Re: [gentoo-user] /etc/hosts include file?

[Alan McKinnon <alan.mckinnon@gmail.com>]

On 08/03/2013 02:29, Michael Mol wrote:
> On 03/07/2013 05:24 PM, Alan McKinnon wrote:
>> Anyone know if there's a way to get /etc/hosts to support the notion of
>> an include file? I did my homework and found nothing, maybe someone else
>> knows more.
>>
>> I really do need this, I have an app that discovers things on the
>> network and knows their address. This makes it's automated way into DNS
>> but takes a few days, and another app needs to use the fqdn right now.
>> So /etc/hosts is the way to go for the interim three days.
>>
>> I've worked around it by creating /etc/hosts.d/ containing a header and
>> a data file. cat the two and redirect to /etc/hosts.d/hosts and the real
>> hosts file is a symlink to that. It's a sub-directory as none of these
>> apps run as root and only root can modiy the real hosts file.
>>
>> This works well enough, but a supported include mechanism would make
>> life so much simpler, not to mention easier for my colleagues to
>> understand what the blazes I set up :-)
> 
> No, there's not an "include" directive.
> 
> There are, however, two other ways to get hostnames recognized.
> 
> The first is /etc/resolv.conf . You can point your host at a local DNS
> server which is aware of the discovered hosts, and which forwards the
> rest of the queries. (This is how Samba 4's internal DNS server
> operates; anything it knows, it responds to. Everything else, it forwards.)
> 
> Read the manpage for resolv.conf...there's a lot of stuff in there
> you'll want to know as you start coping with IPv6. (And some useful
> stuff if you want to favor a particular IP range...)

And the day started off so well. Then you had to come along and mention
IPv6.... :-)

IPv6 is wonderfully easy to use client-side and reasonably easy to plug
into an existing network (the routers mostly know what to do already).
The fun starts when you need to write an app that tracks and does range
allocations at ISP scale, all while keeping the PTRs in line too. Sadly
for me, my team works in that area and such a magic app is one of our
deliverables

One day when I've climbed down off the walls and my fingernails have
grown back, I might be up to relating what it is taking to get that
done.... :-)

> 
> The second is /etc/nsswitch.conf . nsswitch.conf is how you inject
> samba-discovered, NIS-offered -- or whatever provider you care to inject
> -- hostname databases into the system resolver. You could have it query
> your provided database first, moving on to other sources if your
> provided database doesn't have what you're looking for. (I'm actually
> kinda surprised avahi doesn't come with an nss plugin...)

One day I should read nsswitch's man page completely. I never needed to
know more than "dns files" for the hosts directives and that shadow does
user. All those other lookup schemes are things I never use.




-- 
Alan McKinnon
alan.mckinnon@gmail.com