Service health check script in Bash Scripting - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this service health check snippet?

Consider this bash script snippet that checks if the nginx service is active and prints a message accordingly. What will it output if nginx is running?

Bash Scripting

if systemctl is-active --quiet nginx; then
  echo "nginx is running"
else
  echo "nginx is not running"
fi

A nginx is running

B syntax error

C command not found error

D nginx is not running

💡 Hint

The command 'systemctl is-active --quiet' returns success if the service is active.

The script uses 'systemctl is-active --quiet nginx' which returns exit code 0 if nginx is running, so the if condition is true and prints 'nginx is running'.

📝 Syntax

intermediate

Identify the syntax error in this health check script

This script aims to check if the apache2 service is running and print a message. Which option correctly identifies the syntax error?

Bash Scripting

if systemctl is-active apache2; then
  echo "apache2 is running"
else
  echo "apache2 is not running"
fi

A Missing '--quiet' option causes output to appear but no syntax error

B Missing semicolon after 'then' causes syntax error

C Incorrect use of brackets causes syntax error

D Missing 'then' keyword causes syntax error

💡 Hint

Check if the script syntax is valid but consider the command behavior.

The script is syntactically correct. The only issue is that 'systemctl is-active apache2' without '--quiet' outputs the status text, but this does not cause a syntax error.

🔧 Debug

advanced

Why does this health check script always print 'Service is not running'?

This script checks if the mysql service is running but always prints 'Service is not running' even when mysql is active. What is the cause?

Bash Scripting

if systemctl is-active mysql; then
  echo "Service is running"
else
  echo "Service is not running"
fi

A The command 'systemctl is-active mysql' returns output but exit code is non-zero, causing else branch

B The script lacks '--quiet' so output interferes with condition evaluation

C The 'if' condition checks output string instead of exit code, causing wrong branch

D The script uses wrong service name causing failure

💡 Hint

Check how bash evaluates the 'if' condition with commands that output text.

In bash, 'if' checks the exit status of the command, not its output. 'systemctl is-active mysql' outputs text but returns 0 if active. If the script captures output incorrectly, it may cause wrong evaluation.

🚀 Application

advanced

Which script correctly checks multiple services and reports their status?

You want a bash script to check if 'nginx' and 'redis' services are running and print their status lines. Which script does this correctly?

A

for svc in nginx redis
  if systemctl is-active --quiet $svc; then
    echo "$svc is running"
  else
    echo "$svc is not running"
  fi
done

B

for svc in nginx redis; do
  if systemctl status $svc; then
    echo "$svc is running"
  else
    echo "$svc is not running"
  fi
done

C

for svc in nginx redis; do
  if systemctl is-active $svc; then
    echo "$svc is running"
  else
    echo "$svc is not running"
  fi
done

D

for svc in nginx redis; do
  if systemctl is-active --quiet $svc; then
    echo "$svc is running"
  else
    echo "$svc is not running"
  fi
done

💡 Hint

Check for correct loop syntax and quiet status check.

Option D uses correct for-loop syntax with semicolon and 'systemctl is-active --quiet' to check service status silently. Option D misses semicolon after 'redis'. Option D lacks '--quiet' so output may interfere. Option D uses 'systemctl status' which outputs text and always returns 0, causing wrong results.

🧠 Conceptual

expert

What is the best way to handle transient service states in a health check script?

When a service may be restarting or temporarily inactive, how should a bash health check script handle this to avoid false 'not running' reports?

A Use 'systemctl status' once and parse output for 'running' keyword

B Run 'systemctl is-active --quiet' multiple times with delays and confirm consistent inactive status before reporting

C Check service logs instead of status commands for more accurate state

D Assume service is running if last check was successful, ignore current status

💡 Hint

Transient states can cause momentary false negatives; repeated checks help confirm.

Transient states like restarting can cause a single check to report inactive. Repeating checks with short delays reduces false alarms. Parsing logs or assuming previous state is unreliable.

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