下载安装yum：
wget http://yum.baseurl.org/download/3.2/yum-3.2.28.tar.gz
tar xvf yum-3.2.28.tar.gz
cd yum-3.2.28
touch /etc/yum.conf
cp etc/yum.conf /etc/yum.conf
yummain.py install yum
yum check-update
yum update
yum clean all
当使用CentOS源安装软件出现如下错误的解决办法：
PackageKit-0.5.8-19.el6.x86_64 has missing requires of PackageKit-yum = ('0', '0.5.8', '19.el6')
PackageKit-0.5.8-19.el6.x86_64 has missing requires of PackageKit-yum-plugin = ('0', '0.5.8', '19.el6')
运行下面命令
yum remove 'rhn-check-1.0.0.1-16.el6.noarch'
yum instal PackageKit-glib
yum install abrt-addon-ccpp
yum install PackageKit-yum
yum install PackageKit-yum-plugin