CentOS 6.8, 运行完如下命令后，使用yum安装程序会报错： xz compression not available。
rpm -Uvh https://mirror.webtatic.com/yum/el7/epel-release.rpm
rpm -Uvh https://mirror.webtatic.com/yum/el7/webtatic-release.rpm
原因是epel版本不对，需要卸载重新安装：
# yum remove epel-release
# yum install epel-release