转自：http://blog.hexu.org/archives/2060.shtml
遇到这个问题情景：
下午第一台系统是Centos7， 安装配置完成后，接着一台是Centos 6 系统，由于疏忽直接下载并安装了 “epel-release-7-5.noarch.rpm”，安装时提示了问题，于是下载安装“epel-release- 6-8.noarch.rpm” ，安装成功后发现遇到 问题了”Error: xz compression not available”。
遇到问题的原因：
epel-release-75.noarch.rpm 进了cache目录
如何解决这个问题：
需要手动进行清理 cache, 然后重新remove当前的 epel-relase， 最后重装一下正常的“epel-release-6-8.noarch.rpm”即可。
所有操作如下：
#系统是Centos 6.6， 这里错误了安装 epel
[root@ip-127-0-0-1 softs] rpm -ivh http://mirrors.ustc.edu.cn/epel/7/x86_64/e/epel-release-7-5.noarch.rpm
#使用 yum search munin 时提示了错误信息
[root@ip-127-0-0-1 softs] yum search munin
Loaded plugins: amazon-id, rhui-lb, security
Error: xz compression not available
# 开始解决Error, remove 错误的epel
[root@ip-127-0-0-1 softs] yum remove epel-release
Loaded plugins: amazon-id, rhui-lb, security
Setting up Remove Process
Resolving Dependencies
.....
# 中间提示时 输入 y (yes)
Installed size: 22 k
Is this ok [y/N]: y
Downloading Packages:
Running rpm_check_debug
Running Transaction Test
Transaction Test Succeeded
Running Transaction
Warning: RPMDB altered outside of yum.
Erasing : epel-release-7-5.noarch 1/1
Verifying : epel-release-7-5.noarch 1/1
Removed:
epel-release.noarch 0:7-5
Complete!
# 清理epel 缓存
[root@ip-127-0-0-1 softs]# rm -rf /var/cache/yum/x86_64/6Server/epel/
# 重新安装正确的epel
[root@ip-127-0-0-1 softs]# rpm -ivh epel-release-6-8.noarch.rpm
# 再次确认，成功完成
[root@ip-127-0-0-1 softs]# yum search munin
Loaded plugins: amazon-id, rhui-lb, security
epel/metalink | 13 kB 00:00
epel | 4.4 kB 00:00
epel/primary_db | 6.7 MB 00:00
epel/pkgtags | 1.6 MB 00:00
========================= N/S Matched: munin ===============
PyMunin.noarch : Python Module for developing Munin Multigraph Monitoring Plugins
munin-java-plugins.noarch : java-plugins for munin
munin-ruby-plugins.noarch : ruby-plugins for munin
unbound-munin.noarch : Plugin for the munin / munin-node monitoring package
munin.noarch : Network-wide graphing framework (grapher/gatherer)
munin-async.noarch : Network-wide graphing framework (asynchronous client tools)
munin-cgi.noarch : Network-wide graphing framework (cgi files for apache)
munin-common.noarch : Network-wide graphing framework (common files)
munin-netip-plugins.noarch : Network-wide graphing framework (dhcpd3 and ntp plugins)
munin-nginx.noarch : Network-wide graphing framework (cgi files for nginx)
munin-node.noarch : Network-wide graphing framework (node)
Name and summary matches only, use "search all" for everything.