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Re: BIOS Can Not Find Disk

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On 12/01/2017 02:29 PM, Pascal Hambourg wrote:
> Le 01/12/2017 à 19:57, Greg Wooledge a écrit :
>> On Fri, Dec 01, 2017 at 01:50:12PM -0500, Dan Norton wrote:
>>> Disklabel type: gpt
>>
>>> Apparently, BIOS does not see a bootable device. In the dim past, fdisk
>>> could set a partition as "active", which was its euphemism for 
>>> "bootable".
>>> However now:
>>
>> GPT disk labels don't have active/bootable partitions.
>
> Yes they do. They even have two kinds of them.
>
> - Partition attribute bit 2 = legacy BIOS bootable.
> It is supposed to be equivalent to the boot/active flag in partition 
> entries of the MBR. I just wonder how a BIOS would use that, though.
>
> - The good old boot/active flag of the GPT protective partition entry 
> in the MBR. Some BIOSes require it to boot a drive regardless of the 
> presence of a GPT disk label. It can be set with parted which 
> considers it as a disk flag (disk_set pmbr_boot on), or by fdisk by 
> forcing it to use the protective DOS/MBR disk label (-t dos).
>

This really sounds good. I could not figure out how to get at the 
protective mbr and turn on that bit. Here's what I tried, after doing a 
backup:

# fdisk -t dos /dev/sda

...

Command (m for help): m

Help:

   DOS (MBR)
    a   toggle a bootable flag
    b   edit nested BSD disklabel
    c   toggle the dos compatibility flag

...

Command (m for help): a
Selected partition 1
The bootable flag on partition 1 is enabled now.

Command (m for help): p
Disk /dev/sda: 931.5 GiB, 1000204886016 bytes, 1953525168 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x3f90eec3

Device     Boot Start        End    Sectors   Size Id Type
/dev/sda1  *        1 1953525167 1953525167 931.5G ee GPT


Command (m for help): w
The partition table has been altered.
Calling ioctl() to re-read partition table.
Re-reading the partition table failed.: Device or resource busy

The kernel still uses the old table. The new table will be used at the 
next reboot or after you run partprobe(8) or kpartx(8).

# partprobe -s /dev/sda

After removing the cd and shutting down, re-booted from power-off state, 
but unfortunately still got the "disk not found" message on a black screen.

The PC is simply not seeing the 1T sda, which is the only disk. It's not 
even getting as far as the mbr/grub. The PC appears to be no more than 5 
years old, based on the BIOS date, but it may be old enough to have a 
flaky UEFI. Should I abandon the use of GPT?

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Re: BIOS Can Not Find Disk Greg Wooledge <wooledg@eeg.ccf.org> - 2017-12-01 20:00 +0100
  Re: BIOS Can Not Find Disk Dan Ritter <dsr@randomstring.org> - 2017-12-01 20:30 +0100
  Re: BIOS Can Not Find Disk Pascal Hambourg <pascal@plouf.fr.eu.org> - 2017-12-01 20:40 +0100
    Re: BIOS Can Not Find Disk Dan Norton <dnorton@mindspring.com> - 2017-12-01 22:30 +0100
      Re: BIOS Can Not Find Disk Felix Miata <mrmazda@earthlink.net> - 2017-12-01 23:00 +0100

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