首先备份CentOS-Base.repo
mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup
下载对应版本的CentOS-Base.repo, 放入/etc/yum.repos.d/ 这是CentOS 5的:
CentOS-Base.repo
# 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-$releasever - Base - mirrors.ustc.edu.cn
baseurl=http://mirrors.ustc.edu.cn/centos/$releasever/os/$basearch/
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=os
gpgcheck=1
gpgkey=http://mirrors.ustc.edu.cn/centos/RPM-GPG-KEY-CentOS-5
#released updates 
[updates]
name=CentOS-$releasever - Updates - mirrors.ustc.edu.cn
baseurl=http://mirrors.ustc.edu.cn/centos/$releasever/updates/$basearch/
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=updates
gpgcheck=1
gpgkey=http://mirrors.ustc.edu.cn/centos/RPM-GPG-KEY-CentOS-5
#additional packages that may be useful
[extras]
name=CentOS-$releasever - Extras - mirrors.ustc.edu.cn
baseurl=http://mirrors.ustc.edu.cn/centos/$releasever/extras/$basearch/
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=extras
gpgcheck=1
gpgkey=http://mirrors.ustc.edu.cn/centos/RPM-GPG-KEY-CentOS-5
#packages used/produced in the build but not released
[addons]
name=CentOS-$releasever - Addons - mirrors.ustc.edu.cn
baseurl=http://mirrors.ustc.edu.cn/centos/$releasever/addons/$basearch/
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=addons
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-5
#additional packages that extend functionality of existing packages
[centosplus]
name=CentOS-$releasever - Plus - mirrors.ustc.edu.cn
baseurl=http://mirrors.ustc.edu.cn/centos/$releasever/centosplus/$basearch/
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=centosplus
gpgcheck=1
enabled=0
gpgkey=http://mirrors.ustc.edu.cn/centos/RPM-GPG-KEY-CentOS-5
#contrib - packages by Centos Users
[contrib]
name=CentOS-$releasever - Contrib - mirrors.ustc.edu.cn
baseurl=http://mirrors.ustc.edu.cn/centos/$releasever/contrib/$basearch/
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=contrib
gpgcheck=1
enabled=0
gpgkey=http://mirrors.ustc.edu.cn/centos/RPM-GPG-KEY-CentOS-5
这是CentOS 6的:
CentOS-Base.repo
# 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-$releasever - Base - mirrors.ustc.edu.cn
baseurl=http://mirrors.ustc.edu.cn/centos/$releasever/os/$basearch/
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=os
gpgcheck=1
gpgkey=http://mirrors.ustc.edu.cn/centos/RPM-GPG-KEY-CentOS-6
#released updates 
[updates]
name=CentOS-$releasever - Updates - mirrors.ustc.edu.cn
baseurl=http://mirrors.ustc.edu.cn/centos/$releasever/updates/$basearch/
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=updates
gpgcheck=1
gpgkey=http://mirrors.ustc.edu.cn/centos/RPM-GPG-KEY-CentOS-6
#additional packages that may be useful
[extras]
name=CentOS-$releasever - Extras - mirrors.ustc.edu.cn
baseurl=http://mirrors.ustc.edu.cn/centos/$releasever/extras/$basearch/
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=extras
gpgcheck=1
gpgkey=http://mirrors.ustc.edu.cn/centos/RPM-GPG-KEY-CentOS-6
#additional packages that extend functionality of existing packages
[centosplus]
name=CentOS-$releasever - Plus - mirrors.ustc.edu.cn
baseurl=http://mirrors.ustc.edu.cn/centos/$releasever/centosplus/$basearch/
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=centosplus
gpgcheck=1
enabled=0
gpgkey=http://mirrors.ustc.edu.cn/centos/RPM-GPG-KEY-CentOS-6
#contrib - packages by Centos Users
[contrib]
name=CentOS-$releasever - Contrib - mirrors.ustc.edu.cn
baseurl=http://mirrors.ustc.edu.cn/centos/$releasever/contrib/$basearch/
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=contrib
gpgcheck=1
enabled=0
gpgkey=http://mirrors.ustc.edu.cn/centos/RPM-GPG-KEY-CentOS-6
这是CentOS 7的:
CentOS-Base.repo
# CentOS-Base.repo
# The mirror system uses the connecting IP address of the client and the
# update status of each mirror to pick mirrors that are updated to and
# geographically close to the client.  You should use this for CentOS updates
# unless you are manually picking other mirrors.
# If the mirrorlist= does not work for you, as a fall back you can try the
# remarked out baseurl= line instead.
[base]
name=CentOS-$releasever - Base
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=os
baseurl=http://mirrors.ustc.edu.cn/centos/$releasever/os/$basearch/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7
#released updates
[updates]
name=CentOS-$releasever - Updates
# mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=updates
baseurl=http://mirrors.ustc.edu.cn/centos/$releasever/updates/$basearch/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7
#additional packages that may be useful
[extras]
name=CentOS-$releasever - Extras
# mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=extras
baseurl=http://mirrors.ustc.edu.cn/centos/$releasever/extras/$basearch/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7
#additional packages that extend functionality of existing packages
[centosplus]
name=CentOS-$releasever - Plus
# mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=centosplus
baseurl=http://mirrors.ustc.edu.cn/centos/$releasever/centosplus/$basearch/
gpgcheck=1
enabled=0
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7
运行yum makecache生成缓存 官方主页: http://www.centos.org/
邮件列表: http://www.centos.org/modules/tinycontent/index.php?id=16
论坛: http://www.centos.org/modules/newbb/
文档: http://www.centos.org/docs/
Wiki: http://wiki.centos.org/
镜像列表: http://www.centos.org/modules/tinycontent/index.php?id=32