samba - Mar 2018 - dhcp lease time hardware in script at dhcpd/Bind/Samba wiki page

On 29/03/18 15:52, Rowland Penny via samba wrote:
> On Thu, 29 Mar 2018 15:01:26 +0100
> Sebastian Arcus via samba <samba at lists.samba.org> wrote:
> 
>> There seems to be a slight issue with the instructions at the
>> following wiki page:
>>
>>
https://wiki.samba.org/index.php/Configure_DHCP_to_update_DNS_records_with_BIND9
>>
>> The /usr/local/bin/dhcp-dyndns.sh script seems to use a hardwired
>> value for the lease expiry time of 3600 - independent of whatever is
>> configured in dhcpd.conf. With the examples provided, it should work,
>> as the example dhcpd.conf uses 1800 for lease expiry time - so dhcpd
>> will try to renew the lease before it actually expires. However, when
>> I implemented the script, I didn't notice that the lease time is
>> hardwired in the dhcp-dyndns.sh script - so I've set a higher value
>> in dhcpd.conf. This seems to have caused all sorts of strange
>> behaviour, as Bind/samba_dlz were expiring leases and dhcpd wasn't
>> renewing them - thinking they are still valid.
>>
>> Would it be possible to pass the max lease time value from dhcpd.conf
>> to the dhcp-dyndns.sh script somehow? I would have made a suggestion
>> myself, but for the life of me I can't find anywhere on the net a
>> reference of standard variable which can be used in dhcpd.conf.
>>
>> If the above is not possible, maybe a max-lease-time variable should
>> be placed at the top of the dhcp-dyndns.sh script. so that at least
>> it is obvious that this is set again in this script, and not carried
>> over from dhcpd.conf?
>>
> 
> You could try adding something like this near to the top of
> dhcp-dyndns.sh:
> 
> TTL=$(cat /etc/dhcp/dhcpd.conf | grep 'max-lease-time' | awk -F
';'
> '{print $1}' | awk '{print $NF}')
> 
> Then replace the '3600' with '$TTL'
Thank you for that! I take it there is no corresponding variable, which 
can be used as an argument in dhcpd.conf when calling dhcp-dyndns.sh?

Also, I discovered another typo on the wiki page - which was actually a 
bit of a pain to track down. On the following line:

rzone=$(echo ${ip} | awk -F '.' '{print
$3"."$2"."$1".in-addr.arpa"}’)

The last quote should be a single quote, but it is actually a backtick.

I can report that on Slackware-current with dhcpd 4.4.1, the extra 
setting suggested to set the rzone is necessary - otherwise Bind tries 
to use a B class reverse zone instead of a C one and complains that it 
isn't authoritative for it:

updating zone '168.192.IN-ADDR.ARPA/IN': update failed: not 
authoritative for update zone (NOTAUTH)

I have other Slackware servers with dhcpd 4.3.6 and 4.3.4 - and those 
are happy without the rzone line.

On Thu, 29 Mar 2018 16:24:32 +0100
Sebastian Arcus via samba <samba at lists.samba.org> wrote:
> On 29/03/18 15:52, Rowland Penny via samba wrote:
> > 
> > You could try adding something like this near to the top of
> > dhcp-dyndns.sh:
> > 
> > TTL=$(cat /etc/dhcp/dhcpd.conf | grep 'max-lease-time' | awk
-F ';'
> > '{print $1}' | awk '{print $NF}')
> > 
> > Then replace the '3600' with '$TTL'
> 
> Thank you for that! I take it there is no corresponding variable,
> which can be used as an argument in dhcpd.conf when calling
> dhcp-dyndns.sh?
Not that I am aware of.
> 
> Also, I discovered another typo on the wiki page - which was actually
> a bit of a pain to track down. On the following line:
> 
> rzone=$(echo ${ip} | awk -F '.' '{print
$3"."$2"."$1".in-addr.arpa"}’)
OOPs, I don't use that and I cut and pasted it in, which is no excuse
for not noticing, but it is fixed now ;-)

> I can report that on Slackware-current with dhcpd 4.4.1, the extra 
> setting suggested to set the rzone is necessary - otherwise Bind
> tries to use a B class reverse zone instead of a C one and complains
> that it isn't authoritative for it:
> 
> updating zone '168.192.IN-ADDR.ARPA/IN': update failed: not 
> authoritative for update zone (NOTAUTH)
> 
> I have other Slackware servers with dhcpd 4.3.6 and 4.3.4 - and those 
> are happy without the rzone line.
> 
Good to know.

Rowland

On 29/03/18 16:41, Rowland Penny via samba wrote:
> On Thu, 29 Mar 2018 16:24:32 +0100
> Sebastian Arcus via samba <samba at lists.samba.org> wrote:
> 
>> On 29/03/18 15:52, Rowland Penny via samba wrote:
>>>
>>> You could try adding something like this near to the top of
>>> dhcp-dyndns.sh:
>>>
>>> TTL=$(cat /etc/dhcp/dhcpd.conf | grep 'max-lease-time' |
awk -F ';'
>>> '{print $1}' | awk '{print $NF}')
>>>
>>> Then replace the '3600' with '$TTL'
>>
>> Thank you for that! I take it there is no corresponding variable,
>> which can be used as an argument in dhcpd.conf when calling
>> dhcp-dyndns.sh?
> 
> Not that I am aware of.
> 
>>
>> Also, I discovered another typo on the wiki page - which was actually
>> a bit of a pain to track down. On the following line:
>>
>> rzone=$(echo ${ip} | awk -F '.' '{print
$3"."$2"."$1".in-addr.arpa"}’)
> 
> OOPs, I don't use that and I cut and pasted it in, which is no excuse
> for not noticing, but it is fixed now ;-)
Thank you very much!