GETGROUPS(3)               POSIX Programmer's Manual              GETGROUPS(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
       getgroups -- get supplementary group IDs

SSYYNNOOPPSSIISS
       #include <unistd.h>

       int getgroups(int _g_i_d_s_e_t_s_i_z_e, gid_t _g_r_o_u_p_l_i_s_t[]);

DDEESSCCRRIIPPTTIIOONN
       The _g_e_t_g_r_o_u_p_s() function shall fill in the array _g_r_o_u_p_l_i_s_t with the
       current supplementary group IDs of the calling process. It is
       implementation-defined whether _g_e_t_g_r_o_u_p_s() also returns the effective
       group ID in the _g_r_o_u_p_l_i_s_t array.

       The _g_i_d_s_e_t_s_i_z_e argument specifies the number of elements in the array
       _g_r_o_u_p_l_i_s_t.  The actual number of group IDs stored in the array shall be
       returned.  The values of array entries with indices greater than or
       equal to the value returned are undefined.

       If _g_i_d_s_e_t_s_i_z_e is 0, _g_e_t_g_r_o_u_p_s() shall return the number of group IDs
       that it would otherwise return without modifying the array pointed to
       by _g_r_o_u_p_l_i_s_t.

       If the effective group ID of the process is returned with the
       supplementary group IDs, the value returned shall always be greater
       than or equal to one and less than or equal to the value of
       {NGROUPS_MAX}+1.

RREETTUURRNN VVAALLUUEE
       Upon successful completion, the number of supplementary group IDs shall
       be returned. A return value of -1 indicates failure and _e_r_r_n_o shall be
       set to indicate the error.

EERRRROORRSS
       The _g_e_t_g_r_o_u_p_s() function shall fail if:

       EEIINNVVAALL The _g_i_d_s_e_t_s_i_z_e argument is non-zero and less than the number of
              group IDs that would have been returned.

       _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
   GGeettttiinngg tthhee SSuupppplleemmeennttaarryy GGrroouupp IIDDss ooff tthhee CCaalllliinngg PPrroocceessss
       The following example places the current supplementary group IDs of the
       calling process into the _g_r_o_u_p array.


           #include <sys/types.h>
           #include <unistd.h>
           ...
           gid_t *group;
           int nogroups;
           long ngroups_max;

           ngroups_max = sysconf(_SC_NGROUPS_MAX) + 1;
           group = (gid_t *)malloc(ngroups_max *sizeof(gid_t));

           ngroups = getgroups(ngroups_max, group);

AAPPPPLLIICCAATTIIOONN UUSSAAGGEE
       None.

RRAATTIIOONNAALLEE
       The related function _s_e_t_g_r_o_u_p_s() is a privileged operation and
       therefore is not covered by this volume of POSIX.1-2017.

       As implied by the definition of supplementary groups, the effective
       group ID may appear in the array returned by _g_e_t_g_r_o_u_p_s() or it may be
       returned only by _g_e_t_e_g_i_d().  Duplication may exist, but the application
       needs to call _g_e_t_e_g_i_d() to be sure of getting all of the information.
       Various implementation variations and administrative sequences cause
       the set of groups appearing in the result of _g_e_t_g_r_o_u_p_s() to vary in
       order and as to whether the effective group ID is included, even when
       the set of groups is the same (in the mathematical sense of ``set'').
       (The history of a process and its parents could affect the details of
       the result.)

       Application developers should note that {NGROUPS_MAX} is not
       necessarily a constant on all implementations.

FFUUTTUURREE DDIIRREECCTTIIOONNSS
       None.

SSEEEE AALLSSOO
       _g_e_t_e_g_i_d(), _s_e_t_g_i_d()

       The Base Definitions volume of POSIX.1-2017, <<ssyyss__ttyyppeess..hh>>, <<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                         GETGROUPS(3)
