CentOS8报错Failed to download metadata for repo ‘appstream‘

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一、问题描述

CentOS8 下运行 dnf install 报错 Failed to download metadata for repo ‘appstream’：

[root@localhost zabbix-release]# dnf install zabbix-server-mysql zabbix-web-mysql zabbix-nginx-conf zabbix-sql-scripts zabbix-selinux-policy zabbix-agent
CentOS Linux 8 - AppStream                                                                                                                                                 65  B/s | 2.3 kB     00:35    
Errors during downloading metadata for repository 'appstream':
  - Curl error (6): Couldn't resolve host name for http://mirrors.cloud.aliyuncs.com/centos/8/BaseOS/x86_64/os/repodata/repomd.xml [Could not resolve host: mirrors.cloud.aliyuncs.com]
  - Curl error (28): Timeout was reached for http://mirrors.aliyuncs.com/centos/8/BaseOS/x86_64/os/repodata/repomd.xml [Connection timed out after 30000 milliseconds]
  - Status code: 404 for https://mirrors.aliyun.com/centos/8/BaseOS/x86_64/os/repodata/repomd.xml (IP: 119.96.138.216)
Error: Failed to download metadata for repo 'appstream': Cannot download repomd.xml: Cannot download repodata/repomd.xml: All mirrors were tried

二、解决方法

出错的关键信息是：

Couldn't resolve host name for http://mirrors.cloud.aliyuncs.com/centos/8/BaseOS/x86_64/os/repodata/repomd.xml [Could not resolve host: mirrors.cloud.aliyuncs.com]

经查，http://mirrors.cloud.aliyuncs.com/centos/8/BaseOS 路径已不存在，改为 http://mirrors.cloud.aliyuncs.com/centos/8/extras 了，因此将 yum 源路径修改即可：
将：

baseurl=https://mirrors.aliyun.com/centos/$releasever/BaseOS/$basearch/os/
        http://mirrors.aliyuncs.com/centos/$releasever/BaseOS/$basearch/os/
        http://mirrors.cloud.aliyuncs.com/centos/$releasever/BaseOS/$basearch/os/

改为：

baseurl=https://mirrors.aliyun.com/centos/$releasever/extras/$basearch/os/
        http://mirrors.aliyuncs.com/centos/$releasever/extras/$basearch/os/
        http://mirrors.cloud.aliyuncs.com/centos/$releasever/extras/$basearch/os/