In Eclipse the ADT Plugin got invisible on ubuntu OS.

Eclipse ADT plugin on Ubuntu 10.10 after upgrade from 10.04

Recently, after upgrading my Ubuntu to 10.10 from 10.04, I found that my Eclipse Android Development Toolkit plugin stopped working. The Eclipse Help->Installation Details Menu would list ADT under Installed Software Tab. However, neither the Features Tab nor the Plug-ins Tab would list ADT. I noticed that my SVN plugin was not showing up after the upgrade too. Forums such as http://forum.xda-developers.com/showthread.php?p=8613858 were not useful either -- they suggested uninstalling Eclipse which came with Ubuntu 10.10 distribution and replacing it with stock Eclipse from eclipse.org website. I solved this without reinstalling eclipse although, plugins need to reinstalled.

An inotifywatch -r on the ~/.eclipse/org.eclipse.platform_3.5.0_155965261/plugins directory, and subsequently starting eclipse revealed that eclipse was not even trying to read any plugins from that directory. Apparently something in Ubuntu 10.10 build of Eclipse has changed which causes it ignore the previously installed plugins. So I moved out my old ~/.eclipse/org.eclipse.platform_3.5.0_155965261/ directory to /tmp. Restarted my Eclipse and reinstalled my ADT and other plugins. Here are the steps:

1. Exit eclipse if running
2. Delete ~/.eclipse/org.eclipse.platform_3.5.0_155965261
3. Start eclipse
4. Open Help->Install New Software
5. Install GEF plugin from http://download.eclipse.org/tools/gef/updates/releases. Note that GEF is required for ADT
6. Install ADT plugin from https://dl-ssl.google.com/android/eclipse

You should have a working ADT in Eclipse on an upgraded Ubuntu 10.10.


Google explain below....
http://code.google.com/intl/es/eclipse/docs/faq.html#wstinstallerror
Multi-user installs of Eclipse are those where the adminstrator of the machine has performed the installation of Eclipse, and non-administrators (users) run Eclipse.

Unfortunately, Eclipse 3.5 and 3.6 suffer from problems whenever a user upgrades a plugin that exists as part of the base installation; the upgraded plugin is not recognized, which means that any plugins that depend on the upgraded component will not work. When installing GPE as a user, it may cause Eclipse to try and install updates for already-installed plugins at the same time, which leads to GPE not working after the install process.
There are two ways to avoid this problem:

• Each user should have their own install of Eclipse

• The administrator should be the only one who installs or upgrades plugins

If you have already installed/upgraded GPE and are stuck in a broken state, the easiest way to get back to a working state is to remove your<homedir>/.eclipse/org.eclipse.platform_<eclipse.version> directory, and perform the install/upgrade of GPE as an administrator. Note that by deleting this directory, you will be removing any plugins that the user had previously installed.