What is /etc/hosts?
A hosts file, named hosts (with no file extension), is a plain-text file used by all operating systems to map hostnames to IP addresses.
In most operating systems, the hosts file is preferential to DNS. Therefore if a domain name is resolved by the hosts file, the request never leaves your computer.
As your machine gets started, it will need to know the mapping of some hostnames to IP addresses before DNS can be referenced. This mapping is kept in the /etc/hosts file.
In the absence of a name server, any network program on your system consults this file to determine the IP address that corresponds to a host name.
Following is a sample /etc/hosts file:
IPAddress Hostname Alias
127.0.0.1 localhost deep.openna.com
208.164.186.1 deep.openna.com deep
208.164.186.2 mail.openna.com mail
208.164.186.3 web.openna.com web
The leftmost column is the IP address to be resolved. The next column is that host's name. Any subsequent columns are alias for that host. In the second line, for example, the IP address 208.164.186.1 is for the host deep.openna.com. Another name for deep.openna.com is deep.
Having a smart hosts file goes a long way towards blocking malware, adware, and other irritants.
For example, to nullify requests to some doubleclick.net servers, adding these lines to your hosts file will do it:
# block doubleClick's servers
0.0.0.0 ad.ae.doubleclick.net
0.0.0.0 ad.ar.doubleclick.net
0.0.0.0 ad.at.doubleclick.net
0.0.0.0 ad.au.doubleclick.net
0.0.0.0 ad.be.doubleclick.net
# etc...
The use of host file
There are a lot of custom host file hosted on the internet, with a huge variety of options. Here are some nice sources:
StevenBlack's repo
It offers 15 different host file variants, in addition to the base variant.
oisd
Has its own fancy website. Also provide a lot of options. I don't know if this is bigger than StevenBlack's, but at this point I am too afraid to find out. My PC once froze when I tried to open the largest file.
someonewhocares
The host file is embedded directly onto the page. They also wrote a short guide on how to setup host file in some operating systems.
Honorable mentions
- EnergizedProtection's repo (dead i guess)
- hagezi's repo (the biggest)
- pgl.yoyo.org
- fanboy.co.nz
References
