How to make hostname decided by NIS and be fully qualified?

kaza · 11-04-2021, 08:39 AM

Hello!

We have few old servers at work:

Code:

uname -a
Linux <old_hostname>.<domain>.local 2.6.9-78.ELsmp #1 SMP Wed Jul 9 15:46:26 EDT 2008 x86_64 x86_64 x86_64 GNU/Linux

with their hostname being fully qualified. Also we have a NIS server which runs "ypserv"
and each "work" server runs "ypbind".

Recently we added a new server:

Code:

uname -a
Linux <new_hostname> 4.18.0-305.el8.x86_64 #1 SMP Thu Apr 29 08:54:30 EDT 2021 x86_64 x86_64 x86_64 GNU/Linux

I added its IP and both short and fully qualified hostnames to the database
of "ypserv", restarted the "ypserv" and now, on each server, if I run

"ypcat hosts | grep <new_hostname>"

I'm getting:

<IP> <new_hostname>.<domainname>.local <new_hostname>

(2 lines, for some reason, both for old and new host names).

but still running "hostname" on the new server gives only the <new_hostnane>,
without the "<domainname>.local"

I searched a lot (and "drowned" in huge number of different answers from different
years for different types of LINUX) and I still can't understand,
in what order RedHat searches what files/services to get the "hostname" result.

The "hosts" line of /etc/nsswitch :

Code:

#+hosts:      files nis dns myhostname
hosts:      nis dns

The commented line with "+" was the original one, I thought that if I'll remove
other entries I'll force the system to use the "nis" but it didn't produce the
desired result.

The relevant lines of /etc/hosts are:

Code:

#127.0.0.1   localhost localhost.localdomain localhost4 localhost4.localdomain4
#::1         localhost localhost.localdomain localhost6 localhost6.localdomain6

127.0.0.1   localhost.localdomain localhost localhost4.localdomain4 localhost4
::1         localhost.localdomain localhost localhost6.localdomain6 localhost6

The commented lines were the original, I changed the order of "full" and "short"
names but again, nothing changed. When I write "nothing changed" I mean: I rebooted
(after each file change) and the same hostname remained.

The contents of /etc/hostname are just the <new_hostname>

The contents of /etc/host.conf are:

multi on

I know I can play with the local files but I would like the correct (and full)
hostname to be taken from the NIS server so that if in future we'll change the domain name,
the change will propagate to all servers.

TIA,
kaza.

smallpond · 11-07-2021, 10:39 AM

What is NISDOMAIN set to?

How is the NIS server found? By DNS?

MadeInGermany · 11-08-2021, 12:39 AM

The command
hostname
prints a locally defined hostname.
Consider the following commands for more details:

Code:

hostname -s
hostname -f
hostname -i
hostnamectl

Check the files /etc/hosts and /etc/hostname

You should have files before nis in /etc/nsswitch.conf, otherwise during booting there is malfunction/timeout when NIS client did not yet bind. And too many timeouts when the NIS server is down.

The command
ypcat hosts
prints from the NIS server's DB. The DB is usually built from a source file with a make command.

kaza · 11-13-2021, 03:26 PM

Hi, thanks for the answers.

So, if I understand correctly, it's absolutely doesn't matter what the NIS server calls some particular server,
the "hostname" command is ALWAYS governed by the local files?

TIA,
kaza.

MadeInGermany · 11-14-2021, 05:18 AM

Usually the NIS hosts are like the DNS hosts, give global information about all the hosts.
And usually the order is files then nis, so /etc/hosts /etc/hostname hostnamectl are considered for the own hostname.
The resulting hostnames can be listed with

Code:

getent hosts

that usually works like

Code:

cat /etc/hosts; ypcat hosts

A particular hostname lookup can be tested with

Code:

getent hosts <hostname>
getent hosts <ip address>

That searches through /etc/hosts
then does a hash lookup

Code:

ypmatch <hostname> hosts.byname
yomatch <ip address> hosts.byaddr

The available NIS maps on the NIS server are shown with

Code:

ypwhich -m

Note that NIS is very old, does not cache results, does not provide safety against "illegal" hosts so should be restricted to "safe" networks.
BTW a separate old service nscd (name service caching daemon) was developed for caching NIS lookups. It also caches other naming services like LDAP, but conflicts with modern services like sssd.