.\"	$NetBSD: revnetgroup.8,v 1.8 2003/02/25 10:36:24 wiz Exp $
.\"
.\" Copyright (c) 1995
.\"	Bill Paul <wpaul@ctr.columbia.edu>.  All rights reserved.
.\"
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.\" modification, are permitted provided that the following conditions
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.\"    must display the following acknowledgement:
.\"	This product includes software developed by Bill Paul.
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.\"    may be used to endorse or promote products derived from this software
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.Dd October 24, 1995
.Dt REVNETGROUP 8
.Os
.Sh NAME
.Nm revnetgroup
.Nd generate reverse netgroup data
.Sh SYNOPSIS
.Nm
.Op Fl uh
.Bk -words
.Op Fl f Ar netgroup_file
.Ek
.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
.Tn 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
.Tn 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/\*[Lt]domain\*[Gt]/Makefile
when rebuilding the
.Tn YP
netgroup maps.
.Sh OPTIONS
The
.Nm
command supports the following options:
.Bl -tag -width flag
.It Fl u
Generate netgroup.byuser output; only username information in the
original netgroup file is processed.
.It Fl h
Generate netgroup.byhost output; only hostname information in the
original netgroup file is processed. (Note at least one of the
.Fl u
or
.Fl h
flags must be specified.)
.It Op 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 ``-''
as the input file causes
.Nm
to read from the standard input.
.El
.Sh FILES
.Bl -tag -width Pa -compact
.It Pa /var/yp/\*[Lt]domain\*[Gt]/Makefile
The Makefile that calls
.Nm makedbm
and
.Nm revnetgroup
to build the
.Tn YP
databases.
.It Pa /etc/netgroup
The default netgroup database file. This file is most often found
only on the
.Tn 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