A hard connection is a connection to a file on the same file system, where a node is the unique identifier of the file's existence. In this case, instead of using ln A B when linking between different file systems, you should use A symbolic connection, A soft connection, which simply contains A full pathname reference to the system. A hard connection is a record of the address of a file, and every file you see in the file manager is a "hard connection" to a file on disk. When all the hard connections of a file are deleted, the space occupied by the file can be overwritten by the newly added data.