100-Days-Of-DevOps-Challenge-KodeKloud

Setup a Cron Job

The Nautilus system admins team has prepared scripts to automate several day-to-day tasks. They want them to be deployed on all app servers in Stratos DC on a set schedule. Before that they need to test similar functionality with a sample cron job. Therefore, perform the steps below:

• Install cronie package on all Nautilus app servers and start crond service.
• Add a cron */5 * * * * echo hello > /tmp/cron_text for root user.

Steps

1. Login into each server using ssh (check day01)

2. Install cronie package into centos:

    sudo yum install cronie -y
   

3. Start crond service

    sudo systemctl enable crond
    sudo systemctl start crond
   

4. Create cron schedule:

    sudo crontab -e
    */5 * * * * echo hello > /tmp/cron_text
   

5. Verify crontab:

    sudo crontab -l
   

   and wait 5 minutes to check cron_text in /tmp/

Automation Script

#!/bin/sh

# setup_cron_job.sh
# Script to setup cron job on CentOS for Nautilus app servers

set -e  # Exit on any error

echo "=== Setting up Cron Job on CentOS ==="

# Step 1: Install cronie package
echo "Installing cronie package..."
if ! rpm -q cronie &>/dev/null; then
    sudo yum install cronie -y
    echo "✓ cronie package installed successfully"
else
    echo "✓ cronie package already installed"
fi

# Step 2: Start and enable crond service
echo "Starting and enabling crond service..."
sudo systemctl start crond
sudo systemctl enable crond

# Verify service is running
if systemctl is-active --quiet crond; then
    echo "✓ crond service is running"
else
    echo "✗ Failed to start crond service"
    exit 1
fi

# Step 3: Add cron job for root user
echo "Adding cron job for root user..."

# Define the cron job
CRON_JOB="*/5 * * * * echo hello > /tmp/cron_text"

# Check if cron job already exists
if sudo crontab -l 2>/dev/null | grep -q "echo hello > /tmp/cron_text"; then
    echo "✓ Cron job already exists"
else
    # Add the cron job
    (sudo crontab -l 2>/dev/null || true; echo "$CRON_JOB") | sudo crontab -
    echo "✓ Cron job added successfully"
fi

# Step 4: Verify the setup
echo "Verifying cron job setup..."
echo "Current cron jobs for root user:"
sudo crontab -l

echo ""
echo "=== Setup Complete ==="
echo "The cron job will run every 5 minutes and write 'hello' to /tmp/cron_text"
echo "To monitor: sudo tail -f /var/log/cron"
echo "To check output: cat /tmp/cron_text (after 5+ minutes)"

# Optional: Show service status
echo ""
echo "Crond service status:"
sudo systemctl status crond --no-pager -l

Good to Know?

Cron Job Scheduling

• Format: minute hour day month weekday command
• Ranges: 0-59 (min), 0-23 (hour), 1-31 (day), 1-12 (month), 0-7 (weekday)
• Special Characters: * (any), , (list), - (range), / (step)
• Examples: 0 2 * * * (daily 2 AM), */15 * * * * (every 15 min)

Cron Types

• User Crontab: crontab -e (per-user scheduling)
• System Crontab: /etc/crontab (system-wide)
• Cron Directories: /etc/cron.d/, /etc/cron.daily/

Best Practices

• Absolute Paths: Always use full paths in cron jobs
• Environment: Set PATH, SHELL, MAILTO variables
• Logging: Redirect output to files for debugging
• Testing: Test commands manually before scheduling

Troubleshooting

• Logs: Check /var/log/cron for execution history
• Environment: Cron runs with minimal environment
• Permissions: Ensure user has execute permissions

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