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Thread: ubuntu live usb casper-rw RO mode

  1. #1
    Join Date
    Apr 2010

    Smile ubuntu live usb casper-rw RO mode

    Hi all im new to the forum but i have been using ubuntu for some time i relly need my question answering please. OK i have got ubuntu live setup on usb boots fine i have a casper-rw setup on a fat32 drive that all works fine but now i have my ubuntu setup all fine with all the changes i like done so i would like to no how to boot into the persistent mode but in readonly. So what i would have is all my changes but not any more so i cant mess it UP? PLEASE HELP.

  2. #2
    Join Date
    Mar 2006

    Re: ubuntu live usb casper-rw RO mode

    I was trying to to the same thing, since I couldn't get isolinux to understand persistent switch for reading casper-rw file when I boot from DVD.

    This method will not remove stuff that has been in original live-cd that you have removed in persistent mode, so it might mess up things... I should check out how filesystem.squashfs and casper-rw are normally merged when livecd is booted in persistent mode and fix that part where I combine two fs images to one.

    I did following procedure to copy everything from casper-rw filesystem image to filesystem.squashfs image. I did this with osx so I didn't just mount filesystem.squashfs but I actually extracted modified and recompressed it. There might be some errors in following, since I did not test this on linux.

    Naturally before staring you should backup whole memorystick :)

    1. extract filesystem.squashfs content:

    sudo unsquashfs -d extracted_squashfs path_to_your_live_usb/casper/filesystem.squashfs

    2. mount your casper-rw (I did use macfuse and fuse-ext2, but with linux it's easier with loopback device)

    sudo mkdir -p /mnt/casper-rw
    sudo mount -o loop,ro path_to_your_live_use/casper-rw /mnt/casper-rw

    3. copy all data from casper-rw to extracted_squashfs image

    cd extracted_squashfs
    sudo cp -p -R -P -f /mnt/casper-rw/* .

    4. regenerate filesystem.squashfs

    sudo mksquashfs extracted_squashfs path_to_your_live_use/casper/filesystem.squashfs -noappend

    If this gives e.g. zlib error you can try with different switches... with me -processors 1 helped. Also compressing switches could help if anything else does not.

    Now you should have everything from casper-rw in nonpersistent squashfs image, you should boot from stick without "persistent" kernel parameter.

    Then you should maybe regenerate manifest and md5sum etc. files. For that there is instructions in and

    Hope that this helps someone, this should work on any OS that can compile squashfs-tools and mount ext2 partitions.

    Good luck, Mikael Lepistö

    Actually zlib fail happened few times also with processors 1 switch, so looks like it's just about luck, when mksquashfs does not fail.

    I also did not find a way to mount aufs filesystems on os x, so finally I had to do combining casper with squashfs in linux in virtualbox which was like 1000 times easier than tying to battle with this on osx. I just mounted squashfs filesystem and casper-rw and then mounted them as aufs like this:

    sudo mount -t squashfs -o loop,ro filesystem.squashfs /mnt/squashfs
    sudo mount -o loop,rw casper-rw /mnt/casper-rw
    sudo mount -t aufs -o br:/mnt/squashfs=ro:/mnt/casper-rw none /mnt/aufs

    And copied combined files to os x as tar which seems to handle links etc. better (or at least easier without any extra options) than plain copy

    tar -cvvf shared_directory/aufs.tar -C /mnt aufs

    And then untarred aufs.tar in osx and repeated step 4 with aufs directory to generate new filesystem.squashfs.

    However generated bootable iso still does not looks identical to my live usb system :(

    Anyone has ideas e.g. how to enable persistent (which just would mount casper-rw in readonly mode) mode also when booting from dvd isolinux instead of syslinux?
    Last edited by elhigu; October 15th, 2010 at 08:01 PM. Reason: Fixed combining squashfs with casper-rw


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