KodeKloud Days 5-8: SELinux and Cron Jobs

Source: Dev.to

Day 5: SELinux Configuration – “Wait, this isn’t Ubuntu?”

My confident first attempt:

sudo apt update
sudo apt install -y selinux-basics

Result: Command not found.
Turns out I was on CentOS Stream, not Ubuntu. Different package manager, different everything.

Check your OS first (lesson learned)

cat /etc/os-release

CentOS uses dnf, not apt:

sudo dnf install -y selinux-policy selinux-policy-targeted

Edit the SELinux config:

sudo vi /etc/selinux/config
# Change SELINUX=enforcing to SELINUX=disabled

Why this surprised me: Every DevOps tutorial I’d done uses Ubuntu (AWS, Docker, Kubernetes). Encountering CentOS felt like showing up to a JavaScript class and being handed Assembly code.
Lesson: Always check /etc/os-release before assuming the distro. Package managers are not interchangeable.

Day 6: Cron Jobs – Easier Than Expected

Set up a cron job to echo “hello” to /tmp/cron_text every 5 minutes.

# Install cron daemon
sudo dnf install -y cronie
sudo systemctl enable --now crond

# Add the job (as root)
sudo su -
echo "*/5 * * * * echo hello > /tmp/cron_text" >> /var/spool/cron/root

# Verify
crontab -l

Cron syntax breakdown for */5 * * * *

Translation: “Run this every 5 minutes until the heat death of the universe.”

Day 7: Passwordless SSH – The Magic of Public Keys

Set up password‑less SSH from a jump host to all app servers.

# Generate SSH key pair
ssh-keygen -t rsa -b 4096

# Copy to servers (the easy way)
ssh-copy-id tony@stapp01
ssh-copy-id steve@stapp02
ssh-copy-id banner@stapp03

# Test it
ssh tony@stapp01 hostname   # No password prompt = success

Critical permissions

Incorrect permissions cause SSH to silently ignore your keys.

Day 8: Ansible Installation – Version Hell

Install a specific Ansible version globally.

# Wrong: user‑only installation
python3 -m pip install --user ansible

# Right: global installation
sudo python3 -m pip install "ansible==4.8.0"

# Verify
ansible --version
which ansible   # Should show /usr/local/bin/ansible

The difference

• --user → installs to ~/.local/bin (current user only)
• sudo pip install → installs to /usr/local/bin (all users)

Always quote version specifiers: "ansible==4.8.0"; otherwise shell expansion can break the command.

Week 2 Stats

• Package managers tried: 2 (apt failed, dnf worked)
• Cron jobs created: 3 (one per server)
• SSH key pairs generated: 1 (4096‑bit RSA)
• Ansible installations: 2 (user then global)
• “Not Ubuntu” realizations: 1 (the CentOS surprise)
• Times I typed apt on CentOS: ~5 (muscle memory is stubborn)

Key Takeaways

Commands I now know by heart

cat /etc/os-release          # Always check your distro
crontab -l                    # List cron jobs
ssh user@host hostname        # Test passwordless SSH
ansible --version             # Verify Ansible installation

Mistakes that taught me

• Always check your OS before running commands.
• SSH permissions must be exactly right.
• Global vs. user installations matter.
• Version management is not optional.

What’s Next

• Days 9‑12: Ansible playbooks (finally using what I installed)
• Docker fundamentals
• Network configuration
• More troubleshooting (probably)

Full article: For the complete write‑up with more details, all the commands, and the full story of my UI struggles, see the original post 👉 Read the full article