centos6.9安装yum报错

yum install -y ntp
加载插件：fastestmirror, security
设置安装进程
Loading mirror speeds from cached hostfile
YumRepo Error: All mirror URLs are not using ftp, http[s] or file.
 Eg. Invalid release/repo/arch combination/
removing mirrorlist with no valid mirrors: /var/cache/yum/x86_64/6/base/mirrorlist.txt
错误：Cannot find a valid baseurl for repo: base

1.备份：

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

2.下载新的 CentOS-Base.repo 到 /etc/yum.repos.d/

wget -O /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-6.repo

3.运行 yum makecache 生成缓存

[root@hadoop101 yum.repos.d]# yum makecache 
已加载插件：fastestmirror, refresh-packagekit, security
Repository base is listed more than once in the configuration
Repository updates is listed more than once in the configuration
Repository extras is listed more than once in the configuration
Repository centosplus is listed more than once in the configuration
Repository contrib is listed more than once in the configuration
Determining fastest mirrors
 * base: mirrors.aliyun.com
 * extras: mirrors.aliyun.com
 * updates: mirrors.aliyun.com
http://mirrors.aliyun.com/centos/6/os/x86_64/repodata/repomd.xml: [Errno 14] PYCURL ERROR 22 - "The requested URL returned error: 404 Not Found"
尝试其他镜像。
To address this issue please refer to the below knowledge base article 

https://access.redhat.com/articles/1320623

If above article doesn't help to resolve this issue please open a ticket with Red Hat Support.

http://mirrors.aliyuncs.com/centos/6/os/x86_64/repodata/repomd.xml: [Errno 12] Timeout on http://mirrors.aliyuncs.com/centos/6/os/x86_64/repodata/repomd.xml: (28, 'connect() timed out!')
尝试其他镜像。
http://mirrors.cloud.aliyuncs.com/centos/6/os/x86_64/repodata/repomd.xml: [Errno 14] PYCURL ERROR 6 - "Couldn't resolve host 'mirrors.cloud.aliyuncs.com'"
尝试其他镜像。
错误：Cannot retrieve repository metadata (repomd.xml) for repository: base. Please verify its path and try again
[root@hadoop101 yum.repos.d]#   

4.替换源文件配置, 使用https://mirrors.aliyun.com/centos-vault/
4.1官方: 非阿里云ECS用户会出现 Couldn’t resolve host ‘mirrors.cloud.aliyuncs.com’ 信息，不影响使用。用户也可自行修改相关配置: eg:

sed -i -e '/mirrors.cloud.aliyuncs.com/d' -e '/mirrors.aliyuncs.com/d' /etc/yum.repos.d/CentOS-Base.repo

4.2替换http成https

sed -i  's/http/https/g' /etc/yum.repos.d/CentOS-Base.repo

4.3替换版本，$releasever替换6.9, 6.9是我用的版本

sed -i  's/$releasever/6.9/g' /etc/yum.repos.d/CentOS-Base.repo

4.4替换centos为centos-vault

sed -i  's/centos/centos-vault/g' /etc/yum.repos.d/CentOS-Base.repo

5.yum clean all && yum makecache

[root@hadoop101 yum.repos.d]# yum clean all && yum makecache
已加载插件：fastestmirror, refresh-packagekit, security
Cleaning repos: base extras updates
清理一切
Cleaning up list of fastest mirrors
已加载插件：fastestmirror, refresh-packagekit, security
Determining fastest mirrors
base                                                     | 3.7 kB     00:00     
base/group_gz                                            | 226 kB     00:00     
base/filelists_db                                        | 6.4 MB     00:01     
base/primary_db                                          | 4.7 MB     00:00     
base/other_db                                            | 2.8 MB     00:00     
extras                                                   | 3.4 kB     00:00     
extras/filelists_db                                      |  38 kB     00:00     
extras/prestodelta                                       | 1.3 kB     00:00     
extras/primary_db                                        |  37 kB     00:00     
extras/other_db                                          |  51 kB     00:00     
updates                                                  | 3.4 kB     00:00     
updates/filelists_db                                     | 3.5 MB     00:00     
updates/prestodelta                                      | 390 kB     00:00     
updates/primary_db                                       | 5.4 MB     00:01     
updates/other_db                                         |  74 MB     00:12     
元数据缓存已建立
[root@hadoop101 yum.repos.d]# 

解决办法参考：
阿里yum源安装，centos 6已停止维护