---
name: "revnetgroup"
section: "8"
platform: "freebsd"
package: "base"
version: "16.0-CURRENT-20261027-61c70dc16a79"
release: "FreeBSD 16.0-CURRENT (2026-10-27)"
platforms: ["linux", "freebsd", "openbsd"]
url: "https://new.carta.tech/revnetgroup"
---

# revnetgroup(8)

generate reverse netgroup data

## NAME

**revnetgroup** – generate reverse netgroup data

## SYNOPSIS

**revnetgroup** **-u** \| **-h** \[**-f** *netgroup\_file*\]

## DESCRIPTION

The **revnetgroup** utility processes the contents of a file in [netgroup(5)](/netgroup/5.md) format into what is called *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 *netgroup.byuser* and *netgroup.byhost* NIS maps. These reverse netgroup maps are used to help speed up netgroup lookups, particularly for the **innetgr**() library function.

For example, the standard */etc/netgroup* file may list a netgroup and a list of its members. Here, the netgroup is considered the *key* and the member names are the *data*. By contrast, the reverse *netgroup.byuser* 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.

By constructing these reverse netgroup databases (and the corresponding NIS maps) in advance, the [getnetgrent(3)](/getnetgrent/3.md) 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.

The **revnetgroup** utility prints its results on the standard output. It is usually called only by */var/yp/Makefile* when rebuilding the NIS netgroup maps.

## OPTIONS

The **revnetgroup** utility supports the following options:

- **-u**

  Generate *netgroup.byuser* output; only username information in the original netgroup file is processed.

- **-h**

  Generate *netgroup.byhost* output; only hostname information in the original netgroup file is processed. (Note at least one of the **-u** or **-h** flags must be specified.)

- \[**-f** *netgroup\_file*\]

  The **revnetgroup** utility uses */etc/netgroup* as its default input file. The **-f** flag allows the user to specify an alternate input file. Specifying \`\`-'' as the input file causes **revnetgroup** to read from the standard input.

## FILES

- */var/yp/Makefile*

  the Makefile that calls **yp\_mkdb** and **revnetgroup** to build the NIS databases

- */etc/netgroup*

  the default netgroup database file. This file is most often found only on the NIS master server

## SEE ALSO

[getnetgrent(3)](/getnetgrent/3.md), [netgroup(5)](/netgroup/5.md), [yp(8)](/yp/8.md), [yp\_mkdb(8)](/yp_mkdb/8.md)

## AUTHORS

Bill Paul ⟨*wpaul@ctr.columbia.edu*⟩