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I have an ancient Ubuntu 14.04 and I am trying to reinstall my entire system to the 20.04. In order to do that I formatted a flash drive to FAT32 and then used the Unetbooting application to create a Live-USB from the iso image file.

Everything appeared to be alright, Unetbooting did not raise any exceptions and I can access the USB stick from within Ubuntu normally. Hwever when I power off and restart, grub2 does not give me the option of booting from the Live-USB stick. Even if I go into its command-line and type "ls", it shows only a single device, hd0, which is my HDD.

Every solution I find to the problem of booting from a Live-USB stick requires grub2 to recognize the device and since that is not happening, I am stuck at step #0. I thought maybe it could be something wrong with the USB port, but I can mount and access the device just fine so I guess that is crossed off the list?

Does anyone has a hint as to what might be happening and what can I do to solve it and be done with this long overdue reinstallation?

Edit

I tried putting a manual entry in grub loadorder menu as suggested by @C.S.Cameron like so:

menuentry "Boot Ubuntu USB" {
search --set=root --fs-uuid xxxx-xx-xx-xx-xx-xx-xx
    set gfxpayload=keep
    linux   ($root)/casper/vmlinuz  file=/cdrom/preseed/ubuntu.seed maybe-ubiquity quiet splash ---
    initrd  ($root)/casper/initrd
}

And in order to find the UUID for the pendrive I did a # blkid call and came up with this for the USB:

/dev/sdc1: LABEL="Ubuntu 20.04.1 LTS amd64" TYPE="iso9660" 
/dev/sdc2: SEC_TYPE="msdos" UUID="C26E-047E" TYPE="vfat" 

In my gnome-disks application, the partition labelled as sdc1 is recognized as bootable, as shown in the Figure below

enter image description here

But the table does not show any UUID for it, only for de sdc2 which is not tagged as bootable. So I am stuck.

Edit 2

When I use the sdc2 UUID in the menuentry, Grub says that there is nothing with that UUID in its list and says that:

error: failure reading sector 0xfc from 'hd0'. 
error: failure reading sector 0xe0 from 'hd0'. 
error: failure reading sector 0x0 from 'hd0'

and that it couldn't find the vmlinuz because the file does not exist. Which I took as a consequence of not finding the unit requested by the menuentry.

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    I don't quite follow. If I've written an ISO to a thumb-drive (I've never used the program you mention, nor is it mentioned in the tutorials for Ubuntu I believe), I insert in the box, press the firmware specific key that box requires to pull up a menu asking me what device to boot, then select the thumb-drive & install. Why are you using grub? Did you modify grub to boot an ISO on disk/thumb-drive or chainload to the thumb-drive/ISO? – guiverc Oct 31 '20 at 6:06
  • No, I have a dual-boot machine with a Windows installation. Now pressing keys do not open any menus. – urquiza Oct 31 '20 at 10:49
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    The key that needs to pressed is machine specific, it maybe F12, F9, or another key (it's a blue key on a sony, thinkpads have a special key... etc), ie. the key that needs to be pressed is firmware specific (ie. matching your make & model of device) and needs to be pressed at the correct time (& rather quickly for many machines, and can take 2-3 attempts when you know the key & when to press, many more times when you're unsure of key or when to press). To prove your media, I'd suggest trying it in another box, or a third, if it fails to boot & validate on those - it's likely a bad ISO/write – guiverc Oct 31 '20 at 10:54
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    Also, if old system with lower end specs one of the lightweight flavors of Ubuntu may be better. I was able to install 16.04 in my 2006 laptop, but had to install lighter weight flavor of 20.04. ubuntu.com/download/flavours Light weight flavors: Lubuntu, xubuntu, Ubuntu MATE, Budgie – oldfred Oct 31 '20 at 13:51
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Boot USB Stick Using Internal GRUB

Sometimes a computer does not want to boot a USB using the USB's bootloader.

A Bootable USB can usually be booted using the Linux computer's GRUB.

Add the following menuentry to /etc/grub.d/40_custom and then run sudo update-grub

menuentry "Boot Ubuntu USB" {
search --set=root --fs-uuid 2020-07-31-16-51-12-00
    set gfxpayload=keep
    linux   ($root)/casper/vmlinuz  file=/cdrom/preseed/ubuntu.seed maybe-ubiquity quiet splash ---
    initrd  ($root)/casper/initrd
}

Where 2020-07-31-16-51-12-00 is the UUID of the Live USB.

This method should work for any live or Persistent USB that boots ISO9660 files, but may vary with the Linux version on the USB.

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  • What UUID are you using for sdc1? If it is an Etcher or Disks clone of 20.04.1 it should be 2020-07-31-16-51-12-00, At this point that number is worth a try. – C.S.Cameron Nov 2 '20 at 14:24
  • /dev/sdb1: LABEL="UBUNTU 20_0" UUID="0627-66B3" TYPE="vfa – urquiza Nov 2 '20 at 14:24
  • 2020-07-31-16-51-12-00 is a timestamp, isn't it? – urquiza Nov 2 '20 at 14:25
  • No, a UUID, try it. – C.S.Cameron Nov 2 '20 at 14:28
  • @urquiza, Use the UUID of your particular live system (different tools create different UUIDs), -- C.S.Cameron is referring to the UUID of a cloned live system that has preserved the ISO 9660 file system. But if you use Unetbootin, the UUID will be different. – sudodus Nov 2 '20 at 16:13

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