Reinstating the nouveau driver after having installed the NVidia driver on CentOS 7

Due to the NVidia proprietary driver not working with 3D acceleration on VNC, which meant that users had to use MATE (GNOME 2) on VNC sessions, and couldn't use vino-server for the :0 session if the console desktop was GNOME 3, we decided to try the nouveau driver instead.

The steps for removing the NVidia driver are in this post for Fedora. For CentOS 7 the corresponding steps are:

nvidia-uninstall
yum install -y xorg-x11-drv-nouveau (just in case it wasn't installed)
rm -f /etc/modprobe.d/nvidia-installer-disable-nouveau.conf
rm -f /usr/lib/modprobe.d/nvidia-installer-disable-nouveau.conf

dracut -f

systemctl reboot

Note the removal of the second occurrence of the modprobe blacklist file created by the NVidia installer. Without removing this, the blacklist is still in place in the initramfs.

The symptom was that the nouveau driver was loaded only when the X server was started, not at boot, which caused it to not detect anything but one monitor and only one mode setting, as the output of xrandr showed.

NVIDIA driver, libglx.so and hardware acceleration crashing X server

My users on CentOS complained that Firefox would crash the X server after I updated the package xorg-x11-server-Xorg.

A search returned suggestions to disable hardware acceleration in Firefox. However a user mentioned that when he reinstalled the NVIDIA driver, it gave the warning libglx.so is not a symbolic link before setting things right.

An investigation showed that the NVIDIA installer replaces the file /usr/lib64/xorg/modules/extensions/libglx.so with a symlink to /usr/lib64/xorg/modules/extensions/libglx.so.X.Y where X.Y is the NVIDIA package version. So every time the xorg-x11-server-Xorg package is reinstalled, it replaces the symlink and hardware acceleration fails, crashing the X server.

The same problem for Debian is documented in this forum thread.

I could blacklist xorg-x11-server-Xorg in yum but I rather not do that. Since I may forget when an update of that package happens, I wrote a shell script to restore the symlink if removed and a cron job to call it periodically. But I'm also looking to make a Puppet stanza to do this.