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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 dif-
       fer (consult 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 indi-
       cates failure 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  getgroups()  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  administra-
       tive  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, Stan-
       dard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base  Specifica-
       tions  Issue  6,  Copyright (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 Stan-
       dard,  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 .



IEEE/The Open Group                  2003                        GETGROUPS(3P)