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NIS : Linux central authentication

NIS, (Network Information Services), enables account logins and other services (host name resolution, xinetd

network services configuration ...), to be centralized to a single NIS server.

This tutorial covers the configuration and use of NIS for login authentication. NIS+ is slightly more complex as it uses

encryption for the data transfers between the NIS server and NIS client. Regular NIS does not use encryption, thus it

should only be used for isolated or private networks protected by a firewall.

NIS Description:

NIS allows a central server to manage password authentication, host, services, etc which would normally be

provided by the local files /etc/passwd, /etc/shadow, /etc/groups, /etc/hosts, /etc/services, /etc/networks,

/etc/rpc, /etc/protocols, /etc/aliases (sendmail), ...

NIS Client systems look to the NIS server to provide this data. This tutorial will cover the configuration of both an

NIS server and NIS clients.

The logical cluster of the server and clients are known as an NIS "domain".

An NIS domain must have their time synchronized, usually using NTP (Network Time Protocol).

LDAP has overtaken NIS as the preferred central authentication server technology as it has cross platform support

and greater client web and desktop application support. See the following YoLinux LDAP tutorials:

LDAP authentication

LDAP server configuration

Website authentication using LDAP and Apache

NIS has greater legacy UNIX support and is in place and used in many corporate networks. NIS is independent of

NFS (file sharing) although the two are often hosted on a single server and they were both originally developed by

Sun Microsystems.

NIS Configuration:

NIS server configuration

NIS client configuration

NIS server configuration:

Requires RPM packages:

ypbind - RPC port binding service

portmap - RPC port mapping

ypserv - NIS server daemons

yp-tools - NIS support commands (ypcat, yppasswd, ypwhich, ...)

nscd - Handles password and group lookups and caches the results.

NSCD is used by LDAP and NIS. Configuration of nscd defines which files are supported by NIS. i.e. authentication

requires passwd, shadow and group file support. Uses configuration file /etc/ncsd.conf

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The following configuration assumes that the NIS server will also be using NIS for authentication.

File: /etc/sysconfig/network

NETWORKING=yes

HOSTNAME=hostname-of-this-nis-server

NISDOMAIN=name-of-domain

File: /etc/yp.conf

Example:

domain lab2 server 127.0.0.1

Format:

domain name-of-domain server 127.0.0.1

Where 127.0.0.1 is the "localhost" IP address of the NIS server. In this configuration, this NIS server is using NIS to

authenticate logins, not just the client.

File: /etc/nsswitch.conf

passwd: files nis

shadow: files nis

group: files nis

Order by which authentication methods are processed. eg. In this case, check the local /etc/passwd file first before

checking with NIS for password authentication. It is recommended that the root password be authenticated locally

using "files" with all other users authenticated using NIS.

File: /etc/ypserv.conf

dns: no

files: 30

slp: no

slp_timeout: 3600

xfr_check_port: yes

* : * : shadow.byname : port

* : * : passwd.adjunct.byname : port

File: /var/yp/securenets

Configuration authorizes only a single subnet to authenticate with the NIS server:

host 127.0.0.1

255.255.255.0 XXX.XXX.XXX.0

The "host" statement allows access for a specified single host.

Configuration to allow two subnets to authenticate with the NIS server:

host 127.0.0.1

255.255.254.0 192.168.105.0

Allows the range of IP addresses 192.168.105.0 to 192.168.106.255 to authenticate with the NIS server.

Configuration to allow everyone to authenticate with the NIS server:

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255.0.0.0 127.0.0.0

0.0.0.0 0.0.0.0

For more on the use of netmasks with IP addresses, see the YoLinux Networking tutorial and Subnets.

File: /var/yp/nicknames

passwd passwd.byname

group group.byname

networks networks.byaddr

hosts hosts.byname

protocols protocols.bynumber

services services.byname

aliases mail.aliases

ethers ethers.byname

As root, issue the following configuration commands:

# nisdomainname name-of-domain

# service portmap restart

# service yppasswdd start

# service ypserv start

# /usr/lib/yp/ypinit -m

# make -C /var/yp

# service ypbind start

Where:

The nisdomainname command creates the "NISDOMAIN" entry in /etc/sysconfig/network This is usually

configured during Linux OS installation. Note the commands nisdomainname, ypdomainname and

domainname all are soft equivalent. Without specifying an argument, the command returns the domain name.

Network server services:

o portmap: RPC network communications services

o ypserv: NIS server daemon

o ypbind: NIS client daemon

o yppasswd: Password daemon which allows users to change their NIS passwords on the server from their

client systems.

ypinit -m: Configure the NIS server as a "master NIS server" with the option "-m". This will convert

/etc/passwd, /etc/shadow, hosts, ... files into NIS GNU dbm database format and generates a make file.

Traditional UNIX systems use ndbm database format.

The command "make -C /var/yp" is equivalent to:

o cd /var/yp

o make

NIS Clients:

o ypbind: NIS client

See the YoLinux tutorial on the Linux init process and configuring your system to start services upon system boot.

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Test:

Check if portmapper daemon is running and ypbind is a registered service: rpcinfo -u localhost ypbind

o program 10007 version 1 ready and waiting

o program 10007 version 2 ready and waiting

NIS client configuration:

Requires RPM packages:

ypbind

portmap

yp-tools

nscd

File: /etc/sysconfig/network , (RHEL, Fedora, CentOS, ... Red Hat based Linux systems)

NETWORKING=yes

HOSTNAME=client-hostname

NISDOMAIN=name-of-domain

File: /etc/yp.conf

Example:

domain lab2 server 192.168.20.5

Format:

domain name-of-domain server XXX.XXX.XXX.XXX , Where XXX.XXX.XXX.XXX is the IP address of the NIS server.

File: /etc/nsswitch.conf

...

...

passwd: files nis

shadow: files nis

group: files nis

...

...

Options:

compat: Use compatibility setup

nisplus: Use NIS+ (NIS version 3)

nis: Use NIS (NIS version 2), also called YP

dns: Use DNS (Domain Name Service)

files: Use the local files /etc/passwd, /etc/group, ...

[NOTFOUND=return]: Stop searching if not found so far

Create domain with the command: nisdomainname name-of-domain

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Start NIS client services:

service portmap restart

service ypbind start

service nscd start (optional - used to cache login and passwd info to improve authentication response time)

Test:

Check if portmapper daemon is running and ypbind is a registered service: rpcinfo -u localhost ypbind

List passwd file: ypcat passwd

Note:

[Potential Pitfall]: If you find that the daemon ypbind on a client is crashing on a network which extends great

distances, has heavy traffic or is unreliable, try starting ypbind with the option "-no-ping".

Red Hat configuration fix, edit file: /etc/init.d/ypbind and change to:

... OTHER_YPBIND_OPTS="-no-ping" ...

This will keep ypbind from checking its network connection unnecessarily.

Red Hat GUI client configuration:

GUI tool: /usr/bin/system-config-authentication

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Select the "Configure NIS ..." button:

NIS and system users:

User Administration:

Add a new user: (as root on NIS server)

useradd -g user-group user-id (or, also create home directory: useradd -m -g user-group user-id)

make -C /var/yp ( updates local NIS databases.)

Changing a password for a user: yppasswd -p user-id

User password management:

Users will now change their passwords using the NIS password command yppasswd instead of the local password

file affected command, passwd. When using an NIS slave (described below), then do not modify the password while

logged into the NIS master.

NIS maintenance scripts:

Read NIS database files and generate traditional /etc/passwd and /etc/shadow files.

File: nis2pass

1 #!/bin/bash

2 /usr/lib/yp/makedbm -u /var/yp/name-of-domain/passwd.byname | awk -F':' '{split($1,userid," ");print userid[1]

":x:" $3 ":" $4 ":" $5 ":" $6 ":" $7}' > passwd

3 /usr/lib/yp/makedbm -u /var/yp/name-of-domain/passwd.byname | awk -F':' '{split($1,userid," ");print userid[1]

":" $2 ":13539:0:99999:7:::"}' > shadow

Man pages:

makedbm - Create or dump a ypserv database file

Example: makedbm -u dbname

getent - Get entries from administrative database

Example: getent database [key ...]

Hostname resolution:

It is the predominant practice to use DNS (bind) for hostname resolution.

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Note: NIS is capable of performing host name resolution and so is LDAP.

Best Practice: Use DNS for general host resolution and the use the local file /etc/hosts to resolve the host name of

the NIS server. This improves performance so that host name resolution of the NIS server does not require a

network connection.

Configuring a NIS client to use NIS for host name resolution:

File: /etc/nsswitch.conf

...

...

hosts: files nis

...

...

This configuration has the system look at the file /etc/hosts for a host name and then it looks to the NIS server.

Configuring an NIS Master - Slave failover server:

One can create a redundant failover slave server to improve network robustness. The NIS clients will be configured

with an additional host in /etc/yp.conf.

Client File: /etc/yp.conf

domain name-of-domain server XXX.XXX.XXX.XXX

domain name-of-domain server ZZZ.ZZZ.ZZZ.ZZZ

Where XXX.XXX.XXX.XXX is the IP address of the NIS master server and ZZZ.ZZZ.ZZZ.ZZZ is the IP address of the NIS

slave server.

The NIS master and slave servers must arrange for NIS database transfers to stay synchronized. The configurations

of the NIS servers are the same as for the above single master with the following additions and/or changes:

NIS Master:

NIS master file: /etc/ypservers

host-name-of-nis-master

host-name-of-nis-slave

Edit NIS master Makefile to allow database push to slave: /var/yp/Makefile

NOPUSH=false

After performing the NIS server procedures above, start the additional database transfer daemon:

service ypxfrd start

Push configuration change notification to clients: yppush

Perform this after updates to NIS master.

yppush man page

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NIS Slave:

/usr/lib/yp/ypinit -s nis-master-hostname: Configure the NIS server as a "slave NIS server" with the option "-s" and

state the "master" from which the NIS database transfer will occur.

Note: This is a change from the above single NIS master configuration.

Start the additional database transfer daemon: service ypxfrd start

Links:

Homepage of the Linux NIS/NIS+ Projects

Apache web server authentication using NIS - YoLinux.com tutorial

Web CGI interface to manage NIS passwords. - YoLinux.com tutorial

Linux Networking - YoLinux.com tutorial

Linux systems administration - YoLinux.com tutorial

NIS HowTo

Man pages:

nisdomainname - show or set the system’s NIS/YP domain name

ypinit - NIS database install and build program

yppush - Push configuration change notification to clients.

revnetgroup - Generate reverse netgroup data

ypserv - NIS server

ypxfr - Transfer NIS database from remote server to local host

ypinit - NIS database install and build program

yppoll - Return version and master server of a NIS map

ypset - Bind ypbind to a particular NIS server

ypcat - Print values of all keys in a NIS database

ypwhich - Return name of NIS server or map master

ypmatch - Print the values of one or more keys from a NIS map

yptest - Test NIS configuration

yppasswd - (Also: ypchfn, ypchsh) - Change NIS password in the NIS database

yppasswdd - NIS password update daemon

ypxfrd - NIS map transfer server for NIS master/slave servers.

ypserv - NIS server

ypbind - NIS binding process

nscd - Name service cache daemon

Configuration Files:

/etc/yp.conf

/etc/ypserv.conf

/etc/netgroup

/etc/nscd.conf

/etc/nsswitch.conf

/etc/nickname

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Glossary:

NSS: Name Service Switch. The /etc/nsswitch.conf, determines the order of lookups performed.

RPC: Remote Procedure Call, routines allow C programs to make procedure calls on other machines across the n/w

HostName: The name of the computer system. This is typically configured using Linux OS installation.

YP: Yellow Pages(tm), a registered trademark in the UK of British Telecom plc. forcing Sun to rename it to

NIS.

Host Name Resolution: The lookup by a client to find the IP address given the host name so that it can

create a network connection.