一、yum源简介
Yum（全称为 Yellow dog Updater, Modified）是一个在Fedora和RedHat以及CentOS中的Shell前端软件包管理器。基于RPM包管理，能够从指定的服务器自动下载RPM包并且安装，可以自动处理依赖性关系，并且一次安装所有依赖的软件包，无须繁琐地一次次下载、安装。 （来自百度百科）
默认yum源为CentOS官方源：mirrorlist.centos.org。
因其服务器在国外，直接从官方源下载安装软件时稳定性、速度等有时并不是很好，国内有如阿里云源、网易源等镜像站点，比官方源更稳定、速度更快。
二、yum安装软件命令
安装软件(以foo-x.x.x.rpm为例）：yum install foo-x.x.x.rpm
删除软件：yum remove foo-x.x.x.rpm或者yum erase foo-x.x.x.rpm
升级软件：yum update foo或者yum update foo
查询信息：yum info foo
三、修改yum源为阿里云
3.1 yum源配置文件路径：
/etc/yum.repos.d/CentOS-Base.repo
3.2 查看CentOS-Base.repo文件内容：
cat /etc/yum.repos.d/CentOS-Base.repo
[root@sheng yum.repos.d]# cat CentOS-Base.repo
CentOS-Base.repo
The mirror system uses the connecting IP address of the client and the
update status of each mirror to pick mirrors that are updated to and
geographically close to the client. You should use this for CentOS updates
unless you are manually picking other mirrors.
If the mirrorlist= does not work for you, as a fall back you can try the
remarked out baseurl= line instead.
[base]
name=CentOS-$releasever - Base - mirrors.aliyun.com
failovermethod=priority
baseurl=http://mirrors.aliyun.com/centos/$releasever/os/$basearch/
http://mirrors.aliyuncs.com/centos/$releasever/os/$basearch/
http://mirrors.cloud.aliyuncs.com/centos/$releasever/os/$basearch/
gpgcheck=1
gpgkey=http://mirrors.aliyun.com/centos/RPM-GPG-KEY-CentOS-7
#released updates
[updates]
name=CentOS-$releasever - Updates - mirrors.aliyun.com
failovermethod=priority
baseurl=http://mirrors.aliyun.com/centos/$releasever/updates/$basearch/
http://mirrors.aliyuncs.com/centos/$releasever/updates/$basearch/
http://mirrors.cloud.aliyuncs.com/centos/$releasever/updates/$basearch/
gpgcheck=1
gpgkey=http://mirrors.aliyun.com/centos/RPM-GPG-KEY-CentOS-7
#additional packages that may be useful
[extras]
name=CentOS-$releasever - Extras - mirrors.aliyun.com
failovermethod=priority
baseurl=http://mirrors.aliyun.com/centos/$releasever/extras/$basearch/
http://mirrors.aliyuncs.com/centos/$releasever/extras/$basearch/
http://mirrors.cloud.aliyuncs.com/centos/$releasever/extras/$basearch/
gpgcheck=1
gpgkey=http://mirrors.aliyun.com/centos/RPM-GPG-KEY-CentOS-7
#additional packages that extend functionality of existing packages
[centosplus]
name=CentOS-$releasever - Plus - mirrors.aliyun.com
failovermethod=priority
baseurl=http://mirrors.aliyun.com/centos/$releasever/centosplus/$basearch/
http://mirrors.aliyuncs.com/centos/$releasever/centosplus/$basearch/
http://mirrors.cloud.aliyuncs.com/centos/$releasever/centosplus/$basearch/
gpgcheck=1
enabled=0
gpgkey=http://mirrors.aliyun.com/centos/RPM-GPG-KEY-CentOS-7
#contrib - packages by Centos Users
[contrib]
name=CentOS-$releasever - Contrib - mirrors.aliyun.com
failovermethod=priority
baseurl=http://mirrors.aliyun.com/centos/$releasever/contrib/$basearch/
http://mirrors.aliyuncs.com/centos/$releasever/contrib/$basearch/
http://mirrors.cloud.aliyuncs.com/centos/$releasever/contrib/$basearch/
gpgcheck=1
enabled=0
gpgkey=http://mirrors.aliyun.com/centos/RPM-GPG-KEY-CentOS-7
[root@sheng yum.repos.d]#
3.3 备份官方源配置：
cp /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.bak
3.4 下载阿里云yum源配置文件覆盖原官方源配置文件：
curl -o /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo
此时该文件（ /etc/yum.repos.d/CentOS-Base.repo）已是阿里云yum源配置文件，可用 cat /etc/yum.repos.d/CentOS-Base.repo 查看文件内容。
3.5 清理缓存并生成新的缓存：
yum clean all
yum makecache
3.6 更新软件
sudo yum -y update
完
注意：如果Linux 机器中没有CURL 命令，可以COPY 项目aliyun 上面repo 的内容。