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Thread: Can't Create Bootable DVD Of Ubuntu 18.04

  1. #31
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    Jun 2014
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    Re: Can't Create Bootable DVD Of Ubuntu 18.04

    @CatKiller-AKA-DogLover

    Quote Originally Posted by CatKiller
    If you're able to boot from it, there's a "check for errors" option that does the same thing.
    It's been awhile since I've installed from a live DVD -- I'm still on Ubuntu 16.04 -- but I vaguely remember seeing that option somewhere in the past, but I couldn't find it when I tried to boot from the bootable DVD that I just created. Do I need to click on "Try Ubuntu" first, or is it before that?

    Edit: Nevermind, I found the option by holding any key down. I usually check the integrity of any live CD I create through K3b, rather than using that method.
    Last edited by John_Patrick_Mason; November 23rd, 2019 at 04:52 AM.

  2. #32
    Join Date
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    Kubuntu 18.04 Bionic Beaver

    Re: Can't Create Bootable DVD Of Ubuntu 18.04

    Quote Originally Posted by John_Patrick_Mason View Post
    It's been awhile since I've installed from a live DVD -- I'm still on Ubuntu 16.04 -- but I vaguely remember seeing that option somewhere in the past, but I couldn't find it when I tried to boot from the bootable DVD that I just created. Do I need to click on "Try Ubuntu" first, or is it before that?
    Even longer for me: almost all of my machines have no optical drive. I'm pretty sure it's on the very first menu that you see; if the disc's dodgy you don't want to have to load a bunch of (potentially broken) stuff before you get to check. I think they also went through a phase of some menus being hidden behind a keypress, but I don't know if that's still the case.
    None but ourselves can free our minds

  3. #33
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    Re: Can't Create Bootable DVD Of Ubuntu 18.04

    Quote Originally Posted by CatKiller View Post
    Even longer for me: almost all of my machines have no optical drive. I'm pretty sure it's on the very first menu that you see; if the disc's dodgy you don't want to have to load a bunch of (potentially broken) stuff before you get to check. I think they also went through a phase of some menus being hidden behind a keypress, but I don't know if that's still the case.
    You're right. I just tested the bootable DVD that I successfully created. The "check CD for defects" option is hidden by default, unless you press a key -- I think, any key will do -- soon after the boot screen. I had almost forgot about it, since that's not usually how I verify the integrity of my live CDs. And that's true for Ubuntu 16.04, as well; I kept my Ubuntu 16.04 installation disc, in case I rendered my Ubuntu partition unbootable -- it happened to me once, while making changes to system files. Ubuntu 14.04 might have been different, but it's no longer supported, anyway.

    I should say that the reason I've stuck to DVDs for so long is because when I did try to create a bootable USB stick with Ubuntu 16.04 on it, it wouldn't boot. Ubuntu 18.04 works fine, though -- on a USB stick.
    Last edited by John_Patrick_Mason; November 23rd, 2019 at 07:27 AM.

  4. #34
    Join Date
    Feb 2013
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    76

    Re: Can't Create Bootable DVD Of Ubuntu 18.04

    Hi,

    > by closed, you mean the xorriso-burned DVD can no longer be written to,
    > correct?

    Yes. A DVD+R can have three states: Blank, Appendable, Closed.
    Blank means it is yet unused. Appendable means that it contains data and
    still can take another burn run ("session"). Closed means that it cannot
    be written any more.

    CD-RW and unformatted DVD-RW can be blanked to become writable from scratch
    again. CD-R, DVD-R, DVD+R, BD-R stay closed forever. DVD-RAM, DVD+RW, BD-RE,
    formatted DVD-RW, formatted CD-RW can be overwritten without blanking,
    because they are in the fourth possible state: Overwritable.

    > So, what do you think the problem was, a malfunctioning CD/DVD drive?

    Obviously. Now the question is: Does it just have some dust on the lense
    or is it entirely dead. A good blow with pressured air into the open
    drive might work wonders.

    --------------------------------------------------------------------------

    As for checkreading, i would propose to read the plain DVD+R content instead
    of mounting it and checking its files. If the overall image is ok, the files
    can hardly be damaged. (libmath says 0 if i try to estimate the probability.
    Well, numerical math is always a bit optimistic.)

    It is important to read only as many blocks from the DVD as the original
    ISO image has. Else the checksum will hardly match.
    Code:
    blocks=$(expr $(stat -c '%s' ubuntu-18.04.3-desktop-amd64.iso) / 2048)
    dd if=/dev/sr1 bs=2048 count=$blocks | md5sum
    Compare the resultiing hex number with the hex number in line
    Code:
    72491db7ef6f3cd4b085b9fe1f232345 *ubuntu-18.04.3-desktop-amd64.iso
    of http://releases.ubuntu.com/18.04/MD5SUMS


    > I don't know what a non-matching md5sum looks like.

    It will be just some string of 32 hex digits [0-9a-f] which is not the same
    as the one you expect. E.g. "hallo\n" has this MD5:
    Code:
    $ echo hallo | md5sum
    aee97cb3ad288ef0add6c6b5b5fae48a  -
    If you are insecure about comparing 32 digits, let the shell do it for you:
    Code:
    $ test 72491db7ef6f3cd4b085b9fe1f232345 = 72491db7ef6f3cd4b085b9fe1f232345 && echo OK
    OK
    $ test 72491db7ef6f3cd4b085b9fe1f232345 = 72491db7ef6f3cd4b085b9fe1f232340 && echo OK
    $
    (I.e. chirping crickets are a negative outcome.)

    Have a nice day

    Thomas

  5. #35
    Join Date
    Jun 2014
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    282

    Re: Can't Create Bootable DVD Of Ubuntu 18.04

    Code:
    blocks=$(expr $(stat -c '%s' ubuntu-18.04.3-desktop-amd64.iso) / 2048)
    dd if=/dev/sr1 bs=2048 count=$blocks | md5sum
    OK, I've used stat for other purposes, mainly to check access times, which I would think would be useful in a server environment, but, it in this case, stat -c fetches the total number of bytes of the ISO file. Then, what?

    The book that I learned the command line from didn't cover the expr command, but I can see that the expr command uses the output of the stat command as input (command substitution), and that the output of the expr command, ends up getting divided by 2048 in an arithmetic expansion. Is that correct?

  6. #36
    Join Date
    Feb 2013
    Beans
    76

    Re: Can't Create Bootable DVD Of Ubuntu 18.04

    Hi,

    > total number of bytes of the ISO file [...] divided by 2048
    > Is that correct?

    Yes. Ye olde way of doing arithmetics in shell.
    Code:
    $ stat -c '%s' ubuntu-18.04.3-desktop-amd64.iso
    2082816000
    $ expr 2082816000 / 2048
    1017000
    The stat run is put in "$(...)" so that it provides its output as argument
    for the expr run. This too is put in "$(...)" to provide its output as content
    for the variable assignment "blocks=".

    The kids would save 3 characters of line length by
    Code:
    blocks=$(($(stat -c '%s' ubuntu-18.04.3-desktop-amd64.iso) / 2048))
    Reason for this computation is that dd would be awfully slow if we let
    it read and count single bytes (by bs=1). The block size bs=2048 is
    the natural granularity of optical data storage and of ISO 9660 filesystems.
    So we can safely assume that the division yields an integer result.

    The man page of expr can be displaid on a terminal by
    Code:
    man expr
    Have a nice day

    Thomas

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