Doesn't boot Linux on SATA, but OpenBSD

[Uwe Dippel]

Before installing grub, I always - better safe than sorry - try to
boot the OSes from the prompt.

Here I have a SATA disc:

Device Boot      Start         End      Blocks   Id  System
/dev/sda1               1          37      297171   83  Linux
/dev/sda2   *          38        1254     9775552+  a6  OpenBSD
/dev/sda3            1255       30401   234123277+   5  Extended
/dev/sda5            1255        1389     1084356   82  Linux swap / Solaris
/dev/sda6            1390        1426      297171   83  Linux
/dev/sda7            1427        1463      297171   83  Linux
/dev/sda8            1464        1950     3911796   83  Linux
/dev/sda9            1951        2133     1469916   83  Linux
/dev/sda10           2134        3107     7823623+  83  Linux
/dev/sda11           3108        5540    19543041   83  Linux
/dev/sda12           5541        6118     4642753+  83  Linux
/dev/sda13           6119       30401   195053166   83  Linux

So, when I root (hd0,1,a) followed by chainloader +1, it boots to
OpenBSD splendidly.
But root (hd0,0) [ext2 filesystem], makeactive, kernel vmliuz--- ro
root=/dev/sda6, initrd ..., boot
dies with pivot_root ... cannot open /dev/console ... Kernel panic.
Yes, /dev/sda6 is '/'

What is it that I make wrong here ?

Uwe