[TriLUG] multibooting with syslinux not working

[Joseph Mack NA3T]

Following a suggestion from Alan Porter I've installed Mint 
Linux on a usb stick using unetbootin and Systemrescuecd on 
a usb stick, using its own install method.

To be more precise, I installed them to different partitions 
on the same usb stick after finding that both recipes for 
making bootable usb sticks from isos are in fact wrappers to 
the syslinux manual install.

Reading the webpages for syslinux, there is no mention of 
multibooting. Presumably syslinux is just used for single 
boot livecds and usbsticks. syslinux detects the bootable 
partition by the active partition. I can multiboot by 
changing the active partition with fdisk. That this works 
shows that there's nothing has been overwritten for the 
installs on each partition and they both are intact.

Changing the active partition is bit clunky. Knowing that 
both partitions are capable of booting, I tried booting with 
grub (from the harddisk). Both usb partitions boot, but get 
a kernel panic on trying to mount the root partition. The 
error message is that the available / partitions are 
/dev/sda[1..7] (the correct number of partitions for the 
hard disk) or /dev/sr0 (the cdrom). The usb flash drive 
(presumably /dev/sdb) is not seen by the usb kernel booted 
by grub on /dev/sda. There is an entry in device.map on the 
hard disk for

(hd0) /dev/sda
(hd1) /dev/sdb

which I hope tells grub that there's another drive out there 
(whether it looks for sata or usb I don't know). Since these 
usb rescue disks boot and run off the usb stick, I expect 
the kernel and initrd has the appropriate usb drivers, so by 
the time the usb stick goes to mount the root partition, it 
will have loaded the usb drivers (well I hope so, but I 
don't know.)

Looking in syslinux.cfg, there is no entry for the root 
partition, even though syslinux allows you to specify one. 
It seems that syslinux doesn't need you to specify a root 
partition. Presumably syslinux mounts the bootable partition 
and expects it to be root.

Anyone know how to get around the usb stick not finding the 
root partition when booted from grub (but boots OK with 
syslinux)?

thanks Joe

-- 
Joseph Mack NA3T EME(B,D), FM05lw North Carolina
jmack (at) wm7d (dot) net - azimuthal equidistant map
generator at http://www.wm7d.net/azproj.shtml
Homepage http://www.austintek.com/ It's GNU/Linux!