Ubuntu Server and first steps¶

Exercise ubuntu-server-and-first-steps-annex.pdf · PDF

Think of the last WhatsApp message you received. It passed through a computer in a data centre before it reached your phone. What does that computer's screen look like?

It has no screen. It sits in a rack with thousands of others, in a room with no chairs, and nobody ever looks at it. Today you install that kind of system: Ubuntu Server, with no desktop, no mouse, and a black screen with a line of text. It looks less impressive than yesterday's Debian. It is what runs most of the internet.

A computer nobody sits at¶

A server is a computer whose job is to answer other computers, not a person sitting in front of it.

Nobody looks at a server, so a graphical desktop would only waste RAM and add programs that can fail or be attacked. A server is managed with commands, usually from another computer.

Meet Ubuntu¶

Ubuntu appeared on 20 October 2004, made by Canonical, the company founded by the South African Mark Shuttleworth. It is built from Debian — yesterday's system — so it uses the same package tool, apt, and the same commands.

Ubuntu follows a fixed calendar: a new release every six months, numbered year.month. 26.04 means April 2026 (released on 23 April). Every two years, the April release is an LTS — long-term support — with five years of security updates. Servers run LTS releases because nobody wants to reinstall a server every six months.

Install with the keyboard¶

Connect virt-manager to the class server with today's slip, as in Installing Debian (File → Add Connection → Custom URI... → qemu+ssh://<user>@<server>/session), select the connection and create the VM from your plan: ISO typed as /srv/isos/ubuntu-26.04.1-live-server-amd64.iso (not Browse Local), memory 2048, CPUs 2, disk 20 GiB, name ubu-srv, network Bridge device... with Device name virbr0. In the boot menu choose Try or Install Ubuntu Server.

The installer has no mouse. Learn four keys:

The screens, in order, with our answers (the Exercise sheet has them too; the wording on your screen is the authority):

Four screens to understand, not just click:

• Network. The address 192.168.122.x comes from the virtual router virbr0 on the class server — the same family of addresses your earlier VMs got.
• The red box (Confirm destructive action) is yesterday's Write the changes to disks?: the point of no return for the disk.
• OpenSSH server. SSH is the way to type commands on a server from another computer. That is how real servers are managed, since they have no screen — and how virt-manager reaches the class server. You tick it today and use it in Unit 6.
• Ubuntu Pro is Canonical's paid support plan (free for a few personal machines). The system is complete without it.

If it says Please remove the installation medium, then press ENTER, press Enter.

Your first login¶

After the reboot the screen fills with messages and stops. If no login: line is visible, press Enter: start-up messages were printed over it. Type student, Enter, then the password (nothing is shown while you type), Enter.

A welcome text appears, then the prompt:

student@ubu-srv:~$

The prompt tells you who you are (student), on which machine (ubu-srv) and in which folder (~, your home folder). The $ means "ordinary user". Now ask the machine about itself:

whoami                 # who am I?
hostname               # which machine is this?
cat /etc/os-release    # which system? (line PRETTY_NAME)
ip -br a               # my addresses
free -h                # RAM: total and used
df -h /                # the root file system: size and used
lsblk                  # disks and partitions

The master key: root and sudo¶

Every Linux has one all-powerful user, root. It can read, change and delete anything, with no questions asked. Ordinary users can only touch their own files.

Back in the kitchen: the manager has a master key to every room; each cook has the key to their own locker. Working as root all day is walking around with the master key always in the lock: one wrong command, and nothing stops it.

So on Ubuntu root's login is disabled, and trusted users borrow the master key for one command by writing sudo in front of it.

sudo runs one command as root, after checking your own password.

apt update          # as student: refused
sudo apt update     # as root, for this one command

The first line fails with a message that ends in Permission denied: the system is saying "you need the master key". The second asks for your password and works. Borrowing the key instead of owning it gives you three things:

• Mistakes need an extra word. You cannot destroy the system by accident with a normal command.
• Every admin action has a name on it. sudo writes in a log who did what.
• Nobody shares a root password. Each person uses their own.

The two halves of an update¶

Picture a shop with a catalogue and a shelf:

flowchart LR
    M["<b>Mirror</b><br>the supplier's<br>warehouse"] -->|"sudo apt update<br>downloads the new catalogue"| C["<b>Package list</b><br>what versions exist<br>(installs nothing)"]
    C -->|"sudo apt upgrade<br>compares and installs"| S["<b>Your system</b><br>newer versions<br>on the shelf"]

• sudo apt update downloads the newest catalogue: the list of packages and versions on the mirror. It installs nothing.
• sudo apt upgrade compares the catalogue with what is installed and installs the newer versions.

Always in that order. If you run only the second one, it works from an old catalogue and believes there is nothing new. Package managers get a full page of their own later in this unit.

sudo apt update
sudo apt upgrade

The first ends with a line saying how many packages can be upgraded. The second lists them and asks [Y/n]: press Enter. If a purple screen asks about restarting services, use Tab to reach Ok and press Enter.

Switch off properly, then snapshot¶

A server is never switched off by closing its window — the VM keeps running behind it, on the class server, using RAM the whole class shares. Ask the system to shut down:

sudo poweroff

When the VM is off: View → Snapshots → + → name clean → Finish.

What a desktop costs¶

Start deb-lab, open a terminal and run free -h and df -h /. Compare with ubu-srv, then shut deb-lab down. You will see it with your own numbers: the desktop machine uses several times more RAM while doing nothing, and several GB more disk. That difference is the price of the desktop. Keep your numbers: the comparison of the three installs starts from them.

Key takeaways¶

• A server answers other computers; with nobody in front of it, a desktop only wastes resources.
• Ubuntu (2004, Canonical) is built from Debian; 26.04 LTS gets five years of security updates.
• The prompt student@ubu-srv:~$ tells you who you are, where, and that you are an ordinary user ($).
• root holds the master key; sudo borrows it for one command after checking your own password.
• apt update refreshes the catalogue; apt upgrade installs the newer versions — always in that order.
• Shut a server down with sudo poweroff, never by closing its window.

Quick check¶

Two free systems installed in two days, with no key, no account and no special hardware. The next one asks for all three: Installing Windows 11.