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

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 implemen-
       tation-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 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 informa-
       tion. 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 Technol-
       ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications 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 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 .

IEEE
/The Open Group						       2003							      GETGROUPS(P)