Fix GRUB Choose Default Not Working: Troubleshooting Steps

GRUB Choose Default Explained: Pick Your Boot Entry Permanently

GRUB (GRand Unified Bootloader) controls which OS or kernel your machine boots. “Choose Default” means configuring GRUB so a specific menu entry is selected automatically at boot. Below is a concise, actionable guide to set a permanent default and related tips.

How GRUB selects the default

• GRUB_DEFAULT in /etc/default/grub defines the default entry.
  • Numeric index: 0 = first entry, 1 = second, etc.
  • Quoted string: exact menu entry title.
  • submenu_entry syntax: “1>2” selects the third entry inside the second submenu.
• grub-reboot and grub-set-default toggle temporary vs permanent defaults:
  • grub-reboot X — make X the default for the next boot only.
  • grub-set-default X — make X the default until changed.

Step-by-step: Set a permanent default (common Debian/Ubuntu)

1. Open /etc/default/grub with root privileges.
2. Set GRUB_DEFAULT to the desired value:
   • By index: GRUB_DEFAULT=2
   • By full menu title: GRUB_DEFAULT=“Ubuntu, with Linux 5.15.0-xx-generic”
   • By submenu: GRUB_DEFAULT=“1>2”
3. Save and update GRUB configuration:
   • Debian/Ubuntu: sudo update-grub
   • Fedora/RHEL: sudo grub2-mkconfig -o /boot/grub2/grub.cfg
4. Reboot to confirm.

Using grub-set-default (preferred when menu entries change)

• List saved entries:
  • awk -F”‘” ‘/menuentry / {print ++i “ : ” $2}’ /boot/grub/grub.cfg
• Set permanent default by menu title or index:
  • sudo grub-set-default “Ubuntu, with Linux 5.15.0-xx-generic”
  • sudo grub-set-default 2
• Check current saved default:
  • sudo grub-editenv list

Troubleshooting

• Menu titles change after kernel updates — use grub-set-default with full title or use saved entries via grub-editenv.
• Submenu miscounting — verify with the menuentry listing command above.
• UEFI vs BIOS paths differ for grub.cfg; ensure you update the correct file (check distro docs).

Tips

• Use names (quoted titles) for clarity but update them after kernel upgrades.
• For scripting, prefer index-based or use awk to find the matching menuentry dynamically.
• To set a one-time next-boot entry, use grub-reboot; for permanent use grub-set-default.

If you want, I can generate the exact command sequence for your distro and current kernel list.