POSIX User Database

The user database contains POSIX information about the users in the system. For each user, it contains at least the following information:

User name

This is the login name that identifies a POSIX user. It is analogous to a user's user ID on a VM system and is the lowercase version of the VM user ID.

User ID (UID)

This is a numeric identifier for the POSIX user. It will be the user's initial real UID, effective UID and saved set-UID when the user logs on. It identifies the user to the system when certain POSIX functions are being handled, including authorization checks before file access and program execution. Even though multiple users are permitted to have the same UID, this is not recommended, because UIDs are used for various authorizations. If multiple users have the same UID, individual accountability may be lost.

A UID of 0 identifies a user as one with appropriate privileges. POSIX permits processes with appropriate privileges to perform additional or different functions in certain situations. Take care when assigning a UID of 0 to a user. It may be appropriate for certain service virtual machines.

If users are not assigned a UID in the user database, they may each be assigned the same default value by the system. This is what happens when the user database information is contained in the CP directory. If an ESM provides this information, it may behave differently. If multiple users have the same UID, each of them will appear the same to POSIX functions that reference these UIDs. As previously mentioned, this is not recommended.

Primary group id (GID)

This identifies a POSIX group defined in the POSIX group database. It will be the user's initial real GID, effective GID and saved set-GID when the user logs on. A user's group affiliation is referenced when certain POSIX functions are being handled, including authorization checks before file access and program execution.

If users are not assigned a GID in the user database, they may each be assigned the same default value by the system. In this case, all of these users will appear the same to POSIX functions that reference these GIDs. This could be used to permit all these users to access or run certain files, or it could be used to deny all unregistered users from accessing or running any POSIX file.

Initial working directory

This is the user's home directory. Unless overridden by the OPENVM SET DIRECTORY command, it will be the current directory when a user first enters the POSIX environment.

Initial user program

This is the name of an application. It is typically a shell, a program that accepts commands from the user and supervises the execution of other programs. This is the program that will be invoked by the OPENVM SHELL command.

In addition to the above information required by POSIX, the following information may also be contained in the user database:

File system root: This is the user's root file system. Unless overridden by the OPENVM MOUNT command, it is the Byte File System that will be mounted as the root file system when a user first enters the POSIX environment.

When not provided by an ESM, most of the user database information is taken from POSIXINFO directory control statements in the individual users' directory entries. Because some of the database information may consist of very long, mixed-case character strings with embedded blanks and quotation marks, it may be necessary to specify multiple POSIXINFO statements or continue a single statement across multiple records in the user directory file.