why does debian isntaller add extended partition

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Re: why does debian isntaller add extended partition

Postby p.H » 2020-03-04 09:24

Head_on_a_Stick wrote:I've just tried booting the installer in UEFI mode with an MS-DOS partition table and it shows this message

Is it only because of the DOS partition table or because the installer found an operating system installed for BIOS/legacy boot (as the message suggests) ? Does this message happen with an empty DOS partition table ?

MagicPoulp wrote:there was a power issue on SSD drives of the same manufacturer in kernel 4.10

This issue affects only internal NVMe SSDs, not SATA or USB SSDs.
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Re: why does debian isntaller add extended partition

Postby MagicPoulp » 2020-03-04 10:56

Perhaps my firmware booted the installer in legacy mode even though CSM full support is disabled in the bios. When reading in the bios it says enabled will reach full support, but it does not mean that disable will block any attempt to boot in legacy mode. Not sure here. But the bios saying CSM enable or disabled should mean if one boots in legacy mode or not.

Or perhaps it is when I reinstalled grub in debian rescue mode that it changed things.
grub-install --removable
grub-update
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Re: why does debian isntaller add extended partition

Postby p.H » 2020-03-04 11:41

It seems that CSM is not exactly the same as legacy boot. It can be an option of EFI boot. For example, I read that Windows Vista/7 requires CSM when set up for EFI boot. And it's not legacy boot with DOS partitioning and MBR, it's real EFI boot with GPT partitioning and EFI system partition.

Installing GRUB does not change the BIOS/UEFI firmware settings, only EFI boot entries shown by efibootmgr (if installing GRUB for EFI).
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Re: why does debian isntaller add extended partition

Postby MagicPoulp » 2020-03-04 13:13

Then why did the non advanced debian installer install partitions by default with MBR when CSM is disabled in the bios?

People said that EFI boot will result in GPT.

Perhaps the detection of Windows on the hard drive affected the installer, even though I was installing on USB.
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Re: why does debian isntaller add extended partition

Postby p.H » 2020-03-04 14:03

MagicPoulp wrote:Then why did the non advanced debian installer install partitions by default with MBR when CSM is disabled in the bios?

Possible reasons :
- Disabling CSM does not disable BIOS/legacy boot but only legacy support in EFI mode, and the installer booted in BIOS/legacy mode.
- You picked manual partitioning and did not ask to create a new partition table. The installer may create a new partition table only with guided partitioning using a whole disk.

MagicPoulp wrote:Perhaps the detection of Windows on the hard drive affected the installer, even though I was installing on USB.

Is Windows or any installed OS set up for EFI or BIOS/legacy boot ?
If set up for BIOS boot, did you see the screen shown by Head_on_a_Stick and did you answer "no", switching the installer to BIOS/legacy mode ?
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Re: why does debian isntaller add extended partition

Postby MagicPoulp » 2020-03-04 16:29

OK thanks.

MagicPoulp wrote:Perhaps the detection of Windows on the hard drive affected the installer, even though I was installing on USB.

Is Windows or any installed OS set up for EFI or BIOS/legacy boot ?
If set up for BIOS boot, did you see the screen shown by Head_on_a_Stick and did you answer "no", switching the installer to BIOS/legacy mode ?[/quote]

No such screen. But I was not installing on the same device. I was installing on usb and windows was so there was no reason to show the screen.
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Re: why does debian isntaller add extended partition

Postby Head_on_a_Stick » 2020-03-04 17:26

p.H wrote:
Head_on_a_Stick wrote:I've just tried booting the installer in UEFI mode with an MS-DOS partition table and it shows this message

Is it only because of the DOS partition table or because the installer found an operating system installed for BIOS/legacy boot (as the message suggests) ? Does this message happen with an empty DOS partition table ?

The (virtual) disk had a single primary partition with an MD-DOS table but no operating system was installed, I created it fresh with fdisk for testing purposes.

With an empty MS-DOS partition table (ie, no partitions on the disk at all) the installer converts the disk to a GUID partition table but only if the guided partitioning "use entire disk" option is selected. If the "use the largest continuous free space" guided partitioning option is selected then the MS-DOS table is left untouched but the installer only creates the root partition & swap automatically (as if it were installing a non-UEFI system) and then returns an error complaining about a missing EFI system partition afterwards.

I managed to get a working system by creating a FAT32-formatted partition mounted to /boot/efi; gdisk subsequently described it as type 0700 (Microsoft basic data) but the TianoCore UEFI firmware still booted from it. Not sure if that would work on the bare metal though.

It may also be worth noting that the installer will only create a BIOS boot partition automatically when installing a non-UEFI system to a GPT disk if the "use the largest continuous free space" guided partitioning option is selected. If the "use entire disk" option is selected then the (empty) GUID table is automatically converted to MS-DOS.
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Re: why does debian isntaller add extended partition

Postby p.H » 2020-03-05 09:51

Head_on_a_Stick wrote:With an empty MS-DOS partition table (ie, no partitions on the disk at all) the installer converts the disk to a GUID partition table but only if the guided partitioning "use entire disk" option is selected.

As expected.
Head_on_a_Stick wrote:If the "use the largest continuous free space" guided partitioning option is selected then the MS-DOS table is left untouched

As expected.
Head_on_a_Stick wrote:but the installer only creates the root partition & swap automatically (as if it were installing a non-UEFI system) and then returns an error complaining about a missing EFI system partition afterwards.

Good to know. Maybe this guided partitioning option assumes/expects that an EFI partition already exists on any disk.

Head_on_a_Stick wrote:I managed to get a working system by creating a FAT32-formatted partition mounted to /boot/efi; gdisk subsequently described it as type 0700 (Microsoft basic data) but the TianoCore UEFI firmware still booted from it. Not sure if that would work on the bare metal though.

From my experience with real hardware, I think it would work. A registered EFI boot entry already contains the number, position and size of the partition containing the EFI executable. I think the EFI partition identifier is useful only when booting with the removable path, not a registered EFI boot entry. Also, I have seen several UEFI firmware boot using the removable path on a standard FAT partition with the FAT type identifier, not the EFI type identifier.

Head_on_a_Stick wrote:It may also be worth noting that the installer will only create a BIOS boot partition automatically when installing a non-UEFI system to a GPT disk if the "use the largest continuous free space" guided partitioning option is selected. If the "use entire disk" option is selected then the (empty) GUID table is automatically converted to MS-DOS.

As expected, except if the disk has more than 2^32 sectors (size over 2 TiB with 512-byte logical sectors or 16 TiB with 4096-byte logical sectors).
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