Preheat oven to 350 degrees F (175 degrees C). Grease a 9×13 inch pan. Sift together the flour,baking soda and cinnamon. Set aside.
In a large bowl, combine the sugar and oil until blended.Beat in the eggs one at a time, then stir in the vanilla. Stir in the flour mixture just until incorporated.Fold in the pineapple, carrots, coconut and walnuts.Pour batter into prepared pan.
Bake in the preheated oven for 45 minutes, or until a toothpick inserted into the center of the cake comes out clean.While still warm, poke holes in the cake with a fork.
For the glaze:In a saucepan, combine butter, sugar, buttermilk and vanilla.Bring mixture to a boil over medium heat, then reduce heat and cook for 5 minutes.Pour glaze over warm cake, then allow to cool completely.
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