On Wed, 2015-06-24 at 18:05 +0100, Pete Biggs wrote:
> On Wed, 2015-06-24 at 16:59 +0100, Patrick O'Callaghan wrote:
> > On Wed, 2015-06-24 at 10:38 +0100, Pete Biggs wrote:
> > > > command-line ping, dig, or host command returns the new IP for 
> > > > a 
> > > DNS
> > > > name, Evolution should be using that as well.
> 
> [[I wish they would fix this line wrapping of quoted content ...]]
> 
> > > 
> > > Not necessarily, it depends on the individual libraries being 
> > > used.
> > 
> > Strictly that is true, but one would expect a reasonably configured
> > system to use a single resolver library for everything. Usually 
> > that is
> > libresolv.so, which is part of glibc.
> 
> No, that's just not so, it's much more complex than that.  Most user
> programs, like ping, use routines like 'gethostbyname' (or their more
> modern equivalent) - those routines get their information from a
> variety of sources - /etc/hosts, YP/NIS, DNS - which ultimately might
> use libresolv.  Gnome applications tend to use the GIO libraries. 
>  And
> DNS querying programs like nslookup, host and dig go directly to the
> DNS server.

On my system (Fedora 22) nslookup and evolution both link to libresolv,
though ping doesn't.

> Things are complicate further by systems such as nscd - "Name Service
> Cache Daemon" that, as it says in the man page, "provides a cache for
> the most common name service requests" - and that includes hosts. 
>  The
> default TTL for hosts in nscd is 1 hour.

I stopped using nscd when I moved away from Sun workstations so who
knows.

> That's why I said in reply to the original poster that you need to be
> careful about using things like nslookup to verify DNS entries since
> other parts of the system may be caching previous results.

I don't dispute that.

poc

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