[Bug manual/25156] discrepancy between NSS documentation and actual behaviour/code if nsswitch.conf is absent

["carlos at redhat dot com" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=25156

Carlos O'Donell <carlos at redhat dot com> changed:

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                 CC|                            |carlos at redhat dot com

--- Comment #1 from Carlos O'Donell <carlos at redhat dot com> ---
(In reply to Jan Hacker from comment #0)
> I raised this topic in https://github.com/golang/go/issues/35305 :
> 
> https://www.gnu.org/software/libc/manual/html_node/Notes-on-NSS-
> Configuration-File.html
> states that, in absence of /etc/nsswitch.conf, ...:
> "For the hosts and networks databases the default value is dns
> [!UNAVAIL=return] files."
> 
> In contrast,
> https://sourceware.org/git/?p=glibc.git;a=blob;f=nss/nsswitch.c#l157 seems
> to use "files" exclusively, if no /etc/nsswitch.conf is present.
> 
> Could you please confirm that the manual (
> https://sourceware.org/git/?p=glibc.git;a=blob;f=manual/nss.texi;
> h=821469a78a298b83c60ed66884fe08e98bb741e0;hb=HEAD#l327 ) is outdated and
> does not reflect current/actual behaviour (of using "files" exclusively in
> absence of nsswitch.conf) ... and if so, update the manual?
> 
> Furthermore, the
> https://sourceware.org/git/?p=glibc.git;a=blob;f=nss/nsswitch.conf#l60 uses
> "hosts: files dns" as default.
> I wonder whether it's a good idea to provide a default nsswitch.conf (which
> uses "hosts: files dns"), while nsswitch.c effectively uses only "files" as
> "default" if nsswitch.conf is absent. Wouldn't "files dns" be a more
> user-friendly default in code, as it would match the example/default
> nsswitch.conf?

(1) What is the default without nsswitch.conf?

We define DEFAULT_CONFIG in the source file that is used to define the service.

nss/hosts-lookup.c:
 19 #define DATABASE_NAME hosts
 20 #define DEFAULT_CONFIG "dns [!UNAVAIL=return] files"
 21 
 22 #include "XXX-lookup.c"

So here we define it in a way that matches the manual.

Then the lookup uses a DEFAULT_CONFIG which is non-NULL and so the code you
quoted is never used for hosts.

(2) What *should* the default be?

I think it should probably be adjusted to "files dns" as we use in modern day
distributions.

In summary:
- I think we're only talking about (2) in this case, but if you have observed
(1) to be wrong, then please say so and provide some debugging details.

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