How to Build a Fast Local Yum Repository on CentOS and Switch to Domestic Mirrors

1. View the default Yum repository files

# ll /etc/yum.repos.d/

2. (Optional) Backup the existing Yum repository files

# mkdir /opt/centos-yum.bak
# mv /etc/yum.repos.d/* /opt/centos-yum.bak/

3. Mount the CentOS ISO image in the virtual machine

# mount -t iso9660 /dev/sr0 /opt/centos

4. Create a repo file that points to the mounted ISO

# vi /etc/yum.repos.d/local.repo
[local]
name=local
baseurl=file:///opt/centos
enabled=1
gpgcheck=0

5. Clean the Yum cache and rebuild it

# yum clean all
# yum makecache

6. Replace the default repo with the Aliyun mirror

Download the appropriate Aliyun repo file for your CentOS version and overwrite the existing CentOS-Base.repo:

# wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo

# yum clean all
# yum makecache

7. Replace the default repo with the 163 mirror

Download the 163 repo file for your CentOS version:

# wget -O /etc/yum.repos.d/CentOS7-Base-163.repo http://mirrors.163.com/.help/CentOS7-Base-163.repo

# yum clean all
# yum makecache

8. Set repository priority so the local repo is preferred

Install the priority plugin and configure it:

# yum -y install yum-plugin-priorities.noarch

# cat /etc/yum/pluginconf.d/priorities.conf
[main]
enabled = 1

Add priority=1 to the local repo (lower numbers mean higher priority):

# vi /etc/yum.repos.d/local.repo
[local]
name=local
baseurl=file:///opt/centos
enabled=1
gpgcheck=0
priority=1

9. Test package installation before and after setting priority

Before priority (using Aliyun repo):

# yum -y install vim
# ... package is pulled from the "updates" repository

After priority (using local repo):

# yum -y install vim
# ... package and all dependencies are resolved from the "local" repository

These steps provide a fast, offline Yum source and ensure it is used preferentially over external mirrors.