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I have a non-persistent Xubuntu 18.04 LTS live USB. I like to keep it non-persistent EXCEPT for a small change.

I'd like to add radeon.modeset=0 to the line GRUB_CMDLINE_LINUX_DEFAULT="quiet splash" in the file /etc/default/grub so that it reads:

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash radeon.modeset=0"

and make that change permanent.

This is to prevent one of my discrete graphic cards (Radeon) from starting on boot.

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  • What program did you use to create the USB? Most Live and Persistent USB's do not allow sudo update-grub. It returns error: failed to get cononical path of '/cow'.thus editing /etc/default/grub has no effect.
    – C.S.Cameron
    Nov 8, 2020 at 5:56

2 Answers 2

Reset to default
1

Luckily length of new grub option matches length of existing options (it is not longer). I guess --- is used to inform end of options, I've just booted 20.04 LTS (I assume it either applies that same to 18.04 LTS or as one year passed it is Ok for you to use 20.04 LTS now) replacing "quiet splash ---" with "toram" and have not noticed any problems.

Therefore for that particular edit answers to that QA can be directly applied (editing on byte level of iso file or USB stick): How is it easier to make a persistent live drive with Ubuntu 19.10? See "Manual" section of sudodus answer or my answer with script based on sudodus answer.

$python
>>> len ("radeon.modeset=0")
16
>>> len ("quiet splash ") # not enough to replace only those
13
>>> len ("quiet splash ---") # just fits!
16

P.S. Assuming you do not need that splash image and don't mind output of Linux booting on the screen instead ;-)

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Make a Permanent Change on a Persistent Live USB

Programs like Etcher, Win32DiskImager, dd, Gnome-Disks and Startup Disk Creator, create a USB with a read only operating system with a read only bootloader.

Other Programs like Rufus, Ventoy, mkusb, UNetbootin and YUMI create a USB with a Syslinux or GRUB bootloader config file that can be edited regardless if the USB is Persistent or not.

Rufus Windows:

  • If you are working from Windows, use Rufus to create your Live or Persistent USB. Use the Write ISO image option, (Default), if asked.

  • While still in Windows Edit /boot/grub/grub.cfg. adding radeon.modeset=0 after quiet splash in the first menuentry.

  • Then Edit /isolinux/txt.cfg adding radeon.modeset=0 after quiet splash in the first menu item.

Mkusb Ubuntu

  • If you are working from Ubuntu use mkusb to create a persistent USB with your preferred options.

  • Using disks, mount the USB's usbboot partition.

  • Edit /boot/grub/grub.cfg. adding radeon.modeset=0 after quiet splash in the first menuentry.

This should set you up permanently for both BIOS and UEFI boots whether the USB is Live or Persistent.

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  • It's not allowing me to make changes to grub.cfg. Read-only. imgur.com/dXIENfo imgur.com/UygjTaa
    – JJrussel
    Nov 9, 2020 at 3:28
  • You should be able to edit a Rufus USB from Windows. If booted from Linux, (but not the target USB), try opening grub.cfg's or txt.cfg's folders using sudo -H nautilus or install nautilus admin, (sudo apt install nautilus-admin) You can not change it if booted from the live USB unless booted toram.
    – C.S.Cameron
    Nov 9, 2020 at 3:33
  • So is that `sudo -H nautilus grub.cfg'?
    – JJrussel
    Nov 9, 2020 at 5:36
  • sudo -H nautilus will open nautilus as root, then go to /media/xubuntu/xubuntu.../boot/grub/grub.cfg and double click to open it, as root in text. You should be able to edit and save it no problem.
    – C.S.Cameron
    Nov 9, 2020 at 6:09
  • Same reason result. i.imgur.com/Gf3974V i.imgur.com/Q3mxf2P
    – JJrussel
    Nov 9, 2020 at 21:26

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