dhcp with /etc/network/interfaces

[David Henderson]

Thanks for your help with this too Denys.  Answers are inline...


On 9/20/16, Denys Vlasenko <vda.linux at googlemail.com> wrote:
> On Tue, Sep 20, 2016 at 5:31 PM, David Henderson
> <dhenderson at digital-pipe.com> wrote:
>> Hey Martin, thanks again for your help!  So I had to bring back
>> 'sneaker-net' to get strace on the machine via flash drive (after
>> locating one), but it is now on the machine!  I could not see anything
>> in the 'ps' output (and it is the GNU version) regarding what was
>> being called for contacting a DHCP server for the adapter.  I also
>> tried running the command that Peter suggested, but the command he
>> listed has invalid syntax.
>
> An examlpe run works for me:
>
> $ strace -f -e execve sh -c /bin/pwd
> execve("/usr/bin/sh", ["sh", "-c", "/bin/pwd"], [/* 52 vars */]) = 0
> execve("/bin/pwd", ["/bin/pwd"], [/* 52 vars */]) = 0
> /tmp
> +++ exited with 0 +++
>
> You might have an old version of strace.

Possibly, it chokes with the 'execve' parameter as it's not valid in
my 'strace'.


>> After a few more calls and a ton of goop
>> from 'strace'
>
> We need the entire "ton of goop" from strace.
> For example, the "strace -oLOG -f -tt -s99 COMMAND" is my favorite.
>
>
>>, it appears that 'udhcpc' was being called as follows
>> (at least on my dev machine):
>>
>> udhcpc -R -n -p /var/run/udhcpc.eth0.pid -i eth0
>>
>> (Just in case anyone else comes across this post)
>>
>> Now that I know what is being called, can anyone help with the other
>> part of the original question?
>
> Ok, the question:
>
>> scripts that are run in the /etc/network/if-{,pre-,post-}{up,down}.d/
>> directories.  Can/should I specify a script in the proper directory to
>> execute the udhcpc binary (or another binary for that matter) with my
>> own parameters for the interface without BB trying to use its own
>> methods of obtaining an IP address automatically - effectively
>> preventing the duplication of requests to the DHCP server for that
>> interface?
>
> My personal opinion is that as soon as "simple" ifup/ifdown setup
> is too primitive for your needs, e.g.:
> - you need many IPs on one iface,
> - you need dynamical ifaces (ppp, vpn), and you need to redefine
>   routing/firewalling based on what's up and what isn't,
> - you need additional things to be started/stopped
>   (WPA supplicant, babysitter)
>
> at this point ifup becomes more PITA than help. It forces you
> to do stuff in awkward ways.

So can I perform my own methods via the scripts to prevent BB from
attempting its own 'udhcpc' calls?  I don't want duplicate calls to
the same DHCP server.

Thanks,
Dave