gpart and mbr give "no operating system" message at boot.

Warren Block wblock at
Fri Sep 7 20:48:06 UTC 2012

On Fri, 7 Sep 2012, markham breitbach wrote:

> I am trying to partition a disk to be used as the primary boot disk for a FreeBSD 8.3
> installation using gpart to install an MBR partition.
> The system is an existing FreeBSD 5.2.1 system at a remote location (ie impossible to boot
> from CD/netboot/etc), but has no data of value.  To do this I am copying /boot and
> mfsroot.gz from an mfsbsd iso image to boot to an MFS live system so I can wipe the drive
> and do a clean install of 8.3.  After booting to the MFS I do this:
> dd if=/dev/zero of=/dev/ad2 bs=1m count=1
> gpart create -s mbr ad2
> gpart add -b63 -t freebsd ad2
> gpart create -s bsd ad2s1
> gpart add -i1 -s 1g -t freebsd-ufs ad2s1
> gpart add -i2 -s 1g -t freebsd-swap ad2s1
> gpart add -i4 -s 2g -t freebsd-ufs ad2s1
> gpart add -i5 -s 1g -t freebsd-ufs ad2s1
> gpart add -i6 -t freebsd-ufs ad2s1
> gpart set -a active -i 1 ad2
> gpart bootcode -b /boot/mbr ad2
> newfs /dev/ad2s1a
> newfs -U /dev/ad2s1d
> newfs -U /dev/ad2s1e
> newfs -U /dev/ad2s1f
> followed by a sysinstall and some configuration.  When I reboot I get a message that says
> "Operating system not found" and the system hangs.
> If I follow the same procedure but create a gpt partition it works swimmingly.  I am OK
> with using a gpt partition if needed, but for the sake of curiosity I would like to know
> why I can't make the MBR partition partition work.  Am I missing something?

Need to install bootcode to the slice also:

# gpart bootcode -b /boot/boot ad2s1

Why are you skipping partition 3?  For that matter, don't give partition 
numbers when adding, and gpart will just use the next available.

If GPT works, there is little reason to use MBR.

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