Scratch is about beginnings, but to do something from scratch doesn’t mean to scratch something with your fingernail and have it appear. Scratch in this instance finds its origin in sports talk.
Originally, the scratch was the starting line in a race, likely from such a line being scratched into the earth when races were held on soft terrain.
体育赛跑中，在地上用树枝划一条线，表示赛跑的起点，由此引申为起点。从起点开始，即从零开始
Example：
Linux from scratch 从零开始学linux
