why is dnsmasq running?

[Neal Becker]

I was interested in trying to configure a local dnsmasq, but when I tried to 
start it, I found out there was already one running, using port 53.

I don't know who started it or why it's running, or if I really need it.
ps auxwww | grep dns
nobody    1052  0.0  0.0  51124  1100 ?        S    Nov04   0:00 
/sbin/dnsmasq --conf-file=/var/lib/libvirt/dnsmasq/default.conf --leasefile-
ro --dhcp-script=/usr/libexec/libvirt_leaseshelper

Clearly has something to do with libvirt, probably I did some experiment a 
long time back that required it.  But just removing libvirt-daemon is not an 
option, that would remove a lot of stuff.

[Tom Horsley]

On Mon, 07 Nov 2016 13:23:21 -0500
Neal Becker wrote:
> I was interested in trying to configure a local dnsmasq, but when I tried to 
> start it, I found out there was already one running, using port 53.

Libvirtd starts it when the default virtual network is setup to use NAT.
I use bridge for everything, so one way to eradicate it is:

virsh net-destroy default
virsh net-undefine default

Stop libvirtd, stop dnsmasq, the restart libvirtd and it won't
start dnsmasq this time (at least it works that way for me,
but I usually reboot rather than trying to stop start
individual services).

[Chris Adams]

Once upon a time, Neal Becker  said:
> Clearly has something to do with libvirt, probably I did some experiment a 
> long time back that required it.  But just removing libvirt-daemon is not an 
> option, that would remove a lot of stuff.

Libvirt by default sets up a private local network, NATted towards your
Internet connection, with a local dnsmasq for a proxy resolver.  If you
aren't using that network, you can just disable it and set it to not
auto-start:

# virsh net-autostart default --disable
# virsh net-destroy default

Otherwise, you can make dnsmasq only listen on certain interfaces, so
you could set your instance to not listen on the private network (and
IIRC libvirt configures its instance to only listen on that network),
and that should work.  libvirt configures its instance for separate PID
files and such, so that part doesn't conflict with a "regular" instance.

[Neal Becker]

Chris Adams wrote:
> Once upon a time, Neal Becker  said:
> > Clearly has something to do with libvirt, probably I did some experiment
> > a
> > long time back that required it.  But just removing libvirt-daemon is not
> > an option, that would remove a lot of stuff.
>
> Libvirt by default sets up a private local network, NATted towards your
> Internet connection, with a local dnsmasq for a proxy resolver.  If you
> aren't using that network, you can just disable it and set it to not
> auto-start:
>
> # virsh net-autostart default --disable
> # virsh net-destroy default
>
> Otherwise, you can make dnsmasq only listen on certain interfaces, so
> you could set your instance to not listen on the private network (and
> IIRC libvirt configures its instance to only listen on that network),
> and that should work.  libvirt configures its instance for separate PID
> files and such, so that part doesn't conflict with a "regular" instance.

I see in /var/lib/libvirt/dnsmasq/default.conf:
except-interface=lo
bind-dynamic
interface=virbr0

From dnsmasq man page, I think that means it should only listen on virbr0.

But if I edit /etc/dnsmasq.conf:
#interface=
# Or you can specify which interface _not_ to listen on
except-interface=virbr0

So I think the libvirt dnsmasq should only listen on virbr0, and main 
dnsmasq should listen on everything except virbr0, but this doesn't work:

Nov 07 14:09:46 nbecker2 systemd[1]: Started DNS caching server..
Nov 07 14:09:46 nbecker2 dnsmasq[11520]: dnsmasq: failed to create listening 
socket for port 53: Address a
Nov 07 14:09:46 nbecker2 dnsmasq[11520]: failed to create listening socket 
for port 53: Address already in
Nov 07 14:09:46 nbecker2 dnsmasq[11520]: FAILED to start up

I didn't want to just unconditionally get rid of the existing dnsmasq, as I 
don't know how that might bite me in the future and I'll have forgotten all 
about this.