Hitchhiker's Guide to Openbsd

4.13.5 - My fdisk partition table is trashed or blank!
Occasionally, a user will find a system will work, but when doing an 
fdisk wd0
, they see a completely blank (or 
sometimes, garbage) partition table. This is usually caused by having created a partition in 
fdisk(8)
 which had an offset of 
zero sectors, rather than the 
one track offset
 it should have (note: this is assuming the 
i386
or 
amd64
platform. Other 
platforms have different offset requirements, some need NO offset). The system then 
boots
 using the PBR, not using the 
MBR. 
While this configuration can work, it can be a maintenance problem and should be fixed. To fix this, the disk's file 
systems must generally be recreated from scratch (though if you REALLY know what you are doing, you may be able to 
recreate just your disklabel and MBR, and only lose and have to rebuild the first OpenBSD partition on the disk). 
4.13.6 - I have no floppy or CD-ROM on my machine
Some computers people might want to run OpenBSD on lack any obvious way to install OpenBSD, having no floppy or 
CD-ROM drive. Either the machine was designed without it (for example, many laptops and "flash" based machines, like 
Soekris and ALIX systems), or the boot devices have failed or been removed, and would be difficult to replace. Here are 
some tips and techniques you can use to get OpenBSD installed on these systems. 
●
Network boot, using 
PXE
 (i386 or amd64) or 
diskless(8)
 (other platforms). 
●
External USB CD-ROM or USB floppy, if your machine can boot from one. 
●
USB Flash disk or hard disk, again if your computer can boot from a USB device. Prepare the device on another 
computer as described in 
FAQ 14
. Boot from it, but chose the bsd.rd kernel, then install as normal. You could also 
have the file sets pre-loaded on the flash media, as well. 
●
Worst case, if none of the above is suitable, you can usually pull the disk out of the target system, use suitable 
adapters to install it in a "normal" computer, install OpenBSD, then replace the disk back in the target system. 
OpenBSD will then boot nicely in the target machine, though you will very possibly have to adjust the network 
configuration. You may also have to adjust 
/etc/fstab
if you (for example) did your install using a USB-
>IDE/SATA adapter or your target or install machine uses 
ahci(4)
 and the other does not. IDE and some SATA 
disks will normally be recognized as 
wd(4)
 devices, but if attached to a USB adapter, will come up as 
sd(4)
. A 
SATA disk attached to a 
pciide(4)
 interface will come up as wd(4), but attached to an 
ahci(4)
 interface, will come 
up as a sd(4) device. However, once you correct the 
/etc/fstab
file, the system will generally boot just fine. 
In all cases, remember that the machine had an OS installed on it before, and it was usually intended that the OS could be 
reloaded in the field. How this was originally intended to be done will often provide you a good idea how you can install 
OpenBSD now.