Installing multiple Ubuntu copies on different partitions allows you to test new releases, separate projects, or troubleshoot issues without affecting your primary operating system. However, after installing Ubuntu onto a new partition, you may find it unclear how to boot into this separate installation. Properly configuring your boot settings and selecting the correct partition at startup ensures you can smoothly access your newly installed Ubuntu system.

Step 1: Boot into your existing Ubuntu installation or use a live Ubuntu USB drive to access a terminal. Once the system is ready, open a terminal window by pressing Ctrl + Alt + T.

Step 2: In the terminal, type the following command to detect all operating systems installed on your hard drive and update your GRUB bootloader menu accordingly:

sudo update-grub

This command scans your disk partitions, identifies the new Ubuntu installation, and adds it to the GRUB bootloader menu. You will see output indicating the new Ubuntu installation has been found and added.

Step 3: Restart your computer. During boot, the GRUB menu will appear, listing all available operating systems. Use the arrow keys to select the new Ubuntu installation on the different partition, then press Enter to boot into it.

This method is straightforward, reliable, and ensures your new Ubuntu installation is permanently accessible from the boot menu.

Method 2: Manually Boot from BIOS/UEFI Boot Menu

If updating GRUB doesn't immediately detect your new installation or if you prefer manual control, you can directly select the partition from your BIOS or UEFI boot menu.

Step 1: Restart your computer and enter your BIOS or UEFI boot menu. Typically, you can access this menu by pressing keys such as F12, F11, Del, or Esc immediately after turning on your computer. The exact key varies depending on your motherboard manufacturer, so check your device's documentation if unsure.

Step 2: In the boot menu, locate and select the partition containing your new Ubuntu installation. It will typically be labeled by partition number or disk identifier. Confirm your selection by pressing Enter.

Your system will now boot directly into the selected Ubuntu partition. This method is useful for quickly accessing the new installation without modifying GRUB, though it's less convenient for repeated use.

Method 3: Use GRUB Customizer (Graphical Interface)

If you prefer a graphical interface, GRUB Customizer provides an intuitive way to manage boot entries.

Step 1: Install GRUB Customizer by opening a terminal and entering the following commands sequentially:

sudo add-apt-repository ppa:danielrichter2007/grub-customizer
sudo apt update
sudo apt install grub-customizer

Step 2: Launch GRUB Customizer from your application menu. The interface will display all detected boot entries. Click the "Refresh" button to scan for new installations if your new Ubuntu partition isn't listed.

Step 3: Once your new Ubuntu installation appears, you can adjust its position in the boot menu by dragging it up or down. When satisfied, click "Save" to apply changes and update GRUB automatically.

Restart your computer, and your new Ubuntu partition will be easily accessible through the customized GRUB menu.

After booting into your new Ubuntu installation, ensure all updates are installed and configurations are set according to your preferences. Regularly updating GRUB after installing new operating systems or partitions ensures seamless boot management in the future.