[Dnsmasq-discuss] Polling of hosts file

[Simon Kelley]

On 19/03/14 09:24, Franco Broi wrote:
> 
> I hear what you say but for me it would be very convenient, I have
> several dnsmasq servers all reading the same shared hosts file.
> 
> My currently solution is to run a script from cron that detects a change
> and sends HUP to dnsmasq.

That sounds like a good solution, especially if you arrange to replace
the file atomically, ie write hosts.new, then mv hosts.new to hosts
> 
> You could have a few simple safeguards, like delaying the update if the
> number of hosts has reduced drastically etc.. 

You could, and they would have the effect of turning frequent failures
into infrequent and difficult to diagnose failures.


Cheers,

Simon.

> 
> On Wed, 2014-03-19 at 09:07 +0000, Simon Kelley wrote: 
>> On 19/03/14 04:04, Franco Broi wrote:
>>> Hi
>>>
>>> Just wondering why dnsmasq doesn't poll the hosts file for changes like
>>> it does for resolv.conf?
>>>
>>
>> Polling files is dangerous. You can get race conditions where the update
>> time changes but the file is still in the process of being written.
>> Polling resolv.conf is necessary because there are lots of things which
>> just write it and expect the changes to be picked up (because that's
>> what the resolver library does.) That's not true for /etc/hosts, so it's
>> better to mandate the update-then-signal model.
>>
>>
>> Cheers,
>>
>> Simon.
>>
>>
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> 
> 
>