FreeBSD: no booting GPT slices with buggy bios laptops

It seems there is a problem with some bios that refuse to boot when the disk is partitioned with GPT. My laptop is a Lenovo T420s and FreeBSD (indeed PCBSD) is installed in second disk (ultrabay), gpt style partitions and the following partitions:

1) bios boot

2) freebsd-zfs

3) freebsd-swap

Other Lenovo models as T420, T520 or E520 seem to be affected too.

I found a solution in this post:


Basically booting from other disk or a live cd/usb is needed in order to be able to modify the protective MBR in the disk. I have another freebsd in /dev/ada0, so I booted from it.

After booting from other OS, then dump the protective MBR in the freebsd disk with want to ‘fix’:

fdisk -p ada1 > ada1.txt

This file contains:

cat ada1.txt

# /dev/ada1
g c7752336 h1 s63
p 1 0xee 1 488397167

Then I modified ada1.txt as follows:

# /dev/ada1
g c7752336 h1 s63
p 1 0x00 1 488397167
a 1
p 2 0xee 1 488397167

Next, install this MBR to the disk:

fdisk -f ada1.txt    /dev/ada1


Finally reboot and cross fingers.


About jjjesss

I'm a guy interested in technology, bsd fan and concerned about the world around.
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