Dennis Kaarsemaker  wrote:
> The line that should read
> 127.0.0.1 localhost.localdomain localhost myhostname

No it should not.  Read section 10.4 of the Debian reference which also
applies to Ubuntu.

    http://www.debian.org/doc/manuals/reference/ch-gateway.en.html

In general, it is important that the current system hostname be resolvable in 
/etc/hosts
to an IP address and back from that IP address to the same hostname or to a 
fully
qualified variant thereof.

This will not happen if the hostname is included as an alias for "localhost" 
because then
the hostname -> IP address -> canonical hostname lookup sequence will yield 
"localhost".

In other words, in /etc/hosts, the "127.0.0.1" line should look like
this:

    127.0.0.1 localhost

Do not put "localhost.localdomain" on this line.  That is a RedHat-ism.  It is 
not needed
in Debian and Ubuntu.

Assign the current system hostname (e.g., "foo") a permanent IP address if the 
machine
has one, e.g.,

    138.64.21.258 foo.bar.com foo

and assign it the loopback address 127.0.1.1 if it does not:

    127.0.1.1 foo

Note the difference between 127.0.1.1 and 127.0.0.1.

To those who suggest putting the system hostname ("foo" in our example) on both
the 127.0.0.1 line and the 127.0.1.1 line: No, that is an invalid 
configuration.  Each
host name should be associated in /etc/hosts with a single IP address.

What I describe above are /etc/hosts configuration standards for Debian and 
Ubuntu.
In the real world many people are confused about how /etc/hosts should be set up
and this includes many Debian and Ubuntu developers, and even those developing 
and packaging network configuration tools.  I haven't looked recently, but up 
until
two years ago there was no network configurator that even came close to writing
valid network configuration files in Debian and Ubuntu.  For a very long time I 
have
avoid installing or starting network configuration tools in Debian and Ubuntu.

-- 
Missing hostname in /etc/hosts causes sudo to fail
https://bugs.launchpad.net/bugs/19775
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