yum安装软件时，出现“No package XXX available“的解决办法

系统：centos7.8

问题:

root@dev Downloads]# yum install alien
Loaded plugins: fastestmirror, langpacks, product-id, search-disabled-repos, subscription-manager

This system is not registered with an entitlement server. You can use subscription-manager to register.

Loading mirror speeds from cached hostfile
 * base: ftp.sjtu.edu
 * extras: ftp.sjtu.edu
 * updates: ftp.sjtu.edu
No package alien available.
Error: Nothing to do

解决方式：yum install epel-release

再重试就ok了