Day 1: Linux Basics - Commands, File System, Users & Permissions - Challenges

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_{Learning points:}

• Basic Shell Commands - Navigate with cd, list files with ls, view file contents with cat, etc.

• Filesystem Hierarchy - Understand the Linux directory structure (/etc, /var, /home, etc.).

• File Permissions - Learn chmod, chown, ls -l and understand read, write, execute (rwx).

• Users & Groups - Creating users, managing groups, and assigning permissions.

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Initial Tasks:

• ✅ Setup Task: If you’re on Windows, install a Linux VM or use WSL; on Mac/Linux, open the Terminal.

• Challenge 1 : List all files (including hidden ones) in your home directory and sort them by modification time.

• Challenge 2 : Create a directory named devops_challenge_day_1, navigate into it, and create an empty file named day1.txt .

• Challenge 3 : Find the total disk usage of the /var/log directory in human-readable format.

• Challenge 4 : Create a new user called devops_user and add them to the sudo group.

• Challenge 5 : Create a group called devops_team and add devops_user to that group.

• Challenge 6 : Change the permissions of day1.txt to allow only the owner to read and write, but no permissions for others.

• Challenge 7 : Find all files in /etc that were modified in the last 7 days.

• Challenge 8 : Write a one-liner command to find the most frequently used command in your shell history.

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✅ Solutions

Challenge 1 : List all files (including hidden ones) in your home directory and sort them by modification time.

Answer :

Command :

ls -laht ~

Explanation:

• ls → List files.

• -l → Long format (detailed info).

• -a → Show hidden files.

• -h → Human-readable sizes.

• -t → Sort by modification time (newest first).

• ~ → Home directory.

OutPut :

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✅ Challenge 2 : Create a directory named devops_challenge_day_1, navigate into it, and create an empty file named day1.txt.

Answer :

Command :

mkdir devops_challenge_day_1  
cd devops_challenge_day_1  
touch day1.txt

Explanation:

• mkdir devops_challenge_day_1 → Creates the directory.

• cd devops_challenge_day_1 → Moves into the directory.

• touch day1.txt → Creates an empty file named day1.txt.

OutPut :

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✅ Challenge 3: Find the total disk usage of the /var/log directory in human-readable format.

Answer :

Command :

du -sh /var/log

Explanation:

• du → Disk usage command.

• -s → Summary (total size only).

• -h → Human-readable format (KB, MB, GB).

• /var/log → Target directory.

OutPut :

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✅ Challenge 4: Create a new user called devops_user and add them to the sudo group.

Answer :

Command :

sudo useradd -m -s /bin/bash devops_user  
sudo usermod -aG sudo devops_user
sudo passwd devops_user

Explanation:

• sudo useradd -m -s /bin/bash devops_user → Creates devops_user with a home directory and Bash shell.

• sudo usermod -aG sudo devops_user → Adds devops_user to the sudo group.

  Run the below command to verify it:

    id devops_user
  

  OutPut :

  

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  ✅ Challenge 5: Create a group called devops_team and add devops_user to that group.Answer :

  Answer :

  Command :

    sudo groupadd devops_team  
    sudo usermod -aG devops_team devops_user
  

  Explanation:

• sudo groupadd devops_team → Creates the devops_team group.

• sudo usermod -aG devops_team devops_user → Adds devops_user to devops_team.

  Run the below command to verify it:

    groups devops_user
  

  OutPut :

  

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  ✅ Challenge 6: Change the permissions of day1.txt to allow only the owner to read and write, but no permissions for others.

  Answer :

  Command :

    chmod 600 devops_challenge_day_1/day1.txt
  

  Explanation:

• chmod 600 → Sets permissions to read & write for owner, no permissions for others.

• devops_challenge_day_1/day1.txt → Target file.

  Run the below command to verify it:

    ls -l devops_challenge_day_1/day1.txt
  

  OutPut :

  

  Explanation:

Permission Level in numeric (octal) mode

Key Points:

• First digit: Owner permissions

• Second digit: Group permissions

• Third digit: Others' permissions

• r (4) = Read permission

• w (2) = Write permission

• x (1) = Execute permission

• Sum of values (rwx = 4+2+1 = 7) = All allowed

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✅ Challenge 7: Find all files in /etc that were modified in the last 7 days.

Answer :

Command :

sudo find /etc -type f -mtime -7

OutPut :

Explanation:

• sudo → For admin privilege

• find /etc → Search in the /etc directory.

• -type f → Look for files (not directories).

• -mtime -7 → Find files modified in the last 7 days.

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  ✅ Challenge 8: Write a one-liner command to find the most frequently used command in your shell history.

  Answer :

  Command :

    history | awk '{print $2}' | sort | uniq -c | sort -nr | head -1
  

  OutPut :

  

  Explanation:

• • history → Shows command history.

    • awk '{print $2}' → Extracts the command name.

    • sort → Sorts commands alphabetically.

    • uniq -c → Counts occurrences of each command.

    • sort -nr → Sorts by frequency (descending).

    • head -1 → Displays the most used command.

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