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Is it possible to alias a hostname in Linux?

It has been asked by jmillikin at various Ubuntu forums as follows:


Is it possible to create a hostname alias? Sort of like /etc/hosts, but with other hostnames rather than IP addresses. So that with some file like this, you could ping "fakehost1", and it would be re-mapped to "realhost", and then "realhost" would be resolved to an IP address.

# Real host        # Aliases
realhost           fakehost1 fakehost2 fakehost3

Somebody has answered about ssh, but not about ping, etc. My main purpose is to use it as an alias for a Subversion server. In my case, realhost is under a dynamic IP address. So, the "/etc/hosts" alias doesn't work. I want to access my Subversion server as svn://my_svnserver/my_repos instead of svn://realhost/my_repos.

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I guess I may be missing something. Are you saying you couldn't have /etc/hosts look like 10.0.3.4 some.host.org another.domain.com You have to use a reference for some programmatic reason? –  jim_m_somewhere Nov 16 '12 at 23:23
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7 Answers

The use of /etc/hosts.aliases is a standard feature of the bind resolver libraries. It's more robust than adding entries to /etc/hosts and can be used if you can not add CNAMES to your DNS (don't have access to it).

In general the best practice is to use CNAMES in the DNS with appropriate SEARCH defined in /etc/resolv.conf.

Updating /etc/hosts is not very robust as entries have to be kept in sync with IP changes. This only really works on a small scale or when you are using a name service to distribute the hosts map (eg via ldap).

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Linux supports aliasing by setting the HOSTALIASES env variable.

echo "fakehost realhost" > /etc/host.aliases
echo "export HOSTALIASES=/etc/host.aliases" >> /etc/profile
. /etc/profile

then you can

ping fakehost

N.B. ping requires you to set this up as root, but you can do it as any user for any application that runs as that user. ping suids to root.

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For those who don't have an account on the forums (or don't wish to login):

if your main issue is not to ping but to ssh, you can create/edit your ~/.ssh/config adding lines like these:

Host fakehost1
Hostname realhost

Host fakehost2
Hostname realhost

Host fakehost3
Hostname realhost
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The Hostname part needs to be on a new line. Here is a good tutorial on how to make a config file like this: mattryall.net/blog/2008/06/ssh-favourite-hosts –  Code Commander Aug 6 '12 at 18:41
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I often do this with environment variables. I know this only works for the command line, but it is where I am most often craving hostname aliases (I worked with several supercomputer accounts, all with long URLs). Here's an example, if you're using BASH. In ~/.bashrc:

export fakehost="long.ass.annoying.url.org"

then, in a fresh shell:

ssh christopher@$fakehost

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You'll need an dyndns server that will map your current IP address to a hostname. You'll tell this server about your current IP address whenever you login, and it will update your hostname record.

(Dyndns.org is a good choice, IMHO).

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You can setup this on your DNS server, CNAME records allow a machine to be known by more than one hostname. So add CNAME records to your DNS server like that :


fakehost1 IN CNAME realhost 
fakehost2 IN CNAME realhost 
fakehost3 IN CNAME realhost 

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Thanks, I will try it tomorrow after setting up my local dns server. –  user10178 Sep 14 '09 at 16:12
3  
a light-weight DNS server to try would be dnsmasq (it also serves DHCP). –  sybreon Sep 14 '09 at 16:25
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The only way this can be done is if you have your own local dns server.

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Yeah, now it seems the only solution. Thanks. Cannot upvote since I don't have enough reputation. –  user10178 Sep 14 '09 at 16:11
    
If the ever-changing IP address of a DSL or dialup connection is the issue, dyndns is a better solution, IMHO. –  SvW Sep 14 '09 at 16:16
    
No, it's not a better solution. Once the server has a hostname that is handled by something else then all the OP needs is a CNAME for the first hostname. DYNDNS and similar rely on the host informing the dns server that it's ip has changed. –  theotherreceive Sep 14 '09 at 16:37
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