[ltp] Dual-boot with Windows 10

[Joerg Bruehe]

Hi Chris!


On 23.04.21 11:46, cr wrote:
> On Fri, 23 Apr 2021 09:57:29 +0200
> Joerg Bruehe <joerg.bruehe at web.de> wrote:
> 
>> [[ proposal: use a virtual machine ]]
>   
>>> However, in this laptop Windows has been a bit greedy thus:
>>> (according to Gparted):
>>> /dev/sda1	ntfs	Recovery	499MiB	hidden
>>> /dev/sda2	fat32			100MiB	boot
>>> /dev/sda3	Unknown			16MiB	msftres
>>> /dev/sda4	ntfs			465GiB
>>>
>>> ... so the bulk of Windoze is in /dev/sda4 so I can't create an
>>> extended partition there without blowing Windows away.   Which I
>>> will do if I have to, but is there an easy way around this?
>>
>> I have no info how important the first three partitions are for
>> Windows and what would happen in case you remove them. But even if
>> that were possible, you would still have to shrink sda4 and either
>> move it to the end of the disk (let it remain sda4) or leave it where
>> it starts now and rename it sda3.
>>
>> None of that looks nice and easy to me.
> 
> James pointed out that under UEFI the four-partition limit doesn't
> apply.   So I think I can just leave /sda1 to /sda3 alone, shrink /sda4,
> and create /sda5 onwards for Linux use.   I'll give that a try,
> anyway, and see what happens.   Since it's a new-to-me machine,  I have
> no data at risk yet.   The worst I can do is wreck Windows and start
> again with Linux only.

TTBOMK, you can't do it this way: Most probably, your disk has a MBR 
partition table, and this won't support a fifth primary partition.

All my further remarks are based on that assumption, so you should first 
check whether it is a MBR partition table or a new GPT one.
Linux fdisk, parted, ... should tell that.


If it is a MBR table, there are at least three aspects:

The first question is whether your machine really has UEFI firmware.
Maybe it has, but if it hasn't I don't believe you can change that.

The next question is whether there is a way to convert the disk:
 From all I have read, the new GPT (the partition table introduced with 
EFI, which doesn't have the limit of four primary partitions) is 
completely different from the traditional MBR partition table.
Sure it is possible to write a GPT onto an existing disk, overwriting 
the MBR table, but is it possible to do that in place?
You need to backup the contents of all partitions, I fear, and to 
restore it into new partitions once you have created them via the GPT.

And the third issue is whether you can transform a Windows 10 
installation from BIOS boot to UEFI boot. If I remember the articles 
correctly, that is at least complicated, maybe impossible. It might 
require you to re-install Windows.

I won't claim this to be impossible, but it is sure more complicated 
than just shrinking the Windows partition and putting Linux behind it.


I just get an idea of which I don't know whether it is possible:
Can Windows use a logical partition for its C: system disk?
If so, you might be able to shrink the Windows file system, remove the 
existing primary sda4 (just the partition definition), create a new 
extended sda4 partition (probably starting a bit earlier on the disk), 
and then create a logical sda5 (inside sda4) that just covers the 
shrunken C: file system. Everything after that (still within sda4) would 
be more logical partitions for Linux.

But before you take that route, make sure Windows can run from a logical 
partition - I really don't know.

> 
> So many thanks for the offer of help but I'm probably okay.

I wish you success!


Regards

Jörg

-- 
Joerg Bruehe  - persoenliche Aeusserung / speaking only for himself
mailto:joerg.bruehe at web.de