What does Linux do with existing files in a mount point?

When you mount a filesystem on a directory , you can no longer access files under directly. They still exist, but now refers to the root of the mounted filesystem, not to the directory that served as a mount point, so the contents of this directory cannot be accessed, at least in this way. For example: There are ways to get a merged view of the mounted filesystem and the data that was already present, but you need an extra layer called a union filesystem. Under Linux, there is a way to see the …