LFS Grub Confusion

Ultranaut · 04-25-2018, 06:53 PM

Hi guys, so I recently just finished up an LFS project, but I'm having some trouble with GRUB. Background: my host system is Ubuntu, which is located on /dev/sda. My LFS project is on /dev/sdb. Here's my partition info:

Code:

Device     Boot Start        End    Sectors   Size Id Type
/dev/sda1  *     2048 1953523711 1953521664 931.5G 83 Linux

Device       Start       End   Sectors  Size Type
/dev/sdb1     2048    206847    204800  100M BIOS boot
/dev/sdb2   206848   4401151   4194304    2G Linux swap
/dev/sdb3  4401152 625142414 620741263  296G Linux filesystem

It might be worth noting that I set up my second drive as a GPT table.
But when I booted, the GRUB had somehow taken up the /dev/sda drive, and Ubuntu on /dev/sdb. Booting into /dev/sda got me to the GRUB login, but when clicking my LFS distro, it says that the partition is not found. Weirdly enough, going into the sdb drive somehow allowed me to enter the LFS distro, but the Ubuntu boot is there as well???
Here is my grub.cfg:

Code:

# Begin /boot/grub/grub.cfg
set default=0
set timeout=5

insmod ext2
set root=(hd1,3)

menuentry "GNU/Linux, Linux 4.15.3-nebula-8.2" {
        linux   /boot/vmlinuz-4.15.3-nebula-8.2 root=/dev/sdb3 ro
}

(I named my OS Nebula for funsies.)
So I guess my question is, what's going on, and how do I get everything to their right places?

colorpurple21859 · 04-25-2018, 07:46 PM

If this is a uefi computer, mixing legacy booting with efi booting can cause this. Check your boot order in your bios.
at the lfs grub prompt hit c and then ls to see what the grub sees as the lfs drive/partition and change accordingly for lfs menu

Nobutarou · 04-25-2018, 09:03 PM

I suggest to use Ubuntu grub.

- disallow booting from your LFS disk on BIOS.
- Edit grub.cfg on Ubuntu

Even though LFS guides to install grub, you don't need it. You can use grub on your host system.

Or simply, you can use SG2D,
https://www.supergrubdisk.org/super-grub2-disk/

RoLoR · 06-13-2018, 09:24 AM

Most easy way to go if you get to the end of (any) lfs-book at chapter 9.1

Code:

cat > /etc/lsb-release << "EOF"
LSB_VERSION="5.0"
DISTRIB_ID="Linux From Scratch"
...

Add the LSB_VERSION line and let update-grub of Ubuntu do your job of adding the lfs boot, it will be recognized and perfectly added to your grub boot menu

Doing the mentioned version number with respect to chapter LFS and Standards in the start of used lfs-book.

Note: you can skip all instructions about making a grub.cfg file in the lfs-book

Reference

colorpurple21859 · 06-13-2018, 09:37 AM

If you have a grub.cfg file on your LFS partition you can boot lfs from Ubuntu with a menu entry in ubuntu /etc/grub.d/40_custom and run update-grub

Code:

menuentry  LFS{
set root=(hd1,3)
configfile /boot/grub/grub.cfg
}

Head_on_a_Stick · 06-21-2018, 01:04 AM

Quote:

Originally Posted by Ultranaut

when I booted, the GRUB had somehow taken up the /dev/sda drive, and Ubuntu on /dev/sdb.

From GRUB's perspective, "sda" (hd0) is the drive on which the bootloader is installed so that would be the expected behaviour.

Quote:

Originally Posted by Ultranaut

Booting into /dev/sda got me to the GRUB login, but when clicking my LFS distro, it says that the partition is not found.

That's because you have told GRUB to look on the disk from which it has not been booted (hd1,3) so try this instead:

Code:

set root=(hd0,3)

menuentry "GNU/Linux, Linux 4.15.3-nebula-8.2" {
        linux   /boot/vmlinuz-4.15.3-nebula-8.2 root=/dev/sda3 ro
}

With this for Ubuntu:

Code:

menuentry "Ubuntu" {
        set root=(hd1,1)
        linux /vmlinuz root=/dev/sdb1 ro quiet
        initrd /initrd.img
}

But I do agree that using Ubuntu's GRUB would be simpler

hazel · 06-21-2018, 04:10 AM

I would like to add that Debian-based distros update their grub.cfg files fairly often when they do a general software update. This tends to interfere with the handwritten grub.cfg file that LFS uses. That's why it's probably better not to install GRUB in LFS at all when you have this kind of multiboot setup. The developers suggest that if you do, you should have a separate boot partition and transfer all your kernels and initrds onto it.