GRUB Bootloader: Ubuntu 'Not Selecting' vs. 'Ubuntu, Linux 6.2.0-26-generic'

The issue where only "Ubuntu, Linux 6.2.0-26-generic" appears instead of the standard "Ubuntu" menu entry is typically caused by os-prober being disabled or missing in dual-boot configurations. This prevents GRUB from generating the default submenu entries that list all available kernels and operating systems. Restoring this functionality requires enabling the detection tool and updating the bootloader configuration.

Understanding the GRUB Menu Structure

When you install Ubuntu alongside another operating system, such as Windows, the GRUB bootloader is responsible for presenting a selection screen. In a properly configured dual-boot setup, you will see a main entry labeled simply "Ubuntu". Selecting this entry expands into a submenu containing specific kernel versions (like "Linux 6.2.0-26-generic") and recovery modes. You may also see an entry for your other operating system, such as "Windows Boot Manager". If you are seeing only "Ubuntu, Linux 6.2.0-26-generic" directly in the top-level menu, it indicates that GRUB has not generated the expected hierarchical structure. This often happens after a major upgrade, a fresh installation, or when security features like Secure Boot interfere with third-party bootloaders. The absence of the generic "Ubuntu" label suggests that the script responsible for detecting other OSes is either not running or its output is being ignored. This behavior can be confusing for users who expect the standard interface described in guides about Fixing Lubuntu 16.04 - Windows 10 Not Showing in GRUB Menu.

Enabling os-prober

The primary culprit for missing OS entries is the os-prober utility. By default, newer versions of Ubuntu disable os-prober due to security concerns, particularly regarding the potential execution of malicious scripts found on other partitions. However, if you have a legitimate second operating system, you must explicitly enable this feature. First, ensure the package is installed by opening a terminal and running:

sudo apt update
sudo apt install os-prober

Next, you need to modify the GRUB configuration file to allow os-prober to run. Open the /etc/default/grub file using a text editor with root privileges:

sudo nano /etc/default/grub

Look for a line that starts with GRUB_DISABLE_OS_PROBER. If it is set to true, change it to false:

GRUB_DISABLE_OS_PROBER=false

If the line does not exist, add it at the end of the file. Save the changes and exit the editor. This step is crucial because without this flag, the subsequent update command will ignore any detected operating systems. For more context on how GRUB handles different boot scenarios, you might find Grub Shell Startup: Loading Ubuntu from a Hard Drive Next to Win10 helpful for understanding partition identification.

Updating the GRUB Configuration

After modifying the settings, you must regenerate the GRUB configuration files to apply the changes. Run the following command in your terminal:

sudo update-grub

This command scans your disks for other operating systems and writes the new menu structure into /boot/grub/grub.cfg. Upon rebooting, check if the "Ubuntu" submenu has reappeared. If it does, the issue is resolved. If the problem persists, there may be deeper issues related to partition tables or UEFI settings.

Verifying Partition Types

Sometimes, the issue lies not in the software configuration but in the disk layout. Ensure that your EFI System Partition (ESP) is correctly mounted and accessible. If you are using UEFI mode, the ESP must be formatted as FAT32 and mounted at /boot/efi. You can verify this by checking your /etc/fstab file:

cat /etc/fstab

Look for the line corresponding to the EFI partition. It should look similar to:

/dev/sda1 /boot/efi vfat umask=0077 0 1

If the partition is missing or incorrectly formatted, os-prober may fail to detect the other OS. In cases where the UEFI partition was accidentally deleted, as discussed in Accidentally Deleted UEFI Partition: Can't Boot Linux Mint, restoring the partition structure is necessary before GRUB can function correctly.

Alternative Solutions

If enabling os-prober does not resolve the issue, consider checking for recent upgrades that might have introduced bugs. Upgrading between major versions, such as from 22.04 to 24.04, can sometimes result in GRUB misconfigurations. Refer to resources on Upgrading Ubuntu 22.04 to 24.04 results in Grub issue for version-specific fixes. Additionally, ensure that Secure Boot is either disabled or that you are using signed GRUB modules if your system requires it.

Frequently Asked Questions

Why did my GRUB menu lose the "Ubuntu" submenu?

This usually happens when os-prober is disabled or fails to detect other operating systems. Newer Ubuntu releases disable this by default for security reasons, which breaks the automatic generation of the multi-OS menu structure.

Is it safe to enable os-prober?

It is generally safe if you trust the contents of your other partitions. However, os-prober can execute scripts found on other OSes, which poses a theoretical risk if those partitions contain malware. Always keep your systems updated and scanned.

What if os-prober doesn't find my Windows installation?

Ensure that Windows is installed in UEFI mode if your Ubuntu is also in UEFI mode. Mixed BIOS/UEFI installations often cause detection failures. Also, verify that the EFI partition is mounted correctly and contains the Windows bootloader files.

Can I manually edit grub.cfg to fix this?

No, you should never manually edit grub.cfg as it is overwritten every time you run update-grub. Instead, make changes to /etc/default/grub and then run the update command to regenerate the configuration safely.

Does Secure Boot affect GRUB menu options?

Secure Boot itself does not hide menu entries, but it can prevent unsigned kernels or modules from loading. If you have custom kernels or third-party drivers, they may fail to load if Secure Boot is enabled, leading to boot failures that might be mistaken for GRUB issues.