[Hostname-devel] Bug#718393: Bug#718393: hostname --all-fqdns is broken: doesn't list the FQDN

[Vincent Lefevre]

On 2013-09-08 12:16:21 +0200, Michael Meskes wrote:
> On Fri, Sep 06, 2013 at 10:56:26PM +0200, Vincent Lefevre wrote:
> > > hostname(1) clearly says:
> > > 
> > > --all-fqdns
> > >               Displays all FQDNs of the machine. This option enumerates all configured network addresses on all configured network interfaces,  and
> > >               translates  them  to  DNS domain names. Addresses that cannot be translated (i.e. because they do not have an appropriate reverse DNS
> > >               entry) are skipped. Note that different addresses may resolve to the same name, therefore the output may contain  duplicate  entries.
> > >               Do not make any assumptions about the order of the output.
> > > 
> > > So it apparently does what it claims to do. What am I missing?
> > 
> > The bug is in the documentation too, which has contradictions.
> > For instance, "Displays all FQDNs of the machine." is plainly
> > wrong here, since xvii.vinc17.org is a FQDN of the machine, but
> > is not listed.
> 
> But the second sentence in the same paragraph explicitely explains
> what is meant by "all".

This is not clear. It should explicitly say that the FQDN (as
returned by the -f option) may not be part of this list. It
should also explicitly say that the returned FQDNs may be local,
thus may not be unique across all machines on the Internet: the
usual definition of a FQDN[*] implies that it is unique.

[*] https://en.wikipedia.org/wiki/Fully_qualified_domain_name

Because of the issues mentioned above, the sentence "See the warnings
in section THE FQDN above, and avoid using this option; use hostname
--all-fqdns instead." for --fqdn must be removed.

For instance, to generate the right-end part of a message-id, it is
much better to use the --fqdn option rather the --all-fqdns one.

> > Moreover "all configured network addresses" is ambiguous: though
> > for lo, 127.0.0.1 is the default address, all 127.* addresses
> > correspond to the same interface, and they may have their own
> > FQDN too (in particular, 127.0.1.1 in Debian).
> 
> It seems getifaddrs() does not return anything but 127.0.0.1.

Because this is a particular case: there are 2^24 IP addresses, and
no-one would expect all these addresses by using this function.

> > I also wonder what it means by "reverse DNS entry". If I use
> > "dig -x <IP_address_of_xvii.local>", I don't get any name.
> 
> dig doesn't use /etc/hosts, does it? hostname uses getnameinfo()
> which does take /etc/hosts into account, too.

But /etc/hosts isn't part of the DNS (see the hosts(5) man page).
This why dig, which is a "DNS lookup utility", doesn't use it.
So, if you take /etc/hosts entries into account and say
"reverse *DNS* entry", you are lying.

-- 
Vincent Lefèvre <vincent at vinc17.net> - Web: <http://www.vinc17.net/>
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Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)