Network monitoring script in Bash Scripting - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of ping command in a monitoring script

What is the output of this command snippet when the host is reachable?

Bash Scripting

ping -c 1 8.8.8.8 | grep '1 packets transmitted' | awk '{print $4, "received"}'

A 0 received

B 1 packets transmitted

C 1 received

D Destination Host Unreachable

💡 Hint

Look for the part of the ping output that shows how many packets were received.

The command filters the ping output to show the number of packets received. When the host is reachable, it shows '1 received'.

❓ Configuration

intermediate

Correct crontab entry for running a network check every 5 minutes

Which crontab entry correctly runs a script located at /usr/local/bin/netcheck.sh every 5 minutes?

A 5 * * * * /usr/local/bin/netcheck.sh

B */5 * * * * /usr/local/bin/netcheck.sh

C 0 5 * * * /usr/local/bin/netcheck.sh

D * * 5 * * /usr/local/bin/netcheck.sh

💡 Hint

The first field controls minutes and '*/5' means every 5 minutes.

The crontab syntax '*/5 * * * *' runs the command every 5 minutes.

❓ Troubleshoot

advanced

Why does this network monitoring script fail to detect downtime?

Given this script snippet: #!/bin/bash ping -c 1 192.168.1.1 if [ $? -eq 0 ]; then echo "Host is up" else echo "Host is down" fi Why might it fail to detect downtime correctly?

Bash Scripting

#!/bin/bash
ping -c 1 192.168.1.1
if [ $? -eq 0 ]; then
  echo "Host is up"
else
  echo "Host is down"
fi

A The ping command may succeed but the host could still be unreachable due to firewall.

B The script does not redirect ping output, so errors are missed.

C The script checks the exit status immediately, but ping may take time to respond.

D The script uses $? incorrectly; it should check the output string instead.

💡 Hint

Consider network conditions beyond ping success.

Ping may succeed if ICMP packets are allowed, but the host might still be unreachable for other services due to firewall or routing issues.

🔀 Workflow

advanced

Order the steps to create a basic network monitoring script

Put these steps in the correct order to create a simple network monitoring script that alerts on downtime.

A 1,2,3,4

B 2,1,3,4

C 1,3,2,4

D 3,1,2,4

💡 Hint

Think about the logical flow from script creation to scheduling.

First write the ping script, then check its result, send alert if needed, and finally schedule it.

✅ Best Practice

expert

Best practice for handling false positives in network monitoring scripts

Which approach best reduces false positives when a network monitoring script detects downtime?

A Ignore ping failures and rely on manual checks.

B Alert immediately on the first failed ping attempt.

C Increase the ping timeout to a very high value.

D Run multiple ping attempts and alert only if all fail.

💡 Hint

Think about confirming failure before alerting.

Multiple attempts reduce false alarms caused by transient network issues.

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