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Old 28th May 2008
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Nobber Nobber is offline
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Default FreeBSD equivalent of DOS's fdisk /mbr

Just wondering if FreeBSD has an equivalent to the 'fdisk /mbr' command in DOS (which installs a standard, simple bootloader in the MBR that chainloads from the active partition).

The boot0cfg man page suggests using:

# fdisk -B ad0
but all that seems to do is replace the current bootloader with the one that was present before you installed FreeBSD. And since the bootloader that was present before I installed FreeBSD was in fact the FreeBSD bootloader, this fdisk command effectively does nothing.

By the way, the reason I want to revert to the simple bootloader is that FreeBSD is the only OS on this computer, so I have no need for an interactive bootloader.
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Old 28th May 2008
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anomie anomie is offline
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There's probably a nice command-oriented equivalent, but what I'd do is:
  1. # sysinstall
  2. Select -> Configure -> Fdisk
  3. Press 'q' to exit Fdisk
  4. Select your choice from the bootloader menu... (Probably 'Standard' in your case.)

This is untested. Use at your own risk.
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Old 28th May 2008
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AFAIR i could never get the sysinstall thing to work.

this is untested too but i have analysed the hex dump of the mbr boot code, checking fdisk source and double-checked everything.

Disclaimer: try it at your own risk.


# fdisk -B -b mbr ad0

(the required mbr file and its checksum have been attached (zip file).)

- you will be asked if you want to install the boot code - answer yes.
- then you will be asked to install the partition table (actually you will be updating only the boot code and not touching the partition table) - answer yes.
- reboot.

the mbr file and its checksum have been attached (zip file).
Attached Files
File Type: zip mbr.zip (524 Bytes, 99 views)
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Old 29th May 2008
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phoenix phoenix is offline
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You could always boot from a DOS floppy and run fdisk. Or use the Ultimate Boot CD to boot to DOS via CD.

Help for FreeBSD: Handbook, FAQ, man pages, mailing lists.
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Old 30th May 2008
ibutho ibutho is offline
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You can use the FreeDOS disc.
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Old 3rd June 2008
osman osman is offline
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In Linux ive used for SCSIs

dd if=/dev/zero of=/dev/sdX bs=512 count=1 to remove mbr+partition table.

and dd if=/dev/zero of=/dev/sdX bs=446 count=1 to just remove boot loader.

Replacing sdx with da0 or your device name should also work in BSD. Cause this is standard area to place boot loaders and partition table.

Last edited by osman; 3rd June 2008 at 07:23 AM.
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