详解CentOS8更换yum源后出现同步仓库缓存失败的问题

不知道为啥就开始出现同步仓库缓存失败的问题，无法正常安装一些工具包。错误提示如下：

上报错！！！

 然后百思不得其解，我寻思系统默认的yum源可能因为网络的原因连不上也就算了，国内的源不应该啊，是不是配置有问题呢？结果还真是，baseurl中的$releasever和$basearch占位符不知为何无效。故将$releasever改为8，将$basearch改为x86_64后问题解决。修改后的各个配置文件内容如下：

### cat CentOS-Base.repo ###
[base]
name=CentOS-8 - Base - mirrors.aliyun.com
failovermethod=priority
baseurl=https://mirrors.aliyun.com/centos/8/BaseOS/x86_64/os/
     http://mirrors.aliyuncs.com/centos/8/BaseOS/x86_64/os/
     http://mirrors.cloud.aliyuncs.com/centos/8/BaseOS/x86_64/os/
gpgcheck=1
gpgkey=https://mirrors.aliyun.com/centos/RPM-GPG-KEY-CentOS-Official
 
 
### cat CentOS-AppStream.repo ###
[AppStream]
name=CentOS-8 - AppStream - mirrors.aliyun.com
failovermethod=priority
baseurl=https://mirrors.aliyun.com/centos/8/AppStream/x86_64/os/
     http://mirrors.aliyuncs.com/centos/8/AppStream/x86_64/os/
     http://mirrors.cloud.aliyuncs.com/centos/8/AppStream/x86_64/os/
gpgcheck=1
gpgkey=https://mirrors.aliyun.com/centos/RPM-GPG-KEY-CentOS-Official
 
 
### cat CentOS-Extras.repo ###
[extras]
name=CentOS-8 - Extras - mirrors.aliyun.com
failovermethod=priority
baseurl=https://mirrors.aliyun.com/centos/8/extras/x86_64/os/
     http://mirrors.aliyuncs.com/centos/8/extras/x86_64/os/
     http://mirrors.cloud.aliyuncs.com/centos/8/extras/x86_64/os/
gpgcheck=1
gpgkey=https://mirrors.aliyun.com/centos/RPM-GPG-KEY-CentOS-Official
 
### cat CentOS-Epel.repo ###
[epel]
name=CentOS-$releasever - Epel
baseurl=http://mirrors.aliyun.com/epel/8/Everything/$basearch
enabled=1
gpgcheck=0
 
 
### cat CentOS-PowerTools.repo ###
[PowerTools]
name=CentOS-8 - PowerTools - mirrors.aliyun.com
failovermethod=priority
baseurl=https://mirrors.aliyun.com/centos/8/PowerTools/x86_64/os/
     http://mirrors.aliyuncs.com/centos/8/PowerTools/x86_64/os/
     http://mirrors.cloud.aliyuncs.com/centos/8/PowerTools/x86_64/os/
gpgcheck=1
enabled=0
gpgkey=https://mirrors.aliyun.com/centos/RPM-GPG-KEY-CentOS-Official
 
 
### cat CentOS-centosplus.repo ###
[centosplus]
name=CentOS-8 - Plus - mirrors.aliyun.com
failovermethod=priority
baseurl=https://mirrors.aliyun.com/centos/8/centosplus/x86_64/os/
     http://mirrors.aliyuncs.com/centos/8/centosplus/x86_64/os/
     http://mirrors.cloud.aliyuncs.com/centos/8/centosplus/x86_64/os/
gpgcheck=1
enabled=0
gpgkey=https://mirrors.aliyun.com/centos/RPM-GPG-KEY-CentOS-Official

做完以上修改后问题解决，没有再提示同步仓库缓存失败了：