Fedora 20 Gnome 3因更新系统而无法进入桌面的问题的解决过程

X Error of failed request:  BadWindow (invalid Window parameter)
  Major opcode of failed request:  154 (NV-GLX)
  Minor opcode of failed request:  4 ()
  Resource id in failed request:  0x4200003
  Serial number of failed request:  35
  Current serial number in output stream:  35
gnome-session-check-accelerated: Helper exited with code 256
X Error of failed request:  BadWindow (invalid Window parameter)
  Major opcode of failed request:  154 (NV-GLX)
  Minor opcode of failed request:  4 ()
  Resource id in failed request:  0x4200003
  Serial number of failed request:  35
  Current serial number in output stream:  35
gnome-session-check-accelerated: Helper exited with code 256
** (process:5568): WARNING **: software acceleration check failed: Child process exited with code 1

提示是X或显卡驱动出了不兼容问题。用bing搜索答案，找了不少网页，试验了很多次（包括给一些软件包降级什么的），都不中用。

后来通过yumex程序发现Fedora 20在自动更新的过程中竟然擅自将kernel从原来的3.11升级为3.15，于是用uname -r命令发现当前用的正是3.15的内核。猜测极有可能是内核跟nvidia闭源驱动不兼容的问题导致此次致命故障发生。

于是更改boot文件，将内核恢复到3.11，然后重新启动Fedora 20，再重新编译一次nvidia驱动，搞定！

这个大bug浪费了我两个多小时时间。得出一个教训：

教训：千万别轻易更新内核kernel软件包，否则很容易导致硬件问题！