Ubuntu – convert a dmg file to iso in terminal

Upgrading by using the CD or USB image

If you are using 10.04 LTS or 11.10 and you either insert the live CD or boot from the live CD to start installing it will give a option of upgrading to 12.04. It will automatically detect installed applications and install the updated version of your applications also.

If you download an ISO, the recommendation is to perform a md5sum check to ensure both the ISO downloaded and the burned CD are valid.

• Upgrade from 10.04 LTS (here shown with dual boot):

NOTE: Upgrades from 10.04 to 12.04 are not activated yet, see this question for more detail:

• Why is "No new release found" when upgrading from a LTS to the next?

• Upgrade from 11.10
  

Taken from 12.04LTS upgrade

Your question is still somewhat ambiguous and unclear to me (Blaming myself). I'm answering this considering each case:

Case 1: Mount iso which is within another iso file

If you are asking whether you can mount an iso file which is within another iso file, I would say, Yes, You can mount an iso file which is itself in another iso file

For example, Let us assume we have an iso file named file1.iso in our home directory and there is another iso file inside it named inside.iso. One way to mount both iso file is ---

1. Create two folder in your home. Each for each iso file.

    mkdir ~/iso1 ~/isoInside
   

2. Mount the first iso file in the ~/iso1 directory

    sudo mount ~/file1.iso ~/iso1 -o loop
   

3. Then mount the second iso file inside this iso to "~/isoInside" directory

    sudo mount ~/iso1/inside.iso ~/isoInside -o loop
   

Now you have the first iso file mounted in "~/iso1" folder and the second one in "~/isoInside" folder

Case 2: Mount two iso file in a single directory.

If you are asking whether you can mount an iso file to a folder and then mount another iso file in the same previous folder, I would, Yes, you can do that also. But You cannot access the content of first mounted iso file.

That is, if you mount an iso file iso1.iso in a folder, say /mnt and then mount another iso file iso2.iso in the same folder /mnt, you will only see and access the content of iso2.iso file in /mnt. You cannot access the contents of iso1.iso file in /mnt folder until you unmount the second iso file, i.e iso2.iso file.

Take note that, in such cases, you cannot either unmount the first iso file. You must unmount the second one and then first one.

I think, you are having a problem with installation from an iso file (probably from alternate installer iso), if this is indeed the case, I suggest you to ask a question about your problem.

Hope this answer will help.