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Setting the Hostname & Fully Qualified Domain Name (FQDN) on Ubuntu 12.04 or CentOS 6.4

Introduction

A hostname is a label or nickname that is assigned to a computer connected to a network and that is used to identify the machine in various forms of electronic communication within an internal network. Hostnames are also important because they form part of a computer's Fully Qualified Domain Name (FQDN). Assigning a FQDN to a computer makes it reachable via the public Domain Name System (DNS), i.e. the Internet.

Hostname Requirements

Internet standards for protocols mandate that component local host names may contain, only:

  • the ASCII letters a through z (in a case-insensitive manner);
  • the digits 0 through 9; and
  • the hyphen (-).

No other symbols, punctuation characters, or white space are permitted.

Practice Tip: In addition to the above technical requirements, the only practical requirement of a server's hostname, for your environment(s), is that it should be something unique to the other servers within a particular domain.

Restrictions on valid host names

Hostnames are composed of series of labels concatenated with dots, as are all domain names. For example, let's break mail.google.com into its component parts:

  • mail is the host or local hostname; and
  • google.com is the domain or parent domain name.

Each label must:

  • be between 1 and 63 characters long; and
  • the entire hostname (including the domain & delimiting dots) has a maximum of 255 characters.

Checking Current Hostname & FQDN

This article assumes that you are familiar with Step Seven — Log In To Your Droplet of How To Create Your First DigitalOcean Droplet Virtual Server.

To check your hostname, open a terminal or shell session and execute:

hostname

The current hostname, if any, will be displayed. Then, to check the existing FQDN, if any, execute:

hostname -f

which should yield a result such as localhost (which signifies that no FQDN is set) or pbx.yourdomain.tld.

Naming Conventions

So long as the above parameters are complied with, one can use just about any name as a hostname. Many server admins. use planets, places or loosely-labeled abbreviations of a particular server's basic purpose, e.g., pbx, web1, web2, mail, ns1 (for nameserver) and so on. Feel free to have fun with hostnames, if you'd like.

Setting the Hostname

A particular computer's hostname can be changed at any time. To set the initial hostname or subsequently change it, execute the following commands in a terminal or shell session (obviously, you can use whichever text editor you wish; but this guide assumes that you have installed the vim text editor):

Ubuntu 12.04

sudo vim /etc/hostname

CentOS 6.4

sudo vim /etc/sysconfig/network
  • Then, tap on the i key and use the arrow keys on your keyboard to navigate the text area;
  • Next, enter the hostname of your choice; and
  • To save & exit, tap the Esc key, on your keyboard, followed by these keystrokes: :, w, q, and, finally, Enter.

If it exists, edit the file /etc/default/dhcpcd and comment out the SET_HOSTNAME directive, by executing:

sudo vim /etc/default/dhcpcd

Then, insert the # symbol at the beginning of the line that begins with SET_HOSTNAME=, as shown, below:

#SET_HOSTNAME='yes'

Finally, execute:

sudo service hostname restart

You can verify that the hostname was properly set by, again, executing:

hostname

Setting the Fully Qualified Domain Name (FQDN)

In a terminal or shell, execute:

sudo vim /etc/hosts

Then, tap on the i key and use the arrow keys on your keyboard to navigate the text area. Modify your hosts file so that it resembles the following (obviously, substituting the hostname, yourdomain, tld, and YourIP values with your own):

127.0.0.1	localhost.localdomain	localhost
127.0.1.1	hostname.yourdomain.tld	hostname
YourIP		hostname.yourdomain.tld	hostname

To save & exit, tap the Esc key, on your keyboard, followed by these keystrokes: :, w, q, and, finally, Enter.

You can verify that the FQDN was properly set by, again, executing:

hostname -f

DNS Records

If you want your remote server to be reachable over the internet via its FQDN, then you need to create the relevant DNS records. See How To Set Up a Host Name with DigitalOcean.

Additional Resources

Article submitted by: Pablo Carranza • Updated November 12, 2013