What is search domain in linux

Linux: find out information about current domain name and host name

Q . Under Windows Server 2003 I can use active directory domain tools to get information about current domain and hostname. Can you tell me command to list current domain name and hostname under Red hat enterprise Linux 5?

A . Both Linux / UNIX comes with the following utilities to display hostname / domain name:

a) hostname – show or set the system’s host name

b) domainname – show or set the system’s NIS/YP domain name

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c) dnsdomainname – show the system’s DNS domain name

d) nisdomainname – show or set system’s NIS/YP domain name

e) ypdomainname – show or set the system’s NIS/YP domain name

For example, hostname is the program that is used to either set or display the current host, domain or node name of the system. These names are used by many of the networking programs to identify the machine.
$ hostname
Output

The domain name is also used by NIS/YP or Internet DNS:
$ dnsdomainname
Output:

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Configure Linux / UNIX Dns Resolver To Append Domain Search Names And Path ( ndots options )

I ‘m using CentOS Linux server version 5.x/6.x+. How do I configure a system so that the DNS resolver will append search path extensions to hostnames that have dots in them? For example, my domain name is test.com. when I query for mail hostname it should append .test.com and return the IP address of mail.test.com hostname.

You can easily configure the domain search list. The search list is normally determined from the local domain name; by default, it contains only the local domain name.

Tutorial details
Difficulty level	Easy
Root privileges	Yes
Requirements	Linux
Est. reading time	2 mintues

This may be changed by listing the desired domain search path following the search keyword with spaces or tabs separating the names. Resolver queries having fewer than ndots dots (default is 1) in them will be attempted using each component of the search path in turn until a match is found. For environments with multiple subdomains please read options ndots:n below to avoid man-in-the-middle attacks and unnecessary traffic for the root-dns-servers. Note that this process may be slow and will generate a lot of network traffic if the servers for the listed domains are not local, and that queries will time out if no server is available for one of the domains.

Task: SETUP DNS SEARCH LIST FOR HOST-NAME LOOKUP

Open /etc/resolv.conf file, enter:
# vi /etc/resolv.conf
OR
$ sudo vi /etc/resolv.conf
Now add search path as follows for sweet.home domain:
search sweet.home
Save and close the file.

A note about modern Linux distro

You need to use the nmcli command as follows”
nmcli connection modify br0 ipv4.dns-search «sweet.home»
nmcli connection modify br0 ipv6.dns-search «sweet.home»
Ensure you replace br0 with your interface name and “sweet.home” with your actual search domain name.

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Optional ntdots configuration

Please note that you may also need to use ndots:n option to sets a threshold for the number of dots which must appear in a name given to query before an initial absolute query will be made. The default for n is “1”, meaning that if there are any dots in a name, the name will be tried first as an absolute name before any search list elements are appended to it. For example set ndots to 2 as follows, to answer nslookup f1.mail query to get IP for f1.mail.in.test.com hostname:
## config file — /etc/resolv.conf ##
options ndots:2
search sweet.home
Save and close the file. Again replace sweet.home as per your domain name.

Test it

Limitations

• The search list is currently limited to six domains with a total of 256 characters.

Help /etc/resolv.conf file overwritten by dhclient on a Linux based system

You may find that /etc/resolve.conf is being generated and overwritten by dhcp client, so any changes made to /etc/resolv.conf file will be subsequently overwritten. See how to fix this issue by reading the following tutorial:

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What all the Daily Activities need to be done on a freebsd server,

I am using CentOS 5.3 and for me /etc/resolve.conf is being generated by /sbin/dhclient-script, so any changes done to this file will be subsequently overwritten. I am trying to find a different way to add the search order.

In regards to Hari’s question, I guess this was never answered, but I’ll answer it here because this page appears to be one of the first that pops up when I Google this particular question.

These instructions work on my CentOS 5.6 workstation.

The reason /etc/resolv.conf is being overwritten is because you’ve configured your DHCP client to get automatically obtain DNS information from the “provider”, thereby overwriting your changes everytime you reboot or restart your network services.

To stop this, edit the following file:
/etc/sysconfig/network-scripts/ifcfg-eth0
And set “PEERDNS=no”

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Update Search Domains on Red Hat 7, CentOS 7 and Fedora using nmcli

Question sent in from Julio from New York.

Q: I am running Red Hat Enterprise Linux 7 Workstation and having a hard time adding search domains. My work has several domains and I want to be able to use the short names. I have tried the network settings and don’t see a place to add search domains. I have also added search domain1 domain2 to /etc/resolv.conf but it gets replaced every reboot by Network Manager. Any help?

A: This is because Gnome does not give you a place to enter search domains in their Network Settings GUI. Also, the /etc/resolv.conf file is generated every time the Network Manager service starts or restarts which overwrites the manual changes.

What Are Search Domains and Why Use Them?

Search domains are domains used to append to a hostname to create a fully qualified domain name. If you configure your system with three search domains, it will use these names when it receives an incomplete FQDN. For example let’s say your office used a domain of example.com. So the servers are named similar to server1.example.com. If you add example.com to your search domains, you would be able to access the servers using the short name “server1”. The search domains are automatically appended to the end of host names. If you add multiple search domains they will append one by one until they resolve in DNS.

How to Add Search Domains in Network Manager

Now that we understand what a search domain is and why we need it, let’s learn how to add them. Network Manager gives you several ways to interact with it. The GUI is probably the easiest, especially if you rarely need to make these types of changes. If you are a Linux Admin with a lot of systems, you might prefer the command line. Let’s get started.

Adding Search Domains via the GUI

You can run the Network Manager GUI configuration tool by running the following command:

Once the Network Manager Connection Editor opens, select the network adapter you want to change the settings for and click edit (little gear icon).

Go to the IPv4 Settings page and enter the domains in “Additional search domains” field (separate multiple domains with a comma).

Adding Search Domains via Command Line Using NMCLI

Option 2 is to use the Network Manager Command Line Interface (nmcli). First run nmcli without options to find the name of the interface like so:

Interface em1 is our main wired connection, and that is the one we want to change. To add the search domains to em1 interface use the nmcli command like so:

Now use the show option to check the configuration. We we use grep to pull just the dns search information.

Here is an example output:

Now that we have updated the network configuration we need to restart Network Manager so the changes will take effect.

When Network Manager restarts, it should now generate the correct settings in /etc/resolv.conf .

In this tutorial we covered what search domains are, how they are used, and why we might need them. We also looked at some examples of adding them through the GUI and from the command line. If you have any questions or comments we would love to hear them.

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plembo / add-search-domain-nm-ubuntu.md

Add a search domain under NetworkManager on Ubuntu Desktop 18.04 LTS (ipv4)

In older versions of the NetworkManager gui there was a field for the search domain to be written into /etc/resolv.conf, but it was dropped by the time Ubuntu 18.04 LTS shipped. You can add it by editing the system-connections file directly, but running the appropriate nmcli commands is the right way to do it. Note that Ubuntu Server 18.04, which uses netplan and systemd-networkd by default, is completely different. Ubuntu 20.04 involves even more variation (see comments below). It’s enough to drive someone to Debian proper.

Basic wired networking

First, get the name of the interface you want to set a search domain on:

Assuming that the target interface will be «Wired connection 1» (note, interface names are case-sensitive):

Because of the way Ubuntu 18.04’s networking works, if you’re using DHCP («method=auto») this will be ignored. If you really want to force a domain name into resolv.conf, you need to edit /etc/dhcp/dhclient.conf to add this directive:

Server side solution

In general I always try to resolve this issue at the DHCP server by making sure I pass the search domain value to clients. Most routers with a DHCP service will provide some way to specify this configuration detail. This is what that would look like in a standard ISC DHCPD configuration (/etc/dhcp/dhcpd.conf):

The «domain-name» option is ignored by Linux clients, but needed by Windows machines. The «domain-search» option is what Linux machines use, while Windows machines will ignore it.

1. Ubuntu 18.04 LTS Desktop defaults to using NetworkManager to control networking, with systemd-resolved handling name resolution. But in my experience the default Ubuntu config for systemd-resolved links the wrong file to /etc/resolv.conf: /run/systemd/resolve/stub-resolv.conf.

On a properly configured system the other file in that systemd/resolve directory, named resolv.conf, should look like this:

So if you change the link like this:

then things should work the way they’re supposed to.

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marke17 commented Oct 3, 2020

Editing /etc/dhcp/dhclient.conf doesn’t work anymore in Ubuntu 20.04 (I’m actually using LinuxMint based on it, but I don’t think it matters).
I used to add ‘append domain-search «mycompany.com»‘ so that I can always connect to hosts in «mycompany.com» domain without entering FQDN.
Is there another way to do this now, because ubuntu 20.04 does not use dhclient anymore — I’m connected to wifi right now, and there is no process with ‘dhc’ in its name.
I suppose there should be a way to tell NetworkManager to append «mycompany.com» domain to its «ipv4.dns-search» property GLOBALLY instead of adding it to every connection, but I could not find it?

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marke17 commented Oct 4, 2020

Thank you for the reply, but what I am trying to do is to set one, global property that would be applied to every WIFI connection I will make in future. I’m using a laptop to connect to numerous different WIFI networks, so I would like to skip configuring dns-search and dns-servers for every connection.
Sorry that I did not explain this clearly enough.
I found a config property for NetworkManager that should work, but setting it did not change my resolv.conf.
[https://developer.gnome.org/NetworkManager/stable/NetworkManager.conf.html] documents section «global-dns» with property «searches» that should do exactly what I need, but it doesn’t so far.

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mariusse commented Jan 22, 2021 •

Editing /etc/dhcp/dhclient.conf doesn’t work anymore in Ubuntu 20.04 (I’m actually using LinuxMint based on it, but I don’t think it matters).
I used to add ‘append domain-search «mycompany.com»‘ so that I can always connect to hosts in «mycompany.com» domain without entering FQDN.
Is there another way to do this now, because ubuntu 20.04 does not use dhclient anymore — I’m connected to wifi right now, and there is no process with ‘dhc’ in its name.
I suppose there should be a way to tell NetworkManager to append «mycompany.com» domain to its «ipv4.dns-search» property GLOBALLY instead of adding it to every connection, but I could not find it?

/etc/systemd/resolved.conf
Remove comment so it says:
Domains=
and reboot (you can probably restart something, but systemd-resolvd.service didn’t do it) then you should get the domain set in your router (or DHCP server?) and can just ping host to actually ping host.mydomain . Or if your router is not setting domain, set one yourself.
Have a look at the auto generated /etc/resolv.conf after reboot to see search has been set correctly

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lovefore commented Apr 3, 2021

Editing /etc/dhcp/dhclient.conf doesn’t work anymore in Ubuntu 20.04 (I’m actually using LinuxMint based on it, but I don’t think it matters).
I used to add ‘append domain-search «mycompany.com»‘ so that I can always connect to hosts in «mycompany.com» domain without entering FQDN.
Is there another way to do this now, because ubuntu 20.04 does not use dhclient anymore — I’m connected to wifi right now, and there is no process with ‘dhc’ in its name.
I suppose there should be a way to tell NetworkManager to append «mycompany.com» domain to its «ipv4.dns-search» property GLOBALLY instead of adding it to every connection, but I could not find it?

Yes, ubuntu 20.04 does not use /etc/dhcp/dhclient.conf to control /etc/resolv.conf any more. What should I do to add an additional domain-name to it? What is /etc/dhcp/dhclient.conf used for? Just to take my precious disk? Or make me confused and wasting my time? What is ubuntu thinking about! Keep changing things in a weird way

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plembo commented Apr 4, 2021 •

@lovefore In answer to your question about adding a search domain in Ubuntu 20.04, see my comment above (https://gist.github.com/plembo/26027128bc7cbdbb0b967a2fb275da50#gistcomment-3476223). Ubuntu 20.04 Desktop uses NetworkManager to manage DHCP connections (just like Red Hat, Fedora and a number of other distros). Ubuntu 20.04 Server uses netplan on top of systemd-networkd (which no one else uses). I think Canonical’s inconsistency in this and other areas are why they’ve had difficulty breaking into the enterprise space over the years. It’s the also the reason I think a lot of shops could wind up on Debian after the dust clears from IBM’s recent missteps with Red Hat (first version of that statement was made with a lot more certainty, because when dealing with enterprise IT you always have to take the effect of sheer momentum into account).

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lovefore commented Apr 5, 2021 •

@lovefore In answer to your question about adding a search domain in Ubuntu 20.04, see my comment above (https://gist.github.com/plembo/26027128bc7cbdbb0b967a2fb275da50#gistcomment-3476223). Ubuntu 20.04 Desktop uses NetworkManager to manage DHCP connections (just like Red Hat, Fedora and a number of other distros). Ubuntu 20.04 Server uses netplan on top of systemd-networkd (which no one else uses). I think Canonical’s inconsistency in this and other areas are why they’ve had difficulty breaking into the enterprise space over the years. It’s the also the reason I think a lot of shops could wind up on Debian after the dust clears from IBM’s recent missteps with Red Hat (first version of that statement was made with a lot more certainty, because when dealing with enterprise IT you always have to take the effect of sheer momentum into account).

Yes, I agree! And thanks for your information about my problem. Though Ubuntu users amount seems growing, most of them never could make profit for Ubuntu. Only when it break into enterprise market, could it be something real and make money. Still a lot of work to do. And hope it won’t become another stream like centos8

Anyway, thanks for all the efforts so far.

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lovefore commented Apr 5, 2021

@plembo
By the way, there is a little problem with your commands. I think everyone should tell it easily and make it work. Anyway, I listed the corrected ones.Thanks, it solved my problem. Though I do not like this way

$ sudo nmcli con mod ‘Wired connection 1’ ipv4.dns-search «example.com»
$ sudo nmcli con show ‘Wired connection 1’ | grep dns-search

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plembo commented Apr 5, 2021

@lovefore, I like your method better. It’s more precise. With your permission, I’m going to refactor this to use it.

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