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hostname.md

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Host

A host is anything able to send and receive packages over a network: this includes workstations (computers) and routers.

Can be specified by either

  • an IP
  • a string that will be resolved by a DNS server to an IP

TODO merge with DNS.

Host user pair

A user may access a (system) computer from another computer using for example ssh.

To do so, he must be registered in the target computer.

This is why user/host pairs are common: the host pair says from which computer user is trying to access his account.

Hostname

An alias for an IP, local or remote.

Must be converted into an IP via DNS.

When outside the local network, the hostname is added before the domain name, e.g. in:

www.google.com
  • hostname: www
  • domain name: google.com

It is not a good idea to have a dot . in your domain name, since then how could its last part be distinguished from the domain name?

TODO is the hostname www.google.com or just google.com? Contradictory answers: http://superuser.com/questions/59093/difference-between-host-name-and-domain-name

www

www.google.com and google.com are completely different hosts, and can lead to different IPs.

What sane companies do is choose one and redirect the other, be consistent.

But I have seen companies that use www for a different website than without, and it is possible that no redirection happens.

Browsers can store different cookies for both, so you can be logged in at www.a.com but not at a.com.

In the case of FTP, ftp://ftp.a.com URLs which are common, and perhaps in that case it is better to keep the ftp and redirect HTTP requests to ftp.a.com to ftp://ftp.a.com since FTP is less used than HTTP, allowing users to type simply ftp.a.com instead of ftp://a.com.

It is more recommended today not to use the www is noise: http://stackoverflow.com/questions/1109356/www-or-not-www-what-to-choose-as-primary-site-name.

www was more used in the past, so older companies may continue to use them because they are stuck with it.

As of early 2014:

  • facebook.com redirects to www.facebook.com
  • google.com redirects to www.google.com

Domain name

E.g.: google.com, stackoverflow.com are commonly called domain names.

A more precise way of speaking is saying that google is a subdomain of com, and www is a subdomain of google.com.

They identify a network owned by Google. But in order to get an actual IP, you still need to add a hostname such as www.

Domain names may contain more than one .: bbc.co.uk.

Subdomain

The subdomain can include a period (.) but not as the first or last character. Consecutive periods (...) are not allowed. A subdomain cannot exceed 25 characters.

example.com

http://example.com is a test domain reserved by IANA.

It is a serves as a great URL placeholder on simple examples.

Top level domain

.com, .net, .io, .fr are examples.

Every name must be under one of those.

They are controlled by IANA, and there are not that many out there except for the country ones: http://en.wikipedia.org/wiki/List_of_Internet_top-level_domains

To get a country TLD, it seems that you must have some link with the country.

Some TLDs are reserved for certain uses and registrars must check that you/ your organization are eligible: .gov for governments, .mit for US military.

Some interesting ones:

  • .sexy and .xxx. Guess what.
  • .guru. No suggested use. Funny.

Some country ones have become generic: .io is a notable example, popular amongst startups as of 2014-03. Short, sounds good, reminds of IO input output.

Some top level country domain names offer free domains! https://en.wikipedia.org/wiki/.tk https://en.wikipedia.org/wiki/.gq

hosts file

Located at:

/etc/hosts

Tells your computer where to redirect the given names.

Takes precedence over DNS.

Big downside: you have to have one of this file on every PC.

Therefore, use a DNS server instead

cat /etc/hosts

Redirect Wikipiedia to localhost:

echo "127.0.0.1 www.wikipedia.org" | sudo -a /etc/hosts

Now:

firefox www.wikipedia.org &

will go to localhost, and you will see your Apache page if you are running apache.

Undo that, its silly:

sudo sed -i "$ d" /etc/hosts

On Windows the file is:

C:\Windows\System32\Drivers\Etc\hosts

Change hostname

Best method:

hostnamectl set-hostname 'new-hostname'

Regulation aspects

Single letter domain names

http://en.wikipedia.org/wiki/Single-letter_second-level_domain

Before 1993, some of those domains were allowed. The remaining ones were then reserved,

2 letter domains are not reserved, and many are owned by major corporations. E.g. Facebook bought fb.com for 8 million.

Original top-level domains

http://en.wikipedia.org/wiki/List_of_Internet_top-level_domains#Original_top-level_domains

When the net started, there was only com, org, net, gov, mil, int.

Sponsored top-level domains

A few domains that some groups pay for, and for which you must be in the group to have.

hostname utility

Get hostname:

hostname

Likely same as;

cat /proc/sys/kernel/hostname