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Re: CVS commit: src/bin/hostname

On Thu, Jul 25, 2013 at 06:30:54AM +0700, Robert Elz wrote:
> The hostname was always intended to contain the globally unique textual name
> of the host - someone said that it couldn't have always been a FQDN, as they
> didn't exist when the hostname syscall was created, and that's correct.  But 
> back then hostnames (including before even ".arpa" was appended) were
> registered and intended to be unique (it was the growing absurdity of
> continuing that in a flat namespace that led to the development of the DNS).
> Using a (trivially derived) nickname as the hostname instead of the actual
> (unique) hostname is simply stupid.

There are many (well some) systems that don't have a FQDN, and where there
isn't one that can be assigned.

A modern example might be some kind of portable system system that
only ever connects to the outside world using wifi hotspots.
An older example would be a single system using dialup networking.

In both cases the IP addressing info is transient, and nothing from the
'great outside' ever directs requests (of an form) to the machine by name.

IIRC one of the original uses for FQDN was for email routing 
(user@host.domain).But even then we always published addresses user@mail_domain 
so that the
outside world didn't know which machine users read their mail on 'today'
(that involved groging the sendmail masquerade options).

This all begs the question of what the hostname (output by 'uname -n')
is actually for. There are a lot of things it isn't!

Since a system can have multiple IP addresses, subsets of which are returned 
by forwards DNS lookups on many FQDN from different domains it can have
nothing to do with IP addresses!

For smtp EHLO you really want a name that will forwards lookup to the
source IP of the connection, that can only be determined after the
connection is established.
So it isn't anything to do with mail transfer either.
(Yes, I know MTA have a habit of trying to find a FQDN at startup)

So we now get down to things like the name in the security report emails.
Purely local significance.

What have I missed??


David Laight:

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