Take the 2-minute tour ×
Server Fault is a question and answer site for system and network administrators. It's 100% free, no registration required.

When looking at a variety of Linux and FreeBSD systems, I've noticed that on some systems /etc/hosts contains an entry for the public hostname of the host, but not on other systemst.

What is the best practice here? Should my /etc/hosts file contain an entry for the hosts FQDN (e.g. myhost.example.org) and for the short hostname (e.g. myhost)? Should the record for the FQDN point to the localhost or should it point to the external IP of the box?

For example, the default configuration on many RHEL/EL boxes doesn't put the public hostname into /etc/hosts:

myhost # cat /etc/hosts
127.0.0.1   localhost localhost.localdomain localhost4 localhost4.localdomain4
::1         localhost localhost.localdomain localhost6 localhost6.localdomain6
myhost #

The other variant is that the host's short hostname and FQDN also point to 127.0.0.1. I've been told that this is an older practice which is frowned upon these days.

myhost # cat /etc/hosts
127.0.0.1   localhost localhost.localdomain localhost4 localhost4.localdomain4 myhost myhost.example.org
::1         localhost localhost.localdomain localhost6 localhost6.localdomain6
myhost #    

The third variant is that the hosts's FQDN and short hostname are given the external IP address of the host. This third varient seems optimal to me because it reduces lookups against the DNS servers.

myhost # cat /etc/hosts
127.0.0.1   localhost localhost.localdomain localhost4 localhost4.localdomain4
::1         localhost localhost.localdomain localhost6 localhost6.localdomain6
74.125.239.xxx myhost myhost.example.org
myhost #  

What is the best practice here?

share|improve this question
2  
it boils down at what aliases the programs are using (for ex Mysql likes/needs to have a 'localhost' alias), 127.0.0.1 localhost myhost should be enough and 74.125.239.xxx myhost myhost.example.org as you said saves DNS look ups. "Best practice" unless there's a standard it's "what knowledgeable people use". –  LinuxDevOps Mar 25 at 18:38

1 Answer 1

up vote 7 down vote accepted

Are you willing to accept working DNS a point of failure in your environment or not. Some services/applications will fail in certain configurations if a system cannot resolve the local machine's name.

If you have an absolutely critical service that must be running in all situations, it isn't unusual to add a an entry in the hosts file so that service can continue to operate in the situation where DNS resolution fails.

If you can accept your DNS as a point of failure, or if your services don't fail in the case of broken resolution, configuration entries in the hosts file can be avoided.

I strongly suggest you make your DNS servers as rock solid as possible, and if you must configure your hosts file, use a configuration management system to do it. You really should avoid manually avoid touch a hosts file.

share|improve this answer
5  
Just to add to this, in most cases /etc/hosts will supersede DNS, not be used as fallback in the event of a DNS failure. This is a distinction I think should be made. (Not trying to nit-pick.) It all depends on the order defined in /etc/nsswitch.conf. –  Aaron Copley Mar 25 at 19:51
1  
The other issue is that querying the DNS servers is much slower then consulting the /etc/hosts file. Many applications query their hostname over and over, multiple times per second. Adding the hostname to /etc/hosts will reduce latency and should speed up the application. –  Stefan Lasiewski Mar 26 at 14:46

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.