UNIX also allows files to be shared between users and groups of users. If Larry so desired, he could cut off access to his files, such that noother user could access them. However, on most systems the default is to allow other users to read your files, but not modify or delete them in any way. As explained above, every file is owned by a particular user. However, files are also owned by a particular group , which is a system-defined group of users.
Every user is placed into at least one group when that user is created.
However, the system administratormay also grant the user access to more than one group. Groups are usually defined by the type of users which access the machine. For example, on a university UNIX system, users may be placed into thegroups student , staff , faculty or guest . Write permission allows the user towrite to and modify the file. For directories, write permission allowsthe user to create new files or delete files within that directory.