已经2024年了，自从2020年11月30日开始 centos6各大开源镜像站已经停止维护了，所以导致yum的repo源不能正常使用，阿里云的repo库目前还可以使用，可以把repo源切换到阿里云暂时满足使用需求。不过这个也很难说以后不会失效，centos6已经很难换源了，国内纷纷已经停止centos6源的维护。目前唯一可行方法如下：

1.清空CentOS-Base.repo文件或备份现有repo仓库
mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup
2.下载并使用阿里云仓库repo
wget https://www.xmpan.com/Centos-6-Vault-Aliyun.repo

mv  /etc/yum.repos.d/Centos-6-Vault-Aliyun.repo  /etc/yum.repos.d/CentOS-Base.repo

yum clean all

yum makcache

yum update

阿里云CentOS-Base.repo 内容如下

# 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-6.9 - Base
#mirrorlist=http://mirrorlist.centos.org/?release=6.9&arch=$basearch&repo=os&infra=$infra
baseurl=http://mirror.nsc.liu.se/centos-store/6.9/os/$basearch/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-6#released updates 
[updates]
name=CentOS-6.9 - Updates
#mirrorlist=http://mirrorlist.centos.org/?release=6.9&arch=$basearch&repo=updates&infra=$infra
baseurl=http://mirror.nsc.liu.se/centos-store/6.9/updates/$basearch/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-6#additional packages that may be useful
[extras]
name=CentOS-6.9 - Extras
#mirrorlist=http://mirrorlist.centos.org/?release=6.9&arch=$basearch&repo=extras&infra=$infra
baseurl=http://mirror.nsc.liu.se/centos-store/6.9/extras/$basearch/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-6#additional packages that extend functionality of existing packages
[centosplus]
name=CentOS-6.9 - Plus
#mirrorlist=http://mirrorlist.centos.org/?release=6.9&arch=$basearch&repo=centosplus&infra=$infra
baseurl=http://mirror.nsc.liu.se/centos-store/6.9/centosplus/$basearch/
gpgcheck=1
enabled=0
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-6#contrib - packages by Centos Users
[contrib]
name=CentOS-6.9 - Contrib
#mirrorlist=http://mirrorlist.centos.org/?release=6.9&arch=$basearch&repo=contrib&infra=$infra
baseurl=http://mirror.nsc.liu.se/centos-store/6.9/contrib/$basearch/
gpgcheck=1
enabled=0
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-6