1、备份源

cd /etc/yum.repos.d/

mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup

2、更新yum官方源（国内）

wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo
#或
curl -o /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo
# 更新 EPEL 源
wget -O /etc/yum.repos.d/epel.repo http://mirrors.aliyun.com/repo/epel-7.repo
# 或者
curl -O /etc/yum.repos.d/epel.repo http://mirrors.aliyun.com/repo/epel-7.repo

# 执行完成后需要清理缓存生成新的缓存
yum clean all
yum makecache

3、更新yum官方源（国外）

cd /etc/yum.repos.d

cat > CentOS-Base.repo <<'EOF'
[base]
name=CentOS-7.9.2009
enabled=1
failovermethod=priority
baseurl=https://vault.centos.org/7.9.2009/os/$basearch/
gpgcheck=1
gpgkey=https://vault.centos.org/RPM-GPG-KEY-CentOS-7
[updates]
name=CentOS-7.9.2009
enabled=1
failovermethod=priority
baseurl=https://vault.centos.org/7.9.2009/updates/$basearch/
gpgcheck=1
gpgkey=https://vault.centos.org/RPM-GPG-KEY-CentOS-7
[extras]
name=CentOS-7.9.2009
enabled=1
failovermethod=priority
baseurl=https://vault.centos.org/7.9.2009/extras/$basearch/
gpgcheck=1
gpgkey=https://vault.centos.org/RPM-GPG-KEY-CentOS-7
EOF

cd /etc/yum.repos.d

cat > epel.repo <<'EOF'
[epel]
name=Extra Packages for Enterprise Linux 7 - $basearch
#baseurl=http://download.fedoraproject.org/pub/epel/7/$basearch
metalink=https://mirrors.fedoraproject.org/metalink?repo=epel-7&arch=$basearch
failovermethod=priority
enabled=1
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-EPEL-7
 
[epel-debuginfo]
name=Extra Packages for Enterprise Linux 7 - $basearch - Debug
#baseurl=http://download.fedoraproject.org/pub/epel/7/$basearch/debug
metalink=https://mirrors.fedoraproject.org/metalink?repo=epel-debug-7&arch=$basearch
failovermethod=priority
enabled=0
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-EPEL-7
gpgcheck=1
 
[epel-source]
name=Extra Packages for Enterprise Linux 7 - $basearch - Source
#baseurl=http://download.fedoraproject.org/pub/epel/7/SRPMS
metalink=https://mirrors.fedoraproject.org/metalink?repo=epel-source-7&arch=$basearch
failovermethod=priority
enabled=0
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-EPEL-7
gpgcheck=1
EOF

# 清理缓存并生成新的缓存
yum clean all
yum makecache

4、更新yum

yum update -y