时间飞逝，Centos发行大版本早已来到了第八个大版本，当我刚拿到一台新机器时，一般都会先习惯性的执行yum update，随后再安装其它相关服务，但最近在遇到一些小厂的机器时，通常执行会丢出以下报错：
[root@autocontroller ~]# yum update
CentOS-8 - AppStream 70 B/s | 38 B 00:00
Error: Failed to download metadata for repo 'AppStream': Cannot prepare internal mirrorlist: No URLs in mirrorlistPs：国内大厂没碰见此问题
日志信息
2022-02-02T11:39:36Z DEBUG error: Curl error (6): Couldn't resolve host name for http://mirrorlist.centos.org/?release=8&arch=x86_64&repo=AppStream&infra=stock [Could not resolve host: mirrorlist.centos.org] (http://mirrorlist.centos.org/?release=8&arch=x86_64&repo=AppStream&infra=stock).
2022-02-02T11:39:36Z WARNING Errors during downloading metadata for repository 'AppStream':
- Curl error (6): Couldn't resolve host name for http://mirrorlist.centos.org/?release=8&arch=x86_64&repo=AppStream&infra=stock [Could not resolve host: mirrorlist.centos.org]
2022-02-02T11:39:36Z DDEBUG Cleaning up.
2022-02-02T11:39:36Z SUBDEBUG
Traceback (most recent call last):
File "/usr/lib/python3.6/site-packages/dnf/repo.py", line 573, in load
ret = self._repo.load()
File "/usr/lib64/python3.6/site-packages/libdnf/repo.py", line 394, in load
return _repo.Repo_load(self)
RuntimeError: Failed to download metadata for repo 'AppStream': Cannot prepare internal mirrorlist: Curl error (6): Couldn't resolve host name for http://mirrorlist.centos.org/?release=8&arch=x86_64&repo=AppStream&infra=stock [Could not resolve host: mirrorlist.centos.org]能够大概看出，是由于地址域名解析出现问题；但是呢，我们的服务器和DNS服务器之间是工作正常的，那我们改如何修复此问题呢？
[root@autocontroller ~]# ping google.com
PING google.com (172.217.166.206) 56(84) bytes of data.
64 bytes from del03s13-in-f14.1e100.net (172.217.166.206): icmp_seq=1 ttl=115 ti me=43.5 ms
--- google.com ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 43.508/43.508/43.508/0.000 ms解决办法
Fix Failed to download metadata for repo
CentOS Linux 8 had reached the End Of Life (EOL) on December 31st, 2021. It means that CentOS 8 will no longer receive development resources from the official CentOS project. After Dec 31st, 2021, if you need to update your CentOS, you need to change the mirrors to vault.centos.org where they will be archived permanently. Alternatively, you may want to upgrade to CentOS Stream.
大概意思：自2022年开始，Centos官方不再提供开发资源，如果需要更新系统，请自行修改镜像地址为vault.centos.org，所以方法来了。
步骤一: 切换目录到 /etc/yum.repos.d/
[root@autocontroller ~]# cd /etc/yum.repos.d/步骤二：执行以下命令
[root@autocontroller ~]# sed -i 's/mirrorlist/#mirrorlist/g' /etc/yum.repos.d/CentOS-*
[root@autocontroller ~]# sed -i 's|#baseurl=http://mirror.centos.org|baseurl=http://vault.centos.org|g' /etc/yum.repos.d/CentOS-*Ps: 如果你是国内机器，则需要其它国内源，请另行搜索。
步骤三: 现在重新开始执行 yum update
[root@autocontroller ~]# yum update -y