使用yum安装服务报错：[Errno 14] curl#6 - "Could not resolve host: mirrors.cloud.aliyuncs.com; Name or service not known"

现象：使用yum命令安装软件，报以下错误：

failure: repodata/repomd.xml from epel: [Errno 256] No more mirrors to try.
http://mirrors.cloud.aliyuncs.com/epel/6/x86_64/repodata/repomd.xml: [Errno 14] curl#6 - "Could not resolve host: mirrors.cloud.aliyuncs.com; Name or service not known"

原因：yum 源 mirrors.cloud.aliyuncs.com不存在。

解决办法：

1、首先进入 /etc/yum.repos.d 目录，备份CentOS-Base.repo源，

#cp CentOS-Base.repo  CentOS-Base.repo.bak  

2、修改 CentOS-Base.repo 文件

#vi  CentOS-Base.repo

将http://mirrors.cloud.aliyuncs.com  批量替换为  http://mirrors.aliyun.com

3、备份epel.repo源，修改epel.repo文件

#cp  epel.repo  epel.repo.bak

#vi  epel.repo

http://mirrors.cloud.aliyuncs.com 批量替换为  http://mirrors.aliyun.com

4、清理yum缓存和重新生成缓存，

#yum  clean  all

#yum  makecache

之后继续yum就正常了。

 如yum安装时，还报以下错误：

warning: /var/cache/yum/x86_64/7/base/packages/httpd-tools-2.4.6-88.el7.centos.x86_64.rpm: Header V3 RSA/SHA256 Signature, key ID f4a80eb5: NOKEY
Retrieving key from http://mirrors.aliyun.com/centos/RPM-GPG-KEY-CentOS-6

The GPG keys listed for the "CentOS-7 - Base" repository are already installed but they are not correct for this package.

Check that the correct key URLs are configured for this repository.

解决办法：

 执行：#rpm  --import  /etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7