.\"	$OpenBSD: revnetgroup.8,v 1.11 2009/10/20 11:01:31 sobrado Exp $
.\"
.\" Copyright (c) 1995
.\"	Bill Paul <wpaul@ctr.columbia.edu>.  All rights reserved.
.\"
.\" 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. All advertising materials mentioning features or use of this software
.\"    must display the following acknowledgement:
.\"	This product includes software developed by Bill Paul.
.\" 4. 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 Bill Paul 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
.\" ARE DISCLAIMED.  IN NO EVENT SHALL Bill Paul OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\"	$FreeBSD: revnetgroup.8,v 1.4 1997/02/22 14:22:03 peter Exp $
.\"
.Dd $Mdocdate: October 20 2009 $
.Dt REVNETGROUP 8
.Os
.Sh NAME
.Nm revnetgroup
.Nd "generate reverse netgroup data"
.Sh SYNOPSIS
.Nm revnetgroup
.Fl h | u
.Op Fl f Ar netgroup_file
.Sh DESCRIPTION
.Nm
processes the contents of a file in
.Xr netgroup 5
format into what is called
.Pa reverse netgroup
form.
That is, where the original file shows
netgroup memberships in terms of which members reside in a particular
group, the reverse netgroup format specifies what groups are associated
with a particular member.
This information is used to generate the
.Pa netgroup.byuser
and
.Pa netgroup.byhosts
YP maps.
These reverse netgroup maps are used to help speed up
netgroup lookups, particularly for the
.Fn innetgr
library function.
.Pp
For example, the standard
.Pa /etc/netgroup
file may list a netgroup and a list of its members.
Here, the netgroup is considered the
.Pa key
and the member names are the
.Pa data .
By contrast, the reverse
.Pa netgroup.byusers
database lists each unique
member as the key and the netgroups to which the members belong become
the data.
Separate databases are created to hold information pertaining
to users and hosts; this allows netgroup username lookups
and netgroup hostname lookups to be performed using independent keyspaces.
.Pp
By constructing these reverse netgroup databases (and the corresponding
YP maps) in advance, the
.Xr getnetgrent 3
library functions are spared from having to work out the dependencies
themselves on the fly.
This is important on networks with large numbers
of users and hosts, since it can take a considerable amount of time
to process very large netgroup databases.
.Pp
The
.Nm
command prints its results on the standard output.
It is usually called only by
.Pa /var/yp/\<domain\>/Makefile
when rebuilding the YP netgroup maps.
.Pp
The options are as follows:
.Bl -tag -width Ds
.It Fl f Ar netgroup_file
The
.Nm
command uses
.Pa /etc/netgroup
as its default input file.
The
.Fl f
flag allows the user to specify an alternate input file.
Specifying
.Dq -
as the input file causes
.Nm
to read from the standard input.
.It Fl h
Generate netgroup.byhost output; only hostname information in the
original netgroup file is processed.
.It Fl u
Generate netgroup.byuser output; only username information in the
original netgroup file is processed.
.El
.Sh FILES
.Bl -tag -width xxxxxxxxxxxxxxxxxxxxxxxx -compact
.It Pa /var/yp/\<domain\>Makefile
The Makefile that calls
.Xr makedbm 8
and
.Nm
to build the YP databases.
.It Pa /etc/netgroup
The default netgroup database file.
This file is most often found only on the YP master server.
.El
.Sh SEE ALSO
.Xr getnetgrent 3 ,
.Xr netgroup 5 ,
.Xr makedbm 8 ,
.Xr yp 8
.Sh AUTHORS
.An Bill Paul Aq wpaul@ctr.columbia.edu