SETREGID(3)                POSIX Programmer's Manual               SETREGID(3)



PPRROOLLOOGG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

NNAAMMEE
       setregid -- set real and effective group IDs

SSYYNNOOPPSSIISS
       #include <unistd.h>

       int setregid(gid_t _r_g_i_d, gid_t _e_g_i_d);

DDEESSCCRRIIPPTTIIOONN
       The _s_e_t_r_e_g_i_d() function shall set the real and effective group IDs of
       the calling process.

       If _r_g_i_d is -1, the real group ID shall not be changed; if _e_g_i_d is -1,
       the effective group ID shall not be changed.

       The real and effective group IDs may be set to different values in the
       same call.

       Only a process with appropriate privileges can set the real group ID
       and the effective group ID to any valid value.

       A non-privileged process can set either the real group ID to the saved
       set-group-ID from one of the _e_x_e_c family of functions, or the effective
       group ID to the saved set-group-ID or the real group ID.

       If the real group ID is being set (_r_g_i_d is not -1), or the effective
       group ID is being set to a value not equal to the real group ID, then
       the saved set-group-ID of the current process shall be set equal to the
       new effective group ID.

       Any supplementary group IDs of the calling process remain unchanged.

RREETTUURRNN VVAALLUUEE
       Upon successful completion, 0 shall be returned. Otherwise, -1 shall be
       returned and _e_r_r_n_o set to indicate the error, and neither of the group
       IDs are changed.

EERRRROORRSS
       The _s_e_t_r_e_g_i_d() function shall fail if:

       EEIINNVVAALL The value of the _r_g_i_d or _e_g_i_d argument is invalid or out-of-
              range.

       EEPPEERRMM  The process does not have appropriate privileges and a change
              other than changing the real group ID to the saved set-group-ID,
              or changing the effective group ID to the real group ID or the
              saved set-group-ID, was requested.

       _T_h_e _f_o_l_l_o_w_i_n_g _s_e_c_t_i_o_n_s _a_r_e _i_n_f_o_r_m_a_t_i_v_e_.

EEXXAAMMPPLLEESS
       None.

AAPPPPLLIICCAATTIIOONN UUSSAAGGEE
       If a non-privileged set-group-ID process sets its effective group ID to
       its real group ID, it can only set its effective group ID back to the
       previous value if _r_g_i_d was -1 in the _s_e_t_r_e_g_i_d() call, since the saved-
       group-ID is not changed in that case. If _r_g_i_d was equal to the real
       group ID in the _s_e_t_r_e_g_i_d() call, then the saved set-group-ID will also
       have been changed to the real user ID.

RRAATTIIOONNAALLEE
       Earlier versions of this standard did not specify whether the saved
       set-group-ID was affected by _s_e_t_r_e_g_i_d() calls. This version specifies
       common existing practice that constitutes an important security
       feature. The ability to set both the effective group ID and saved set-
       group-ID to be the same as the real group ID means that any security
       weakness in code that is executed after that point cannot result in
       malicious code being executed with the previous effective group ID.
       Privileged applications could already do this using just _s_e_t_g_i_d(), but
       for non-privileged applications the only standard method available is
       to use this feature of _s_e_t_r_e_g_i_d().

FFUUTTUURREE DDIIRREECCTTIIOONNSS
       None.

SSEEEE AALLSSOO
       _e_x_e_c, _g_e_t_e_g_i_d(), _g_e_t_e_u_i_d(), _g_e_t_g_i_d(), _g_e_t_u_i_d(), _s_e_t_e_g_i_d(), _s_e_t_e_u_i_d(),
       _s_e_t_g_i_d(), _s_e_t_r_e_u_i_d(), _s_e_t_u_i_d()

       The Base Definitions volume of POSIX.1-2017, <<uunniissttdd..hh>>

CCOOPPYYRRIIGGHHTT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  In the event of any discrepancy between this version and the
       original IEEE and The Open Group Standard, the original IEEE and The
       Open Group Standard is the referee document. The original Standard can
       be obtained online at http://www.opengroup.org/unix/online.html .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2017                          SETREGID(3)
