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Re: [Bug-xorriso] ISO installer image: GPT versus MBR partitions

From: pelzflorian (Florian Pelz)
Subject: Re: [Bug-xorriso] ISO installer image: GPT versus MBR partitions
Date: Wed, 17 Apr 2019 10:59:52 +0200
User-agent: NeoMutt/20180716

The Parabola ISO parabola-systemd-cli-i686-netinstall-2018.06.02.iso
does not inhibit the boot process but also contains no EFI partition
so I cannot boot from it.

Debian 9.8.0 works, see the end of this mail.

On Tue, Apr 16, 2019 at 11:15:56PM +0200, Thomas Schmitt wrote:
> Hi,
> i wrote:
> > > A broken backup GPT is not supposed to stop EFI from finding its partition
> Florian Pelz wrote:
> > On the 2011 Macbook I am using, the boot process gets stuck before I
> > can select the drive to boot from, as long as a USB flash drive with
> > this GPT error is in a USB port.
> Did you already test whether it works after you treated the stick
> with gdisk expert option 'x' 'e' ?

Nope, it does not.

> If it really does work, then i am glad to have written "supposed".
> It would then be interesting to see whether this picky machine boots
> from a MBR partition table.
> Is
>   guixsd-install-0.15.0.i686-linux.iso
> suitable for that machine (modulo GPT backup position) ?

Without changing the ISO’s partition tables, it does not work.

What should I change?

> If so, i will use my copy of this ISO to develop a xorriso run on
> the mounted ISO which produces a new ISO with MBR-only layout.
> (next mail from Florian):
> > Actually it still gets stuck after I used fdisk to repair the drive’s
> > GPT.  I will check again with a Debian ISO tomorrow.
> Did the GPT repair really work ?
> I.e. do other partition editors or kernels have no complaints about the
> stick any more ?

I have overwritten the fdisk-corrected one, but the gdisk-corrected
flash drive is considered correct by fdisk.

> Another try would be to deface the Apple Partition Map. It's a Mac.
> So APM and HFS+ might have some impact. But other than expected by
> grub-mkrescue.
> With APM the first bytes of the ISO are
>   45  52  08  00  eb  02  ff  ff
> (which is the APM magic number and also x86 code without effect.)
> Without APM they are other intentionally effectless x86 code:
>   eb  63  90  90  90  90  90  90
> If you write the latter 8 bytes over the start of your USB stick, then
> APM should not be recognizable any more.

I inserted the gdisk-corrected USB flash drive and did:

$ ghex bytes  # put in eb  63  90  90  90  90  90  90
$ sudo dd if=bytes of=/dev/sdc
0+1 Datensätze ein
0+1 Datensätze aus
8 bytes copied, 0,030945 s, 0,3 kB/s

It still does not work.

> > I will check again with a Debian ISO tomorrow.
> Debian installation ISOs have APM but no HFS+. I.e. their APM is quite
> useless. These are: "netinst" ISOs, and the ISO sets for CD, DVD, BD, BDDL.
> Debian 9 Live ISOs have no APM (and no HFS+).
> Version 8 has no EFI equipment but only for legacy BIOS.
> Have a nice day :)
> Thomas

The Debian ISO works fine and is bootable from its EFI partition.

gdisk prints:

$ gdisk Downloads/debian-live-9.8.0-amd64-xfce.iso
GPT fdisk (gdisk) version 1.0.4

Partition table scan:
  MBR: MBR only
  BSD: not present
  APM: not present
  GPT: present

Found valid MBR and GPT. Which do you want to use?
 1 - MBR
 2 - GPT
 3 - Create blank GPT

Your answer: 2
Using GPT and creating fresh protective MBR.
Warning! Main partition table overlaps the first partition by 64 blocks!
You will need to delete this partition or resize it in another utility.

Command (? for help): p
Disk Downloads/debian-live-9.8.0-amd64-xfce.iso: 3811392 sectors, 1.8 GiB
Sector size (logical): 512 bytes
Disk identifier (GUID): C05B92F2-4B16-4592-BA53-A2025E420B60
Partition table holds up to 248 entries
Main partition table begins at sector 2 and ends at sector 63
First usable sector is 64, last usable sector is 3811328
Partitions will be aligned on 8-sector boundaries
Total free space is 1 sectors (512 bytes)

Number  Start (sector)    End (sector)  Size       Code  Name
   2            1432            2263   416.0 KiB   0700  ISOHybrid1


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