【CentOS7.6】yum 报错：Could not retrieve mirrorlist http://mirrorlist.centos.org

今天安装了一个虚拟机，准备用yum命令安装jdk的时候，出现了以下报错。

[root@node1 yum.repos.d]# yum install ifconfig
Loaded plugins: fastestmirror, langpacks
Loading mirror speeds from cached hostfile
Could not retrieve mirrorlist http://mirrorlist.centos.org?arch=x86_64&release=7&repo=sclo-sclo 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: centos-sclo-sclo/x86_64

此前搞过很多虚拟器，第一次碰到这个问题，所以也网上百度了一下。

大致以下几个步骤：

1. 检查网络连接：确保你的设备可以正常访问互联网。

2. 检查防火墙设置：确保没有防火墙规则阻止访问上述 URL。

3. 更换镜像源：可以手动编辑 /etc/yum.repos.d/CentOS-Base.repo 文件，将其中的 mirrorlist 改为 baseurl，并指向一个可用的镜像地址。

4. 使用 CentOS 镜像：如果你在国内，可以考虑使用国内的镜像，如阿里云、清华大学等。

5. 临时使用其他镜像：在执行 yum 命令时，可以通过 --disablerepo 和 --enablerepo 选项临时指定其他镜像。（未使用）

关于步骤3 和步骤4，我修改后的配置文件如下：

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

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

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

[centosplus]
name=CentOS-$releasever - Plus
baseurl=https://mirrors.aliyun.com/centos/$releasever/centosplus/$basearch/
gpgcheck=1
enabled=0
gpgkey=https://mirrors.aliyun.com/centos/RPM-GPG-KEY-CentOS-7

最终解决问题。

但是并没有解答我的疑惑，因为本人有很多虚拟机从未出现过这个问题，其他虚拟机的yum配置文件没有修改，但是并没有出现上述这种情况。欢迎大家帮忙解惑！！