Re: Contents of /etc/hosts

[Hartmut Goebel <h.goebel@goebel-consult.de>]

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Am 06.10.2016 um 02:57 schrieb John Darrington:
>        127.0.0.1 localhost
>        ::1       localhost
>        127.0.0.1 gambrinus
>        ::1       gambrinus
>      
>      Or am I missing something?
>
> Hmm.  I have never seen it done this way elsewhere, and I really wonder how some
> services will react if they discover that 127.0.0.1 is not called "localhost"?  
> Or that one address is known by two names.  I think it possible they might 
> assume a security breach and refuse to work. 

This should not be a problem. One could always add several entries for
the same IP-address. And "getent hosts 127.0.0.1" will return the first
entry in /etc/hosts AFAIKT.

I started digging through the man pages, but did not finish. It's a deep
maybe recursive mess of documentation where nothing is said about  Maybe
we need to refer to the gethostbyname(2) and gethostbyname(3)
documentation, which both are listed in "man hostname".

* gethostbyname(2) [1], uses uname[2], which returns what ever has been
set with sethostname (AFAICT) and always returns a single string.

* gethostbyname(3) [3] returns a structure capable to hold an name,
several aliases, and several addresses.

Nevertheless my conclusion is that any program should be able to handle
any ip-address and and hostname and must not rely on any assumtion
regarding these. (Exept perhaps to assume "localhost" is defined.)

[1] http://man7.org/linux/man-pages/man2/gethostname.2.html
[2] http://man7.org/linux/man-pages/man2/uname.2.html
[3] http://man7.org/linux/man-pages/man3/gethostbyname.3.html
[4] http://man7.org/linux/man-pages/man5/hosts.5.html

> Kerberos is very fussy about such things.

Yes, it is, forward and backward resolution must match. But this can be
done with a the hostname's non-loopback IP-address being in front of the
loopback entry. ASAIK


-- 
Schönen Gruß
Hartmut Goebel
Dipl.-Informatiker (univ), CISSP, CSSLP, ISO 27001 Lead Implementer
Information Security Management, Security Governance, Secure Software
Development

Goebel Consult, Landshut
http://www.goebel-consult.de

Blog: http://www.goebel-consult.de/blog/feiertagsarbeit-bei-teletrust
Kolumne:
http://www.cissp-gefluester.de/2011-02-fleisige-datensammler-fur-lukratives-geschaeftsmodell-gesucht



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