Plugins installed on Eclipse not visible

When I install a plugin in Eclipse everything goes well. But after restarting the new plugin is not visible. I have tried it with different plugins, but they have all the same problem. The only place where I can see them is when I look at "What is already installed?".

What could be the problem?

This issue and its solution is described in a DZone article and at the nWire blog.
It all boils down to these two options:

• Install Eclipse to a folder where your user has full rights or
• Start Eclipse as an administrator

sudo eclipse -clean;  

Help --> Install software --> Re-install the plugins and software;

Explanation:
Eclipse is installed and the majority of programs are also installed initially with root privileges.

Typically 'Ownership' of hidden install folders like this belong to the 'Sudo' or Root user. Therefore changes and installs to these hidden folders will not take.

Have you tried running Eclipse with the -clean argument ? You need to do this only once and not every time you start Eclipse, you it is recommended to do so after a plugin installation.

If that doesn't help, verify if you have privileges to write onto the features and plugins subdirectories. The plugin installation process requires the write privilege, but I've never seen a plugin installation succeed without one; still, it is worth checking for.