As noted in the CentOS project timeline, traditional CentOS 7 repositories (mirrorlist.centos.org) became unavailable after December 31, 2021, when CentOS shifted focus to CentOS Stream. However, many production systems still running CentOS 7 need maintenance updates.

First verify basic network functionality:

ping -c 4 google.com
nslookup mirrorlist.centos.org
curl -I https://www.centos.org

If these fail, you're dealing with either DNS resolution issues or network connectivity problems.

Edit your resolv.conf:

sudo vi /etc/resolv.conf

Add reliable nameservers:

nameserver 8.8.8.8
nameserver 8.8.4.4
nameserver 1.1.1.1

Since official mirrors are deprecated, use these alternatives:

1. Vault.centos.org (archive):

sudo sed -i 's/mirrorlist/#mirrorlist/g' /etc/yum.repos.d/CentOS-*
sudo sed -i 's|#baseurl=http://mirror.centos.org|baseurl=http://vault.centos.org|g' /etc/yum.repos.d/CentOS-*

2. Alibaba Cloud mirrors (faster in Asia):

sudo curl -o /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-7.repo

For critical packages like wget when yum fails:

curl -O http://vault.centos.org/7.9.2009/os/x86_64/Packages/wget-1.14-18.el7_6.1.x86_64.rpm
sudo rpm -ivh wget-*.rpm

To prevent DNS changes from reverting after reboot:

sudo vi /etc/sysconfig/network-scripts/ifcfg-eth0

Add:

DNS1=8.8.8.8
DNS2=8.8.4.4

sudo yum clean all
sudo yum makecache
sudo yum install -y nano

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The error occurs when your CentOS 7 system cannot resolve the official repository domains. This typically indicates either:

• DNS resolution problems
• Outdated repository configurations
• Network connectivity issues

First, verify basic network connectivity:

ping -c 4 google.com

If this fails, check your network configuration:

nmcli connection show
cat /etc/resolv.conf

If DNS resolution is the problem, manually configure resolvers:

echo "nameserver 8.8.8.8" | sudo tee /etc/resolv.conf
echo "nameserver 1.1.1.1" | sudo tee -a /etc/resolv.conf

Option 1: Using vault.centos.org

Edit the base repository file:

sudo vi /etc/yum.repos.d/CentOS-Base.repo

Replace mirrorlist entries with:

[base]
name=CentOS-$releasever - Base
baseurl=https://vault.centos.org/centos/$releasever/os/$basearch/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7

Option 2: Using Community Mirrors

Example using MIT mirror:

[base]
name=CentOS-$releasever - Base
baseurl=http://mirrors.mit.edu/centos/$releasever/os/$basearch/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7

For immediate needs, download packages manually:

curl -O https://vault.centos.org/centos/7/os/x86_64/Packages/wget-1.14-18.el7_6.1.x86_64.rpm
sudo rpm -ivh wget-*.rpm

After making changes:

sudo yum clean all
sudo yum makecache
sudo yum install -y wget