You can absolutely install Ubuntu onto an external USB drive so that it's a fully portable operating system. The key is to avoid installing the bootloader onto your internal drive and to make sure you don't accidentally overwrite your existing Ubuntu installation.
What you'll need
- Your current Ubuntu PC
- Two USB drives:
- One USB stick (4 GB+) for the Ubuntu installer
- One external USB drive or SSD (this is where Ubuntu will be installed)
- Ubuntu ISO (if you don't already have it)
Step 1: Create the installer USB
Use Startup Disk Creator (already included with Ubuntu), Balena Etcher, or Rufus (if using Windows).
Step 2: Connect both drives
You should have:
- Internal drive with your current Ubuntu
- Installer USB
- External USB drive (installation target)
Step 3: Boot from the installer USB
Restart and enter your computer's boot menu (often F12, F10, Esc, or F9 depending on the manufacturer).
Choose the installer USB.
Select Try or Install Ubuntu.
Step 4: Start the installer
When asked about installation type, choose:
- Something Else (recommended)
This gives you full control.
Step 5: Identify the external drive
Be very careful here.
For example:
Internal SSD
/dev/nvme0n1 1 TB
Installer USB
/dev/sdb 8 GB
External SSD
/dev/sdc 500 GB
Use the sizes to identify the correct drive.
Step 6: Partition the external drive
Delete any existing partitions on the external drive (if you don't need the data).
A simple layout is:
| Mount | Size | Filesystem |
|---|
| EFI System Partition | 512 MB | FAT32 |
| / | Remaining space | ext4 |
If you're using Legacy BIOS instead of UEFI, you don't need an EFI partition.
You can also add swap, but modern Ubuntu versions can use a swap file automatically.
Step 7: Install the bootloader to the external drive
This is the most important step.
At the bottom of the partitioning screen you'll see:
Device for boot loader installation:
Choose the external drive itself, for example:
/dev/sdc
Not
/dev/nvme0n1
This keeps your internal Ubuntu installation untouched.
Step 8: Finish installation
Continue the installation normally.
When it finishes:
- Shut down.
- Remove the installer USB.
- Leave the external drive connected.
Step 9: Boot from the external drive
Use your computer's boot menu and select the external USB drive.
Ubuntu should boot from it.
Things to watch out for
Secure Boot
If Ubuntu won't boot, you may need to disable Secure Boot in your firmware settings (although recent Ubuntu versions generally support Secure Boot).
UEFI vs Legacy
It's best to install Ubuntu in the same mode (UEFI or Legacy BIOS) that you intend to use when booting. Most modern systems use UEFI.
Prevent the installer from using the internal EFI partition
Some Ubuntu installers may detect an existing EFI System Partition on the internal drive and use it automatically, even if you're installing the OS onto the external drive. To avoid this:
- Temporarily disconnect the internal drive if possible (the safest option), or
- Ensure the external drive has its own EFI System Partition and double-check that the bootloader is being installed to the external drive.
Optional: Make it portable
If you plan to use the external Ubuntu on different computers:
- Install proprietary GPU drivers only if needed (generic drivers are more portable).
- Avoid hardware-specific tweaks.
- Keep Secure Boot considerations in mind, as different PCs may have different firmware settings.
If you tell me:
- whether your PC uses UEFI or Legacy BIOS,
- whether the external drive is a USB flash drive or an external SSD/HDD,
- and whether you want to keep the existing data on the external drive,
I can give you the safest partition layout and installation steps for your specific setup.
