Compiz in Ubuntu 18.04 Not Working

If Compiz does not work after installing Ubuntu 18.04, make sure you are actually running a Unity session. Compiz is the window manager used by Unity, but Ubuntu 18.04 defaults to GNOME Shell, where Compiz is not the active window manager.

Install the Unity desktop session:

sudo apt update
sudo apt install ubuntu-unity-desktop

After installation, log out. On the login screen, click the session selector, usually the gear icon near the password field, and choose Unity. Then log in again.

You can check the current desktop session with:

echo "$XDG_CURRENT_DESKTOP"

If Unity is running, Compiz settings should apply normally. For example, ccsm changes should affect the desktop only when the session is using Compiz as its window manager.

If the CompizConfig Settings Manager is not installed, install it with:

sudo apt install compizconfig-settings-manager

Then start it with:

ccsm

Be careful when disabling core Compiz plugins, especially window decoration, move window, resize window, and Unity-related plugins. Disabling required plugins can make the desktop difficult to use. If the session becomes broken, reset Compiz and Unity settings from a terminal:

dconf reset -f /org/compiz/
setsid unity

In short: install ubuntu-unity-desktop, select Unity at login, and configure Compiz from that session rather than from the default GNOME session.