Undo MBR

[Jerry McAllister]

Hi,
 
>  I have just installed FBSD-CURRENT on a test box. During install I
> unwittingly installed a BootMgr entry for the second HDD (it will
> just be a data disk, no need to boot from it).
> 
>  If I do 'dd if=/dev/zero of=/dev/rad2 count=15' will this "erase" the
> BootMgr or will I have to redo Fdisk and etcetera. There is no data
> on the disk yet so this would be no hardship, but is there a "proper"
> way of doing what I want?

So, if there is nothing to be lost, just try it out and see what
happens.  Smoke testing is a tried and true technique.

Anyway, you really don't need to bother, but yes, that should wipe it.
There are some examples at the bottom of  'man disklabel'  that you 
might want to check out - even though you really are talking about 
fdisk stuff.   The fdisk man page is weak, for example it doesn't even 
document the -I switch (tho it lists it at the top) which is what you want. 
You kind of have to read the disklabel man page in conjunction with the
fdisk man page to make any sense of things, and then it may still take 
some experimenting.

>From man disklabel:

           dd if=/dev/zero of=/dev/da0 bs=512 count=32
           fdisk -BI da0
           dd if=/dev/zero of=/dev/da0s1 bs=512 count=32
           disklabel -w -B da0s1 auto
           disklabel -e da0s1

     Completely wipe any prior information on the disk, creating a new
     bootable disk with a DOS partition table containing one ``whole-disk''
     slice.  Then initialize the slice, then edit it to your needs.  The dd
     commands are optional, but may be necessary for some BIOSes to properly
     recognize the disk.

Actually, the first dd sometimes fails, if the disk has never had
anything put on it.   If so, just ignore it and go on with the fdisk.

////jerry