When a new UNIX file is created on z/OS®, by default, the owning UID is initialized from the effective UID of the creating process, and the owning GID is copied from the parent directory. The POSIX standard allows the owning GID to be taken either from the parent directory, or from the effective GID of the creating process.

Many versions of UNIX and Linux use the set-gid bit of the parent directory to determine how to set a new object's group owner. If the parent's set-gid bit is on, then the group owner is set to that of the parent directory. Otherwise, it is set from the effective GID of the process. Further, the set-gid bit for a new directory is inherited from the parent directory.

This behavior can be configured on z/OS by defining the FILE.GROUPOWNER.SETGID profile in the UNIXPRIV class.