When you mount drives from other system,USB,or mount a remote folder.There will be icons on your desktop by default.You may not prefer your desktop with those icons and want a clean desktop.Here’s an easy way to get them disable.

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Press Alt+F2 and type gconf-editor to open the app,or run gconf-editor in terminal.

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In following screen,navigate to app–>nautilus–>desktop ,and at the right side you will see the key volumes_visible,it need to be uncheck.

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Now,all those icons disappear from your desktop and you can always access them at Places–>Computer.