[Dnsmasq-discuss] Why is dnsmasq reading /var/run/dnsmasq/resolv.conf twice when it starts up?

[Dan Williams]

On Thu, 2013-10-03 at 17:05 +0100, Chris Green wrote:
> On Thu, Oct 03, 2013 at 04:42:59PM +0100, Simon Kelley wrote:
> > On 03/10/13 16:29, Chris Green wrote:
> > >When I start dnsmasq I see the following in syslog:-
> > >
> > >Oct  3 16:09:03 revo dnsmasq[2819]: started, version 2.63rc6 cachesize 150
> > >Oct 3 16:09:03 revo dnsmasq[2819]: compile time options: IPv6 GNU-getopt 
> > DBus i18n IDN DHCP DHCPv6> 
> > >Oct 3 16:09:03 revo dnsmasq-dhcp[2819]: DHCP, IP range 192.168.1.80 -- 
> > 192.168.1.150, lease time 1h 
> > >Oct  3 16:09:03 revo dnsmasq[2819]: using local addresses only for domain zbmc.eu
> > >Oct  3 16:09:03 revo dnsmasq[2819]: reading /var/run/dnsmasq/resolv.conf
> > >Oct  3 16:09:03 revo dnsmasq[2819]: ignoring nameserver 192.168.1.2 - local interface
> > >Oct  3 16:09:03 revo dnsmasq[2819]: using nameserver 194.72.0.114#53
> > >Oct  3 16:09:03 revo dnsmasq[2819]: using nameserver 212.159.6.10#53
> > >Oct  3 16:09:03 revo dnsmasq[2819]: ignoring nameserver 127.0.0.1 - local interface
> > >Oct  3 16:09:03 revo dnsmasq[2819]: using local addresses only for domain zbmc.eu
> > >Oct  3 16:09:03 revo dnsmasq[2819]: read /etc/hosts - 12 addresses
> > >Oct 3 16:09:03 revo dnsmasq-dhcp[2819]: not giving name revo.zbmc.eu to 
> > the DHCP lease of 192.168.> 
> > >Oct 3 16:09:03 revo dnsmasq-dhcp[2819]: not giving name revo to the DHCP 
> > lease of 192.168.1.148 be> 
> > >Oct  3 16:09:05 revo dnsmasq[2819]: reading /var/run/dnsmasq/resolv.conf
> > >Oct  3 16:09:05 revo dnsmasq[2819]: ignoring nameserver 192.168.1.2 - local interface
> > >Oct  3 16:09:05 revo dnsmasq[2819]: using nameserver 194.72.0.114#53
> > >Oct  3 16:09:05 revo dnsmasq[2819]: using nameserver 212.159.6.10#53
> > >Oct  3 16:09:05 revo dnsmasq[2819]: ignoring nameserver 127.0.0.1 - local interface
> > >Oct  3 16:09:05 revo dnsmasq[2819]: using local addresses only for domain zbmc.eu
> > >
> > >Why is it doing everything twice?
> > >
> > Probably because whatever populates /var/run/dnsmasq/resolv.conf
> > alters the modification time just after it starts dnsmasq.
> > 
> That makes sense I guess!

While I don't know how Ubuntu has configured it, NetworkManager spawns a
private instance of dnsmasq to handle local caching nameserver if you've
configured that in /etc/NetworkManager/NetworkManager.conf.  Otherwise,
it might be some interaction between resolvconf (a resolv.conf manager
that Debian-based systems use) and dnsmasq that's set up outside
NetworkManager.

Dan

> > >
> > >While I'm about it, what creates/populates /var/run/dnsmasq/resolv.conf?
> > 
> > We need more context to have a hope of answering that.
> > 
> OK.  As you may gather I'm playing about a bit with my dnsmasq
> configuration on the server machine at 192.168.1.2.  It's a small Acer
> Revo machine running Ubuntu 12.10.
> 
> I recently changed ISP and thus needed to change the DNS servers that
> dnsmasq uses upstream of itself.  That was my first problem because I
> couldn't find where these are set.  I *think* I have found it now,
> they're in the files in /etc/NetworkManager/system-connections.  I have
> in "Wired connection 1":-
> 
>     [802-3-ethernet]
>     duplex=full
>     mac-address=00:01:6C:6C:C7:9B
> 
>     [connection]
>     id=Wired connection 1
>     uuid=2262541a-2106-4e4d-b2b7-ab631dddcbf1
>     type=802-3-ethernet
>     timestamp=1361810287
> 
>     [ipv6]
>     method=ignore
> 
>     [ipv4]
>     method=manual
>     dns=127.0.0.1;212.159.6.9;212.159.13.49;
>     dns-search=zbmc.eu;
>     addresses1=192.168.1.2;24;192.168.1.1;
>     may-fail=false
> 
> Presumably (relating to the other thread) I can add a 'manual' ipv4
> section like the one above to the file in the same directory that
> relates to the wireless interface.
> 
> The "doing things twice" was just something I noticed, probably
> NetworkManager is doing things at boot time and happens, as you said, to
> change the file just after dnsmasq reads it.  Not a big issue really, it
> only happens at boot time I think.
> 
> 
> Hopefully all these things are resolved now and I can leave the list in
> peace.  However I did have one issue where, after rebooting the dnsmasq
> server machine nothing worked at all (i.e. no DNS or DHCP) until I
> manually restarted dnsmasq itself.  I'll try it all again, carefully,
> and see if the same happens again.
>