How does MAAS pick which volume to boot from?

[Daniel K]

Looks like the hd0 may be hardcoded :-/

> root at maas1:~# cat
/usr/lib/python3/dist-packages/provisioningserver/templates/pxe/config.local.amd64.template
> DEFAULT local
>
> LABEL local
>   SAY Booting local disk ...
>   KERNEL chain.c32
>   APPEND hd0



On Tue, Dec 5, 2017 at 10:38 PM, Daniel K <sathackr at gmail.com> wrote:

> So attacking this from the angle I'm most familiar with I've captured the
> traffic between the maas server and a booting node to see if I can catch
> the data in flight.
>
> PXE first downloads a file called pxelinux.0 - I see this file in
> /var/lib/maas/boot-resources.
> Then requests(and receives) a file called ldlinux.c32.
>
> Then requests a non existent file: pxelinux.cfg/<some sort of uuid/guid?>
> > # Packet 344 from C:\Users\user\asdf.pcap
> > - 345
> > - 166.825599
> > - 10.20.128.111
> > - 10.20.4.30
> > - TFTP
> > - 121
> > - Read Request, File: pxelinux.cfg/36383031-3839-3255-5831-353130303732,
> Transfer type: octet, tsize=0, blksize=1408
> > - # Packet 345 from C:\Users\user\asdf.pcap
> > - 346
> > - 166.836864
> > - 10.20.4.30
> > - 10.20.128.111
> > - TFTP
> > - 61
> > - Error Code, Code: File not found, Message: File not found
>
> Then requests and receives a file called pxelinux.cfg/01-<mac address>
> > # Packet 346 from C:\Users\user\asdf.pcap
> > - 347
> > - 166.837008
> > - 10.20.128.111
> > - 10.20.4.30
> > - TFTP
> > - 105
> > - Read Request, File: pxelinux.cfg/01-e8-39-35-2b-c9-5c, Transfer type:
> octet, tsize=0, blksize=1408
>
> which contains the following printable text:
> > 95+\W1ExL@@T
> > oad*DEFAULT local
> > LABEL local
> >   SAY Booting local disk ...
> >   KERNEL chain.c32
> >   APPEND hd0
>
> which I can correlate to log entries:
> > 2017-12-05 22:17:49 provisioningserver.rackdservices.tftp: [info]
> ldlinux.c32 requested by e8:39:35:2b:c9:5c
> > 2017-12-05 22:17:49 provisioningserver.rackdservices.tftp: [info]
> pxelinux.cfg/36383031-3839-3255-5831-353130303732 requested by
> e8:39:35:2b:c9:5c
> > 2017-12-05 22:17:49 provisioningserver.rackdservices.tftp: [info]
> pxelinux.cfg/01-e8-39-35-2b-c9-5c requested by e8:39:35:2b:c9:5c
>
> I assume the "APPEND hd0" is what is telling the pxelinux loader which
> disk to boot.
> I searched but I cannot find a directory called pxelinux.cfg anywhere on
> the maas servers, nor a file with any part of the mac address in it's name.
> I'll assume then that some piece of maas is responding to that request
> after fetching the config from some sort of database for that MAC
> address/node.
>
> So then there must be a knob somewhere in MAAS that I can tweak to cause a
> different disk to be sent in the APPEND hd0 command.
>
>
>
>
>
>
>
> On Tue, Dec 5, 2017 at 5:24 PM, Lloyd Parkes <lloyd+lp at must-have-coffee.
> gen.nz> wrote:
>
>> I originally sent this from the wrong email address and so it got hung
>> up on list moderation.
>>
>>
>> On 5 December 2017 at 10:45, Daniel K <sathackr at gmail.com> wrote:
>> >
>> > There must be something that tells the PXE loader which physical disk
>> to try
>> > to boot
>>
>> This is almost certainly hard coded in the PXELinux boot script to
>> default to BIOS disk 0x80. Have a look at
>> http://www.syslinux.org/wiki/index.php?title=SYSLINUX#LOCALBOOT_type
>> and see if it helps.
>>
>> I would dig into this myself because I want to make my HPE servers
>> boot as well, but I'm 3265km and two months away from my MAAS servers.
>>
>> Cheers,
>> Lloyd
>>
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>
>
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