User Identification Codes

A User Identification Code (UIC) is associated with each user account. A UIC is the combination of a group number and a member number.

A UIC takes the format "[group,member]." If you are member 100 of group 35, your UIC is [35,100]. These numbers are displayed in octal format, so they may contain only the digits 0 through 7. UICs may be displayed as alphanumeric names rather than numbers (see "Identifiers," below).

A system manager usually defines UIC groups to associate users who are related in some way, such as the faculty as opposed to the students at a university or all the employees in a given department of a corporation—say, the accounting department.

Your UIC is used to grant or deny access to system objects, such as files. When a file is created, the UIC of the owner is associated with the file. Later, when some user requests access to the file, his or her UIC is used to determine whether access will be allowed. File protection is divided into four categories, based on the requesting user's classification:

• SYSTEM user. The requestor is either OpenVMS itself, the system manager, or another user with a SYSTEM UIC, as defined by the system manager. The system manager may assign an arbitrary number of users to this category, usually system operators or those who perform system backups.

• File OWNER. The requestor's UIC exactly matches the UIC attached to the file.

• GROUP member. The requestor is in the same UIC group as the file owner.

• WORLD user. This category includes every other user not mentioned above.

Each of these four categories may be granted or denied the ability to read (examine), write (modify), execute (if the file is a program or procedure), or delete the file.

The ability to change the protection of the file (CONTROL access) is granted automatically to the OWNER and SYSTEM categories. As a practical matter, this means you cannot accidentally deny yourself access to your files (as you can always grant yourself access again), nor can you prevent SYSTEM users from gaining access. You can also grant other users CONTROL access via Access Control Lists (ACLs).

File protections and ACLs are described further in Chapter 7, "The User Environment."