Assigning identifiers for users

Assigning the same UID to more than one person is strongly discouraged. If you assign the same UID to more than one user ID, z/OS UNIX and RACF® treat, in some ways, the users as if they were a single z/OS UNIX user. For example:

The users share the same MAXPROCUSER limit, which is defined in the BPXPRMxx member, unless each user profile contains its own user limit for MAXPROCUSER.
The users count as a single user for the MAXUIDS limit in BPXPRMxx.
One user can enter the kill command for the other's processes.
The users share ownership and access to the same files.
Services such as the getpwuid() callable service cannot distinguish which user is meant. Such services return data about one of the users, but which user is unpredictable.

If you assign users the same UID, you should warn them of the effects. For UID(0), the effects are less significant, because superusers have access to all processes and files and because most BPXPRMxx limits are not enforced against superusers.

To assign a non-unique UID, you can use the SHARED keyword of the RACF ADDGROUP or ALTGROUP command if the SHARED.IDS profile is defined in the UNIXPRIV class.