RACF segment
A section of a RACF user or group profile that holds settings for one part of the system, such as TSO or Unix System Services.
Also written OMVS segment, TSO segment, CICS segment, UID, GID
A RACF user profile has a base section, with the user's name, groups and attributes, and can have extra sections, called segments, for other parts of the system.
The TSO segment holds the user's TSO settings: the logon procedure, account number and default region size. Without one, the user cannot log on to TSO. The OMVS segment holds Unix settings: the user's UID, a number Unix uses to identify them, their home directory and their default shell. Without it, the user cannot use Unix System Services, and some z/OS functions that rely on it fail. Groups have an OMVS segment too, holding a GID. Other segments hold settings for CICS, for storage defaults, for MFA and more.
Segments are added and changed with the same commands as the rest of the profile, such as ALTUSER userid OMVS(UID(1234) HOME('/u/userid')).
When a user can do one thing but not another, for example log on to TSO but not start a Unix shell, a missing or incomplete segment is a common cause. LISTUSER with the segment name shows what is set.
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- RACF user IDA person or program's identity on the system. Short, unique, and the basis of every access decision.
- RACFThe security manager for z/OS, which decides who may sign on, read a dataset, or run a transaction.
- Unix System ServicesA full Unix environment built into z/OS, with a shell, directories and files alongside the traditional mainframe world.
- ALTUSERA RACF command that changes an existing user ID: a new password, a revoke, a resume or other details.
- RACF groupA named collection of users, used to grant access to many people at once rather than one at a time.