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+.\"-
+.\" SPDX-License-Identifier: BSD-3-Clause
+.\"
+.\" Copyright (c) 1991, 1993
+.\"	The Regents of the University of California.  All rights reserved.
+.\" Copyright (c) 2025 The FreeBSD Foundation
+.\"
+.\" Portions of this documentation were written by Olivier Certner
+.\" <olce@FreeBSD.org> at Kumacom SARL under sponsorship from the FreeBSD
+.\" Foundation.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\" 3. Neither the name of the University nor the names of its contributors
+.\"    may be used to endorse or promote products derived from this software
+.\"    without specific prior written permission.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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+.\"
+.Dd October 9, 2025
+.Dt GETGROUPLIST 3
+.Os
+.Sh NAME
+.Nm getgrouplist
+.Nd produce a user's effective group list
+.Sh LIBRARY
+.Lb libc
+.Sh SYNOPSIS
+.In unistd.h
+.Ft int
+.Fn getgrouplist "const char *name" "gid_t basegid" "gid_t *groups" "int *ngroups"
+.Sh DESCRIPTION
+The
+.Fn getgrouplist
+function retrieves from the group database the supplementary groups for the user
+specified in
+.Fa name
+and returns the effective group list, whose first group is the value of
+.Fa basegid
+and the others are the supplementary groups.
+.Fa basegid
+typically is the user's initial numerical group ID from the password database.
+.Pp
+The effective group list is returned in the array pointed to by
+.Fa groups .
+The caller specifies the length of the
+.Fa groups
+array in the integer pointed to by
+.Fa ngroups .
+The number of groups of the effective group list, which may be greater than the
+.Fa groups
+array's length, is returned through
+.Fa ngroups .
+.Sh RETURN VALUES
+The
+.Fn getgrouplist
+function returns 0 on success and \-1 if the length of the group list is too
+small to hold all the user's groups.
+In the latter case, the
+.Fa groups
+array is filled with as many groups as possible from the start of the effective
+group list, and the length pointed to by
+.Fa ngroups
+is set to the full length of the latter, thus to a value strictly greater than
+before the call.
+.Sh FILES
+.Bl -tag -width /etc/group -compact
+.It Pa /etc/group
+group membership list
+.El
+.Sh SEE ALSO
+.Xr setcred 2 ,
+.Xr setgroups 2 ,
+.Xr initgroups 3
+.Sh HISTORY
+The
+.Fn getgrouplist
+function first appeared in
+.Bx 4.4 .