Network monitoring script in Bash Scripting

Introduction

A network monitoring script helps you check if your internet or network devices are working well. It alerts you if something is wrong.

You want to check if your website server is reachable.

You need to monitor if a printer or other device on your network is online.

You want to log network uptime and downtime automatically.

You want to get notified if your internet connection drops.

You want to track network response times over time.

Syntax

Bash Scripting

#!/bin/bash
ping -c <count> <host>
if [ $? -eq 0 ]; then
  echo "Host is reachable"
else
  echo "Host is unreachable"
fi

ping sends small messages to check if a host is reachable.

-c sets how many messages to send.

Examples

Sends 3 ping messages to google.com to check if it is reachable.

Bash Scripting

ping -c 3 google.com

Checks if the router at 192.168.1.1 is online and prints a message.

Bash Scripting

if ping -c 1 192.168.1.1 > /dev/null 2>&1; then
  echo "Router is online"
else
  echo "Router is offline"
fi

Sample Program

This script pings Google's DNS server twice. It prints if the network is up or down based on the ping result.

Bash Scripting

#!/bin/bash

HOST="8.8.8.8"
COUNT=2

ping -c $COUNT $HOST > /dev/null 2>&1
if [ $? -eq 0 ]; then
  echo "Network is up: $HOST is reachable"
else
  echo "Network is down: $HOST is unreachable"
fi

Important Notes

Use chmod +x script.sh to make your script executable.

Redirect ping output to /dev/null to keep the script output clean.

Check the exit status $? to know if the ping succeeded (0 means success).

Summary

A network monitoring script uses ping to check device reachability.

It helps detect network problems early by alerting when devices are unreachable.

Simple scripts can be automated to run regularly for continuous monitoring.

Practice

1. What is the main purpose of a network monitoring script using ping?

easy

A. To increase the speed of the network

B. To install software on remote devices

C. To change the IP addresses of devices

D. To check if devices on the network are reachable

Solution

1. Step 1: Understand the role of ping

   ping sends a small message to a device to see if it replies, showing if it is reachable.

2. Step 2: Identify the script's goal

   The script uses ping to detect if devices respond, helping find network problems early.

3. Final Answer:

   To check if devices on the network are reachable -> Option D

4. Quick Check:

   Ping checks reachability = B [OK]

Hint: Ping tests if a device replies to confirm reachability [OK]

Common Mistakes:

• Confusing ping with speed testing
• Thinking ping changes device settings
• Assuming ping installs software

2. Which of the following is the correct syntax to ping a device once in a bash script?

easy

A. ping /c 1 192.168.1.1

B. ping -n 1 192.168.1.1

C. ping -c 1 192.168.1.1

D. ping 192.168.1.1 -count 1

Solution

1. Step 1: Recall the ping option for count

   In Linux bash, -c specifies the number of ping requests to send.

2. Step 2: Verify the correct command format

   ping -c 1 192.168.1.1 sends exactly one ping to the IP address.

3. Final Answer:

   ping -c 1 192.168.1.1 -> Option C

4. Quick Check:

   Use -c for count in ping = D [OK]

Hint: Use -c to specify ping count in bash [OK]

Common Mistakes:

• Using Windows ping options like -n in bash
• Incorrect option syntax like /c or -count
• Omitting the count option for single ping

3. What will be the output of this script snippet?

if ping -c 1 8.8.8.8 > /dev/null; then
  echo "Host is reachable"
else
  echo "Host is unreachable"
fi

medium

A. Host is reachable

B. Syntax error

C. Host is unreachable

D. No output

Solution

1. Step 1: Understand the ping command behavior

   The command ping -c 1 8.8.8.8 sends one ping to Google's DNS server, which is usually reachable.

2. Step 2: Analyze the if condition and output

   If ping succeeds, the script prints "Host is reachable"; otherwise, it prints "Host is unreachable".

3. Final Answer:

   Host is reachable -> Option A

4. Quick Check:

   Successful ping prints reachable = C [OK]

Hint: Ping 8.8.8.8 usually succeeds, so output is reachable [OK]

Common Mistakes:

• Assuming ping always fails
• Confusing output redirection with errors
• Missing that output is suppressed with > /dev/null

4. Identify the error in this script snippet for monitoring a device:

for ip in 192.168.1.1 192.168.1.2
 do
  ping -c 1 $ip
  if [ $? -eq 0 ]; then
    echo "$ip is up"
  else
    echo "$ip is down"
  fi

medium

A. Incorrect ping option '-c'

B. Missing 'done' to close the for loop

C. Wrong variable name for IP address

D. No error, script is correct

Solution

1. Step 1: Check for loop syntax completeness

   The for loop starts with for ip in ... but lacks the closing done keyword.

2. Step 2: Confirm other parts are correct

   The ping command and if condition use correct syntax and variable names.

3. Final Answer:

   Missing 'done' to close the for loop -> Option B

4. Quick Check:

   For loops need 'done' to end = A [OK]

Hint: Always end bash loops with 'done' [OK]

Common Mistakes:

• Forgetting 'done' after loops
• Using wrong ping options
• Using undefined variables

5. You want to create a script that checks multiple IPs and logs only unreachable ones to a file named unreachable.log. Which snippet correctly does this?

hard

A. for ip in 192.168.1.1 192.168.1.2; do
ping -c 1 $ip > /dev/null || echo "$ip unreachable" >> unreachable.log
done

B. for ip in 192.168.1.1 192.168.1.2; do
if ping -c 1 $ip > /dev/null; then
echo "$ip unreachable" >> unreachable.log
fi
done

C. for ip in 192.168.1.1 192.168.1.2; do
ping -c 1 $ip >> unreachable.log
done

D. for ip in 192.168.1.1 192.168.1.2; do
ping -c 1 $ip || echo "$ip reachable" >> unreachable.log
done

Solution

1. Step 1: Understand the goal

   The script should log only unreachable IPs to unreachable.log.

2. Step 2: Analyze each option

   for ip in 192.168.1.1 192.168.1.2; do ping -c 1 $ip > /dev/null || echo "$ip unreachable" >> unreachable.log done uses ping -c 1 $ip > /dev/null || echo "$ip unreachable" >> unreachable.log, which logs IPs only if ping fails (unreachable). for ip in 192.168.1.1 192.168.1.2; do if ping -c 1 $ip > /dev/null; then echo "$ip unreachable" >> unreachable.log fi done logs reachable IPs incorrectly. for ip in 192.168.1.1 192.168.1.2; do ping -c 1 $ip >> unreachable.log done logs all ping output, not just unreachable. for ip in 192.168.1.1 192.168.1.2; do ping -c 1 $ip || echo "$ip reachable" >> unreachable.log done logs reachable IPs as unreachable.

3. Final Answer:

   for ip in 192.168.1.1 192.168.1.2; do ping -c 1 $ip > /dev/null || echo "$ip unreachable" >> unreachable.log done -> Option A

4. Quick Check:

   Use '||' to log failures only = A [OK]

Hint: Use '||' to log only when ping fails [OK]

Common Mistakes:

• Logging reachable IPs instead of unreachable
• Appending all ping output to log
• Using wrong conditional logic