11.10.2016 10:27, Marc Chamberlin пишет:
On 10/10/2016 8:27 PM, Andrei Borzenkov wrote:
11.10.2016 05:36, Marc Chamberlin пишет:
Hello - am going to start a new thread for this question. In my recent set of machinations with setting up a new disk for my system, to replace one that may be failing, I encountered a problem for which I couldn't find an easy answer. It appears that when I tell the YaST boot loader setup tool to configure and create a new MBR it does so on the same disk which has the partition that contains the OS files. My system now has 4 drives installed and the BIOS only allows me to select just 3 drives (it's choice as to which 3 drives I get to choose from) to specify the order in which to search the drives for a boot loader. And my new drive now contains the partition which contains my Leap42.1 system. Because I was adding a new 4rth drive, the BIOS is not presenting the new drive to me as one of the options to use for setting up the search order, for a boot loader. I finally managed to get the BIOS to present it by disconnecting one of the other drives but that is an unacceptable solution in the long run.
BTW the way I managed to boot up the Leap42.1 system was to boot up an older SuSE system located on one of the other drives and use Yast there to discover all the available OS's, create a boot menu for them, and then use the MBR/Grub menu it wrote out to select the Leap42.1 system. That works, but it took a lot of head scratching to figure out that was what I needed to do.
So my question is this - is there some way to tell the YaST boot setup tool that I want to specify which drive that I want it to create an MBR on?
If BIOS does not allow booting from this drive, it does not matter whether YaST does something or not. If the problem is only boot device selection in BIOS, you can simply install bootloader on any other drive. If BIOS does not see your drive at all, then the whole /boot must be located on a drive, accessible to BIOS.
Thanks Andrei for trying to help but I guess I am somewhat confused. (And I will admit I don't fully grok the documentation on Grub2 and Yast)
I don't think the issue is that BIOS is not allowing booting from my new drive,
Really?
But when I reconnected the drive that I had disconnected, I lost the ability to boot off the new drive and the system when back to booting up from one of the other drives.
This says exactly opposite. ...
I think your second comment was the jist of my original question. How do I get YaST to allow me to select a drive to install an MBR bootloader on? It seems to want to only install it on the same drive that I installed the operating system on that YaST is running under.
Select "Custom boot partition" and chose any device you want. Do *not* select any other option.
If I understand your third statement, (and I admit I am on unsure footing here) I think you are saying that I should create a partition on one of the drives that the BIOS is seeing when I have all four drives connected?
If drive appears in BIOS when you disconnect one of other drives, it is not necessary (as long as you install in MBR of another drive and have enough space post MBR so grub2 fits into it). ...
If I understand the boot loader model correctly, then I believe the MBR exists outside of partitions and is just located on the first section of a drive.
Well, MBR is highly ambiguous. MBR stands for Master Boot Record and actually means code that is executed by BIOS. This code is in the very first sector of disk. Now this sector *also* contains partition table. But there is nothing that prevents one of partitions to start at sector 0 thus including MBR. Normally nobody does it.
This means each drive can have an MBR. And the MBR contains bootloader code and a pointer to a partition/file system where a GRUB bootloader (or some other OS bootloader) is stored. And the GRUB bootloader brings up a menu via which a user can use to select an actual OS to load.
Yes, that is correct.
But it seems to me that there is a potential disconnect here. The BIOS has to find an MBR somehow and makes it's assumptions about where to look to find it. And YaST is making assumptions about where to write an MBR based on characteristics associated with the OS that it is running under (mount points perhaps???)
YaST simply takes the very first device in the list. If EDD is available it can make educated guess which device is the very first device in BIOS order; unfortunately this (usually) is not available when booting using grub2. You can reorder devices manually though.
And what I found is that these two sets of assumptions don't necessarily overlap.
Which is why grub2 itself does not rely on or care about device order.
Especially if I use YaST in one OS to set up a GRUB option to start a different OS on a different drive.
In this case grub in one OS directly loads kernel of another OS so device order is not relevant at all.
And then start that second OS, and use YaST in that second OS to create a new MBR and a new GRUB bootloader with a new/different set of boot menu options. In my situation that new MBR was not placed on a drive that the BIOS had in it's search list, instead it was place on the new drive where the second OS was installed. Therefore the BIOS does not find it, and the new GRUB bootloader is not executed. So to get around this problem, shouldn't I simply be able to tell YaST which drive I want it to create and install an MBR on rather than have it make (wrong) assumptions?
See above. You are able to tell it, using at least two methods.
I recognize there is a risk of overwriting an existing MBR that points to a different GRUB bootloader, but in this scenario that seems like exactly what I want to do. This is all very unclear to me from my reading the documentation....
Sorry for the long effort to express my confusion.... Marc...
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