Remounting a root filesystem

Question

I'm using a Linux based diagnostic OS initially intended to be installed on a CD-ROM, available as an ISO 9660 image. I have changed the image with isohybrid and I have copied it to an USB stick. Using fdisk and mke2fs, I have created and initialized an ext4 filesystem in the free space of this USB stick. It's intended to be mounted rw while the diagnostic OS is running.

When booting from this USB stick, no problem occurs, but the root filesystem of the OS is mounted on /dev/sdb, which is the whole USB stick. In fact, on the USB stick, it's only located on /dev/sdb1. Now, I'm not able to mount rw my additional partition in /dev/sdb2. The mount command refuses because there is already a mount in action.

What is the best way to remount the root filesystem of the OS as /dev/sdb1, so that I can mount /dev/sdb2 ? Or is there a way to mount /dev/sdb2 although the root filesystem of the OS remains mounted on /dev/sdb ?

I have copied the ISO 9660 image using dd, after I have performed isohybrid.

On the USB stick, there are 2 partitions now. The first one is from the initial ISO 9660 image, the second one was created as explained above. The first partition is marked with the boot flag.

I have just discovered that / has the filesystem type "aufs". In this environment, anything is probably different. I have never worked previously with aufs.

Additional information:

Yes, I have copied using dd, as it was suggested on the System Rescue CD site.

Now, I was able to find a solution. I have installed the Super GRUB2 disk on a USB stick. Then I have fixed the partition size problem of the USB stick, using fdisk. At next, I have created a partition for the System Rescue CD on the stick, as well as a data partition. I have created an ext4 filesystem on both. Then, I have mounted the iso file of the System Rescue CD as loop and I have copied recursively all the files to the newly created filesystem on the stick.

Now, I can boot GRUB2 from the USB stick and I can enter the GRUB commands in order to boot the System Rescue CD from its own ext4 partition. When it's running, I'm free to mount any other partition. There is no more blocking of the whole USB. stick.