i5-2300 的cpu，自带GPU，更新Gnome-shell 3.8.1后进不去gdm,一番搜索以后发现是 Intel的GPU加速模式有问题，默认是uxa,需要更新至SNA,详见官方文档
https://wiki.archlinux.org/index.php/Intel#Choose_acceleration_method
具体方法:
创建
/etc/X11/xorg.conf.d/20-intel.conf
添加以下内容:
Section "Device"
Identifier "Intel Graphics"
Driver "intel"
Option "AccelMethod" "sna"
EndSection