更换CentOS 8 yum 源的笨办法

1. 首先运行以下命令

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

   1. 如果不报错，直接用官方的办法

      centos镜像-centos下载地址-centos安装教程-阿里巴巴开源镜像站 (aliyun.com)

   2. 如果报 CentOS-Base.repo 文件不存在的错误，可以尝试我的这个笨办法

2. 运行以下命令，然后看看会不会报错

   yum clean all && yum makecache
   

   1. 如果报错，就替换 baseurl，在我运行这条命令报了两次错误，先后替换了/etc/yum.repos.d/ 目录下的 CentOS-Linux-AppStream.repo 和 CentOS-Linux-BaseOS.repo 的 baseurl。他们的 baseurl 在附录的代码中有，对应的内容为首字母小型下面的baseurl，如CentOS-Linux-BaseOS.repo对应的是[base]下的url。
   2. 快速替换baseurl，以CentOS-Linux-AppStream.repo为例，运行前先备份。

以下内容为执行wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.cloud.aliyuncs.com/repo/Centos-vault-8.5.2111.repo命令所得。

# CentOS-Base.repo
#
# The mirror system uses the connecting IP address of the client and the
# update status of each mirror to pick mirrors that are updated to and
# geographically close to the client.  You should use this for CentOS updates
# unless you are manually picking other mirrors.
#
# If the mirrorlist= does not work for you, as a fall back you can try the 
# remarked out baseurl= line instead.
#
#
 
[base]
name=CentOS-8.5.2111 - Base - mirrors.aliyun.com
baseurl=http://mirrors.aliyun.com/centos-vault/8.5.2111/BaseOS/$basearch/os/
        http://mirrors.aliyuncs.com/centos-vault/8.5.2111/BaseOS/$basearch/os/
        http://mirrors.cloud.aliyuncs.com/centos-vault/8.5.2111/BaseOS/$basearch/os/
gpgcheck=0
gpgkey=http://mirrors.aliyun.com/centos/RPM-GPG-KEY-CentOS-Official
 
#additional packages that may be useful
[extras]
name=CentOS-8.5.2111 - Extras - mirrors.aliyun.com
baseurl=http://mirrors.aliyun.com/centos-vault/8.5.2111/extras/$basearch/os/
        http://mirrors.aliyuncs.com/centos-vault/8.5.2111/extras/$basearch/os/
        http://mirrors.cloud.aliyuncs.com/centos-vault/8.5.2111/extras/$basearch/os/
gpgcheck=0
gpgkey=http://mirrors.aliyun.com/centos/RPM-GPG-KEY-CentOS-Official
 
#additional packages that extend functionality of existing packages
[centosplus]
name=CentOS-8.5.2111 - Plus - mirrors.aliyun.com
baseurl=http://mirrors.aliyun.com/centos-vault/8.5.2111/centosplus/$basearch/os/
        http://mirrors.aliyuncs.com/centos-vault/8.5.2111/centosplus/$basearch/os/
        http://mirrors.cloud.aliyuncs.com/centos-vault/8.5.2111/centosplus/$basearch/os/
gpgcheck=0
enabled=0
gpgkey=http://mirrors.aliyun.com/centos/RPM-GPG-KEY-CentOS-Official
 
[PowerTools]
name=CentOS-8.5.2111 - PowerTools - mirrors.aliyun.com
baseurl=http://mirrors.aliyun.com/centos-vault/8.5.2111/PowerTools/$basearch/os/
        http://mirrors.aliyuncs.com/centos-vault/8.5.2111/PowerTools/$basearch/os/
        http://mirrors.cloud.aliyuncs.com/centos-vault/8.5.2111/PowerTools/$basearch/os/
gpgcheck=0
enabled=0
gpgkey=http://mirrors.aliyun.com/centos/RPM-GPG-KEY-CentOS-Official


[AppStream]
name=CentOS-8.5.2111 - AppStream - mirrors.aliyun.com
baseurl=http://mirrors.aliyun.com/centos-vault/8.5.2111/AppStream/$basearch/os/
        http://mirrors.aliyuncs.com/centos-vault/8.5.2111/AppStream/$basearch/os/
        http://mirrors.cloud.aliyuncs.com/centos-vault/8.5.2111/AppStream/$basearch/os/
gpgcheck=0
gpgkey=http://mirrors.aliyun.com/centos/RPM-GPG-KEY-CentOS-Official
```