Service health check script in Bash Scripting

Introduction

A service health check script helps you quickly see if a service on your computer or server is running well or needs attention.

You want to know if your website server is working before telling users.

You need to check if a background job is running without logging into the server.

You want to automate alerts if a service stops unexpectedly.

You are managing multiple servers and want a quick status report.

You want to restart a service automatically if it is not running.

Syntax

Bash Scripting

#!/bin/bash

if systemctl is-active --quiet SERVICE_NAME; then
  echo "SERVICE_NAME is running"
else
  echo "SERVICE_NAME is NOT running"
fi

Replace SERVICE_NAME with the actual name of the service you want to check.

The script uses systemctl, which works on systems with systemd (common in modern Linux).

Examples

Checks if the Apache web server is running and prints the status.

Bash Scripting

#!/bin/bash

if systemctl is-active --quiet apache2; then
  echo "Apache is running"
else
  echo "Apache is NOT running"
fi

Checks if the SSH service is running to allow remote connections.

Bash Scripting

#!/bin/bash

if systemctl is-active --quiet sshd; then
  echo "SSH service is running"
else
  echo "SSH service is NOT running"
fi

Sample Program

This script checks if the cron service is running and prints the result. Cron runs scheduled tasks on Linux.

Bash Scripting

#!/bin/bash

SERVICE_NAME="cron"

if systemctl is-active --quiet "$SERVICE_NAME"; then
  echo "$SERVICE_NAME is running"
else
  echo "$SERVICE_NAME is NOT running"
fi

Important Notes

Make sure to run the script with enough permissions to check the service status.

You can replace systemctl with service command on older Linux systems, but syntax differs.

Use quotes around variables to avoid errors if service names have spaces (rare but safe).

Summary

A service health check script tells you if a service is running or stopped.

It uses simple commands like systemctl to check service status.

You can customize it for any service by changing the service name.

Practice

1. What is the main purpose of a service health check script in bash?

easy

A. To install new software packages

B. To check if a service is running or stopped

C. To delete files from the system

D. To create new user accounts

Solution

1. Step 1: Understand the script's goal

   A service health check script is designed to verify the status of a service, whether it is running or stopped.

2. Step 2: Compare options with the goal

   Only To check if a service is running or stopped matches the purpose of checking service status; others are unrelated tasks.

3. Final Answer:

   To check if a service is running or stopped -> Option B

4. Quick Check:

   Service health check = check running status [OK]

Hint: Focus on what 'health check' means for a service [OK]

Common Mistakes:

• Confusing service check with installation
• Thinking it manages users
• Assuming it deletes files

2. Which of the following is the correct syntax to check the status of a service named nginx using systemctl in bash?

easy

A. systemctl status nginx

B. systemctl check nginx

C. service nginx status

D. systemctl run nginx

Solution

1. Step 1: Recall systemctl command syntax

   The correct command to check status is systemctl status servicename.

2. Step 2: Match options with correct syntax

   systemctl status nginx matches the correct syntax. systemctl check nginx uses a wrong verb 'check'. service nginx status uses 'service' command which is older but not systemctl. systemctl run nginx uses 'run' which is invalid here.

3. Final Answer:

   systemctl status nginx -> Option A

4. Quick Check:

   systemctl status = check service [OK]

Hint: Remember: systemctl status + service name checks status [OK]

Common Mistakes:

• Using 'check' instead of 'status'
• Confusing 'service' and 'systemctl'
• Using 'run' instead of 'status'

3. What will be the output of this script snippet if the ssh service is running?

if systemctl is-active --quiet ssh; then
  echo "SSH service is running"
else
  echo "SSH service is stopped"
fi

medium

A. No output

B. SSH service is stopped

C. Syntax error

D. SSH service is running

Solution

1. Step 1: Understand systemctl is-active --quiet

   This command returns success (exit code 0) if the service is active (running), otherwise failure.

2. Step 2: Follow the if-else logic

   If the service is running, the then branch echoes "SSH service is running"; else branch echoes stopped.

3. Final Answer:

   SSH service is running -> Option D

4. Quick Check:

   is-active true = running message [OK]

Hint: is-active --quiet returns success if running [OK]

Common Mistakes:

• Assuming output is from systemctl status
• Confusing exit codes with output text
• Missing the echo command effect

4. Identify the error in this health check script snippet:

if systemctl status apache2; then
  echo "Apache2 is running"
else
  echo "Apache2 is stopped"
fi

medium

A. Missing --quiet option causes wrong output

B. The if statement syntax is incorrect

C. systemctl status returns output but not exit code for running check

D. echo commands are missing quotes

Solution

1. Step 1: Check systemctl status behavior

   systemctl status outputs verbose service information to stdout every time it is called, which pollutes the output of the health check script with extra details before the echo. Although it returns exit code 0 if active and non-zero (e.g., 3) if stopped, the verbose output makes it unsuitable for clean scripting.

2. Step 2: Understand correct command for status check

   Use systemctl is-active --quiet to get proper exit code check without any output.

3. Final Answer:

   systemctl status returns output but not exit code for running check -> Option C

4. Quick Check:

   Use is-active for exit code check [OK]

Hint: Use is-active --quiet for exit code, not status [OK]

Common Mistakes:

• Assuming systemctl status exit code indicates running
• Syntax errors in if statement
• Forgetting quotes in echo

5. You want to write a bash script that checks multiple services: nginx, mysql, and redis. Which script snippet correctly loops over these services and prints their status using systemctl is-active --quiet?

hard

A. for service in nginx mysql redis; do
if systemctl is-active --quiet $service; then
echo "$service is running"
else
echo "$service is stopped"
fi
done

B. for service in [nginx, mysql, redis]; do
if systemctl status $service; then
echo "$service is running"
else
echo "$service is stopped"
fi
done

C. for service in nginx mysql redis
do
systemctl is-active $service
echo "$service status checked"
done

D. services=(nginx mysql redis)
for service in ${services[@]}; do
if systemctl is-active --quiet $service; then
echo "$service is running"
else
echo "$service is stopped"
fi
done

Solution

1. Step 1: Check loop syntax and service list

   for service in nginx mysql redis; do if systemctl is-active --quiet $service; then echo "$service is running" else echo "$service is stopped" fi done uses correct bash for loop syntax with space-separated service names. for service in [nginx, mysql, redis]; do if systemctl status $service; then echo "$service is running" else echo "$service is stopped" fi done uses invalid list syntax with brackets. for service in nginx mysql redis do systemctl is-active $service echo "$service status checked" done misses if condition and uses wrong output. services=(nginx mysql redis) for service in ${services[@]}; do if systemctl is-active --quiet $service; then echo "$service is running" else echo "$service is stopped" fi done uses correct array and loop syntax without $ in variable declaration.

2. Step 2: Verify status check command usage

   for service in nginx mysql redis; do if systemctl is-active --quiet $service; then echo "$service is running" else echo "$service is stopped" fi done uses systemctl is-active --quiet correctly to check service status and prints appropriate message.

3. Final Answer:

   for service in nginx mysql redis; do if systemctl is-active --quiet $service; then echo "$service is running" else echo "$service is stopped" fi done -> Option A

4. Quick Check:

   Correct loop + is-active --quiet = for service in nginx mysql redis; do if systemctl is-active --quiet $service; then echo "$service is running" else echo "$service is stopped" fi done [OK]

Hint: Use for service in list; do ... done with is-active --quiet [OK]

Common Mistakes:

• Using brackets [] for list in for loop
• Adding $ in for variable declaration
• Not using is-active --quiet for status check