Linux Administration Handbook, Second Edition

3.1. Ownership of files and processes

Every file has both an owner and a “group owner.” The owner of the file enjoys one special privilege that is not shared with everyone on the system: the ability to modify the permissions of the file. In particular, the owner can set the permissions on a file so restrictively that no one else can access it.^[1] We talk more about file permissions in Chapter 5, The Filesystem.

Although the owner of a file is always a single person, many people can be group owners of the file, as long as they are all part of a single Linux group. Groups are traditionally defined in the /etc/group file, but these days group information is more commonly stored on an NIS or LDAP server on the network; see Chapter 17, ...