8.0-RELEASE / gpart / GPT / marking a partition as "active"

Dan Naumov dan.naumov at gmail.com
Tue Jan 19 21:09:11 UTC 2010

On 1/19/2010 12:11 PM, Dan Naumov wrote:
> It seems that quite a few BIOSes have serious issues booting off disks
> using GPT partitioning when no partition present is marked as
> "active". See http://www.freebsd.org/cgi/query-pr.cgi?pr=115406&cat=bin
> for a prime example.
> In 8.0-RELEASE, using gpart, setting a slice as "active" in MBR
> partitioning mode is trivial, ie:
> gpart set -a active -i 1 DISKNAME
> However, trying to do the same thing with GPT partitioning yields no results:
> gpart set -a active -i 1 DISKNAME
> gpart: attrib 'active': Device not configured
> As a result of this issue, I can configure and make a succesfull
> install using GPT in 8.0, but I cannot boot off it using my Intel
> D945GCLF2 board.
> I have found this discussion from about a month ago:
> http://www.mail-archive.com/freebsd-stable@freebsd.org/msg106918.html
> where Robert mentions that "gpart set -a active -i 1" is no longer
> needed in 8-STABLE, because the pmbr will be marked as active during
> the installation of the bootcode. Is there anything I can do to
> archieve the same result in 8.0-RELEASE or is installing from a
> snapshop of 8-STABLE my only option?

> After using gpart to create the GPT (and thus the PMBR and its
> bootcode), why not simply use "fdisk -a -1 DISKNAME" to set the PMBR
> partition active?

According to the fdisk output, the partition flag did change from 0 to
80. Can the "fdisk: Class not found" error showing up at the very end
of the procedure of doing "fdisk -a -1 DISKNAME" be safely ignored?

- Dan Naumov

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