How can i format and finaly mount??

Question

Hi guys,
i'm trying to create an image bootable from scratch, but i fell in error right at the beginning .
I've created an image filled by zero with
dd if=/dev/zero of=deb.iso bs=1M count=2048
after that i've partitioning this file with
cfdisk deb.iso
and the resultant partition table is
Disk ../deb.iso: 2 GiB, 2147483648 bytes, 4194304 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x114cf359
Device Boot Start End Sectors Size Id Type
../deb.iso1 * 2048 718847 716800 350M 83 Linux
../deb.iso2 718848 4194303 3475456 1,7G 83 Linux
At this point i've create a block devices for each partition, so
losetup -o $((2048*512)) /dev/loop0 ../deb.iso
losetup -o $((718848*512)) /dev/loop1 ../deb.iso
then i formatted it in ext4
mkfs.ext4 /dev/loop0
mkfs.ext4 /dev/loop1
and until here everything goes right.
Now i decided to mount my formatted loop devices, so
mkdir root
mount /dev/loop1 root
cd root
mkdir boot
but when i give the command for mount the /dev/loop0, this give me back an error
mount /dev/loop0 boot
mount: wrong fs type, bad option, bad superblock on /dev/loop0,
missing codepage or helper program, or other error
In some cases useful info is found in syslog - try
dmesg | tail or so.
The permission of directory and the privilege for mount devices it's ok.
I also tried mount the partition without use losetup, directly from
mount -o loop,offset=$((2048*512)) -t ext4 ../deb.iso boot/
or format directly the partition with
mkfs.ext4 -E offset=$((2048*512)) deb.iso
but always is the same.
My dmesg said:
[ 3123.395788] JBD2: no valid journal superblock found
[ 3123.395796] EXT4-fs (loop0): error loading journal
Can someone help me with this damn trouble?? Thanks you very much
Last edited by Gianlucode (2014-12-01 12:17:26)

Answer 1

How we are used to hear in computer science, Divide et impera!
I divided my deb.iso in 3 pices using dd. Remebering the partitions table
Gianlucode wrote:Disk ../deb.iso: 2 GiB, 2147483648 bytes, 4194304 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x114cf359
Device Boot Start End Sectors Size Id Type
../deb.iso1 * 2048 718847 716800 350M 83 Linux
../deb.iso2 718848 4194303 3475456 1,7G 83 Linux
I use dd in this way
dd if=deb.img of=deb.img.mbr bs=512 skip=0 count=2048
dd if=deb.img of=deb.img.0 bs=512 skip=2048 count=716800
dd if=deb.img of=deb.img.1 bs=512 skip=718848
To be sure that i haven't corrupted something i've calculeted the md5 hash of this file and the original
cat deb.img.mbr deb.img.0 deb.img.1 | md5sum
f33fed42eb63666d325e4fff796bfef9
md5sum deb.img
f33fed42eb63666d325e4fff796bfef9
So i was able to format my partitions and then mount them
mkfs.ext4 deb.iso.0
mkfs.ext4 deb.iso.1
mkdir root
mount deb.iso.1 root
cd root
mkdir boot
mount ../deb.iso.0 boot
touch boot/test
cd ..
umount root/boot
umount root
I've reassembled the image
cat deb.img.mbr deb.img.0 deb.img.1 > deb_final.img
and obviously if i recalculate the md5 is different then the initaly deb.img because i formatted and wrote some file in these partitions.
md5sum deb.img
f33fed42eb63666d325e4fff796bfef9
md5sum deb_final.img
b1b5656781b28803759d46ee67c428d5
To be sure, i've done the ultimately proof
sudo mount -o loop,offset=$((2048*512)) deb_final.img root
ls root
test lost+found
Et voilà there is the file test as i aspected.
Now do not forget to umont the partition
sudo umount root
I hope that this post will be useful for someone in future. If you have other solution to the initial problem, write it below.
Last edited by Gianlucode (2014-12-02 14:48:39)