DevOps Interview sample Bash script with Explanations

1. Bash Script to Check and Start a Service

This script monitors a service, starts it if not running, and logs all actions.

#!/bin/bash

# Service name (can be changed to any service)
SERVICE_NAME="nginx"
LOG_FILE="service.log"

# Check if service is running
if systemctl is-active --quiet $SERVICE_NAME; then
    echo "$(date): $SERVICE_NAME is running." | tee -a $LOG_FILE
else
    echo "$(date): $SERVICE_NAME is not running. Starting service..." | tee -a $LOG_FILE
    
    # Try to start the service and log the output
    systemctl start $SERVICE_NAME 2>&1 | tee -a $LOG_FILE
    
    # Check if service started successfully
    if systemctl is-active --quiet $SERVICE_NAME; then
        echo "$(date): $SERVICE_NAME started successfully." | tee -a $LOG_FILE
    else
        echo "$(date): Failed to start $SERVICE_NAME." | tee -a $LOG_FILE
    fi
fi

Line-by-Line Explanation

1. #!/bin/bash
   • This is called a “shebang” line
   • It tells the system to use the Bash shell to interpret this script
   • Essential for any bash script to run properly
2. SERVICE_NAME="nginx" and LOG_FILE="service.log"
   • These are variables that store the name of the service to check and the log file path
   • Using variables makes the script reusable and easy to modify
   • You can change “nginx” to any service name (like “apache2”, “mysql”, etc.)
3. if systemctl is-active --quiet $SERVICE_NAME; then
   • This checks if the specified service is currently running
   • systemctl is the command used to control services in modern Linux systems
   • is-active checks the service status
   • --quiet suppresses normal output, giving only the exit code
   • The script uses this exit code to determine if the service is running
4. echo "$(date): $SERVICE_NAME is running." | tee -a $LOG_FILE
   • Logs that the service is running
   • $(date) inserts the current timestamp
   • tee -a $LOG_FILE sends the output to both the terminal and appends it to the log file
   • -a means “append” instead of overwriting the log file
5. else statement
   • The code in this block runs if the service is NOT running
6. systemctl start $SERVICE_NAME 2>&1 | tee -a $LOG_FILE
   • Attempts to start the service
   • 2>&1 redirects both standard output and errors to the pipe
   • This ensures that error messages are also captured in the log file
7. Second if check
   • After trying to start the service, this verifies if the start attempt was successful
   • This double-check is important for proper error handling
8. Final status messages
   • The script logs whether the service was successfully started or if it failed
   • This creates a clear audit trail of actions and results

Why This Script Works Well for Interviews

• It demonstrates knowledge of service management with systemctl
• It shows proper logging practices with timestamps
• It implements error handling and status checking
• It uses variables for flexibility and maintainability
• It’s simple enough to explain quickly but complete enough to be functional ~eof~