1.更新yum源
yum -y update
2.尝试安装sl
yum install sl
执行yum命令时会去centos镜像查找sl包，但是镜像中没有sl包，所以要安装额外包，需要安装epel-release-6-8.noarch.rpm
3.下载epel-release-6-8.noarch.rpm
wget http://dl.fedoraproject.org/pub/epel/6/x86_64/epel-release-6-8.noarch.rpm
4.安装
rpm -ivh epel-release-6-8.noarch.rpm
5.再次安装sl
yum -y install sl
6.执行sl命令