[Dnsmasq-discuss] dumping current dhcp leases without always updating the leasefile curing normal ?

Rick Jones rick.jones2 at hp.com
Fri Oct 11 16:37:35 BST 2013

On 10/11/2013 07:16 AM, Simon Kelley wrote:
> On 11/10/13 01:39, Rick Jones wrote:
>> I am still on the steep learning slope for dnsmasq.  The manpage lists a
>> -l/--dhcp-leasefile option into which dnsmasq will store lease
>> information. I gather though that it will be updating that all the time
>> as leases come and go.
>> Is there a version post 2.59 where one can send dnsmasq a signal to
>> cause it to dump a copy of its current lease information to a file, but
>> without the continuous updates in normal operation?
> No. there's a mode meant for use on flash filesystems that updates the
> lease file less often, if that helps.

It might actually.  I'll try to take a look at it.

> See also this thread
> http://lists.thekelleys.org.uk/pipermail/dnsmasq-discuss/2013q3/007555.html

 From that I should take away that the lease file format is not fixed 
and there but for the grace of the developers go I should I start 
grubbing through it, yes?  I can accept that.

> More context about what youre trying to achieve would help.

What I would like to be able to do is "know" (make an informed guess) 
which of the clients which could have a lease probably have a lease (or 
probably do not have a lease), but in an environment where I might have 
either rather busy dnsmasq processes, or a large number of individually 
not very busy dnsmasq processes and want to minimize the storage load. 
But I don't need to know all the time, just occasionally and not 
necessarily on a schedule and not necessarily all the dnsmasq processes. 
  So, I figured some sort of "dump your current leases" feature would 
satisfy that.

I cannot really rely on the clients being willing to respond to the 
likes of ping, they may only respond to things they've initiated 
themselves.  I also do not have other access to the clients (eg their 
console).  So, all I can think of presently is trying to ask the dnsmasq 
process(es) what it believes its active leases happen to be.


BTW, sorry about botching the last part of the subject there.

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