一、解决wget无法解析DNS问题
解决方法：
1. 进入/etc/resolv.conf
2.修改或增加内容：
nameserver 8.8.8.8
二、卸载redhat7自带的yum组件
# rpm -qa|grep yum
yum-utils-1.1.31-24.el7.noarch
yum-langpacks-0.4.2-3.el7.noarch
yum-metadata-parser-1.1.4-10.el7.x86_64
yum-rhn-plugin-2.0.1-4.el7.noarch
PackageKit-yum-0.8.9-11.el7.x86_64
yum-3.4.3-118.el7.noarch
卸载以下组件：
# rpm -e yum-utils-1.1.31-24.el7.noarch --nodeps
# rpm -e yum-langpacks-0.4.2-3.el7.noarch --nodeps
# rpm -e yum-rhn-plugin-2.0.1-4.el7.noarch --nodeps
# rpm -e yum-3.4.3-118.el7.noarch --nodeps
# rpm -qa|grep yum|xargs rpm -e --nodeps
三、下载安装包
mkdir /home/linuxprobe/testyum
wget -P /home/linuxprobe/testyum http://mirrors.ustc.edu.cn/centos/7/os/x86_64/Packages/yum-utils-1.1.31-50.el7.noarch.rpm
wget -P /home/linuxprobe/testyum http://mirrors.ustc.edu.cn/centos/7/os/x86_64/Packages/yum-langpacks-0.4.2-7.el7.noarch.rpm
wget -P /home/linuxprobe/testyum http://mirrors.ustc.edu.cn/centos/7/os/x86_64/Packages/yum-rhn-plugin-2.0.1-10.el7.noarch.rpm
wget -P /home/linuxprobe/testyum http://mirrors.ustc.edu.cn/centos/7/os/x86_64/Packages/yum-3.4.3-161.el7.centos.noarch.rpm
wget -P /home/linuxprobe/testyum http://mirrors.ustc.edu.cn/centos/7/os/x86_64/Packages/yum-metadata-parser-1.1.4-10.el7.x86_64.rpm
wget -P /home/linuxprobe/testyum http://mirrors.ustc.edu.cn/centos/7/os/x86_64/Packages/yum-plugin-fastestmirror-1.1.31-50.el7.noarch.rpm
wget -P /home/linuxprobe/testyum http://mirrors.ustc.edu.cn/centos/7/os/x86_64/Packages/python-iniparse-0.4-9.el7.noarch.rpm
wget -P /home/linuxprobe/testyum http://mirrors.ustc.edu.cn/centos/7/os/x86_64/Packages/python-urlgrabber-3.10-9.el7.noarch.rpm
wget -P /home/linuxprobe/testyum http://mirrors.ustc.edu.cn/centos/7/os/x86_64/Packages/rpm-4.11.3-35.el7.x86_64.rpm
wget -P /home/linuxprobe/testyum http://mirrors.ustc.edu.cn/centos/7/os/x86_64/Packages/rpm-libs-4.11.3-35.el7.x86_64.rpm
wget -P /home/linuxprobe/testyum http://mirrors.ustc.edu.cn/centos/7/os/x86_64/Packages/rpm-python-4.11.3-35.el7.x86_64.rpm
wget -P /home/linuxprobe/testyum http://mirrors.ustc.edu.cn/centos/7/os/x86_64/Packages/rpm-build-libs-4.11.3-35.el7.x86_64.rpm
四、安装软件包
包之间有关联关系，按顺序安装
cd /home/linuxprobe/testyum
rpm -ivh python-iniparse-0.4-9.el7.noarch.rpm
rpm -ivh yum-metadata-parser-1.1.4-10.el7.x86_64.rpm
rpm -qa | grep python-urlgrabber | xargs rpm -e --nodeps(卸载之前安装过的python-urlgrabber)
rpm -ivh python-urlgrabber-3.10-9.el7.noarch.rpm
rpm -Uvh rpm-4.11.3-35.el7.x86_64.rpm --nodeps(升级rpm至4.11.3-35)
rpm -Uvh rpm-libs-4.11.3-35.el7.x86_64.rpm --nodeps
rpm -Uvh rpm-python-4.11.3-35.el7.x86_64.rpm --nodeps
rpm -Uvh rpm-build-libs-4.11.3-35.el7.x86_64.rpm --nodeps
rpm -ivh yum-3.4.3-161.el7.centos.noarch.rpm yum-plugin-fastestmirror-1.1.31-50.el7.noarch.rpm
rpm -ivh yum-utils-1.1.31-50.el7.noarch.rpm
rpm -ivh yum-langpacks-0.4.2-7.el7.noarch.rpm
rpm -ivh yum-rhn-plugin-2.0.1-10.el7.noarch.rpm
rpm -qa | grep redhat-release-server | xargs rpm -e --nodeps
或(rpm -e redhat-release-server-7.0-1.el7.x86_64 --nodeps)
五、创建repo配置文件
vim /etc/yum.repos.d/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-$releasever - Base
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=os
baseurl=http://mirrors.ustc.edu.cn/centos/$releasever/os/$basearch/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7
#released updates
[updates]
name=CentOS-$releasever - Updates
# mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=updates
baseurl=http://mirrors.ustc.edu.cn/centos/$releasever/updates/$basearch/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7
#additional packages that may be useful
[extras]
name=CentOS-$releasever - Extras
# mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=extras
baseurl=http://mirrors.ustc.edu.cn/centos/$releasever/extras/$basearch/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7
#additional packages that extend functionality of existing packages
[centosplus]
name=CentOS-$releasever - Plus
# mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=centosplus
baseurl=http://mirrors.ustc.edu.cn/centos/$releasever/centosplus/$basearch/
gpgcheck=1
enabled=0
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7
注：$releasever 替换成相应的版本号(7)
$basearch 替换成想要的系统位数(x86_64)
gpgcheck=1
enabled=1
将RPM－GPG－KEY－CentOS-7文件拷贝到/etc/pki/rpm-gpg/目录下
六、清除缓存
yum clean all
yum makecache
yum update
全部文档每步都经过实践检测。至此大功靠成，希望对学习中的朋友们有所帮助。
此文档在形成中也参考了大量网友的文章，在此不一一列出名字了，一并感谢！
