libGL error: failed to load driver: swrast

c71系统，以前装过bumblebee能成功运行，最近运行报错

[san /home/san]$ optirun glxgears
libGL error: failed to load driver: swrast
[VGL] WARNING: The OpenGL rendering context obtained on X display
[VGL]    :8 is indirect, which may cause performance to suffer.
[VGL]    If :8 is a local X display, then the framebuffer device
[VGL]    permissions may be set incorrectly.
[VGL] ERROR: in readPixels--
[VGL]    396: GL_ARB_pixel_buffer_object extension not available

[san /home/san]$ echo $LD_LIBRARY_PATH
/lib64:/lib:/usr/lib

去掉路径中的/lib64，再执行
[san /home/san]$ optirun glxgears
7264 frames in 5.0 seconds = 1452.634 FPS