You can assign a user identifier (UID) to a RACF® user by specifying a UID value in the OMVS segment of the RACF user profile. When assigning a UID to a user, make sure that the user's default group has an assigned GID. If the user specifies a group during logon or on a batch job, this current connect group must also have an assigned GID. A user with a UID and a default group (and current connect group, if applicable) with a GID can use z/OS UNIX functions and access z/OS UNIX files based on the assigned UID and GID values. If a UID and GID are not available as described, the user cannot use z/OS UNIX functions.

The following command defines a UID, and other OMVS segment information, for an existing RACF user:

ALTUSER KAMAL OMVS(UID(122649) HOME('/') PROGRAM('/bin/sh'))

For more information about UIDs, see The OMVS segment in user profiles and "Defining UIDs and GIDs" in z/OS UNIX System Services Planning.

Although you can assign the same UID to multiple users, it is not recommended. However, it might be necessary for some cases, such as superusers. If you assign the same UID to multiple users, control at an individual user level is lost because the UID is used in z/OS UNIX security checks. Users with the same UID assignment are treated as a single user during z/OS UNIX security checks.

You can enforce identity uniqueness when automatically assigning UNIX identifiers. For more on controlling UID uniqueness, refer to Controlling the use of shared UNIX identities. A unique UID can be defined using the AUTOUID operand, as described in Enabling automatic assignment of unique UNIX identities.