Questions[fqdn](server)

In my work with servers I have come across in configuration files where you should enter the address to an external server. I have seen some use the server's IP address directly, but I have heard many recommendations to use a hostname fully qualified domain name (FQDN) instead. Why should I use a hostname instead of the direct IP address?

Because if you use a hostname then you would need a local DNS server that would link each hostname to an IP address. What is the disadvantage between using a hostname or an IP address?

I've searched quite a bit and can't seem to find a straight, modern answer on this.

If I am hosting a domain, say, mydomain.com, on a machine which is going to solely be used for that domain, and there are no subdomains, is there a real, practical reason besides compliance to create an arbitrary hostname (i.e. myhost) just in order to have a three-part FQDN (myhost.mydomain.com) to satisfy some sort of RFC or convention that's expected.

This seems to make a lot of undue complexities from my perspective, and I'm not sure if there's an advantage to this or if it's just a hold-over from a time where all web resources came from a subdomains such as www and ftp which may need to scale to separate machines.

I don't use www on my domain, either, which is ill-advised for all I know from an administrators perspective (though removing it is the norm from a designer's perspective)...

I am looking to sort a list of domain names (a web filter whitelist) starting from the TLD and working upwards. I am looking any *nix or windows tools that can do this easily, though a script would be fine too.

So if the is the list you are given

www.activityvillage.co.uk 
ajax.googleapis.com 
akhet.co.uk 
alchemy.l8r.pl 
au.af.mil 
bbc.co.uk 
bensguide.gpo.gov 
chrome.angrybirds.com 
cms.hss.gov 
crl.godaddy.com 
digitalhistory.uh.edu 
digital.library.okstate.edu 
digital.olivesoftware.com

This is what I want as the output.

chrome.angrybirds.com 
crl.godaddy.com 
ajax.googleapis.com 
digital.olivesoftware.com 
digital.library.okstate.edu 
digitalhistory.uh.edu 
bensguide.gpo.gov 
cms.hss.gov 
au.af.mil 
alchemy.l8r.pl 
www.activityvillage.co.uk 
akhet.co.uk 
bbc.co.uk

Just in case you are wondering why, Squidguard, has a bug/design flaw. If both www.example.com and example.com are both included in a list, then the example.com entry is ignored and you can only visit content from www.example.com. I have several large lists that need some cleanup because someone added entries without looking first.

We've got seperate environments at my workplace for development, testing, integration, and staging.

Within those envs, we've overloaded the hostnames in DNS - e.g. in the dev environment, the primary web machine is called web1.dev.example.com, and in the test environment, the primary web machine is web1.test.example.com.

To distinguish between machines in the different environments, I want to customise the bash prompts to display the FQDN rather than just the hostname. Well and good; I should be able to replace \h with \H in $PS1, right? Hmm. They show the exact same thing.

me@web1:~$ hostname
web1
me@web1:~$ hostname -f
web1.dev.example.com
me@web1:~$ export PS1="\[\u@\h: \w\]\$ "
me@web1: ~$ export PS1="\[\u@\H: \w\]\$ "
me@web1: ~$ 

In /etc/hostname, I've got just the hostname (web1). hostname and hostname -f both return the correct results ("web1" and "web1.test.example.com" respectively), and I've got the correct entries in /etc/hosts.

What gives?

These are Ubuntu 10.04 hosts, if that makes a difference.

I've recently been "forced" to perform some sysadmin work, while this isn't something that I absolutely love doing I've been reading, experimenting and learning a lot.

There is one fundamental aspect of server configuration that I've not been able to grasp - hostnames.

In Ubuntu for instance, one should set the hostname like this (according to the Linode Library):

echo "plato" > /etc/hostname
hostname -F /etc/hostname

File: /etc/hosts

127.0.0.1        localhost.localdomain        localhost
12.34.56.78      plato.example.com            plato

I assume that plato is an arbitrary name and that plato.example.com is the FQDN.

Now my questions are:

• Is it mandatory?
• To what purpose?
• Where is it needed / used?
• Why can't I define "localhost" as the hostname for every machine?
• Do I have to set up a DNS entry for the plato.example.com FQDN?
• Should plato.example.com be used as the reverse DNS entry for my IP?

Also, are there any "best practices" for picking hostnames? I've seen people using Greek letters, planet names and even mythological figures... What happens when we run out of letters / planets?

I'm sorry if this is a dumb question but I've never been too enthusiastic with network configurations.