yum install python-pip 报错：GPG key retrieval failed: [Errno 14] Could not open/read file:///etc/pki/rpm-gpg/RPM-GPG-KEY-EPEL-6

解决方法：
vim /etc/yum.repos.d/epel.repo
[epel]
name=Extra Packages for Enterprise Linux 6 – $basearch

baseurl=http://download.fedoraproject.org/pub/epel/6/$basearch

mirrorlist=https://mirrors.fedoraproject.org/metalink?repo=epel-6&arch=$basearch
failovermethod=priority
enabled=1
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-EPEL-6
把gpgcheck=1改为gpgcheck=0

为了保险，装完后再改回1