samba - Jan 2021 - Dynamic Updates to Bind DLZ through DHCP have repeated errors in syslog

On Fri, Jan 29, 2021 at 11:34 AM Rowland penny via samba
<samba at lists.samba.org> wrote:
>
> The update is failing because, for some reason, the record does not
> exist. This has nothing to do with the script, unless it is because the
> script never created it in the first place, but then surely there would
> be something in the logs about this.
>
>
> As I said, the script is run with the output of DHCP, this can succeed
> or fail, but it would be logged, at the same time, dhcp does its thing
> and this usually works. The script can fail, but dhcp work, the only
> thing that connects them is that dhcp runs the script with the required
> arguments (or not)
These records specifically are generated by the script from DHCP.
Looking at what it's passing (in the previous log file), I think the
issue is stemming from the script grabbing and passing the MAC, but
not the hostname, which is what Samba-tool uses.
I just tested it manually, and deleting a record in DNS took the following args:
samba-tool dns delete <server> <zone> <name> <Record
Type> <record data>

The example I used and succeeded on manually was: samba-tool dns
delete dc1 domain.com sys-rstrebbing A 10.60.2.35 (My laptop). It ran
fine.
If I understand the logs correctly from your script, this is what it's
passing:
samba-tool dns delete dc1 domain.com 0 A 10.60.2.11 <---Example based
on args given in the log file.
So would it even be possible to grab the hostname on an expiring
lease? Looking over the wiki again I noticed this comment on the code
in dhcpd.conf
In the on expiry block:
# cannot get a ClientMac here, apparently this only works when
actually receiving a packet
and
# cannot get a ClientName here, for some reason that always fails
By chance has the second one changed? Because otherwise samba doesn't
seem to allow removing the record since the name of the record
(ClientName) almost seems like it's a critical piece of this. Or if
anyone else has come to another solution to get the information
another way while the script runs.

Ralph

On 29/01/2021 18:06, ralph strebbing wrote:
> These records specifically are generated by the script from DHCP.
> Looking at what it's passing (in the previous log file), I think the
> issue is stemming from the script grabbing and passing the MAC, but
> not the hostname, which is what Samba-tool uses.

If you are adding a record, dhcp should be passing the hostname:

Jan 11 15:08:50 dc4 dhcpd[2228]: Commit: IP: 192.168.0.73 DHCID: 
cc:4e:ec:1f:48:ef Name: HUMAX
Jan 11 15:08:50 dc4 dhcpd[2228]: execute_statement argv[0] = 
/usr/local/bin/dhcp-dyndns.sh
Jan 11 15:08:50 dc4 dhcpd[2228]: execute_statement argv[1] = add
Jan 11 15:08:50 dc4 dhcpd[2228]: execute_statement argv[2] = 192.168.0.73
Jan 11 15:08:50 dc4 dhcpd[2228]: execute_statement argv[3] = 
cc:4e:ec:1f:48:ef
Jan 11 15:08:50 dc4 dhcpd[2228]: execute_statement argv[4] = HUMAX

If it isn't, you need to find out why, the script depends on receiving 
the required data.

If you are deleting a record, then the script just requires the IP, the 
hostname will be found by this:

# Exit if no computer name supplied, unless the action is 'delete'
if [ -z "${name}" ]; then
 ??? if [ "${action}" = "delete" ]; then
 ??????? name=$(host -t PTR "${ip}" | awk '{print $NF}' | awk
-F '.'
'{print $1}')
 ??? else
 ??????? usage
 ??????? exit 1;
 ??? fi
fi

That piece of code should obtain the short hostname from the IP, unless 
the record does not exist or the wrong data is being returned by the 
'host' command.

> I just tested it manually, and deleting a record in DNS took the following
args:
> samba-tool dns delete <server> <zone> <name> <Record
Type> <record data>
>
> The example I used and succeeded on manually was: samba-tool dns
> delete dc1 domain.com sys-rstrebbing A 10.60.2.35 (My laptop). It ran
> fine.
> If I understand the logs correctly from your script, this is what it's
passing:
> samba-tool dns delete dc1 domain.com 0 A 10.60.2.11 <---Example based
> on args given in the log file.

No, my script isn't 'passing' 10.60.2.11 , it is what is being
passed to
it by dhcp

> So would it even be possible to grab the hostname on an expiring
> lease? Looking over the wiki again I noticed this comment on the code
> in dhcpd.conf
> In the on expiry block:
> # cannot get a ClientMac here, apparently this only works when
> actually receiving a packet
> and
> # cannot get a ClientName here, for some reason that always fails

This is an artefact of dhcp, the bash script can only use what is passed 
to it.

> By chance has the second one changed? Because otherwise samba doesn't
> seem to allow removing the record since the name of the record
> (ClientName) almost seems like it's a critical piece of this. Or if
> anyone else has come to another solution to get the information
> another way while the script runs.

The different IP has something to do with your setup and is not 
something I have ever seen, I cannot fix this, you need to find out why 
the IP changed.

Rowland