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I've got an mkusb live USB (Ubuntu 18.04 with persistence) that boots fine on some of my computers. On one laptop I get the following error:

error: disk `hd0,4' not found.
error: you need to load the kernel first.

What do I need to do to, "load the kernel first"?


EDIT: An SD card occupying an SD slot was causing this issue. Removing the SD card allows mkusb to boot properly, and eliminates the error. Once booted I reinsert the SD card into the SD slot if I need to use it.

@sudodus I'll run your diagnostics in a little bit when I get more time, and report back at that time

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    1. In what computer are there problems? Please specify brand name and model; 2. Please tell me which settings you used, when you created the persistent live drive. If you cannot remember, and have another USB pendrive or a memory card (and a USB card adapter), please create a new persistent live drive and use the default settings (when asked by mkusb); 3. Please check in the grub menu environment, as suggested in the answer by @Jos, grub> ls ... and report the result by editing your original question. – sudodus Feb 11 at 17:17
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    4. In what operating system (distro and version, for example Ubuntu 18.04.1 LTS) are you running mkusb? I'm asking because I need these data in order to find the cause of this problem (if possible reproduce the problem); 5. If you have a USB pendrive or memory card with at least 16 GB, you can try a new compressed image file. Use mkusb to clone from that file into a pendrive or card, and check if that system works in the computer with problems. – sudodus Feb 11 at 17:33
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    6. Are there more than one USB pendrives with persistent live systems connected to the computer, when you boot? In that case, there may be confusion with the drives and partitions. – sudodus Feb 11 at 17:38
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    @sudodus updated my post to answer those questions. This is the only live USB drive attached to the system. Although there are other SD cards attached to the system I haven't tried removing. I'll try that! And report back tomorrow. – Jason Hunter Feb 11 at 17:52
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    Thanks for the details about tasks/questions #1,2,4 :-) It should work in that computer. For example I have tested in a NUC computer with an M2 drive. I use mkusb a lot in 18.04.1 LTS. -- What about the other tasks/questions (#3,5,6)? 7. And a new task about the file mountpoint/boot/grub/grub.cfg in partition #3 of the persistent live drive: Please mount the partition and copy/paste that grub.cfgfile to your original question and indent each line 4 spaces to render it as 'code'. – sudodus Feb 11 at 19:53
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If you get to a grub prompt, it means that grub can't find the boot files that it expects. The sequence of commands to load the files and boot when grub doesn't do that for you goes something like this. First, find all partitions that grub sees:

grub> ls
(hd0) (hd0,msdos2) (hd0,msdos1)

This lists disks and partitions on the disks. One of these partitions holds your Linux system. Say it is (hd0,1). Then do:

grub> set root=(hd0,1)
grub> linux /boot/vmlinuz-4.15.0-45-generic root=/dev/sda1

Replace (hd0,1), the version number and the partition (/dev/sda1) by what is valid for your system. In the case of vmlinuz you can just type vmlinuz- and press Tab.

grub> initrd /boot/initrd.img-3.13.0-29-generic

The version string should be identical to the one for vmlinuz.

grub> boot

should now boot up your system.

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