[syslinux] lpxelinux.0 issues with larger initrd.img files from RHEL >= 7.5 on UCS servers?

[Ady Ady]

> > Sounds like you may want to contact Cisco...
> 
> And tell them what? There's a bug in their PXE/BIOS stack somewhere?
 
 
Just some random and humble thoughts...

Perhaps it would be worth some additional tests?

Maybe a test with pxelinux.0 version 4.07? And using "LINUX", not 
"KERNEL":

###
DEFAULT biginitrd
PROMPT 0
LABEL biginitrd
LINUX mykernel
INITRD mybiginitrd
APPEND myoptions
###

Maybe a packet capture might reveal something about the network setup?

Maybe it is not the size of the initrd file but rather a time 
limitation (which gets triggered by a big-enough file)?

What about trying with 6.04-pre1, and/or (even better) with Debian 
Sid's packages and using debug.c32 (from the corresponding 
package/version/build):

###
DEFAULT dbg
PROMPT 1
SAY First press [Enter] for debug.c32, then [1][Enter] for OS.

# Once in the boot prompt, press "Enter".
LABEL dbg
COM32 debug.c32
APPEND -e pxe_call,malloc
# Additional functions for debug might be of interest.


# After debug.c32 returns to the boot prompt,
# press "1" and "Enter".
LABEL 1
LINUX mykernel
INITRD mybiginitrd
APPEND myoptions
###


Once the label named "1" is launched, is there any info (that could 
help)?

Please avoid using boot menus for these tests; use the boot prompt.

Sometimes a "cold" boot behaves differently than a "warm" boot. This 
might be (particularly) relevant when performing multiple cycles of 
(network) booting (tests).

Another possible test could be to use UEFI mode instead of CSM; in such 
case the bootloader would be (efi64's) syslinux.efi + ldlinux.e64 ( + 
efi64's debug.c32). As usual, all files from the same set of 
package/version/build.

Considering the lack of specific, knowledgeable replies about this 
topic in this Syslinux mailing list so far, maybe a test with a 
different bootloader (at least for comparison of resulting behavior) 
would be worth?

Recurrent failures in all tests would probably indicate either:
 _ a bug in the firmware; or,
 _ some problem with the specific kernel+initrd combo (in this 
hardware); or,
 _ some problem with the network setup.

OTOH, if a successful boot can be achieved by at least one test, then 
either a bug or a limitation in (l)pxelinux.0 might be exposed by this 
hardware/firmware.

As I mentioned, these are some random and humble thoughts; they might 
not be 
worth much (or even nothing at all).

Regards,
Ady.