PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

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

PROLOG         top

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

NAME         top

       getgroups — get supplementary group IDs

SYNOPSIS         top

       #include <unistd.h>

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

DESCRIPTION         top

       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         top

       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         top

       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         top

   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         top

       None.

RATIONALE         top

       The related function setgroups() is a privileged operation and
       therefore is not covered by this volume of POSIX.1‐2008.

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

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       getegid(3p), setgid(3p)

       The Base Definitions volume of POSIX.1‐2008, sys_types.h(0p),
       unistd.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The Open
       Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
       applied.) 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.unix.org/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                 2013                       GETGROUPS(3P)

Pages that refer to this page: unistd.h(0p)id(1p)open(3p)