CentOS 8 上运行 `yum update`报错如下

[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 mirrorlist

/var/log/dnf.log更多调试信息的输出

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]

尝试ping google.com

[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

正常没有问题

修复无法为 repo 下载数据

Step 1: Go to /etc/yum.repos.d/ .

[root@autocontroller ~]# cd /etc/yum.repos.d/

Step 2: 运行以下命令

[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-*

CentOS-* * 如果无法匹配，可手动ls -la查看挨个更改

Step 3: 再次执行 yum update 成功