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I would like to have two Ubuntu-OS on a virtual machine and to test grub boot loader on this system.

I can change the order from one Ubuntu to another, but it does not work on reverse case. I am changing the grub file(/etc/default/grub) but there is no effect on grub order.

I have already tried to fix it with help of the program "Grub Customizer", but it did not work as well.

  • Grub Customizer View

    Grub Customizer View

  • Content of Grub file on Ubuntu

    Content of Grub file on Ubuntu

  • Content of Grub file on Ubuntu 18.04.5 LTS(18.04)

    Content of Grub file on Ubuntu 18.04.5 LTS(18.04)

  • Grub selection view

    Grub selection view

Simon Sudler
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NiceCodeBro
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  • Best not to use Grub Customizer as it creates its own versions of grub's scripts with proxy in the name. To fully uninstall it, you also have to do a full total reinstall of grub and that will reset everything to defaults. See: https://askubuntu.com/questions/848119/how-to-update-grub-on-a-dual-boot-machine/848614#848614 & https://help.ubuntu.com/community/Grub2/CustomMenus & https://ubuntuforums.org/showthread.php?t=2076205, but read first post or two and then go to last and work backwards for latest info. – oldfred Aug 21 '20 at 14:37
  • @oldfred thank you for your comment. I have tried to apply all steps. What I have understood by doing this that it just help to create a list entry to grub menu and change appearance of the list. Not more. Am I right? By doing stept, there is only one extra menu entry which refers to one OS. If I set it like that GRUB_DISABLE_OS_PROBER=true, I dont have grub list more. If I create a new list entry, it does not help me, because there is still problem on changing default boot order in first ubuntu. – NiceCodeBro Aug 21 '20 at 17:32
  • There are multiple ways to change order in grub menu, change default boot line in grub (number or description) and change boot parameters. And with two grubs from two installs changes to one does not change the other. I prefer to turn off os-prober, and create my own boot entry in 40_custom. But you can copy 40_custom to 06_custom and then it is first in boot order as shown in link above. Also: https://help.ubuntu.com/community/Grub2/Setup#Specific_Entries – oldfred Aug 21 '20 at 17:32
  • @oldfred I am so appreciated with your answers, but it does not apply any grub changes from second Ubuntu. I always want to change the grub order not only from the 1st but also from the 2nd operating system. I think somewhere that the 2nd OS is defined as secondary and only changes from the 1st OS are considered valid. – NiceCodeBro Aug 24 '20 at 08:36
  • With two Ubuntu installs, you have to separately edit each grub when booted into that system. But unless you have old BIOS and multiple drives with grub in different MBR, you only will have one grub as default boot. A major grub update, will add its boot as default so second install may become first. You just have to manage boot with multiple grub. – oldfred Aug 24 '20 at 14:19
  • @oldfred Thank you for your highlights. I have solved my problem by changing /boot/grub/grub.cfg file of second intalled Ubuntu by hand from other first installed Ubuntu where I can not update grub normally with update commands. Maybe, It is not a good practice, but it fulfill my requirements. – NiceCodeBro Aug 27 '20 at 14:15
  • I typically turn off os-prober as I have many installs and some now are obsolete, but not deleted. I do not want those in grub menu. And then I add only the entries I want into 40_custom. https://help.ubuntu.com/community/MaintenanceFreeCustomGrub2Screen & mega thread, read first several posts then jump to end & work backwards for latest info: http://ubuntuforums.org/showthread.php?t=2076205 – oldfred Aug 27 '20 at 15:07

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