更新centos5，6，7yum源库

Centos下更新yum软件管理器下载来源

1.备份软件包下载源
#/cd /etc/yum.repos.d/

#mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup

2.下载新的CentOS-Base.repo
CentOS 5
#wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-5.repo

或者

#curl -o /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-5.repo

CentOS 6
#wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-6.repo

或者

#curl -o /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-6.repo

CentOS 7
#wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo

或者

#curl -o /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo

3.之后运行yum makecache生成缓存
#yum clean all

#yum makecache

如果报错

Error: Cannot retrieve repository metadata (repomd.xml) for repository: rpmforge.
Please verify its path and try again

请删除除CentOS-Base.repo以外的rpm软件更新包