最近在重写项目，然后就是Linux去安装Docker，结果遇上了报错提示：

[vagrant@localhost ~]$ sudo yum install -y yum-utils \
> device-mapper-persistent-data \
> lvm2
Loaded plugins: fastestmirror
Determining fastest mirrors
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
[vagrant@localhost ~]$

解决办法

1. 怀疑网络问题，于是ping baidu.com

ping www.baidu.com

没啥问题。。

2. 查了资料，应该是Centos 7太老了。人家已经更换了yum对应源的位置，所以提示了Cannot find a …；

解决思路就是替换‘CentOS-Base.repo’文件。

1. 首先进入 /etc/yum.repos.d目录下，然后查看有没有CentOS-Base.repo文件

   cd /etc/yum.repos.d
   ll
   

2. 拷贝一份‘CentOS-Base.repo’文件为：CentOS-Base.repo.backup

   cp  CentOS-Base.repo   CentOS-Base.repo.backup
   

3. vi模式进入该文件

   vi CentOS-Base.repo 
   

4. 按下i键，可进入编辑模式，然后粘贴内容：

   # 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-$releasever - Base
   #mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=os&infra=$infra
   #baseurl=http://mirror.centos.org/centos/$releasever/os/$basearch/
   #baseurl=http://vault.centos.org/7.9.2009/x86_64/os/
   baseurl=http://vault.centos.org/7.9.2009/os/$basearch/
   gpgcheck=1
   gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7
    
   #released updates 
   [updates]
   name=CentOS-$releasever - Updates
   #mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=updates&infra=$infra
   #baseurl=http://mirror.centos.org/centos/$releasever/updates/$basearch/
   #baseurl=http://vault.centos.org/7.9.2009/x86_64/os/
   baseurl=http://vault.centos.org/7.9.2009/updates/$basearch/
   gpgcheck=1
   gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7
    
   #additional packages that may be useful
   [extras]
   name=CentOS-$releasever - Extras
   #mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=extras&infra=$infra
   #$baseurl=http://mirror.centos.org/centos/$releasever/extras/$basearch/
   #baseurl=http://vault.centos.org/7.9.2009/x86_64/os/
   baseurl=http://vault.centos.org/7.9.2009/extras/$basearch/
   gpgcheck=1
   gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7
    
   #additional packages that extend functionality of existing packages
   [centosplus]
   name=CentOS-$releasever - Plus
   #mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=centosplus&infra=$infra
   #baseurl=http://mirror.centos.org/centos/$releasever/centosplus/$basearch/
   #baseurl=http://vault.centos.org/7.9.2009/x86_64/os/
   baseurl=http://vault.centos.org/7.9.2009/centosplus/$basearch/
   gpgcheck=1
   enabled=0
   gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7
   

5. 粘贴之后，按下Esc键推出编辑模式，再按下:wq推出vi模式。

6. 最后执行命令

   sudo yum clean all
   sudo yum makecache
   

7. 执行完以上命令，可以再次重新尝试安装Docker的命令了：

   $ sudo yum install -y yum-utils\ device-mapper-persistent-data\ lvm2