User categories

Unix defines permissions for access to a file according to three categories of users:

• user -- a specific user, the owner of the file.
• group -- a specific group of users, to which the file belongs.
• other -- all other users with accounts on the system.

(The word world is often used as a synonym for other.) Also, all is used to mean all three categories together.

For example, a particular system might have accounts for users smith and curry, who belong to the group named students, and for user adams, who belongs to the group named staff. A particular file may be owned by user smith, and belong to group students. Permissions for access to this file (described below) can be defined separately for smith as the user or owner of the file, for all members of the students group (smith and curry), and for all users.