Hitchhiker's Guide to Openbsd

Bad/invalid/incompatible MBR: Usually, a used hard disk has some MBR code in place, but if the disk is 
new or moved from a different platform, AND you don't answer "w" to the "Use (W)hole disk or (E)dit the 
MBR?" question of the 
installation process
, you may end up with a disk without a valid MBR, and thus, it 
will not be bootable, even though it has a valid partition table. 
You may install the OpenBSD MBR on your hard disk using the fdisk program. Boot from your install 
media, choose "Shell" to get a command prompt: 
# fdisk -u wd0
You may also install a specific MBR to disk using fdisk: 
# fdisk -u -f /usr/mdec/mbr wd0 
which will install the file 
/usr/mdec/mbr
as your system's MBR. This particular file on a standard 
OpenBSD install happens to be the standard MBR that is also built into fdisk, but any other MBR could be 
specified here. 
●
Invalid 
/boot
 location installed in PBR: When installboot(8) installs the partition boot record, it writes 
the block number and offset of 
/boot
's inode into the PBR. Therefore, deleting and replacing 
/boot
without re-running 
installboot(8)
 will render your system unbootable, as the PBR will load whatever 
happens to be pointed to by the inode specified in it, which will almost certainly no longer be the desired 
second-stage boot loader! Since 
/boot
is being read using BIOS calls, old versions of the PBR were 
sensitive to BIOS disk translation. If you altered the drive's geometry (i.e., took it out of one computer that 
uses CHS translation and moving it into one that uses LBA translation, or even changed a translation 
option in your BIOS), it would have appeared to the BIOS to be in a different location (a different 
numerical block must be accessed to get the same data from the disk), so you would have had to run 
installboot(8) before the system could be rebooted. The new (as of OpenBSD 3.5 and later) PBR is much 
more tolerant to changes in translation. 
As the PBR is very small, its range of error messages is pretty limited, and somewhat cryptic. Most likely 
messages are: 
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