1：卸載原先的yum
2：安裝centos的yum
有以下的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
3：下載以下yum的包（2019/9/18日還行，以后不行，自己去網站找）
wget http://mirrors.163.com/centos/7/os/x86_64/Packages/yum-3.4.3-118.el7.centos.noarch.rpm http://mirrors.163.com/centos/7/os/x86_64/Packages/yum-3.4.3-118.el7.centos.noarch.rpm
wget http://mirrors.163.com/centos/7/os/x86_64/Packages/yum-3.4.3-163.el7.centos.noarch.rpm
wget http://mirrors.163.com/centos/7/os/x86_64/Packages/yum-utils-1.1.31-52.el7.noarch.rpm
wget http://mirrors.163.com/centos/7/os/x86_64/Packages/yum-langpacks-0.4.2-7.el7.noarch.rpm
wget http://mirrors.163.com/centos/7/os/x86_64/Packages/yum-metadata-parser-1.1.4-10.el7.x86_64.rpm
wget http://mirrors.163.com/centos/7/os/x86_64/Packages/yum-rhn-plugin-2.0.1-10.el7.noarch.rpm
wget http://mirrors.163.com/centos/7/os/x86_64/Packages/yum-plugin-fastestmirror-1.1.31-52.el7.noarch.rpm
wget http://mirrors.163.com/centos/7/os/x86_64/Packages/yum-updateonboot-1.1.31-52.el7.noarch.rpm
4：rpm -ivh yum-*發現報以下錯
error: Failed dependencies:
python-urlgrabber >= 3.10-8 is needed by yum-3.4.3-163.el7.centos.noarch
rpm >= 0:4.11.3-22 is needed by yum-3.4.3-163.el7.centos.noarch
是說python的版本必須大於3.10-8
5：卸載原有python安裝新的python
可以直接進行更新這個軟件包
去rpm.pbone.net搜索這個包 python-urlgrabber-3.10-8.el7.noarch.rpm
然后去下載下來 wget ftp://ftp.pbone.net/mirror/ftp.scientificlinux.org/linux/scientific/7.4/x86_64/os/Packages/python-urlgrabber-3.10-8.el7.noarch.rpm
卸載原來的包 rpm -e --nodeps python-urgrabber-*
安裝包 rpm -ivh --nodeps python-urlgrabber-3.10-8.el7.noarch.rpm
查看有沒有安裝上：[root@localhost ~]# rpm -qa |grep python-url
python-urlgrabber-3.10-8.el7.noarch
6：安裝yum
rpm -ivh yum-* --nodeps
7：下載yum源
wget -c -P /etc/yum.repos.d http://mirrors.163.com/.help/CentOS7-Base-163.repo
8：替換版本為7
vim /etc/yum.repos.d/CentOS7-Base-163.repo
:%s/$releasever/7/g
9：yum repolist all