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djentoo
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PostPosted: Tue Oct 17, 2017 9:21 am    Post subject: !! Could not find the root block device in UUID=<disk> Reply with quote

EDIT: Please scroll down; original post problems have been resolved.

On boot, I am getting an error "!! Could not find root block device in UUID=<disk>
I thought this meant I should change the UUIDs for the partitions in fstab to labels, so I did. I'm still getting the error. What is wrong?







First of all, when I generate grub.cfg, the image listed has "openstack" at the end, leading me to believe I installed the incorrect version. Am I right?

Second of all, also the main issue... I am running Windows 7 with MBR, and I want to chainload Linux with Grub using EasyBCD... after configuring with EasyBCD and selecting the Linux boot option, it loads into Grub, but does not chainload Gentoo. I am not sure what to do. I installed to /dev/sdb. The disk is partitioned as follows:

/dev/sdb1 BIOS boot partition
/dev/sdb2 Boot partition
/dev/sdb3 Swap partition
/dev/sdb4 Root partition (ext4)

Please help! First time Gentoo install here, but I am pretty familiar with Linux distros.


Last edited by djentoo on Wed Oct 18, 2017 9:02 pm; edited 5 times in total
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eccerr0r
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PostPosted: Tue Oct 17, 2017 6:09 pm    Post subject: Reply with quote

What is the error that you're getting?

as for the first question - grub-mkconfig detects stuff, and it probably detected something you didn't intend, so you probably had the wrong partition mounted when building the config.

for the second question, I have to assume that Windows boot loader is your main boot chooser. You say that it does chainload, so that means it did load into grub. So what you're saying that grub doesn't load Gentoo - here it'd be helpful to know what error you're seeing.

Possible things that are going on here:

-grub can't find your kernel - your grub.cfg probably has the wrong set root=XXXX directive due to grub-mkconfig guessing your hard drive boot order wrong (though it may be using a label identifier too). I think you may need to edit the grub.cfg manually.
-kernel loads but can't find root image. The root= kernel command line is set incorrectly by grub-mkconfig guessing hard drives wrong again. Again you may need to edit grub.cfg manually.

A look at one of the entries in grub.cfg would be interesting, if you're at least getting to the grub menu.
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PostPosted: Tue Oct 17, 2017 7:36 pm    Post subject: Reply with quote

eccerr0r wrote:
What is the error that you're getting?

as for the first question - grub-mkconfig detects stuff, and it probably detected something you didn't intend, so you probably had the wrong partition mounted when building the config.

for the second question, I have to assume that Windows boot loader is your main boot chooser. You say that it does chainload, so that means it did load into grub. So what you're saying that grub doesn't load Gentoo - here it'd be helpful to know what error you're seeing.

Possible things that are going on here:

-grub can't find your kernel - your grub.cfg probably has the wrong set root=XXXX directive due to grub-mkconfig guessing your hard drive boot order wrong (though it may be using a label identifier too). I think you may need to edit the grub.cfg manually.
-kernel loads but can't find root image. The root= kernel command line is set incorrectly by grub-mkconfig guessing hard drives wrong again. Again you may need to edit grub.cfg manually.

A look at one of the entries in grub.cfg would be interesting, if you're at least getting to the grub menu.


Thanks eccerr0r, yes, grub could not locate the kernel when I was troubleshooting. I will learn more about configuring grub.cfg and if I run into problems, I will post them here. As for the grub-mkconfig - it listed the images on the partition, but the names of the images ended with openstack. It was gentoo-[version number]-openstack.... leading me to believe I grabbed the wrong packages from the mirror or something.
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PostPosted: Tue Oct 17, 2017 7:45 pm    Post subject: Reply with quote

Oh, now that's a bit more clear. It should be searching whatever is in your boot partition for kernel images, whatever you have there will be included in the grub.cfg.
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PostPosted: Tue Oct 17, 2017 7:54 pm    Post subject: Reply with quote

eccerr0r wrote:
Oh, now that's a bit more clear. It should be searching whatever is in your boot partition for kernel images, whatever you have there will be included in the grub.cfg.


I see, so the likely problem is that the cfg file isn't set up properly to place the kernel image on the boot partition, and thus Grub is not able to locate it? If so, that makes too much sense.

If I did mount the wrong partition when building the config, how do I locate it and remove it? Just locate it in /boot/grub on the incorrect partition? (Do I also remove the directories?)

I believe I first installed it to /dev/sdb (because BIOS), and when that didn't work, I tried /dev/sdb1, since that was set to boot with parted.
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PostPosted: Tue Oct 17, 2017 9:06 pm    Post subject: Reply with quote

Major trouble with grub is that I think it makes too many assumptions that you'll be installing it on your primary/boot hard drive. When it is not, all bets are off.

When you run grub-mkconfig it will scan your /boot partition for kernel images. If you have anything in that directory vmlinuz-* kernel-* and sometimes vmlinux-* it will pick it up and put it in your cfg file.

If you dedicated sdb to linux, you might well install grub to sdb. If you installed to sdb1 then you have to chain sdb1.

One thing that I'm confused at, you have two "boot" partitions. Since you are using MBR and not EFI, this is kind of redundant and makes it a bit confusing. Which partition do you have your kernel on? Perhaps this is the reason why it's confused.

Normally one would install grub to the boot partition directly, and only one is needed, and this is OK for EFI too.
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PostPosted: Tue Oct 17, 2017 9:40 pm    Post subject: Reply with quote

eccerr0r wrote:
Major trouble with grub is that I think it makes too many assumptions that you'll be installing it on your primary/boot hard drive. When it is not, all bets are off.

When you run grub-mkconfig it will scan your /boot partition for kernel images. If you have anything in that directory vmlinuz-* kernel-* and sometimes vmlinux-* it will pick it up and put it in your cfg file.

If you dedicated sdb to linux, you might well install grub to sdb. If you installed to sdb1 then you have to chain sdb1.

One thing that I'm confused at, you have two "boot" partitions. Since you are using MBR and not EFI, this is kind of redundant and makes it a bit confusing. Which partition do you have your kernel on? Perhaps this is the reason why it's confused.

Normally one would install grub to the boot partition directly, and only one is needed, and this is OK for EFI too.


Yeah I was wondering why I created two boot partitions as well... good question! I think I just followed the example provided in the partition section of the installation guide without really questioning anything. Looking back I see this example provides a BIOS boot part and a UEFI boot part. I can probably do away with the BIOS one, which is 2mb. Perhaps it is the size of the partition causing the problem? But since I installed to "sdb" first, it should not have been an issue. That said: sdb2 should be boot, sdb3 should be swap, sdb4 should be rootfs.

Is there another bootloader that would work better for this setup?
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PostPosted: Tue Oct 17, 2017 10:18 pm    Post subject: Reply with quote

When you grub-installed, did you point it to /dev/sdb2 ?

What's on /dev/sdb1 now? This is your 2MB partition?

I think for your setup if you don't want to touch windows boot, you have to put the MBR on sdb somewhere, whether you put it on sdb or sdb2 shouldn't matter.

If you have your kernel and initramfs images on /dev/sdb2 and install grub to sdb2, then that's one way to do it. Just need to ensure that grub ignores sdb1 completely.

You should see something like this in your grub.cfg that grub-mkconfig generated:
Code:
menuentry 'label' junkjunkjunkjunk {
junk
junk
set root='somethingimportant1'
if [blah blah = blah]; then
 search blah
else
 search blah
fi
echo 'Loading ....'
linux /somepathtoakernel root=somethingimportant2 ....
...
}


The 'somethingimportant1' should be some reference to a disk on your system. There are a lot of ways to specify, I wonder what it is on your system. This is a "GRUB" name not a "Linux" name.
The '/somepathtoakernel' is a rooted path to a kernel on that disk. If you installed grub to a boot disk, it may be in the root directory or in /grub/kernel-file-. If you installed grub to a disk with the rest of your root filesystem, it will show up as /boot/grub/kernel-file- - this is a Linux complete path filename.
The 'somethingimportant2' should be a linux root path. Usually it will need to be a /dev/something or PARTUUID=XXXX.

The other question is if you're using an initramfs or not. If you're using a precut initramfs, you could also use UUID=XXX or LABEL=XXXX for the root path.
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PostPosted: Wed Oct 18, 2017 6:54 pm    Post subject: Reply with quote

I decided to repartition sdb and start over. Everything went well; I changed the boot order of the disk drives so that Grub is the bootloader. I haven't configured it to include Windows yet.

Now my problem is that selecting Gentoo from Grub leads to a blank screen. I tried recompiling with genkernel, but the issue persisted. Right now I am recompiling the previous kernel config. I wonder if this is maybe due to having not installed initramfs... it turns out I am using GPT (and that is why two boot partitions were created).

Things I am still needing to do:
install e2fsprogs
enable systemd USE flag globally
configure Grub2 for systemd (where I left off in the systemd guide)
complete the 'finalize' section of the installation process.
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PostPosted: Wed Oct 18, 2017 6:59 pm    Post subject: Reply with quote

Do you mean "blank" as it prints out "Loading xxxxx" after selecting a choice on grub and gets stuck there, or does it clear the screen and get stuck there?

I would not put USE=systemd in your make.conf. Instead choose a systemd profile with "eselect profile" . If you did not want systemd I would however utilize USE=-systemd , but this isn't the case for you.
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PostPosted: Wed Oct 18, 2017 7:12 pm    Post subject: Reply with quote

EDITED:
The screen does very briefly print Loading xxxx and then goes blank and gets stuck there. - this was due to something not working with the graphics card's HDMI port; the DVI port does work. Integrated graphics do not work.

On boot, I am getting an error "!! Could not find root block device in UUID=<disk>
I thought this meant I should change the UUIDs for the partitions in fstab to labels, so I did. I'm still getting the error. What is wrong?
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PostPosted: Wed Oct 18, 2017 11:20 pm    Post subject: Reply with quote

Probably best to have the topic include the problem at hand so that people can be alerted to the issue.

So your DVI port does print out kernel messages and actually boots? Normally all outputs of a specific graphics card should dump out the kernel startup sequence. BIOS also usually picks one card to do the initial startup sequence on. It would be strange that the DVI port works and HDMI does not on the same card - though on different cards (including using onboard graphics) all bets are off.

I think I ran into a similar problem, but with a virtual EFI machine. Selecting a Linux option within GRUB makes the screen go blank, but if I run the kernel from the EFI command line, the machine boots just fine... alas this is probably unrelated to your problem. I'm still investigating why my virtual machine is behaving this way... not sure what the problem is yet, though probably something to do with initial drivers...
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