Comment 12 for bug 855943

sudo apt-get install --reinstall libgl1-mesa-glx
...
Unpacking replacement libgl1-mesa-glx ...
Setting up libgl1-mesa-glx (7.11-0ubuntu3) ...
update-alternatives: warning: alternative /usr/lib/fglrx/ld.so.conf (part of link group x86_64-linux-gnu_gl_conf) doesn't exist. Removing from list of alternatives.
update-alternatives: warning: alternative /usr/lib/pxpress/ld.so.conf (part of link group x86_64-linux-gnu_gl_conf) doesn't exist. Removing from list of alternatives.
update-alternatives: warning: /etc/alternatives/x86_64-linux-gnu_gl_conf is dangling, it will be updated with best choice.
update-alternatives: using /usr/lib/x86_64-linux-gnu/mesa/ld.so.conf to provide /etc/ld.so.conf.d/x86_64-linux-gnu_GL.conf (x86_64-linux-gnu_gl_conf) in auto mode.
Processing triggers for libc-bin ...
ldconfig deferred processing now taking place