What is host file in linux

How to Setup Local DNS Using /etc/hosts File in Linux

DNS (Domain Name System or Service) is a hierarchical decentralized naming system/service that translates domain names into IP addresses on the Internet or a private network and a server that provides such a service is called a DNS server.

This article explains, how to setup a local DNS using the hosts file (/etc/hosts) in Linux systems for local domain resolution or testing the website before taking live.

For example, you may want to test a website locally with a custom domain name before going live publicly by modifying the /etc/hosts file on your local system to point the domain name to the IP address of the local DNS server you configured.

The /etc/hosts is an operating system file that translate hostnames or domain names to IP addresses. This is useful for testing websites changes or the SSL setup before taking a website publicly live.

Attention: This method will only work if the hosts have a static IP address. Therefore ensure that you have set static IP addresses for your Linux hosts or nodes running other operating systems.

For the purpose of this article, we will be using the following domain, hostnames and IP addresses (use values that apply to your local setting).

Understanding Name Service Switch in Linux

Before moving any further, you should understand a few things about another important file that is /etc/nsswitch.conf. It provides Name Service Switch functionality which controls the order in which services are queried for name service lookups.

The configuration is based on order; if files is before dns it means the system will query the /etc/hosts file before checking DNS for name service requests. But if DNS is before files then the domain lookup process will consult DNS first before any other appropriate services or files.

In this scenario, we want to query the “files” service. To check the order, type.

Check Name Service Switch

Configure DNS Locally Using /etc/hosts File in Linux

Now open the /etc/hosts file using your editor of choice as follows

Then add the lines below to the end of the file as shown in the screen shot below.

Next, test if everything is working well as expected, using the ping command from Host 1, you can ping Host 2 using it domain name like so.

Ping Domain Locally

On the Host 2, we have setup Apache HTTP server. So we can also test if the name translation service is working as follows by going to URL http://centos.tecmint.lan.

Check Domain Locally

Important: To use the domain names on any host on the network, you must configure the above settings in its /etc/hosts file.

What does this mean, in the above example, we only configured the hosts file of Host 1 and we can only use the domain names on it. To use the same names on Host 2, we have to add the addresses and names to its hosts file as well.

Lastly, you should use host command or nslookup command to test if the name translation service is actually working, these commands only query DNS and overlook any configurations in /etc/hosts and /etc/nsswitch.conf files.

You may also like to read these following related articles.

That’s it! Do share any additional thoughts or questions about this topic with us, via the comment section below.

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How to Use and Edit the Hosts File in Linux

If you’ve ever managed multiple servers from a Linux machine or set up some kind of home lab, then you know how useful the “hosts” file can be in Linux. However, some of you might not even know it exists, much less how to leverage it to make your life easier. That’s why we are guiding you through how to use and edit the hosts file in Linux.

What Is the Hosts file?

The “/etc/hosts” file is where your system keeps an internal map of IP Addresses -> hostnames. This doesn’t require a DNS server because it’s stored locally on your machine. This is a great way to manage things like internal servers or other devices on your network that commonly require you to enter an IP Address. I use this all the time for Raspberry Pi projects and managing commonly-used KVM Virtual Machines.

How Do I Use the Hosts File?

First, take a look at what’s already in the hosts file. Type the following command into the terminal and press enter:

In the output, you’ll find two IP addresses that are meant for your local machine to identify itself. If you run the ping localhost command, you’ll see one of these IP addresses come up. That’s because Linux automatically generates these two entries into the hosts file. If you want to add more entries, all you have to do is follow the formatting of the file, and you’ll be all set to go.

Editing the Hosts File

To edit the hosts file, just open it in your preferred text editor. You can use Vim, Nano, Gedit, Kate, or whichever you like best. You should see the content in the following format:

So if I have a Pi Hole server with an IP address of 192.168.122.7, my format would be something like this:

It’s, of course, dependent on what you want to name it. That means that any time you want to address that Pi Hole server, whether it’s via ping , ssh , or some other tool, you don’t have to enter the IP address. You can just type pihole.local into the terminal. It’s quite the timesaver, especially if you get to shorter server hostnames.

It’s also important to note that you don’t have to use “.com,” “.net,” or “.org” addresses. You can even just call it pihole , and your system will recognize it. I used a .local address to show you the “proper” way to do it, but you can call them server if it’s your only one.

It’s also useful for virtual machines on a virtualization server or workstation. Remembering VM IP addresses is a huge pain, and using the hosts file is perfect to manage that. With my VM IP Address, 192.168.122.202, I’ll take that and edit my hosts file with this:

Then I can ping that VM with the hostname, which makes it much easier to remember what I’m looking for. You can see that rather than an IP address, I’m pinging the hostname, and that shows up in the output of the command. The system has an internal map of that IP and hostname, so it’s easy to slot into that spot.

Wrapping Up

As you can see, learning how to edit the Hosts file in Linux can be a useful skill, as it allows you to save you a lot of time later down the line. If you are on Windows, you can also edit the Hosts file and use it exactly the same way as stated above. If you are looking for a simple way to block websites, then these Chrome extensions may do a better job.

John is a young technical professional with a passion for educating users on the best ways to use their technology. He holds technical certifications covering topics ranging from computer hardware to cybersecurity to Linux system administration.

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Linux Hosts File Explained — Syntax and Uses

Linux hosts File – What Is This?

The purpose of the hosts file is simple – to map hostnames to IP addresses. Its function is the same as the function of the Domain Name System (DNS) but the difference is that unlike DNS, the hosts file is stored locally on the machine. This means that the administrator of the local machine can enter and edit the entries in the hosts file as required.

The hosts file is not unique to Linux. In fact, the hosts file is present in many operating systems, such as UNIX/Linux, the various Windows OS, Mac, Symbian, OS/2, etc. Actually, if an operating system can be used to access the Net, then most likely it has a hosts file. However, the location of the hosts file varies under different operating systems. Under Linux the typical location for the hosts file is in /etc/hosts but this is not an absolute rule for absolutely any Linux distro.

Syntax of the Linux hosts File

The syntax of the Linux hosts file isn’t sophisticated. The format for the hosts file is the same on Linux/UNIX and Windows and it is as follows:

[IP address] [domain name] [alias]

Therefore, if you want to add localhost, here is how the entry will look like:

It is important to note that /,\, and https:// are omitted. Otherwise, there is nothing special about the syntax of the entries in the Linux hosts file.

If you want to temporarily exclude some entries without deleting them forever, you can comment them out. The sign # is used for that.

The syntax of the Linux hosts file is pretty simple and for a small number of entries, you can use a conventional text editor. However, when you have many entries to input, then automated tools are what you need because they not only speed the process but also reduce the amount of errors.

Uses of the Linux hosts File

Linux hosts file isn’t an obsolete file, as it might look at first. Its basic uses are these:

• To facilitate network testing. When you need to make a test server behave as if it were a real production server and to test how a particular applications or service performs, the hosts file is perfect for the purpose.
• To accelerate browsing speed. When your browser doesn’t have to send DNS requests to a remote system, this speed browsing. However, have in mind that when the hosts file is large and/or it doesn’t contain a particular IP. This could seriously slowdown browsing speed.
• To block adware and other pests. Finally, one more use of the Linux hosts file is to block adware and spyware. Fortunately, malware isn’t such a problem under Linux as it is under Windows but still there are tons of browser adware and spyware that are cross-platform, and because of this you can encounter them under Linux as well. When you add the IPs of such known adware and spyware networks to your hosts file, you won’t be seeing these nuisances.

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Understanding /etc/hosts file in Linux

What Is /etc/hosts And Why Is It Used?

In order to send network traffic to a host, the numeric Internet Protocol (IP) address for that host must be known. The IP address is traditionally written as xxx.xxx.xxx.xxx where each xxx represents a value from 0 to 255, for an IPv4 network address. Computers require these addresses but humans find remembering numeric values difficult. The Domain Name Service (DNS) provides a mechanism to associate one or more alphanumeric names with a numeric IP address. On a Linux system, these readable names are converted to their numeric IP equivalents by the Resolver Library, contained in the libresolve.so files provided as part of the glibc RPM package. Programs that need to lookup the numeric IP address for a name issue calls to this library.

Host names and their IP addresses may be found in a variety of places: local files, remote DNS servers, or NIS+ servers, to name a few. The order these resources are searched depends on the hosts: entry in the /etc/nsswitch.conf file. This line typically looks like this:

This causes the resolver library to consult the local /etc/hosts file first; if the host name is not found there, then consult the remote DNS name servers identified by the /etc/resolv.conf file.

Linux does provide the bind RPM package to allow an administrative domain to configure and maintain its own DNS service, but frequently the size of the local network is only a few hosts and makes justifying the effort of maintaining a DNS service unwarranted.

Format of /etc/hosts File

The /etc/hosts file is an ordinary text file. Two types of lines are permitted:

1. Empty Lines
2. Host name definitions

Lines may be intermingled as needed. Comments begin with a hash symbol (#) and continue to the end of the line.

Associating Host Names And IP Addresses

For each host a single line should be present with the following information:

Fields of the entry are separated by any whitespace (spaces or tabs). The first field is the numeric IP address to be used for all the host names on this entry. Either an IPv4 address (10.1.2.3), an IPv6 address (2001:0db8:0000:0000:0000:0000:1428:57ab), or an IPv6 abbreviation (::1) may be used, depending on your requirements.

After the IP address, remaining tokens specify the locally-known hostnames associated with that IP address. By convention, the first name after the IP address is the canonical or fully-qualified domain name. An example of a canonical name would be server.example.com; this is the official name of the host.

Any remaining names defined for the IP address are aliases or alternate names for the official host name. For example, suppose that one of the duties assigned to server.example.com is to be the corporate FTP site. A suitable alias might then be myftp.example.com and this name could be added to the /etc/hosts entry after the canonical name. Many times, an alias is simply the host name, without any domain suffix. For example:

The advantage to listing the canonical host name as the first definition on the line is that IP-to-hostname conversion (similar to reverse DNS lookups) usually display only the first name found; convention uses the canonical name for this. In our example, the command:

Note that we pinged myftp but results come from host myhost: this is a reliable hint that you are addressing an alias, not the actual host.

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Файл hosts в Linux

Система доменных имен DNS используется для определения, какой IP принадлежит к нужному домену в сети интернет. Когда какой-либо программе понадобится обратиться к сайту по его доменному имени, операционная система отправляет к DNS-серверу запрос, чтобы узнать, по какому IP ей дальше передавать пакеты. Но так происходит не всегда. Например, когда мы обращаемся к домену localhost, то всегда запрос отправляется нашему локальному компьютеру.

Всему причиной файл hosts. Если вы раньше пользовались Windows, то, наверное, уже слышали о таком файле. Там чаще всего он использовался для того, чтобы быстро заблокировать доступ к какому-либо ресурсу. Но применение его гораздо шире. В этой статье мы рассмотрим, как настроить файл hosts в Linux, а также какие возможности он нам предоставляет.

Разрешение доменных имён в Linux

Прежде чем мы перейдём к самому файлу hosts, нужно разобраться, как происходит поиск IP-адреса для доменного имени в Linux. Я говорил, что операционная система сразу же отправляет запрос DNS-серверу, но это не совсем так. Существует определённый порядок поиска, согласно которому он выполняется. Этот порядок установлен в конфигурационном файле /etc/nsswitch.conf

Здесь нас интересует строчка hosts. В ней в порядке очередности записаны службы, которые используются для поиска IP-адреса для доменного имени. Пункт files означает использование файла /etc/hosts, а dns — сервиса доменных имён интернета. Если files расположена перед hosts, это означает, что сначала система попытается найти домен в /etc/hosts, а уже потом по DNS. По умолчанию дело обстоит именно так.

Настройка файла hosts в Linux

Нужный нам файл находится в директории /etc/. Для его открытия можно использовать любой текстовый редактор как в командной строке, так и в графическом интерфейсе, только открывать его нужно с правами суперпользователя. Например, с помощью vim:

sudo vi /etc/hosts

sudo gedit /etc/hosts

Синтаксис файла довольно простой. В нём находится несколько строчек с доменными именами и IP-адресами, которые нужно для них использовать. Каждая из них выглядит вот так:

ip_адрес домен алиас

Обычно первая же строчка создаёт правило для перенаправления всех запросов к домену localhost на локальный IP-адрес — 127.0.0.1:

Также в этом файле по умолчанию размещаются перенаправления для имени вашего компьютера и для IPv6-адресов. Вы можете создать свои настройки для любого нужного домена. Для этого нужно добавить строчку в конец файла. Например, направим все запросы к домену losst.ru на ip 127.0.0.1:

Обратите внимание, что здесь указывается только домен, без протокола. Префикс http или https указывать не нужно, иначе ничего работать не будет. А вот для поддомена www нужно создавать отдельную запись или записывать его в виде алиаса. Например:

127.0.0.1 losst.ru www.losst.ru

Теперь при запросе домена losst.ru будет открываться наш локальный IP. Чтобы вернуть доступ к оригинальному ресурсу, достаточно убрать добавленную строчку. Но вы можете использовать не только локальный адрес, но и любой другой. Это очень удобно, если вы только зарегистрировали домен и доменная зона ещё не успела обновиться, а вы уже хотите работать с новым сайтом. Просто добавьте данные в /etc/hosts и работайте как обычно.

Выводы

В этой небольшой статье мы разобрали, как выполняется настройка DNS через файл hosts Linux. Как видите, с его помощью вы можете блокировать доступ к нежелательным ресурсам, например, к которым программы не должны получить доступ, а также использовать его в работе веб-мастера.

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