Exercise 05 — Package Management¶

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Before You Start¶

Read Note 05 first.

These exercises use APT (Ubuntu/Debian). If you're on Fedora or RHEL, substitute apt with dnf — the concepts are identical.

You'll need internet access and sudo privileges.

Exercise 5.1 — Update Your Package List¶

Always do this before installing anything.

Step 1: Update the package list:

sudo apt update

You'll see output like this:

Hit:1 http://archive.ubuntu.com/ubuntu jammy InRelease
Get:2 http://archive.ubuntu.com/ubuntu jammy-updates InRelease [128 kB]
Fetched 3,456 kB in 4s (864 kB/s)
57 packages can be upgraded. Run 'apt list --upgradable' to see them.

This downloaded updated package information. Nothing was installed yet — it's just refreshing the catalogue.

Step 2: See which packages have available updates:

apt list --upgradable 2>/dev/null

What is 2>/dev/null? 2> redirects error messages. /dev/null is a "black hole" that discards anything sent to it. This hides a harmless warning that apt list always prints. You'll often see this pattern when you want to suppress noise.

Step 3: Count how many packages can be upgraded:

apt list --upgradable 2>/dev/null | wc -l

Reflect: Why is it important to run apt update before apt install? What happens if you skip it?

Exercise 5.2 — Research a Package Before Installing¶

It's good practice to look at what you're about to install.

Step 1: Search for packages related to "network scanner":

apt search "network scanner" 2>/dev/null

You'll see a list of packages with their names and descriptions.

Step 2: Get detailed information about nmap (a popular network scanner):

apt show nmap 2>/dev/null

Expected output (abbreviated):

Package: nmap
Version: 7.80+dfsg1-2build1
Depends: libc6, liblinux-procfs-perl, ...
Description: The Network Mapper
 Nmap is a utility for network exploration or security auditing.
 ...

Read the Depends: line — that's the list of other packages nmap needs to work. APT will install all of these automatically.

Step 3: Check if a package is already installed:

dpkg -s curl

If it's installed, you'll see Status: install ok installed. If not, you'll see an error.

Exercise 5.3 — Install, Use, and Remove a Package¶

Step 1: Install tree — a handy tool that shows directories visually:

sudo apt install -y tree

-y automatically answers "yes" to the confirmation prompt. You'll see it downloading and installing.

Step 2: Try it out:

tree ~/linux-practice/ 2>/dev/null || tree ~ -L 2

Expected output (something like):

/home/jahid/linux-practice/
├── logs
│   └── app.log
├── notes
│   ├── day1.txt
│   └── day2-renamed.txt
└── scripts

3 directories, 3 files

See how much clearer this is than ls -R? That's the value of tree.

Step 3: Find out where tree was installed:

which tree

Expected output:

/usr/bin/tree

which shows the path to the executable file of a command.

Step 4: List every file the tree package installed:

dpkg -L tree

You'll see a list of files — the binary, man page, etc. All of these will be removed when you uninstall.

Step 5: Remove tree:

sudo apt remove tree

Step 6: Verify it's gone:

which tree

Expected output:

(nothing — no output means the command is not found)

Or you might see:

/usr/bin/which: no tree in (/usr/local/bin:/usr/bin:/bin:...)

Step 7: Remove leftover dependencies:

sudo apt autoremove -y

This removes any packages that were installed automatically to support tree but are no longer needed by anything else.

Exercise 5.4 — Install a Useful Tool and Explore It¶

Now install something you'll actually keep and use.

Step 1: Install htop — a better version of top:

sudo apt install -y htop

Step 2: Open it:

htop

You'll see a colorful, real-time view of your processes and resources. Click on a column header to sort by it. Press q to quit when you're done exploring.

Step 3: Install ncdu — an interactive disk usage explorer:

sudo apt install -y ncdu

Step 4: Use it to explore your home directory:

ncdu ~

Navigate with arrow keys, press Enter to open a directory, press q to quit. This makes it easy to find what's eating up disk space.

Exercise 5.5 — Investigate an Installed Package with dpkg¶

dpkg gives you low-level package information.

Step 1: List all installed packages (there will be many):

dpkg -l | head -30

Each line follows this format:

ii  packagename  version  architecture  description

The ii at the start means "installed, install ok". Other codes: rc means the package was removed but config files remain.

Step 2: Find all installed packages with "python" in the name:

dpkg -l | grep python

You'll likely see several Python-related packages — Python is used by many system tools.

Step 3: Find which package owns a specific file:

dpkg -S /bin/ls

Expected output:

coreutils: /bin/ls

This tells you ls comes from the coreutils package. Try it with other commands too:

dpkg -S /usr/bin/python3
dpkg -S /usr/bin/curl

Step 4: Check if nginx is installed (it probably isn't yet):

dpkg -s nginx

If nginx isn't installed, you'll see an error message. That's expected — we use nginx in the mini-projects later.

Exercise 5.6 — Upgrade a Package¶

Step 1: Upgrade all packages with available updates:

sudo apt upgrade -y

This is safe to run — it only upgrades existing packages, never removes them. The output shows you exactly what's being upgraded.

Step 2: After upgrading, check if a reboot is needed:

cat /var/run/reboot-required 2>/dev/null && echo "Reboot is needed!" || echo "No reboot needed."

Some kernel updates only take effect after a reboot. This file exists only when a reboot is required.

Challenge — Find, Install, Explore, Remove¶

Pick one package from this list that you find interesting:

Package	What it does
`jq`	Pretty-prints and queries JSON data
`net-tools`	Classic network tools (ifconfig, netstat)
`dstat`	Live system resource stats
`bat`	A better version of `cat` with syntax highlighting
`fzf`	Fuzzy finder — interactive search for the terminal

Use apt show to read about it before installing
Install it
Find out where it installed its binary using which
List the files it installed with dpkg -L
Try using it with --help to understand basic usage
Remove it with apt remove
Confirm it's gone with which

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