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+.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
+.TH "GETGROUPS" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
+.\" getgroups 
+.SH NAME
+getgroups \- get supplementary group IDs
+.SH SYNOPSIS
+.LP
+\fB#include <unistd.h>
+.br
+.sp
+int getgroups(int\fP \fIgidsetsize\fP\fB, gid_t\fP \fIgrouplist\fP\fB[]);
+.br
+\fP
+.SH DESCRIPTION
+.LP
+The \fIgetgroups\fP() function shall fill in the array \fIgrouplist\fP
+with the current supplementary group IDs of the calling
+process. It is implementation-defined whether \fIgetgroups\fP() also
+returns the effective group ID in the \fIgrouplist\fP
+array.
+.LP
+The \fIgidsetsize\fP argument specifies the number of elements in
+the array \fIgrouplist\fP. 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.
+.LP
+If \fIgidsetsize\fP is 0, \fIgetgroups\fP() shall return the number
+of group IDs that it would otherwise return without
+modifying the array pointed to by \fIgrouplist\fP.
+.LP
+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.
+.SH RETURN VALUE
+.LP
+Upon successful completion, the number of supplementary group IDs
+shall be returned. A return value of -1 indicates failure and
+\fIerrno\fP shall be set to indicate the error.
+.SH ERRORS
+.LP
+The \fIgetgroups\fP() function shall fail if:
+.TP 7
+.B EINVAL
+The \fIgidsetsize\fP argument is non-zero and less than the number
+of group IDs that would have been returned.
+.sp
+.LP
+\fIThe following sections are informative.\fP
+.SH EXAMPLES
+.SS Getting the Supplementary Group IDs of the Calling Process
+.LP
+The following example places the current supplementary group IDs of
+the calling process into the \fIgroup\fP array.
+.sp
+.RS
+.nf
+
+\fB#include <sys/types.h>
+#include <unistd.h>
+\&...
+gid_t *group;
+int nogroups;
+long ngroups_max;
+.sp
+
+ngroups_max = sysconf(_SC_NGROUPS_MAX) + 1;
+group = (gid_t *)malloc(ngroups_max *sizeof(gid_t));
+.sp
+
+ngroups = getgroups(ngroups_max, group);
+\fP
+.fi
+.RE
+.SH APPLICATION USAGE
+.LP
+None.
+.SH RATIONALE
+.LP
+The related function \fIsetgroups\fP() is a privileged operation and
+therefore is not covered by this volume of
+IEEE\ Std\ 1003.1-2001.
+.LP
+As implied by the definition of supplementary groups, the effective
+group ID may appear in the array returned by
+\fIgetgroups\fP() or it may be returned only by \fIgetegid\fP(). Duplication
+may exist,
+but the application needs to call \fIgetegid\fP() 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
+\fIgetgroups\fP() 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.)
+.LP
+Application writers should note that {NGROUPS_MAX} is not necessarily
+a constant on all implementations.
+.SH FUTURE DIRECTIONS
+.LP
+None.
+.SH SEE ALSO
+.LP
+\fIgetegid\fP() , \fIsetgid\fP() , the Base Definitions volume of
+IEEE\ Std\ 1003.1-2001, \fI<sys/types.h>\fP, \fI<unistd.h>\fP
+.SH 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 .