[syslinux] Loading files from another tftp server

[Jeffrey Hutzelman]

--On Monday, January 12, 2009 10:13:35 AM +0100 Erwan Velu 
<erwan at seanodes.com> wrote:

> Jeffrey Hutzelman wrote:
>> --On Friday, January 09, 2009 05:51:47 PM +0100 Erwan
>> <erwan at seanodes.com>  wrote:
>>
>>
>>> Hi,
>>>
>>> I run Pxelinux for ages on my cluster without troubles, I have to say...
>>> that's a great project.
>>> I'm facing a new challenge that I don't really know how to solve it.
>>> That's a mission for pxelinux :o)
>>>
>>> My pxelinux and my kernels/initrds are stored on the same tftp server.
>>> Now I'd like to tweak the next-server field of the DHCP answer and then
>>> reload another bootstrap from another tftp-server.
>>>
>>
>> You can use PXECHAIN.COM for this; it's included with Syslinux starting
>> with version 3.72.
>>
> Any information or advice about the usage ? I couldn't find any
> documentation on it.

Apparently not.  I suppose I should do something about that.
Use configuration like this:

label wds
  kernel pxechain.cbt
  append windows-wds.example.com::\boot\x86\wdsnbp.com

label f7
  kernel pxechain.cbt
  append ::i386_f7/pxelinux.0

The "append" line contains the TFTP filename of the new bootstrap to load, 
in exactly the same format supported by PXELINUX itself, which looks like 
[[ipaddress]::]tftp_filename, where ipaddress defaults to the same TFTP 
server PXELINUX was loaded from, and the :: prefix makes the filename 
absolute instead of relative to the PXELINUX configuration directory.
PXECHAIN will load the new bootstrap program and arrange for the DHCP 
response reported by PXE to reflect the new server and path.  The examples 
above are real ones that work for us in production (except for the obvious 
hostname difference).

BTW, I haven't looked at 3.72 yet, so I don't know whether PXECHAIN gets 
installed as PXECHAIN.COM or PXECHAIN.CBT, but it should be the latter, as 
it depends on features in the comboot API which are not provided by real 
DOS.

-- Jeff