Packages and Networking Tools

Introduction

Software on Linux is not downloaded from random websites. It comes from repositories, managed by a package manager. This lesson also covers the tools you use to check networks and connect to other machines.

Package managers

Different distributions use different tools. On Debian and Ubuntu it is apt:

sudo apt update              # refresh the list of available packages
sudo apt install htop        # install a program
sudo apt upgrade             # update installed packages
apt search "text editor"     # search
sudo apt remove htop         # uninstall

Fedora uses dnf, Arch uses pacman, and macOS has the popular third-party Homebrew (brew install). Packages come from signed repositories, which is much safer than downloading and running unknown scripts. Keep your system updated for security fixes.

Environment variables and PATH

An environment variable is a named setting available to programs.

echo $HOME           # your home folder
echo $PATH           # folders searched for commands
export GREETING="Hello"
echo $GREETING

PATH is a list of folders, separated by colons. When you type git, the shell looks through each folder in PATH for a program with that name. which git shows the one it finds.

To add a folder, put this in your shell startup file (such as ~/.bashrc):

export PATH="$HOME/bin:$PATH"

Checking the network

ping -c 4 example.com       # is the host reachable? (4 tries)
ip addr                     # your IP addresses (Linux)
nslookup example.com        # DNS lookup
curl -I https://example.com # fetch only the response headers
curl -O https://example.com/file.zip   # download a file
curl -s https://api.example.com/data | head   # fetch and pipe the result

curl is the Swiss Army knife for talking to web servers and APIs. -s hides the progress meter. Treat downloaded scripts carefully: never pipe an unknown script straight into a shell.

Connecting to another computer with ssh

SSH (Secure Shell) gives you an encrypted terminal on a remote machine.

ssh [email protected]

The first time, you are asked to confirm the server's fingerprint, which identifies it. Once connected, commands you type run on the remote machine. Type exit to return. Better security comes from using key pairs instead of passwords, covered in the advanced course.

Copy files with scp:

scp report.txt [email protected]:/home/alice/

Try it yourself

Check where git is installed with which git. Run ping -c 3 example.com, then curl -I https://example.com and find the status line at the top of the output.

Summary

• A package manager such as apt installs and updates software from trusted repositories.
• Environment variables hold settings, and PATH tells the shell where to find commands.
• ping, curl, ssh and scp test networks, fetch content and connect to other machines.