Note: All three methods should be preceded by an action

1. The default yum source after Centos installation is as follows

[root@kangvcar ~]# ll /etc/yum.repos.d/
total 32
-rw-r--r--. 1 root root 1664 Dec  9  2015 CentOS-Base.repo
-rw-r--r--. 1 root root 1309 Dec  9  2015 CentOS-CR.repo
-rw-r--r--. 1 root root  649 Dec  9  2015 CentOS-Debuginfo.repo
-rw-r--r--. 1 root root  290 Dec  9  2015 CentOS-fasttrack.repo
-rw-r--r--. 1 root root  630 Dec  9  2015 CentOS-Media.repo
-rw-r--r--. 1 root root 1331 Dec  9  2015 CentOS-Sources.repo
-rw-r--r--. 1 root root 1952 Dec  9  2015 CentOS-Vault.repo

2. Back up or delete the default or original yum source directly (optional)

[root@kangvcar ~]# mkdir /opt/centos-yum.bak
[root@kangvcar ~]# mv /etc/yum.repos.d/* /opt/centos-yum.bak/

Local yum source configuration

Step 1: Mount the CentOS image file on the virtual machine

[root@kangvcar ~]# mount -t iso9660 /dev/sr0 /opt/centos
mount: /dev/sr0 is write-protected, mounting read-only

Step 2: Write a repo file and point to the mirror mount directory

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

Step 3: Run yum makecache to generate the cache

    yum clean all

Run yum makecache to generate cache

    yum makecache

Update System

    yum -y update

Substitute yum Source for Ali Cloud Source under Centos

Official Aliyun Tutorial: http://mirrors.aliyun.com/help/centos

Ali Cloud Linux Installation Mirror Source Address: http://mirrors.aliyun.com/

Step 1: Download CentOS-Base.repo to/etc/yum.repos.d/

CentOS 5

    wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-5.repo

CentOS 6

    wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-6.repo

CentOS 7

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

Step 2: Run yum makecache to generate the cache

    yum clean all

Run yum makecache to generate cache

    yum makecache

Update System

    yum -y update

Replace yum source under Centos with domestic source 163

163 Official Tutorial: http://mirrors.163.com/.help/centos.html

Step 1: Download the 163 yum source repo file

CentOS 5

    wget -O /etc/yum.repos.d/CentOS5-Base-163.repo http://mirrors.163.com/.help/CentOS5-Base-163.repo

CentOS 6

    wget -O /etc/yum.repos.d/CentOS6-Base-163.repo http://mirrors.163.com/.help/CentOS6-Base-163.repo

CentOS 7

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

Step 2: Run yum makecache to generate the cache

    yum clean all

Run yum makecache to generate cache

    yum makecache

Update System

    yum -y update

Modify priority of yum source

ps: When installing packages with both local Yum source and 163 source, of course, we want to install the packages with the local Yum source first, and install the software with the 163 source when the available packages are not found locally. This involves priority issues, which can be solved by the plug-in yum-plugin-priorities.noarch provided by yum.

First: Check to see if the system has priority plug-ins installed

    [root@kangvcar ~]# rpm -qa | grep yum-plugin-
    yum-plugin-fastestmirror-1.1.31-34.el7.noarch        
    //You can see here that yum-plugin-priorities is not installed.noarchThis plugin
    [root@kangvcar ~]# yum search yum-plugin-priorities        
    //Use search to see if this plug-in is available
    Loaded plugins: fastestmirror
    Loading mirror speeds from cached hostfile
    * base: mirrors.aliyun.com
    * extras: mirrors.aliyun.com
    * updates: mirrors.aliyun.com
    ====================================================== N/S matched: yum-plugin-priorities =======================================================
    yum-plugin-priorities.noarch : plugin to give priorities to packages from different repos

Second: Install the yum-plugin-priorities.noarch plugin

    [root@kangvcar ~]# yum -y install yum-plugin-priorities.noarch

Third: Check if the plug-in is enabled

    [root@kangvcar ~]# cat /etc/yum/pluginconf.d/priorities.conf
    [main]
    enabled = 1
    //1 is enabled; 0 is disabled

Fourth: Modify local yum source to take precedence

    [root@kangvcar ~]# ll /etc/yum.repos.d/
    total 8
    -rw-r--r--. 1 root root 2573 May 15  2015 CentOS-Base.repo
    -rw-r--r--. 1 root root   67 Jun 20 06:04 local.repo
    //There are two repo files
    [root@kangvcar ~]# vi /etc/yum.repos.d/local.repo
    [local]
    name=local
    baseurl=file:///opt/centos
    enabled=1
    gpgcheck=0
    priority=1
    //Add priority=1 to the original; the smaller the number, the higher the priority
    //You can continue to modify the priority values of other sources, and after testing, configuring only local sources with priority=1 will give priority to local sources

Fifth: Testing

Before configuring priority: (use Ali yum source)

    [root@kangvcar ~]# yum -y install vim
    Dependencies Resolved
    =================================================================================================================================================
    Package                            Arch                         Version                                     Repository                     Size
    =================================================================================================================================================
    Installing:
    vim-enhanced                       x86_64                       2:7.4.160-1.el7_3.1                         updates                       1.0 M
    Updating for dependencies:
    vim-common                         x86_64                       2:7.4.160-1.el7_3.1                         updates                       5.9 M
    ······
    ······
    ······

After configuring priority: (using local yum source)

    [root@kangvcar ~]# yum -y install vim
    Dependencies Resolved
    =================================================================================================================================================
    Package                                     Arch                        Version                                Repository                  Size
    =================================================================================================================================================
    Installing:
    vim-enhanced                                x86_64                      2:7.4.160-1.el7                        local                      1.0 M
    Installing for dependencies:
    gpm-libs                                    x86_64                      1.20.7-5.el7                           local                       32 k
    perl                                        x86_64                      4:5.16.3-286.el7                       local                      8.0 M
    perl-Carp                                   noarch                      1.26-244.el7                           local                       19 k
    perl-Encode                                 x86_64                      2.51-7.el7                             local                      1.5 M
    perl-Exporter                               noarch                      5.68-3.el7                             local                       28 k
    perl-File-Path                              noarch                      2.09-2.el7                             local                       26 k
    perl-File-Temp                              noarch                      0.23.01-3.el7                          local                       56 k
    ······
    ······
    ······