Re: kernel panic booting from USB flash drive

On 2024/10/14 12:22, Michael Peters ([email protected] via 
lfs-support Mailing List) wrote:
> Build Host: x86_64 LFS 11.3 SystemV running kernel 6.6.56
>
> I'm building LFS 12.2 SystemD (also kernel 6.6.56, I prefer LTS 
> kernels) to a
> USB flash drive (using shell scripts) with the intent of then booting 
> from the
> USB flash drive to re-run my scripts to build it to a partition on the hd.
>
> Everything is working well *except* the boot.
>
> The flash drive is a single ext4 partition created by using fdisk (LFS 
> 11.3) to
> delete what the manufacturer put on it, create a single primary 
> partition of
> type Linux, and marking the partition bootable in fdisk.
>
> I then format the single partition with mkfs.ext4 (I *probably* should 
> have used
> ext2 but that's not the issue).
>
> LFS builds on it (albeit slowly), kernel installs, grub-install on 
> /dev/sdi from
> within the chroot after building kernel reports no problems.
>
> This is the grub.cfg I initially tried:
>
>     # Begin /boot/grub/grub.cfg
>     set default=0
>     set timeout=5
>
>     insmod part_gpt
>     insmod ext2
>     search --set=root --fs-uuid add2119a-1a46-4c72-b212-863ee869ebd1
>
>     #USB Flash Grub
>
>     menuentry "USB Flash GNU/Linux, Linux 6.6.56-lfs-12.2-systemd" {
>       linux /boot/vmlinuz-6.6.56-lfs-12.2-systemd 
> root=PARTUUID=8d5d11ba-01 ro
>     }
>
> The UUID and PARTUUID are from the `blkid` command and are correct, 
> and LFS 11.3
> booting from a hard drive is just fine with me using them so that 
> changes in the
> device name don't cause issues.
>
> When booting off the flash drive, the grub menu appears and it 
> actually starts
> to boot but I get
>
>     [    0.605403]  msdos
>     [    0.605474]  iso9660
>     [    0.605545]
>     [    0.605685] Kernel panic - not syncing: VFS: Unable to mount 
> root fs on unkno
>     wn-block(0,0)
>     [    0.605770] CPU: 5 PID: 1 Comm: swapper/0 Not tainted 6.6.56 #1
>     [    0.605850] Hardware name: Supermicro X10SLH-F/X10SLM+-F/X10SLM+-F,
>     BIOS 3.3 03/27/2020
>     [    0.605934] Call Trace:
>     [    0.606011]  <TASK>
>     [    0.606077]  dump_stack_lvl+0x38/0x50
>     [    0.606157]  panic+0x170/0x320
>     [    0.606238]  mount_root_generic+0x24b/0x300
>     [    0.606317]  ? rest_init+0xc0/0xc0
>     [    0.606394]  prepare_namespace+0x5e/0x270
>     [    0.606471]  kernel_init+0x11/0x1a0
>     [    0.606567]  ret_from_fork+0x28/0x40
>     [    0.606646]  ? rest_init+0xc0/0xc0
>     [    0.606722]  ret_from_fork_asm+0x11/0x20
>     [    0.606799]  </TASK>
>     [    0.606897] Kernel Offset: 0x16c00000 from 0xffffffff81000000 
> (relocation ran
>     ge: 0xffffffff80000000-0xffffffffbfffffff)
>     [    0.606987] ---[ end Kernel panic - not syncing: VFS: Unable to 
> mount root fs
>      on unknown- block(0,0) ]---
>
> (above manually transcribed from photo)
>
> It's definitely the Linux kernel and not a bios related kernel as the 
> kernel
> version is clearly visible.
>
> I tried changing
>
>     search --set=root --fs-uuid add2119a-1a46-4c72-b212-863ee869ebd1
>
> to
>
>     set root=(hd4,1)
>
> and I tried changing
>
>     root=PARTUUID=8d5d11ba-01
>
> to
>
>     /dev/sdi1
>
> but when I do that, grub can't even find the kernel. Clearly one or 
> both of
> those relative device references is wrong when I try it, I suspect the
> `set root=(hd4,1)` as I have four physical SATA drives which I think 
> should
> correspond to (hd0--hd3) but with bios boot order set to USB first, 
> who knows?
>
> But anyway I think the `UUID` and `PARTUUID` should work and when 
> used, clearly
> the kernel loads enough to panic.
>
> Same kernel config used as what works with LFS 11.3 but I wonder if 
> maybe there
> are some kernel options I need (or need as built-in instead of 
> modular) to boot
> a kernel off of USB? Anyone know?
>
> Would it be better to make an initramfs that lets kernel modules load 
> before the
> filesystem is mounted and does anyone have a clear reference to that 
> process?
>
> Thank you for your time.
>
I had my initramfs install on the USB drive and I didn't encounter this 
issue although I never try to boot  without initramfs. And I think it is 
better to go with the UUID method.

Here is a link: About initramfs (linuxfromscratch.org) 
<https://www.linuxfromscratch.org/blfs/view/svn/postlfs/initramfs.html>

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