Booting with SYSLINUX on Loopback Device: Kernel Panic - Where to Start?

[Patrick]

On Fri, Mar 4, 2016 at 3:56 PM, Kristof Provost <kristof at sigsegv.be> wrote:

>
> On 04 Mar 2016, at 23:50, Patrick <plafratt at gmail.com> wrote:
> ​Thanks for the response.​ I had seen that StackOverflow post and done
> that a couple of days ago. I was hoping there was another answer, since I
> wouldn't be able to do that if I weren't using QEMU.
>
> If you weren’t using Qemu I’d point you at netconsole. The first step in
> debugging panics is always to figure out what the panic is.
>
> When I looked at the output from QEMU a couple of days ago, the kernel was
> saying that it couldn't find a device to mount with the root filesystem. So
> I generated an initrd image on the host Linux system, and I used that on
> the guest which got me to a BusyBox prompt. But this was totally a hack,
> since I didn't even know if getting an initrd image was really the next
> thing I needed to do. I was hoping someone might be able to point me to
> something that might explain what to do to get the kernel to mount a device
> with the root filesystem.
>
> You want to pass the ‘root=/dev/foo’ option to your kernel. Obviously
> change /dev/foo into whatever device you’re booting from.
>
> Regards,
> Kristof
>

Ok, thanks. I will try to look into netconsole.​

I had tried changing the "root" option. I had noticed that the QEMU output
showed the kernel printing out this:

[    4.312088] VFS: Cannot open root device "(null)" or unknown-block(0,0):
error -6
[    4.322029] Please append a correct "root=" boot option; here are the
available partitions:
[    4.327850] 0100           65536 ram0  (driver?)
[    4.337399] 0101           65536 ram1  (driver?)
[    4.345170] 0102           65536 ram2  (driver?)
[    4.345691] 0103           65536 ram3  (driver?)
[    4.346251] 0104           65536 ram4  (driver?)
[    4.346825] 0105           65536 ram5  (driver?)
[    4.347442] 0106           65536 ram6  (driver?)
[    4.350055] 010a           65536 ram10  (driver?)
[    4.352624] 010b           65536 ram11  (driver?)
[    4.353597] 010c           65536 ram12  (driver?)
[    4.354517] 010d           65536 ram13  (driver?)
[    4.354977] 010e           65536 ram14  (driver?)
[    4.358393] 010f           65536 ram15  (driver?)
[    4.359420] 0b00         1048575 sr0  driver: sr
[    4.360499] 0800          102400 sda  driver: sd
[    4.367898] Kernel panic - not syncing: VFS: Unable to mount root fs on
unknown-block(0,0)

I hadn't noticed "sda" before. So I tried pointing root at this. Then I got
this:

[    4.375721] List of all partitions:
[    4.383491] 0100           65536 ram0  (driver?)
[    4.386418] 0101           65536 ram1  (driver?)
[    4.388736] 0102           65536 ram2  (driver?)
[    4.390931] 0103           65536 ram3  (driver?)
[    4.391266] 0104           65536 ram4  (driver?)
[    4.391726] 0105           65536 ram5  (driver?)
[    4.392812] 0106           65536 ram6  (driver?)
[    4.393340] 0107           65536 ram7  (driver?)
[    4.393932] 0108           65536 ram8  (driver?)
[    4.394906] 0109           65536 ram9  (driver?)
[    4.396283] 010a           65536 ram10  (driver?)
[    4.399212] 010b           65536 ram11  (driver?)
[    4.400067] 010c           65536 ram12  (driver?)
[    4.401832] 010d           65536 ram13  (driver?)
[    4.402775] 010e           65536 ram14  (driver?)
[    4.403572] 010f           65536 ram15  (driver?)
[    4.404046] 0800          102400 sda  driver: sd
[    4.412148] 0b00         1048575 sr0  driver: sr
[    4.413323] No filesystem could mount root, tried:  ext3 ext2 ext4 vfat
fuseblk
[    4.415310] Kernel panic - not syncing: VFS: Unable to mount root fs on
unknown-block(8,0)

So, I think maybe now the kernel is missing some things it needs on
/dev/sda. Right now, I don't think there is anything on it other than the
bootloader. Do you happen to know where I can find what the kernel needs to
proceed?

Thanks,
Patrick

>
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