Unity Launcher has disappeared!

Yesterday, I freshly installed Ubuntu 12.04 and it worked fine, but today when I booted the computer something strange happened. The Unity Launcher disappeared!

Any help would be appreciated.

You need to launch CCSM and make sure that Enable Ubuntu Unity Plugin is ticked.

If you don't have CCSM installed, do the following:

1. Press Ctrl+Alt+T to launch the Terminal.

2. Type the following command and press Enter

   sudo apt-get install compizconfig-settings-manager
   

3. Now, launch CCSM by running this command from the Terminal:

   sudo ccsm
   

4. In the CCSM window, select Desktop → Ubuntu Unity Plugin.

   

5. In the next window, make sure Enable Ubuntu Unitu Plugin is checked.

   

I had pretty much the same problem under 12.04 (64 bit). Unity was slow with my aged GPU, so I was using Unity 2d as my desktop for months. For no apparent reason, it suddenly refused to display launchpad and title bar (for all users). Autohide was disabled. Reenabling Unity in CCSM as sugggested above was part of the solution, but none of the other measures suggested in several other related threads, including, but not limited to:

1. Reinstalling unity

2. Reinstalling ubuntu desktop

3. Removing all relevant (e.g. compiz, gconf, etc.) configuration information

helped me to completely resolve these symptoms.

unity --reset

would not work for me. After delivering a variety of error and information messages, it would always hang at:

Setting Update "run_key"

as shown in the log posted in the thread titled "unity has vanished" for unity run with no arguments.

I noticed that the error message delivered by:

/usr/lib/nux/unity_support_test -p

was similar to some of the errors reported by unity --reset:

error while loading shared libraries: libGL.so.1: cannot open shared object file: No such file or directory.

After extensive searching, I found the following solution:

1. Get the path of libGL.so.1 by using the command locate libGL.so.1.

2. Add a link to the library in /usr/lib/ as shown in the following example:

   sudo ln -s /usr/lib/i386/mesa/libGL.so.1 /usr/lib

   (courtesy of J.D. Bartlett)

3. Restart the computer.

This not only allowed both unity_support_test-p and unity --reset to run, it also allowed Unity 2d to start. Like the author of the above-mentioned post, I have no idea what caused my problems. I am also still not sure whether the link is a complete solution, or whether I should reinstall the graphics libraries completely, as described by Cynical here.