On Thu, Dec 2, 2021 at 1:35 AM Geert Stappers via Dnsmasq-discuss
<dnsmasq-discuss@lists.thekelleys.org.uk> wrote:
>
> On Wed, Dec 01, 2021 at 08:36:47PM -0800, Carl Karsten wrote:
> > Subject: Re: [Dnsmasq-discuss] tftp hook for "not found"
> > or some way to create a symlink when needed.
> >
> > when a pi net boots, it injects its serial number into the path that
> > it requests:
> > dnsmasq-tftp[678]: file /srv/tftp/7a6d27f6/autoboot.txt not found
> >
> > When thathappens, I need to create a symlink:
> > id=7a6d27f6
> > ln -s /srv/tftp/boot /srv/tftp/${id}
> >
> > and ideally catch that before it decides to error. otherwise I'll
> > just power cycle the pi and the 2nd time it should work.
> >
> > if I understand the docs the hook only gets called on "sent" -
> >
> > "The "tftp" action is invoked when a TFTP file transfer completes: the
> > arguments are the file size in bytes, the address to which the file
> > was sent, and the complete pathname of the file. "
> > https://thekelleys.org.uk/dnsmasq/docs/dnsmasq-man.html
> >
> > I only expect to have 20 - 40 pi's, so it isn't a huge problem if I
> > have to boot from SD card to harvest the serial number. but it would
> > be nice if we didn't need to do that.
>
> It would be nice if the clients did not mengle next filename request.
I hear pi v3 ignores next-server.
for more details on what it does:
it first does many ftp get /<filenam> and it isn't clear what files it
needs from the boot partition.if t can't find the file in / then it
tries /<serial>/<filename>
so I could put all 41 files in /srv/tftp ... but that makes me grumpy.
>
> Is the serial number also visible in the DHCP request?
>
IRC #raspberypi clever: i believe it is, run wireshark and you should
see it in a dhcp option
good idea. if this works, then I don't need to worry about the ftp error.
>
> > id=7a6d27f6
>
> Is that a MAC address?
>
>
no, but.. also no:
"there's a serial-number hard-coded into the SoC (you can see yours
with "cat /proc/cpuinfo"), and the serial number determines the
Ethernet MAC address "
https://forums.raspberrypi.com/viewtopic.php?f=29&t=8985
algorithm is proprietary to the chip manufacturer. Which effectively
means, "nobody knows if the serial number can be counted on to be
truly unique".
https://raspberrypi.stackexchange.com/questions/2086/how-do-i-get-the-serial-number
>
> Anyway, this if is from the manual page of dnsmasq
>
> --dhcp-script=<path>
> Whenever a new DHCP lease is created, or an old one destroyed,
> or a TFTP file transfer completes, the executable specified by
> this option is run.
> The arguments to the process are "add", "old" or "del", the
> MAC address of the host (or DUID for IPv6) , the IP address,
> and the hostname, if known.
>
>
>
> Groeten
> Geert Stappers
> --
> Silence is hard to parse
>
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--
Carl K
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