Every file has an owner which is one of the registered user names defined on the system.
Each file also has a group , which is one of the defined groups. The file owner and group play a role in determining access because the file has one set of access permission bits for the user that is the owner, another set that apply to users who belong to the file's group, and a third set of bits that apply to everyone else. See Access Permission , for the details of how access is decided based on this data. The file's group ID may be set from either effective group ID of the process, or the group ID of the directory that contains the file, depending on the system where the file is stored. When you access a remote file system, it behaves according to its own rule, not according to the system your program is running on.