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bin/51230: 'gpt biosboot' needs to mark protective mbr partition as 'active'
>Synopsis: 'gpt biosboot' needs to mark protective mbr partition as 'active'
>Arrival-Date: Thu Jun 09 12:25:00 +0000 2016
>Originator: Hauke Fath
>Release: NetBSD 7.0_STABLE
Technische Universitaet Darmstadt
System: NetBSD Gstoder 7.0_STABLE NetBSD 7.0_STABLE (MONOLITHIC) #1: Fri Apr 1 14:41:59 CEST 2016 hf@Hochstuhl:/var/obj/netbsd-builds/7/i386/sys/arch/i386/compile/MONOLITHIC i386
Because of disklabel's size limitations, NetBSD on inteloid
hardware is migrating to the gpt partition format. Although
gpt is also used by UEFI, we don't support that, and require
machines to use the legacy mbr format. Our gpt-enabled mbr
will then know how to use the gpt partition table.
When gpt(8) creates a gpt table on a disk, it also writes a
protective mbr partition table, to keep legacy tools from
showing an empty disk.
When 'gpt biosboot' prepares a bootable disk, it will install
its custom mbr to block 0, and mark the indicated disk slice
as bootable, but it will not update the protective mbr table.
well as the HP Elitebook 2170p here) require all Ts crossed
and Is dotted before recognizing a legacy mbr as
bootable. They will especially not execute the mbr code unless
the mbr table has a partition marked 'active', and present you
with a terse "Boot Device Not Found" error.
'gpt biosboot' should mark the protective mbr's partition
'active', and does not.
Get a newish laptop from HP, switch it to legacy boot,
partition the disk with gpt(8), and install NetBSD. You will
find the lapop boots with the disk on an external USB adapter,
but not as an internal disk.
Teach 'gpt biosboot' to set the 'active' flag on the
protective mbr table's (sole) partition.
(a) punt, and disklabel(8) the disk
(b) 'gpt create <drive>', then 'fdisk -0 -a <drive>', then
'gpt create <drive>' again, bedause the fdisk run will have
stomped on the gpt. Interesting enough, the second 'gpt
create' will leave the protective mbr intact. Then partition
and make bootable with gpt(8), and install.
(c) running 'fdisk -0 -a <drive>' against the protective mbr
of an existing partition will trash the gpt. I tried this, and
'gpt recover' did not find a backup gpt (that's a bug in its
own right) - luckily I could re-create start and end of my
installation's one partition from memory. The installation was
bootable from internal disk afterwards.
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