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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 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 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,  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 .