由于我是用的系统是CentOS 5.11以停止更新很多年，故此yum也不能用，找了很多方法，最终yum能稳定的运行在CentOS 5.11上，下面开始一一讲解步骤：
1：首先更新yum源
地址：http://vault.centos.org/
网站是有各个版本镜像的，所以 通过lsb_release -a查询下，系统版本如图
下面是我的yum源完整版本，下面会说出具体针对系统版本进行修改yum源方法：
vim /etc/yum.repos.d/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-$releasever - Base
baseurl=http://vault.centos.org/5.11/os/x86_64/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-5
#released updates
[updates]
name=CentOS-$releasever - Updates
baseurl=http://vault.centos.org/5.11/os/x86_64/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-5
#packages used/produced in the build but not released
[addons]
name=CentOS-$releasever - Addons
baseurl=http://vault.centos.org/5.11/os/x86_64/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-5
#additional packages that may be useful
[extras]
name=CentOS-$releasever - Extras
baseurl=http://vault.centos.org/5.11/os/x86_64/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-5
#additional packages that extend functionality of existing packages
[centosplus]
name=CentOS-$releasever - Plus
baseurl=http://vault.centos.org/5.11/os/x86_64/
gpgcheck=1
enabled=0
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-5
#contrib - packages by Centos Users
[contrib]
name=CentOS-$releasever - Contrib
baseurl=http://vault.centos.org/5.11/os/x86_64/
gpgcheck=1
enabled=0
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-5
注：如果你的版本是5.10（举例说明），打开此网站，http://vault.centos.org，根据上述地址http://vault.centos.org/5.11/os/x86_64/来进行修改，比如系统是5.10的话，是x86_64的，我们可以修改成http://vault.centos.org/5.10/os/x86_64/，修改完成后，浏览器打开输入地址，看看是不是可以显示出以下页面：
如果显示出上述页面，那根据我上面的5.11版本的Centos源把baseurl=http://vault.centos.org/5.11/os/x86_64/ 修改成 baseurl=http://vault.centos.org/5.10/os/x86_64/（是上述文件内容中，所有http://vault.centos.org/5.11/os/x86_64/地址），即可
修改完成后，保存，使用如下命令进行测试
yum clean all
yum makecache
测试成功后，可用yum进行安装、卸载软件。
更多CentOS相关信息见CentOS 专题页面 https://www.linuxidc.com/topicnews.aspx?tid=14