What you'll learn
- Navigate the Linux filesystem safely
- Recognize basic Linux file permissions
- Explain how DNS and HTTP help a browser open a website
Explore Linux without risk
The terminal lets you interact with your own operating system. Start by working in your home directory rather than changing system files.
Hands-on steps
- Open a terminal on your own Linux machine or Kali VM.
- Run pwd to show your current directory and ls to list its contents.
- Run mkdir -p ~/bcs-practice and then cd ~/bcs-practice to create and enter a safe practice folder.
- Run printf "Hello, security learner!\n" > notes.txt, then cat notes.txt to view the file.
Commands to try (in your own lab)
pwd
ls
mkdir -p ~/bcs-practice
cd ~/bcs-practice
printf "Hello, security learner!\n" > notes.txt
cat notes.txt
Remember: Practice inside ~/bcs-practice. Avoid copying commands that delete or overwrite files you do not understand.
Knowledge check: What command prints your current working directory?
pwd (print working directory).
Understand ownership and permissions
Linux separates users and groups and controls access using file permissions. Common letters are r (read), w (write), and x (execute).
Hands-on steps
- In your practice folder, run ls -l notes.txt to see the current permission string.
- Run chmod 600 notes.txt to allow the file owner to read and write while removing permissions for group and others.
- Run ls -l notes.txt again and compare the permission string.
- Write down why sensitive files should not be world-readable.
Commands to try (in your own lab)
cd ~/bcs-practice
ls -l notes.txt
chmod 600 notes.txt
ls -l notes.txt
Remember: Only change permissions on files you own; do not use sudo for this practice.
Knowledge check: What does chmod 600 generally permit?
Read and write access for the owner, with no permission for group or others.
Learn how a domain resolves
DNS translates domain names into records browsers and other tools can use. A and AAAA records point to IP addresses; CNAME records alias hostnames.
Hands-on steps
- Write down a domain you control or use example.com for demonstration.
- Run nslookup example.com in a terminal, if installed.
- Identify at least one returned IP address and explain that DNS resolution is different from website hosting.
- For your own Cloudflare-hosted domain, compare what Cloudflare DNS lists with what you expected to configure.
Commands to try (in your own lab)
nslookup example.com
Remember: Changing nameservers changes who answers DNS. The DNS records must then exist at that provider.
Knowledge check: Which DNS record type generally maps a hostname to an IPv4 address?
An A record.
Read website headers and status codes
HTTP runs on top of the network path. An HTTPS connection adds transport encryption; website security also depends on application code and configuration.
Hands-on steps
- In a terminal, run curl -I https://example.com to request response headers without the page body.
- Identify the HTTP status line and one response header.
- Read about request methods in MDN and compare GET with POST.
- In your notes, explain why HTTPS alone does not mean a website is free of vulnerabilities.
Commands to try (in your own lab)
curl -I https://example.com
Remember: Headers and status codes help debugging, but they cannot prove a site is safe by themselves.
Knowledge check: Does the padlock/HTTPS symbol prove a site is trustworthy?
No. It shows an encrypted connection, not the honesty or security of the organization behind the site.
Reliable places to learn more
These are independent educational resources, not paid endorsements.
