centos 更换yum源 ，解决下载慢的问题

　　先看有没有安装wget wget -V　　　　　　如果没有执行 yum -y install wget　　 进行安装

　　然后进行配置的备份

　　mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup

　　然后执行(这个是centos7的配置安装)

　　wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo

　　然后执行

　　yum clean all

　　yum makecache

　　yum update 或者 yum -y upgrade

　　yum需要安装需要的软件包， yum-util 提供yum-config-manager功能，另外两个是devicemapper驱动依赖的

　　yum install -y yum-utils device-mapper-persistent-data lvm2

　　更换yum源:

　　yum-config-manager --add-repo http://mirrors.aliyun.com/docker-ce/linux/centos/docker-ce.repo (使用这个安装docker更快)

　　yum-config-manager --add-repo https://download.docker.com/linux/centos/docker-ce.repo

　　查看特定版本 yum list docker-ce --showduplicates | sort -r

yum -y update

升级所有包，改变软件设置和系统设置,系统版本内核都升级

yum -y upgrade

升级所有包，不改变软件设置和系统设置，系统版本升级，内核不改变

　　创建多个数据源

方法二： 手动修改文件 
1、进入源目录：

cd /etc/yum.repos.d

2、添加多个源文件，如：shlug.repo，ustc.repo，两个源的内容如下：
（可以创建独立的repo文件，也可以把以下的内容加到/etc/yum.repos.d/CentOS-Base.repo 后面）

[shlug.repo]

#mirrors-shlug-org.repo 
# 
# rpm --import http://mirrors.shlug.org/centos/RPM-GPG-KEY-CentOS-6
# 
# This file uses a new mirrorlist system developed by Lance Davis for CentOS. 
# 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=mirrors-shlug-org--CentOS-$releasever - Base 
baseurl=http://mirrors.shlug.org/centos/$releasever/os/$basearch/ 
gpgcheck=1 
gpgkey=http://mirrors.shlug.org/centos/RPM-GPG-KEY-CentOS-6 
#released updates 
[update] 
name=mirrors-shlug-org--CentOS-$releasever - Updates 
baseurl=http://mirrors.shlug.org/centos/$releasever/updates/$basearch/ 
gpgcheck=1 
gpgkey=http://mirrors.shlug.org/centos/RPM-GPG-KEY-CentOS-6
#packages used/produced in the build but not released 
#[addons] 网站上的源目录没有addon，故注释掉
#baseurl=http://mirrors.shlug.org/centos/$releasever/addons/$basearch/ 
#gpgcheck=1 
#gpgkey=http://mirrors.shlug.org/centos/RPM-GPG-KEY-CentOS-6 
#additional packages that may be useful 
[extras] 
name=mirrors-shlug-org--CentOS-$releasever - Extras 
baseurl=http://mirrors.shlug.org/centos/$releasever/extras/$basearch/ 
gpgcheck=1 
gpgkey=http://mirrors.shlug.org/centos/RPM-GPG-KEY-CentOS-6 
#additional packages that extend functionality of existing packages 
[centosplus] 
name=mirrors-shlug-org--CentOS-$releasever - Plus 
baseurl=http://mirror.centos.org/centos/$releasever/centosplus/$basearch/ 
gpgcheck=1 
gpgkey=http://mirrors.shlug.org/centos/RPM-GPG-KEY-CentOS-6 
#contrib - packages by Centos Users 
[contrib] 
name=mirrors-shlug-org--CentOS-$releasever - Contrib 
baseurl=http://mirror.centos.org/centos/$releasever/contrib/$basearch/ 
gpgcheck=1 
enabled=0 
gpgkey=http://mirrors.shlug.org/centos/RPM-GPG-KEY-CentOS-6

[ustc.repo]

# CentOS-Base.repo
#
# This file uses a new mirrorlist system developed by Lance Davis for CentOS.
# 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-$releasever - Base
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=os
baseurl=http://centos.ustc.edu.cn/centos/$releasever/os/$basearch/
gpgcheck=1
gpgkey=http://centos.ustc.edu.cn/centos/RPM-GPG-KEY-CentOS-6

#released updates
[updates]
name=CentOS-$releasever - Updates
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=updates
baseurl=http://centos.ustc.edu.cn/centos/$releasever/updates/$basearch/
gpgcheck=1
gpgkey=http://centos.ustc.edu.cn/centos/RPM-GPG-KEY-CentOS-6

#packages used/produced in the build but not released
#[addons] 网站上的源目录没有addon，故注释掉
#name=CentOS-$releasever - Addons
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=addons
#baseurl=http://centos.ustc.edu.cn/centos/$releasever/addons/$basearch/
#gpgcheck=1
#gpgkey=http://centos.ustc.edu.cn/centos/RPM-GPG-KEY-CentOS-6

#additional packages that may be useful
[extras]
name=CentOS-$releasever - Extras
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=extras
baseurl=http://centos.ustc.edu.cn/centos/$releasever/extras/$basearch/
gpgcheck=1
gpgkey=http://centos.ustc.edu.cn/centos/RPM-GPG-KEY-CentOS-6

#additional packages that extend functionality of existing packages
[centosplus]
name=CentOS-$releasever - Plus
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=centosplus
baseurl=http://centos.ustc.edu.cn/centos/$releasever/centosplus/$basearch/
gpgcheck=1
enabled=0
gpgkey=http://centos.ustc.edu.cn/centos/RPM-GPG-KEY-CentOS-6

3、导入KEY

rpm --import http://mirrors.shlug.org/centos/RPM-GPG-KEY-CentOS-6
rpm --import http://centos.ustc.edu.cn/centos/RPM-GPG-KEY-CentOS-6

4、安装自动源选择插件--自动选择最快的源

yum install yum-fastestmirror -y

5、如何确认正在使用的是哪个源？

cd /var/cache/yum
cat timedhosts.txt