The access permission bits are set for three classes. When a user's process accesses a file, the system determines the class of the process and then uses the permission bits for that class to determine if the process can access the file. For a file, a process can be in only one class. The class for a process can be different for each file or directory.

To change the UID of a file, a person with superuser authority, or the file owner with appropriate access to the CHOWN.UNRESTRICTED profile in the UNIXPRIV class, can enter a chown command or use the chown() callable service. To change the GID of a file, a superuser or the file owner (that is, a process in the owner class) can enter a chgrp command or use the chgrp() function. You can define profiles in the UNIXPRIV class to grant RACF® authorization for certain z/OS® UNIX privileges, as explained in Using UNIXPRIV class profiles.

If you want to specify that, by default, the group owner of a new file is to come from the effective GID of the creating process, you need to set up a profile in the UNIXPRIV class called FILE.GROUPOWNER.SETGID. Steps for setting up the FILE.GROUPOWNER.SETGID profile describes the process.