Syslinux - Mar 2010 - Availability of a variable of the TFTP server IP addressto be used in pxelinux.cfg/default

Hello Shao,

Thank you for your hint.
I saw this one already earlier but I wanted to avoid it for two reasons:
- One of my images uses a CPIO INITRD which I found rather complicated
editing (like I wrote I'm quite new to all that Linux stuff).
- For each new release I will need to do the changes to the prebuilt
images again. I'm not the one who creates the images. I'm downloading
prebuilt open source tools and customize them to be PXE bootable, in
some cases I also customize the INITRD which is simple when it can be
mounted with the "mount -o loop ...".

Also for the information passed to the Linux OS via the APPEND in
pxelinux.cfg/default I don't even know how/where these are
passed/executed. I expect to find it somewhere in the INITRD of the
distributions but it could be also in the compressed kernel file which I
simply don't know.

Well, as you might have read in the lines above I try to avoid using
IPAPPEND as it makes the whole thing quite complex for a novice. If
there's nothing else that would be the way to go then but... Am I really
the only one having the same boot images deployed to many different
PXE/TFTP servers? How are others passing PXE/TFTP server specific
information to the PXE bootable OS? Especially when I read in the docs
that the usage of IPAPPEND is not recommended.


Thanks,
Michael

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Good day Michael,

In regards to your challenge of passing the boot-server info on to Linux
from PXELINUX:

Items passed with the APPEND directive are available to Linux at
/proc/cmdline .  /proc/ should be mounted at some point during Linux'
startup processes.  IPAPPEND will add to what you find there.

I've seen communications from H. Peter Anvin expressing an interest in
supporting variables in Syslinux.  It isn't implemented at this time.

For some folks booting Linux, their Linux will itself perform another
DHCP transaction...  If you can use a Linux DHCP client to gain access
to the boot-server information, that's another way your Linux can find
out the boot server.

An initramfs "initrd" can be extracted into a directory.  You can
modify
the files and directory structure, then rebuild it.  See
linux/Documentation/filesystems/ramfs-rootfs-initramfs.txt for more
information there.

If you are customizing Linux distributions to be PXE-bootable, I'm under
the impression you'd have to customize each new release anyway.  If
that's not the case, you might check to see if the distribution's
author/vendor/distributor already has a preferred, network-bootable
flavour.  If so, you might be able to determine how they make use of the
boot-server IP information.

- Shao Miller

"STEFFENS, Michael" <Michael.STEFFENS at newellco.com> writes:
> Also for the information passed to the Linux OS via the APPEND in
> pxelinux.cfg/default I don't even know how/where these are
> passed/executed. I expect to find it somewhere in the INITRD of the
> distributions but it could be also in the compressed kernel file which I
> simply don't know.
>
> Well, as you might have read in the lines above I try to avoid using
> IPAPPEND as it makes the whole thing quite complex for a novice. If
> there's nothing else that would be the way to go then but... Am I
really
> the only one having the same boot images deployed to many different
> PXE/TFTP servers? How are others passing PXE/TFTP server specific
> information to the PXE bootable OS? Especially when I read in the docs
> that the usage of IPAPPEND is not recommended.
The solution detailed at
http://syslinux.zytor.com/wiki/index.php/Comboot_API wasn't accepted.
But that page mentions the -dhcpinfo option of linux.c32, which is
available in the stock binaries.
-- 
Cheers,
Feri.

On 03/26/2010 12:06 AM, STEFFENS, Michael wrote:
> 
> Well, as you might have read in the lines above I try to avoid using
> IPAPPEND as it makes the whole thing quite complex for a novice. If
> there's nothing else that would be the way to go then but... Am I
really
> the only one having the same boot images deployed to many different
> PXE/TFTP servers? How are others passing PXE/TFTP server specific
> information to the PXE bootable OS? Especially when I read in the docs
> that the usage of IPAPPEND is not recommended.
> 
ipappend 1 is not recommended for anything long term because it means
DHCP leases will not be renewed.  This is a very bad thing, especially
if the network you're on has short leases.  However, all you need it for
is something "immediate", i.e. download another file, it serves the
purpose just fine.

ipappend 2 has no such problem; all it does is identify the boot
interface by its MAC address.

	-hpa