Tente:
Go System > Preferences > Screensaver and uncheck the box that says lock when screensaver is active.
Outra
gconftool-2 --type boolean -s /apps/gnome-power-manager/lock_on_blank_screen false
gconftool-2 --type boolean -s /apps/gnome-power-manager/lock_use_screensaver_settings false
Se esses dois não funcionarem,
Open the terminal, and type gconf-editor In the window that comes up go to apps > gnome-power-manager > lock On the right, UNCHECK suspend and hibernate and make sure that the use_screensaver_settings is CHECKED
ou -
In your terminal type sudo gedit /etc/default/acpi-support
Go to the line that says LOCK_SCREEN=true and put a # in front of it.
Feche, salve e experimente.
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