GETGROUPS(3P)                                       POSIX Programmer's Manual                                      GETGROUPS(3P)



PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (con-
       sult the corresponding Linux manual page for details of Linux behavior), or the  interface  may  not  be  implemented  on
       Linux.

NAME
       getgroups - get supplementary group IDs

SYNOPSIS
       #include <unistd.h>

       int getgroups(int gidsetsize, gid_t grouplist[]);


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

       The gidsetsize argument specifies the number of elements in the array grouplist. 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 gidsetsize is 0, getgroups() shall return the number of group IDs that it would otherwise return without modifying the
       array pointed to by grouplist.

       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.

RETURN VALUE
       Upon successful completion, the number of supplementary group IDs shall be returned. A return value of -1 indicates fail-
       ure and errno shall be set to indicate the error.

ERRORS
       The getgroups() function shall fail if:

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


       The following sections are informative.

EXAMPLES
   Getting the Supplementary Group IDs of the Calling Process
       The following example places the current supplementary group IDs of the calling process into the group 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);

APPLICATION USAGE
       None.

RATIONALE
       The  related  function  setgroups()  is  a  privileged  operation  and  therefore  is  not  covered  by  this  volume  of
       IEEE Std 1003.1-2001.

       As implied by the definition of supplementary groups, the effective group ID may appear in the  array  returned  by  get-
       groups()  or  it may be returned only by getegid(). Duplication may exist, but the application needs to call getegid() 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 getgroups() 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 writers should note that {NGROUPS_MAX} is not necessarily a constant on all implementations.

FUTURE DIRECTIONS
       None.

SEE ALSO
       getegid(), setgid(), the Base Definitions volume of IEEE Std 1003.1-2001, <sys/types.h>, <unistd.h>

COPYRIGHT
       Portions  of  this  text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for
       Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6,  Copy-
       right (C) 2001-2003 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.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                                 GETGROUPS(3P)