GEDA - cannot edit attributes
It sounds like you are not managing to select anything other than the default attribute name. Click the dropdown arrow for the "Name" field where it defaults to 'netname' and select 'value' from the list. Then enter your value in the large "value" text area. Then select the visible button and choose name and value or not as you need for this attribute (value is normally visible and "Show Value Only"). Then click Add and it should put the new element in the list for you. If it doesn't look anything like the following image (also from Ubuntu) then your installation likely is broken in some manner.