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Is there any way to skip the disk check in Ubuntu 20.04 LTS by editing the ISO with Cubic? If possible, can we edit it in such a way that I get a new menu-entry on the try/install page. So, right above the "Try Ubuntu without installing", I'll have something like "Try Ubuntu (Custom)" which skips the disk check?

Edit: Please excuse my bad habit of referring to 20.04 LTS as 20 LTS

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  • There is no Ubuntu 20 LTS.
    – David
    Aug 31 at 5:16
  • Are you talking about Ubuntu Core 20? (the year format is reserved for snap only products such as Ubuntu Core 20, they all come with 10 years of supported life so the LTS isn't usually mentioned for year format releases)
    – guiverc
    Aug 31 at 5:47
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    Please tell us the name of the iso file, that you want to modify. I think you will get what you want, if you use mkusb to create a persistent live drive. In such a drive you can select different options to boot at the grub menu also live-only boot options, and if still necessary you can easily edit the grub.cfg file in partition #3 of the pendrive to skip the disk check in every option. (This is easier than to make a new iso file.)
    – sudodus
    Aug 31 at 6:57
  • Hey all, I meant to say 20.04 LTS. I keep saying 20 though. Bit of a bad habit
    – n00dles
    Aug 31 at 12:46
  • Hey @sudodus, I did consider going the mkusb route, but I really like the idea of modifying the ISO.
    – n00dles
    Aug 31 at 12:59
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I'll assume you mean Ubuntu 20.04 or Ubuntu 20.10. The process is the same for Ubuntu desktop releases.

In Cubic, when you get to the Options page, click on the Boot tab and edit the files shown.

For the boot/grub/grub.cfg and boot/grub/loopback.cfg files, create a new menuentry item, such as "Try Ubuntu (Custom)" with the parameter fsck.mode=skip added to the linux line.

For the isolinux/txt.cfg file, create a new label item, such as "live-no-fsck" with the parameter fsck.mode=skip added append line.

For example, in the file boot/grub/grub.cfg:

menuentry "Try Ubuntu (Custom)" {
    set gfxpayload=keep
    linux   /casper/vmlinuz boot=casper fsck.mode=skip file=/cdrom/preseed/ubuntu.seed maybe-ubiquity quiet splash ---
    initrd  /casper/initrd.lz
}

For example, in the file boot/grub/loopback.cfg:

menuentry "Try Ubuntu (Custom)" {
    set gfxpayload=keep
    linux   /casper/vmlinuz boot=casper fsck.mode=skip file=/cdrom/preseed/ubuntu.seed maybe-ubiquity iso-scan/filename=${iso_path} quiet splash ---
    initrd  /casper/initrd.lz
}

For example, in the file isolinux/txt.cfg:

default live-no-fsck
label live-no-fsck
  menu label ^Try Ubuntu (Custom)
  kernel /casper/vmlinuz
  append  boot=casper fsck.mode=skip file=/cdrom/preseed/ubuntu.seed initrd=/casper/initrd.lz quiet splash ---

Note that in the boot/grub/grub.cfg and boot/grub/loopback.cfg files, the first entry is default. In isolinux/txt.cfg, you specify the default entry using the directive default <your default entry>.

(Also, be aware that this only affects the ISO boot. If you want the same behavior for an installed system, you will need to modify grub in Cubic's Terminal page, and you will need to take special steps in the preseed file to ensure your customized grub is not overwritten during installation.)

Here is a screenshot of Cubic's Options page, Boot tab, showing a new menu entry that skips the file system check.

Screenshot of Cubic's Options page, Boot tab

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  • Thanks, this was exactly what I was looking for
    – n00dles
    Aug 31 at 13:00

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