centOS7执行sudo yum install -y yum-utils device-mapper-persistent-data lvm2报错

在centos7学习安装docker时遇到错误

安装命令： sudo yum install -y yum-utils device-mapper-persistent-data lvm2

错误信息：

Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
Could not retrieve mirrorlist http://mirrorlist.centos.org/?release=7&arch=x86_64&repo=os&infra=vag error was
14: curl#6 - "Could not resolve host: mirrorlist.centos.org; Unknown error"


 One of the configured repositories failed (Unknown),
 and yum doesn't have enough cached data to continue. At this point the only
 safe thing yum can do is fail. There are a few ways to work "fix" this:

     1. Contact the upstream for the repository and get them to fix the problem.

     2. Reconfigure the baseurl/etc. for the repository, to point to a working
        upstream. This is most often useful if you are using a newer
        distribution release than is supported by the repository (and the
        packages for the previous distribution release still work).

     3. Run the command with the repository temporarily disabled
            yum --disablerepo=<repoid> ...

     4. Disable the repository permanently, so yum won't use it by default. Yum
        will then just ignore the repository until you permanently enable it
        again or use --enablerepo for temporary usage:

            yum-config-manager --disable <repoid>
        or
            subscription-manager repos --disable=<repoid>

     5. Configure the failing repository to be skipped, if it is unavailable.
        Note that yum will try to contact the repo. when it runs most commands,
        so will have to try and fail each time (and thus. yum will be be much
        slower). If it is a very temporary problem though, this is often a nice
        compromise:

            yum-config-manager --save --setopt=<repoid>.skip_if_unavailable=true

Cannot find a valid baseurl for repo: base/7/x86_64

解决方案：
执行了修改dns没用，最后修改 Yum 仓库配置

1、备份原有的 Yum 配置文件：
sudo cp /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.bak
2、编辑 Yum 仓库配置文件：
sudo vi /etc/yum.repos.d/CentOS-Base.repo
3、编辑文件内容为下面内容

[base]
name=CentOS-$releasever - Base
baseurl=http://mirrors.aliyun.com/centos/7/os/$basearch/
gpgcheck=1
gpgkey=http://mirrors.aliyun.com/centos/RPM-GPG-KEY-CentOS-7

[updates]
name=CentOS-$releasever - Updates
baseurl=http://mirrors.aliyun.com/centos/7/updates/$basearch/
gpgcheck=1
gpgkey=http://mirrors.aliyun.com/centos/RPM-GPG-KEY-CentOS-7

[extras]
name=CentOS-$releasever - Extras
baseurl=http://mirrors.aliyun.com/centos/7/extras/$basearch/
gpgcheck=1
gpgkey=http://mirrors.aliyun.com/centos/RPM-GPG-KEY-CentOS-7

4、清除 Yum 缓存并重试
sudo yum clean all
sudo yum makecache
然后再尝试安装 Docker：
sudo yum install -y yum-utils device-mapper-persistent-data lvm2

注意：
在执行此命令：sudo yum install -y yum-utils device-mapper-persistent-data lvm2
后出现下面的错误实际上是因为修改的yum仓库配置文件不对，“gpgkey=http://mirrors.aliyun.com/centos/RPM-GPG-KEY-CentOS-7”，有些后面没有带-CentOS-7，要加上在执行就可以了。

Retrieving key from http://mirrors.aliyun.com/centos/RPM-GPG-KEY

GPG key retrieval failed: [Errno 14] HTTP Error 404 - Not Found