[syslinux] Cannot chainload a formerly working Linux system

alex lupu alupu01 at gmail.com
Mon Sep 11 10:45:42 PDT 2017

Chainloading a Linux system with syslinux fails unexpectedly with the lines:

WARN: No MBR magic, treating disk as raw.
ERR: Unable to find requested disk / partition combination.

coming after the usual lines
 SyslinuxBOOT ....                       (in UEFI menu)
 linuxBLFS                               (in syslinux menu)

SUMMARY (additional gory details available upon request)
Latest ASUS motherboard, Z270I (UEFI 2.6)
SSD with Arch on it. AOK.  The "staging" point I use for tests on an
 SSD with "old" Linux system (BLFS) to be booted with syslinux.
SSD (M.2) with Win10. AOK. NOT IN THE PICTURE (afaic).

DETAILS (a few I consider basic)
- Arch SSD:  latest version, kern 4.12.12.  64 bits.  /dev/sda.
- BLFS SSD:  left "frozen" (in good condition) at kern 4.5.  32 bits.
- syslinux 6.3, installed on /dev/sdb first partition.  Works OK (as far as
it  goes).

Device     Boot     Start       End   Sectors   Size Id Type
/dev/sdb1  *         2048   2042239   2040192 996.2M ef EFI (FAT-12/16/32)
/dev/sdb2         2042240   3070399   1028160   502M 82 Linux swap / Solaris
/dev/sdb3         3072000 244244479 241172480   115G 83 Linux
/dev/sdb4       244244480 499196591 254952112 121.6G  7 HPFS/NTFS/exFAT

The BLFS system (on sdb3) used to be booted from a Win7 (sdb4), no longer
active now
(hence the current attempts at booting through syslinux).
First sector of sdb3 (with "legacy", 0.97, GRUB STAGE2 used to be copied to
creating a dual boot with Windows through a menu set-up by Windows BCD

File 'EFI/syslinux.cfg':
DEFAULT menu.c32
SAY Now booting the kernel from SYSLINUX...
   COM32 chain.c32
   APPEND hdX 3
#KERNEL LFSkernel-4.4.5-1
#APPEND root=/dev/sdb3 video=HDMI-A-2:640x480M

Notes on file 'syslinux.cfg' above:
1. X=0-5.  I also tried (in desperation) higher values for X (to no avail).
2. I chose 0-5 based on the MAP/fs results from UEFI Shell v2.2 run from
3. For reference, FS0 -> sda1.  FS1 -> sdb1.
4. I tried other values for partition number (also in desperation).
5. The last two lines (LFSkernel and root) are temporarily commented out for
   readability.  syslinux would obviously never have a chance to run them.

1.  The first WARN message is particularly mystifying.
The MBR of /dev/sdb may have suffered a lot of abuse over the years but a
examination of it still shows a perfect 4-partition table and the x55AA at
the end.
(no surprise there;  all Arch linux utilities like fdisk -l, hexdump, dd,
etc. work just fine and I can still access any of my files left (in OK
btw) on /dev/sdb3.  So, it seems, the MBR has managed to clearly retain its

2.  Per above, the ERR is also puzzling.  Unless syslinux identifies drives
partitions differently than Linux utilities and/or UEFI Shell.

Any help on clearing up / troubleshooting the situation will be highly
-- Alex

More information about the Syslinux mailing list