解决目前市面上大多数centos6yum源失效，经过一番捣腾 终于找到适合的源。
1.cd /etc/yum.repos.d
2.mv CentOS-Base.repo CentOS-Base.repo.backup
3.在网上找到阿里的yum源CentOS-Base.repo配置 然后修改里面的网址在https://vault.centos.org/找到你系统版本及相应地址进行替换
4.将修改后CentOS-Base.repo上传到/etc/yum.repos.d目录
centos6.8修改好的示例：
# 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-$releasever - Base - mirrors.aliyun.com
failovermethod=priority
baseurl=http://vault.centos.org/6.8/os/$basearch/
http://vault.centos.org/6.8/os/$basearch/
http://vault.centos.org/6.8/os/$basearch/
gpgcheck=1
gpgkey=http://vault.centos.org/6.8/os/x86_64/RPM-GPG-KEY-CentOS-6
#released updates
[updates]
name=CentOS-$releasever - Updates - mirrors.aliyun.com
failovermethod=priority
baseurl=http://vault.centos.org/6.8/updates/$basearch/
http://vault.centos.org/6.8/updates/$basearch/
http://vault.centos.org/6.8/updates/$basearch/
gpgcheck=1
gpgkey=http://vault.centos.org/6.8/os/x86_64/RPM-GPG-KEY-CentOS-6
#additional packages that may be useful
[extras]
name=CentOS-$releasever - Extras - mirrors.aliyun.com
failovermethod=priority
baseurl=http://vault.centos.org/6.8/extras/$basearch/
http://vault.centos.org/6.8/extras/$basearch/
http://vault.centos.org/6.8/extras/$basearch/
gpgcheck=1
gpgkey=http://vault.centos.org/6.8/os/x86_64/RPM-GPG-KEY-CentOS-6
#additional packages that extend functionality of existing packages
[centosplus]
name=CentOS-$releasever - Plus - mirrors.aliyun.com
failovermethod=priority
baseurl=http://vault.centos.org/6.8/centosplus/$basearch/
http://vault.centos.org/6.8/centosplus/$basearch/
http://vault.centos.org/6.8/centosplus/$basearch/
gpgcheck=1
enabled=0
gpgkey=http://vault.centos.org/6.8/os/x86_64/RPM-GPG-KEY-CentOS-6
#contrib - packages by Centos Users
[contrib]
name=CentOS-$releasever - Contrib - mirrors.aliyun.com
failovermethod=priority
baseurl=http://vault.centos.org/6.8/contrib/$basearch/
http://vault.centos.org/6.8/contrib/$basearch/
http://vault.centos.org/6.8/contrib/$basearch/
gpgcheck=1
enabled=0
gpgkey=http://vault.centos.org/6.8/os/x86_64/RPM-GPG-KEY-CentOS-6
5.清理缓存并生成新的缓存
yum clean all
yum makecache