Linux Exercise 3 - Exploring File Contents

📝 Linux Exercise: Exploring File Contents

🎯 Objective

Students will practice inspecting files in Linux using commands such as file, head, tail, objdump, od, strings, xxd, less, and cat.
They will create a protocol documenting all commands, outputs, and observations.

🔨 Task Instructions

Part 1: Identifying File Types

1. Choose several files from your system:

A text file (e.g., /etc/hosts)
A binary executable (e.g., /bin/ls)
A compressed archive (e.g., a .zip file)

2. Create a zip file for analysis (if you don’t already have one):

zip sample.zip /etc/hosts /etc/resolv.conf

This creates sample.zip containing two files.

3. Use `file` to determine the type of each file:

file /etc/hosts
file /bin/ls
file sample.zip

Observation: Note what type each file is and why that matters.

Part 2: Inspecting Text Files

4. Use `head` and `tail`:

View the first 10 lines of a text file:

head /etc/hosts

For tail, use a file that is regularly updated, e.g., the system log:

sudo tail -f /var/log/syslog

Observe new log entries as they appear in real-time.

5. Experiment with more lines:

head -n 20 /etc/hosts
tail -n 20 /var/log/syslog

Part 3: Examining Binary Files

6. Use `objdump` on a binary executable (`/bin/ls`):

Show headers:

objdump -x /bin/ls

Disassemble a few instructions:

objdump -d /bin/ls | head -n 20

7. Use `od` to dump the binary in different formats:

od -c /bin/ls     # ASCII characters
od -x /bin/ls     # Hexadecimal
od -b /bin/ls     # Octal

Part 4: Extracting and Viewing Text from Binaries

8. Use `strings` to list readable text from the binary:

strings /bin/ls | head -n 20

9. Use `xxd` to create a hex dump:

xxd /bin/ls | head -n 20

Part 5: Viewing Full Content

10. Use `cat` and `less` on a text file:

Print the whole file:

cat /etc/hosts

Scroll interactively:

less /etc/hosts

📑 Protocol (What to Hand In)

Each student must create a protocol (log) containing:

Command executed
Output received (full or partial if very long)
Explanation (1–2 sentences) of what the command did
Observation/interpretation of what they learned

Example:

Command: file sample.zip
Output: sample.zip: Zip archive data, at least v2.0 to extract
Explanation: Identified sample.zip as a compressed archive file.
Observation: Shows that zip files are binary and need archive tools to inspect contents.

Command: sudo tail -f /var/log/syslog
Output: (live log output appears)
Explanation: Monitors new log entries in real-time.
Observation: Useful for watching system activity as it happens.