How you get this effect on a cake?  I was thinking of icing it smooth and then using the serrated edge of an icing spatula to make the lines but it wouldn't have the same rustic effect as this cake.  

link to cake

your link said i needed permission to proceed so maybe someone else can see it or post another link -- rustic cakes are some of my favorites

Here's a new link.  This one should be "shareable"

https://drive.google.com/file/d/0B7LttX7gd_haU3NHSXZaaWtTRUVxR2NyZHN4Skhma2RvenpN/view?usp=sharing

i would do that with the tip of a knife -- might have to test a few -- i also thought of using a wooden fork that would have a little bit wider prong -- and you don't clean it off as you hold it up to the cake and swirl around the turntable -- the icing builds up and  it flakes off and leaves the little bits all around all around -- but that looks to be done one swirl around at at time -- not several like a fork would do --

i use a regular fork to do that on the edges of a book like if i was making a vintage book -- but those are much closer together so you just need something that's a bit wider --