Cubic

Increase the maximum size of the custom iso file

Asked by Ludwig Englbrecht

Dear ladies and gentlemen,

I would like to create a larger iso file (15 GB) with a custom OS. This should not be burned on a DVD at all but used as live os for a virtual machine. Is there an option to increase the maximum size of the custom iso file?

It shows an error message that my data is larger than 4GB and this is not compliant with the ISO standard 9660 during the iso creation.

I am very grateful for any advice.

Kind regards,
Ludwig

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Cubic PPA (cubic-wizard) said : 		#1

This is a copy of my response to Question https://answers.launchpad.net/cubic/+question/670290 ...

Cubic uses mkisofs to create the ISO_9660 file system. (See https://linux.die.net/man/8/mkisofs).

I believe that the 2^32-1 GiB (i.e. 4GiB) maximum size is a limitation of the ISO_9660 standard.
(See https://en.wikipedia.org/wiki/ISO_9660#The_2/4_GiB_file_size_limit).

Note that there seems to be a capability in ISO_9660 to support "multi-extent (fragmentation)" that could allow files larger than 4 GiB, but I have not looked into it, and I don't know if the generated ISO will be "burnable" to a USB stick or DVD. If you have some insight on how to get mkisofs create files larger than 4 GiB, I would be interested in hearing about it.

Finally, if you insist on testing Cubic with a higher ISO size limit check, you can execute the following to set the size limit to 8 GiB. This isn't a hidden feature; you are simply modifying the installed application. (Note, this will ONLY change the *check* Cubic does, so Cubic will not complain if your image size is larger than 4 GiB. However, the resulting ISO may be unusable, or mkisofs may just silently error out in the background, but you will not be presented with an error on the Cubic UI).

Nevertheless, if you test this, please let us know what your experience was?

# SET SIZE CHECK TO 8 GiB

    $ grep "maximum_iso_size_gib = " /usr/share/cubic/transitions.py
    $ sudo sed -i "s|maximum_iso_size_gib = 4.0|maximum_iso_size_gib = 8.0|g" /usr/share/cubic/transitions.py
    $ grep "maximum_iso_size_gib = " /usr/share/cubic/transitions.py

# REVERT SIZE CHECK TO 4 GiB
# NOTE: You can also simply reinstall Cubic to revert to the default size limit check

    $ grep "maximum_iso_size_gib = " /usr/share/cubic/transitions.py
    $ sudo sed -i "s|maximum_iso_size_gib = 8.0|maximum_iso_size_gib = 4.0|g" /usr/share/cubic/transitions.py
    $ grep "maximum_iso_size_gib = " /usr/share/cubic/transitions.py

Revision history for this message
Cubic PPA (cubic-wizard) said : 		#2

The maximum ISO size is now 8TB.

Cubic will no longer display an error if the generated ISO size exceeds 4GB, as long as the size is less than 8TB.

It is not clear if this change results in compatibility issues.

Fixed in Development version 2019-03-190.
Fixed in Release version 2019-03-49.

To get this change, simply upgrade to the latest release:
    $ sudo apt-add-repository ppa:cubic-wizard/release
    $ sudo apt update
    $ sudo apt install cubic

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