1.\"- 2.\" SPDX-License-Identifier: BSD-3-Clause 3.\" 4.\" Copyright (c) 1991, 1993 5.\" The Regents of the University of California. All rights reserved. 6.\" Copyright (c) 2025 The FreeBSD Foundation 7.\" 8.\" Portions of this documentation were written by Olivier Certner 9.\" <olce@FreeBSD.org> at Kumacom SARL under sponsorship from the FreeBSD 10.\" Foundation. 11.\" 12.\" Redistribution and use in source and binary forms, with or without 13.\" modification, are permitted provided that the following conditions 14.\" are met: 15.\" 1. Redistributions of source code must retain the above copyright 16.\" notice, this list of conditions and the following disclaimer. 17.\" 2. Redistributions in binary form must reproduce the above copyright 18.\" notice, this list of conditions and the following disclaimer in the 19.\" documentation and/or other materials provided with the distribution. 20.\" 3. Neither the name of the University nor the names of its contributors 21.\" may be used to endorse or promote products derived from this software 22.\" without specific prior written permission. 23.\" 24.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 25.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 26.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 27.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 28.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 29.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 30.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 31.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 32.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 33.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 34.\" SUCH DAMAGE. 35.\" 36.Dd October 9, 2025 37.Dt GETGROUPLIST 3 38.Os 39.Sh NAME 40.Nm getgrouplist 41.Nd produce a user's effective group list 42.Sh LIBRARY 43.Lb libc 44.Sh SYNOPSIS 45.In unistd.h 46.Ft int 47.Fn getgrouplist "const char *name" "gid_t basegid" "gid_t *groups" "int *ngroups" 48.Sh DESCRIPTION 49The 50.Fn getgrouplist 51function retrieves from the group database the supplementary groups for the user 52specified in 53.Fa name 54and returns the effective group list, whose first group is the value of 55.Fa basegid 56and the others are the supplementary groups. 57.Fa basegid 58typically is the user's initial numerical group ID from the password database. 59.Pp 60The effective group list is returned in the array pointed to by 61.Fa groups . 62The caller specifies the length of the 63.Fa groups 64array in the integer pointed to by 65.Fa ngroups . 66The number of groups of the effective group list, which may be greater than the 67.Fa groups 68array's length, is returned through 69.Fa ngroups . 70.Sh RETURN VALUES 71The 72.Fn getgrouplist 73function returns 0 on success and \-1 if the length of the group list is too 74small to hold all the user's groups. 75In the latter case, the 76.Fa groups 77array is filled with as many groups as possible from the start of the effective 78group list, and the length pointed to by 79.Fa ngroups 80is set to the full length of the latter, thus to a value strictly greater than 81before the call. 82.Sh FILES 83.Bl -tag -width /etc/group -compact 84.It Pa /etc/group 85group membership list 86.El 87.Sh SEE ALSO 88.Xr setcred 2 , 89.Xr setgroups 2 , 90.Xr initgroups 3 91.Sh HISTORY 92The 93.Fn getgrouplist 94function first appeared in 95.Bx 4.4 . 96