NETGROUP(5) Standards, Environments, and Macros NETGROUP(5)


netgroup - list of network groups




A netgroup defines a network-wide group of hosts and users. Use a
netgroup to restrict access to shared NFS filesystems and to restrict
remote login and shell access.

Network groups are usually stored in network information services, such
as LDAP, or NIS, but may alternatively be stored in the local
/etc/netgroup file. The netgroup line of the nsswitch.conf(5) file
determines which of those sources are used.

This manual page describes the format for a file that is used to supply
input to a program such as ldapaddent(8) for LDAP, or makedbm(8) for NIS.
The same file format is used in the local /etc/netgroup file.

Each line of the file defines the name and membership of a network group.
The line should have the format:

groupname member...

The items on a line can be separated by a combination of one or more
spaces or tabs.

The groupname is the name of the group being defined. This is followed by
a list of members of the group. Each member is either another group name,
all of whose members are to be included in the group being defined, or a
triple of the form:


In each triple, any of the three fields hostname, username, and
domainname, can be empty. An empty field signifies a wildcard that
matches any value in that field. Thus:

everything (,,this.domain)

defines a group named "everything" for the domain "this.domain" to which
every host and user belongs.

The domainname field refers to the domain in which the triple is valid,
not the domain containing the host or user. In fact, applications using
netgroup generally do not check the domainname. Therefore, using


is equivalent to


You can also use netgroups to control NFS mount access (see share_nfs(8))
and to control remote login and shell access (see hosts.equiv(5)). You
can also use them to control local login access (see passwd(5),
shadow(5), and compat in nsswitch.conf(5)).

When used for these purposes, a host is considered a member of a netgroup
if the netgroup contains any triple in which the hostname field matches
the name of the host requesting access and the domainname field matches
the domain of the host controlling access.

Similarly, a user is considered a member of a netgroup if the netgroup
contains any triple in which the username field matches the name of the
user requesting access and the domainname field matches the domain of the
host controlling access.

Note that when netgroups are used to control NFS mount access, access is
granted depending only on whether the requesting host is a member of the
netgroup. Remote login and shell access can be controlled both on the
basis of host and user membership in separate netgroups.


Used by a network information service's utility to
construct a map or table that contains netgroup
information. For example, ldapaddent(8) uses
/etc/netgroup to construct an LDAP container.
Alternatively, the /etc/netgroup file may be used
directly if the files source is specified in
nsswitch.conf(5) for the netgroup database.


innetgr(3C), hosts(5), hosts.equiv(5), nsswitch.conf(5), passwd(5),
shadow(5), ldapaddent(8), makedbm(8), share_nfs(8)


Applications may make general membership tests using the innetgr()
function. See innetgr(3C).

Because the "-" character will not match any specific username or
hostname, it is commonly used as a placeholder that will match only
wildcarded membership queries. So, for example:

onlyhosts (host1,-,our.domain) (host2,-,our.domain)
onlyusers (-,john,our.domain) (-,linda,our.domain)

effectively define netgroups containing only hosts and only users,
respectively. Any other string that is guaranteed not to be a legal
username or hostname will also suffice for this purpose.

Use of placeholders will improve search performance.

When a machine with multiple interfaces and multiple names is defined as
a member of a netgroup, one must list all of the names. See hosts(5). A
manageable way to do this is to define a netgroup containing all of the
machine names. For example, for a host "gateway" that has names "gateway-
subnet1" and "gateway-subnet2" one may define the netgroup:

gateway (gateway-subnet1,,our.domain) (gateway-subnet2,,our.domain)

and use this netgroup "gateway" whenever the host is to be included in
another netgroup.

June 17, 2021 NETGROUP(5)