[Bug 234543] Re: /etc/hosts: hostname alias of loopback

[Thomas Hood]

#0. The original report seems to be that

    127.0.1.1 HOSTNAME

is not appropriate when the machine is on a local network.

That is not true.  It is correct to resolve the local machine's
hostname to a loopback address.

The reason for choosing 127.0.1.1 as that loopback address
is that 127.0.0.1 is reserved for the special hosthame "localhost".
It is important that there be a one-to-one mapping between
loopback addresses and canonical hostnames, thus

    127.0.0.1 <---> localhost
    127.0.1.1 <---> HOSTNAME


#5. Here is is claimed that "[i]t is highly unusual to use the
hostname for a loopback address."  Not true.  It is actually
standard in Debian and Ubuntu, for the reason given above.


#10. Here is is asked "I move them to the public net and hand
assign them an IP in /etc/network/interfaces.  At this point,
IIRC, I should edit /etc/hosts and replace 127.0.1.1 with the
public IP I'm giving to the server.  Is this right?"

If a machine is given a *static* IP address then it is
acceptable, but not necessary, to replace "127.0.1.1" with
that static address in /etc/hosts.


#11.  Here it is claimed that the 127.0.1.1. line needs
to be changed because XDMCP doesn't like it.  It that is
true then it is, or was, a bug in XDMCP.


#12 claims that in Maverick NetworkManager futzes with
the /etc/hosts file, replacing the "127.0.1.1 HOSTNAME"
line with a "IP_ADDRESS HOSTNAME" line.  That is
acceptable and probably introduced to work around bugs
in other applications, but should not be necessary.  Local
applications are required to work correctly when
HOSTNAME resolves to 127.0.1.1, for the simple reason
that some computers are not connected to a network
and have no public IP address.


#14 mentions nss-myhostname.  This is an alternative to
/etc/hosts futzing which is itself a workaround for bugs
in applications which don't work properly with 

   127.0.1.1 <---> HOSTNAME.

But it is better to fix those bugs than to rely upon a
workaround.

This report can be closed.
-- 
Thomas Hood

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https://bugs.launchpad.net/bugs/234543

Title:
  /etc/hosts: hostname alias of loopback

Status in “netcfg” package in Ubuntu:
  New
Status in “ubiquity” package in Ubuntu:
  New

Bug description:
  There is a bug in /etc/hosts. Your hostname is NO alias of 127.0.1.1.
  Only "localhost" is an alias for the loopback. When an application
  want to know your ip adresss, it will get 127.0.1.1. But this is not
  your ip adress in your local network!

  This is not right:
  127.0.1.1	HOSTNAME

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