今天安装ntp时遇到报错，错误信息显示，yum无法从 <code>http://mirrorlist.centos.org/ 获取镜像列表，报错如下：

[root@node1 network-scripts]# yum -y install ntp

已加载插件：fastestmirror, langpacks

Loading mirror speeds from cached hostfile

Could not retrieve mirrorlist http://mirrorlist.centos.org/?release=7&arch=x86_64&repo=os&infra=stock error was

14: curl#6 - "Could not resolve host: mirrorlist.centos.org; 未知的错误"

One of the configured repositories failed (未知),

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：

替换 CentOS 镜像源

1.备份原始配置文件：在进行任何更改之前，最好备份原始的 <code>.repo 文件。

cp /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup

2.编辑配置文件：打开 CentOS-Base.repo 文件,如图。

vim /etc/yum.repos.d/CentOS-Base.repo

3.修改或替换镜像源：

        3.1注释掉 <code>mirrorlist 行：在每个 [base]、[updates] 和 [extras]、 [centosplus] 部分，使用 # 在行首添加注释，以禁用自动选择镜像源的功能。

        3.2取消注释 baseurl 行：找到每个部分中被注释掉的 baseurl 行，并取消注释。或者直接加一行

        3.3指定镜像源：将 baseurl 中的 http://mirror.centos.org/ 替换为您选择的镜像源的 URL。

使用阿里云的镜像：

baseurl=http://mirrors.aliyun.com/centos/$releasever/os/$basearch/

或者使用清华大学的镜像：

baseurl=http://mirrors.tuna.tsinghua.edu.cn/centos/$releasever/os/$basearch/

4.保存并关闭文件：如上图，然后:wq保存即可。

5.清除 yum 缓存：清除 <code>yum 缓存以确保使用新的镜像源。

sudo yum clean all

6.再次测试安装ntp:

yum install -y ntp

成功！如果对你有所帮助，不妨点个免费的赞哦，收藏关注不迷路~