[Qemu-devel] requirements of root filesystem image when passed to qemu

["Peter Teoh" <htmldeveloper@gmail.com>]

First, after installing debian (8.04) on a qemu image - debian.cow - I
then used it to mount the latest kernel:

qemu -kernel /boot/vmlinuz-2.6.26-rc5 -hda debian.cow -append
"root=/dev/hda console=ttyS0" -nographic

[    5.493332] 0300    1331200 hda driver: ide-disk
[    5.494978]   0301     248976 hda1
[    5.496151]   0302    1076355 hda2
[    5.497403] No filesystem could mount root, tried:  ext3 ext2 iso9660
[    5.499552] Kernel panic - not syncing: VFS: Unable to mount root
fs on unknown-block(3,0)

But when I downloaded the root filesystem image at:

http://bellard.org/qemu/download.html

for linux-0.2.img, and execute:

qemu -kernel /boot/vmlinuz-2.6.26-rc5 -hda linux-0.2.img -append
"root=/dev/hda console=ttyS0" -nographic

everything went through to the root prompt level, even though the
linux-0.2.img image has its own kernel version (0.2).   And I noticed
that (using "file"):

linux-0.2.img: x86 boot sector, LInux i386 boot LOader
debian.cow: QEMU Copy-On-Write disk image version 1, size 0 + 1363148800

Next, using another rootfs image:

file FedoraCore5-x86-root_fs
FedoraCore5-x86-root_fs: x86 boot sector

I run qemu successfully.

Next I entered ubuntu installation image:

ubuntu-8.04-desktop-i386.iso: ISO 9660 CD-ROM filesystem data UDF
filesystem data (unknown version, id 'NSR01') 'Ubuntu 8.04 i386
       ' (bootable)

qemu -kernel /boot/vmlinuz-2.6.26-rc5 -hda
ubuntu-8.04-desktop-i386.iso -append "root=/dev/hda console=ttyS0"
-nographic

And the result is:

[    6.136373] Unable to load NLS charset utf8
[    6.144019] VFS: Mounted root (iso9660 filesystem) readonly.
[    6.144826] debug: unmapping init memory c0795000..c07d4000
[    6.145575] Write protecting the kernel text: 2352k
[    6.146417] Write protecting the kernel read-only data: 1068k
[    6.147388] Warning: unable to open an initial console.
[    6.148323] Kernel panic - not syncing: No init found.  Try passing
init= option to kernel.

So what is the requirement for -hda then?   1.   presence of
bootsector image 2.   presence of /sbin/init???

Next I created the busybox rootfs image following this instruction:

http://dev.gentoo.org/~solar/busybox/bbemu

And run qemu as before, just substituting only the -hda option, it result in:

[    5.564894] debug: unmapping init memory c0795000..c07d4000
[    5.565539] Write protecting the kernel text: 2352k
[    5.565891] Write protecting the kernel read-only data: 1068k
[    5.656106] mount used greatest stack depth: 2240 bytes left
Bummer, could not run '/bin/sh': No such file or directory
Bummer, could not run '/bin/sh': No such file or directory
Bummer, could not run '/etc/init.d/rcS': No such file or directory
Bummer, could not run '/bin/sh': No such file or directory
Bummer, could not run '/bin/sh': No such file or directory
Bummer, could not run '/bin/sh': No such file or directory

Endless repetition here..

Why?

Why the difference?   (ie, why can't I mount the latest kernel on the
debian image)  How to resolve the error as shown above?

-- 
Regards,
Peter Teoh