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I have installed ubuntu 15.04 and 14.04. First i had installed 14.04 after that i installed 15.04 and the grub boot menu changed to 15.04. Now i want to revert it, that means i want to change the grub that appears on startup to grub of 14.04. How to do it?

Ashish Pal
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  • How the "shift" key during boot to show the grub menu and pick another option to boot from. See for instance: http://askubuntu.com/questions/82140/how-can-i-boot-with-an-older-kernel-version – Rinzwind Feb 02 '17 at 07:30
  • My grub menu is appearing fine. Order is also fine but the problem is I want the grub linked with 14.04 to appear on startup rather than 15.04. – Ashish Pal Feb 02 '17 at 07:53
  • Boot to 14.04, then open terminal and run command sudo grub-install sdX Replace the X with your drive-letter, if you have only one drive it will be likely sudo grub-install sda. – mook765 Feb 04 '17 at 04:42

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If you look in /etc/default/grub, you have a variable GRUB_DEFAULT:

↳ grep GRUB_DEFAULT /etc/default/grub 
GRUB_DEFAULT=0

This is the menu entry that will be used by default. To see which menu entries you have, have a look in /boot/grub/grub.cfg (nl -v 0 is used to add the line numbers):

↳ egrep "^menuentry |^submenu " /boot/grub/grub.cfg | nl -v 0                                                                                                                                                                                                                                                                
 0  menuentry 'Ubuntu' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-simple-bf88b0d6-7f16-4314-87f5-ce3e84a6a396' {
 1  submenu 'Advanced options for Ubuntu' $menuentry_id_option 'gnulinux-advanced-bf88b0d6-7f16-4314-87f5-ce3e84a6a396' {
 2  menuentry 'System setup' $menuentry_id_option 'uefi-firmware' {

Having GRUB_DEFAULT=0 means booting the first menuentry. So if you wanted to boot to System setup by default (as a silly example), set GRUB_DEFAULT=2 and run sudo update-grub.

In the case you want to boot something in the submenu by default, you'd have to use the submenu index, > and the index of the menuentry in the submenu. E.g, 4th entry in submenu, then GRUB_DEFAULT should be set to "1>3"

It is also possible to set GRUB_DEFAULT to name label of a menuentry (first parameter), so GRUB_DEFAULT='System setup' would also be a valid setting.

Whenever changing /etc/default/grub, do not forget to run sudo update-grub.

More reading at https://help.ubuntu.com/community/Grub2/Submenus.

mgor
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  • I dont want to change the order of grub menu. I want to change the grub that appears on startup to grub of 14.04. Currently grub of 15.04 is installed. – Ashish Pal Feb 02 '17 at 07:51
  • I interpret that as you want to change the default boot option from 15.04 to 14.04? Then the easiest way would be to change GRUB_DEFAULT. – mgor Feb 02 '17 at 07:55
  • No. I dont want to do that. I dont want the ubuntu 15.04 anymore and want to delete it. But if I delete it I will get grub rescue error. So I thought to change the grub to 14.04 first. – Ashish Pal Feb 02 '17 at 07:58
  • http://askubuntu.com/questions/79813/how-to-remove-a-second-ubuntu-install – mgor Feb 02 '17 at 08:03
  • I did what was said in above link and ran into the problem of grub rescue :( – Ashish Pal Feb 02 '17 at 09:18