在centos7 GUI中安装pptp vpn client需要安装ppp pptp pptp-setup 及 NetworkManager-pptp-gnome.x86_64
1、pptp ppp pptp-setup通过yum install安装就可以完成
2、NetworkManager-pptp-gnome需要先安装第三方包Nux Dextop
Nux Dextop是类似CentOS、RHEL、ScientificLinux的第三方RPM仓库，关于Nux Dextop的介绍附上文章链接https://www.jianshu.com/p/86d16189832e
安装步骤：
1、yum安装pptp ppp pptp-setup
2、安装Nux Dextop
yum -y install epel-release
rpm -Uvh http://li.nux.ro/download/nux/dextop/el7/x86_64/nux-dextop-release-0-5.el7.nux.noarch.rpm
3、安装NetworkManager-pptp-gnome.x86_64
yum install NetworkManager-pptp-gnome.x86_64