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+.\"
+.\" SPDX-License-Identifier: BSD-2-Clause
+.\"
+.\" Copyright (C) 2023 Olivier Certner <olce.freebsd@certner.fr>
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
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+.\"    the first lines of this file unmodified other than the possible
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+.\" 2. Redistributions in binary form must reproduce the above copyright
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+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
+.\" EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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+.\" DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE LIABLE FOR ANY
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+.\"
+.Dd June 19, 2023
+.Dt REALGROUPMEMBER 9
+.Os
+.Sh NAME
+.Nm realgroupmember
+.Nd checks whether credentials indicate membership of some group
+.Sh SYNOPSIS
+.In sys/param.h
+.In sys/ucred.h
+.Ft int
+.Fn groupmember "gid_t gid" "struct ucred *cred"
+.Sh DESCRIPTION
+The
+.Fn realgroupmember
+function checks if credentials
+.Fa cred
+indicate that the associated subject or object is a member of the group
+designated by the group ID
+.Fa gid .
+.Pp
+Considered groups in
+.Fa cred
+are the real and supplementary groups.
+The effective group is not taken into account.
+.Sh RETURN VALUES
+If the
+.Fa gid
+is found, 1 is returned, otherwise 0.
+.Sh SEE ALSO
+.Xr groupmember 9