Before answering the question, I want to comment on the answer of gokulvarma and the conversation between gokulvarma and daniel:
Having no sudo permission is not the reason of daniel's failure to add System Tools to Applications menu. He couldn't add it because he tried to add an empty category. System Tools is a category or a sub-menu, if we add an application which will fall under any category, that category is automatically created. On the other hand, if there's nothing under it, we can't create the category; when we try, the tick disappears in some seconds. If we clear all elements under a category, category is cleared automaticaly.
daniel tried to add that category by selecting Applications from the left pane and ticking the System Tools from the right pane. Like this:
Instead, he should select System Tools from the left pane -which is already visible there- and he should tick Configuration Editor from the right pane. Like this:
When he is done, in his Applications menu, System Tools category/sub-menu should appear with Configuration Editor in it. Like this:
There's no need to be a sudoer to do this because the tool we are adding can be used by any user to arrange his/her own preferences.
But will this tool, Configuration Editor, help daniel to solve his problem? In my opinion, it won't, because this is the same of what he calls gconf-editor. Either via Alt+F2 or via Terminal, gconf-editor command will open that application and it sounds that daniel already can reach that application but he can't find gnome-system-tools in it. He wants to find the gnome-system-tools there in order to reach users section of it.
In my Configuration Editor, which can be accessed by comand line as well, I can't see something as gnome-system-tools, too. neither can I find users section. Maybe its somewhere there hidden under some category or it isn't there anymore. (GNOME setting managers have evolved a lot, recently; the sites daniel told about might be a old) lets refer to GNOME System Tools' official documentation: What are the GNOME System Tools? There, among others, we see a screenshot of the tool to manage users and groups:
And this is the tool that we know as Users and Groups.(Yes interface is slightly changed, but this is it.) It can be reached via System->Administration. So, there's no need to struggle to reach it from inside other tools. Its there. But as Bobby who commented on the question, I couldn't get well what "fix show all users" means.
What is Gconf?
GConf is a system for storing application preferences. These preferences are stored in XML files under the user's home directory, ~/.gconf. Each preference is represented as a key-value pair.
GConf is meant to be a way for developers to easily store user preferences and system administrators to set default values for particular preferences. In most cases, there is no need for a user to edit Gconf keys directly.
The vast majority of keys correspond to entries in the various applications' preference menus. Though on occasion, developers will use Gconf keys as a way to enable undocumented features. These are "hidden" from users for a number of reasons. Sometimes the feature is still a work in progress. Other times it is a feature that the developer wants to do away with but still leave accessible to users that don't want to give it up. Frequently, the features are targeted at "power users," and the developer simply doesn't want to clutter up the normal preference dialog.
In some ways it is similar to Windows' Registry. One major difference is that, unlike the Windows' Registry, Gconf does not store system settings. It only stores application preferences. While editing Gconf keys may potentially cause minor issues with specific programs, it should never lead to system wide issues such as rendering your system unbootable. In fact, deleting the entire ~/.gconf directory will simply revert all programs using Gconf back to their defaults.
Managing Gconf from the command-line.
The program gconftool-2 allows the user to interact with Gconf from the command-line. It is often simpler to enter a one line command in the terminal than digging around in Gconf's GUI tool. For instance, if you would like to show the icon for you trash on the desktop simply run:
gconftool-2 --set /apps/nautilus/desktop/trash_icon_visible --type=bool true
This also illustrates what I meant by key-value pair above. In this case, the key is /apps/nautilus/desktop/trash_icon_visible which has a value of true.
You can perform a variety of operations with gconftool-2. If you'd simply like to see a key's value, use --get:
gconftool-2 --get /apps/nautilus/desktop/trash_icon_visible
If you'd simply like to reset a value to its default, use --unset:
gconftool-2 --unset /apps/nautilus/desktop/trash_icon_visible
gconftool-2 can be particularly useful for system administrators. For instance, /etc/gconf/gconf.xml.mandatory can be used to set mandatory preferences for all users. Further information on more advanced uses can be found with man gconftool-2 as well as in the GNOME Desktop System Administration Guide
How do I use the Gconf editor?
What was your question again? Oh, that's right: How do I use the Gconf editor?
gconf-editor is the graphical interface to manage Gconf settings. By default, it is not displayed in the menus. The easiest way to start it is by pressing Alt+F2 to bring up the "Run Dialog." Next, enter gconf-editor.
gconf-editor allows you to browse through the key-value pairs in a tree. Let's look at the example from above. Browse to apps > nautilus > desktop and you will see the trash_icon_visible key.
Best Answer
gnome-system-tools now uses dconf instead of gconf so you have to use
dconf-editor(not installed by default, install packagedconf-tools) instead ofgconf-editor.