redhat man page for initgroups

INITGROUPS(3)						     Linux Programmer's Manual						     INITGROUPS(3)

NAME
       initgroups - initialize the supplementary group access list

SYNOPSIS
       #include <grp.h>
       #include <sys/types.h>

       int initgroups(const char *user, gid_t group);

DESCRIPTION
       The  initgroups() function initializes the group access list by reading the group database /etc/group and using all groups of which user is
       a member.  The additional group group is also added to the list.

RETURN VALUE
       The initgroups() function returns 0 on success, or -1 if an error occurs.

ERRORS
       EPERM  The calling process does not have sufficient privileges.

       ENOMEM Insufficient memory to allocate group information structure.

FILES
       /etc/group	   group database file

CONFORMING TO
       SVID 3, BSD 4.3

NOTES
       The prototype for initgroups is only available if _BSD_SOURCE is defined (either explicitly, or implicitly, by not  defining  _POSIX_SOURCE
       or compiling with the -ansi flag).

SEE ALSO
       getgroups(2), setgroups(2)

GNU
								    1993-04-05							     INITGROUPS(3)