Prepare installation and recovery

Installation can erase a disk or interrupt network access. Resolve the exact target hardware and preserve anything needed to recover before you boot an installer.

Verify the installer image

Download Ubuntu Server from ubuntu.com over HTTPS, then record image integrity before writing media:

shasum -a 256 ubuntu-server.iso
# Linux commonly uses: sha256sum ubuntu-server.iso

Compare the hash with Ubuntu’s published checksum over a trusted HTTPS path. The two long hex strings must match character for character.

A corrupted download produces confusing installer failures halfway through, which you will otherwise blame on the hardware. Thirty seconds of checking saves an evening of that.

Write the verified image to a USB stick, and double-check you picked the stick and not a data drive. This is the first place people erase the wrong device.

Identify the target disk

Boot the machine from the USB stick. Before confirming any destructive step, identify the install target by model and size, not by device name:

lsblk -o NAME,SIZE,MODEL

Label the target disk in your notes: “Samsung 870 EVO, 500 GB, system disk”. Never choose an install disk by a broad wildcard or assumption. Disconnect unrelated removable drives when practical, so the wrong choice isn’t even on the menu.

If the disk currently holds anything you might want, copy it off now. The installer will not ask twice.

Keep a recovery path open

Assume the first attempt fails halfway. You want, ready before you start:

• a second device (laptop or phone) to look up documentation
• keyboard and monitor access to the server itself
• your router’s admin address and credentials
• a written plan: hostname, username, and disk layout

The failure mode to respect here is writing the installer to the wrong disk. You notice when a drive that held data suddenly shows as empty. There is no fix after the fact, only the copy you made beforehand.