3.1 Ownership of files and processes

Every UNIX 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 take up the subject of file permissions in Chapter 5, The Filesystem.

While the owner of a file is always a single person, many people may be group owners of the file, so long as they are all part of a single UNIX group. Groups are defined in the /etc/group file.

See page 79 for more information about groups.

The owner of a file gets to specify what the group owners can do with it. This scheme ...

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