Week 1 of KodeKloud’s 100 Days Challenge: Days 1-4 (Or: How I Learned to Stop Worrying and Love the Slow Labs

Source: Dev.to

Day 1 – Non‑Interactive Users

The challenge was to create a user with a non‑interactive shell.

sudo useradd -s /usr/sbin/nologin username
getent passwd username

Mistake: Ran the commands on the wrong host. Spent several minutes wondering why validation failed before realizing I was on my local terminal instead of the lab VM.

Lesson: Always double‑check which host you’re on (run hostname first).

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Day 2 – Temporary Users

Create a user account with an expiration date.

sudo useradd anita -e 2023-06-05
chage -l anita

This creates a “ticking time‑bomb” account—useful for temporary contractors or interns.

Bonus trick: Auto‑lock the account after 20 minutes.

echo "usermod --lock username" | at now + 20 minutes

Mistake: Again executed on the wrong host.

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Day 3 – Disabling Root SSH

Manual approach

sudo vi /etc/ssh/sshd_config
# Change: #PermitRootLogin no → PermitRootLogin no
sudo systemctl restart sshd

Doing this manually on three servers was tedious (≈30 s per SSH connection).

Automated solution

for server in app1 app2 app3; do
    ssh "$server" "sudo sed -i 's/#PermitRootLogin no/PermitRootLogin no/' /etc/ssh/sshd_config && sudo systemctl restart sshd"
done

What took 30 minutes became a 2‑minute coffee break.

Lesson: If you repeat a task more than twice and it’s boring, automate it.

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Day 4 – File Permissions

Make a script executable for all users.

chmod 755 /tmp/xfusioncorp.sh
ls -l /tmp/xfusioncorp.sh

Output: -rwxr-xr-x

Permission breakdown

• 7 (rwx) – full access for owner
• 5 (r-x) – read & execute for group
• 5 (r-x) – read & execute for others

Common patterns

chmod 644 file.txt    # Owner: rw, Group/Others: r
chmod 755 script.sh   # Owner: rwx, Group/Others: rx
chmod 600 secret.txt  # Owner: rw, Group/Others: none

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Week 1 Stats

• Commands run: ~50
• Wrong‑host mistakes: 2
• Lab loading time: ~5 min per lab
• “Why isn’t this working?” moments: 7
• Times I questioned my career: 3

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Key Takeaways

Commands I now know by heart

useradd -s /usr/sbin/nologin username
chage -l username
chmod 755 script.sh

Mistakes that taught me

• Always check hostname before running commands.
• Automate anything you do more than twice.
• Lab speed ≠ learning speed.

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What’s Next

Days 5‑8 will cover:

• Package management (yum, apt, dnf)
• Service management (systemctl deep dive)
• Cron jobs and scheduling
• More automation

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