一、配置软件仓库（软件仓库位置：/media/CentOS）
1、建立目录 “CentOS” 。()
mkdir -p /media/CentOS
2、挂载光盘“CentOS-Stream-8-x86_64-20210506-dvd1.iso”或者U盘。
3、将光盘文件夹“AppStream”、“BaseOS” 复制到 “/media/CentOS”目录。
cp -r AppStream/ BaseOS/ /media/CentOS
二、配置软件仓库文件（/etc/yum.repos.d/）
开启仓库，将 “enabled=0”, 改为“enabled=1”
# CentOS-Stream-Media.repo
#
# You can use this repo to install items directly off the installation media.
# Verify your mount point matches one of the below file:// paths.
[media-baseos]
name=CentOS Stream $releasever - Media - BaseOS
baseurl=file:///media/CentOS/BaseOS
file:///media/cdrom/BaseOS
file:///media/cdrecorder/BaseOS
gpgcheck=1
enabled=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-centosofficial
[media-appstream]
name=CentOS Stream $releasever - Media - AppStream
baseurl=file:///media/CentOS/AppStream
file:///media/cdrom/AppStream
file:///media/cdrecorder/AppStream
gpgcheck=1
enabled=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-centosofficial
三、测试本地源仓库：
dnf clean all dnf makecache dnf grouplist
下载速度已经很快了。