When you first building a new Ubuntu 12.04 or 14.04/10 server, there are a few configuration steps that you should take early on as part of the basic setup.This will increase the security and usability of your server and will give you a solid foundation for subsequent actions.

Step One — Root Login

To log into your server, you will need to know your server's public IP address and the password for the "root" user's account. Please check your VPS Server Login email for server credentials.

If you are not already connected to your server, go ahead and log in as the root user using the following command (substitute the highlighted word with your server's public IP address):

  local$  ssh root@SERVER_IP_ADDRESS

Complete the login process by accepting the warning about host authenticity, if it appears, then providing your root authentication (password or private key). If it is your first time logging into the server, with a password, you will also be prompted to change the root password.

About Root

The root user is the administrative user in a Linux environment that has very broad privileges. Because of the heightened privileges of the root account, you are actually discouraged from using it on a regular basis. This is because part of the power inherent with the root account is the ability to make very destructive changes, even by accident.

The next step is to set up an alternative user account with a reduced scope of influence for day-to-day work. We'll teach you how to gain increased privileges during the times when you need them.

Step Two — Create a New User

Once you are logged in as root, we're prepared to add the new user account that we will use to log in from now on.

This example creates a new user called "demo", but you should replace it with a user name that you like:

 # adduser demo

You will be asked a few questions, starting with the account password.

Enter a strong password and, optionally, fill in any of the additional information if you would like. This is not required and you can just hit "ENTER" in any field you wish to skip.

Step Three — Root Privileges

Now, we have a new user account with regular account privileges. However, we may sometimes need to do administrative tasks.

To avoid having to log out of our normal user and log back in as the root account, we can set up what is known as "super user" or root privileges for our normal account. This will allow our normal user to run commands with administrative privileges by putting the word sudo before each command.

To add these privileges to our new user, we need to add the new user to the "sudo" group. By default, on Ubuntu 14.04, users who belong to the "sudo" group are allowed to use the sudo command.

As root, run this command to add your new user to the sudo group (substitute the highlighted word with your new user):

            # gpasswd -a demo sudo

Now your user can run commands with super user privileges! 

Step Four — Add Public Key Authentication (Recommended)

The next step in securing your server is to set up public key authentication for your new user. Setting this up will increase the security of your server by requiring a private SSH key to log in.

Generate a Key Pair

If you do not already have an SSH key pair, which consists of a public and private key, you need to generate one. If you already have a key that you want to use, skip to the Copy the Public Key step.

To generate a new key pair, enter the following command at the terminal of your local machine (ie. your computer):

local$ ssh-keygen

Assuming your local user is called "localuser", you will see output that looks like the following:

Generating public/private rsa key pair.
Enter file in which to save the key (/Users/localuser/.ssh/id_rsa):

Hit return to accept this file name and path (or enter a new name).

Next, you will be prompted for a passphrase to secure the key with. You may either enter a passphrase or leave the passphrase blank.

Note: If you leave the passphrase blank, you will be able to use the private key for authentication without entering a passphrase. If you enter a passphrase, you will need both the private key and the passphrase to log in. Securing your keys with passphrases is more secure, but both methods have their uses and are more secure than basic password authentication.

This generates a private key, id_rsa, and a public key, id_rsa.pub, in the .ssh directory of thelocaluser's home directory. Remember that the private key should not be shared with anyone who should not have access to your servers!

Copy the Public Key

After generating an SSH key pair, you will want to copy your public key to your new server. We will cover two easy ways to do this.

Option 1: Use ssh-copy-id

If your local machine has the ssh-copy-id script installed, you can use it to install your public key to any user that you have login credentials for.

Run the ssh-copy-id script by specifying the user and IP address of the server that you want to install the key on, like this:

local$ ssh-copy-id demo@SERVER_IP_ADDRESS

After providing your password at the prompt, your public key will be added to the remote user's.ssh/authorized_keys file. The corresponding private key can now be used to log into the server.

Option 2: Manually Install the Key

Assuming you generated an SSH key pair using the previous step, use the following command at the terminal of your local machine to print your public key (id_rsa.pub):

local$ cat ~/.ssh/id_rsa.pub

This should print your public SSH key, which should look something like the following:

ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQDBGTO0tsVejssuaYR5R3Y/i73SppJAhme1dH7W2c47d4gOqB4izP0+fRLfvbz/tnXFz4iOP/H6eCV05hqUhF+KYRxt9Y8tVMrpDZR2l75o6+xSbUOMu6xN+uVF0T9XzKcxmzTmnV7Na5up3QM3DoSRYX/EP3utr2+zAqpJIfKPLdA74w7g56oYWI9blpnpzxkEd3edVJOivUkpZ4JoenWManvIaSdMTJXMy3MtlQhva+j9CgguyVbUkdzK9KKEuah+pFZvaugtebsU+bllPTB0nlXGIJk98Ie9ZtxuY3nCKneB+KjKiXrAvXUPCI9mWkYS/1rggpFmu3HbXBnWSUdf localuser@machine.local



Select the public key, and copy it to your clipboard.

Add Public Key to New Remote User

To enable the use of SSH key to authenticate as the new remote user, you must add the public key to a special file in the user's home directory.

On the server, as the root user, enter the following command to switch to the new user (substitute your own user name):

            # su - demo

Now you will be in your new user's home directory.

Create a new directory called .ssh and restrict its permissions with the following commands:

            $ mkdir .ssh

            $ chmod 700 .ssh

Now open a file in .ssh called authorized_keys with a text editor. We will use nano to edit the file:

            $ nano .ssh/authorized_keys

Now insert your public key (which should be in your clipboard) by pasting it into the editor.

Hit CTRL-X to exit the file, then Y to save the changes that you made, then ENTER to confirm the file name.

Now restrict the permissions of the authorized_keys file with this command:

           $ chmod 600 .ssh/authorized_keys

Type this command once to return to the root user:

           $ exit

Now you may SSH login as your new user, using the private key as authentication.

Step Five — Configure SSH Daemon

Now that we have our new account, we can secure our server a little bit by modifying its SSH daemon configuration (the program that allows us to log in remotely) to disallow remote SSH access to the rootaccount.

Begin by opening the configuration file with your text editor as root:

       # nano /etc/ssh/sshd_config

Next, we need to find the line that looks like this:

PermitRootLogin yes

Here, we have the option to disable root login through SSH. This is generally a more secure setting since we can now access our server through our normal user account and escalate privileges when necessary.

Modify this line to "no" like this to disable root login:

PermitRootLogin no

Disabling remote root login is highly recommended on every server!

When you are finished making your changes, save and close the file using the method we went over earlier (CTRL-X, then Y, then ENTER).

Step Six -- Reload SSH

Now that we have made our change, we need to restart the SSH service so that it will use our new configuration.

Type this to restart SSH:

         # service ssh restart

Now, before we log out of the server, we should test our new configuration. We do not want to disconnect until we can confirm that new connections can be established successfully.

Open a new terminal window on your local machine. In the new window, we need to begin a new connection to our server. This time, instead of using the root account, we want to use the new account that we created.

For the server that we showed you how to configure above, you would connect using this command. Substitute your own user name and server IP address where appropriate:

        local$ ssh demo@SERVER_IP_ADDRESS

Note: If you are using PuTTY to connect to your servers, be sure to update the session's port number to match your server's current configuration.

You will be prompted for the new user's password that you configured. After that, you will be logged in as your new user.

Remember, if you need to run a command with root privileges, type "sudo" before it like this:

            $ sudo command_to_run

If all is well, you can exit your sessions by typing:

            $ exit

Where To Go From Here?

At this point, you have a solid foundation for your server. You can install any of the software you need on your server now. We'll keep posting new tutorials like firewall setup and installation of software stacks soon.

All the best with your cloud server.

Happy VPS Hosting.

When you first begin to access your fresh new virtual private server, there are a few early steps you should take to make it more secure. Some of the first tasks can include setting up a new user, providing them with the proper privileges, and configuring SSH.

Step One—Root Login

Once you know your IP address and root password, login as the main user, root.

It is not encouraged to use root on a regular basis, and this tutorial will help you set up an alternative user to login with permanently.

ssh root@123.45.67.890

The terminal will show:

The authenticity of host '69.55.55.20 (69.55.55.20)' can't be established.
ECDSA key fingerprint is 79:95:46:1a:ab:37:11:8e:86:54:36:38:bb:3c:fa:c0.
Are you sure you want to continue connecting (yes/no)? 

Go ahead and type yes, and then enter your root password.

Step Two—Change Your Password

Currently, your root password is the default one that was sent to you when you ordered VPS. The first thing to do is change it to one of your choice.

passwd

CentOS is very cautious about the passwords it allows. After you type your password, you may see a BAD PASSWORD notice. You can either set a more complex password or ignore the message—CentOS will not actually stop you from creating a short or simple password, although it will advise against it.

Step Three— Create a New User

After you have logged in and changed your password, you will not need to login again to your VPS as root. In this step, we will make a new user, with a new password, and give them all of the root capabilities.

First, create your user; you can choose any name for your user. Here I’ve suggested Demo

/usr/sbin/adduser demo

Second, create a new user password:

passwd demo

Step Four— Root Privileges

As of yet, only root has all of the administrative capabilities. We are going to give the new user the root privileges.

When you perform any root tasks with the new user, you will need to use the phrase “sudo” before the command. This is a helpful command for 2 reasons: 1) it prevents the user from making any system-destroying mistakes 2) it stores all the commands run with sudo to the file ‘/var/log/secure' which can be reviewed later if needed.

Let’s go ahead and edit the sudo configuration. This can be done through the default editor, which in CentOS is called ‘vi’

/usr/sbin/visudo

Find the section called user privilege specification.

It will look like this:

# User privilege specification
root    ALL=(ALL)       ALL

Under the details of root's privileges, add the following line, granting all the permissions to your new user.

To began typing in vi, press “a”.

demo    ALL=(ALL)       ALL

Press Escape, :, w, q, then Enter to save and exit the file.

Step Five— Configure SSH (OPTIONAL)

Now it’s time to make the server more secure. These steps are optional. They will make the server more secure by making login more difficult.

Open the configuration file

sudo vi /etc/ssh/sshd_config

Find the following sections and change the information where applicable:

Port 25000
Protocol 2
PermitRootLogin no
UseDNS no

We’ll take these one by one.

Port: Although port 22 is the default, you can change this to any number between 1025 and 65535. In this example, I am using port 25000. Make sure you make a note of the new port number. You will need it to login in the future, and this change will make it more difficult for unauthorized people to log in.

PermitRootLogin: change this from yes to no to stop future root login. You will now only login as the new user.

Add this line to the bottom of the document, replacing demo with your username:

AllowUsers demo

Save and Exit

Step Six— Reload and Done!

Reload SSH, and it will implement the new ports and settings.

service sshd reload

To test the new settings (don’t logout of root yet), open a new terminal window and login into your virtual server as your new user.

Don’t forget to include the new port number.

ssh -p 25000 demo@123.45.67.890

Your prompt should now say:

[demo@yourname ~]$

Once new VPS is ready, it is important to create a new user and provide it with root privileges. This not only makes your virtual server more secure, but also prevents any drastic system damage/change that can happen when operating as root.

1) Root Login

Once you know your IP address, login as the "root" user from the command line.

ssh root@xxx.xxx.xx.xx

Prompt: Are you sure you want to continue connecting (yes/no)?

Go ahead and type yes.

Potential Warning

If you happen to receive a "man in the middle" warning, this is most likely because another fingerprint is associated with the virtual server's IP. To fix this, simply remove the files in the .ssh/known_hosts directory by utilizing the "remove" command:

rm .ssh/known_hosts

Retry logging in as the root user.

2) Change Your Password

The next step is to change root password received to one of your choice from the command line:

passwd

It will ask you to type and confirm a password of your choice.

3) Create a New User

In this step, we will make a new user and give them all of the root capabilities.

You can make your username whatever you wish. Here, we'll be using "demo"-- simply replace it with your chosen username when applicable.

adduser demo

After you set the password, you do not need to enter any further information about the new user. You can leave all the following lines blank if you wish.

4) Root Privileges

As of yet, only root has all of the administrative capabilities. We are going to give the new user the root privileges.

When you perform any root tasks with the new user, you will need to use the phrase “sudo” before the command. This is a helpful command for a few reasons, primarily in that it prevents the user from making any system-destroying mistakes and stores all the commands run with sudo to the file ‘/var/log/secure' (which can be reviewed later if needed).

Let’s go ahead and edit the sudo configuration. This can be done by using a text editor:

visudo

Find the section called user privilege specification. It will look like this:

# User privilege specification
root    ALL=(ALL:ALL) ALL

Add the following line right below the root privilege specification, granting all the

permissions to your new user:

demo    ALL=(ALL:ALL) ALL

Type ‘cntrl x’ then 'y' to save and exit the file. Hit 'enter' to return to the command line.

5) SSH as New User

At the moment, you are still logged into the root directory. In the future, login to your server directly with your newly setup username:

ssh demo@xxx.xxx.xx.xx

However, since you are already logged into your server as root, you can save time by using the sudo command to change over to your new user.

su demo

Remember, although you are now logged into your new username, you are still operating in the root directory. Simply use the cd command in order to switch over to your username's home directory.

Now you're all set!

By default, FastWebHost provides VPS with basic OS installation with unmanaged service.

You can use the server for any application hosting ( WordPress, Joomla, Drupal or any development apps) and customize it.

Things get complicated to setup domains on a plain server If you are not a Linux administrator or with limited Linux knowledge. If you are looking to host websites on your VPS, then we recommend to get/install control panel for your server.

Web-based Control Panels:

Web-based control panels are for system administration for Linux. Using any modern web browser, you can setup user accounts, Apache, DNS, file sharing and much more. 

The web control panels allow you to setup domains, install other software applications on the server with just a few clicks.

There are two types of web control panels, Licensed and Free panels. 

1) Licensed Web Panels like Cpanel ( we use this officially)

cPanel -  http://cpanel.net Worlds #1 control panel for easy web hosting businesses.
You can get Cpanel License after placing an order. The Cpanel license costs $14.99 per month.

Open helpdesk ticket at http://support.fastwebhost.com, to generate an invoice for cPanel.

Webuzo -   http://webuzo.com  

Webuzo License costs are $5 per month.

2) Free Web Control Panels (Open Source)

CentOS web panel - http://centos-webpanel.com/ 
Kloxo - http://lxcenter.org/software/kloxo
zPanel - http://www.zpanelcp.com/about/features/
webmin - http://www.webmin.com/
Ajenti -  http://ajenti.org/

Before installing any Control Panel on VPS, check OS Compatability and resource requirements.

In the case of Free Web Control panels, FastWebHost doesn't provide support for all third party applications.

PuTTY is a free software application for Windows 95, 98, XP, Vista, 7 and 10 which can be used to make an SSH connection to your server.

REQUIREMENTS

Before you start, you'll need:

• Your VPS SSH login credentials. Please check VPS Welcome email.

Step One—Dowload PuTTY

To log into your VPS on windows, you will need to have PuTTY, an SSH client, installed on your computer.

If you do not have it yet, you can download the program here. Choose the windows installer.

Step Two—Set Up the Configuration Screen

Once PuTTY is downloaded and installed, starting the program will take you to the configuration screen, where you need to make just a couple of changes.

• Fill in the “Host Name (or IP address)” field with the VPS IP address from the welcome email, make sure the port number is 22, and the connection type is SSH.
• Additionally, click on the sidebar entry, SSH, and select “2 only” as the preferred SSH protocol version.
• Once everything is configured, you can name and save these preferences for the future by clicking on Session in the sidebar and typing a title into the Saved Sessions field.
• Then click save.

Step Three—Connect

Double click on the session name to connect, and accept the subsequent pop up that asks if you want to connect to the host.

If this is your first time connecting to the server from this computer, you will see the following output. Accept the connection by clicking Yes.

a) Once the SSH Connection is open, you should see a terminal prompt asking for your username:

login as:

Connect with your SSH user root.

b) Next, enter your password. Please note that you will NOT see your cursor moving, or any characters typed (such as ******), when typing your password. This is a standard PuTTY security feature. Hit enter.

Using keyboard-interactive authentication.
Password:

c) You are now logged into your server with SSH. You should see output like this:

The programs included with the Debian GNU/Linux system are free software;
the exact distribution terms for each program are described in the
individual files in /usr/share/doc/*/copyright.

Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent
permitted by applicable law.

example.com@n11:~$

You can begin typing commands at the prompt.

You can Start/Stop/Reboot server from your billing manager. Once you login to billing click on  My Products & Services  >>  View Details

Once you open VPS page, you can see all the features to Start/Stop/Shutdown/Recovery and Reboot buttons. Just click respective operation to do on your server.

2) Can I SSH to my Server?

Absolutely. You can use any standard SSH client to connect server. Default port is 22.

3) How many IPs do I get?

All servers come with 1 dedicated IP address.

4) Can I get Control Panel to manage web sites my server?

Yes, we provide cPanel/WHM as an optional service ($14.99/mo) for VPS servers. Cpanel is the standard control panel used in web hosting industry. www.cpanel.net

5) Can I setup third-party control panel on my server?

You can buy and install any third-party control panel software on your server. There are lot of web hosting control panel vendors. Please go to below link for more information.

http://en.wikipedia.org/wiki/Comparison_of_web_hosting_control_panels

6) Can you suggest any control panel which works better on your servers?

We recommend following control panel softwares.

1) cPanel  ($14.99/mo) as an add-on service to our servers.

2) Webuzo ($2.5) from http://www.webuzo.com/

7) How much technical knowledge do I need?

VPS/Cloud server systems with FastWebHost are very easy to get up and running with pre-installed software and require very little experience to get started. However, remember that this is not a managed service by default, so you will be responsible for maintaining your server. We therefore recommend that you take the time to gain a basic understanding of Linux administration.

8) What are the support services covered on my VPS server?

We have given full access to manage server from our billing manager. You can Start/Stop/Shutdown/Reboot your server anytime without our help. Infact, you can even rebuild OS with clean installation by yourself.

We can’t provide support for software/scripts installed on your server.

9) What if I want to change my OS?

If you require OS changes open HelpDesk ticket to get support from our staff.

10) What if I break my cloud/VPS server?

If you break your system, you can quickly get it running again, either by restoring a recent available backup, or by deleting it and creating a new VM with a clean installation.

11) Can I firewall my server?

Absolutely. We recommend configuring iptables on all cloud servers, as well as keeping up-to-date with patches to keep your systems secure. We also recommend installing Advanced Policy Firewall (APF). See more about APF Here

12) How do you backup server?

Once backups are enabled on your server, it will automatically be backed up every week and every month, so you will always have the opportunity to roll back your cloud server in case something goes wrong.

14) Do you provide MySQL DBs?

Yes, you can install MySQL Database server on your server. Running a MySQL service is quick and simple, giving you full control over your database.

15) How many web sites I can host on my VPS server?

We don’t limit to how many services, domains, or applications you can run from your server. However, you need to make sure you allocate enough resources to deal with the services you expect to provide.

Mitigate the risks of your servers being attacked

General Security Guidelines to be followed for securing your Web Server

• Sign up for updates and announcements from the Web Server Mailing List.
• Upgrade to the latest version whenever there is an update.
• Install only the modules you require and disable unnecessary ones.
• Make sure you log all admin level accesses with date, times and usernames
• Do not display your server version or OS version in error messages.

For Servers with Apache:

1.   Hide the Apache Version number, and other sensitive information

It is essential to hide the Apache Version Number your server is running, as well as other sensitive information. You can do this by following the simple steps listed below.

Add or Edit the following two directives in your httpd.conf file

ServerSignature Off
ServerTokens Prod

The ServerSignature appears on the bottom of pages generated by apache such as 404 pages, directory listings, etc.

The ServerTokens directive is used to determine what Apache will put in the Server HTTP response header. By setting it to Prod it sets the HTTP response header as follows:

Server: Apache

2.   Make sure apache is running under its own user account and group

When Apache is installed, the default user is set as “nobody”. However if there other applications that also run as the user nobody on your system, then a compromise of apache can also compromise other installations. It is best to add a separate user “apache” and then modify the following directives in httpd.conf to run apache as it own user.

User apache
Group apache

3.   Ensure that files outside the web root directory are not accessed.

It is always good practice to restrict access for files outside the web root directory to maintain security and ensure that these files are only accessed by people who need to access them.

<Directory />
Order Deny,Allow
Deny from all
Options None
AllowOverride None
</Directory>
<Directory /html>
Order Allow,Deny
Allow from all
</Directory>

Note that because we set “Options None” and “AllowOverride None “this will turn off all options and overrides for the server. You now have to add them explicitly for each directory that requires an Option or Override.

4.   Turn off directory browsing, Follow symbolic links and CGI execution

You can do this with an Options directive inside a Directory tag.

• If you want to turn off all Options simply use:

Options None

• If you only want to turn off some, separate each option with a space in your Options directive:

Options -ExecCGI -FollowSymLinks -Indexes

5.  Install modsecurity

ModSecurity is an Apache add on module which can detect and prevent http attacks.  It can come in really handy in preventing SQL injections in case your developers forget to add input validation or identify and block information disclosure issues such as leaking detailed error messages, Social Security Numbers or Credit Card Numbers. Follow these steps to install mod-security

On CentOS:

yum install mod_security

On Ubuntu:

apt-get install mod_security.

service httpd restart

6.  Disable any unnecessary modules

There are several modules that are enabled on your Apache Web Server that you may not need. To search for modules installed run:

grep LoadModule httpd.conf

Here are some modules that are typically enabled but often not needed:

mod_imap

mod_include

mod_info

mod_userdir

mod_status

mod_cgi

mod_autoindex.

To disable them add a # sign in front of them.

You can also go through the Apache module documentation and disable or enable any that you need.

7.  Lower the Timeout value

The default Timeout directive is set to 300 seconds. Decreasing this value help’s mitigating the potential effects of a denial of service attack.

Timeout 45

8.  Limit large requests

In order to mitigate the effects of a denial of service attack, limit the amount of body that can be

sent in an http request.  If you do not have large uploads then you can limit this to 1Mb via the below directive.

LimitRequestBody 1048576

Application and Database Security

SQL injection is another common way of extracting data from poorly coded websites. Here is how you can prevent it and other such attacks.

• Ensure your Applications like Joomla, WordPress, Drupal etc are upto date.
• Subscribe to Bug updates and Vulnerability reports.
• Try and avoid world writable 777 permissions your files or folders.
• Regularly check for viruses or infections by scanning your web package.
• If you are using MySQL or MariaDB run the mysql secure installation script.
• If your application requires you to store confidential information like username, passwords, credit card data etc. then ensure that all communication is encrypted by using a Digital Certificate.

For servers with PHP:

1.  Run PHP as a separate User

It is recommended to Install php as a separate user than as an Apache Module. If you install php as an Apache Module then php will run with the apache user permission and any compromise of a vulnerable php script can lead to a server wide compromise.

A better way to install php would be with php-fpm a fastcgi process manager which lets you run and manage php scripts as a separate user.

2.  Use the POST method to pass important parameters like credit card information

Many developers already know this. PHP has two methods to pass variable information via a form the GET method and the POST method. The most important difference between these methods is that the GET method makes your pass information visible to everyone via a URL while POST method does not. Hence sensitive information like usernames, passwords should always be passed via the POST method.

3.  Always Validate Form and Text Input

Cross site scripting and SQL injection can both be prevented if form or file input is validated.

Cross site scripting allows a hacker to run malicious code on your server by simply uploading a file with malicious code in it to be run on the server and SQL injection allows a hacker to get access to your database by injecting malicious queries in your form to get database information like table name. A simple way to validate php code can be found at http://www.w3schools.com/php/php_form_validation.asp

4 . Hide the PHP version

Open php.ini and add the following

Vim /etc/php.ini

expose_php = Off

5.Log all php errors to a file and not on the website

display_errors = Off

log_errors = On

error_log = /var/log/httpd/php_error.log

For servers with MySQL or MariaDB:

1.      Run MySQL Secure Install

After installing MySQL run the mysql_secure_installation script.

sudo   /usr/bin/mysql_secure_installation

This script will prompt you to add a mysql root password, lock root access to localhost and remove any unwanted databases like the test database.

2.     Secure MySQL users and Database

Log into your MySQL Server and ensure that all MySQL users have a password and delete any unwanted user. Grant access to only those databases that the respective users would use.

Following the steps detailed above, you can go a long way in ensuring that your customer’s data remains secure.  In the next article I will add detail steps on Linux OS and Firewall Security.

You’ll need to set your system’s hostname and fully qualified domain name (FQDN). Your hostname should be something unique. Note that the system’s hostname has no relationship to websites or email services hosted on it, aside from providing a name for the system itself. Your hostname should not be “www” or anything too generic.

Hostname's examples, "server1", "wwwbox2", or "server50.mydomain.com".

CentOS 7 / Debian 8 / Fedora version 18 and above / Ubuntu 15.04

Replace hostname with one of your choice.

hostnamectl set-hostname hostname

Debian 7 / Slackware / Ubuntu 14.04

Replace hostname with one of your choice.

echo "hostname" > /etc/hostname 

hostname -F /etc/hostname

ls /etc/default

1) echo "HOSTNAME=hostname" >> /etc/sysconfig/network
2) hostname "hostname"