7. Setting Up the NIS Client

7.1. The ypbind daemon

After you have succesfully compiled the software you are now ready to install it. A suitable place for the ypbind daemon is the directory /usr/sbin. Some people may tell you that you don't need ypbind on a system with NYS. This is wrong. ypwhich and ypcat need it always.

You must do this as root of course. The other binaries (ypwhich, ypcat, yppasswd, yppoll, ypmatch) should go in a directory accessible by all users, normally /usr/bin.

Newer ypbind versions have a configuration file called /etc/yp.conf. You can hardcode a NIS server there - for more info see the manual page for ypbind(8). You also need this file for NYS. An example:

  ypserver 10.10.0.1
  ypserver 10.0.100.8
  ypserver 10.3.1.1

If the system cam resolv the hostnames without NIS, you may use the name, otherwise you have to use the IP address. ypbind 3.3 has a bug and will only use the last entry (ypserver 10.3.1.1 in the example). All other entries are ignored. ypbind-mt handle this correct and uses that one, which answerd at first.

It might be a good idea to test ypbind before incorporating it in the startup files. To test ypbind do the following:

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

  /bin/domainname nis.domain

  where nis.domain should be some string _NOT_ normally associated with the DNS-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.

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

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

• Start up "/usr/sbin/ypbind"

• Use the command "rpcinfo -p localhost" to check if ypbind was able to register its service with the portmapper. The output should look 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

  or

  program vers proto port 100000 2 tcp 111 portmapper 100000 2 udp 111 portmapper 100007 2 udp 758 ypbind 100007 1 udp 758 ypbind 100007 2 tcp 761 ypbind 100007 1 tcp 761 ypbind

  Depending on the ypbind version you are using.

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

  program 100007 version 2 ready and waiting

  or

  program 100007 version 1 ready and waiting program 100007 version 2 ready and waiting

  The output depends on the ypbind version you have installed. Important is only the "version 2" message.

At this point you should be able to use NIS client programs like ypcat, etc... For example, "ypcat passwd.byname" 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

    /var/yp

This directory MUST exist for ypbind to start up succesfully.

To check if the domainname is set correct, use the /bin/ypdomainname from yp-tools 2.2. It uses the yp_get_default_domain() function which is more restrict. It doesn't allow for example the "(none)" domainname, which is the default under Linux and makes a lot of problems.

If the test worked you may now want to change your startupd files so that ypbind will be started at boot time and your system will act as a NIS client. Make sure that the domainname will be set before you start ypbind.

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

7.2. Setting up a NIS Client using Traditional NIS

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.

Add the following line to /etc/passwd on your NIS clients:

+::::::

You can also use the + and - characters to include/exclude or change users. If you want to exclude the user guest just add -guest to your /etc/passwd file. You want to use a different shell (e.g. ksh) for the user "linux"? No problem, just add "+linux::::::/bin/ksh" (without the quotes) to your /etc/passwd. Fields that you don't want to change have to be left empty. You could also use Netgroups for user control.

For example, to allow login-access only to miquels, dth and ed, and all members of the sysadmin netgroup, but to have the account data of all other users available use:

      +miquels:::::::
      +ed:::::::
      +dth:::::::
      +@sysadmins:::::::
      -ftp
      +:*::::::/etc/NoShell

Note that in Linux you can also override the password field, as we did in this example. We also remove the login "ftp", so it isn't known any longer, and anonymous ftp will not work.

The netgroup would look like

sysadmins (-,software,) (-,kukuk,)

IMPORTANT: The netgroup feature is implemented starting from libc 4.5.26. If you have a version of libc earlier than 4.5.26, every user in the NIS password database can access your linux machine if you run "ypbind" !

7.3. Setting up a NIS Client using NYS

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.

You should install ypbind. It isn't needed by the libc, but the NIS(YP) tools need it.

If you wish to use the include/exclude user feature (+/-guest/+@admins), you have to use "passwd: compat" and "group: compat" in nsswitch.conf. Note that there is no "shadow: compat"! You have to use "shadow: files nis" in this case.

The NYS sources are part of the libc 5 sources. When run configure, say the first time "NO" to the "Values correct" question, then say "YES" to "Build a NYS libc from nys".

7.4. Setting up a NIS Client using glibc 2.x

The glibc uses "traditional NIS", so you need to start ypbind. The Name Services Switch configuration file (/etc/nsswitch.conf) must be correctly set up. If you use the compat mode for passwd, shadow or group, you have to add the "+" at the end of this files and you can use the include/exclude user feature. The configuration is excatly the same as under Solaris 2.x.

7.5. 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. 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 through the domain name service (/etc/resolv.conf and named), at which point if no match is found an error is returned. This file must be readable for every user! You can find more information in the man-page nsswitch.5 or nsswitch.conf.5.

A good /etc/nsswitch.conf file for NIS is:

#
# /etc/nsswitch.conf
#
# An example Name Service Switch config file. This file should be
# sorted with the most-used services at the beginning.
#
# The entry '[NOTFOUND=return]' means that the search for an
# entry should stop if the search in the previous entry turned
# up nothing. Note that if the search failed due to some other reason
# (like no NIS server responding) then the search continues with the
# next entry.
#
# Legal entries are:
#
#	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
#	db			Use the /var/db databases
#	[NOTFOUND=return]	Stop searching if not found so far
#

passwd:     compat
group:      compat
# For libc5, you must use shadow: files nis
shadow:     compat

passwd_compat: nis
group_compat: nis
shadow_compat: nis

hosts:      nis files dns

services:   nis [NOTFOUND=return] files
networks:   nis [NOTFOUND=return] files
protocols:  nis [NOTFOUND=return] files
rpc:        nis [NOTFOUND=return] files
ethers:     nis [NOTFOUND=return] files
netmasks:   nis [NOTFOUND=return] files
netgroup:   nis
bootparams: nis [NOTFOUND=return] files
publickey:  nis [NOTFOUND=return] files
automount:  files
aliases:    nis [NOTFOUND=return] files

passwd_compat, group_compat and shadow_compat are only supported by glibc 2.x. If there are no shadow rules in /etc/nsswitch.conf, glibc will use the passwd rule for lookups. There are some more lookup module for glibc like hesoid. For more information, read the glibc documentation.

7.6. Shadow Passwords with NIS

Shadow passwords over NIS are always a bad idea. You loose the security, which shadow gives you, and it is supported by only some few Linux C Libraries. A good way to avoid shadow passwords over NIS is, to put only the local system users in /etc/shadow. Remove the NIS user entries from the shadow database, and put the password back in passwd. So you can use shadow for the root login, and normal passwd for NIS user. This has the advantage that it will work with every NIS client.

#%PAM-1.0
auth       required	/lib/security/pam_securetty.so
auth       required	/lib/security/pam_unix.so
auth       required	/lib/security/pam_nologin.so
account    required	/lib/security/pam_unix.so
password   required	/lib/security/pam_unix.so
session    required	/lib/security/pam_unix.so