4.4BSD/usr/share/man/cat2/setgid.0

SETUID(2)                   BSD Programmer's Manual                  SETUID(2)

NNAAMMEE
     sseettuuiidd, sseetteeuuiidd, sseettggiidd, sseetteeggiidd, - set user and group ID

SSYYNNOOPPSSIISS
     ##iinncclluuddee <<ssyyss//ttyyppeess..hh>>
     ##iinncclluuddee <<uunniissttdd..hh>>

     _i_n_t
     sseettuuiidd(_u_i_d___t _u_i_d);

     _i_n_t
     sseetteeuuiidd(_u_i_d___t _e_u_i_d);

     _i_n_t
     sseettggiidd(_g_i_d___t _g_i_d);

     _i_n_t
     sseetteeggiidd(_g_i_d___t _e_g_i_d);

DDEESSCCRRIIPPTTIIOONN
     The sseettuuiidd() function sets the real and effective user IDs and the saved
     set-user-ID of the current process to the specified value.  The sseettuuiidd()
     function is permitted if the specified ID is equal to the real user ID of
     the process, or if the effective user ID is that of the super user.

     The sseettggiidd() function sets the real and effective group IDs and the saved
     set-group-ID of the current process to the specified value.  The sseettggiidd()
     function is permitted if the specified ID is equal to the real group ID
     of the process, or if the effective user ID is that of the super user.

     The sseetteeuuiidd() function (sseetteeggiidd()) sets the effective user ID (group ID)
     of the current process.  The effective user ID may be set to the value of
     the real user ID or the saved set-user-ID (see intro(2) and execve(2));
     in this way, the effective user ID of a set-user-ID executable may be
     toggled by switching to the real user ID, then re-enabled by reverting to
     the set-user-ID value.  Similarly, the effective group ID may be set to
     the value of the real group ID or the saved set-user-ID.

RREETTUURRNN VVAALLUUEESS
     Upon success, these functions return 0; otherwise -1 is returned.

     If the user is not the super user, or the uid specified is not the real,
     effective ID, or saved ID, these functions return -1.

SSEEEE AALLSSOO
     getuid(2),  getgid(2)

SSTTAANNDDAARRDDSS
     The sseettuuiidd() and sseettggiidd() functions are compliant with the IEEE
     Std1003.1-1988 (``POSIX'') specification with _POSIX_SAVED_IDS not de-
     fined.  The sseetteeuuiidd() and sseetteeggiidd() functions are extensions based on the
     POSIX concept of _POSIX_SAVED_IDS, and have been proposed for a future
     revision of the standard.

4.2 Berkeley Distribution        June 4, 1993                                1