清華大學開源映象站：https://mirrors.tuna.tsinghua.edu.cn/centos-vault/6.9/os/x86_64/

首先確保我的虛擬機器網路是通的。

網絡卡域名伺服器配置：
cat /etc/sysconfig/network-scripts/ifcfg-eth0

然後cat /etc/resolv.conf，這裡的nameserver與網絡卡配置中的DNS配置對應就可。

測試網路是否通：ping www.baidu.com

網路是通的，排除DNS域名，防火牆沒關，網路介面卡必須修改為橋接這種可能性。

網上還有些人說是/etc/yum.repos.d/CentOS-Base.repo這個檔案的配置問題，註釋掉mirrorlist這個配置項就能成功，試下看看。

mirrorlist都註釋掉了，執行sudo yum update試試

還是沒能成功

把源站點配置改為國內清華大學站點https://mirrors.tuna.tsinghua.edu.cn/centos-vault找到對應的Centos版本，最終成功。

這裡參考了這位老兄的文章，https://blog.csdn.net/fangeqin/article/details/106170479?utm_medium=distribute.pc_relevant.none-task-blog-BlogCommendFromBaidu-3.control&depth_1-utm_source=distribute.pc_relevant.none-task-blog-BlogCommendFromBaidu-3.control
確認清華大學站點能訪問：

修改yum源站點配置：vi /etc/yum.repos.d/CentOS-Base.repo

對照清華大學映象站中的目錄修改後如下：

[base]
name=CentOS-$releasever - Base
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=os&infra=$infra
#baseurl=http://mirror.centos.org/centos/$releasever/os/$basearch/
baseurl=https://mirrors.tuna.tsinghua.edu.cn/centos-vault/6.8/os/x86_64/
 

gpgcheck=1
#gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-6
gpgkey=https://mirrors.tuna.tsinghua.edu.cn/centos-vault/6.8/os/x86_64/RPM-GPG-KEY-CentOS-6

#released updates
[updates]
name=CentOS-$releasever - Updates
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=updates&infra=$infra
#baseurl=http://mirror.centos.org/centos/$releasever/updates/$basearch/
baseurl=https://mirrors.tuna.tsinghua.edu.cn/centos-vault/6.8/updates/x86_64/
gpgcheck=1
#gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-6
gpgkey=https://mirrors.tuna.tsinghua.edu.cn/centos-vault/6.8/os/x86_64/RPM-GPG-KEY-CentOS-6

#additional packages that may be useful
[extras]
name=CentOS-$releasever - Extras
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=extras&infra=$infra
#baseurl=http://mirror.centos.org/centos/$releasever/extras/$basearch/
baseurl=https://mirrors.tuna.tsinghua.edu.cn/centos-vault/6.8/extras/x86_64/
gpgcheck=1
#gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-6
gpgkey=https://mirrors.tuna.tsinghua.edu.cn/centos-vault/6.8/os/x86_64/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=$basearch&repo=centosplus&infra=$infra
#baseurl=http://mirror.centos.org/centos/$releasever/centosplus/$basearch/
baseurl=https://mirrors.tuna.tsinghua.edu.cn/centos-vault/6.8/centosplus/x86_64/
gpgcheck=1
enabled=0
#gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-6
gpgkey=https://mirrors.tuna.tsinghua.edu.cn/centos-vault/6.8/os/x86_64/RPM-GPG-KEY-CentOS-6

#contrib - packages by Centos Users
[contrib]
name=CentOS-$releasever - Contrib
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=contrib&infra=$infra
#baseurl=http://mirror.centos.org/centos/$releasever/contrib/$basearch/
baseurl=https://mirrors.tuna.tsinghua.edu.cn/centos-vault/6.8/contrib/x86_64/
gpgcheck=1
enabled=0
#gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-6
gpgkey=https://mirrors.tuna.tsinghua.edu.cn/centos-vault/6.8/os/x86_64/RPM-GPG-KEY-CentOS-6

配置YUM源出現Errno 14 Could not open/read repomd.xml

Loaded plugins: fastestmirror, refresh-packagekit, security
Loading mirror speeds from cached hostfile
* base: mirrors.aliyun.com
* c6-media:
* extras: mirrors.aliyun.com
* updates: mirrors.aliyun.com
base | 3.7 kB 00:00
base/group_gz | 226 kB 00:00
base/filelists_db | 6.4 MB 00:06
base/other_db | 2.8 MB 00:02
file:///media/CentOS/repodata/repomd.xml: [Errno 14] Could not open/read file:///media/CentOS/repodata/repomd.xml
Trying other mirror.
file:///media/cdrecorder/repodata/repomd.xml: [Errno 14] Could not open/read file:///media/cdrecorder/repodata/repomd.xml
Trying other mirror.
file:///mnt/cdrom/repodata/repomd.xml: [Errno 14] Could not open/read file:///mnt/cdrom/repodata/repomd.xml
Trying other mirror.
Error: Cannot retrieve repository metadata (repomd.xml) for repository: c6-media. Please verify its path and try again
解決辦法就是把本地源關閉：將/etc/yum.repos.d/CentOS-Media.repo裡面的enabled=1改成enabled=0即可，因為yum尋包的順序應該先是本地源，再尋網路源。