum info docker-1.12.6
已加载插件：fastestmirror, priorities
Loading mirror speeds from cached hostfile
28 packages excluded due to repository priority protections
可安装的软件包
名称    ：docker
架构    ：x86_64
时期       ：2
版本    ：1.12.6
发布    ：55.gitc4618fb.el7.centos
大小    ：15 M
源    ：c7-media_CentOS
简介    ： Automates deployment of containerized applications
网址    ：https://github.com/docker/docker
协议    ： ASL 2.0
描述    ： Docker is an open-source engine that automates the deployment of any
         : application as a lightweight, portable, self-sufficient container that will
         : run virtually anywhere.
         : 
         : Docker containers can encapsulate any payload, and will run consistently on
         : and between virtually any server. The same container that a developer builds
         : and tests on a laptop will run at scale, in production*, on VMs, bare-metal
         : servers, OpenStack clusters, public instances, or combinations of the above.

　　

英文RPM包信息：对应的的是Epoch

[root@CentOs7 yum.repos.d]# yum info docker-1.12.6
Loaded plugins: fastestmirror, priorities
Loading mirror speeds from cached hostfile
28 packages excluded due to repository priority protections
Available Packages
Name        : docker
Arch        : x86_64
Epoch       : 2
Version     : 1.12.6
Release     : 55.gitc4618fb.el7.centos
Size        : 15 M
Repo        : c7-media_CentOS
Summary     : Automates deployment of containerized applications
URL         : https://github.com/docker/docker
License     : ASL 2.0
Description : Docker is an open-source engine that automates the deployment of any
            : application as a lightweight, portable, self-sufficient container that will
            : run virtually anywhere.
            : 
            : Docker containers can encapsulate any payload, and will run consistently on
            : and between virtually any server. The same container that a developer builds
            : and tests on a laptop will run at scale, in production*, on VMs, bare-metal
            : servers, OpenStack clusters, public instances, or combinations of the above.

　　

 参考：

http://unix.stackexchange.com/questions/543384/what-is-the-meaning-of-1-in-the-version-of-a-yum-package