Linux NIS HOWTO (part 1/1)

Linux NIS HOWTO (part 1/1)

Post by Erwin Embse » Fri, 01 Dec 1995 04:00:00

Archive-name: linux/howto/nis
Last-modified: 29 Apr 95


*** The `Linux NIS HOWTO' is posted automatically by the
*** Linux HOWTO coordinator, Greg Hankins <>.  Please
*** direct any comments or questions about this HOWTO to the author,
*** Erwin Embsen <>.

- --- BEGIN Linux NIS HOWTO part 1/1 ---

  Andrea Dell'Amico, Mitchum DSouza, Erwin Embsen, Peter Eriksson
  v0.5, 24 January 1995

  1.  Glossary of Terms

  In this document a lot of acronyms are used. Here are the most
  important acronyms and a brief explanation:

        DataBase Management, a library of functions which maintain key-
        content pairs in a data base.

        Dynamically Linked Library, a library linked to an executable
        program at run-time.

        A name "key" that is used by NIS clients to be able to locate a
        suitable NIS server that serves that domainname key. Please note
        that this does not necessarily have anything at all to do with
        the DNS "domain" (machine name) of the machine(s).

        File Transfer Protocol, a protocol used to transfer files
        between two computers.

        Name services library, a library of name service calls
        (getpwnam, getservbyname, etc...) on SVR4 Unixes.

        Socket services library, a library for the socket service calls
        (socket, bind, listen, etc...) on SVR4 Unixes.

        Network Information Service, a service that provides
        information, that has to be known throughout the network, to all
        machines on the network. There is support for NIS in Linux's
        standard libc library, which in the following text is referred
        to as "traditional NIS".

        Network Information Service (Plus :-), essentially NIS on
        steroids. NIS+ is designed by Sun Microsystems Inc. as a
        replacement for NIS with better security and better handling of
        _large_ installations.

        This is the name of a project and stands for NIS+, YP and Switch
        and is managed by Peter Eriksson <>. It
        contains among other things a complete reimplementation of the
        NIS (=YP) code that uses the Name Services Switch functionality
        of the NYS library.

        Remote Procedure Call. RPC routines allow C programs to make
        procedure calls on other machines across the network.  When
        people talk about RPC they most often mean the SunRPC variant.

     YP Yellow Pages(tm), a registered trademark in the UK of British
        Telecom plc.

        Transmission Control Protocol/Internet Protocol. It's a data
        communication protocol often used on Unix machines.

  1.1.  Some General Information

  The next three lines are quoted from the Sun(tm) System & Network
  Administration Manual:

           "NIS was formerly known as Sun Yellow Pages (YP) but
            the name Yellow Pages(tm) is a registered trademark
            in the United Kingdom of British Telecom plc and may
            not be used without permission."

  NIS stands for Network Information Service. It's purpose is to provide
  information, that has to be known throughout the network, to all
  machines on the network. Information likely to be distributed by NIS

  o  login names/passwords/home directories (/etc/passwd)

  o  group information (/etc/group)

  So, for example, if your password entry is recorded in the NIS passwd
  database, you will be able to login on all machines on the net which
  have the NIS client programs running.

  Sun is a trademark of Sun Microsystems, Inc. licensed to SunSoft, Inc.

  2.  Introduction

  More and more, Linux machines are installed as part of a network of
  computers. To simplify network administration, most networks (mostly
  Sun-based networks) run the Network Information Service. Linux
  machines can take full advantage of existing NIS service or provide
  NIS service themselves. It can also (with the NYS library) act as a
  limited NIS+ client.

  This document tries to answer questions about setting up NIS(YP) on
  your Linux machine. It does not talk about how to set up NIS+. Don't
  forget to read section 5.1, The RPC Portmapper.

  2.1.  New versions of this document

  New versions of this document will be posted periodically (about every
  month) to the newsgroups comp.os.linux.announce and
  comp.os.linux.misc.  The document is archived on a number of Linux FTP
  sites, including in /pub/Linux/docs/HOWTO.

  2.2.  Disclaimer

  Although this document has been put together to the best of our
  knowledge it may, and probably does contain errors. Please read any
  README files that are bundled with any of the various pieces of
  software described in this document for more detailed and accurate
  information. We will attempt to keep this document as error free as

  2.3.  Feedback

  If you have any comments, questions or suggestions please email them
  to Erwin Embsen <>. Definitely contact him if you find
  errors or obvious omissions.

  2.4.  Acknowledgements

  We would like to thank all the people who have contributed (directly
  or indirectly) to this document. In alphabetical order:

       Andrea Dell'Amico <>
       Mitchum DSouza    <Mitch.Dso...@Dubai.Sun.COM>
       Erwin Embsen      <>
       Byron A Jeff      <>
       Peter Eriksson    <>

  Theo de Raadt <> is responsible for the original yp-
  clients code.  Swen Thuemmler <> ported the yp-
  clients code to Linux and also ported the yp-routines in libc (again
  based on Theo's work).

  3.  NIS or NIS+ ?

  The choice between NIS and NIS+ is easy - use NIS if you don't have to
  use NIS+ or have severe security needs. NIS+ is _much_ more
  problematic to administer (it's pretty easy to handle on the client
  side, but the server side is horrible). Another problem is that the
  support for NIS+ under Linux is still under developement - one major
  thing it still lacks is support for data encryption/authentication
  which is _the_ major thing why anyone would want to use NIS+...

  3.1.  Traditional NIS or the NYS library ?

  The choice between Traditional NIS or the NIS code in the NYS library
  is a choice between laziness and maturity vs. flexibility and love of

  The "traditional NIS" code is in the standard C library and has been
  around longer and sometimes suffers from it's age and slight

  The NIS code in the NYS library, on the other hand requires you either
  to recompile and relink all your programs to the libnsl library, or
  recompile the libc library to include the libnsl code into the libc
  library (or maybe you can go get a precompiled version of libc from
  someone who has already done it).

  Another difference is that the traditional NIS code has some support
  for NIS Netgroups, which the NYS code doesn't (yet). On the other hand
  the NYS code allows you to handle Shadow Passwords in a transparent

  4.  How it works

  Within a network there must be at least one machine acting as a NIS
  server. You can have multiple NIS servers, each serving different NIS
  "domains" - or you can have cooperating NIS servers, where one is said
  to be the master NIS server, and all the other are so-called slave NIS
  servers (for a certain NIS "domain", that is!) - or you can have a mix
  of them...

  Slave servers only have copies of the NIS databases and receive these
  copies from the master NIS server whenever changes are made to the
  master's databases.  Depending on the number of machines in your
  network and the reliability of your network, you might decide to
  install one or more slave servers.  Whenever a NIS server goes down or
  is too slow in responding to requests, a NIS client connected to that
  server will try to find one that is up or quicker.

  NIS databases are in so-called DBM format, derived from ASCII
  databases.  For example, the files /etc/passwd and /etc/group can be
  directly converted to DBM format using ASCII-to-DBM translation
  software ("dbload", it's included with the server software). The
  master NIS server should have both, the ASCII databases and the DBM

  Slave servers  will be notified of any change to the NIS maps, (via
  the "yppush" program), and automatically retrieve the necessary
  changes in order to synchronize their databases. NIS clients does not
  need to do this since they always talks to the NIS server to read the
  information stored in it's DBM databases.

  The author of the YP clients for linux has informed us that the newest
  ypbind (from yp-clients.tar.gz) is able to get the server from a
  configuration file - thus no need to broadcast (which is insecure -
  due to the fact that anyone may install a NIS server and answer the
  broadcast queries...)

  5.  What do you need to set up NIS?

  5.1.  The RPC Portmapper

  To run any of the software mentioned below you will need to run the
  program /usr/sbin/rpc.portmap. Some Linux distributions already have
  the code in /etc/rc.d/rc.inet2 to start up this daemon.  All you have
  to do is comment it out and reboot your Linux machine to activate it.

  The RPC portmapper (portmap(8c)) is a server that converts RPC program
  numbers into TCP/IP (or UDP/IP) protocol port numbers. It must be
  running in order to make RPC calls (which is what the NIS client
  software does) to RPC servers (like a NIS server) on that machine.
  When an RPC server is started, it will tell portmap what port number
  it is listening to, and what RPC program numbers it is prepared to
  serve.  When a client wishes to make an RPC call to a given program
  number, it will first contact portmap on the server machine to
  determine the port number where RPC packets should be sent.

  Normally, standard RPC servers are started by inetd(8C), so portmap
  must be started before inetd is invoked.

  5.2.  Determine whether you are a Server, Slave or Client.

  To answer this question you have to consider two cases:

  1. Your machine is going to be part of a network with existing NIS

  2. You do not have any NIS servers in the network yet

  In the first case, you only need the client programs (ypbind, ypwhich,
  ypcat, yppoll, ypmatch). The most important program is ypbind. This
  program must be running at all times, that is, it should always appear
  in the list of processes. It's a so-called daemon process and needs to
  be started from the system's startup file (eg. /etc/rc.local).  As
  soon as ypbind is running, your system has become a NIS client.

  In the second case, if you don't have NIS servers, then you will also
  need a NIS server program (usually called ypserv). Section 6 describes
  how to set up a NIS server on your Linux machine using the "ypserv"
  implementation by Peter Eriksson (<>). Note that
  this implementation does NOT support the master-slave concept talked
  about in section 3. Using this software, all your NIS servers will be
  master servers. There is also another free NIS server available,
  called "yps", written by Tobias Reber in Germany which does support
  the master-slave concept, but has other limitations.

  5.3.  The Software

  The system library "/usr/lib/libc.a" (version 4.4.2 and better) or the
  shared library "/usr/lib/" and its related DLL contain all
  necessary system calls to succesfully compile the NIS client and
  server software.

  Some people reported that NIS only works with "/usr/lib/libc.a"
  version 4.5.21 and better so if you want to play it safe don't user
  older libc's.  The NIS client software can be obtained from:

    Site                   Directory                        File Name   /pcsoft2/linux/local/yp          yp-clients.tar.gz           /pub/OS/Linux/BETA/NYS/clients   yp-clients.tar.gz     /pub/NYS/clients                 yp-clients.tar.gz        /pub/Linux/system/Network/admin  yp-clients.tar.gz

  Once you obtained the software, please follow the instructions which
  come with the software.

  5.4.  Setting up a NIS Client using Traditional NIS

  Assuming you have succesfully compiled the software you are now ready
  to install the software. A suitable place for the ypbind daemon is the
  directory /usr/sbin.

  You'll need to do this as root of course. The other binaries (ypwhich,
  ypcat, yppoll, ypmatch) should go in a directory accessible by all
  users, for example /usr/etc or /usr/local/bin.  It might be a good
  idea to test ypbind before incorporating it in /etc/rc.d/rc.inet2.

  To test ypbind do the following:

  o  Make sure you have your domain name set. If it is not set then
     issue the command:

                   /bin/domainname-yp nis.domain

  where nis.domain should be some string, _NOT_ normally associated with
  the domain name of your machine! The reason for this is that it makes
  it a little harder for external crackers to retreive the password
  database from your NIS servers. If you don't know what the NIS domain
  name is on your network, ask your system/network administrator.

  o  Start up "/usr/sbin/rpc.portmap" if it is not already running.

  o  Create the directory "/var/yp" if it does not exist.

  o  Start up "/usr/sbin/ypbind"

  o  Use the command "rpcinfo -p localhost" to check if ypbind was able
     to register its service with the portmapper. The rpcinfo should
     produce something like:

         program vers proto   port
          100000    2   tcp    111  portmapper
          100000    2   udp    111  portmapper
          100007    2   udp    637  ypbind
          100007    2   tcp    639  ypbind
          300019    1   udp    660

  o  You may also run "rpcinfo -u localhost ypbind". This command should
     produce something like:

               program 100007 version 2 ready and waiting

  Finally, do not forget that for host lookups you must set (or add)
  "nis" to the lookup order line in your /etc/host.conf file. Please
  read the manpage "resolv+.8" for more details.

  At this point you should be able to use NIS client programs like
  ypcat, etc...  For example, "ypcat passwd" will give you the entire
  NIS password database.

  IMPORTANT: If you skipped the test procedure then make sure you have
  set the domain name, and created the directory:


  This directory MUST exist for ypbind to start up succesfully.

  If the test worked you may now want to change the files /etc/rc.d/rc.M
  and /etc/rc.d/rc.inet2 on your system so that ypbind will be started
  up at boot time and your system will act as a NIS client. Edit the
  file /etc/rc.d/rc.M and look for the commands which set the domain
  name.  Change the domain name into the name of your domain. Also, edit
  the file /etc/rc.d/rc.inet2, comment out the lines which start up the
  rpc.portmap daemon, and add the following lines just after the place
  where rpc.portmap is started:

           # Start the ypbind daemon
           if [ -f ${NET}/ypbind -a -d /var/yp ]; then
               echo -n " ypbind"

  Unlike Sun's implementation of NIS you do not need to edit /etc/passwd
  and /etc/group to take advantage of NIS. Sun's implementation needs a
  line "+:*:0:0:::" in /etc/passwd and a line "+:*:0:" in /etc/group to
  tell NIS to search the NIS password and group databases.

  IMPORTANT: Note that the command finger will report "no such user"
  messages if you do not add the line "+:*:0:0:::" to /etc/passwd.
  Putting the line "+:*:0:0:::" back in /etc/passwd fixes finger.

  Well, that's it. Reboot the machine and watch the boot messages to see
  if ypbind is actually started.

  IMPORTANT: Note that the netgroup  feature is implemented starting
  from libc 4.5.26. Netgroups allow access control for every machine and
  every user in the NIS domain, and they require an entry like:


  in /etc/passwd. But if you have a version of libc erlier than 4.5.26,
  every  user  in  the  NIS password database can access your linux
  machine if you run "ypbind".

  6.  What you need to set up NYS?

  6.1.  Determine whether you are a Server, Slave or Client.

  To answer this question you have to consider two cases:

  o  Your machine is going to be part of a network with existing NIS

  o  You do not have any NIS servers in the network yet

  In the first case you have two choices:

  o  Either you relink all client and daemon programs with the NYS
     library (or statically link them with libnsl.a). This
     means adding the line:


  to your Makefile signifing you want to link the Network Services
  Library. Basically all network deamons and the "login" program need to
  be recompiled.

  o  Or you can recompile the standard C library libc to include the NYS
     client library functions into the normal libc library, and then
     relink all statically linked programs (the dynamically linked
     programs automatically get the new version of libc).  See section
     6.5 below for more information about this option.
  Similarly like in the case of traditional NIS, if you don't have NIS
  servers, then you will also need a NIS server program (usually called
  ypserv) and you have to designate one of the machines in your network
  as a master NIS server. Again, you might want to set up at least one
  slave server as well.

  6.2.  The Software

  You need to retrieve and compile the NYS services library
  If you don't have the DLL tools installed you may retrieve a
  precompiled shared, static and stub library from the same site
  mentioned below. Note, however, that the precompiled version may be
  (and probably is) older than the latest source code release.

  The NYS library (source and precompiled version)  can be obtained

           Site                Directory                      File Name

   /pub/NYS/libs                  nys-0.27.4.tar.gz

         /pub/OS/Linux/BETA/NYS/libs    nys-0.27.4.tar.gz

  Precompiled "login" and "su" programs may also be fetched from

           Site                Directory                      File Name

   /pub/NYS/binaries/bin          login
   /pub/NYS/binaries/bin          su

         /pub/OS/Linux/BETA/NYS/bin     login
         /pub/OS/Linux/BETA/NYS/bin     su

  Similarly, example configuration files may be retrieved from

           Site                Directory                      File Name

   /pub/NYS/binaries/etc          *conf
         /pub/OS/Linux/BETA/NYS/etc     *conf

  For compilation of the nsl library, please follow the instructions
  which come with the software. If you wish to compile the shared DLL
  library you must have the DLL tools installed in the standard place
  (/usr/dll). The DLL tools (the package tools-2.11.tar.gz or later) can
  be obtained from many sites.

  6.3.  Setting up a NYS Client using NYS

  Unlike traditional NIS, there is no setting up required for a NIS
  client. All that is required is that the NIS configuration file
  (/etc/yp.conf) points to the correct server(s) for its information.
  Also, the Name Services Switch configuration file (/etc/nsswitch.conf)
  must be correctly set up.

  Please refer to the examples provided with the source code.

  6.4.  The nsswitch.conf File

  The Network Services switch file /etc/nsswitch.conf determines the
  order of lookups performed when a certain piece of information is
  requested, just like the /etc/host.conf file which determines the way
  host lookups are performed. Again, look at at the example file
  provided in the source distribution. For example, the line

           hosts: files nis dns

  specifies that host lookup functions should first look in the local
  /etc/hosts file, followed by a NIS lookup and finally thru the domain
  name service (/etc/resolv.conf and named), at which point if no match
  is found an error is returned.

  6.5.  Making your binaries NYS aware

  Instead of relinking each binary with the NYS library (, a
  cleaner solution has been achieved by providing the user with the
  ability to build a NYS aware libc. This means all you need to do is
  recompile a new libc and replace your existing /lib/ for
  all (non-static compiled) programs to be NYS aware.

  This merge also gives you the advantage over the traditional NIS
  implementation in the linux libc in that it allows transparent shadow
  passwords support (via the /etc/nisswitch.conf file).

  Follow the simple steps below to rebuild a NYS aware libc.

  o  Make sure you have the latest DLL tools installed. Refer to the the
     GCC-FAQ for more info on where to get this.

  o  Get the latest libc sources. (again see GCC-FAQ)

  o  Get the latest nys sources from


  and extract it under this libc-linux source directory.  The current
  NYS distribution is "nys-0.27.4.tar.gz".

  o  Do the ./configure as before and first answer "n" to the question

                 Values correct (y/n) [y] ?

  Then go thru all the other questions and the last question will now be

                 Build a NYS libc from nys-0.27 (y default) ?

  answer "y" to this.

  o  Then issue the command

                 % make

  The library generated after compilation is named something like


  and placed under the directory jump/libc-nys. To install this library
  our advise would be copying it to /lib with a name lexiographically
  greater than the version number it currently has. Just appending the
  letter "a" should do the trick.  For example:

           % cp jump/libc-nys/ /lib/

  Alternatively, append "nys" to it so you can quickly identify it.  Now
  run the command

           % ldconfig

  which will reset your cache to use the new library. The dynamic linker
  strategy may be examined with the command "ldconfig -p".

  That's basically it. All your programs should now be NYS aware. Please
  note that usually the program "login" is compiled static and thus
  cannot access the new NYS functions from the NYS aware libc. You must
  either recompile "login" without the -static flag, or else statically
  link it to the libnsl.a library.

  7.  Setting up a NIS Server

  7.1.  The Server Program ypserv

  This document only describes how to set up the "ypserv" NIS server.
  The "yps" server setup is similar, _but_ not exactly the same so
  beware if you try to apply these instructions to "yps"!

  The NIS server software can be found on:

           Site                Directory                          File Name

   /pub/NYS/servers                   ypserv-0.11.tar.gz
         /pub/OS/Linux/BETA/NYS/servers     ypserv-0.11.tar.gz
         /os/linux/BETA/NYS/servers         ypserv-0.11.tar.gz

  The server setup is the same for both traditional NIS and NYS.

  Compile the software to generate the "ypserv", "dbcat" and "dbload"
  programs.  Firstly, determine what files you require to be available
  via NIS and then add or remove the appropriate entries to the
  ypMakefile. Install the file ypMakefile into /var/yp as the file

  Now build the DBM files by typing:

           % cd /var/yp; make

  Make sure the portmapper (rpc.portmap) is running, and start the
  server "ypserv". The command

           % rpcinfo -u localhost ypserv

  should output something like

      program 100004 version 2 ready and waiting

  That's it, your server is up and running.

  7.2.  The Program yppasswdd

  Whenever users change their passwords, the NIS password database and
  probably other NIS databases, which depend on the NIS password
  database, should be updated.  The program "yppasswdd" is a server that
  handles password changes and makes sure that the NIS information will
  be updated accordingly. The software for "yppasswdd" can be found on:

           Site                   Directory                      File Name

     /pub/NYS                        yppasswdd-0.5.tar.gz
           /pub/OS/Linux/BETA/NYS/servers  yppasswdd-0.5.tar.gz

  Once you obtained the software, please follow the instructions which
  come with the software.

  8.  Verifying the NIS/NYS Installation

  If everything is fine (as it should be), you should be able to verify
  your installation with a few simple commands. Assuming, for example,
  your passwd file is being supplied by NIS, the command

           % ypcat passwd

  should give you the contents of your NIS passwd file. The command

           % ypmatch userid passwd

  (where userid is the login name of an arbitrary user) should give you
  the user's entry in the NIS passwd file. The "ypcat" and "ypmatch"
  programs should be included with your distribution of traditional NIS
  or NYS.

  9.  Common Problems and Troubleshooting NIS

  Here are some common problems reported by various users:

  1. The libraries for 4.5.19 are broken. NIS won't work with it.

  2. If you upgrade the libraries from 4.5.19 to 4.5.24 then the su
     command breaks. You need to get the su command from the slackware
     1.2.0 distribution. Incidentally that's where you can get the
     updated libraries.

  3. You could run into trouble with NIS and DNS on the same machine.
     My DNS server occasionally will not bring up NIS. Haven't yet
     tracked down why.

  4. When a NIS server goes down and comes up again ypbind starts
     complaining with messages like:

              yp_match: clnt_call:
                          RPC: Unable to receive; errno = Connection refused

  and logins are refused for those who are registered in the NIS
  database. Try to login as root and if you succeed, then kill ypbind
  and start it up again.

  10.  Frequently Asked Questions

  Most of your questions should be answered by now. If there are still
  questions unanswered you might want to post a message to


  or contact one of the authors of this HOWTO.

- --- END Linux NIS HOWTO part 1/1 ---

Version: 2.6.2
Comment: finger for public key