Ubuntu uses IcedTea I think, which in its latest version supports 1024-bit and 2048-bit DHE on the server side (768-bit DHE is still default though) and up to 4

Ubuntu uses IcedTea I think, which in its latest version supports 1024-bit and 2048-bit DHE on the server side (768-bit DHE is still default though) and up to 4096-bit DHE on the client side.