What is name server in linux

Linux Find Out My Machine Name/Hostname

The procedure to find the computer name on Linux:

1. Open a command-line terminal app (select Applications > Accessories > Terminal), and then type:
2. hostname
   OR
   hostnamectl
   OR
   cat /proc/sys/kernel/hostname
3. Press [Enter] key

Linux find hostname using hostnamectl

Type the following command if you are using systemd based Linux distro:
$ hostnamectl

It is possible to filter output using the grep command:
$ hostnamectl | grep ‘hostname’
OR simply use the cat command as follows too:
$ cat /proc/sys/kernel/hostname

Linux find computer name using hostname command

At the terminal type hostname command:
$ hostname
Sample outputs
vivek-laptop.nixcraft.in
Where,

• vivek-laptop : You computer name.
• nixcraft.in : Your dNS domain name.
• vivek-laptop.nixcraft.in : Your computer name with Fully Qualified Domain Name (FQDN).

To see the domain part of the FQDN (Fully Qualified Domain Name), enter:
$ dnsdomainname
Sample outputs:

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How Do I Change My Hostname?

The hostname commands set the host name using the following syntax. Please note that only the super-user / root can change the names. To switch to the root user by typing su – and entering the root password, when prompted.
# hostname newhostname.nixcraft.in
# hostname laptop.nixcraft.net.in
# hostnamectl set-hostname laptop.nixcraft.in
You need to edit /etc/hostname or /etc/sysconfig/network file to set hostname permanently. See our previous FAQ about changing hostname using configuration files.

Conclusion

The hostnamectl command may be used to query and change the system hostname and related settings on modern Linux distros such as Debian, Ubuntu, CentOS/RHEL, Fedora, Arch Linux and more.

Getting help

I strongly suggest that your read the man pages by typing the man command:
$ man hostname
$ man hostnamectl
$ hostnamectl —help

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How to Find My DNS Server IP Address in Linux

DNS (Domain Name System) is a fundamental facilitator of several networking technologies such as mail servers, Internet browsing, and streaming services e.g. Netflix and Spotify, among others.

It works on a special computer called a DNS server – which keeps a database record of several public IP addresses along with their corresponding hostnames in order for it to resolve or translate hostnames to IP addresses upon user request.

This happens so that we would not need to bother ourselves with remembering the IP addresses of the different websites we visit.

While there are several things we can discuss on DNS servers such as redirection and malware attack prevention, our focus today is on how to find out your very own dns server IP address.

There are several ways to check for it depending on the Operating System that you’re running but Linux, BSD, and Unix-like systems all share the same method so let’s begin with them.

How to Find My DNS Server IP Address

1. To find out your DNS Server IP address, use the following cat command or less command.

2. Another way is to use the following grep command.

Here, nameserver 109.78.164.20 is a name server IP address in what is called the dot notation – the format that applications on your workstation use for DNS routing.

How to Find My Website DNS Server IP Address

3. To find out a website DNS Server IP address, you can use the following dig command.

Sample Output

Easy right? Perhaps we’ll talk about primary and secondary DNS Server addresses next time. Till then, feel free to share and drop your comments/suggestions in the discussion section below.

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Domain Name Service (DNS)

Domain Name Service (DNS) is an Internet service that maps IP addresses and fully qualified domain names (FQDN) to one another. In this way, DNS alleviates the need to remember IP addresses. Computers that run DNS are called name servers. Ubuntu ships with BIND (Berkley Internet Naming Daemon), the most common program used for maintaining a name server on Linux.

Installation

At a terminal prompt, enter the following command to install dns:

A very useful package for testing and troubleshooting DNS issues is the dnsutils package. Very often these tools will be installed already, but to check and/or install dnsutils enter the following:

Configuration

There are many ways to configure BIND9. Some of the most common configurations are a caching nameserver, primary server, and secondary server.

When configured as a caching nameserver BIND9 will find the answer to name queries and remember the answer when the domain is queried again.

As a primary server, BIND9 reads the data for a zone from a file on its host and is authoritative for that zone.

As a secondary server, BIND9 gets the zone data from another nameserver that is authoritative for the zone.

Overview

The DNS configuration files are stored in the /etc/bind directory. The primary configuration file is /etc/bind/named.conf , which in the layout provided by the package just includes these files.

• /etc/bind/named.conf.options : global DNS options
• /etc/bind/named.conf.local : for your zones
• /etc/bind/named.conf.default-zones : default zones such as localhost, its reverse, and the root hints

The root nameservers used to be described in the file /etc/bind/db.root . This is now provided instead by the /usr/share/dns/root.hints file shipped with the dns-root-data package, and is referenced in the named.conf.default-zones configuration file above.

It is possible to configure the same server to be a caching name server, primary, and secondary: it all depends on the zones it is serving. A server can be the Start of Authority (SOA) for one zone, while providing secondary service for another zone. All the while providing caching services for hosts on the local LAN.

Caching Nameserver

The default configuration acts as a caching server. Simply uncomment and edit /etc/bind/named.conf.options to set the IP addresses of your ISP’s DNS servers:

Replace 1.2.3.4 and 5.6.7.8 with the IP Addresses of actual nameservers.

To enable the new configuration, restart the DNS server. From a terminal prompt:

See dig for information on testing a caching DNS server.

Primary Server

In this section BIND9 will be configured as the Primary server for the domain example.com . Simply replace example.com with your FQDN (Fully Qualified Domain Name).

Forward Zone File

To add a DNS zone to BIND9, turning BIND9 into a Primary server, first edit /etc/bind/named.conf.local :

If bind will be receiving automatic updates to the file as with DDNS, then use /var/lib/bind/db.example.com rather than /etc/bind/db.example.com both here and in the copy command below.

Now use an existing zone file as a template to create the /etc/bind/db.example.com file:

Edit the new zone file /etc/bind/db.example.com and change localhost. to the FQDN of your server, leaving the additional . at the end. Change 127.0.0.1 to the nameserver’s IP Address and root.localhost to a valid email address, but with a . instead of the usual @ symbol, again leaving the . at the end. Change the comment to indicate the domain that this file is for.

Create an A record for the base domain, example.com . Also, create an A record for ns.example.com , the name server in this example:

You must increment the Serial Number every time you make changes to the zone file. If you make multiple changes before restarting BIND9, simply increment the Serial once.

Now, you can add DNS records to the bottom of the zone file. See Common Record Types for details.

Many admins like to use the last date edited as the serial of a zone, such as 2020012100 which is yyyymmddss (where ss is the Serial Number)

Once you have made changes to the zone file BIND9 needs to be restarted for the changes to take effect:

Reverse Zone File

Now that the zone is setup and resolving names to IP Addresses, a Reverse zone needs to be added to allows DNS to resolve an address to a name.

Edit /etc/bind/named.conf.local and add the following:

Replace 1.168.192 with the first three octets of whatever network you are using. Also, name the zone file /etc/bind/db.192 appropriately. It should match the first octet of your network.

Now create the /etc/bind/db.192 file:

Next edit /etc/bind/db.192 changing the same options as /etc/bind/db.example.com :

The Serial Number in the Reverse zone needs to be incremented on each change as well. For each A record you configure in /etc/bind/db.example.com , that is for a different address, you need to create a PTR record in /etc/bind/db.192 .

After creating the reverse zone file restart BIND9:

Secondary Server

Once a Primary Server has been configured a Secondary Server is highly recommended in order to maintain the availability of the domain should the Primary become unavailable.

First, on the Primary server, the zone transfer needs to be allowed. Add the allow-transfer option to the example Forward and Reverse zone definitions in /etc/bind/named.conf.local :

Replace 192.168.1.11 with the IP Address of your Secondary nameserver.

Restart BIND9 on the Primary server:

Next, on the Secondary server, install the bind9 package the same way as on the Primary. Then edit the /etc/bind/named.conf.local and add the following declarations for the Forward and Reverse zones:

Replace 192.168.1.10 with the IP Address of your Primary nameserver.

Restart BIND9 on the Secondary server:

In /var/log/syslog you should see something similar to the following (some lines have been split to fit the format of this document):

Note: A zone is only transferred if the Serial Number on the Primary is larger than the one on the Secondary. If you want to have your Primary DNS notifying other Secondary DNS Servers of zone changes, you can add also-notify < ipaddress; >; to /etc/bind/named.conf.local as shown in the example below:

The default directory for non-authoritative zone files is /var/cache/bind/ . This directory is also configured in AppArmor to allow the named daemon to write to it. For more information on AppArmor see Security — AppArmor.

Troubleshooting

This section covers diagnosing problems with DNS and BIND9 configurations.

Testing

resolv.conf

The first step in testing BIND9 is to add the nameserver’s IP Address to a hosts resolver. The Primary nameserver should be configured as well as another host to double check things. Refer to DNS client configuration for details on adding nameserver addresses to your network clients. In the end your nameserver line in /etc/resolv.conf should be pointing at 127.0.0.53 and you should have a search parameter for your domain. Something like this:

To check which DNS server your local resolver is using, run:

You should also add the IP Address of the Secondary nameserver to your client configuration in case the Primary becomes unavailable.

If you installed the dnsutils package you can test your setup using the DNS lookup utility dig:

After installing BIND9 use dig against the loopback interface to make sure it is listening on port 53. From a terminal prompt:

You should see lines similar to the following in the command output:

If you have configured BIND9 as a Caching nameserver “dig” an outside domain to check the query time:

Note the query time toward the end of the command output:

After a second dig there should be improvement:

Now to demonstrate how applications make use of DNS to resolve a host name use the ping utility to send an ICMP echo request:

This tests if the nameserver can resolve the name ns.example.com to an IP Address. The command output should resemble:

named-checkzone

A great way to test your zone files is by using the named-checkzone utility installed with the bind9 package. This utility allows you to make sure the configuration is correct before restarting BIND9 and making the changes live.

To test our example Forward zone file enter the following from a command prompt:

If everything is configured correctly you should see output similar to:

Similarly, to test the Reverse zone file enter the following:

The output should be similar to:

The Serial Number of your zone file will probably be different.

Quick temporary query logging

With the rndc tool, you can quickly turn query logging on and off, without restarting the service or changing the configuration file.

To turn query logging on, run:

Likewise, to turn it off, run:

The logs will be sent to syslog and will show up in /var/log/syslog by default:

The amount of logs generated by enabling querylog could be huge!

Logging

BIND9 has a wide variety of logging configuration options available, but the two main ones are channel and category, which configure where logs go, and what information gets logged, respectively.

If no logging options are configured the default configuration is:

Let’s instead configure BIND9 to send debug messages related to DNS queries to a separate file.

We need to configure a channel to specify which file to send the messages to, and a category. In this example, the category will log all queries. Edit /etc/bind/named.conf.local and add the following:

The debug option can be set from 1 to 3. If a level isn’t specified, level 1 is the default.

Since the named daemon runs as the bind user the /var/log/named directory must be created and the ownership changed:

Now restart BIND9 for the changes to take effect:

You should see the file /var/log/named/query.log fill with query information. This is a simple example of the BIND9 logging options. For coverage of advanced options see More Information.

References

Common Record Types

This section covers some of the most common DNS record types.

A record: This record maps an IP Address to a hostname.

CNAME record: Used to create an alias to an existing A record. You cannot create a CNAME record pointing to another CNAME record.

MX record: Used to define where email should be sent to. Must point to an A record, not a CNAME .

NS record: Used to define which servers serve copies of a zone. It must point to an A record, not a CNAME . This is where Primary and Secondary servers are defined.

More Information

DNS and BIND is a popular book now in it’s fifth edition. There is now also a DNS and BIND on IPv6 book.

A great place to ask for BIND9 assistance, and get involved with the Ubuntu Server community, is the #ubuntu-server IRC channel on freenode.

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